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sanjibghosh
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let's the speed of light is constant(c) but any information(interaction) can not travel with 'c'. let's it is travel with the speed of sound. then ,is relativity remain unchanged?
Mentz114 said:Information can travel at the speed of light. Perhaps you mean something else ?
I can't imagine such a world. Would we still be able to use our eyes ? Light is such a fundamental part of our reality that reality without it seems impossible. Not a line of thought I wish to pursue.suppose,there is an world where information can travel only through the sound, light still exist, but can not carry any information.
DaleSpam said:The question as posed is very difficult to answer. Light carries information and there are tons of experiments that show it or that use that fact. We would have to go back to each of those experiments, change the results and then come up with a new theory that explains all of those imagined results.
Here is a different question which would not contradict any previous experiments, but should get to your underlying concern:
The mass of the photon is believed to be zero, but that is something that cannot be established experimentally. All you can do is put an upper bound on the mass. So, let's say that the next experiment to measure the mass of a photon detects a small (consistent with previous experiments) but non zero mass? Then light would not travel at c nor would the information carried by light.
Is that a suitable substitute?
The Lorentz transform would remain unchanged. The invariant speed c is a property of spacetime, not just a property of light. In that sense calling c "the speed of light" is a historical misnomer.sanjibghosh said:if information can not travel with 'c' then what are the transformation equations?
confinement said:I understand the question sanjibghosh, and the answer is yes, as long as the sublight speed barrier (speed of sound in your example) is a true upper bound on speed, as opposed to an approximate upper bound i.e. only holds or some range of energies.
Even in the latter case we have the mainstream treatment of phonons on a lattice which will satisfy approximate lorentz symmetry, where the speed of light is literally replaced with the speed of sound in the material. This can be found in most modern condensed matter books.
Vanadium 50 said:The answer to that question is "no".
sanjibghosh said:hi,
neopolitan
I'm very happy with sanjibghoshian(!.. ) transformation.but i do not understand clearly,so can you tell me some sources where it was discussed.
DaleSpam said:There are two main formulations of SR: the traditional two-postulate formulation and the modern Minkowski geometry formulation. In the two-postulate formulation all that would be necessary to adapt it is that the second postulate would need to refer to "the invariant speed" rather than to "the speed of light". For the Minkowski geometric formulation all that would be needed is to draw the worldlines of light pulses at a less than a 45 degree angle. No changes to the Lorentz transform would be necessary for either formulation.
I have no problem concieving of an information-less tachyon. In fact it is easier than one that carries information since you avoid all of the nasty causality problems. However, it is contrary to an enormous amount of evidence to consider that light does not carry information, which is why I re-posed the question as I did. I think my re-framing of the question is physically reasonable and still addresses his root concern.neopolitan said:I am not sure that Dale fully grasped one aspect of the question. It's no surprise because as I said, it is difficult to conceive of a situation where the maximum speed of information is lower than the speed of light.
The invariant speed is the speed which is the same in all inertial reference frames. I.e. it is the speed "c" in the Lorentz transform. The invariant speed is a feature of spacetime, and is not directly a feature of either light or information. The invariant speed is equal to the speed at which light propagates to current experimental precision, but future experiments could concievably determine that light propagates at a slightly different speed without any impact on the Lorentz transform.neopolitan said:What is "the invariant speed"? I'm not being silly (I hope) but pointing out that the definition in terms of the original question will have to be such that light can go faster than it. For the Minkowski space explanation, remember again that in the original question information travels at less than the speed of light, not light slower than the speed of information.
DaleSpam said:However, it is contrary to an enormous amount of evidence to consider that light does not carry information
DaleSpam said:The invariant speed is the speed which is the same in all inertial reference frames. I.e. it is the speed "c" in the Lorentz transform. The invariant speed is a feature of spacetime, and is not directly a feature of either light or information. The invariant speed is equal to the speed at which light propagates to current experimental precision, but future experiments could concievably determine that light propagates at a slightly different speed without any impact on the Lorentz transform.
DaleSpam said:I explicitly said that I was not answering the OP as posed ...
It would depend on why the speed was limited to "s". For example, the speed of information travel in air is limited to less than c, yet c is still the invariant speed.nathatanu0 said:but if in some media "s" is the ultimate speed and through this the information can travel and no more than that speed... then it is obvious that "s" will remain invariant... because we are using "s" for highest precision to measure "s" itself... as its the highest speed with which information can travel in that media... so "s" will be invariant speed...in that space time of the media...(if observers are confined inside the media)... then "s" will be definitely a property of that space-time (the media)... so for the observers confined in that media... "c" of STR should have to be replaced by "s" in that media... for the sake of Physics of the people inside...
if m not to wrong!
I don't really buy this argument. Let's say that you have a completely opaque material (perfect blackbody) with a speed of sound of 100 m/s. Then information can only move through that material at a speed of 100 m/s. But in a frame where it is moving at 1 m/s a sound wave will propagate at ~101 m/s in one direction and ~99 m/s in the other. Therefore the speed of information is not invariant.nathatanu0 said:but if in some media "s" is the ultimate speed and through this the information can travel and no more than that speed... then it is obvious that "s" will remain invariant... because we are using "s" for highest precision to measure "s" itself... as its the highest speed with which information can travel in that media... so "s" will be invariant speed...in that space time of the media...(if observers are confined inside the media)... then "s" will be definitely a property of that space-time (the media)... so for the observers confined in that media... "c" of STR should have to be replaced by "s" in that media... for the sake of Physics of the people inside...
if m not to wrong!
You are correct that isotropy and homogeneity are assumed in deriving the Lorentz transform, but I am not violating that here at all. The wave equation in a moving medium is both homogenous (translate your initial conditions and your coordinate system and you get the same equation) and isotropic (rotate your initial conditions and your coordinate system and you get the same equation).nathatanu0 said:you must remember the fact that deriving Lorentz transformation "the isotropy of space and homogeneity of time" was assumed... and now you are violating that here...
Hi neopolitan, http://arxiv.org/abs/0806.1234v1" is a paper that you might enjoy on the subject. I just found it and have only made it part way through, but so far he seems to agree with your conclusion though his derivation is different.neopolitan said:However, what the OP posed has interesting possibilities, at least historically.
I've often wondered how (and when) we could have otherwise come to our current understanding of at least special relativity.
...
In any event, if Galileo had gone through the process that I laid out in https://www.physicsforums.com/showpost.php?p=2103428&postcount=18" (noting that you don't have to use "the speed of information" which just makes things more awkward - you can and should use the speed of light), then he would have arrived at the Lorentz transformations and the basics of Special Relativity.
That means that we could have had SR a little under 300 years earlier than we did.
Well, the speed of information propagation is limited to about 0.9997c in air, 0.75c in water. c is the invariant speed of the universe, and is the theoretical speed of light in a perfect vacuum, which doesn't exist.nathatanu0 said:@Al6
if speed of information in air is limited to "c" then how does "c" enter into the story?? "c" is speed of what then...if the ultimate information speed is limited to speed less than "c"?
Not in an absolute sense, but it is if the info is carried via light in that medium. For example, if a light signal is sent through water, it will propagate at 0.75c. But the event signal could be sent via a different medium to the same destination faster. My point was that the actual propagation speed of information is not c. It is always less than c.Ich said:AL68, the speed of light in media is no limit for information transfer, see http://en.wikipedia.org/wiki/Cerenkov_radiation" .
sanjibghosh said:what about my last post?
please reply...