Is a photon simply a vibration of the spacetime lattice?

In summary, there is no evidence that photons have any mass, they travel through spacetime differently than masses, and they bend when the spacetime lattice bends near massive bodies.
  • #1
Curiousphy
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Is a photon simply a propagating vibration of the spacetime lattice similar to gravitational waves but at a different wavelength and amplitude, and the electron that creates it plucks a single lattice string rather than a bunch? Therefore it has no mass and travels differently through spacetime than massed entities, and it bends when the spacetime lattice bends near massive bodies...
 
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  • #2
Curiousphy said:
Is a photon simply a propagating vibration of the spacetime lattice similar to gravitational waves but at a different wavelength and amplitude

No. Spacetime is not a lattice. A lattice is broadly defined as a repeated arrangement of something, such as atoms in a metallic lattice or a repeated arrangement of points in group theory. Spacetime is continuous and is not composed of repeated structures like a lattice is.

Photons are fully described by Quantum Electrodynamics, and no evidence has yet arisen suggesting it is inaccurate or incorrect. QED also cannot be combined with General Relativity at this time.
 
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  • #3
No. For a start there is no "spacetime lattice". Spacetime is modeled as a smooth manifold.

A photon is an excited state of the electromagnetic field. A gravitational wave is part of spacetime, which you can view as a traveling wave. Light and gravitational waves are very different in a great many ways - notably one is a vector wave and the other a tensor wave.

They travel at the same speed (to the best of our knowledge) because ##c## is more or less the only available defined speed.
 
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  • #4
So perhaps the use of the word "lattice" is incorrect or imprecise, but the generation of propagating EM waves also involves moving electrons in alternating directions, and it correlates with how electrons release photons during a state change. It is consistent how electrons can impart spatial ripples that propagate out at c. If spacetime consisted of anything, it would seem like electrons had the ability to cause a propagating vibration along an invisible spacetime "string" in the direction of the propagation. How do we rule out the possibility that spacetime itself was the medium for the energy propagation and that itself was vibrating?
 
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  • #5
Electromagnetism is sourced by the electromagnetic current, gravitational effects are sourced by the stress-energy tensor. They are completely different concepts. Comparing things that they do share in common just using words is not going to change that.
 
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  • #6
Curiousphy said:
How do we rule out the possibility that spacetime itself was the medium for the energy propagation and that itself was vibrating?
One of Einstein's key realisations was that you can model gravity as spacetime curvature because everything reacts the same way to gravitational fields. The same cannot be said of electromagnetic fields - particle paths curve one way or the other or not at all depending on their charge. That makes it extremely difficult to view electromagnetic phenomena as anything like gravitational ones.

I believe there have been attempts to include fields other than gravity in the structure of spacetime (Kaluza-Klein theory for example). I don't think they were ever really successful.
 
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  • #7
Gravity waves distort spacetime but light, or any electromagnetic wave, does not.
 
  • #8
Curiousphy said:
How do we rule out the possibility that spacetime itself was the medium for the energy propagation and that itself was vibrating?
Easy. Waves that cause vibrations in spacetime as a medium are called gravitational waves. They are both theoretically and observationally distinct from electromagnetic waves.

Edit: @FactChecker for the win!
 
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  • #9
FactChecker said:
Gravity waves distort spacetime but light, or any electromagnetic wave, does not.
Nitpick: gravity waves are a kind of surface wave on water. Gravitational waves are what you mean.

Less nitpicky, electromagnetic waves have a non-zero energy density, so do lead to spacetime curvature. I believe the relevant class of solutions are called pp-wave spacetimes and don't generally include gravitational waves, but know little beyond that. Given the actual energy densities of practical EM waves, this is entirely irrelevant to anybody except theorists. The difference with gravitational waves is that they don't cause spacetime curvature, they are spacetime curvature.
 
