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  1. #2101
    CoccoBill's Avatar
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    Quote Originally Posted by MadMojoMonkey View Post
    Gov'ts limit the spread of technology all the time.

    Just one example
    Confidential / Top Secret tech is in the nose of nearly all of our military aircraft, and the detection and avoidance hardware and software we sell to our allies is many years behind the current tech we're using ourselves.
    That means they're using it though, not delaying it. I think that "this is too dangerous, humankind is not ready yet" stuff only happens in movies.
    Our brains have just one scale, and we resize our experiences to fit.

  2. #2102
    Quote Originally Posted by CoccoBill View Post
    "this is too dangerous, humankind is not ready yet"
    You mean like my biceps?
  3. #2103
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    Quote Originally Posted by CoccoBill View Post
    That means they're using it though, not delaying it. I think that "this is too dangerous, humankind is not ready yet" stuff only happens in movies.
    Did you catch the most recent John Oliver about facial recognition software?

    Turns out it was developed like 3 different times and then halted because too dangerous for humans until some unscrupulous person went ahead with it. It was inevitable.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  4. #2104
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    Quote Originally Posted by wufwugy View Post
    You mean like my biceps?
    No, the world is definitely ready for those, you manly man manthing.
    Our brains have just one scale, and we resize our experiences to fit.

  5. #2105
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    Quote Originally Posted by MadMojoMonkey View Post
    Did you catch the most recent John Oliver about facial recognition software?

    Turns out it was developed like 3 different times and then halted because too dangerous for humans until some unscrupulous person went ahead with it. It was inevitable.
    Hm ok, maybe there are some instances, but like the quote from Google's chairman said "this is the one technology where we've held back". I'm not optimistic about anyone holding back AGI or quantum computers or death stars too much.
    Our brains have just one scale, and we resize our experiences to fit.

  6. #2106
    https://www.forbes.com/sites/waynera.../#38bd4a7e5939

    “Our machine performed the target computation in 200 seconds,” the announcement said, “and from measurements in our experiment we determined that it would take the world’s fastest supercomputer 10,000 years to produce a similar output.”

    But while it was wowing scientists, computer security experts became worried. Very worried.
    If someone has a quantum computer, and the world still relies on classical encryption, then kiss goodbye to your savings. And banking is just the tip of the iceberg. Imagine if you could bypass India's nuclear security and gain access to their systems.

    What Google have done is impressive, but not yet useful. But quantum computers aren't that far away, and the first nation to successfully create a useful quantum computer will likely have a very serious advantage over other nations.
    Quote Originally Posted by wufwugy View Post
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  7. #2107
    Point being, quantum computers will not be allowed into the general market until they have quantum security.
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  8. #2108
    CoccoBill's Avatar
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    Well sure, but that doesn't mean they're delayed, it just means the ones with the technology are gonna do their best no one else gets it. Restricted would be a better word.

    I thought you said you were pedantic about the meaning of words.

    But yeah, quantum computing probably isn't going to be the next breakthrough in gaming.
    Our brains have just one scale, and we resize our experiences to fit.

  9. #2109
    Well I mean "delayed" in the context of us, the general public, getting it. So it means exactly the same a "restricted" in that context. I'm not quite defining words myself.

    Governments won't delay their efforts to get these things, quite the opposite, so yeah if you took "delay" in that context you're right.
    Quote Originally Posted by wufwugy View Post
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  10. #2110
    So according to General Relativity, all reference frames are equally as valid as one another. So if I observe someone travelling at 0.9c, and take ten minutes or whatever to get to the sun, and the distance he traveled is around 150 million km, that's a valid observation. Likewise, to the lunatic travelling to the sun, he gets there in like 20 seconds or whatever (didn't calculate that but it's obviously much faster than ten minutes). The distance he thinks he traveled is much less than 150 m km, let's say a million km (again can't be bothered to calculate). This too is a valid observation. This is fine, I've got no problems with this.

    However, let's look at this from the FoR of a photon. It gets there in zero time, and travels zero distance. Also a valid observation. The implication of this is that, from the photon's pov, the sun and the Earth occupy the same region of spacetime.

