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Show ALL Forums  > Science/philosophy  > what happens to the general and special theory of relativity if light      Home login  
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 Ubiquitous.
Joined: 11/7/2009
Msg: 2
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what happens to the general and special theory of relativity if light speed isnt a constant ? Page 1 of 6    (1, 2, 3, 4, 5, 6)
It's been measured and verified time and time again.

The reason behind the defining it as a constant is for a number of reasons.. not the least of which is cost. It is terribly expensive to measure the speed of light with a high degree of accuracy.
 CoolBreezez
Joined: 8/20/2006
Msg: 3
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what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 3/15/2010 7:07:29 PM
The speed of light most often referred to is in a vaccum. I don't think we've been able to do it in a "perfect" vacuum so their could alway be some difference but its generally insignificant for most calculations.
("damn... I want to know what happens when that light barrier breaks. When we break the speed of sound, we get a 'sonic boom' :)"

You never watched Star Trek? Its right at the beginning of most of the old episodes-
 Divorced, Broke, Bald
Joined: 7/9/2009
Msg: 7
what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 3/15/2010 10:34:24 PM
Actually, Einstein understood this. And the ramifications of it stood science on its ear.

Among other things, it means that perspective "warps" everything. It doesn't mean that time and space cannot be measured; it means that there is an amount of uncertainty involved and that the results can - actually, do - vary according to your field of reference.

I do believe that Hawking covers it in "A Brief(er) History of Time" quite nicely. (Much better than I did here. lol)
 CountIbli
Joined: 6/1/2005
Msg: 8
what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 3/16/2010 12:02:59 AM
There have been a number of claims that the speed of light has been decreasing over time. This has been done primarily by Creationists. For the most part their research on the topic has been extremely shoddy. However, Lambert Dolphin (a Creationist and mathematician) did do an analysis that looked pretty good, which showed a decreasing c. It's been many years since I looked at it and I've never been good at statistics so it's hard for me to comment on his analysis. I've never seen his work critiqued.

There is one physicist (his name escapes me, but he is not a Creationist) who came up with a version of GR in which c was allowed to vary. He did this to see if he could solve some cosmological problems without recourse to dark matter, inflation, and dark energy. Apparently it works quite well. I think his name might be Paul Davies, but I'm not sure.
 desertrhino
Joined: 11/30/2007
Msg: 11
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what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 3/16/2010 4:53:36 PM
Mike, I think you mean PARTICLES will exceed the phase velocity of light in a specific medium, leading to Cherenkov radiation.
 lateā„¢
Joined: 2/1/2010
Msg: 12
what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 3/16/2010 7:24:03 PM

There is a place that birds cannot fly.
Somewhere between the everything and behind the space that your hand does move through.
This framework is the softest song that can be drawn from imagination.
It's the canvas behind the painting.
It's the air inside the water.
This is as certain as the speed of light exists, only to be broken.


Dude, ...that's awesome.

It reminds me of a song by Julie Miller:


"The Speed of Light"

time and space are relative
einstein said back when he lived
the only thing that doesn't change
makes everything else rearrange
is the speed of light, the speed of light
your love for me must be the speed of light

the man on the moon said the earth was blue
but you don't have to leave to know that's true
the only thing that doesn't change
makes everything else rearrange
is the speed of light, the speed of light
 CountIbli
Joined: 6/1/2005
Msg: 14
what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 3/17/2010 10:34:53 AM


But for now, I'll say that its much nicer to consider c a constant, otherwise the universe is much more strange that we think already!


The universe really is stranger than we think. Light, as it happens, travels faster than the speed of light.