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  • #10
Curiousphy said:
Is a photon simply a propagating vibration of the spacetime lattice similar to gravitational waves but at a different wavelength and amplitude,
You might be interested in this description of how gravity waves were detected. https://www.ligo.caltech.edu/WA/page/ligo-gw-interferometer
If light did anything like this, it would be detected all the time. Furthermore, the theoretical basis does not hint at any spacetime vibrations.
 
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  • #11
Ibix said:
Nitpick: gravity waves are a kind of surface wave on water. Gravitational waves are what you mean.

Less nitpicky, electromagnetic waves have a non-zero energy density, so do lead to spacetime curvature. I believe the relevant class of solutions are called pp-wave spacetimes and don't generally include gravitational waves, but know little beyond that. Given the actual energy densities of practical EM waves, this is entirely irrelevant to anybody except theorists. The difference with gravitational waves is that they don't cause spacetime curvature, they are spacetime curvature.
I stand corrected.
 
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  • #12
One more point about the difference between electromagnetic and gravitational waves. A plane electromagnetic wave normally incident on a ring of electrons will displace the ring bodily up and down, while a gravitational wave will deform the ring into an ellipse (or make it oscillate between two perpendicular ellipses, more precisely). The electromagnetic wave and its effects are symmetric under 360° rotation, while the gravitational wave and its effects are symmetric under 180° rotation. This reflects differences in the way the electromagnetic and gravitational fields work which impose different constraints on what sources and waves can look like.
 
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  • #13
Ibix said:
No. For a start there is no "spacetime lattice". Spacetime is modeled as a smooth manifold.

A photon is an excited state of the electromagnetic field. A gravitational wave is part of spacetime, which you can view as a traveling wave. Light and gravitational waves are very different in a great many ways - notably one is a vector wave and the other a tensor wave.

They travel at the same speed (to the best of our knowledge) because ##c## is more or less the only available defined speed.
Vectors and tensors are equivalen/isomorphict when there is a metric; any relationship between the two in this respect?
 
  • #14
WWGD said:
Vectors and tensors are equivalen/isomorphict when there is a metric; any relationship between the two in this respect?
In this context "vector" means "rank 1 tensor" and "tensor" means "rank 2 tensor"
 
  • #15
Dale said:
In this context "vector" means "rank 1 tensor" and "tensor" means "rank 2 tensor"
Thanks, I mean, are light and gravitational waves dual to each other under this equivalence? EDIT: Apologies if I am derailing the thread, I can ask this as a stand-alone if that is best.
 
  • #16
Curiousphy said:
So perhaps the use of the word "lattice" is incorrect or imprecise...
Precision matters in formulating a question that will produce answers that satisfy your underlying curiosity.
This is one of the key things that distinguishes popular science from real science.
 
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  • #17
WWGD said:
Thanks, I mean, are light and gravitational waves dual to each other under this equivalence? EDIT: Apologies if I am derailing the thread, I can ask this as a stand-alone if that is best.
No. Rank 1 and rank 2 tensors are not dual to each other. Covariant tensors are dual to contravariant tensors of the same rank.
 
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  • #18
WWGD said:
Thanks, I mean, are light and gravitational waves dual to each other under this equivalence? EDIT: Apologies if I am derailing the thread, I can ask this as a stand-alone if that is best.
Not as far as I know. Gravity, including gravitational waves, is the metric, while the electromagnetic field is a field on top of spacetime.
 
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  • #19
Dale said:
No. Rank 1 and rank 2 tensors are not dual to each other. Covariant tensors are dual to contravariant tensors of the same rank.
I think we probably are getting off topic, but there are dualities such as the Hodge dual that relate tensors of different ranks. The Hodge dual of a rank ##k## tensor is of rank ##n-k##, where ##n## is the dimension of the space - four, in GR. And, in my (limited) understanding, it's just mathematical playing around in the same sense as index raising and lowering. Potentially very useful, yes, but taking the dual (any dual) of a vector does not change the physics. An electromagnetic wave still moves the ring of charges I was talking about bodily up and down, whether you describe the electric field as a vector or as its dual (Hodge or otherwise).
 
