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### Author Topic: What restricts the speed of light?  (Read 6364 times)

#### Super Hans

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##### What restricts the speed of light?
« on: 22/04/2013 00:19:16 »
I'm not asking why things with mass can't go faster than light, my question is why/how is light itself restricted to ~299,792,458 m/s.

Maybe it would make more sense if I asked why light has a speed limit anyway. Why can't it be instant, we say the speed of light, but is it that light sets the speed limit or is it restricted by a universal speed limit, and if that speed limit happened to be higher light could go that speed? Is light that speed because that's just how fast light is or because that's how fast the universe allows it to go, and if so why doesn't it allow light to go faster?
« Last Edit: 22/04/2013 00:33:18 by Super Hans »

#### yor_on

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##### Re: What restricts the speed of light?
« Reply #1 on: 22/04/2013 01:24:20 »
I would say it's a property of the universe, we measure on. If you imagine yourself getting infinitesimally close to 'c'. it also should mean that from your perspective it should shrink to a 'nothing', in your direction of  'motion'. So the speed is connected to the way the universe exist, and what more dimensions we find it to have (3 spatial and the arrow), at least how I think of it.

#### Pmb

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##### Re: What restricts the speed of light?
« Reply #2 on: 22/04/2013 03:41:44 »
I'm not asking why things with mass can't go faster than light, my question is why/how is light itself restricted to ~299,792,458 m/s.

Maybe it would make more sense if I asked why light has a speed limit anyway. Why can't it be instant, we say the speed of light, but is it that light sets the speed limit or is it restricted by a universal speed limit, and if that speed limit happened to be higher light could go that speed? Is light that speed because that's just how fast light is or because that's how fast the universe allows it to go, and if so why doesn't it allow light to go faster?
Maxwell's equations describe electrodynamics. They are postulates, i.e. laws of nature. That means that we assume that they are true at all times and in all places and have been verified to be so by countless experiments. They describe light waves as moving at a finite speed, c. The special theory of relativity postulates that the laws of nature (including Maxwell's equations) are valid in all frames of reference, i.e. are covariant. The otgher postulate states that the speed of light is the same in all inertial frames of reference. So Maxwell's equations postulate a finite speed and relativity postulates that its invariant with respect to a Lorentz transformation which is a transformation from one inertial Cartesian coordinate system and time to another.

#### HellsMascot

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##### Re: What restricts the speed of light?
« Reply #3 on: 22/04/2013 05:40:32 »
To expound upon what Pmb was saying, the speed of light (which is actually the speed of all massless particles) in empty space is a universal constant. Much like many means by which we can comprehend universal phenomena, the speed of light in vacuum must be absolutely static or else our modern understanding of physics (down to the Planck length) holds no weight.

The speed of light was indirectly measured many times by scientists (Weber, Kirchhoff, et al.) that were exploring the nature of electromagnetism, and then Maxwell came along and showed that light is indeed a form of electromagnetic radiation, but he didn't know how to test for the means by which it was propagated. Then Einstein, in his approach to electrodynamic phenomena, said that the current physical models and equations describing these things were flawed. He proposed his own model, and gave it to the scientific community to test with experiments which would deduce the characteristics of electromagnetism; Einstein basically founded Special Relativity on the notion that the Lorentz transformation must transcend its connection with Maxwell's equations. So Special Relativity introduced light as a universal constant in that it always travels the same speed through empty space no matter the inertial frame of reference. Special Relativity denied the concept of position in space or time being absolute determinants of physical phenomena, and said that things could differ depending on the observer's location and velocity. There are books and books on the implications of this theory. Later Einstein solved the issue of the photoelectric effect by demonstrating that light has wavicle properties and therefore doesn't need a medium to travel in, answering Maxwell's question about how light is propagated.

So with Special Relativity, which has yet to see any serious counter-evidence, we rely on c, the one constant that is truly constant. The future-past light cone model of Minkowski Spacetime basically shows that anything going faster than the speed of light starts to mess with causality because c interrelates space and time. Because simply approaching the speed of light causes time dilation, actually exceeding it would blur the line between past, present, and future. If you could go faster than c, you could send things into the past and then things that are occurring relative to you would have no reference frame in time to determine when it is actually happening. Then all sorts of time paradoxes would occur.

So that is a pretty damn good reason why movement throughout the universe is restricted to a particular speed. Now to address the issue of the speed of light in vacuum being a 'speed limit for the universe' - or is it the other way around? Does the nature of our universe constrain the speed of light?

Well, some things travel faster than the speed of light in vacuum, but they don't carry any matter, energy, or 'information' - i.e. they cannot be used by the universe. By this I mean they do not have any physical properties while traveling faster than lightspeed and therefore they cannot interact with anything. This means the universe itself essentially depends on particles (massless or not) having phenomenological properties for things to 'occur.' This brings to mind virtual particles, and whether or not they are just placeholders or if they really do pop into and out of existence, and if they could be travelling faster than light when they don't 'exist.'