    How is this not a violation of physics? How does the photon not observe a much denser object that is a black hole? How can two objects occupy the same location in spacetime from one FoR, but not another?
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  11. #2111
    MadMojoMonkey's Avatar
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    Quote Originally Posted by OngBonga View Post
    So according to General Relativity, all reference frames are equally as valid as one another.
    I'm pretty sure you mean all inertial reference frames are equally valid.
    Inertial reference frames (non-accelerating frames) are probably what you mean. If not, just say so.

    GR can handle accelerating frames just fine, too, but that wont really help us in the case of photons or any massless particles.

    Quote Originally Posted by OngBonga View Post
    However, let's look at this from the FoR of a photon. It gets there in zero time, and travels zero distance. Also a valid observation. The implication of this is that, from the photon's pov, the sun and the Earth occupy the same region of spacetime.
    I just had a conversation about this last night that ran until 2:30 in the morning.

    My issue is trying to visualize how it is that a photon which does not experience time can be a wave in the E-M fields.
    My issue is visualizing how the 2D planar timeless universe of a photon can stretch out into a regular wave pulse that travels through 4d spacetime.

    Quote Originally Posted by OngBonga View Post
    How is this not a violation of physics? How does the photon not observe a much denser object that is a black hole? How can two objects occupy the same location in spacetime from one FoR, but not another?
    The short answer is
    A reference frame moving at c is neither an inertial reference frame, nor is it an accelerating reference frame.
    The equations we're using to try to understand it do not actually tell us about that special case.

    It is a special case that we can only interpret the nature of through the use of mathematical limits. There are infinities in there, and we can't say what happens at c. We can only say the limit as something approaches c.
    This is problematic because no object with mass can cross from less than c to c, and no object without mass can cross from c to less than c.

    When we take the limit as v -> c, we are implicitly assuming that any object with mass will behave the same if it reaches c, but that's a false assumption. All we can really say is what happens as the difference between v and c becomes very small to an outside observer.
    The speed of light is c in all inertial reference frames. No matter how fast you're going relative to another reference frame, light still moves at c according to you. So the idea that you've gotten closer to moving at c is bad language. No matter what you do, light moves at c in your reference frame.
    The statement "as you approach c" is problematic. In your reference frame, you're not approaching c. The speed of light is unchanging, so you're not approaching it.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  12. #2112
    GR can handle accelerating frames just fine, too, but that wont really help us in the case of photons or any massless particles.
    Yeah and I'm assuming the guy going on a trip to the sun is moving at constant velocity, so yes, inertial frame of reference. I'm sure GR can handle non-inertial FoR, but my brain can't!

    My issue is trying to visualize how it is that a photon which does not experience time can be a wave in the E-M fields.
    That's a good question, not sure if it's essentially the same question, gonna mull this over for a bit.

    and no object without mass can cross from c to less than c.
    Interesting side note - light appears to travel at <c through a non-vacuum due to refraction. Apparently this is due to the photon exciting electrons, which in turn create EM waves, which interact with the photon. The sum of all these waves result in a lower observed value for c. But the photon still moves at c, it just appears not to. I'd be curious if you can explain this in language I can understand, because I'm not really getting it.

    The statement "as you approach c" is problematic. In your reference frame, you're not approaching c. The speed of light is unchanging, so you're not approaching it.
    I do get this, but it doesn't really answer the question of how the photon observes two objects clearly separated by space to be occupying the same location. More than that, it observes ALL objects in the direction of travel, in both directions (behind and in front of) infinitely, to occupy the same location in space.

    I mean the best I can do is to conclude that space emerges when something moves at <c, the photon doesn't "observe" anything because from its FoR it's stationary in a timeless spaceless universe, it occupies a singularity with everything in the universe. But that's akin to saying the photon's FoR is not valid. Not sure if that's a problem for GR.
    Quote Originally Posted by wufwugy View Post
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  13. #2113
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    Quote Originally Posted by OngBonga View Post
    Yeah and I'm assuming the guy going on a trip to the sun is moving at constant velocity, so yes, inertial frame of reference. I'm sure GR can handle non-inertial FoR, but my brain can't!
    I think you mean "free-falling in a gravitational field," rather than "moving at constant velocity."

