**Ask a monkey a physics question thread**

[Savy]

For water, it's 1 - 5 minutes, depending on your altitude, using 1 minute for sea level, and 5 minutes for ~1 mile up - say in Denver, the so-called mile-high city.

Using this as a rule of thumb... bringing it to 100C and holding it there for a minute or so should kill any parasites or bacteria present.

You'll know in 30 minutes to an hour if you have food poisoning.

Actually, I just learned that most bacteria associated with food rot will not cause food poisoning. So there's that.


I can't find any general rule of thumb for identifying if food is safe. There's such a wide variety in what people consider food.
I found plenty of helpful sites for telling me what parts of my refrigerator are for what foods and why, though, which were fascinating. There are other sites that told me how to identify and save (if possible) common food items like fruits, veg and meats.

Google, "how to tell if food is safe to eat"

The thing is I know you know better than me and will 100% google to prove me wrong. It's kind of why I ask. Basically I assume fruits are nonsense (as they are as a concept), veg lasts a week or so and meat does the same if not frozen.

Since otherwise I've eaten a lot of broccoli, spinach. peppers, onion and green beens.

[Savy]

So I was clearly drunk when I posted (both of) that but basically it came down to a GMM thing where they "boil for satefy" which I think is quite an interesting question. What I was getting at with my line "Since otherwise I've eaten a lot of broccoli, spinach. peppers, onion and green beens " I don't know bar I've eaten more of those things recently than usual but it doesn't really relate to the point.

Anyway here is my next non-physics question I expect you to google better than I do.

Why are some animals so at home with living with humans whilst others are not? I can get why some wild animals are going to think you're a threat no matter what but when animals are brought up from birth to have humans why is this? Do they just develop a I'm going to ignore you/eat your face mechanic?

[MadMojoMonkey]

@CoccoBill: A tame(d) animal is not the same as a domesticated species.

Why are some animals so at home with living with humans whilst others are not? I can get why some wild animals are going to think you're a threat no matter what but when animals are brought up from birth to have humans why is this? Do they just develop a I'm going to ignore you/eat your face mechanic?

The domestication of a species happens over many generations, guided by human intervention and selective breeding.

Different animals were "first" to be domesticated by various cultures with various indigenous fauna. Livestock could be herded and penned, but those big impaling horns are dangerous. So breed the individuals with smallest horns until there are no more horns (modern cattle). You got them in pens, but they are terrified of humans and hard to manage... except for a couple of them, which are a tad more docile. So breed the more docile ones until the herd is no longer terrified of humans... or at least isn't behaving like they are. Etc.

Pets are in the fossil record as far back as any domesticated herd animals, if I remember my college anthropology right. Something about the oldest-known bone piles, where the bones are all from 1 species of herd animal, and were in use for generations, have humans and dog skeletons buried together near there. So it seems that some people had pet dogs in the earliest known herding communities.

[CoccoBill]

Not sure what exactly you're asking but I think it boils down to nature vs nurture. Pretty much any animal exposed to humans from birth will be domesticated. There are pet snakes, reptiles, bears, tigers, scorpions and whatnot. At times they eat their owners, but I guess not always. The properly domesticated animals became that way over generations and generations of exposure.

[MadMojoMonkey]

At times they eat their owners, but I guess not always.

[CoccoBill]

Soo...these guys at the Aalto university in Finland came up with this shit. Apparently if theory holds, the universe isn't expanding. Thoughts?

More here: https://journals.aps.org/pra/abstrac...RevA.95.063850

[MadMojoMonkey]

Fine, this has noticeable effects in a crystal, but what about deep vacuum?

"The optical force of the light pulse"
Has what counterpart which satisfies the conservation of energy?
I.e. it has an equal and opposite effect on what? The wavelength of the photon?
So their argument is that photons from distant events are red-shifted not by universal expansion, but by "bleeding" energy into the intergalactic medium.
Wouldn't this serve to heat the atoms which absorb the energy? This heat would result in blackbody emission as the atoms cool to equilibrium temperature with the microwave background, resulting in a glowing light (of lower energy photons) emitted.
This glow is not observed, to my knowledge.

The deep vacuum of intergalactic space is about as far from a crystal as you can get.
The structure of a crystal is well-defined by the "neighbor interactions" of the individual atoms in the crystal.
The interstellar (inside a galaxy, but outside a solar system) medium has approximate density of 1 atom per cubic centimeter.
That actually seems like a lot to me, which goes to show just how many atoms per cc we are breathing on a regular basis (~2.5*10^19 molecules per cc in air, making a heap of assumptions about temperature, pressure and specific molecular composition of the air. Multiply by 2, since 99% of the air molecules are either diatomic Nitrogen or diatomic Oxygen. All told, ~5(10)^19 atoms per cc). You can see why scientists took a while to figure out that air isn't a continuum, but made of inconceivable numbers of tiny particles.

The moral of the story is that 1 atom per cc is considered the vacuum of space, and it is characterized by the fact that atoms in the medium "rarely" interact with any other atoms. I've never heard anyone assert any correlations to crystalline behavior of a bulk solid exist in this rarefied state.

If you divide the density of air by a billion, you get a value which is in the ballpark of the best vacuum chambers humans can produce.
If you divide that by a billion again, you get a density ~ 50 times greater than that of the interstellar medium.
If you divide that by 1,000 again, you get the density (approximate) of the universe as a whole. This figure (1 atoms per cubic meter) is often quoted as the density of intergalactic space (I think even by me in this thread), but that isn't where that number comes from. It's from a calculation of the total density of the universe, and not the density of the deep voids between galactic clusters. That density is therefore lower, since the density inside galaxies is higher than the universal average, then it must be lower than the average somewhere outside the galaxies.

The intergalactic medium hasn't been directly measured, for the obvious reasons that there is no know means of sending any vessel from Earth out of this galaxy, let alone into the voids between galactic clusters.

[OngBonga]

So their argument is that photons from distant events are red-shifted not by universal expansion, but by "bleeding" energy into the intergalactic medium.

Can redshift not also occur as a consequence of moving out of a gravity field?

[MadMojoMonkey]

Can redshift not also occur as a consequence of moving out of a gravity field?

Yes.
Hubble accounted for this when analyzing the spectra of distant galaxies.
The word "distant" is poorly defined, but relevant, here. It's not that all galaxies are distant, and he's studying galaxies.

The Hubble constant (actually Hubble was first to confirm it; it was hypothesized by Lemaitre) increases with distance. At "close" distances (lol), the local motions within a galaxy are like a mask of white noise through which it is hard to pinpoint an exact "general motion" of the galaxy. I mean... there are wide error bars on that value, because the internal motions of the galaxy are on the same order of magnitude as the recession velocity. When you look at "distant" galaxies, the local motions are about the same as the close galaxies, but their recession velocity is now much greater than their internal velocities. This allows a sharper resolution (finer error bars) on the measurement.

The mass of the galaxy is taken into account, but with galaxies of relatively equal mass, this is a wash.

[OngBonga]

That mostly went over my head.

Are you saying they are certain that gravtational redshift is not the cause of the observed redshift of distant light?