There is also the issue of quantum entanglement, whereby two 'entangled' particles can instantly transmit information, non-locally, faster than c. Einstein and friends did not like this at all and constructed the thought of local realism to combat it, but they ended up being proven wrong. Einstein said that was because quantum physics is incomplete (which it is). If an instrument observes an entangled particle, thereby affecting it when determining what information it carries (such as spin), its entangled brethren will instantaneously be determined to have the opposite (in some sense matching) property, which is bonkers. Despite everything I said in the above paragraph, this cannot be explained and it really does transmit information. This could be due to quintessence (a non-local fifth fundamental force which validates Bell Inequalities) and has been proposed to be able to realize the concept of teleportation of quantum information, and consequently, of mass (via reconstructing an object with entangled particles containing all the same information but at a distant location). Whole 'nother topic.

I could go on and on but this is a very philosophical question and perhaps you can give me some feedback so I know what direction to take the discussion in. The antipenultimate paragraph is the one you should read if you feel I wrote too much to read.
« Last Edit: 22/04/2013 07:53:08 by HellsMascot »

#### damocles

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##### Re: What restricts the speed of light?
« Reply #4 on: 22/04/2013 06:06:43 »
To expound upon what Pmb was saying, the speed of light (which is actually the speed of all bosons) in empty space is a universal constant.

Sorry, but there is something I do not understand here. An alpha particle is a boson, but alpha particles have mass, and travel at speeds far below the speed of light in empty space.

#### evan_au

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##### Re: What restricts the speed of light?
« Reply #5 on: 22/04/2013 12:18:47 »
Taking a somewhat different approach which also why explains why light doesn't travel at ~299,792,458 m/s when it isn't in a vacuum:
• Light is an electromagnetic wave
• A vacuum has a certain permitivity to electric fields, ε0
• A vacuum has a certain permeability to magnetic fields, μ0
• Velocity of light in a vacuum c0 =
• A Non-Vacuum has an equal or higher permittivity than a vacuum, ε
• A Non-Vacuum has an equal or higher permeability than a vacuum μ
• Velocity of light in a Non-vacuum c = ≤ c0
• ...and in fact similar equations govern the speed of waves in other media such as strings and solids.
To me, this says something about the nature of light as a wave which is composed of electric and magnetic fields.

However, why gravity should also travel at c0 is beyond me; although gravitons can be represented as a wave, they do not have electric and magnetic fields.

Maybe one day when we spot two black holes colliding, and detect their gravitational waves, we will be able to see if gravity really does travel at c0. (It surprised a lot of physicists when it was discovered that neutrinos don't travel at c0!)

#### damocles

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##### Re: What restricts the speed of light?
« Reply #6 on: 22/04/2013 12:33:47 »
Does gravity really travel at c0? Is the Earth attracted to the position where the sun was 8.5 minutes ago? What are the implications for the laws of planetary motion?

#### yor_on

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##### Re: What restricts the speed of light?
« Reply #7 on: 22/04/2013 13:42:12 »
Yes Damocles, that one, gravity's infinite speed, I think has been debunked. And the sun relative a dynamically updated position (at 'c') for Earth has been proven logically. I remember me too wondering about that one, using some rather good arguments from the net. I can see if I find what convinced me.. We discussed it here.

But i also expect 'gravity' to 'exist' instantaneously. and I think of that in terms of the inertia shown, in a course change, in deep space (flat if we like). It's the metric of space, so it must be there, but it updates at 'c'.

#### yor_on

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##### Re: What restricts the speed of light?
« Reply #8 on: 22/04/2013 14:02:54 »
speed of gravity.
And here is a rebuttal to it. Aberration and the Speed of Gravity
=

Ah better correct myself. There is no 'flat space' macroscopically, defining it as I do. but it will be very weak in deep space.
« Last Edit: 22/04/2013 14:13:27 by yor_on »

#### percepts

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##### Re: What restricts the speed of light?
« Reply #9 on: 22/04/2013 17:54:12 »
I heard or read somewhere that it is possible that gravitational waves may occur. If that is correct, would they effect the speed of electromagnetic waves. i.e. the speed of light. In my ignorance I am assuming that something about the higgs field would need to alter for a gravitational wave to happen and I'm wondering if that change would have an effect on the speed of light.

#### lightarrow

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##### Re: What restricts the speed of light?
« Reply #10 on: 22/04/2013 18:13:07 »
I'm not asking why things with mass can't go faster than light, my question is why/how is light itself restricted to ~299,792,458 m/s.