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  • #20
WWGD said:
Thanks, I mean, are light and gravitational waves dual to each other under this equivalence? EDIT: Apologies if I am derailing the thread, I can ask this as a stand-alone if that is best.

The short answer is no.

There are several tensors involved, I would point to the rank 2 Faraday tensor, and it's dual, the rank 2 Maxwell tensor, as the source of electromagnetic radiation in flat space-time in a 4-tensor treatment. Components of these tensors include the electric and mangetic fields, which satisfy the wave equation. See for instance <<wiki link>>.

You'll note that components of this rank 2 Faraday tensor are the electric and magnetic fields. In the 4-tensor treatment of electromagnetism, which I would call the "realtivistic" treatment, the electric and magnetic fields are not rank 1 tensors (vectors) themselves. This may not be familiar, unfortunately - a detailed explanation of the 4-tensor treatment is beyond the scope of what I want to write, though learning about the Faraday tensor, which I've linked to, would be the first step.

For gravitational waves, what satisfies the wave equation is the metric tensor. This is something completely different than either the Faraday or Maxwell tensors.

These are the most important tensors, but there are a bunch more that one might wish to use. For gravitation, one can derive the rank 4 Riemann tensor from the metric tensor, from the rank 4 Riemann tensor one can derive the rank 2 Ricci tensor and the rank 2 Einstein tensor, which gives Einstein's field equations ##G_{\mu \nu} = 8 \pi T_{\mu \nu}##. Here ##G_{\mu \nu}## is the Einsten tensor, ##T_{\mu \nu}## is the stress-energy tensor.

The electromagnetic contribution to the total stress-energy tensor, the "electromagnetic stress-energy tensor", can be computed from the Faraday tensor, see for instance <<yet another wiki link>>.

So, electromagnetic fields (incuding electromagnetic waves) have a stress-energy tensor (computable from the Faraday tensor) which is an incomplete part of the total stress energy tensor ##T_{\mu\nu}## in Einstein's field equations.

Einstein's field equations themselves involve ##G_{\mu \nu}##, the Einstein tensor, computed from the metric tensor ##g_{\mu \nu}##, and the stress-energy tensor ##T_{\mu \nu}##. The stress-energy tensor is not very intuitive, but it's the key element as being the "source of gravity", replacing the idea of "mass" as the source of gravity in Newtonian theory.
 
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  • #21
Ibix said:
One more point about the difference between electromagnetic and gravitational waves. A plane electromagnetic wave normally incident on a ring of electrons will displace the ring bodily up and down, while a gravitational wave will deform the ring into an ellipse (or make it oscillate between two perpendicular ellipses, more precisely). The electromagnetic wave and its effects are symmetric under 360° rotation, while the gravitational wave and its effects are symmetric under 180° rotation. This reflects differences in the way the electromagnetic and gravitational fields work which impose different constraints on what sources and waves can look like.

Could this be because gravitational waves are longitudinal while EM waves are transverse?
 
  • #22
Curiousphy said:
Could this be because gravitational waves are longitudinal

No, because they aren't, they're transverse.
 
  • #23
Curiousphy said:
Could this be because gravitational waves are longitudinal while EM waves are transverse?
No. Longitudinal waves would bodily displace the ring of electrons backwards and forwards. Gravitational waves are transverse tensor waves - the gravitational field won't support longitudinal waves or transverse vector waves (at least in vanilla GR, and I believe most variants that allowed other kinds of wave were ruled out with some certainty by analysis of the LIGO detections). The electromagnetic field, in contrast, won't support longitudinal waves or transverse tensor waves.

And there's still the fact that a gravitational wave will stretch-and-squish a ring of free-floating anythings in the same way. But an electromagnetic wave will displace negative charges up and down, positive charges down and up, and neutral objects not at all. Electromagnetic and gravitational waves really cannot be different kinds of the same thing, except in the very broad sense that they are both waves.
 