[MadMojoMonkey]

That mostly went over my head.

Stuff moves around the galaxy in orbits. There is some average velocity of stuff moving in their orbits, but some of it is moving toward us, and some is moving away from us and some to the left, some to the right.

Let's say the average speed is 100 [units].

OK, so if I want to measure the recession velocity and the actual value I wish to measure is ~10 [units], then my result will be 10 +/- 100 [units]. That's not a very helpful result.
However, if the actual value I wish to measure is 1,000,000 [units], then my result will be 1,000,000 +/- 100, which is a much more helpful result.

Are you saying they are certain that gravtational redshift is not the cause of the observed redshift of distant light?

Yes.

These are different effects, and the universal redshift is still present after the gravitational redshift is accounted for.

[OngBonga]

Stuff moves around the galaxy in orbits. There is some average velocity of stuff moving in their orbits, but some of it is moving toward us, and some is moving away from us and some to the left, some to the right.

Ok I mean I get this, galaxies are basically acting like a fluid, with different densities and currents. For example, probably every river in the world will have water travelling against the flow because of eddies. The river is moving downhill at an average speed of x, but particular regions move fatser (where it's narrower) and slower (where it's wider), while a small percentage of the river is actually flowing upstream.

Yes.

These are different effects, and the universal redshift is still present after the gravitational redshift is accounted for.

How are they accounting for the gravitational redshift? Wouldn't they need to know the total mass of the universe, and also the density of the centre compared to outer regions? Considering we can't be certain of its geometry, I fail to see how we can determine this with certainty.

[MadMojoMonkey]

Ok I mean I get this, galaxies are basically acting like a fluid, with different densities and currents. For example, probably every river in the world will have water travelling against the flow because of eddies. The river is moving downhill at an average speed of x, but particular regions move fatser (where it's narrower) and slower (where it's wider), while a small percentage of the river is actually flowing upstream.

Yeah.
If you're only looking where the eddies are prevalent, it's hard to get a good measure of the overall flow.

How are they accounting for the gravitational redshift? Wouldn't they need to know the total mass of the universe, and also the density of the centre compared to outer regions? Considering we can't be certain of its geometry, I fail to see how we can determine this with certainty.

Hmm. Good question.

I'm not well-versed in GR calculations, and this would be well-served by someone with a stronger background there.

I think it's a matter of the magnitude of the gravitational potential at the source and the magnitude of the gravitational potential at the destination.

Consider a basic conservation of energy problem, like a pendulum of mass m. It starts at rest, at some height, h2. It swings down from h2 to a new height h1, without noticeable losses to friction. We know its initial energy (mgh2) and its final energy (mgh1), so we know it's change in energy: mg(h2-h1). With a non-photon, this is usually associated with a change in speed. For a photon, this would be a change in its wavelength, i.e. a red shift or a blue shift.

The topology in-between doesn't matter, only the end-points.
(I think. It's GR, so maybe more convoluted that this.)

[OngBonga]

I think it's a matter of the magnitude of the gravitational potential at the source and the magnitude of the gravitational potential at the destination.

Hmm yeah ok. So do we know for certain how much dark energy or dark matter is between the start and end points? Or, at least, how much mass there is, even if we don't know what type of mass?

[wufwugy]

It is my understanding that the threat of nuclear winter comes from burning of material after detonation such that a funnel is created such that smoke and debris reaches the stratosphere, where it would disperse and linger for a long time. Why didn't the Hiroshima or Nagasaki bombs cause this? Were the cities not sufficiently dense to have enough burning material? Were the bombs too small to create sufficiently enough burning? What is the lowest level and placement of nuclear bomb that could create nuclear winter? (Ex: could a well-placed suitcase nuke in NYC be enough or would it take some serious monster bombs igniting half the city?)

[Savy]

It is my understanding that the threat of nuclear winter comes from burning of material after detonation such that a funnel is created such that smoke and debris reaches the stratosphere, where it would disperse and linger for a long time. Why didn't the Hiroshima or Nagasaki bombs cause this? Were the cities not sufficiently dense to have enough burning material? Were the bombs too small to create sufficiently enough burning? What is the lowest level and placement of nuclear bomb that could create nuclear winter? (Ex: could a well-placed suitcase nuke in NYC be enough or would it take some serious monster bombs igniting half the city?)

It's a hypothetical thing that probably doesn't ever happen.

[MadMojoMonkey]

It is my understanding that the threat of nuclear winter comes from burning of material after detonation such that a funnel is created such that smoke and debris reaches the stratosphere, where it would disperse and linger for a long time. Why didn't the Hiroshima or Nagasaki bombs cause this? Were the cities not sufficiently dense to have enough burning material? Were the bombs too small to create sufficiently enough burning? What is the lowest level and placement of nuclear bomb that could create nuclear winter? (Ex: could a well-placed suitcase nuke in NYC be enough or would it take some serious monster bombs igniting half the city?)

We (humans) have not yet made a bomb that big. Even the Tsar Bomba isn't big enough for that.

We're talking energy release on the order of a 15 km diameter asteroid impact, such as is likely to have caused (or at least heavily contributed to) the Cretaceous Paleogene extinction event which killed off all the non-avian dinosaurs.

It would take a full scale international nuclear war to release that kind of energy, and I'm not sure it would be a long enough winter to compare with the one mentioned above.

Hiroshima and Nagisaki were altogether tiny explosions on the scale of nuclear weapons. We had much better technology in the following decades (see Tsar Bomba), and are many more decades past that, now.

IDK about the density of the cities as pertains to this discussion. The bombs themselves didn't create much burning. The widespread destruction of buildings and power lines is what created the ensuing firestorm. The Japanese didn't even believe that the bombs were a problem. They were convinced that we sent in massive waves of fire bombers behind the nukes, which of course we did not have the logistical capacity to have done.

I don't think any single nuclear explosion can trigger nuclear winter.

I don't think you can fit an actual nuclear weapon in a suitcase, either. You can fit a dirty bomb in a suitcase, but initiating a multi-stage nuclear event is not child's play.

[OngBonga]

I would have thought it's analogous to two volcanos going off, or hundreds. Nuclear winter happens as a result of full-scale nuclear war. A couple of nukes, I assume the cooling effect is negligible, at least on a global scale.

[OngBonga]

I'd also theorise that the best way to initiate a nuclear winter would be to drop a nuke on Yellowstone.

Well, it'd be a nuclear/volacanic hybrid winter, but the nuke started it.

[wufwugy]

You think the hypothesis is likely wrong?

[Savy]

You think the hypothesis is likely wrong?

Given a certain set of criteria it probably does happen. are those criteria likely to ever manifest in reality? Probably not. Very short term cooling effects are likely & happen to some degree but long term nah.

[BananaStand]

I've picked out a few potential mountain tops from which to view and photograph the Supermoon this Sunday.

I see LOTS of articles posted saying "How to view the Supermoon this weekend", and they all say pretty much "look up"

The mountains I've picked do not all of 360 views of the horizon. Some of them are wooded and only have outlooks in one or some directions. And nothing I can find online is telling me from which direction, the moon will rise.

[Poopadoop]

And nothing I can find online is telling me from which direction, the moon will rise.