Maybe it would make more sense if I asked why light has a speed limit anyway. Why can't it be instant, we say the speed of light, but is it that light sets the speed limit or is it restricted by a universal speed limit, and if that speed limit happened to be higher light could go that speed? Is light that speed because that's just how fast light is or because that's how fast the universe allows it to go, and if so why doesn't it allow light to go faster?
As far as I know, c is not simply the speed of light in the void, but the maximum speed at which any signal can travel in the void. Why it's not infinite and, in particular, why it has that value, can maybe depend on the fact space and time are interconnected in some way; maybe in the future we will be able to find a more general theory from which the value of this constant comes out, but at the moment we can't do it.

#### David Cooper

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##### Re: What restricts the speed of light?
« Reply #11 on: 22/04/2013 18:43:25 »
Maybe it would make more sense if I asked why light has a speed limit anyway. Why can't it be instant, we say the speed of light, but is it that light sets the speed limit or is it restricted by a universal speed limit, and if that speed limit happened to be higher light could go that speed? Is light that speed because that's just how fast light is or because that's how fast the universe allows it to go, and if so why doesn't it allow light to go faster?

Your question is really asking how fast a universe which lacks Newtonian time can run under Newtonian time. If you do attempt to run it under Newtonian time, you can indeed run it at any speed you like, including running through the whole of time instantly. Einstein's model lacks Newtonian time altogether, so it also lacks speed altogether and movement too: it gives us an eternal block universe where past, present and future all simply exist as a static block. Clearly it's difficult to think around such a model, so Newtonian time gets dragged back into it by accident whenever people try to explain how it hangs together through normal langauge, and that repeatedly introduces all manner of confusions. Many of the key words we use to describe things automatically smuggle in Newtonian time along with them, so you have to be continually on your guard.

#### Pmb

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##### Re: What restricts the speed of light?
« Reply #12 on: 23/04/2013 03:54:35 »
Quote from: HellsMascot
To expound upon what Pmb was saying, the speed of light (which is actually the speed of all massless particles) in empty space is a universal constant. Much like many means by which we can comprehend universal phenomena, the speed of light in vacuum must be absolutely static or else our modern understanding of physics (down to the Planck length) holds no weight.
There is something called the Proca Lagrangian. It's the Lagrangian density for the EM field for a non-zero proper mass of the photon. I.e. if the photon mass was measured to be non-zero someday then Maxwell's equations would be described by this Lagrangian. Our understanding of modern physics wouldn't change that much. However I have never personally investigated the consequences of a non-zero proper photon mass. Someday! :)

Quote from: HellsMascot
Later Einstein solved the issue of the photoelectric effect by demonstrating that light has wavicle properties and therefore doesn't need a medium to travel in, answering Maxwell's question about how light is propagated.
It wasn't that much later. In fact it's published in the same issue of the journal that SR was published in. He wrote them only a few months apart. If anyone would like the details of the exact times and dates please let me know and I'll look them up and post them.

Quote from: HellsMascot
So with Special Relativity, which has yet to see any serious counter-evidence, ...
It's my understanding that there is precisely zero counter evidence, non-serious or not.

Quote from: HellsMascot
Because simply approaching the speed of light causes time dilation, actually exceeding it would blur the line between past, present, and future.
The sequence of events can be frame dependant even for speeds less than the speef of light.

Quote from: HellsMascot
Well, some things travel faster than the speed of light in vacuum, but they don't carry any matter, energy, or 'information' - i.e. they cannot be used by the universe.
Actually QM does not allow anything to go faster than the speed of light. Quantum entanglement is not faster than light.

#### HellsMascot

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##### Re: What restricts the speed of light?
« Reply #13 on: 23/04/2013 04:01:04 »
And here is a rebuttal to it. newbielink:http://xxx.lanl.gov/pdf/gr-qc/9909087v2 [nonactive]

Thank you for these links. These papers are just thoughts on gravity put into writing (as any investigation of gravity will be for a long time, until we find an instance in which it is possible to observe it directly) but they really helped further my understanding of how physicists think of gravity; beforehand my only knowledge of the subject came from general relativity and its irreconcilability with the Standard Model

#### HellsMascot

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##### Re: What restricts the speed of light?
« Reply #14 on: 23/04/2013 04:28:02 »
Quote from: HellsMascot
So with Special Relativity, which has yet to see any serious counter-evidence, ...
It's my understanding that there is precisely zero counter evidence, non-serious or not.

There is plenty of counter-evidence, but it's mostly not very well regarded by the scientific community. Some critics of special relativity: Herbert Dingle, Louis Essen, Petr Beckmann, Maurice Allais and Tom van Flandern.

Quote from: HellsMascot
Because simply approaching the speed of light causes time dilation, actually exceeding it would blur the line between past, present, and future.
The sequence of events can be frame dependant even for speeds less than the speef of light.

This is absolutely true, but I meant in one frame of reference.

