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  1. #2176
    MadMojoMonkey's Avatar
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    P dV is mechanical work.

    Work is energy, as the Work/Energy Theorem reminds us. Both have units of Joules.

    [digression]
    So does torque, which is a little confusing, but also interesting. 1 Nm = 1 J. It results from radians being a dimensionless unit, so angular velocity squared has the same units as angular acceleration, which is not true for linear terms.

    Defining radians: radius*{radians} = arc length
    {radians} = {arc length} / {radius}
    Both arc length and radius are measured in length, so the units of radians vanish:
    [radian] = [m/m] = 1

    So the angular velocity, squared has the same units as the angular acceleration:
    [rad/s]^2 = [rad/s^2]
    but this is not true for linear motion, because the numerator has non-vanishing units.
    [m/s]^2 != [m/s^2]

    Square brackets indicate I'm only talking about the units.
    [/digression]


    Like the pushing of a piston in a car engine. There's an increase in pressure due to the combustion, the piston moves, changing the volume, and the work (energy) transmitted to the piston is P(x) * A dx, since the area of the piston head is constant, and the changing volume is due to movement in 1-dimension. Here, P(x) is the pressure as a function of x, and A is the surface area of the top of the piston, dx is the distance traveled by the piston, due to the volume of the cylinder changing by a factor of ~7 in a gasoline engine, the pressure change is not negligible.

    (The volume change is only more dramatic in diesel engines, which initiate combustion only by compression of the fuel-air mixture, without the injection of heat cause by a spark, so they need to compress the fuel-air more to achieve the heat needed for spontaneous combustion.)
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  2. #2177
    MadMojoMonkey's Avatar
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    Oh... What? But... Yeah... OK... So...

    https://www.youtube.com/c/veritasium/videos

    I still kinda have this issue with the CMB, though.

    If the speed of light is not the same in all directions to the extend that it's c/2 in one direction and inf in the opposite, then that means that when we look one direction, we see that the universe was hot and dense in the past, and when we look the other direction, we see the universe is hot and dense right now, in the naive sense of now.

    Which I guess isn't necessarily a problem, but it kinda throws cosmology on its head when it comes to determining the age of the universe. It destroys the Hubble Constant, too.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  3. #2178
    I saw that vid and thought of a few problems. For one, doppler. Also, he's saying that if c is different in two directions, then so too is time dilation. If that's true, then so too is length contraction, which means it's meaningless to even say the light travelled the same distance in both directions. In fact, if time dilation is balancing it so it appears c is the same, even if it is not, then length contraction must balance it, which in turn means c was constant after all.

    Basically it's clickbait. I like veritasium a lot, I watch his uploads as soon as they are released, but it's his job to find things to talk about. I think he's getting a bit thin on ideas, frankly.

    And yeah, the CMB is a problem too.
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  4. #2179
    MadMojoMonkey's Avatar
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    Oh... I bet even poopy will love this one.

    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  5. #2180
    I hate thinking about free will in physics. It's a real conflict for me. On the one hand, I think the universe is completely deterministic, while on the other it horrifies me to think I am not in control of my future. I kinda don't want science to resolve it for me, because either way I'd be unhappy.

    On another note, I've been thinking about the heat death of the universe, something else I've always felt uncomfortable with. I propose that the second law of thermodynamics actually forbids heat death. Here's why...

    The entropy of a system always increases with time. That's the 2nd law. But heat death is the spreading out of all energy into perfect equilibrium. The "final state" of the universe is pure radiation. But radiation moves at light speed, and therefore has no mass. So the final state of the universe is massless, and therefore lacking in gravity, which critically implies no time.

    With no time, there is no space. So it is meaningless to say there is space between each unit of energy. This makes the end of the universe indistinguishable from the beginning of the universe, where all energy was compressed into a singularity. A universe with no time is a singularity.

    Heat death implies a new big bang. And the big bang is as low entropy as possible. So the 2nd law is broken, entropy decreased.
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  6. #2181
    MadMojoMonkey's Avatar
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    Sounds like you're familiar with Penrose's conformal cyclic cosmological model.

    If not, look into it... it puts a physics underpinning to what you've described.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  7. #2182
    I've heard of it but will watch a refresher.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  8. #2183
    Yeah, I'm familiar with it, though it was five months ago when I saw this so I'd kind of forgotten. But this is where I'd have picked the ideas up from.

    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  9. #2184
    Watching that again reminds me of another problem... if all energy is radiation, then does that not imply that quantum information is lost? How can you go back in time to calculate the events of the universe if... there is no time?
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  10. #2185
    MadMojoMonkey's Avatar
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    Quote Originally Posted by OngBonga View Post
    Watching that again reminds me of another problem... if all energy is radiation, then does that not imply that quantum information is lost? How can you go back in time to calculate the events of the universe if... there is no time?
    All that matters is that the path of the photons could be time reversed, such that they would be traveling in the opposite directions, and that doesn't change the laws of physics or what you would observe in the universe, which is still true.

    There wont be anything non-photon to observe this universe, but that doesn't mean there's no spacetime, I think. I didn't follow your argument that without matter, there's no space. I don't see that at all. Without matter, there's only flat spacetime, sure, but to say that spacetime cannot exist unless there's mass to curve it doesn't sound right to me.

    Quantum information is like, the energy of the photon, the fact that it's a boson, not a fermion, it's a spin 1 object that propagates in c in all inertial reference frames. All that information is there, and there's no problem with quantum information loss in the production of photons in the first place, so the continued existence of produced photons is indeed the conservation of that information.


    EDIT: I think the mere fact that photons are in the universe implies inertial reference frames through which they travel. It's not only mass that curves spacetime, because of the mass-energy equivalence, the photons will still curve spacetime as they propagate. Maybe.

    IDK. It just doesn't seem right at all to assume that just 'cause no matter = no space and/or no time.
    Last edited by MadMojoMonkey; 11-19-2020 at 08:13 PM.
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  11. #2186
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    Interesting read guys, thanks. Ong, stick to physics, political science isn't your forte.
    Our brains have just one scale, and we resize our experiences to fit.

  12. #2187
    There wont be anything non-photon to observe this universe, but that doesn't mean there's no spacetime, I think.
    I think no spacetime is exactly what a universe full of photons implies.

    I didn't follow your argument that without matter, there's no space.
    Let's just clear up what we mean by "matter"... I would say anything with mass. Things with mass are the only things that experience time, photons do not. A photon travels from the sun to Earth instantly, from the FoR of the photon. It takes 8.5 minutes from our FoR, but not the photon due to time dilation. This can only make sense when we also factor in length contraction... from its FoR, the distance the photon has travelled is zero, so of course it takes zero time.

    So if the universe is full of photons, there is no time, and if there is no time, there is no space.

    Flat spacetime is a concept that doesn't exist in the universe. Spacetime can only be flat in the absence of mass, and the absence of mass means no time. How can there be space but no time?

    I'm probably wrong about quantum information, I can't say I have a good understanding of that. But I don't think I'm wrong about flat spacetime. Although your counterpoint that photons curve spacetime is something I need to consider.
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  13. #2188
    Quote Originally Posted by CoccoBill View Post
    Interesting read guys, thanks. Ong, stick to physics, political science isn't your forte.
    The difference between physics and politics is that physics is not a subject that generally causes division. I'm either right or wrong. Politics is a great deal more subjective. When we talk politics, neither is right or wrong, we're discussing opinions and ideology.
    Quote Originally Posted by wufwugy View Post
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  14. #2189
    Ok a quick bit of googling seems to suggest photons do not curve space, rather anything that absorbs a photon curves space. I'm going to have to do more reading to get a grasp of this.
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    ongies gonna ong
  15. #2190
    I don't even use google anymore.

    A quick bit of duckduckgoing.
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  16. #2191
    Let's look at this another way. If we accept that a photon travels from the sun to Earth in zero time through zero space from its FoR, then we accept the photon does not exist in a universe with space and time. It is the observer who lives in this world. Spacetime emerges when an observer is moving at less than c.

    If all that exist are photons, then each photon is moving through zero space in zero time, and there exist no observers to contradict this. So how is this any different to all photons existing in the same place at the same time? That's how they "observe" the universe.

    Spacetime is something that exists to an observer. A photon is not an observer, as it has no clock.
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  17. #2192
    MadMojoMonkey's Avatar
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    You're messing with my head with this line of reasoning. Because as a physicist, I don't want to talk about what cannot be observed under the banner of physics.


    What each specific physicist means exactly when they use the word "observe" can vary widely. Especially in the early days of QM. The great pioneers of QM in the last century had little to no agreement on what was meant by "observation."

    It's not that observation is not well defined. It's that each of them found a consistent way to think about observation and so long as you just pick one definition, you can remain consistent. It will change the specific way you describe things, but not the actual content of your meaning.

    So that much is a minefield. You can't just read 1 physicist and think, OK, that's what observation is, then read another physicist and expect them to be using the same definition of observation.


    For me, I find the most consistency between authors if I start from the assumption that "all interaction is observation." That means when we talk about something like Young's double-slit experiment, we can say, "If the wave function observes the slits, it changes." or "When the wall's wave function observes the electron's, there is an interaction that changes them."

    In this way, the observation simply means, it "saw" the other particle in a metaphorical way... it "saw" it by interacting.


    So as long as the photons are capable of interacting, then nothing has changed. But... in the Heat Death scenario... enough time passes that all potential interactions have happened, and everything is just photons zipping away from each other, with none of them left on a "collision" course to interact with another photon.


    ... and I'm back to the top of this page. We agree that there wont be anything to observe the universe, so the question is whether observation creates spacetime, or if spacetime creates a playground for observations.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  18. #2193
    You're messing with my head with this line of reasoning. Because as a physicist, I don't want to talk about what cannot be observed under the banner of physics.
    This is a fine point. If the end of the universe is spaceless and timeless, and therefore unobservable, does that mean it isn't physics?