http://www.telegraph.co.uk/science/science-news/3303699/We-have-broken-speed-of-light.html

http://abcnews.go.com/Technology/story?id=120094&page=1
 IgorFrankensteen
Joined: 6/29/2009
Msg: 16
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what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 3/17/2010 4:09:47 PM
I'm not a physicist, but since you are talking about Einsteins equation E=MC squared, if the speed of light in a vacuum (the speed of light DOES fluctuate, and is slowed down by various things) were to vary, the answer to the equation would vary accordingly, and thus be harder to answer on a test. I don't see how that could change the limits of speed for travel, ie make faster-than-light-travel possible.
What the theory says, if I understand it at all, is that your mass actually changes as you speed up, such that if you reached the speed of light, your mass would increase to the point where...you'd have a really hard time slowing down. The relativity theories talk about how things influence each other, how fundamental things like speed and gravity and mass are interlinked, interactive. Therefore changing our idea of what the speed of light was, would NOT change how it RELATES to the other basic "functions" (mass, energy).
 abelian
Joined: 1/12/2008
Msg: 17
what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 3/17/2010 4:23:48 PM
Nothing happens to special or general relativity if the speed of light is not constant. What changes is Maxwell's theory of electromagnetism. Both theories of relativity are theories of spacetime geometry. The possibility that the speed of light was contemplated at least a century ago (google ``proca lagrangian.'') On the onther hand, since gravity is a manifestation of spacetime geometry, the speed of gravity must be constant or general relativity is dead.
 CountIbli
Joined: 6/1/2005
Msg: 18
what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 3/17/2010 5:36:53 PM


Well now I've picked my jaw up off the floor. Hopefully they can verify and reproduce the phenomenon! And how did none of my profs mention this today!?


Similar experiments have been done by at least 3 separate groups. As to why your prof. hasn't mentioned it, it's probably because physicists are loath to contradict Einstein.
 abelian
Joined: 1/12/2008
Msg: 19
what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 3/17/2010 6:36:57 PM
The universe really is stranger than we think. Light, as it happens, travels faster than the speed of light.

http://www.telegraph.co.uk/science/science-news/3303699/We-have-broken-speed-of-light.html


Unfortunately, Nimitz' understanding of his experiment is, well, flawed. I've read his papers (He's been making the same claim for a number of years prior to the 2007 date on the article you've referenced.) His entire claim rests on his (unique) personal re-invention of what information means and/or (depending on which experiment) his idea that the only relevant feature of of the pulses is the relative locations of the centroids of each pulse. The latter is fairly easily seen to be incorrect. If you have a pulse (e.g., gaussian is fairly common) and you compare it to a pulse of the same shape but for which the amplitude of the pulse is significantly smaller and compare the transit times for both pulses, the smaller pulse can fit anywhere inside the larger pulse (up to the pont where the leading edges coincide, not the centroids) without violating special relativity. (Physicists at (I think) NEC made a similar claim based on the same (incorrect argument) about 10 years ago.

A slightly more subtle error is in presuming that the original pulse contains the same information that the smaller pulse contains by asserting that the only relevant factor is the shape of the pulse. If that were true, it would be possible to transmit an infinite amount of information with zero bandwidth. That violates the assumptions that led to information theory upon which all modern communications systems rely (e.g., Shannon's limit). This goes back to an earlier experiment of Nimitz in which he claims to have transmitted one of Mozart's symphonies faster than light. To evade this problem, and make his claim for faster than light signal transmission, Nimitz instead invents his own definitions of information to to fit his claim.

In particular, he divides ``information'' into two different things which he calls ordinary information and technical information, (and disregards the fact that his claims of actually transmitting Mozart's symphony did not actually happen. His recording of what he received bears some resemblence to what was transmitted, but that's the best one could say about it. A considerable amount of the information transmitted was never received at the other end, hence the need for him to invent new definitions for information to justify his claim. To the best of my knowledge, he did not actually make a bit comparison of the transmitted and received copy of the symphony to check that his claims made sense. In fact, if I recall, his experiment did not even provide the means to do that. The much simpler explanation for Nimitz' results is to just apply the existing theories exactlt as they are.
 abelian
Joined: 1/12/2008
Msg: 20
what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 3/17/2010 6:54:25 PM
As to why your prof. hasn't mentioned it, it's probably because physicists are loath to contradict Einstein.