Quote from: HellsMascot
Well, some things travel faster than the speed of light in vacuum, but they don't carry any matter, energy, or 'information' - i.e. they cannot be used by the universe.
Actually QM does not allow anything to go faster than the speed of light. Quantum entanglement is not faster than light.
[/quote]

The speed of light in vacuum is the upper limit for the speeds of objects with positive rest mass, but that doesn't mean that things don't travel faster than it. The models provided by quantum mechanics depend on c being the absolute limit because anything with mass that could match the speed of light in vacuum would have to have infinite energy, but that doesn't explicitly mean nothing can travel faster than c - only that information cannot be conveyed faster than the speed of light in empty space.

For instance: The phase velocity of an electromagnetic wave, when traveling through a metamaterial with a negative refractive index, can routinely exceed c. This occurs in most glasses at X-ray frequencies. However, the phase velocity of a wave corresponds to the propagation speed of a theoretical single-frequency component of the wave at that frequency, which means that superluminal communication is NOT occurring. So basically, information cannot be propagated faster than the speed of light, even though lots of things (evanescent waves during quantum tunneling, etc.) do not strictly obey the rules we adhere to. Quantum entanglement people purport that information can indeed be propagated faster than c but that's probably because it's not yet understood.

#### Pmb

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##### Re: What restricts the speed of light?
« Reply #15 on: 23/04/2013 05:28:09 »
Quote from: HellsMascot
The speed of light in vacuum is the upper limit for the speeds of objects with positive rest mass, but that doesn't mean that things don't travel faster than it.
You're right. I forgot. Tachyon's could go faster than the speed of light if they exist. But that would violate causality.

Quote from: HellsMascot
For instance: The phase velocity of an electromagnetic wave, when traveling through a metamaterial with a negative refractive index, can routinely exceed c.
But that's not observable. It's wrong to give to much physical meaning to the wave function when it's only the square magnitude of the amplitude that is observable. I was warned about this today by a friend of mine on this. He wrote an article on quantum entanglement. His name is John Stachel (former editor of the Einstein papers project, Einstein/relativity historian), Professopr Emeretis at Boston University. Would you like to read it when he sends it to me?

#### HellsMascot

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##### Re: What restricts the speed of light?
« Reply #16 on: 23/04/2013 06:16:06 »
Certainly! I guess you could link it here if possible. I'm just playing devil's advocate, really. You are more knowledgeable on the subject than I, and all alleged faster-than-light phenomena are really just misleading, just as is the case with interpretation/observation of a given wavefunction with the instruments we currently have. But I like to entertain the notion that so-called tachyons could indeed defy the currently prevailing dogma of lightspeed being the final word.

#### Pmb

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##### Re: What restricts the speed of light?
« Reply #17 on: 23/04/2013 08:48:06 »
Quote from: HellsMascot
Certainly! I guess you could link it here if possible. I'm just playing devil's advocate, really. You are more knowledgeable on the subject than I, ..
That's very kind and generous of you to say. Thank you! :)  It's nice to know that I can still be useful even if I have to be disabled. Thanks.

Quote from: HellsMascot
But I like to entertain the notion that so-called tachyons could indeed defy the currently prevailing dogma of lightspeed being the final word.
Me too.

I'll post it when I get it. I don't think that he'd mind. I'll post a Scientific American article on faster than light communication. Not only do the authors think that its possible but they claim that they've done it and describe the experiment.

#### yor_on

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##### Re: What restricts the speed of light?
« Reply #18 on: 23/04/2013 11:05:43 »
I would put it this way. There is nothing stopping us from imagining a negative mass, and make some mathematics for it, but when we measure we find it to be another way, relative our measurements. If there is a experiment verifying this effect then? We're in a box of sorts, set by constants in my mind. I don't think we will pass that box myself, maybe we might be able to 'distort space' though? I don't know.

#### Pmb

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##### Re: What restricts the speed of light?
« Reply #19 on: 23/04/2013 12:37:20 »
I would put it this way. There is nothing stopping us from imagining a negative mass, and make some mathematics for it, but when we measure we find it to be another way, relative our measurements. If there is a experiment verifying this effect then? We're in a box of sorts, set by constants in my mind. I don't think we will pass that box myself, maybe we might be able to 'distort space' though? I don't know.
Herman Bondi wrote an article on the concept of negative mass. Would you like to read it? The article is

Negative Mass in General Relativity, Herman Bondi, Rev. Mod. Phys, 29(3), July 1967

« Last Edit: 23/04/2013 12:44:00 by Pmb »

#### yor_on

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##### Re: What restricts the speed of light?
« Reply #20 on: 23/04/2013 15:54:57 »
=

Eh both papers actually, the one about entanglement too.
« Last Edit: 23/04/2013 15:56:36 by yor_on »

#### The Naked Scientists Forum

##### Re: What restricts the speed of light?
« Reply #20 on: 23/04/2013 15:54:57 »