    The problem with this though is that it implies the interior of a black hole is not physics.

    What each specific physicist means exactly when they use the word "observe" can vary widely.
    My understanding of the word "observer" in GR is basically anything with an internal clock, since without an internal clock no observation is possible, no measurement is possible, due to the lack of time. So a photon is not an observer, but a neutrino is. Perhaps this definition is not right.

    So as long as the photons are capable of interacting, then nothing has changed. But... in the Heat Death scenario... enough time passes that all potential interactions have happened, and everything is just photons zipping away from each other, with none of them left on a "collision" course to interact with another photon.

    I think physics breaks down again here. You talk about "enough time" and photons "zipping away from each other". This doesn't make sense if the universe contains only photons. Let's assume a photon is an observer. It observes the universe to be spaceless and timeless. On this we surely agree. GR teaches us that no frame of reference is preferable to another, so we can't say the photon's FoR is wrong. If only photons exist, it's the only FoR we can use. So in a universe with only photons, the only observers that exist will agree there is no space and no time. So how can they zip away from each other? That implies movement through space.

    I think this paradox probably implies that actually a universe with just photons is not possible, ie heat death is wrong.
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  19. #2194
    ... and I'm back to the top of this page. We agree that there wont be anything to observe the universe, so the question is whether observation creates spacetime, or if spacetime creates a playground for observations.
    I think mass creates spacetime.
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  20. #2195
    MadMojoMonkey's Avatar
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    Quote Originally Posted by OngBonga View Post
    This is a fine point. If the end of the universe is spaceless and timeless, and therefore unobservable, does that mean it isn't physics?
    It means that we're into speculation range. We know the laws of physics now (pretty good at least), and I think if we extrapolate to the "final" interaction before the Heat Death, then we are pretty safe in asserting that the laws of physics as we know them still describe that final interaction. (This is a clear bias, but it's one that we get a lot of mileage out of in physics).

    What you're suggesting is that the moment of that final interaction is a significant phase change in the character of spacetime and the universe as a whole.

    What about the problem of simultaneity? Are you assuming that from the origin of the final interaction, there's an expanding wavefront, moving at c that is devoid of spacetime? Wouldn't that mean there's now an expanding sheet of spacetime, with spacetime neither inside nor outside of it?

    Quote Originally Posted by OngBonga View Post
    The problem with this though is that it implies the interior of a black hole is not physics.
    In the sense that we're trusting a model that is making predictions that cannot be observed, I think we're well-suited to keep this in mind.

    It is not to say there are no laws which describe what happens on the other side of an event horizon. It's only saying we cannot know if the laws on the other side are identical to the laws on this side. We can only assume they are, and draw the conclusions our model describes.

    Quote Originally Posted by OngBonga View Post
    My understanding of the word "observer" in GR is basically anything with an internal clock, since without an internal clock no observation is possible, no measurement is possible, due to the lack of time. So a photon is not an observer, but a neutrino is. Perhaps this definition is not right.
    There could well be differences between what GR calls an observer and what QM calls an observer.

    The best way to move forward is probably for me to just accept what you mean by observer and let my notions go. So long as we're consistent, we'll be able to tell if your definition creates paradoxes or not. That may indicate it's not the best way to think of observers, but we'll cross that bridge when we come to it.

    Quote Originally Posted by OngBonga View Post
    I think physics breaks down again here. You talk about "enough time" and photons "zipping away from each other". This doesn't make sense if the universe contains only photons. Let's assume a photon is an observer. It observes the universe to be spaceless and timeless. On this we surely agree. GR teaches us that no frame of reference is preferable to another, so we can't say the photon's FoR is wrong. If only photons exist, it's the only FoR we can use. So in a universe with only photons, the only observers that exist will agree there is no space and no time. So how can they zip away from each other? That implies movement through space.
    ehhh... IDK, still.

    GR teaches that no inertial frame of reference is preferable to another.
    A frame moving at c is not inertial.

    Quote Originally Posted by OngBonga View Post
    I think this paradox probably implies that actually a universe with just photons is not possible, ie heat death is wrong.
    What else could happen? The Heat Death is simply what happens if no hypothetical catastrophe prevents the physics we currently understand from playing out in the fullness of time.

    In order to get around Heat Death, all you have to do is end the universe sooner. If Entropy runs its course, the Heat Death is as inevitable in one direction of time as the big bang is in the other.
    Last edited by MadMojoMonkey; 11-20-2020 at 02:20 PM.
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  21. #2196
    What you're suggesting is that the moment of that final interaction is a significant phase change in the character of spacetime and the universe as a whole.
    But if we're to assume the universe had a start, and that start was a singularity containing all the energy that exists, then we have the same problem. There is a transition from no space and time, to space and time.

    To say this transition cannot happen is the same as saying the universe had no beginning.

    What about the problem of simultaneity? Are you assuming that from the origin of the final interaction, there's an expanding wavefront, moving at c that is devoid of spacetime? Wouldn't that mean there's now an expanding sheet of spacetime, with spacetime neither inside nor outside of it?
    No idea, but this does remind me of a long forgotten recurring dream I had as a young child, it's hard to explain but there was basically a line moving through space and on the one side everything was normal and on the other side it was black, this line was basically consuming the universe. I don't think that happens but it's interesting that this caused me to remember a childhood dream.

    I mean, I would imagine a sudden collapse. If there's nothing but photons, it becomes meaningless to even talk of the speed of light. Speed through what? At the instant of the last interaction, spacetime suddenly collapses into a singularity. All of it, instantly. Nothing else can make any sense to me.

    A frame moving at c is not inertial.
    What acceleration is this frame undergoing?

    What else could happen? The Heat Death is simply what happens if no hypothetical catastrophe prevents the physics we currently understand from playing out in the fullness of time.
    We also have to understand that we know that we don't understand physics completely yet. We can't actually expect to successfully predict what happens in the very late universe based on a current understanding of physics that is yet to unify QM and GR. There's always got to be a certain amount of philosophy to physics. The goal is to convert philosophy into fact over time. Science starts with banging rocks together. It's all philosophy and no fact. If we ever achieve complete knowledge, then it's all fact and no philosophy. The relationship between physics and philosophy is kinda like converting potential energy into kinetic energy.

    So I don't think it's unreasonable to answer the question of "what else could happen" with "something", and to then speculate. I assume the universe had a beginning, and it certainly appears that it did, so I assume it has an end. And since it can be argued that the beginning and end are indistinguishable from one another, ie all the energy compressed into a singularity, then my best guess on what happens next is a new big bang.

    A complete decay into radiation takes me down this path. I can imagine a heat death that is basically like counting to infinity, where it approaches heat death while never actually getting there, but the problem I have here is that it implies there was a start but not an end. It also implies an infinite universe with infinite time, because otherwise we're not counting to infinity, just a very large number.

    So for me, heat death means a total decay, followed by a collapse of space and time since there is nothing left to observe it, there is no more mass to cause gravity, there is nothing left that experiences time. At this point all of the photons, which is all of the energy in the universe, are in the same place at the same time... a singularity, and, based on observations from the very distant past, I assume that a singularity that contains all of the energy that exists is not stable and will explode.

    Or we're counting to infinity. It's one or the other.
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  22. #2197
    MadMojoMonkey's Avatar
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    Quote Originally Posted by OngBonga View Post
    But if we're to assume the universe had a start, and that start was a singularity containing all the energy that exists, then we have the same problem. There is a transition from no space and time, to space and time.

    To say this transition cannot happen is the same as saying the universe had no beginning.
    You said it correctly that we assume the universe had a start. We assume this start was a singularity. We don't know that.

    The most popular model rising in support among cosmologists now is not of a singular point going all Big Bang. The exponential expansion of the universe doesn't have to start after the Big Bang. It could be the entire Big Bang. That is to say, the Universe may extend into the infinite past to where it was a singularity, and it has been undergoing exponential expansion forever.

    Either way, the symmetry of having a beginning and an end is nice from a human storytelling perspective, but I don't see any reason the Universe should follow rules of plot.

    Quote Originally Posted by OngBonga View Post
    No idea, but this does remind me of a long forgotten recurring dream I had as a young child, it's hard to explain but there was basically a line moving through space and on the one side everything was normal and on the other side it was black, this line was basically consuming the universe. I don't think that happens but it's interesting that this caused me to remember a childhood dream.


    Quote Originally Posted by OngBonga View Post
    I mean, I would imagine a sudden collapse. If there's nothing but photons, it becomes meaningless to even talk of the speed of light. Speed through what? At the instant of the last interaction, spacetime suddenly collapses into a singularity. All of it, instantly. Nothing else can make any sense to me.
    I have real difficulties with the simultaneity, here. You're invoking GR to support this hypothesis, but you're ignoring GR in the conclusion.

    If there's 1 thing the Universe loves to do to us as physicists, it's remind us that all equivalent descriptions are equivalent. I.e. if you can describe something with a function, and there are mathematically equivalent ways to construct that function, then the Universe "sees" all those descriptions as valid, and will do anything any of those descriptions allows.

    Like the fact that linearly polarized photons have their electric fields disturbed only parallel or anti-parallel to some vector (which is itself perpendicular to the direction of propagation and the disturbances in the magnetic field). However, mathematically, a sine wave in a plane is equivalent to the sum of 2 counter-rotating helices. We observe interactions which can only be described as those 2 helices interacting with 1 molecule in different ways, rotating the plane in which the linearly polarize photon's electric field disturbances occur.

    So if there is a mathematical equivalence to a photon being described as a disturbance in the EM fields that propagates through spacetime, then I have a very strong suspicion that description will always be a way the Universe "sees" what photons are.

    Quote Originally Posted by OngBonga View Post
    What acceleration is this frame undergoing?
    I only know for certain that Einstein said so. What follows is some guesswork on my part that seems to make some sense of why.