Well Timmy, the Earth spins around so that the Sun rises in the East and sets in the West.

So where do think the Moon rises and sets?

[OngBonga]

Well Timmy, the Earth spins around so that the Sun rises in the East and sets in the West.

So where do think the Moon rises and sets?

Well, considering it's a "supermoon", it's a full moon, which means it's the opposite side to the sun. As the sun sets, the moon rises. So you want an easterly view. We're approaching winter (or summer) solistice, so bear in mind the further north (or south) from the equator you are, the further south (or north) from true east the sun will set. Which means the moon will rise further north (or south) from true east.

It's not rocket surgery.

[Poopadoop]

So you want an easterly view.

No, you got it right. The moon rises in the east.

[MadMojoMonkey]

@ ong:
Aside from the obvious typo, you got it right.
(You said, "[...] from true east the sun will set," but everything else you said indicates you fully well meant to say the sun sets in the west.)

[BananaStand]

Your sister's ass hole?

[Poopadoop]

Your sister's ass hole?

I don't have any sisters. So fuck you.

And next time instead of posting your question in the physics thread, maybe start a new one called 'dumb ass questions from someone who failed grade 2'

[MadMojoMonkey]

I can't leave you guys alone for a few hours without this?
Who pooped in your cheerios, poopadoop?

Anyway.

The Earth spins from West to East, so celestial objects appear to rise from the East and set in the West.

I totally encourage anyone to get out and do some sky watching, but don't get too, too worked up about a perigee syzygy (super moon). It's basically just a full moon unless you're an avid moon watcher. You kinda want to compare it to a full moon from a month or two ago or a month or two from now to get a sense of how it was "super."

So plan on going back to said mountain in a month or two to really appreciate how it's not too much less super under any conditions.

[OngBonga]

The Earth spins from West to East, so celestial objects appear to rise from the East and set in the West.

Mojo's right, I got my brain science wrong.

[OngBonga]

I confuse myself sometimes, like a dog shocked by its own fart.

[MadMojoMonkey]

Dat poetry.

[pantherhound]

Hello Monkey

I've found a number of these types of videos that zoom in on things with an electron microscope, and I love them.

https://www.youtube.com/watch?v=dNvdrpEmS48

What sort of preparation would one have to do to recreate a process like this, and is it because it's complicated that we don't see very many of them?

[MadMojoMonkey]

Hello Monkey

I've found a number of these types of videos that zoom in on things with an electron microscope, and I love them.

https://www.youtube.com/watch?v=dNvdrpEmS48

What sort of preparation would one have to do to recreate a process like this, and is it because it's complicated that we don't see very many of them?

Hi, Panther.

The short answer is money. A cheap, used, low resolution microscope is going to cost in the tens of thousands. Those jobs can't go anywhere near the zoom shown in the video.

Something capable of producing that video definitely cost in the millions, perhaps up to 10 million... for the microscope. That's just one piece of the puzzle, and while that cost is a big chunk of the budget, it's not more than half the lifetime cost of building a lab around that machine, maintaining it and staffing it with high dollar technicians.

[hlester25]

I'm not 100% convinced that nuclear weapons even exist... haha troll me now

[OngBonga]

I'm not 100% convinced you exist. You could be a Russian bot.

[BananaStand]

http://www.foxnews.com/tech/2018/02/...ace-apart.html

It can tear a hole in space?? Huh??

The idea is to achieve a phenomenon known as "breaking the vacuum", whereby electrons are torn away from positrons (their antimatter counterparts) in the empty vacuum of space.

So is space an empty vacuum or not?? If it is, then how are there electrons in it? Wouldn't that make it not-empty??

[OngBonga]

China is building a mega-laser that's so powerful it could literally tear space apart.

You think a Fox News article with this as the leading headline is "physics"?

Dude.

[OngBonga]

I will give points to Fox though for the use of the word "literally" to describe something that noone can even define.

[Savy]

So is space an empty vacuum or not?? If it is, then how are there electrons in it? Wouldn't that make it not-empty??

There is no such thing as a perfect vacuum. You are correct in what you say.

Even if there are no particles there energy is enough to make matter so yeah vacuums don't exist.

[OngBonga]

"That would be very exciting. It would mean you could generate something from nothing," he explained.

What absolute fucking twaddle.

You're not creating something from nothing... you're creating a stable atom from energy. So it's not like it was pulled out of a magic vacuum hat. If there's energy there, it's not a true vacuum. So he's talking out of his arse.

Rip space apart indeed. You might as well be worried about blinding god with that fucking giant laser pen.

[MadMojoMonkey]

You think a Fox News article with this as the leading headline is "physics"?

Dude.

More telling was that the article was originally reported in The Sun. Not a bastion of scientific literature.

There is no such thing as a perfect vacuum. You are correct in what you say.

Even if there are no particles there energy is enough to make matter so yeah vacuums don't exist.

In general the energy is not enough to precipitate particles out of the "empty" space. However, in certain environments, like the extreme spacetime curvature near a black hole's event horizon, particle creation from the ambient, sloshing energy of that curvature can create particles, carrying away some of that energy.

What absolute fucking twaddle.

You're not creating something from nothing... you're creating a stable atom from energy. So it's not like it was pulled out of a magic vacuum hat. If there's energy there, it's not a true vacuum. So he's talking out of his arse.

Rip space apart indeed. You might as well be worried about blinding god with that fucking giant laser pen.

Despite the tone, this seems all good.

We can dicker over the phrase "true vacuum" and whether that should be a theoretical ideal or if that should be an observed quantity, but we're not really disagreeing on what anything is or means, just which collection of syllables means what.

Nothing in the article said it was going to create stable atoms. It'd be far, far more likely that it created random ions and isotopes, the vast majority will decay in nuclear reactions over time. Most of those decays will happen basically immediately, but plenty will have longer half-life times and will linger about slowly irradiating their surroundings.

[MadMojoMonkey]

It can tear a hole in space?? Huh??

I'm not sure what is lost in translation from the Chinese to English, but that's odd phrasing for pair production, which is all they seem to be talking about. However, pair production happens just over 1.022 MeV, which is way less than their current laser, so it's possible the article isn't talking about anything associated with this, even though it specifically mentions pair production.

My gut says this is just an intersection of QM definitions being used colloquially by the reporter.

There's literally not enough of a hint at actual physics to even guess at what the scientists are actually trying to accomplish.

So is space an empty vacuum or not?? If it is, then how are there electrons in it? Wouldn't that make it not-empty??

Is the vacuum empty? No, not really.
We cannot measure absolute energy, only relative energy. We can measure if and how much one thing's energy is higher than another thing's energy, but we cannot really know if any of the values is exactly 0 J of energy. This is obvious to anyone who has studied electronics. You can't measure the potential (short for: electrical potential energy) at a point, you must measure the potential across 2 points. It is common to set ground to 0 V as a convenience, but it is not possible to prove that ground is 0 V. This is why we only really talk about the delta-V, or change in potential, but in short-hand, this specific use of language is thrown by the wayside.

The best way to describe the vacuum is not that it's "empty," but that it bears the minimum possible allowable energy in this universe (at this time).