    But maybe I'm forcing an assumption.

    Quote Originally Posted by OngBonga View Post
    That's a good question, not sure if it's essentially the same question, gonna mull this over for a bit.
    I can settle on an answer that is both good and bad.
    If the photon's existence in the plane bears some angular momentum (nevermind that without time, momentum cannot be defined, take it as an intrinsic value of photons)
    then we can describe that angular momentum with a vector, a 2D object.
    When that photon is viewed in 4D spacetime, it is still described by a 2D vector - it's Poynting vector (which is pointing where the photon is headed, conveniently enough).
    So I can find a way to visualize some aspect of this conundrum.

    The big problem is that not all photons have rotational polarization. Some have planar polarization.

    Quote Originally Posted by OngBonga View Post
    Interesting side note - light appears to travel at <c through a non-vacuum due to refraction. Apparently this is due to the photon exciting electrons, which in turn create EM waves, which interact with the photon. The sum of all these waves result in a lower observed value for c. But the photon still moves at c, it just appears not to. I'd be curious if you can explain this in language I can understand, because I'm not really getting it.
    It comes down to phase lag and interference. The accelerated electrons (and other charged particles to a lesser extent) are accelerated by the photon, not moved by the photon. The phase lag between the acceleration and velocity of the charged particles results in new wave, with equal magnitude and direction, but a new phase.

    As the phase is continually being shifted, the photon's location is moved "backward" a little bit... in a continuous manner.

    It's important to note that phase velocity and group velocity are different. The phase change isn't changing the phase velocity, but it's changing the group velocity. So the E-M fields are still propagating at c, but the group velocity of the wave packet appears to move at less than c due to the interference.

    (This one is difficult to explain, so don't count these answers as an expert opinion, but a good metaphor.)

    Quote Originally Posted by OngBonga View Post
    I do get this, but it doesn't really answer the question of how the photon observes two objects clearly separated by space to be occupying the same location. More than that, it observes ALL objects in the direction of travel, in both directions (behind and in front of) infinitely, to occupy the same location in space.
    It's more a matter of physics not describing the photon's "rest" frame in a satisfying, intuitive way.

    We have an easy time thinking of something with mass moving faster and faster, but a hard time accepting that no matter how fast it gets, it's still effectively infinitely slower than c, as no amount of acceleration could ever get an object with mass up to c. We have a hard time understanding that no matter how fast you're moving, you still measure c as much faster than you.
    Moving at c is a totally different beast.

    It just has to be that way, though, IMO, no matter how hard it is to visualize.
    If light didn't move at c, which is the upper limit of all speeds in the universe, then causality is broken, and a cause no longer has to precede its effect.

    Quote Originally Posted by OngBonga View Post
    I mean the best I can do is to conclude that space emerges when something moves at <c, the photon doesn't "observe" anything because from its FoR it's stationary in a timeless spaceless universe, it occupies a singularity with everything in the universe. But that's akin to saying the photon's FoR is not valid. Not sure if that's a problem for GR.
    It's not a problem for GR. It's a consequence of SR.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  14. #2114
    Quote Originally Posted by CoccoBill View Post
    No, the world is definitely ready for those, you manly man manthing.
    brofist
  15. #2115
    I think you mean "free-falling in a gravitational field," rather than "moving at constant velocity."
    High quality pedantry.

    I'll rephrase it into language I like... in motion along a geodesic.

    They all mean the same thing though. If something is not moving along a geodesic, it is accelerating, ie not moving at constant velocity.

    I can settle on an answer that is both good and bad.
    If the photon's existence in the plane bears some angular momentum (nevermind that without time, momentum cannot be defined, take it as an intrinsic value of photons)
    then we can describe that angular momentum with a vector, a 2D object.
    When that photon is viewed in 4D spacetime, it is still described by a 2D vector - it's Poynting vector (which is pointing where the photon is headed, conveniently enough).
    So I can find a way to visualize some aspect of this conundrum.