    The frame undergoes no accelerations, not because the sum of forces = 0 N, but because all the laws of forces and motion break down when you have infinite relativistic gamma factor.

    You could say that with infinite relativistic mass, no matter how big a force you apply, F = ma will mean that a is always 0, because m is infinite. So no matter what force is applied, it cannot be enough to accelerate any mass moving at c.

    Or you could say that with infinite time dilation, there is no passage of time that allows a force to apply a change in momentum via F = dp/dt. Anything described mathematically with a d/dt in it becomes undefinable when dt can only equal 0 s.

    Quote Originally Posted by OngBonga View Post
    We also have to understand that we know that we don't understand physics completely yet. We can't actually expect to successfully predict what happens in the very late universe based on a current understanding of physics that is yet to unify QM and GR. There's always got to be a certain amount of philosophy to physics. The goal is to convert philosophy into fact over time. Science starts with banging rocks together. It's all philosophy and no fact. If we ever achieve complete knowledge, then it's all fact and no philosophy. The relationship between physics and philosophy is kinda like converting potential energy into kinetic energy.

    So I don't think it's unreasonable to answer the question of "what else could happen" with "something", and to then speculate. I assume the universe had a beginning, and it certainly appears that it did, so I assume it has an end. And since it can be argued that the beginning and end are indistinguishable from one another, ie all the energy compressed into a singularity, then my best guess on what happens next is a new big bang.

    A complete decay into radiation takes me down this path. I can imagine a heat death that is basically like counting to infinity, where it approaches heat death while never actually getting there, but the problem I have here is that it implies there was a start but not an end. It also implies an infinite universe with infinite time, because otherwise we're not counting to infinity, just a very large number.

    So for me, heat death means a total decay, followed by a collapse of space and time since there is nothing left to observe it, there is no more mass to cause gravity, there is nothing left that experiences time. At this point all of the photons, which is all of the energy in the universe, are in the same place at the same time... a singularity, and, based on observations from the very distant past, I assume that a singularity that contains all of the energy that exists is not stable and will explode.

    Or we're counting to infinity. It's one or the other.
    This is all pretty great thinking, IMO. It's fine to be lead by your suspicions, or your intuition, or whatever you want to call it. I'd even argue that this purely subjective drive is the backbone of excellent science. Just follow it up with research and experiment and try to prove yourself wrong. If you can't... you might be on to something.


    The Universe doesn't seem to have any issues at all with things moving ever-toward infinite values.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  23. #2198
    Either way, the symmetry of having a beginning and an end is nice from a human storytelling perspective, but I don't see any reason the Universe should follow rules of plot.
    Well, physics shouldn't care about the direction of time. And it's not just because it's a nice story. It's consistent with the argument that the hypothesised beginning in indistinguishable from the hypothesised end. And if they're indistinguishable, then we should expect them to behave the same. But you are of course right, I'm making assumptions, about there being a beginning, and about the final state of the universe being pure radiation. But I think the least unrealistic assumption I'm making is that space and time do not exist in a universe full of photons. That kinda seems inevitable.

    I have real difficulties with the simultaneity, here. You're invoking GR to support this hypothesis, but you're ignoring GR in the conclusion.
    There are only photons left, the concept of simultaneity kinda becomes redundant. From the FoR of each photon, everything in the universe happens in the exact same instant. You're invoking time in a universe where there is nothing left to experience time. You're an imaginary observer with an internal clock, in a universe with no clocks.

    A photon already breaks simultaneity, if this is what you think is happening. A photon that leaves the sun and is then absorbed on Earth by leaf, from our FoR that took just over 8 minutes. From its FoR, it took zero time. So observers on Earth already disagree with the photon about the order of events. The photons says everything that happened during its existence happened at precisely the same time. The observer says no, this happened and then this happened. Simultaneity only holds if you actually have clocks.

    I only know for certain that Einstein said so.
    Fair enough. In a universe with only photons though, with there only being one FoR that exists, is it still non-inertial? Once we have only photons, this FoR is not accelerating relative to every other FoR that exists... it is now truly inertial, surely? There is no other frame it has relative motion to.

    The Universe doesn't seem to have any issues at all with things moving ever-toward infinite values.
    Unless the universe is infinite, then decay must eventually be completed. Why would the last interaction never happen? Why would the last particle not decay into a photon if all the others did? Even if the time between each particle decay was increasing at an exponential rate as the mass in the universe slowly evaporated, it's still finite.

    If the universe is infinite, then I can see how decay will take forever. But if it's finite, then I can't.
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  24. #2199
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    Quote Originally Posted by OngBonga View Post
    Well, physics shouldn't care about the direction of time. And it's not just because it's a nice story. It's consistent with the argument that the hypothesized beginning in indistinguishable from the hypothesized end. And if they're indistinguishable, then we should expect them to behave the same. But you are of course right, I'm making assumptions, about there being a beginning, and about the final state of the universe being pure radiation. But I think the least unrealistic assumption I'm making is that space and time do not exist in a universe full of photons. That kinda seems inevitable.
    The notion of there being a direction of time is presupposing the existence of time, and you go back and forth on whether you talk about time being a property of the Universe. The fact that you're asserting what time must be in order to satisfy your hypothesis is fine, but keep an eye on that assumption.

    I.e. the Big Bang may be an exponential expansion that goes back into infinite time. We do not understand what caused inflation, nor what failed to turn the Big Bang into a black hole. We can only use our current models from what would be something like 10^-35 s after what would be a singularity if we project constant contraction in backwards time. But we don't know anything about what could have happened before that moment in time.
    Maybe it was a true singularity that was somehow not a black hole that experienced a sudden inflation. That Universe has a "beginning" as you say.
    Maybe the inflation goes back to the infinite past, asymptotic to a singularity, but never truly a singularity in any "real," "finite" time. That Universe does not have a "beginning" as you describe.

    Quote Originally Posted by OngBonga View Post
    There are only photons left, the concept of simultaneity kinda becomes redundant. From the FoR of each photon, everything in the universe happens in the exact same instant. You're invoking time in a universe where there is nothing left to experience time. You're an imaginary observer with an internal clock, in a universe with no clocks.
    Just because there is one way to view the universe that contains only non-inertial frames, that doesn't mean it's the only way to view the universe. Physics doesn't actually care if anyone is there to observe anything, it only describes what you would observe if you were there. That doesn't change. If you were an inertial observer in the Heat Death universe, you would see photons moving at c. I don't see anything in your arguments that invalidates that (albeit conditional) statement. If you're asserting that the laws of physics as we know them now describe the Universe getting to Heat Death, then it seems inconsistent to toss this principle out at the end-game.

    Whether or not there is an observer to observe doesn't change the physics of what an observer would observe if they are there. It's all conditional statements in physics.

    Which is why I'm saying that if your specific hypothesis is that we rule out anything depending on an observer, then I have nothing to comment on that as a physicist.

    Quote Originally Posted by OngBonga View Post
    A photon already breaks simultaneity, if this is what you think is happening. A photon that leaves the sun and is then absorbed on Earth by leaf, from our FoR that took just over 8 minutes. From its FoR, it took zero time. So observers on Earth already disagree with the photon about the order of events. The photons says everything that happened during its existence happened at precisely the same time. The observer says no, this happened and then this happened. Simultaneity only holds if you actually have clocks.
    Emphatically no. Photons define simultaneity, they don't break it. There's no problem with causality that different observers see the same events happen in different orders. That's not causality. The apparent order of events to a naive observer is not fixed unles c is inf.

    What all observers will agree on is whether or not event A could have caused event B (or vise versa), based on applying relativity correctly and determining the "light cones" of each event, and seeing if one event lies inside or outside the other event's light cone. If it is inside, then it could have been caused by the other event. If it is outside, then it could not have. The only way for both events to be able to "cause" each other, is if both events happened at the identical same point in space-time. I.e. that it was indistinguishable from a single event.

    The "simultaneous" connection of light is a prerequisite for causality, as light moves at c, the speed of causality. (most popular opinion)

    I know a physicist with a doctorate who says it's not necessary that c is the same for light and for information, we only know those 2 speeds are currently indistinguishably close based on our ability to measure these things. So there could be a tiny discrepancy to causality to be measured that we haven't yet been able to measure, but there's nothing to suggest it's there... just that as good scientists, we must acknowledge the limitations of our equipment.

    Quote Originally Posted by OngBonga View Post
    Fair enough. In a universe with only photons though, with there only being one FoR that exists, is it still non-inertial? Once we have only photons, this FoR is not accelerating relative to every other FoR that exists... it is now truly inertial, surely? There is no other frame it has relative motion to.
    There's isn't 1 FoR, there's a unique non-inertial FoR for each photon.
    If you want to talk about an (any!) inertial FoR, then all the photons are moving at c.

    Quote Originally Posted by OngBonga View Post
    Unless the universe is infinite, then decay must eventually be completed. Why would the last interaction never happen? Why would the last particle not decay into a photon if all the others did? Even if the time between each particle decay was increasing at an exponential rate as the mass in the universe slowly evaporated, it's still finite.

    If the universe is infinite, then I can see how decay will take forever. But if it's finite, then I can't.
    If we have a universe of photons, it would be something like the total mass-energy of the photons is exactly enough to create exactly the right spacetime curvature to drive all photons to infinite red-shift, but only given infinite time.

    This is talked about in physics as the universe being "open" or "closed." What I just described would be the critical point between open and closed. If open, the photons keep being red-shifted, but it's never ever going to be enough to infinite red-shift them (making them 0-energy / non-existent). If closed, then the infinite red-shift happens in less than infinite time.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  25. #2200
    The notion of there being a direction of time is presupposing the existence of time, and you go back and forth on whether you talk about time being a property of the Universe. The fact that you're asserting what time must be in order to satisfy your hypothesis is fine, but keep an eye on that assumption.
    Good point, noted. I'm not sure time is a property of the universe, rather a property of mass.