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  • #24
OK, thank you all. You've convinced me that EM waves and gravitational waves are different; however, many questions remain... for example, do EM waves and/or matter displace spacetime, or are they manifestations of the properties of spacetime itself? (in other words, are they in it, or part of it? I guess they could be in it but not "displace" it, too, in a "superposed" manner) if they are "in" it, can they theoretically exist outside of it?
 
  • #25
It feels like these questions are just pure speculation. As far as I know there is no standard meaning for the term “displace spacetime”.

Usually when scientists speak of a quantity we first think of either a way to measure it or to calculate it from other measurable quantities. We give it a name afterwards. So when you say “displace spacetime” can you describe the measurement you could use to determine the amount of spacetime displacement or the formula you would use to calculate it?
 
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  • #26
I guess these would be unresolved mysteries per current knowledge? Not being a scientist myself, I am just in my little curiosity quest to make sense of the world... I agree some of these questions are speculative and we may never know... like, if spacetime gives matter dimensions and light/photons exist dimensionless and outside of time, if you took away spacetime, could matter or photons still exist as a dimensionless and timeless "singularity" or "nullarity"... if so, maybe the big bang expansion of the universe wasn't so unfathomable... if all the mass/energy/information was already there just dimensionless and timeless.
 
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  • #27
Dale said:
It feels like these questions are just pure speculation.

It's worse. It's a bunch of scientifically sounding words strung together, but there is no meaning there. These might be grammatical sentences, but they are meaningless. "Colorless green ideas sleep furiously". If there were meaning there, they could be expressed mathematically.

Many of our hopeful and homegrown theoretical physicists think that the mission of a theoretical physicist is to come up with the right combination of words to explain nature. But physics is a quantitative science.
 
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  • #28
So, in the spirit of forum compliance, does physicsforums have a "speculations" section for people like me to interact with scientists/physicists to ask these questions? Not everyone would be able to capture "meaning" mathematically, and it may not be my questions, but sometimes speculative questions may spark new perspectives for scientists?
 
  • #29
Curiousphy said:
So, in the spirit of forum compliance, does physicsforums have a "speculations" section for people like me to interact with scientists/physicists to ask these questions? Not everyone would be able to capture "meaning" mathematically, and it may not be my questions, but sometimes speculative questions may spark new perspectives for scientists?
Absolutely not. "Been there, done that, will never do it again" is the rule on speculation here at PF.

PF is for the discussion of ESTABLISHED science.
 
  • #30
Curiousphy said:
So, in the spirit of forum compliance, does physicsforums have a "speculations" section for people like me to interact with scientists/physicists to ask these questions? Not everyone would be able to capture "meaning" mathematically, and it may not be my questions, but sometimes speculative questions may spark new perspectives for scientists?
I think that your initial question deserved a response and got one. The next step is for you to study those answers and the basic relevant physics. On such a complicated subject, that may take significant time and effort, but it is a very interesting subject. You will undoubtedly have more specific and scientific questions as you study. Those type of questions are welcome. But without further study, there are many more speculative theories than anyone can possibly answer. IMHO, this is not the place to try.
 
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  • #31
FactChecker said:
I think that your initial question deserved a response and got one. The next step is for you to study those answers and the basic relevant physics. On such a complicated subject, that may take significant time and effort, but it is a very interesting subject. You will undoubtedly have more specific and scientific questions as you study. Those type of questions are welcome. But without further study, there are many more speculative theories than anyone can possibly answer. IMHO, this is not the place to try.
what he said (very small).jpg
 
  • #32
@Curiousphy to expand slightly on my previous answer, and along with what factchecker said, PF has tried speculative sections before, but here's the problem. Before you can meaningfully "think outside the box" you have to know what's IN the box. Speculative posts pretty much never go anywhere useful, and as I said, PF has tried it and found that it definitely does not work. So much so in fact that I can imagine the mentor's response on seeing you asking for it once again (which happens about once a month).

not that again.jpg
 
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  • #33
Science is like a jigsaw puzzle. Only we don't have all the pieces and we don't have the picture on the box. We have experimentalists out there hunting down the back of the sofa for pieces and putting the pieces we have together in different ways. And we have theoreticians suggesting ways that bits might fit together and trying to work out what the picture might be.