One of the odd universe-ending physics things is spontaneous tunneling of the vacuum energy to a lower state. Meaning that the vacuum is tiny, but could be tinier if not for some unknown barrier keeping it from falling. However, QM says that all non-infinite barriers have a non-0 probability of not working (in a process called quantum tunneling). This means that IF the universe's current vacuum energy is not its absolute minimum, AND IF the barrier preventing the universe's vacuum energy from reaching its minimum energy is non-infinite, THEN at any given moment, the universe as we know it will cease to exist at some infinitessimal point. That ceasing of existence as we know it will expand out radially from that point at the speed of light, and will annihilate the universe with an event horizon that expands at the speed of light without anything to oppose it. Our universe would simply end in one instant without any warning that it was going to end.

[OngBonga]

Despite my tone, this has tweaked my curiosity a little.

I mean, taking energy and mashing it all together to make, well either an ion or even a stable atom, that's kind of like collecting all the ash up and making a log out of it. Is this actually possible, in theory? I was always told it wasn't possible, but I was never really convinced. I mean it's impossible because we're going to lose ash, which means we never reproduce exactly what was burned, but let's assume we can collect 100% of the ash and heat... I'm not asking if we can do it, because obviously we can't, but could a super-intelligent alien?

[MadMojoMonkey]

Despite my tone, this has tweaked my curiosity a little.

I mean, taking energy and mashing it all together to make, well either an ion or even a stable atom, that's kind of like collecting all the ash up and making a log out of it. Is this actually possible, in theory? I was always told it wasn't possible, but I was never really convinced. I mean it's impossible because we're going to lose ash, which means we never reproduce exactly what was burned, but let's assume we can collect 100% of the ash and heat... I'm not asking if we can do it, because obviously we can't, but could a super-intelligent alien?

In theory, the log can be unburned at a cost of even more entropy than it originally produced in burning, plus all the released energy in the form of heat and light and noise, etc. and you have to have all the original matter to reassemble into the pre-combusted molecules.

Maybe a talented chemist could coax that chemical process to run in reverse on the microscopic level, but IDK.
I suspect that un-rusting iron would be easier to do. Rust and fire are chemically similar in that they're both exothermic oxidation processes.

Quantum Mechanically, all processes are reversible, so entropy doesn't exist at the particle level. Entropy is an emergent property of many-particle systems. "Many" is still poorly defined and understood. Active research in this field is called mesoscale (in-between-sized) physics.

In theory, everything we see happening "forward in time" can be seen "backward in time," but dissipating energy in the form of heat, light, sound, etc. has an incredibly low probability of happening in reverse. A thing exploding from a central source is easy to create. Unexploding a thing by trying to get all the particles moving exactly just so to come together in a dynamite stick is, like, super hard [citation needed].


***
Upon further reflection, all those unstable isotopes will decay into stable atoms or ions, so the assertion that it creates stable atoms isn't really that terrible.

[OngBonga]

So this "incredibly low probability"... am I to assume that while I sit by my fire, the vast majority of the heat is moving from a warm place to a cool place, but not quite all of it? I assume the heat moving from the cooler area to the warmer area is utterly overwhelmed by the heat moving in the opposite direction, rather like trying to piss up a waterfall.

What causes that "incredibly low probabiltiy"? Is it environmental, or completely random? Or do we not know?

[MadMojoMonkey]

So this "incredibly low probability"... am I to assume that while I sit by my fire, the vast majority of the heat is moving from a warm place to a cool place, but not quite all of it? I assume the heat moving from the cooler area to the warmer area is utterly overwhelmed by the heat moving in the opposite direction, rather like trying to piss up a waterfall.

What causes that "incredibly low probabiltiy"? Is it environmental, or completely random? Or do we not know?

Heat transport is a function of relative temperature between 2 sources, and some coefficient of heat diffusion, which characterizes the specific material through which the heat is flowing.

Newton's Law of Cooling:
dT/dt = -k(T(t) - T_inf)

The time rate of change of the temperature of an object is proportional to the difference in temperature between that body and its "ambient" environment.

Solving this 1st order differential equation yields an equation of the form
T(t) = T_inf + (T_init - T_inf)*e^(-kt)

That e^(-kt) part is what we're looking at now.

I'm running out of time.
I'm trying to get to a point where I state that the transport of heat from low temp to high temp is exponentially less than the transport from high temp to low temp the further apart the high and low temps are. When the high and low temps approach the same value due to this exchange process, the amount of transport approaches equilibrium. I.e. when things are the same temperature, the amount of heat flowing between them is the same.

(I need to add a lot of caveats to pin that down to a specific case, but I hope you can do some of that yourself. Feel free to ask for clarity where I trailed off. I'll come back to it later.)

[OngBonga]

I'm also very much glad this isn't a "random" function, because to be quite honest, whenever science talks of "random", what I actually read is "unknown dynamic".

[OngBonga]

I'm trying to get to a point where I state that the transport of heat from low temp to high temp is exponentially less than the transport from high temp to low temp the further apart the high and low temps are. When the high and low temps approach the same value due to this exchange process, the amount of transport approaches equilibrium. I.e. when things are the same temperature, the amount of heat flowing between them is the same.

You might be surprised how logical this is. Two objects of the same temperature are still exchanging heat, it's just the heat transfer cancels out to net neutral. Something that is hot is losing more heat than it gains, and the hotter it is the faster it loses its heat relative to the cool object.

Is this a function of radiation? Is it simply the case that the hot object radiates more than the cool object?

[OngBonga]

The lovely Holly Krieger.

Dr Holly Krieger.

10/10

[MadMojoMonkey]

Yes, Dr. Holly Krieger is a delightfully attractive person with an equally delightfully bubbly demeanor.

Anyway, she makes a good point. The Earth is not exceptionally big as far as planets go, but it is much bigger than a drop of water [citation needed].
The fact that the altogether weak intermolecular interactions which cause surface tension are strong enough to overcome the gravitation pull of an entire planet is noteworthy.

Gravity plays a noticeable role on the largest scales due to the fact that mass-charges of the same sign are attractive, and not repulsive like electric-charges of the same sign. This means that the tendency of an ensemble of electrically charged particles tends to 0, as the ensemble acquires a charge disparity, the forces act to bring it back to equilibrium. With gravity, this isn't the case, so mass-charge tends to accumulate into planets, stars, black holes, etc.

Since more mass is always more attractive to other masses, and there is no counter-gravity caused by negative mass, the altogether tiny force of gravity has dominance on large scales.

[OngBonga]

Inertia = resistance. What is mass resisting? Expansion.

/solved

[OngBonga]

Gravity plays a noticeable role on the largest scales due to the fact that mass-charges of the same sign are attractive, and not repulsive like electric-charges of the same sign.

This is all a little simplistic for me.

I just had an idea while rolling this spliff.

Space is expanding, right? What does that actually mean? Can it be that if space is expanding, then not-space is not expanding? Let's call not-space something nicer... how about energy?

Where energy exists, expansion does not happen. Where energy does not exist, expansion happens. In this way, spacetime curvature is created. Gravity is lack of spacetime expansion caused by inertia.