    I.e. the Big Bang may be an exponential expansion that goes back into infinite time
    Sure, but it certainly appears that the universe was once very small, at least in terms of the Plank scale. I know we've discussed the Plank unit before and you didn't seem to think it was an important threshold, but everything I have read about it seems to imply it is. That is, if everything occupies a single Plank volume, then we might as well call it a singularity. The significance of the Plank scale is related to it being smaller than the shortest wavelength of light. So even to a photon, it's a significant measure. If the universe is less than a Plank volume, then light cannot even propagate. That is, it no longer a wave.

    ...nor what failed to turn the Big Bang into a black hole.
    How do we know we're not inside a black hole? I mean, cosmic expansion is indistinguishable to the accelerating spacetime within a black hole.

    That Universe does not have a "beginning" as you describe.
    Again, Plank units come into play here. If light cannot exist as a wave, then nothing exists that is slower than light. So again we come to the problem of what time actually means in this world. It seems to me that a beginning of time is inevitable, it emerges when something moves slower than light. That can't happen until light can actually move. But of course there's a paradox here... it takes time for this process to happen. I have no idea how to resolve this paradox.

    Physics doesn't actually care if anyone is there to observe anything, it only describes what you would observe if you were there.
    I understand this, but in a universe of photons, a physical observer appearing radically changes the entire landscape of the universe. How can we possibly imagine what the universe would be like if we were a non-physical (imaginary) observer?

    If you were an inertial observer in the Heat Death universe, you would see photons moving at c.
    Indeed, because you exist. But if you're, idk, an observer from another universe somehow peering into this universe, things could be very different. If only photons exist, what does it mean to move at c? Does a photon move at c relative to another photon? Or does it move at 0?

    Whether or not there is an observer to observe doesn't change the physics of what an observer would observe if they are there.
    I think this is only true in a universe with mass. A massless universe is a different ball game altogether. An observer appearing introduces gravity to the universe. Without mass, there is no gravity. Like I say, a radical change of landscape.

    Which is why I'm saying that if your specific hypothesis is that we rule out anything depending on an observer, then I have nothing to comment on that as a physicist.

    I appreciate physics cannot answer these question, not now and probably never, because we're talking about things that can never be measured. Ultimately, we're talking here about what time actually is, not how we observe it and measure it. And we're talking about a massless universe, something that will never exist while we exist. So it's always going to be philosophy.

    What all observers will agree on is whether or not event A could have caused event B (or vise versa), based on applying relativity correctly and determining the "light cones" of each event, and seeing if one event lies inside or outside the other event's light cone.
    I'm pretty sure that here you imply that all observers have mass. A photon is clearly a different kind of observer to a human, or a cat, or a hydrogen atom. How does a photon observe causality? To the photon, the past, present and future are all the same thing. A photon can say "A could have caused B, but B could have caused A", because the photon observes everything happening at the same time. In fact it's absurd to even say the A could have caused B, or B caused A, rather the photon would say A and B are the same thing because they happened at the same time in the same place. The universe is a completely different world to a photon, due to infinite time dilation and length contraction.

    The only way for both events to be able to "cause" each other, is if both events happened at the identical same point in space-time. I.e. that it was indistinguishable from a single event.

    Exactly! I didn't read this before making that last comment! The difference between an observer with mass and an observer without mass is not to be ignored. If you don't have mass, then you're moving at c. It's absurd to assume an observation from the FoR of something that has no mass yet doesn't move at c.

    There's isn't 1 FoR, there's a unique non-inertial FoR for each photon.
    This feels like as much an assumption as saying the opposite, that a photon's FoR is indistinguishable from another photon's FoR. Only the latter seems to make more sense to me, because it experiences no time, and therefore no space. It exists in a singularity for all existence. That's its FoR. Only things that move slower than it will disagree.

    If we have a universe of photons, it would be something like the total mass-energy of the photons is exactly enough to create exactly the right spacetime curvature to drive all photons to infinite red-shift, but only given infinite time.

    I don't see why it would be an infinite red shift. The universe seems to be quantum. There's a minimum unit of energy, there's a minimum wavelength of light, so there comes a point where something can't red shit any more because it's already at the minimum "colour".
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  26. #2201
    A cookie for the first person to find my outstanding typo.
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  27. #2202
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    I don't want your cookie. It's probably what caused that "typo."

    The reference frames of the photons in your description are not equivalent. They may lack time, and see the universe as a volumeless sheet, but they all see a different sheet. Their FoR's are not equivalent.

    E = hf for a photon.
    There's no minimum energy, E, nor minimum frequency, f. h is Plank's Constant and describes the proportional relationship between energy and frequency.
    There is no quantization of allowed energies aside from the maximum wavelength that could fit in the Universe, stretching from end to end. So long as the universe is finite, that wavelength is non-0. If the universe can reach "infinite" length across it, then there can be photons which are infinite red-shifted... Stretched to non-existence.

    It's interesting to speculate a quantum entangled ground state where all photons have been stretched to overlap... that's at least like what you're describing... though from a QM argument and not a GR argument.
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  28. #2203
    I don't want your cookie. It's probably what caused that "typo."
    More fibre needed.

    There's no minimum energy, E, nor minimum frequency, f
    I don't think this is right. I'm not trying to outsmart you or anything, I'm not waving my dick about. I just believe this contradicts Planck's discovery, where he assumed a minimum energy value to predict the black body spectrum, and his "hack" solved the problem of predictions failing to match observations, aka the Ultraviolet Catastrophe. The "hack" in question was to assume that energy is quantum, that it is found in integer values. Planck himself expected his "constant" to be zero, but instead it was a very small but non-zero number. This was the birth of quantum mechanics. Well, perhaps not the birth. The maturity. Planck's work was built on foundations laid during the 19th century, but his constant was confirmation that light comes in discrete packets - photons - and allowed physicists of the day to develop quantum theory.



    I could definitely be jumping to conclusions, failing to fully understand what Planck actually discovered, but it seems to me to be the first concrete evidence of the quantum nature of the universe, including space, time, length, and indeed energy. That is, a minimum integer value. It's so tiny that from the pov of the macro world, it appears infinitely divisible, but this doesn't seem to be the case.

    By the way, I made a schoolboy error with my assumptions. Where I say "minimum frequency", I actually mean "maximum frequency", or "minimum wavelength". But of course, shorter wavelengths mean more energy, not less. So there would likely still be a "minimum frequency" associated with the lowest energy level possible for a photon. But that "minimum frequency" or "maximum wavelength" could be larger than the universe, frankly I can't even begin to guess at that.
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  29. #2204
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    The blackbody radiation spectrum describes the emission of photons by electric charges that are not at absolute 0. There is a conservation of angular momentum involved, in that the photons are spin-1 objects, and the object emitting it will have to be able to shed rotation (if you'll allow the sloppy language) to emit the photon. The rotational states are quantized, so the emitted photons have quantized energies.

    More broadly and more generalized, particles in bound states have quantized "allowable" states. Among those parameters confined by the boundaries of the system is the energy of a particle.

    The blackbody spectrum is emitted by accelerating particles in a bound system - an atom for instance, or an ion in a plasma. The "allowed" energy of those particles in the bound system are quantized, and thus the photons they emit when changing energy states are discrete in frequency, corresponding to the difference in energy between the final and initial state of the particle's transition.


    In the Heat Death universe, there are no particles left to be bound to any system. Thus the only boundary left is mere existence. The photons exist "in" the universe. So if the universe has a finite size, then that size quantizes the minimum frequency that can resonate, but it's not quantized unless the size of the universe is quantized. I.e. so long as the boundaries of the universe expand "smoothly" and not like a step function, then there is nothing left to quantize the bound states.

    I suspect you'll dither over the propagation of photons in the EM fields being observation by the EM fields, and without that, there are no photons at all... but if those photons propagate through EM fields, then the expansion of spacetime will inevitably stretch their wavelengths to longer and longer lengths, corresponding to lower frequency and thus energy.

    ***
    There's an open question in physics about the Conservation of Energy and how it relates to the changing energy of photons as they propagate through spacetime. It is readily observable that photons decrease in energy as they travel through expanding spacetime, but it is not remotely clear where that energy goes.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  30. #2205
    Something I watched earlier seems to imply there is compelling evidence (though far from proof) that light from before the big bang survived into what we call our universe. This supports Penrose's CCC theory, indeed he even went as far as to predict such "rings" of light in the CMB. It does seem there was a "before", but I still have a huge problem with the concept of time, and therefore space, in a massless universe.



    It seems the theory predicts that the last "universe" ended after the last supermassive black holes evaporated... it's still leading me down the path that a massless universe is unstable and marks an important threshold that radically changes the nature of the universe. If the last universe really did end with Hawking radiation, why did the new universe begin? And should we not expect a heat death to have the same effect?

    It is readily observable that photons decrease in energy as they travel through expanding spacetime, but it is not remotely clear where that energy goes.
    It kinda feels like we're stretching an elastic band. The energy is converted from kinetic energy into potential energy - tension. If expansion stops, all that tension is released. Maybe this is what causes the big bang... when there is no mass left in the universe, there is nothing left to experience time, and therefore space, expansion ceases, and all these "stretched" photons "snap" from maximum red shift to maximum blue shift. Obviously this is highly speculative, and the tension analogy is very classical and not remotely quantum, but it's appealing.
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  31. #2206
    Going back to the discussion about causality. In the very early universe, cosmic inflation was insanely fast... as in, much faster than the speed of light. It took a fraction of a second to go from near singularity to a massive universe. Furthermore, we observe spacetime expanding faster than c when we observe very distant galaxies.