    The big problem is that not all photons have rotational polarization. Some have planar polarization.
    Not gonna lie, I don't understand this. What makes some photons different to others though?

    It comes down to phase lag and interference. The accelerated electrons (and other charged particles to a lesser extent) are accelerated by the photon, not moved by the photon. The phase lag between the acceleration and velocity of the charged particles results in new wave, with equal magnitude and direction, but a new phase.


    As the phase is continually being shifted, the photon's location is moved "backward" a little bit... in a continuous manner.


    It's important to note that phase velocity and group velocity are different. The phase change isn't changing the phase velocity, but it's changing the group velocity. So the E-M fields are still propagating at c, but the group velocity of the wave packet appears to move at less than c due to the interference.


    (This one is difficult to explain, so don't count these answers as an expert opinion, but a good metaphor.)

    It's really difficult to grasp this, I'll probably have to research it a little to see if it's something I can get my head around. I'm happy with the word "interference", that does make me think I can get it, but it's not immediately clear to me.

    We have an easy time thinking of something with mass moving faster and faster, but a hard time accepting that no matter how fast it gets, it's still effectively infinitely slower than c, as no amount of acceleration could ever get an object with mass up to c. We have a hard time understanding that no matter how fast you're moving, you still measure c as much faster than you.

    I'm actually ok with this, at least I think I am. If the guy going to the sun decides to shine a torch towards the sun, both he and the observer at home (with the help of an amazing telescope) see the light moving at the same speed. What the two observers don't agree on is the distance the light has traveled, and in how much time. Observer A will say it moved x distance in x time, while observer B will say it moved y distance in y time. The ratios of these two figures will always be the same... c. Space and time changes, but velocity does not.

    The guy moving at 0.9c doesn't think he's going that fast. He didn't take 20 seconds to travel 150 million km, he took 20 seconds to move 1 million km (these numbers are clearly arbitrary and incorrect). He doesn't think "woah I'm going fast", he thinks "woah the sun is closer than I thought".

    I'm still not close to understanding this from the pov of something actually moving at c though. No space, no time, the universe is a singularity. But clearly it isn't. There is time and space. I'm struggling here.

    It's not a problem for GR. It's a consequence of SR.

    This might be a dumb thing to say, but isn't SR basically GR in flat spacetime (no gravity)? My understanding of SR is that it's a special case of GR where gravity is negligible.
    Quote Originally Posted by wufwugy View Post
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  16. #2116
    Not gonna lie, I don't understand this. What makes some photons different to others though?

    *other than frequency
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  17. #2117
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    Quote Originally Posted by MadMojoMonkey View Post
    We have a hard time understanding that no matter how fast you're moving, you still measure c as much faster than you.
    Wait much faster? Doesn't that difference get infinitely small?
    Our brains have just one scale, and we resize our experiences to fit.

  18. #2118
    Quote Originally Posted by CoccoBill View Post
    Wait much faster? Doesn't that difference get infinitely small?
    No. The speed of light is constant for all observers. So if I observe you moving at 0.99999999999999999999999999999999999999 c, you still observe light to move away from you at c, not at 0.00000000000000000000000000000000000001 c.
    Quote Originally Posted by wufwugy View Post
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  19. #2119
    It's space and time that are not constant for all observers.
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  20. #2120
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    Ok yeah I've heard that, my mind had just blocked that silliness away.
    Our brains have just one scale, and we resize our experiences to fit.

  21. #2121
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    What I mean is that none of that is any more intuitive than QM.
    Our brains have just one scale, and we resize our experiences to fit.

  22. #2122
    Quote Originally Posted by CoccoBill View Post
    What I mean is that none of that is any more intuitive than QM.
    I would respectfully disagree. I mean "intuitive" is subjective, of course, but I can get my head around time dilation (which is what this is), at least for objects not moving at c.

    QM is another beast altogether. Nobody understands it!
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  23. #2123
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    Yeah but things moving around at a constant speed related to everyone else moving at various speeds is just bizarre. Or cheating. I'm guessing it's a crude software hack in our simulation.
  24. #2124
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    Quote Originally Posted by OngBonga View Post
    High quality pedantry.
    TY, sir. I do my best.