Holly can have my Nobel prize for inspiring me (strings attached).

[MadMojoMonkey]

This is all a little simplistic for me.

It was an overly simplistic explanation, but I think I've gone into deeper detail at some point in this thread.

I just had an idea while rolling this spliff.

Strap in, boys, this gon' go good.

Space is expanding, right?

so the data shows

What does that actually mean?

It's based on Hubble's Law (empirical), which states that (simplisticly) the further away from us something is, the faster it's moving away from us*.

* on average. Objects in a rotating galaxy will have a bell-curve of recession velocities, centered around the average velocity of the whole galaxy. So, while they are for the most part all the same distance from us, they will not all be moving at the same speed relative to us. Those deviations are tiny compared to the average recession velocity, but my original statement can't be true if we don't take things like this into account.

Also, the Andromeda Galaxy is racing toward us, despite it's distance, but, again, this is not contradictory with Hubble's Law.

Can it be that if space is expanding, then not-space is not expanding?

Ummm... what, now?

Sure. I guess. IF something that we can't measure is doing something, then I cannot measure anything which refutes your assertion. It's just outside the purview of physics until it can be measured.

Let's call not-space something nicer... how about energy?

Not a great choice, since energy is already well-defined and complicating it with a new, altogether different definition will muddy up conversations. Especially when the already defined version of energy is a measurable scalar, and "not-space" is a dearth of anything known to mankind.

Where energy exists, expansion does not happen. Where energy does not exist, expansion happens. In this way, spacetime curvature is created. Gravity is lack of spacetime expansion caused by inertia.

There is plenty of energy in so-called "empty" space. Photons zipping hither and thither, plus the energy of the quantum ground-state of vacuum. Not to mention the non-0 gravitational curvature at all locations in space, as well as all the other fields which permeate and define space-time.

Maybe there are transient locations where the total energy in a finite volume can be 0 J, but I can't think of any way to produce that using any known methods. I could be well under-informed on the finer points of GR, though.

Holly can have my Nobel prize for inspiring me (strings attached).

As soon as I'm empowered to hand out Nobels, I'll let her know.

[MadMojoMonkey]

Ugh. I shouldn't have said there's non-0 gravitational curvature at all locations in space.
That is wrong.

The curvature is the derivative of the gravitational field, and the derivative can certainly be 0 between mass charges. E.g. the slope on the top of a hill is always 0.


I was thinking that the absolute value of the potential is always negative, but that's not really meaningful unless we assert that the gravitational energy is 0 J an infinite distance away from all mass, which sounds reasonable, but can't be proven via experiment. That said, what I really meant was that whatever the value of the gravitational energy an infinite distance away from all masses, all other values must be less than that, since all masses have the same charge. So the absolute magnitude of the field a non-infinite distance from all masses can never equal the "infinity magnitude."
... which again, was NOT what I said, and not really relevant to the discussion.

[OngBonga]

...but that's not really meaningful unless we assert that the gravitational energy is 0 J an infinite distance away from all mass, which sounds reasonable, but can't be proven via experiment

Well it's neither reasonable nor provable because the concept of infinite distance is itself flawed.

Surely every region of spacetime is curved? Surely your original comment was techincally correct? I mean the top of the hill, it's not "flat" except from the frame of reference of those on earth looking at it. And even then, down to the molecular level, it's not flat at all.

[Poopadoop]

The surface of the Earth is smoother than the surface of a billiard ball, scaled to size.

Fact.

[MadMojoMonkey]

Well it's neither reasonable nor provable because the concept of infinite distance is itself flawed.

Yes. Whenever we handle infinities, we have to be careful not to use them foolishly.

In this case, we're asking, "What is the gravitational potential energy of a mass when you measure it from 'very far' away?"
And to do so, we write the equation for the effect as a function of distance. In this case, it's U = GMm/r, where U is the potential energy in J, G is Newton's gravitational constant in N*m^2/kg^2, M is the mass of the object in question in kg, m is the "test mass" in kg, and r is the distance between the 2 masses, in m.

The "test mass" is a mathematical construct, but unimportant to explain, as it is a constant and the only variable in the equation is the r in the denominator.

We can see that as r increases, U decreases. There is no limit to the bigness of r, so no limit to the smallness of U. What we're really saying is that if r is arbitrarily large, then U is arbitrarily slight, which is perfectly reasonable.

Surely every region of spacetime is curved? Surely your original comment was techincally correct?

:/
I'm now torn, because I'm thinking I got it wrong 2 times, and I'm hesitant to put anything out there at this point.
My GR is weak.
I'm currently leaning toward you being correct, here.


OK, I flagged down a grad. student to make sure I'm not putting my foot in my mouth for the 3rd time on this.
Curvature is related to the 2nd derivative of the field in question. Since all mass charge has the same sign, there are no inflection points within the field, meaning there is nowhere where the sign of the curvature flips. Therefore there is nowhere that the 2nd derivative is 0, and therefore there is nowhere that the curvature is 0.

I mean the top of the hill, it's not "flat" except from the frame of reference of those on earth looking at it. And even then, down to the molecular level, it's not flat at all.

OK, not for nothing, but you inspired me to take a question you didn't pose a bit too seriously, and after talking to a couple of doctorates in physics who work in GR, I can only say that it's an excellent question which exposes a contradiction in my understanding and which I haven't rooted out as of now. I.e. something that I think I'm saying is not what I'm saying and no one I've spoken to has figured out exactly which of the many things I'm saying is the wrong one(s).

So. Your statement that "what is the top of the hill is a matter of perspective" is boneheaded UNLESS you're talking about observers moving at relativistic speeds, and in that case, it's a doozy.

OK, so how shall we define the "top" of the hill. I propose that we generalize away from a hill (made of molecules) to a field which is curved. Instead of talking about the "top" of a hill, let's talk about an equilibrium position in the field. This does describe a hill, but generalizes to a more broad collection of cases.

Now, a reasonable definition of an equilibrium position is one where the slope of the field is perpendicular to the force caused by that slope. This is nice, as it means that we can definitively say that an object at rest w.r.t. the field is invariant to all observers, as predicted by GR. I.e. no observer should see the object moving w.r.t. the field, no matter how that observer is moving or accelerating.

However, that annihilates the previous definition of the force being perpendicular to the field, because angles are not preserved in Lorentz transformations. So something is wrong. That definition of an equilibrium position seems to not fit, but it has to fit because no observer should observe the object moving w.r.t. the field, which means no portion of the force is parallel to the slope of the field, which gets us right back where we started.

Summary: This is a fun question to ponder, and I wouldn't suggest holding your breath for me to deliver a concise explanation any time soon. There's a clear contradiction in my understanding and even the people I spoke to didn't see the flaw right away.

Kudos for this. It was an otherwise boring day until you got me thinking about this.

[OngBonga]

I can barely follow you unfortunately. Maybe I'll start to get it as I quote and reply...

We can see that as r increases, U decreases. There is no limit to the bigness of r, so no limit to the smallness of U. What we're really saying is that if r is arbitrarily large, then U is arbitrarily slight, which is perfectly reasonable.

