5 ms·

It wouldn't break current theory, it would just mean that photons travel slower than "speed of light" and have non-zero rest mass. Constant c in relativity inst

by gaika 15y ago

It wouldn't break current theory, it would just mean that photons travel slower than "speed of light" and have non-zero rest mass. Constant c in relativity instead of speed of photons would just mean fastest speed possible.

jasonkolb 15y ago
Isn't the speed at which photons travel, by definition, the speed of light? And as for the "c" in e=mc^2, doesn't this suddenly make "c" an unknown constant? Doesn't the fact that "c" changes suddenly change the values of the other variables in that equation as well? That seems pretty fundamental to me...
- zipdog 15y ago
  As I understand it, Einstein's work rests on there being a fundamental maximum 'speed' and it seemed to him as though the speed of photons was that limit, so 'speed of light' became synonymous with this maximum. But it doesn't necessarily have to be so. So if there's something faster, it changes our understanding of photons but not the existence of this fundamental maximum speed. As you note, our efforts to measure c may have been off due to measuring the wrong thing, but I don't know the ramifications of a small % change in c. (I'm not a physicist)
  - kaybe 15y ago
    Yes, it is -the- basic assumptions for special relativity. And no, it doesn't just change our understanding of photons, it changes everything, since it's all connected. All theories I've looked at so far have (at least in higher versions) incorporate relativitity. (Another basic assumption, this time for general relativity, is the equality of inertial and gravitational mass, which is not a self-evident thing. However, so far no difference has been found. (see http://en.wikipedia.org/wiki/E%C3%B6tv%C3%B6s_experiment http://en.wikipedia.org/wiki/E%C3%B6tv%C3%B6s_experiment)
- dfranke 15y ago
  Isn't the speed at which photons travel, by definition, the speed of light? Photons speed up and slow down routinely, depending on what medium they're traveling through. c, as it is used in the equations of relativity, is currently believed to be equal to the speed of light in a vacuum. But, with my limited knowledge of GR, my understanding is that gaika is correct and that the rest of the theory can still stand if this equality is broken.
  - doctoboggan 15y ago
    This isn't technically correct. Photons always travel the same speed but in certain materials they are absorbed and emitted by atoms, causing their apparent speed to slow down. A photon's instantaneous speed is always the speed of light.
  - felipemnoa 15y ago
    >>Photons speed up and slow down routinely, depending on what medium they're traveling through Do they really? As far as I know their speed is always constant in any medium. They just seem to slow down because they get absorbed and re-transmited. That is where the lost of velocity comes from. When traveling between one atom and another, which is a vacuum, they are always traveling at the speed of light.
- kevinpet 15y ago
  I think what he's getting at is that there's this value "c" that's really important to physics appearing in equations like e=mc^2 and determining the absolute upper bound on speed, and by the way, we used to assume that photons traveled at c, rather than their actual rate of 99.9975% of c. I don't know whether changing c by this amount would break many experimental results. Adding a rest mass to photos sounds potentially revolutionary.
- iand 15y ago
  Einstein based his theory on the maximum speed at which information can propogate. That's always been assumed to be the speed of light (photons). It may be possible that there is something else that can propogate information faster (e.g. neutrinos). There would still be an upper speed limit, but it wouldn't be the one we thought it was :)
dholowiski 15y ago
Don't forget... c is the speed of light 'in a vacuum'. Light travels slower through gas, water or glass. Light has even been slowed down to walking speed in a laboratory. The speed of light is not constant. The speed of light in a vacuum is. We assume.
- felipemnoa 15y ago
  >>The speed of light is not constant I think this is wrong. Regardless of the medium the speed of light is always constant. It seems to slow down because the photons are getting absorbed and re-transmited by atoms. But the speed of light is always the same regardless.
  - deleted 15y ago
    [deleted]
  - Confusion 15y ago
    That's splitting hairs in a way that makes you deviate from standard usage of the term. Physicists say things like "the speed of light in water is lower than the speed of light in a vacuum".
    - felipemnoa 15y ago
      But to a lay person that statement does not mean the same thing as for a physicists. To a lay person it sounds as if literally the photons slow down. And I bet that a lot of people repeat this statement thinking that light actually slows down.
  - devijvers 15y ago
    No, it's correct. The light actually gets slowed down in material (anything else than a vacuum.) That has nothing to do with observation, it's an actual physical effect. The speed of light in a vacuum is constant and so is the speed of light in any particular pure material (like a pure gas.) It's just that those constant speeds are different.
Florin_Andrei 15y ago
No. Non-zero rest mass photons will break a lot of theories. Plus, the "speed of light" is not merely an experimental result coming out of an interferometer. It's also a theoretical result, e.g. from Maxwell's equations - that's the one referred to by special relativity.
hardtke 15y ago
An alternative is that neutrinos and photons travel a different distance because there are extra dimensions that affect the two types of particles differently. These are the so-called space-time foam models.
monochromatic 15y ago
It wouldn't break current theory for photons to have nonzero rest mass?
jxcole 15y ago
I have a comment about this. C, as is used in general relativity, is involved in a lot more than just the speed that light travels. It is also relevant to a lot of other equations, like time dilation in a gravitational field. Now, if this experiment resulted in changing our concept of c as the "speed of light" to the "speed of neutrinos", then your probably right. But I have to imagine that c has been verified experimentally in non-light related experiments. For example, there is a certain speed where if you exceed it you are able to violate causal time relationships. I can't think of any experiments that would validate this. However, there is also the fact that theoretically, if you attempt to accelerate matter to the speed of light it's mass will increase infinitely. So if you accelerate it a little bit it's mass should increase a little bit, and you should be able to confirm the speed of light through an experiment where you measure infinitesimal increases in mass during large acceleration. So my comment is that if he just broke the speed at which light travels, then everything is fine. But if he broke the speed at which you are able to violate causality, or the speed at which the mass of an object is infinite, then our entire understanding of physics is likely to be invalid. Related reading - tachyon pistols http://sheol.org/throopw/tachyon-pistols.html http://sheol.org/throopw/tachyon-pistols.html
Jun8 15y ago
Not really. The reason the idea of fixing c as the speed limit is that the number arises naturally as the speed of EM waves from Maxwell's equations. Briefly put, these these equations are valid in all frames, the Galilean speed addition rule has to be wrong and c should be standard in all inertial frames. So you can't just use c for "the highest speed any particle can have in vacuum".