    Quote Originally Posted by OngBonga View Post
    Not gonna lie, I don't understand this. What makes some photons different to others though?
    Some photons travel with circular polarization and others travel with planar polarization.
    Circularly polarized photons' E and M fields rotate about the axis defined by the photon's line of travel.
    Linearly polarized photons' E and M fields oscillate in planes.
    At all times, in both cases, the E and M fields of the photon are orthogonal (at right angles).

    Quote Originally Posted by OngBonga View Post
    It's really difficult to grasp this, I'll probably have to research it a little to see if it's something I can get my head around. I'm happy with the word "interference", that does make me think I can get it, but it's not immediately clear to me.
    Start by learning the difference between phase velocity and group velocity.
    A photon is a wave packet, and as such it has an "internal" waviness that is bounded by an "external" envelope. These words in quotes are only referring to a plot of the wave. I'm not saying a particle has any internal waviness... all the waviness taken together is the photon.

    The phase velocity is not necessarily limited by c. The group velocity is. It's a tricky distinction.

    Quote Originally Posted by OngBonga View Post
    I'm actually ok with this, at least I think I am. [...]

    I'm still not close to understanding this from the pov of something actually moving at c though. No space, no time, the universe is a singularity. But clearly it isn't. There is time and space. I'm struggling here.
    I don't really get it, either.

    Quote Originally Posted by OngBonga View Post
    This might be a dumb thing to say, but isn't SR basically GR in flat spacetime (no gravity)? My understanding of SR is that it's a special case of GR where gravity is negligible.
    I think that's a good way to put it. My point is that a photon's frame of reference is "not valid" as you say, since it's neither inertial nor accelerating.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  25. #2125
    MadMojoMonkey's Avatar
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    The best answers I can find for the reasons light appears to move more slowly in a dielectric medium rely heavily on field theories of matter and light. It's hard to explain them without a rigorous mathematical background without losing all the richness of conveying meaning without hand waving.

    My above statements about phase velocity and group velocity are probably as close as we're going to get without talking about how electric fields interact with charged particles, and by extension, atoms and molecules, in the language of field theory.


    The photon transfers some energy to the electrons, which the electrons, being massive particles, respond to with a time lag. The velocity lags behind the acceleration like the derivative of sine is cosine - same shape, but behind in phase.
    This is understood by citing F = ma = m dv/dt.
    Note that F = qE, the origin of the force on the electron is the electron's charge, q, interacting with the instantaneous value of the E field (not the derivative of the E field).
    Now we have qE = m dv/dt and note the velocity responds like a time derivative of the E field, and that should motivate us to see the phase change in the way a photon accelerates an electron with the motion of the electron. The photon oscillates in a sinusoid, so the electron responds like a sinusoid with offset phase.

    Then we have to understand that part of Maxwell's Equations which says that accelerating charges create changing electric fields. In this case the electrons are being accelerated in a sinusoid with the same frequency as the photon, so create a changing electric field which is of the same frequency, but with a phase lag.


    All of this is missing a huge amount of important information... if we just keep moving the phase back a little bit, and adding it to the incident wave, then we can easily visualize a phase shift of 180 degrees, which exactly destructively interferes with the incident wave and exactly cancels it out. That doesn't happen. The reason (I think) is that I've only talked about the effects in the electric field and not the effects in the magnetic field.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  26. #2126
    Struggling for time today but will revisit this tomorrow. I'm not ignoring you! I appreciate your replies very much.
    Quote Originally Posted by wufwugy View Post
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  27. #2127
    Ok so I've had a busy couple of days, but while thinking about what we've been talking about, I do have another related question...

    Gravity depends on mass, and, crucially, distance between masses. The problem here is that on the one hand, distance is relative, depending on your frame of reference. But on the other hand, the gravitational attraction between two objects is absolute, which heavily implies the distance between them is absolute.

    How is this paradox resolved?