Yes this is very much reasonable. Basically 1/x... just don't divide by zero.

Therefore there is nowhere that the 2nd derivative is 0, and therefore there is nowhere that the curvature is 0.

I have no idea what you mean by this, but I like the conclusion. I'm ok with expansion into infinity, but I see the universe as finite. Like a Koch snowflake...



What's the perimeter of a Koch snowflake of a given area? Knowing it's finite, despite expanding into fractal infinity, is actually quite profound. That's how I see universal expansion... infinity bounded.

So. Your statement that "what is the top of the hill is a matter of perspective" is boneheaded UNLESS you're talking about observers moving at relativistic speeds, and in that case, it's a doozy.

Well why is moving at "relativistic speeds" important? I'm being technical and pedantic here. Motion at 1/1000000000th of c is motion, and subject to fractional time dilation. You can say it's negligible if you wish, but even the slightest bit of curvature is curvature.

Now, a reasonable definition of an equilibrium position is one where the slope of the field is perpendicular to the force caused by that slope. This is nice, as it means that we can definitively say that an object at rest w.r.t. the field is invariant to all observers, as predicted by GR. I.e. no observer should see the object moving w.r.t. the field, no matter how that observer is moving or accelerating.

I really don't like the term "at rest". Everything, literally everything, that has mass, is in motion. The idea that something is "at rest" might be useful when it comes to doing sums, but it's misleading imo. And it could be partly to blame for the contradiction you seem to face.

I have to be honest though, I'm still nonethewiser, I don't understand your contradiction.

[MadMojoMonkey]

I can barely follow you unfortunately. Maybe I'll start to get it as I quote and reply...

I think you get most of it.

I'm getting a bit mentally exhausted trying to unravel this whole thing, so I'm going to pause thinking on it for the evening.

Yes this is very much reasonable. Basically 1/x... just don't divide by zero.

Yep.

I have no idea what you mean by this, but I like the conclusion. I'm ok with expansion into infinity, but I see the universe as finite. Like a Koch snowflake...



What's the perimeter of a Koch snowflake of a given area? Knowing it's finite, despite expanding into fractal infinity, is actually quite profound. That's how I see universal expansion... infinity bounded.

The area of a Koch snowflake is finite, but the perimeter is infinite. I think you know that, but it's worded funny.

How do you account for time dependence? I.e. the Koch snowflake doesn't change in time, but the universe does.

If the universe exists on the perimeter of the Koch snowflake, then it's either infinite, and the notion of expansion is absurd, or the perimeter is finite and ever-increasing in crinkliness over time, expanding without bound.

Well why is moving at "relativistic speeds" important? I'm being technical and pedantic here. Motion at 1/1000000000th of c is motion, and subject to fractional time dilation. You can say it's negligible if you wish, but even the slightest bit of curvature is curvature.

You got me. I have no critiques of this.

I really don't like the term "at rest". Everything, literally everything, that has mass, is in motion. The idea that something is "at rest" might be useful when it comes to doing sums, but it's misleading imo. And it could be partly to blame for the contradiction you seem to face.

This makes me terribly uncomfortable as well, but we just have to deal with it for the foreseeable future.
QM says nothing with mass is at rest in any inertial reference frame.
GR says only photons cannot be at rest in an inertial reference frame (because a reference frame moving at c is explicitly non-inertial).
They don't exactly agree on everything. It's an ongoing investigation.

Nonetheless, we're not talking about QM at all in this discussion. So the GR assertion that an object can be at rest in an inertial reference frame is fine.

I have to be honest though, I'm still nonethewiser, I don't understand your contradiction.

I'll get you there. In a bit.
I'm mentally tired from trying to think through this, and I need a break.
I'll come back on this later, but I'm gonna play some Skyrim for a bit.

[OngBonga]

Do I get a gold star for making you think so hard?

The area of a Koch snowflake is finite, but the perimeter is infinite.

Incorrect. This is the same as saying one plus a half plus a quarter plus an eighth plus a sixteenth etc equals infinity. It doesn't, it equals two. The "infinite" perimeter is only infinite in the fractal sense, like a circle having an "infinite" number of sides while having a finite circumference.

How do you account for time dependence? I.e. the Koch snowflake doesn't change in time, but the universe does.

The Koch snowflake is self similar, the universe is not. Take the Mandlebrot set for an example.. there's a fractal that is *nearly* similar at different scales.

If the universe exists on the perimeter of the Koch snowflake, then it's either infinite, and the notion of expansion is absurd, or the perimeter is finite and ever-increasing in crinkliness over time, expanding without bound.

The latter. Meanwhile, the area of the snowflake remains constant. If the volume of the universe is increasing due to expansion, what remains constant? Net energy? It must, but this implies an ever decreasing density. It's 9.30am and I'm already beginning to get exhausted myself thinking about this!

GR says only photons cannot be at rest in an inertial reference frame (because a reference frame moving at c is explicitly non-inertial).

Weird. I would expect the opposite to be true... photons are "at rest" for all intents and purposes, since they have the same velocity to all observers.

Nice start to the day.

[OngBonga]

I'm wrong.

Incorrect. This is the same as saying one plus a half plus a quarter plus an eighth plus a sixteenth etc equals infinity. It doesn't, it equals two.

This is true, but what we're doing here with each iteration is adding a factor of 0.5... it's less than one, so our sum is always decreasing in magnitude... we're tending towards a finite number... in this case 1/0.5, which of course is 2.

The Koch snowflake's curve increases with each iteration at a factor of 4/3... it's higher than one, so the amount we add each time increases, it's more than what we added last time. It therefore tends towards infinity.

Mind blown.

[MadMojoMonkey]

Do I get a gold star for making you think so hard?

Incorrect. This is the same as saying one plus a half plus a quarter plus an eighth plus a sixteenth etc equals infinity. It doesn't, it equals two. The "infinite" perimeter is only infinite in the fractal sense, like a circle having an "infinite" number of sides while having a finite circumference.

That's a convergent series. The perimeter of a Koch under finite iterations is a divergent series, as you've noted below.

The Koch snowflake is self similar, the universe is not. Take the Mandlebrot set for an example.. there's a fractal that is *nearly* similar at different scales.

I'm not sure how this point relates to the greater discussion.

The latter.

This is a different statement than your original position, "That's how I see universal expansion... infinity bounded."
"The latter," is unbounded expansion.

Are you changing your position?

Meanwhile, the area of the snowflake remains constant. If the volume of the universe is increasing due to expansion, what remains constant? Net energy? It must, but this implies an ever decreasing density. It's 9.30am and I'm already beginning to get exhausted myself thinking about this!

Everything for which we have a conservation law is a viable candidate for the "constant area."
Net energy, net momentum, net charge, etc. There are others, but those are pretty solid.
The momentum and charge conservation laws are perhaps the most robust statements in physics, with no known violations existing on any scales. The same cannot be said for energy, depending on your interpretation of the following uncertainty law:
{delta_E}*{delta_t} >= h/2pi
The uncertainty in the energy associated with a quantum interaction times the uncertainty in the time it takes for that interaction to happen is always greater than or equal to some finite value (Plank's reduced constant). Some physicists interpret this to mean that particle interactions can "borrow" energy from the quantum vacuum, provided they pay it back really quickly.
This is a hand-wavey explanation to me. It tends to come up when discussing Feynman diagrams and virtual particles. There are energy imbalances within the diagrams (unobservable), but never outside the diagrams (observable).