Newton suggested the picture was a mountain. Maxwell suggested it was two mountains. Einstein realized the mountains were identical, and suggested it was one mountain, reflected in a lake.

The problem with "speculation" by non-experts is that they've only read vague descriptions of the jigsaw and have no idea what we know fits together, nor ways it cannot fit together. So your "spacetime lattice vibrations" is a bit like barging in and saying "maybe it's a cat!" While I'm perfectly happy to point out that it would be a very strange cat with trees and a snowline and discuss the evidence for it being a mountain and a reflection, addressing in detail why it's not a cat is not an efficient way for you to learn. And a mountain is so clearly not a cat, I'm not likely to learn anything.

Frankly, making speculations based on (at best) vague pop-sci descriptions is a waste of your time. A mountain is not a cat. And answering you becomes a waste of mine if you keep doing it. Nor is a mountain a dog, nor a mouse, nor a chicken, nor a... A billion blind guesses is not helpful - it's just noise.

If you want to contribute you need to put in the time to learn the maths and the evidence so that you actually know what is known. What is plausible and what is not. It is hard work, but it's absolutely fascinating and strange.

If you don't or can't do the studying, that's perfectly fine. But you have to accept that ideas you come up with without study are like wondering if the mountain might be a cat.
 
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  • #34
Curiousphy said:
I guess these would be unresolved mysteries per current knowledge?
I wouldn't say that either. As far as I know there is no meaning to the phrase "displace spacetime". There isn't a standard scientific meaning for the term, and you don't appear to have a specific meaning in mind either, in terms of either experimentally measurable quantities or things that could be calculated from other quantities. So it isn't an unresolved mystery, it hasn't even been defined well enough to merit the status as a mystery let alone an unresolved one.

You may as well ask if the farglesnap is a flubnubitz. It is not an unresolved mystery, it is an undefined question. One of the most important things that we do as scientists is to define our questions so carefully that they can be answered by performing an experiment. When a question is posed with that level of clarity and the answer is unknown, then that becomes an "unresolved mystery".

Curiousphy said:
I am just in my little curiosity quest to make sense of the world
I applaud that. Over the course of the last few centuries we have made enormous strides towards exactly that goal. I would strongly recommend seeking to learn that. Even Newton famously "stood on the shoulders of giants" to learn and understand how the world works. Physics Forums can help you in that goal.

In the meantime, I am going to go ahead and close this thread as the original question has been answered to your satisfaction, and I don't want to engender bad feelings in the community with this tangent.
 
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1. What is a photon?

A photon is a fundamental particle that is the basic unit of light and all other forms of electromagnetic radiation. It has no mass and travels at the speed of light.

2. What is a spacetime lattice?

A spacetime lattice is a theoretical framework that describes the structure of space and time. It proposes that space and time are not continuous, but rather made up of discrete units, similar to a grid or lattice.

3. How is a photon related to the spacetime lattice?

According to some theories, a photon is thought to be a vibration or disturbance in the spacetime lattice. This means that the photon's energy is transferred through the lattice, similar to how a wave travels through water.

4. Is the concept of a photon being a vibration of the spacetime lattice widely accepted?

The idea of a photon being a vibration of the spacetime lattice is still a topic of debate and is not universally accepted among scientists. Some theories and experiments support this idea, while others propose different explanations for the behavior of photons.

5. How does the concept of a photon being a vibration of the spacetime lattice impact our understanding of light and the universe?

If the concept of a photon being a vibration of the spacetime lattice is proven to be true, it would greatly impact our understanding of light and the universe. It would suggest that the fabric of space and time plays a crucial role in the behavior of light and other forms of electromagnetic radiation, and could potentially lead to new discoveries and advancements in physics.

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