    I've got some time tomorrow, so I'm going to get round to my homework of learning about phase and group velocity.
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  28. #2128
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    Quote Originally Posted by OngBonga View Post
    Gravity depends on mass, and, crucially, distance between masses. The problem here is that on the one hand, distance is relative, depending on your frame of reference. But on the other hand, the gravitational attraction between two objects is absolute, which heavily implies the distance between them is absolute.

    How is this paradox resolved?
    4-D spacetime curvature


    You described Newton's law of gravity in a GR universe.
    The classical law has to give way to the full GR treatment when dealing with relativistic effects.


    [EDIT] or maybe if you just take into account relativistic masses, it balances out the space contraction and time dilation to work. Just a thought. [/EDIT]
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  29. #2129
    I think I get it actually. Let's imagine the orbit of Earth, as observed by a traveler going to the sun at 0.9c. It will be an extremely eccentric ellipse, with a perihelion much smaller than observed from earth, but the aphelion will be identical (assuming direct motion to the sun). The lateral velocity of the orbit will be the same, but the observed longitudinal velocity will be much slower for the traveler than the person back home. So balance is restored, the orbital path and velocity will make sense, regardless of the frame of reference.

    The observed orbits change to balance out the difference in observed distance.

    Paradox resolved.
    Quote Originally Posted by wufwugy View Post
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  30. #2130
    It's probably not resolved. Because the perihelion is much less, the traveler should expect to see a much faster lateral orbital velocity. Hmm this is headbending, especially for 7.30am.
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  31. #2131
    You described Newton's law of gravity in a GR universe.

    This is clearly the problem I'm having.
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  32. #2132
    MadMojoMonkey's Avatar
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    If you want a mind-bending thought experiment, consider a relativistic disk.

    A disk is spinning such that the edge of the disk is moving at relativistic speeds. (Never mind that no known material could handle the centripetal forces.)

    What does an observer on the edge of the disk see?
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  33. #2133
    That's interesting, I'll think that through.

    I just watched a youtube vid about phase and group velocity. I now know the difference between the two. There's some interesting questions that arise though.

    For a wave that describes a particle, a higher frequency (shorter wavelength) means a faster phase velocity, but the opposite is true of classical waves (water or sound). Why is this?

    I at least appreciate now why a photon can move slower than c though. The phase velocity is c, but if several interfering waves have different wavelengths, the group velocity can be faster or slower. But this raises another question... if the sum of phase velocities can result in a slower photon, why not a faster photon?
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  34. #2134
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    Quote Originally Posted by OngBonga View Post
    For a wave that describes a particle, a higher frequency (shorter wavelength) means a faster phase velocity, but the opposite is true of classical waves (water or sound). Why is this?
    I don't there's any dispersion in empty space. The change in speed for different frequencies is a matter of the dielectric properties of a medium through which the photon travels.

    For classical waves the phase velocity may be faster or slower than the group velocity. It depends on the viscous properties of the material though which the wave travels.

    For waves on a string the phase velocity is equal to the group velocity.
    For water waves, the phase velocity is 2x the group velocity.
    Unless I'm missing something, for quantum wave functions of free particles (not bound states), the phase velocity is 1/2 the group velocity.

    [EDIT]The group velocity is 0 for bound states, which are standing waves.[/EDIT]

    Quote Originally Posted by OngBonga View Post
    I at least appreciate now why a photon can move slower than c though. The phase velocity is c, but if several interfering waves have different wavelengths, the group velocity can be faster or slower. But this raises another question... if the sum of phase velocities can result in a slower photon, why not a faster photon?
    Good fucking question. Wow. I never thought of that.

    IDK. I'm asking around.
    Last edited by MadMojoMonkey; 06-21-2020 at 01:19 PM.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  35. #2135
    So this disc thought experiment... I'm visualising a massive disc, basically the size of the observable universe. It's rotating very slowly, however it is so big that the velocity at the edge is massive, relativistic even. Assuming the disc is strong enough (lol), and assuming constant rotational velocity, oh and also assuming the observer is fixed into position and is an infinitesimal point (fuck you tidal forces), the observer wouldn't notice how fast he was going. In fact from his pov, he is stationary and the centre is rotating around him at relativistic velocity. From his pov, time is normal, while the centre is dilated and in a slower time reference frame.