    If spacetime can expand faster than light, why should we assume it can't contract faster than light?
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  32. #2207
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    Quote Originally Posted by OngBonga View Post
    Going back to the discussion about causality. In the very early universe, cosmic inflation was insanely fast... as in, much faster than the speed of light. It took a fraction of a second to go from near singularity to a massive universe. Furthermore, we observe spacetime expanding faster than c when we observe very distant galaxies.

    If spacetime can expand faster than light, why should we assume it can't contract faster than light?
    IDK.

    We don't have a model for the cause of inflation or the cause of the accelerating expansion of the universe we currently observe.

    We don't have any good reason to assert that something like cosmic inflation but in reverse could never happen because we don't even know how it happens forward. All we know is that we do not observe anything moving faster than c, no matter how hard we try to. And we have to accept that as a fact and find the consequences, which bear out more facts. Those predictions are observed, so we're probably on to something, but we can never know how far from "finished" physics is because physics describes what we observe and we can never prove that we have observed all there is to observe.

    So ... yeah.


    I do like the idea that once it's a universe of photons, the expansion of the universe keeps stretching those photons to lower and lower frequencies, longer and longer wavelengths, and (if there is space and time) that is asymptotic behavior to a ground state like a Bose-Einstein condensate... where all the bosons (photons are bosons) in the system share the ground state. 'Cause there's an opposite effect on Bosons to Fermions - where fermions express what manifests as a force pushing out another identical particle from being in the same state at the same time, bosons actually express what manifests as a force pulling identical particles into the same state at the same time.

    And if everything is tending toward that ground state where literally everything in the universe is in the same state at the same time... then I think we have your model though QM arguments without denying the existence of space or time in the universe.
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  33. #2208
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    Oh, my idea doesn't work for a lot of reasons.

    In an expanding universe, the energy density can only go down, and the effect on the photon's wavelengths is less than the effect on the space they traverse... in short... it stretches the photons, but never in a way that the photon's wavelengths are longer than the space expanded... so they will not expand to "fill" the space.

    There something called the Schwinger limit that I need to look into that probably has something to do with this.
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  34. #2209
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    Me asking questions of a proper PhD in GR physics in another forum.

    Me: I have a friend asking a lot of questions based on his uneducated (but nonetheless pretty darn good) understanding of GR. And he's got this notion that in a universe of only photons, it becomes meaningless to talk about inertial reference frames, and since all that's left is photons, the only things left to observe the universe see it with no volume or time.

    ProbablyMagnets: I think he's mostly right about a universe of just photons, under some assumptions that theres no unification. It's true at least that to completely describe the hilbert space of that universe you dont need the whole thing, only a single lightcone.but in that context theres no analogy to measurement so you're bound to find some things that dont make sense



    IDK exactly what he just said, but I'm pretty sure he said you're onto something, ong.


    EDIT: Dafuq happened to the formatting when I copy/pastad?
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  35. #2210
    That's definitely not easy to understand word salad, but I'm glad your colleague didn't just laugh and say "yeah uneducated lol".

    I really don't know about "onto something", I still haven't resolved the paradox of a process that takes time in a universe with no time. The best I can do is to say the "timeless" era is instant and actually does not take time to transition from massless to big bang to mass. At the instant of the "final interaction", a new big bang. But that's still cause and effect, so there's something not right.

    As for the copy/paste, hold down shift with ctrl/v and it'll "paste in plain text" instead of whatever font you copied it.
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  36. #2211
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    I'm pretty sure that "uneducated (but nonetheless pretty darn good) understanding of GR" is a good way to describe what you understand. Maybe it's harsh that someone with a PhD considers anyone without a PhD uneducated, but I have a BS and next to ProbablyMagnets, I just have my foot in my mouth the whole time. I wouldn't consider myself educated in GR, so don't take it like a casual comment that you're uneducated.

    You 'tard.

    His attitude on Conformal Cyclic Cosmology is pretty much a brick wall. He says it's too far fetched to bother with applying actual physics to it because there are much better things to spend time on, basically. That statement reflects a typical attitude among people elbows deep in their tiny corner of post doctoral research.

    I think you sussed out part of what he meant with a measurement problem. If what he means is that distances are ill defined, then it is equivalent to saying time is ill defined, and thus we have problems with saying a "timeless, volumeless" universe, because those words are meaningless in that universe.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  37. #2212
    I am uneducated, it's definitely not a term I have a problem with. And actually it's kinda liberating, as I feel I have more freedom to speculate and to philosophise.

    This really does come down to what time actually is. It's not really about measurement, which is why it's not physics. I can totally understand why someone educated would dismiss these kind of speculations, because like your friend says, it's a waste of time when there are more productive things to think about. I'm not living within that boundary.
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  38. #2213
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    I'll just leave this here:
    (vrchat map of a rotating space station)



    Would these need energy to keep spinning? I know conservation and all that, but every time you move weight up and down its radius you make it spin slightly faster/slower. There could be various losses there, right? I saw two guys fight about it on quora. seemed inconclusive.
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  39. #2214
    I don't think so. If you move up and down, you're just converting one form of energy to another, and then converting it back. It might spin slightly faster as you move to the centre, and then slow down again as you return to the edge. The total mass, and therefore inertia, remains constant. If such a city were to rely on imported resources such as water, then its mass is increasing, and this would slow the rotation down as inertia increases.

    That's my best guess anyway. I look forward to mojo's comments.
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  40. #2215
    Space isn't a perfect vacuum, so there would be very slight friction, which converts rotation into heat, but the energy lost will be miniscule on short timescales. A boost every century or so should sort that problem out.

    I'd be more worried about asteroids. I can't imagine that would end well, what with there being no atmosphere to burn up the approaching danger.
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  41. #2216
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    The total angular momentum of an isolated system never changes. So long as nothing is carrying angular momentum away from the ship, any changes in the rate of spinning due to changes of geometry will return to the same rate of spin for each geometry. (I specifically mean the geometry of mass distribution about the rotational axis, here).

    I_total * {omega} = [constant]

    Where I_total is the total moment of inertia for the object about its rotational axis, {omega} is the angular velocity of rotation about that axis, and [constant] is whatever number that is at one time is the same number at all times.

    If the spaceship burns fuel or otherwise transfers angular momentum away from itself, that is an "external" angular momentum in my model, just for clarity. It's arbitrary where we draw our boundary, but if we don't care about the angular momentum of the spent fuel, then we should not consider it "internal" to our system. Even though the fuel leaves the ship in a straight line, IF that straight line does not intersect the ship's axis of rotation, THEN it is carrying angular momentum away from that ship/system.

    Yes, moving mass toward or away from the axis changes the moment of inertia of that object about the ship's axis of rotation, and if the I_total increases, then the {omega} decreases and vise versa. Moving enough mass could well move the axis of rotation, relative to the ship. Like making the station "wobble." However, provided those masses are moved about inside the ship by forces inside the ship, then there is no transfer of angular momentum away from the ship, and so it's total is constant.

    The ship can wobble if the masses are pushed out of line, and you could effectively deform the ship into a rotated copy of it's prior self with enough moving of mass in the right ways. So while the direction of the ships angular momentum cannot change, the ships orientation with respect to that axis can change. Assuming one goes moving masses around willy nilly with no care to the greater effect on the stations dynamical false gravity.

    I mean... an nice circular space station spinning the way it should could end up spinning like a flipped coin, but about the same rotational axis, if the movement of masses isn't done carefully or with a reactive system to counteract the humans moving about in their "random" ways.
    Last edited by MadMojoMonkey; 12-08-2020 at 12:26 AM.
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  42. #2217
    I did think when I watched it that it was a little unrealistic to go the the centre. The closer to the centre you are, the more centrifugal force you experience and the "gravity" is stronger. If the ship is too small, even at the edge the "gravity" your head feels is more than your feet, to the point you would notice. I would imagine this would be very noticeable in the centre.
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  43. #2218
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    Quote Originally Posted by OngBonga View Post
    I did think when I watched it that it was a little unrealistic to go the the centre. The closer to the centre you are, the more centrifugal force you experience and the "gravity" is stronger. If the ship is too small, even at the edge the "gravity" your head feels is more than your feet, to the point you would notice. I would imagine this would be very noticeable in the centre.
    You have it backwards. The "gravity" is really a centripetal acceleration in this rotating reference frame.

    a_cent = -{v_perp}^2 / r

    where a_cent is the centripetal acceleration felt by the object, v_perp is the speed of the object perpendicular to the vector r, which points perpendicularly from the axis of rotation to the object.
    (bold indicating a vector)

    Note the - sign indicates a_cent is in the opposite direction of r, as a_cent points toward the center and r points away from the center.

    v_perp is proportional to |r| for an object in circular motion, and always perpendicular to r.
    We can derive this from the definition of radians {arc length} = r {theta} if we take the time derivative of both sides.

    v_perp = r {omega}

    where omega is the angular velocity of the spaceship, and r is the distance from the axis of rotation.


    Plugging this in to the first equation above, dropping the - sign and vector notation to talk about the magnitudes of these forces, now.

    a_cent = (r {omega})^2 / r = r {omega}^2

    We see that for a given omega, increasing r is increasing a_cent, which means we feel that gravity increases with increasing distance from the axis of rotation.

    EDIT: we also see that when we move toward the center, we keep decreasing our distance from the axis of rotation. Decreasing r decreases the a_cent, i.e. the strength of the artificial gravity. At the axis of rotation, there is no a_cent, and the artificial gravity is 0 m/s^2 at the axis.

    EDIT2: OH FFS!!! Me losing points for rookie mistakes!!! a force is not equal to an acceleration!!! Gah!
    Shame on me!!
    All those times I talk about F_cent I really meant to say a_cent, the centripetal acceleration.
    I am so ashamed. I have corrected my errors.
    Last edited by MadMojoMonkey; 12-08-2020 at 12:17 PM.
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  44. #2219
    So wrong inertial force and wrong vector. Oops!
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  45. #2220
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    80 second physics demonstration showing the relationship between moment of inertia, I, and angular speed {omega} being conserved.