by gaika 15y ago

jasonkolb 15y ago

Isn't the speed at which photons travel, by definition, the speed of light? And as for the "c" in e=mc^2, doesn't this suddenly make "c" an unknown constant? Doesn't the fact that "c" changes suddenly change the values of the other variables in that equation as well? That seems pretty fundamental to me...

zipdog 15y ago
As I understand it, Einstein's work rests on there being a fundamental maximum 'speed' and it seemed to him as though the speed of photons was that limit, so 'speed of light' became synonymous with this maximum. But it doesn't necessarily have to be so. So if there's something faster, it changes our understanding of photons but not the existence of this fundamental maximum speed. As you note, our efforts to measure c may have been off due to measuring the wrong thing, but I don't know the ramifications of a small % change in c. (I'm not a physicist)
- kaybe 15y ago
  Yes, it is -the- basic assumptions for special relativity. And no, it doesn't just change our understanding of photons, it changes everything, since it's all connected. All theories I've looked at so far have (at least in higher versions) incorporate relativitity. (Another basic assumption, this time for general relativity, is the equality of inertial and gravitational mass, which is not a self-evident thing. However, so far no difference has been found. (see http://en.wikipedia.org/wiki/E%C3%B6tv%C3%B6s_experiment http://en.wikipedia.org/wiki/E%C3%B6tv%C3%B6s_experiment)
dfranke 15y ago
Isn't the speed at which photons travel, by definition, the speed of light? Photons speed up and slow down routinely, depending on what medium they're traveling through. c, as it is used in the equations of relativity, is currently believed to be equal to the speed of light in a vacuum. But, with my limited knowledge of GR, my understanding is that gaika is correct and that the rest of the theory can still stand if this equality is broken.
- doctoboggan 15y ago
  This isn't technically correct. Photons always travel the same speed but in certain materials they are absorbed and emitted by atoms, causing their apparent speed to slow down. A photon's instantaneous speed is always the speed of light.
- felipemnoa 15y ago
  >>Photons speed up and slow down routinely, depending on what medium they're traveling through Do they really? As far as I know their speed is always constant in any medium. They just seem to slow down because they get absorbed and re-transmited. That is where the lost of velocity comes from. When traveling between one atom and another, which is a vacuum, they are always traveling at the speed of light.
kevinpet 15y ago
I think what he's getting at is that there's this value "c" that's really important to physics appearing in equations like e=mc^2 and determining the absolute upper bound on speed, and by the way, we used to assume that photons traveled at c, rather than their actual rate of 99.9975% of c. I don't know whether changing c by this amount would break many experimental results. Adding a rest mass to photos sounds potentially revolutionary.
iand 15y ago
Einstein based his theory on the maximum speed at which information can propogate. That's always been assumed to be the speed of light (photons). It may be possible that there is something else that can propogate information faster (e.g. neutrinos). There would still be an upper speed limit, but it wouldn't be the one we thought it was :)