    One of two things is going to happen... either the disc appears to be stationary, or an observe at both the edge and the centre would observe extreme spacetime warping, resulting in an ever-tightening spiral. I'd guess the latter.

    Definitely headbending.
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  36. #2136
    Good fucking question. Wow. I never thought of that.
    I'm wasting my life.
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    ongies gonna ong
  37. #2137
    What's the scoop on older generation stars? What I'm getting at is that AFAIK over the life of the universe, there have been different generations of stars. Like, say, the stars that popped up 10bn years ago were fundamentally different than the ones that pop up now.

    If this is true, I'd like to know more, because of my interest in the Great Filter and Fermi's Paradox. If, for example, complex life could be supported in 10bn year old star systems, it means there is probably a Great Filter that is killing off virtually every advanced species. Otherwise, one or more would have expanded galactically by now.

    However, if it is thought that complex life might only be able to exist in the kind of star generation we have -- and if that system didn't exist long enough in the past -- then it could make sense why the galaxy is not populated by a species that had billions of years of technological advancement before our star system even came about.
  38. #2138
    MadMojoMonkey's Avatar
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    The early universe was almost entirely composed of Hydrogen, with a bit of Helium and very small amounts of Lithium. Those are the smallest 3 atoms.

    The earliest planets, if there were planets around 1st generation stars in the early universe, would have been gas giants, sometimes called "failed stars" if they're particularly large, but not large enough for fusion. There's no strong reason to think there was any solid land on those planets, as Hydrogen does not form a solid, and Helium only does so under extreme pressures and low temperatures. Lithium was only present in trace amounts, so not likely to significantly contribute.

    At any rate, there was certainly no carbon, the atom most associated with life.


    H, He, and Li composed the earliest stars. Heavier elements are made through stellar fusion up to Iron and Nickel. The fusion of Iron and Nickel initiates a death spiral for a star, as the fusion of Iron and Nickel is not exothermic. The fusion processes for smaller elements creates energy to push back against the gravitational collapse. The fusion of Iron and Nickel does not supply any external pressure, so the gravitational collapse is not countered, and the star falls into its core. The massive increase in density and pressure causes all the heavier elements to be produced.

    A lot of different outcomes can happen at the end of a star's fusion, but for massive stars, a supernova happens.

    That ensuing supernova disperses those heavier elements out back into the stars galaxy, creating a planetary nebula. That nebula is now full of "heavy elements" (in this context meaning all elements larger than Lithium). As the galaxy ages, and other stars supernova, and shock waves pass through those planetary nebula, new stars may form.

    The presence of heavy elements includes Carbon, so it's the dust of a supernova that supplies the carbon to make life.


    There's no reason to say that all the early stars have burned out. The smaller the star, the longer its life. So there are still primordial stars burning in the universe. The composition of those early stars is still the most prevalent elements in the universe, so stars that are basically chemically identical to the primordial stars can still form today.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  39. #2139
    Thanks. Found this:





    Seems like the conditions for life existed long before Earth's formation. Really does bring into question why we don't see billions-of-years life older than us everywhere. Some say Great Filter. Others say The Simulation.
  40. #2140
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    It's especially strange because there's not only life on Earth, but it's just everywhere. There's life in places we never thought it could exist, in highly toxic environments, where sunlight doesn't reach. In deep sea near volcanic vents. In secluded caves that were cut off from the outside world for millennia. In the antarctic... it's just everywhere on Earth.

    The Fermi Paradox doesn't really have an answer. The Great Filter hypothesis has strong proponents, but I don't think it really solves the paradox. It just adds one more small number to multiply into the Drake Equation.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  41. #2141
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    I'm spamming this one website left and right, but again, this guy has my favorite piece on this:

    https://waitbutwhy.com/2014/05/fermi-paradox.html
    Our brains have just one scale, and we resize our experiences to fit.

  42. #2142
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    "Our night sky consists of a small selection of the very brightest and nearest stars in the red circle."

    Not only is that not the Milky Way galaxy, but also, it sure looks like a Hubble picture of a galaxy that is not the Milky Way.