That's patently false. If you ask a few physicists, you will discover that the vast majority of physicists will tell you that after he finished his general theory of relativity, he spent the remainder of his life pursuing a unified field theory which is widely held to have no chance of being correct. What physicists are loath to criticize are theories which have been extensively tested and found to correctly predict the experimental data and known natural phenomena. At present, quantum electrodymics (qed), for which special relativity is the foundation) has been experimentally verified in agreement with the theoretical calculations to 13 decimal places. That makes qed the most precisely tested theory in the history of science. Scientists are loath to abandon such a theory for alternative theories which deviate from the experimental data well befor reaching a level of precision a million or more times less precise. Any physicist alive would be deleriously happy to prove Einstein wrong. Doing so would gaurantee a Nobel prize and countless offers for prestigious positions with very generous funding at the very best universities. There is a great deal of incentive to prove relativity is wrong and much effort has gone into doing just that. All you have to do is read the physics literature to discover this for yourself. In fact, the entire point of experimental physics is to prove existing theories are wrong.
 abelian
Joined: 1/12/2008
Msg: 21
what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 3/17/2010 7:19:00 PM

in 1975 in Geneva the international geo - physical union said from now on we will have to DEFINE the speed of light, no one shoud go and measure it lol if you wanna know the speed of light read about it in your handbook about physical constants .. and in 1983 the metre was redefined and the speed of light was defined as 299,792,458 m per second

The reason that was done is that one can measure the speed of light and the second with much greater precision than something like a standard meter made of some material. Since these three things are all interrelated, it makes more sense to use the two which can be most precisely determined to serve as definitions. However, the constant `c'' is really not a fundamental constant of nature. It's merely a constant which converts meters to seconds in exactly the same way that the constant 2.54 converts cm to inches. Since relativity treats space and time on equal footing, the natural units for time used in any relatively modern text on relativity, uses the same units (meters) for measuring both time and spatial distances and hence the conastant `c' is 1. In modern treatments of relativity you will almost always see the metric written as ds^2 = dt^2 - dx^2 - dy^2 - dz^2 (or with signs reversed) rather than (ct)^2 - dx^2 - dy^2 -dz^2. Similarly, no one (in real physics papers) writes the mass-energy-momentum relation as E^2 = (pc)^2 + (mc^2)^2. It's always written as E^2 = p^2 + m^2 (which reduces to E = m instead of E = mc^2). This makes the mass energy equivalence more transparent and consistent with treating space and time on equal footing.
 CountIbli
Joined: 6/1/2005
Msg: 26
what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 2/7/2011 9:32:26 PM


Galileo was wrong also about the different (5 + 10#) weights dropped from the leaning tower of Pisa the larger ten pound weight will reach the earth first because it will pull the earth towards it with it's gravitational field twice as far as the smaller five pound weight.because of this(tugging) back and forth it will also accelerate with greater speed over time. this will occur despite the fact that the earth will exert an equal gravitational force on each pound in each weight.


There's also air resistence to consider.
 abelian
Joined: 1/12/2008
Msg: 28
what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 2/9/2011 12:57:27 PM

the reason the speed of light appears to be a constant. is that you can't use atoms to push

The speed of light is constant if the photon is massless. The same is true for any massless particle. That is a consequence of spacetime geometry alone.
 abelian
Joined: 1/12/2008
Msg: 31
what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 2/14/2011 7:11:39 PM

and from what position of absolute rest was it determined that (a) photon was massless as far

Huh? There is no frame in which a photon is at rest. That's why it's massless. If it had a mass, Maxwell's equations would be wrong. There's 100 years of scientific literature on this subject.
 .dej
Joined: 11/6/2007
Msg: 32
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what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 2/15/2011 3:37:10 PM

The speed of light is constant if the photon is massless. The same is true for any massless particle. That is a consequence of spacetime geometry alone.

Can you elaborate on this? I always enjoy reading your posts. My undergraduate physics obviously never went this far.
 abelian
Joined: 1/12/2008
Msg: 35
what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 2/17/2011 11:30:11 PM
Can you elaborate on this?

Sure. To avoid being long winded I'll sketch it out and you can ask about details.