    This system is analogous to moving masses about on a rotating spaceship. In this model, all the masses move in a spherically symmetric way, but that's not a necessary part of the law of conservation of angular momentum.




    EDIT: the V-sauce video "Laws and Causes" gives a beautiful link between the conservation of angular momentum and forces. I can link that, too if you're interested.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  46. #2221
    I came across this post on youtube...

    Einstein Violated? Objects lower in altitude accelerate toward the ground at a greater rate than those higher up by the ratio of the squares of their distances from the center of the attracting mass. So wouldn’t someone in a very long windowless elevator falling toward the ground of an atmosphere-less planet see a free floating object that is closer to the floor of the elevator than the observer (and thus at an incrementally lesser altitude) see that object drift away from him toward the floor of the elevator since it is accelerating downward at a greater rate than he is? If so that would violate Einstein’s principle of equivalency because an observer in a window-less elevator free-floating in deep space far removed from any gravitational field would see such an object within its walls not moving at all.
    I replied with this...

    This is actually a good thought experiment. I'm not sure of this, but my best guess is that time dilation (and therefore length contraction) becomes a factor. The person looking at the ball won't see it accelerate at all, it will appear the same distance away until it hits the ground, even though it is subject to greater gravitation. This is because the observer and the object are not experiencing time flowing at the same rate... the lower object is "slower" from the point of view of the person.

    This is just my speculation though. I'm going to ask someone smarter than me their opinion on this. I'll update if I get a reply.
    Am I thinking along the right lines here? Or is there a simpler explanation?
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  47. #2222
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    Einstein's thought experiment elevator is in a uniform gravitational field. The one described in by the poster is not a uniform field, it varies in magnitude.

    In the Einstein elevator, the acceleration of gravity is the same everywhere, the elevator isn't falling "toward a planet," it's in a hypothetical universe where gravity points the same direction with the same strength everywhere... or a "hand of God" is pulling the elevator "upward" with a constant force - giving the illusion of a constant acceleration due to gravity pointing "down."


    EDIT: this uniform gravitational field in Einstein's thought experiment is not caused by any mass. It's simply hypothesized to illustrate a point.

    A mass distribution that would create this kind of uniform field would be an infinite flat Earth. It's analogous to an infinite capacitor plate, replacing electric charge with gravitational mass and the Electric field with a gravitational field.
    Last edited by MadMojoMonkey; 01-12-2021 at 10:44 AM.
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  48. #2223
    So you're saying that the observer would see the object moving away from him?
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  49. #2224
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    Quote Originally Posted by OngBonga View Post
    So you're saying that the observer would see the object moving away from him?
    Yes.

    The gradient in the gravitational potential is observable. Take it to the extreme. You're falling into a black hole. You experience spaghettification. This is perfectly in line with GR, and not in violation of the Equivalence Principle.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  50. #2225
    Cool, thanks.
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  51. #2226
    I thought the moon went around the Earth. What's this parabola shit?

    https://twitter.com/amazing_nature0/...29863297003523
    I just think we should suspend judgment on Trump until we have all the facts through an inquiry
  52. #2227
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    Quote Originally Posted by Poopadoop View Post
    I thought the moon went around the Earth. What's this parabola shit?

    https://twitter.com/amazing_nature0/...29863297003523
    I mean... throw me a softball, why don't ya?

    https://twitter.com/PicPedant/status...44063486091266

    Literally just scrolled down the page to find the answer.


    Also... parabolas only curve in one direction, no inflection points.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  53. #2228
    Not really a question, but did you see the recent PBS Spacetime? They *might* have detected the gravity wave background, basically the sum of all gravitational waves, by observing pulsars across the galaxy. Pulsars are so accurate at timekeeping that the slightest discrepancy tells us something about the fluctuating distance between it and us.

    Here's some pulsar porn...



    The last one is spinning at 1/7 the speed of light, which would obviously create immense centrifugal forces. The fact this doesn't cause the star to disintegrate shows just how fucking ridiculous the gravity is.
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  54. #2229
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    Not really going to answer what is not really a question, I suppose.

    I wonder what centrifugal force corrections you need when the spacetime is being frame dragged along with the rotation.


    Did anyone watch the video of the Mars rover Perseverance landing? I get all squishy inside when I see that. Like... humans had to pre-program a million things correctly and then push a button and step back and wait and hope that they didn't just waste billions of dollars. To see it all go off flawlessly under automated control to gently set down a nuclear powered SUV with a scout helicopter on another planet just gets me all excited. It's a nice counter to the political world of doom and gloom to see how truly amazing humans can be sometimes.

    Last edited by MadMojoMonkey; 02-23-2021 at 01:58 PM.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  55. #2230
    At around the 1:05 mark there looks like a river valley.

    It's very exciting. We're obviously a long way off putting humans on Mars, probably won't see it in my life, but this is really great to see. It's worth every single penny. Humans can't survive the end of the world if we're stuck on this planet, so these missions are extremely important for our future as a species.

    Absolutely wonderful.
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  56. #2231
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    What is the muon discovery?

    It's that there's been an experiment running at multiple locations to test a vibrational (rotational?) movement of muons in a magnetic field (I think). The Standard model predicts a behavior. The experimental behavior observed is not that. It's sped up. Something is making the muons move faster. Something is increasing the energy of the movement. It's easy to hypothesize that there's some not-as-of-yet described force acting on the muons.

    They've not officially released the results, yet, out of an abundance of caution and the luxury in physics to demand a 5 sigma result before making any bold claims. That is, they've already shown that this phenomenon is almost certainly not a mistake in collecting data or data analysis. (There could be mistakes in the experimental setup or the interpretation of the data, but the data, if good, is almost certainly disproving the prediction of the Standard Model) They've already reproduced the results at a 2nd (presumably independent) lab. As much as I'm holding out for the official announcement, as of today, I'm expecting that announcement in the coming years.

    What it means is that there is something going on that is not explained by the Standard Model. That hasn't happened in about 100 years. The Standard Model has been the most precise and powerful predictive model ever developed by humans. The fact that a spotlight has been shown on what seems to be a phenomenon not accurately described by the SM is exciting. People are wildly speculating a lot of stuff that could come from a new discovery being real and a new group of physicists digging in to that and explaining it. At this time, that is all pure speculation.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  57. #2232
    It's easy to hypothesize that there's some not-as-of-yet described force acting on the muons.
    This is how the BBC presented it, but their article was super dumbed down. I watched PBS Spacetime last night and they didn't mention a "new" force at all.

    What stuck me from PBS was that a muon is basically a "heavy" electron... it's identical to an electron in all ways except mass. I find that very interesting. My best guess is the muon interacts with the Higgs field differently to an electron. What makes a muon different to an electron? Why does the muon interact differently? Why is it otherwise identical?

    I'm not going to pretend to have anywhere near as good an understanding of the SM than I do GR, so this is all way beyond my grasp. A new "force" seems a little unrealistic though. The BBC even referred to gravity as a fundamental force. But GR says gravity is an inertial force, aka a "fictitious" force. And that makes sense when you understand what GR says gravity is... spacetime curvature rather than particle interaction. So I'm not paying any attention to what the BBC say.

    I'm not surprised we have found something that doesn't agree with the SM though. It's clear there is something missing, from both the SM and GR, because they don't work together. I hope we're moving in that direction... unification.
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  58. #2233
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    Here's an article by Fermilab - much less dumbed down, but still dumbed down.

    https://news.fnal.gov/2020/06/physic...t-calculation/

    The actual experiment is subtle and ingenious, IMO. They have some muons in a magnetic field, and the muons rotate in that magnetic field, such that their intrinsic magnetic moment is rotating between aligned and anti-aligned with the magnetic field. When muons decay, they do so via the weak interaction, which is not parity conserving - it ejects an electron when the muon's magnetic moment is aligned with the external field, but it ejects a positron when it is anti-aligned. By observing the emission of electrons and positrons, the precession frequency (rotation frequency of the muons) can be calculated. This is being used to determine what is called the g-factor of muons.

    I don't really want to get into g-factor, because it's one of those relatively deep QM things that comes up where the theory was off from experiments by a factor - named with the variable g - which is predicted to be equal to 2 by the Dirac equation (the fully relativistic big brother of the Schroedinger equation).

    Basically, we had to inject this factor of 2 to make the theory meet up with experiments until an equation came along that actually predicted the value of 2 - putting the g-factor = 2 on firm theoretical footing.

    Now we have an experiment that is indicating that g is not equal to 2 for muons. So there's something amiss with the Dirac equation - subtle though it must be. Or something more than the Dirac equation at play. We don't know, yet. We just have an indication that a prediction is not bearing out to experiment thus far. The explanation is not yet known.


    EDIT: Apparently the real talking point is that physicists have quantified the light-light interaction - by which a muon emits and immediately re-absorbs a photon. Until now, the error bars on the experimental data *could have been* wide enough to encompass the theoretical predicted result. While the light-light interaction plays a tiny role in the muons motion, it plays the dominant role in the uncertainty of a measurement. It has been worked out that the contribution to the uncertainty from this interaction is not enough to close the gap between experiment and theory.
    Last edited by MadMojoMonkey; 04-08-2021 at 12:45 PM.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  59. #2234
    Thanks for the article, bookmarked for later consumption.

    it ejects an electron when the muon's magnetic moment is aligned with the external field, but it ejects a positron when it is anti-aligned.
    This is super interesting. It kinda implies that natural processes result in 50% matter and 50% antimatter, which of course begs the question of why we only observe matter in our observable universe. Of course I understand the idea that a simple imbalance of 0.00000000000000000001% is enough over time to result in a universe of matter and photons, but that imbalance is still weird. This is a digression though.