    Even if it's not an actual Hubble photo, the fact remains that we have photographs of other galaxies, that are obviously not inside the Milky Way.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  43. #2143
    Quote Originally Posted by CoccoBill View Post
    I'm spamming this one website left and right, but again, this guy has my favorite piece on this:

    https://waitbutwhy.com/2014/05/fermi-paradox.html
    Great read.
  44. #2144
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    Quote Originally Posted by MadMojoMonkey View Post
    "Our night sky consists of a small selection of the very brightest and nearest stars in the red circle."

    Not only is that not the Milky Way galaxy, but also, it sure looks like a Hubble picture of a galaxy that is not the Milky Way.

    Even if it's not an actual Hubble photo, the fact remains that we have photographs of other galaxies, that are obviously not inside the Milky Way.
    I'd say it's this one:
    https://commons.wikimedia.org/wiki/F...Way_Galaxy.jpg

    Don't know whether it's a photo of some other galaxy or cgi, but yeah, obviously not a photo of the milky way.
    Our brains have just one scale, and we resize our experiences to fit.

  45. #2145
    That article brought up some more Great Filters that I hadn't thought of before.

    A counter (which I'm not sure what to think about): we would still see the old technology of advancing civilizations spread everywhere before some Great Filters like the secret empire civilization that got big first and wipes everything else out. Although, if that old technology is old enough, we probably wouldn't.

    Then there's the Simulation. We don't see anything because there is nothing, because this is a simulation. The only thing I've come up with that counters the simulation hypothesis is that (I think) it assumes math exists outside this reality. I can't say that's a good assumption or not.
  46. #2146
    Rather, I should say The (3 condition) Simulation Hypothesis assumes math exists outside this reality because it relies on the exponential function to say under which conditions the probability we're in a simulation converges to 1.
  47. #2147
    MadMojoMonkey's Avatar
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    @cocco: Yeah, there's simply no photo of the Milky Way from that perspective. The furthest man-made object from earth is Voyager, and it's barely away from the sun on those scales.

    It's just that we do see the Milky Way band across the night sky, which is brightness from stars, just too many and too far away to make out as individual stars with just our eyes. We can see distant galaxies with our eyes, though. They look like blurry stars - nebulae - as in nebulous or blurry.

    We have been observing the galactic center for long enough to plot the orbits of things, and to show that there must be a supermassive black hole at the center.

    Their deeper point that the stars we observe with our eyes are really not that far away from us on a galactic scale is fine.

    ***
    One conundrum with Great Filter is that the further out into space we look, the further back in time we look. It could be that civilizations have cropped up in distant places from us, but the evidence has not yet reached us.


    I mean... if there are multiple universes, then numbers exist - and therefore math exists. QED.
    If there's an "outside" of this reality, then the phrase "all is one" is not the only useful description of the universe, and therefore numbers exist.
    (not sure if serious)
    Last edited by MadMojoMonkey; 06-27-2020 at 11:37 AM.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  48. #2148
    MadMojoMonkey's Avatar
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    Quote Originally Posted by OngBonga View Post
    I at least appreciate now why a photon can move slower than c though. The phase velocity is c, but if several interfering waves have different wavelengths, the group velocity can be faster or slower. But this raises another question... if the sum of phase velocities can result in a slower photon, why not a faster photon?
    FYI, I've asked my colleagues in the intro physics program, and 2 of them responded that they don't know the answer to this.
    None of them are experts in QM. It's crazy how much you forget when you're not using it for a few years.

    I'll ask some of the professors who teach QM when I can.

    It'll probably have to wait until August, though, as it's frowned upon for me to use the university email while I'm furloughed.
    You can find any pattern you want to any level of precision you want, if you're prepared to ignore enough data.
  49. #2149
    It's awesome that I've asked a question that three physics guys can't answer.

    I'm mean I can answer the question myself in a wholly unsatisfying way... because causality would be broken. But obviously that's as hand wavy as it gets.

    I'll see if I can beat you to it. I'll try to learn the answer to this before August. Homework for July!
    Quote Originally Posted by wufwugy View Post
    ongies gonna ong

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