Weird. I would expect the opposite to be true... photons are "at rest" for all intents and purposes, since they have the same velocity to all observers.

I'd like to think that the one thing you know about photons is that they are never at rest, but always (ALWAYS!) moving at c, for all observers.
How do you go from a statement that all observers agree it's moving, to the conclusion that it is at rest?

Nice start to the day.

Yeah.

[OngBonga]

The area of a Koch snowflake is finite, but the perimeter is infinite.

The perimeter is a simple curve. Ok you construct the snowflake with traingles, ie straight lines, but one can never construct a perfect Koch snowflake because we can never replicate the fractal detail. Same with circles... we're essentially constructing a circle with a very large number of very small straight lines. One can never construct a perfect circle... find me a circle, and a good enough magnifying glass, and I'll prove it's not a circle. Eventually, at a small enough scale, the curvature will be broken.

We know a circle's circumference is directly proportional to its radius... so if the radius is finite, then so is the circumference. What makes the snowflake different? I'm going to confidently propose that the perimeter of a Koch snowflake is directly proportional to its radius (probably at a ratio related to pi), which therefore makes it very much finite.

[MadMojoMonkey]

The perimeter is a simple curve. Ok you construct the snowflake with traingles, ie straight lines, but one can never construct a perfect Koch snowflake because we can never replicate the fractal detail. Same with circles... we're essentially constructing a circle with a very large number of very small straight lines. One can never construct a perfect circle... find me a circle, and a good enough magnifying glass, and I'll prove it's not a circle. Eventually, at a small enough scale, the curvature will be broken.

We know a circle's circumference is directly proportional to its radius... so if the radius is finite, then so is the circumference. What makes the snowflake different? I'm going to confidently propose that the perimeter of a Koch snowflake is directly proportional to its radius (probably at a ratio related to pi), which therefore makes it very much finite.

You may be technically right about circles, but not about the line-segments.
Fields are continuously valued and exist at all points in spacetime.
At any rate, approximating things as circles is quite powerful and while it may not be a perfect description, the predictions are good, so we roll with it.

The Koch is different because it has no curvature at any location on its "curve." It lacks smoothness on any scale.
This explains it well:
https://www.youtube.com/watch?v=D2xYjiL8yyE

[OngBonga]

This is a different statement than your original position, "That's how I see universal expansion... infinity bounded."
"The latter," is unbounded expansion.

Are you changing your position?

idk, I need another smoke before I can be certain wtf I'm talking about.

[OngBonga]

There's one thing that strikes me... the number 4/3.

That makes me think of the volume of a sphere. This can't be a coincidence?

[OngBonga]

Looking at the triangle to star iteration... we can see where the 4/3 comes from.

The star has four times as many sides, and each side is three times smaller than the traingle's sides.

Ok, so why 4/3 when it comes to spheres?

The volume of a sphere is pi * radius cubed * 4/3, while the area of a circle is simply pi * radius squared.

Where does that 4/3 come from? This must be directly related to the snowflake.

[OngBonga]

Ok so if we didn't mutliply by 4/3, are we left with a cube? Is that extra 1/3 of volume the "rounding" of a cube to make a sphere?

[OngBonga]

I'd like to think that the one thing you know about photons is that they are never at rest, but always (ALWAYS!) moving at c, for all observers.
How do you go from a statement that all observers agree it's moving, to the conclusion that it is at rest?

Just because you *observe* something to be in motion, doesn't mean it is in motion. Have you ever been sat on a train at a station, and there's a train on the next platform that starts moving, and for a second you're not sure if it's you or them moving? Forget the fact that both are moving through spacetime, it's time for me to conveniently disregard spacetime curvature.

The photon can be "at rest", while we move away from it. This is expansion... imagine a singularity of light, which then expands inwards at c. Well, anything caught in the slipstream of that newly created space (anything with mass) will see the light shoot away from them, but the opposite happened... the new space we presently occupy is getting further and further away from the light source.

And for good measure, this can explain quantum entanglement... two entangled photons that *appear* a great distance apart actually occupy the same region of spacetime. This makes sense from the pov of the photon, since it experiences no time. So certainly from its pov, it's not moving. How can it be? Motion happens over time.

[MadMojoMonkey]

Just because you *observe* something to be in motion, doesn't mean it is in motion.

Careful.
Motion is relative, not absolute, yes. However, I've stipulated what the motion is relative to, an observer, any observer, under any observing conditions.

NO observer (whether that observer is an atom or a person or a microscope) ever observes a photon moving at any speed besides c.
That is the empirical datum.

The photon can be "at rest", while we move away from it.

A photon at rest in an inertial reference frame has never been observed.
Nothing is at rest with respect to (w.r.t.) us "while we move away from it." That's contradictory. If you're asserting it's at rest, you need to state w.r.t. what.

A photon can only be at rest in a reference frame which is comoving with it, which means that reference frame is moving at c, which is a non-inertial reference frame.

This is expansion... imagine a singularity of light, which then expands inwards at c.

I don't know what you mean by a singularity which expands inwards. A singularity is already an infinitely localized object, i.e. it exists at exactly one point.
That definition seems to make any "inward expansion" absurd, but ... black holes are weird, so maybe you're trying to make use of that?

Inside a black hole, the singularity is a location toward which all spacial directions point, and time is all weird-like. All we can say for certain is that an object inside a black hole's event horizon will never move away from the singularity. We cannot say that anything will reach the singularity in a finite amount of time.

So it's weird.

Well, anything caught in the slipstream of that newly created space (anything with mass) will see the light shoot away from them, but the opposite happened... the new space we presently occupy is getting further and further away from the light source.

I'm finding it hard to reconcile how light can traverse any space in that model.
If photons just sit still, and space expands around them, then how does light from the sun ever reach the Earth?

And for good measure, this can explain quantum entanglement... two entangled photons that *appear* a great distance apart actually occupy the same region of spacetime.

If 2 things appear (have been measured) to have distance between them in spacetime, then that is data.
A theory with is contradictory with the data is false.

Which is not to say that these particles may not occupy the same state in another field, but that's already beyond the conversation because we're talking about relative positions in spacetime.

This makes sense from the pov of the photon, since it experiences no time. So certainly from its pov, it's not moving. How can it be? Motion happens over time.

No matter how fast your reference frame is moving (or any other GR effects), you always observe your own time to be "normal." A photon isn't frozen in its own frame, everything BUT the photon is at frozen in time, due to infinite time dilation.

[OngBonga]

If photons just sit still, and space expands around them, then how does light from the sun ever reach the Earth?

Let me try and make sense of my stoned thoughts. Imagine we have a light source that shines in all directions, so that one second later we have a sphere with a radius of 1 light second. What happened? Did the light move through existing space to create this sphere? Or did new space get created at light speed? How can we tell the difference? And if it's the latter, did the light move through space?