    I don't really want to get into g-factor
    Matt on PBS did go into this, at least scratching the surface, and I got it enough to understand why they're excited. They were talking about G-2, which would be zero if SM predictions held, but it was a small fraction above zero. This involved Feynman diagrams, which are really cool in their own right and because I have a little knowledge of what they are, I could follow this line of thought. I know the most simple Feynman diagrams represent the highest probability, and that there are potentially infinite amounts of different configurations, but with more complexity they become ever more unlikely. I get what's happening here mathematically... we're converging like an infinite fraction that doesn't blow up to infinity. So I could understand how they got to this G-2 number mathematically using Feynman diagrams.

    I'll read that article after dinner.
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  60. #2235
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    The weak interaction is the only hypothesis I know of that uses currently known physics to explain why there is an abundance of matter and not anti-matter in the universe. Basically, as bad-ass as you already imagine the Big Bang to be, it probably contained more than a billion times more energy than the mass energy left in the universe we observe. Nearly all of that annihilated in matter / anti-matter cancellation, but a tiny imbalance in the chaos of that event left one weak interaction process favored over its equal opposite. And there is matter left in the universe. All of this is pure speculation, AFAIK. I don't think I've seen a mathematical model that lays out that imbalance in the early universe.

    Oh. Did PBS Spacetime already hit this? I'll check it out right away.

    On the Feynmann diagrams... I know some people doing research into them and apparently the diverging pathways available in the diagrams begin to dominate the diminishing probabilities after about 20 iterations down. The total energy in the exponentiating pathways possible drops and drops out to about 20-ish steps... so the early speculation was that they'd keep diminishing and be convergent. But now we're finding that the total energy available in the really complicated pathways starts to rise again. So the initial assumption that the more complicated terms played ever less relevant roles seems to have some doubts attached to it.

    However, this is one group of researchers, and they're all quite convincing, but time will tell.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  61. #2236
    I just think we should suspend judgment on Trump until we have all the facts through an inquiry
  62. #2237
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    broken link?
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  63. #2238

    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  64. #2239
    ^ that's what the "broken link" was showing.

    Not sure why it didn't work for you.
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  65. #2240
    How many Planck mass sized black holes would it take to account for dark matter? This seems such a simple solution for dark matter that you have to wonder why it's 2021 and they're only just considering it. The hypothesis is that when a black hole evaporates, it leaves behind a naked singularity with enough mass to be non-zero, but too little mass to evaporate.

    That's after a talk about why dark matter probably isn't larger black holes.

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  66. #2241
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    A Planck mass (assuming h-bar and not h is used as Planck's constant - an arbitrary choice), is 22 micrograms. Not that small, on a particle scale. I mean, unlike the Planck length, which happens to be quite small, other Planck units are not dazzlingly evocative of quantum woo woo weirdness - something the Planck length enthusiasts don't really talk about much, but I digress.

    It would take an astronomical number of them to account for the mass in the galaxies that we cannot see, but whose effects we can see.

    What is the proposed mechanism that prevents Hawking radiation from evaporating this micro black hole?

    If there are naked singularities in the universe, they are almost certainly quite rare. The mechanisms by which a black hole can shed its event horizon require it to somehow acquire angular momentum at a rate great enough to compensate for its increasing mass. There isn't a single known observation of a naked singularity, and if they exist, they are lost in the uncertainty of the data. Which means that if they are *there*, their effect on the universe we see is not a dominant factor in the universe's structure. I.e. for any proposed naked singularity that is consistent with GR, we can rule out that those are the dark matter that we see the effects of, but not the cause of.


    What says that a naked singularity will not interact with light at all.. i.e. be dark - a signature requirement of dark matter?



    My gut says, if they are possible in the theory of GR, and the vastness of the universe is what it is, then they're out there somewhere.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  67. #2242
    What is the proposed mechanism that prevents Hawking radiation from evaporating this micro black hole?
    No idea, I guess it comes down to the quantum nature of energy. QM tells us that energy is quantised, that is comes in integer values and not in between. Perhaps a black hole with one base unit of energy is unable to evaporate further. What mechanism causes Hawking radiation? I'm not sure if this was a simplification or a correct interpretation, but my assumption was that virtual particles forming at the event horizon emit a particle in one direction and an antiparticle in the other, resulting in a photon escaping and therefore slow decay of mass. In this way, the black hole can only lose half of its mass. If energy is quantised, then we have a problem when the black hole is one unit in mass.

    I used the term "Planck mass" because I (probably naively) assumed that was one base unit of energy. But maybe it isn't.

    There isn't a single known observation of a naked singularity
    The vid sums up by saying that if this hypothesis is true, it's a problem, because such black holes would be undetectable. We may have a situation arise where the most simple explanation for dark matter is the most difficult to prove, if not impossible. We might never be able to detect dark matter.

    What says that a naked singularity will not interact with light at all.. i.e. be dark - a signature requirement of dark matter?
    Not sure. Gravitational lensing was used to rule out moon-mass type black holes as dark matter candidates though, so it's not something they overlooked in their hypothesis.

    Dark matter doesn't directly influence light, but its gravity does. Dark matter still causes gravitational lensing.

    My gut says, if they are possible in the theory of GR, and the vastness of the universe is what it is, then they're out there somewhere.
    My gut says that if a black hole can't completely evaporate, then there will be an enormous amount of these undetectable relics in the universe. It seems like a great candidate for dark matter to me.
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  68. #2243
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    Quote Originally Posted by OngBonga View Post
    No idea, I guess it comes down to the quantum nature of energy. QM tells us that energy is quantised, that is comes in integer values and not in between.
    Only in bound systems, but the BH is a bound system.

    I'm just pointing out that energy is not always quantized. It's the boundary conditions that create quantization of energy and other things.

    A particle not confined in any way (meaning a bit of hand waving about it's existence "in" the universe) can have any energy at all. A photon can have any wavelength, and therefore any energy.

    Quote Originally Posted by OngBonga View Post
    Perhaps a black hole with one base unit of energy is unable to evaporate further. What mechanism causes Hawking radiation? I'm not sure if this was a simplification or a correct interpretation, but my assumption was that virtual particles forming at the event horizon emit a particle in one direction and an antiparticle in the other, resulting in a photon escaping and therefore slow decay of mass. In this way, the black hole can only lose half of its mass.
    You had me until "half of its mass."
    An anti-particle falls in to the black hole, while its non-anti/normal particle partner escaped. It doesn't matter which is anti. The BH ejected mass/energy, which is conserved. If nothing counters this process, the BH evaporates... smaller BH's evaporate faster, so it's a runaway event, albeit with a very slow run-up, even in universal time scales.

    Quote Originally Posted by OngBonga View Post
    If energy is quantised, then we have a problem when the black hole is one unit in mass.
    The quantization of mass/energy is a thing, but it's not messing with us, here. At least, not in any way that I understand.

    Particles decay into smaller particles all the time. Elementary particles decay into photons. The mass of particles may be quantized, but the energy of the photons they emit is not quantized. They can emit multiple photons at once, so long as all the conservation laws are followed.

    Quote Originally Posted by OngBonga View Post
    I used the term "Planck mass" because I (probably naively) assumed that was one base unit of energy. But maybe it isn't.
    Mass and energy are different things. Apples and oranges, if you will.

    FYI, 1 unit of Planck Energy is 2 GJ -> 2 billion Joules. It's certainly not an upper or lower limit on anything.

    Quote Originally Posted by OngBonga View Post
    The vid sums up by saying that if this hypothesis is true, it's a problem, because such black holes would be undetectable. We may have a situation arise where the most simple explanation for dark matter is the most difficult to prove, if not impossible. We might never be able to detect dark matter.
    That sounds like no change from the current situation. There's something causing a gravitation-like force out there, and we don't see anything that would be the culprit.

    We'll get there. The progress of science comes in bursts.

    Quote Originally Posted by OngBonga View Post
    Not sure. Gravitational lensing was used to rule out moon-mass type black holes as dark matter candidates though, so it's not something they overlooked in their hypothesis.
    Yeah, I'm not claiming to understand all the nuance, here.

    Quote Originally Posted by OngBonga View Post
    Dark matter doesn't directly influence light, but its gravity does. Dark matter still causes gravitational lensing.
    Yeah. I don't consider that light interacting with dark matter, personally. I consider that dark matter interacting with spacetime and photons propagating through that spacetime interact with it. Maybe that's not the best distinction, but its working for me pretty good so far.

    Quote Originally Posted by OngBonga View Post
    My gut says that if a black hole can't completely evaporate, then there will be an enormous amount of these undetectable relics in the universe. It seems like a great candidate for dark matter to me.
    IDK. There are plenty of not-yet-explained things out there in the universe. I was hearing about black holes that are simply too big to have formed in the 13.7 billion years the universe has been here. IDK how they determine that, but it just shows that there is a lot of stuff out there that we don't quite understand.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  69. #2244
    A photon can have any wavelength, and therefore any energy.
    Forgive me for arguing with someone far more qualified about these matters than I am, but really? I was under the impression that there was a lower bound, ie the Planck length, further that the Planck length represents the base unit of length at that wavelength would go up in these integer values.

    You had me until "half of its mass."
    That was pretty sloppy language, reading it back. Obviously a large black hole isn't losing half its mass in a single quantum process.

    This really does come down to the idea that energy is quantized. I guess I need to read more about this concept but for the sake of argument, in the hope you can see what I'm getting at, let's assume it is, let's assume there is a smallest possible particle, with a corresponding antiparticle, and each has a mass of P. Let's say we have a black hole that has a mass of 2P. A quantum event on the event horizon causes the spontaneous forming of a particle-antiparticle pair. This pair is equal to the entire mass of the black hole. The particle escapes, and the antiparticle falls into the singularity. Now the black hole has a mass of 1. There is no longer enough mass to form a particle-antiparticle pair. This is what I meant by "half its mass". The final act of evaporation is for the black hole to lose half its mass, not all of it. The runaway evaporation process is the transition from a ridiculously tiny fraction of its mass evaporating, to 50%.