dholowiski 15y ago

Don't forget... c is the speed of light 'in a vacuum'. Light travels slower through gas, water or glass. Light has even been slowed down to walking speed in a laboratory. The speed of light is not constant. The speed of light in a vacuum is. We assume.

felipemnoa 15y ago
>>The speed of light is not constant I think this is wrong. Regardless of the medium the speed of light is always constant. It seems to slow down because the photons are getting absorbed and re-transmited by atoms. But the speed of light is always the same regardless.
- deleted 15y ago
  [deleted]
- Confusion 15y ago
  That's splitting hairs in a way that makes you deviate from standard usage of the term. Physicists say things like "the speed of light in water is lower than the speed of light in a vacuum".
  - felipemnoa 15y ago
    But to a lay person that statement does not mean the same thing as for a physicists. To a lay person it sounds as if literally the photons slow down. And I bet that a lot of people repeat this statement thinking that light actually slows down.
- devijvers 15y ago
  No, it's correct. The light actually gets slowed down in material (anything else than a vacuum.) That has nothing to do with observation, it's an actual physical effect. The speed of light in a vacuum is constant and so is the speed of light in any particular pure material (like a pure gas.) It's just that those constant speeds are different.

Florin_Andrei 15y ago

No. Non-zero rest mass photons will break a lot of theories. Plus, the "speed of light" is not merely an experimental result coming out of an interferometer. It's also a theoretical result, e.g. from Maxwell's equations - that's the one referred to by special relativity.

hardtke 15y ago

An alternative is that neutrinos and photons travel a different distance because there are extra dimensions that affect the two types of particles differently. These are the so-called space-time foam models.

monochromatic 15y ago

It wouldn't break current theory for photons to have nonzero rest mass?

jxcole 15y ago

I have a comment about this. C, as is used in general relativity, is involved in a lot more than just the speed that light travels. It is also relevant to a lot of other equations, like time dilation in a gravitational field. Now, if this experiment resulted in changing our concept of c as the "speed of light" to the "speed of neutrinos", then your probably right. But I have to imagine that c has been verified experimentally in non-light related experiments. For example, there is a certain speed where if you exceed it you are able to violate causal time relationships. I can't think of any experiments that would validate this. However, there is also the fact that theoretically, if you attempt to accelerate matter to the speed of light it's mass will increase infinitely. So if you accelerate it a little bit it's mass should increase a little bit, and you should be able to confirm the speed of light through an experiment where you measure infinitesimal increases in mass during large acceleration. So my comment is that if he just broke the speed at which light travels, then everything is fine. But if he broke the speed at which you are able to violate causality, or the speed at which the mass of an object is infinite, then our entire understanding of physics is likely to be invalid. Related reading - tachyon pistols http://sheol.org/throopw/tachyon-pistols.html http://sheol.org/throopw/tachyon-pistols.html

Jun8 15y ago

Not really. The reason the idea of fixing c as the speed limit is that the number arises naturally as the speed of EM waves from Maxwell's equations. Briefly put, these these equations are valid in all frames, the Galilean speed addition rule has to be wrong and c should be standard in all inertial frames. So you can't just use c for "the highest speed any particle can have in vacuum".