Can Dark Matter Exist in Higher Dimensions?

[PeterDonis]

A massive photon just seems contradict the entirety of modern physics.

If this were true, it would also be true of the W and Z weak gauge bosons, since those are spin-1 particles. But those are known experimentally to have mass. Why doesn't that "contradict the entirety of modern physics"?

 

[Vanadium 50]

You are confusing our best current observations with the possible theoretical models.

It sounds more like he is confusing "what is" with "what he is comfortable with." Nature doesn't care.

As you say, there is nothing wrong with the photon having a small but non-zero mass. This was all worked out by Alexandru Proca in the late 30's.

 

[phinds]

If a photon had mass, of course its antiparticle would as well. This is straightforward quantum field theory.

So a massless photon is its own antiparticle, but if photons DID have mass they would have a separate antiparticle? Interesting. I never thought about that.

 

[Ibix]

A massive photon just seems contradict the entirety of modern physics.

Peter has answered your specific points. I think the general point is that you are confusing how we normally model light (massless, always travels at $c$) with reality, which is whatever it is. Reality isn't measurably different from our model (it wouldn't be a useful model if it was), but that doesn't mean the model is exactly correct.

A really tiny photon mass isn't inconsistent with anything (although we'd have to add a lot of footnotes to relativity texts and rewrite a lot of particle physics texts). For example we would, in principle, be able to stop a photon if it had mass - but the mass is tiny and a microbe sneezing on the other of the room would accelerate it to near $c$, which would be why we don't see them routinely.

 

[PeterDonis]

So a massless photon is its own antiparticle, but if photons DID have mass they would have a separate antiparticle?

Not necessarily. I didn't mean to imply that a massive photon's antiparticle must be distinct, just that the antiparticle's mass has to be the same as the particle's mass even if the antiparticle is distinct.

 

[phinds]

Not necessarily. I didn't mean to imply that a massive photon's antiparticle must be distinct, just that the antiparticle's mass has to be the same as the particle's mass even if the antiparticle is distinct.

Thanks, Peter. So am I right then in the following thought: If a massive photon's antiparticle WERE distinct that would actually be an argument against massive photons, using the following reasoning. Massless photons don't interact since they are pure waves and pass through each other so we see no interactions. If photons had distinct antiparticles, given the number of photons zipping around there WOULD be interactions (annihilations) but we never see any such thing.

 

[PeterDonis]

If photons had distinct antiparticles, given the number of photons zipping around there WOULD be interactions (annihilations)

There are two problems with this argument.

One is that a photon-antiphoton pair can only annihilate if there is some other particle-antiparticle pair that the photons could annihilate into. But even if the photon has mass, its mass has to be much, much, much, much smaller than the mass of any other particle, so the hypothetical massive photon-antiphoton pairs flying around have far too small an energy to produce any other particle-antiparticle pair. So they can't annihilate each other because there's no other accessible state for the pair to go into.

The other is that even massless photon pairs can "annihilate" and convert themselves into other particle-antiparticle pairs if they have enough energy. The simplest case is gamma rays producing electron-positron pairs, which AFAIK has been observed in experiments.

 

[phinds]

Thanks.

 

[Helios]

Folks, I remarked that a ( hypothetical ) massive photon had strange consequences. Just wondering. These were not objections. I did not use this as evidence in an attempt to disprove the existence of massive photons. I don't need to show why a massive photon is not possible, unless I asserted that they are impossible. I am allowed to say that it is possible that there are no massive photons. This is also a hypothesis, I suppose. Another is allowed to say that it is possible that there are massive photons. I don't know of any compelling reason to suppose this. Who is required to prove or disprove?

I said "contradict the entirety of modern physics"

Ibex said "we'd have to add a lot of footnotes to relativity texts and rewrite a lot of particle physics texts."

 

[PeterDonis]

I remarked that a ( hypothetical ) massive photon had strange consequences.

"Strange" compared to what we're used to observing, sure. But that's because all of our current evidence says photons are massless.

Your claim of "strange" is much stronger than just "different from our current evidence".

I said "contradict the entirety of modern physics"

This is still much stronger than what @Ibix said. Scientists revise our best current theories all the time as we get new evidence. That doesn't mean new evidence "contradicts the entirety" of our best current theories. It can't possibly do that, since our best current theories are based on mountains of evidence we already have that confirm them.