    They can emit multiple photons at once, so long as all the conservation laws are followed.
    Sure, but "multiple" photons will always be an integer value. Isn't this what Einstein means by "discreet" when he talks about packets of photons? You can't have half a photon.

    Mass and energy are different things.
    Not so sure. I might be wrong here, but I consider them to be related in the same way electricity and magnetism are. And while we might think they are different things, they're not, since it depends on your frame of reference. One person might observe an electric field while someone else observes a magnetic field.

    I have a better idea of what mass is than energy though. Mass is a measure of inertia and is a property of things that move slower than light. That's your rest mass. But if you're moving relative to what you want to measure, it has some relativistic mass. That relativistic mass only exists though in the frame of reference of someone moving at a different velocity. If you're moving at 0.999c, then something else moving at 0.999c in the same direction has no relativistic mass and only rest mass, from your FoR. So relativistic mass is not a measure of inertia, it's a measure of velocity. I just turned relativistic mass into kinetic energy. And rest mass is essentially potential energy. Saying mass isn't energy seems the same as saying kinetic energy isn't potential energy, but again that depends entirely on your frame of reference.
    Last edited by OngBonga; 04-15-2021 at 01:04 PM.
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  70. #2245
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    Quote Originally Posted by OngBonga View Post
    Forgive me for arguing with someone far more qualified about these matters than I am, but really? I was under the impression that there was a lower bound, ie the Planck length, further that the Planck length represents the base unit of length at that wavelength would go up in these integer values.
    The shorter the wavelength, the higher the energy.

    A photon with a wavelength of the Planck Length would have energy of the Planck Energy - ~2 GJ

    There is no upper bound on the energy a photon can have. Any photon's energy can be arbitrarily increased in accordance with Special Relativity. Its wavelength can correspondingly be arbitrarily short, with no relation to or limit set by the Planck Length.

    Man... there's some stuff about Planck Length and micro black holes not evaporating in this article:
    https://en.wikipedia.org/wiki/Planck_length

    I don't understand this quote:
    "The entire mass of the black hole will "evaporate", except for that part of it, which is associated with the energy of zero, quantum vibrations of the black hole's substance."

    Then:
    "Such vibrations do not raise the temperature of the object and their energy cannot be radiated"
    That sounds like an object that has a temperature of absolute 0, and I'm not comfortable at all.

    Quote Originally Posted by OngBonga View Post
    That was pretty sloppy language, reading it back. Obviously a large black hole isn't losing half its mass in a single quantum process.

    This really does come down to the idea that energy is quantized. I guess I need to read more about this concept but for the sake of argument, in the hope you can see what I'm getting at, let's assume it is, let's assume there is a smallest possible particle, with a corresponding antiparticle, and each has a mass of P. Let's say we have a black hole that has a mass of 2P. A quantum event on the event horizon causes the spontaneous forming of a particle-antiparticle pair. This pair is equal to the entire mass of the black hole. The particle escapes, and the antiparticle falls into the singularity. Now the black hole has a mass of 1. There is no longer enough mass to form a particle-antiparticle pair. This is what I meant by "half its mass". The final act of evaporation is for the black hole to lose half its mass, not all of it. The runaway evaporation process is the transition from a ridiculously tiny fraction of its mass evaporating, to 50%.
    Oh, I see what you mean. You're saying the 1P mass of the BH is not enough to spawn the spontaneous production of a particle/antiparticle pair with combined mass of 2P.

    The energy for the pair production doesn't come from the mass of the BH.
    It comes from the so-called "quantum foam." All of spacetime, but especially the region of spacetime immediately surrounding a particle is a wash of virtual particles, particles that cannot be directly observed by definition. When virtual particles become observable, they are no longer virtual, they are particles.

    The quantum foam is causing these pairs to pop into and out of existence all the time. The pair move slightly apart and then back together. If one of them crosses an event horizon and the other doesn't, then they cannot come back together.

    The production of virtual particle pairs is not caused by the BH.

    Quote Originally Posted by OngBonga View Post
    Sure, but "multiple" photons will always be an integer value. Isn't this what Einstein means by "discreet" when he talks about packets of photons? You can't have half a photon.
    An integer multiplied by a non-integer still may or may not be an integer. Photons can have any energy. An integer number of photons can have any energy.

    Consider different observers observing the same photon. The observers are moving relative to each other. Relative motion is not quantized (position is not quantized, and time is not quantized, so velocity is not). So given one of them measures the photon to have a certain energy, the other could measure that same photon's energy to be literally anything.

    Even if speed was quantized, the relative angle between the 2 observers is almost definitely not quantized. Directional invariance is the symmetry behind Conservation of Angular Momentum, a conservation law not known to be or even hinted to be violated in any prediction or experiment.

    I mean - Emmy Noether taught us that for every conservation law, there is an associated symmetry. For angular momentum, the symmetry is the fact that physics is the same in inertial coordinate reference frames, even if the coordinate axes are not aligned with each other. If Conservation of Angular momentum is true, then this directional invariance is true.

    So even if the energy of photons is quantized (not saying it is) the Conservation of Angular Momentum implies that relative velocity cannot be quantized.

    If relative velocity cannot be quantized, then different observers may observe photons moving relative to them with any (unquantized) energy due to the relativistic doppler effect.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  71. #2246
    MadMojoMonkey's Avatar
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    Quote Originally Posted by OngBonga View Post
    Not so sure. I might be wrong here, but I consider them to be related in the same way electricity and magnetism are. And while we might think they are different things, they're not, since it depends on your frame of reference. One person might observe an electric field while someone else observes a magnetic field.

    I have a better idea of what mass is than energy though. Mass is a measure of inertia and is a property of things that move slower than light. That's your rest mass. But if you're moving relative to what you want to measure, it has some relativistic mass. That relativistic mass only exists though in the frame of reference of someone moving at a different velocity. If you're moving at 0.999c, then something else moving at 0.999c in the same direction has no relativistic mass and only rest mass, from your FoR. So relativistic mass is not a measure of inertia, it's a measure of velocity. I just turned relativistic mass into kinetic energy. And rest mass is essentially potential energy. Saying mass isn't energy seems the same as saying kinetic energy isn't potential energy, but again that depends entirely on your frame of reference.
    You were simply exchanging mass and energy as though there's no conversion factor between them, is all.

    You said, "I used the term "Planck mass" because I (probably naively) assumed that was one base unit of energy. But maybe it isn't."

    I was just pointing out that there is a Planck energy, and it is the energy associated with a photon of a Planck length.

    It is just assuming the Planck Length is the wavelength of the photon and we know that E = hf, and that wave speed is c, so we tie all that together and ignore the difference between h and h_bar and call it the Planck energy, even though we used h_bar in our calculation and it's clearly E = hf, and not E = h_bar f, but ... what's a factor of 2 pi among physicists?

    I mean... I'm talking a bit of trash at the whole notion that the Planck Length is more than a trick of juggling numbers with the whole 2 pi talk, but ... I'm not wrong. That factor of 2 pi is just ignored, because the method of juggling numbers with various units to get out another number with another unit - called the Buckingham Pi method - completely ignores any constant factors in the conversion.


    IDK if I'd put mass and energy on the same tit for tat relationship as electric and magnetic fields, though. Energy takes a lot of forms and all.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  72. #2247
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    This was recommended in my YouTube feed and it's amazing.
    Over my head, really, so any questions you may have about this I probably can't answer, but give it a shot.

    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  73. #2248
    That's my dinner time entertainment sorted. Chicken pie and chips tonight.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  74. #2249
    Dinner was good. That video was a bit heavier than PBS. Questions I have none, other than ones you can't answer... such as, where's gravity?

    I thought this would be about string theory tbh, To someone uneducated, that seems like the most promising theory when it comes to combining QM and GR. The SM is great except for the elephant in the room.
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong
  75. #2250
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    Quote Originally Posted by OngBonga View Post
    Dinner was good. That video was a bit heavier than PBS. Questions I have none, other than ones you can't answer... such as, where's gravity?
    Dude. I got this. It's not in the Standard Model of Particle Physics.

    It's in the Lambda-CDM model.
    Lambda for dark energy, CDM for Cold, Dark Matter.

    The Lambda-CDM model assumes Einstein's GR is correct and adds on some hypotheses about dark energy and dark matter.

    The current state of physics is we use the both the Standard Model and Lambda-CDM Model as proves most useful.
    The SM describes 3 of the 4 known forces and Lambda-CDM describes the other 1.
    It certainly doesn't feel complete, or like we have full understanding, yet. We have come a long way in the past 200 years, though. A long way.

    Quote Originally Posted by OngBonga View Post
    I thought this would be about string theory tbh, To someone uneducated, that seems like the most promising theory when it comes to combining QM and GR. The SM is great except for the elephant in the room.
    While there is a lot of work yet to be done, it's not as though there is no bridge at all between QM and relativity.

    The Dirac Equation (the relativistic big brother of the Schroedinger Equation) takes relativistic effects into account for quantum wave functions. Applying this equation to gold atoms shows that the innermost electrons absorb light in the blue-purple band, explaining why gold is yellow-ish in color.

    We have a piece of how QM describes mass in the Higgs field (7%) and a piece that describes mass in the spacetime field (93%). So we do use both theories together in many useful cases.

    Not to downplay the work that needs to be done, of course. But I think there's a popular misconception that there is no link at all between QM and GR - that the 2 models are totally incompatible - which is not the case.

    ***
    I can't help but point out that string hypotheses (they're not theories by scientific standards) have been "the most promising" lead for almost 50 years, now. I'm less and less enamored of string hypotheses every year that goes by.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.

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