I guess that's what I mean whan I say "at rest"... wrt to space.

So how does light get to Earth? I guess it doesn't... the Earth gets to the light. That light basically is a stain in spacetime, and we're heading in its direction at c because that's how fast space is expanding, and we're moving in its direction because the sun is so massive and curves space in such a manner that we move more toward it that anything else. Of course, the sun itself is collapsing into this newly expanded space, so when we "collide" with the stationary light, the sun is over 8 light minutes away from us.

Do I believe this? I don't think so. But... I don't really feel that we're all that close to understanding nature. This idesa of light being constant to all observers... does that inlucde light itself? Are two photons moving very close and parallel to one another observing each other to be moving at c? What happens if you're on a spaceship moving at v=c and you turn the headlights on? I know what happens if you're at v<c, the light moves away from you at c. But if you're already at c?

Something doesn't feel intuitively right. There's something I like about a theory that incorporates spacial expansion, gravity and entanglement, it's just a shame I have absolutely no idea how to go about proving or disproving such a claim.

[MadMojoMonkey]

Do I believe this? I don't think so. But... I don't really feel that we're all that close to understanding nature.

Yeah. It sounds pretty bunk to me, but ya know... I'm so clearly biased that my opinion can't really matter. Who ever let a physicist be in charge of a physics thread? nonsense. You'll never get an unbiased opinion on photons, here.


As for understanding nature... well... we've got a lot of reason to think we've pretty much got atoms sussed out. That's a good deal of what we currently think of as "nature." Having sussed out atoms means we've got photons and gluons and the W and Z bosons pretty much nailed.

Dark matter, on the other hand... and the accelerating expansion of the universe (dark energy)?
You're really right. We don't understand them at all, and they simply dominate the structure of the universe.
(I'm walking back my statement that gravity is king on the largest scales. Up to the scale of accelerating expansion, but then that takes over.)

This idesa of light being constant to all observers... does that inlucde light itself?

What we know about photons is expressed in equations, and interpreting those equations beyond their exact statements is risky business.

Are two photons moving very close and parallel to one another observing each other to be moving at c?

How are the photons observing each other? (What are they exchanging?)
Don't forget infinite space contraction in the direction of motion, along with infinite time dilation.
The concept of simultaneity is tricky, too.

Also, a photon does not have a well-defined position function, since its energy is well-defined and therefore its momentum can be known exactly. The HUP says if the momentum is defined exactly, then the position is undefined.

What happens if you're on a spaceship moving at v=c and you turn the headlights on? I know what happens if you're at v<c, the light moves away from you at c. But if you're already at c?

The Higgs mechanism is a beast.
If you're already at c, then you are massless.
There is no way to accelerate to c from less than c.
Either a particle is massless and moves at c, or it is not massless and moves at less than c.
So "you" can't be on a [thing made of atoms] at v=c.

but that's no fun.
Let's simply apply conservation of momentum and say that if you're moving at c and you emit a photon, then you have less momentum than before you emitted the photon ('cause headlights presumably face your direction of motion), but the same mass.

A photon can change it's wavelength to change momentum without changing speed. You'd need to do something similar, but IDK what that means for a non-photon.

Something doesn't feel intuitively right. There's something I like about a theory that incorporates spacial expansion, gravity and entanglement, it's just a shame I have absolutely no idea how to go about proving or disproving such a claim.

You are trying to unify QM and GR in an ex-poker forum.

We've got the deck stacked against us, but it's still a fun game.

[OngBonga]

I thought of another way to explain my thinking. Consider the following... in every direction we look, we observe the past. Perhaps a nanosecond ago, perhaps 8 minutes ago, perhaps billions of years ago. Every single direction in 3d space is the past. Consider walking from A to B. When you get to B, are you in the same place that B was when you started your journey? Of course, B has moved, in time (and therefore space).

So in what direction is our motion? We're moving into the 4th dimension... the future. Everything (with mass) moves into this unseen dimension. Time is expansion.

We don't move into pre-existing spacetime. Two objects with mass (let's say the Earth and Moon) are both moving into new spactime, and both resist this motion, creating curvature. This curvature keeps both bodies entangled in space, which is why we don't expand away from each other at light speed.

A photon can change it's wavelength to change momentum without changing speed. You'd need to do something similar, but IDK what that means for a non-photon.

Yeah I mean this is excellent. I can't think of another way for something with mass to change momentum other than to accelerate.

You are trying to unify QM and GR in an ex-poker forum.

It's more fun than massaging my ego on flat earth youtube videos.

[MadMojoMonkey]

I thought of another way to explain my thinking. Consider the following... in every direction we look, we observe the past. Perhaps a nanosecond ago, perhaps 8 minutes ago, perhaps billions of years ago. Every single direction in 3d space is the past. Consider walking from A to B. When you get to B, are you in the same place that B was when you started your journey? Of course, B has moved, in time (and therefore space).

Yes. I agree.

Except that being at a different location in time does not imply being at a different location in space, necessarily. Here on the surface of a planet, it certainly does, but not necessarily in the abstract discussion of the nature of motion.

So in what direction is our motion? We're moving into the 4th dimension... the future. Everything (with mass) moves into this unseen dimension. Time is expansion.

Sure. We can say that the 4-vector which describes our motion has a time component which is of constant direction and non-0 length. We can still have our 3 spacial components as 0-vectors, though, showing that motion in time, but not space is possible.

We don't move into pre-existing spacetime. Two objects with mass (let's say the Earth and Moon) are both moving into new spactime, and both resist this motion, creating curvature. This curvature keeps both bodies entangled in space, which is why we don't expand away from each other at light speed.

I'm not entirely sure I follow this part.
You're equating inertial mass and gravitational mass, which isn't a huge deal, since they agree to like 30+ decimal places, and I'm not certain if recent developments in the Higgs mechanism hasn't shown them to be the same, but as I currently understand it, they don't have to be the same. At any rate, if they are the same, then I think your description is pretty good. I think it breaks down at the end because you don't need the 2nd object to rule out motion at light speed. The curvature is enough (again, if inertial mass and gravitational mass are the same).

Whether or not the future exists before we arrive in it seems unmeasurable. I'm not sure how one could measure something "in the future" in that regard. Of course, I can measure something tomorrow, but by the time I measure it, it will be the present, not the future. I cannot acquire the result of tomorrow's measurement before tomorrow.
If we stipulate faster then light travel, then we have tachyon particles (FTL particles), which would for all observational purposes be moving backwards in time. The existence of tachyons would break causality.

The many worlds interpretation of QM would imply that all possible futures exist, but that's not science, so much as intellectualizing how hard it is for our human brains to accept the counter-intuitive statements of QM.

You're kind of on to something big, though. In a very real and practical sense, the reason for gravitational attraction toward massive bodies is due to time dilation. In short, the closer you are to a massive object, the slower time flows. So the rate of time for your feet is slower than the rate of time for your head, and this culminates in an acceleration toward your feet (assuming you're standing up).

It's more fun than massaging my ego on flat earth youtube videos.

Thanks?
Being slightly above the intellectual rigor of a YouTube comments section is better than being slightly below, I guess.