 

[PeterDonis]

These were not objections. I did not use this as evidence in an attempt to disprove the existence of massive photons. I don't need to show why a massive photon is not possible, unless I asserted that they are impossible. I am allowed to say that it is possible that there are no massive photons. This is also a hypothesis, I suppose. Another is allowed to say that it is possible that there are massive photons. I don't know of any compelling reason to suppose this. Who is required to prove or disprove?

Basically, this amounts to "there might be massive photons, or there might not be". What's the point of saying that? It's a logical tautology.

You are hijacking someone else's thread with irrelevant quibbles. Therefore, you have been banned from further posting in this thread.

 

[Klystron]

It may be the case, speculating, that we may just perceive 'shadows' or projections into lower dimensions, as in the book 'Flatland'. But this is just an educated guess.

Nice, added to the reading list.
[snip...]

I also recommend reading Edwin Abbott's (AKA 'A. Square') novella "Flatland" and to add to the OP's reading list consider "Spaceland" by Rudy Rucker.

 

[kimbyd]

Is it correct that dimensions more than the three (4th being time) that we perceive can be mathematically modeled but as yet remain unobserved?

If so, is it possible that dark matter/energy are "elements" which exist in those higher dimensions, and as such remain invisible to those constrained to four?

The general picture is as follows. There are two general possibilities:
1) The extra dimensions are too small to be observed (much smaller than an atomic nucleus). While matter technically moves in those dimensions, it moves so little those motions leave no observational results (yet).
2) The extra dimensions are somewhat larger, but the particles and forces we are familiar with are confined to a 3-dimensional surface within the larger space. In such a model, all of the components of the standard model (quarks, leptons, gauge bosons) would all be confined. But gravity would not: it would necessarily leak out into the larger volume. This model has been used as an attempt to explain why gravity is so incredibly weaker than the other fundamental forces we currently know (electromagnetic and the strong and weak nuclear forces). The "large" extra dimensions would still have to be pretty small (nanometers at most, if I recall correctly).

In general such models are entirely speculative at the moment. Sadly, it's possible for these models to be true, but completely impossible to ever measure. The best we can say right now is that if we get extremely lucky and the model parameters are just right, maybe we'll be able to measure them. But in the mean time they're generally just neat mathmatical models that may have nothing to do with reality.

 

[Janus]

I said "contradict the entirety of modern physics"

How so? It wouldn't contradict Relativity. Relativity only requires that there is a invariant speed for the universe, it doesn't require light to light to travel at that speed unless light were truly massless. The fact that light is assumed to travel exactly at c is a convenience when working with Relativity, not a requirement.

Ibex said "we'd have to add a lot of footnotes to relativity texts and rewrite a lot of particle physics texts."

Because, those Relativity texts assume light moves exactly at c when dealing with examples like the light clock and simultaneity of relativity thought experiments. Light that travels almost at c, would give pretty damn close to, but not exactly, the same results. Adding a footnote would make this clarification without having to rewrite the whole text.

 

[PeroK]

Light that travels almost at c, would give pretty damn close to, but not exactly, the same results. Adding a footnote would make this clarification without having to rewrite the whole text.

It might be more of a nuisance for texts on classical electromagnetism.

 

[Theory]

Yes; string theory does this. But we have no experimental evidence for any such model.
They can't remain "invisible" in our four dimensions, since we observe their effects.

Where can I submit my theory of cosmic evolution for others to give their opinions?

 

[Orodruin]

Where can I submit my theory of cosmic evolution for others to give their opinions?

If you have original research you should submit it to any of the many leading journals in the field that you are regularly reading to keep up to date with the latest development in the field.

 

[berkeman]

Where can I submit my theory of cosmic evolution for others to give their opinions?

https://www.physicsforums.com/insights/wont-look-new-theory/

 

[PeroK]

If you have original research you should submit it to any of the many leading journals in the field that you are regularly reading to keep up to date with the latest development in the field.

If not, there's always twitter!

 

[PeterDonis]

Where can I submit my theory of cosmic evolution for others to give their opinions?

PF is not for original research. As @Orodruin said, the correct venue for original research is submission to a peer-reviewed journal.

 

[PeterDonis]

The OP question has been answered. Thread closed.