First of all, space (or spacetime) could be a lot of things, but in our universe, we can measure things like distance, so for example, in Euclidean geometry we have the Pythagorean theorm, which tells you how to construct coordinates to measure distances, i.e., most generally, it would be written as:

ds^2 = dx^2 + dy^2 + dz^2

which could also be called a metric (or by taking the square root, the arc length or line element in calculus). This is also necessary to define a scalar (or dot product) of two vectors, but is generally glossed over in undrgraduate physics because you can get away with ignoring it in a Euclidean space. But, other types of spaces are possible. In particular, the signs could be some combination of + and - minus signs and you could do that in higher dimensions as well. The important feature here is that the length of the line, ds^2 is invariant. Regardless of how you pick your x,y,z axes, ds^2 gives the same number. You can see this by rotating the x and y axes using the coordinate transformation:

dx' = cos(A) dx - sin(A) dy
dy' = cos(A) dy + sin(A) dx

and multiplying it all out. In special relativity, one includes another dimension for time. I'll call it the w-axis. The metric (or equivalent of the Pythagorean theorem) is then:

ds^2 = -dw^2 + dx^2 + dy^2 + dz^2

Since we are treating space and time on equal footing, we'll use meters to measure distances along all four axes. The minus sign can in front of the dw^2 can be inferred on physical grounds. In the x,y and z directions, itispossible to turn around and face the opposite direction. It's not possible to just turn around in time, so the time direction can't just be another direction in a Euclidean space. I'll ignore the x and z directions to make this less cluttered and just deal with the time axis and the z spatial axis so that the geometry is defined by the metric:

ds^2 = -dw^2 + dz^2

If you draw a coordinate system with the w axis as the vertical axis and the z axis horizontal, you'll see some interesting features. First is that if you draw two lines through the origin at 45 degrees to the axes (i.e., those with a slope of 1 and -1 where dw = dz, those lines have a length of zero, since ds^2 = -dw^2 + dz^2. That divides the spacetime into 4 quadrants. The cones that open upward and downward represent the future and past of an observer at the origin. The cones opening to the left and right of the origin are the points an observer at the origin cannot reach. Points outside the future and past cones (i.e., the points in the cones opening left and right) are not in the future or the past of an observer at the origin. We can also change coordinates analagously to the rotation I mentioned above. However, because of the minus sign, we don't get sines and cosines, we get sinh and cosh,

dw' = dw cosh(A) - dz sinh(A)
dz' = dz cosh(A) - dw sinh(A)

These are actually the Lorentz transforms (boosts) and the hyperbolic rotation by the angle `A' is just a change of velocity. So far, we've made no reference to the speed of light. It's all hyperbolic geometry and the velocity which is special is the 45 degree lines through the origin that divides spacetime into 4 parts. The lines,

dw = +/-dz

are at 45 degrees regardless of what coordinates you choose. Hence lines with a slope of +/-1 are just velocities that are the same in any frame. So, what is the constant `c?' It's a constant that converts meters to seconds just like the constant 2.54 converts cm to inches. If we want to measure time in seconds, rather than meters, we can write cdt = dw = dz for those 45 degree lins and,

c = dz/dt

That velocity is a constant regardless of what frame you choose. To find out the value of the constant `c,' we need a physical phenomenon to use as a reference. Before getting to that, note that the momenta correspond to motion in the x,y,z directions, so we should have a momentum that corresponds to the w direction as well. We have one. It's called the energy. However, since we are meauring time and distance using the same units, we should use the same units for momentum and energy to avoid the `c' in the equations for the moment. In that case, we also use the same units for mass and we have:

m^2 = E^2 - p^2

(which in more familiar form, using the constant `c' would be E^2 = (pc)^2 + (mc^2)^2 )

If m = 0, then we get:

E = pc or c = E/p

That happens to be the slope of those 45 degree lines, so that velocity corresponds to a particle with m = 0. Since the energy of a photon is related to the momentum by E = h nu and p = h/wavelength, h nu = hc/wavelength and
therefore, a massless photon has the familiar relationship frequency x wavelength = c.

Einstein postulated that the value for c was the speed of light because (1) he derived special relativity from a completely different starting point - a desire to reconcile Maxwell's equations with Newtonian physics and the relastionship between frequency and wavelength follows from Maxwell's equations which are already relativistically correct; and (2) he knew nothing about hyperbolic geometry at the time.

Since it's possible to write down a theory of electromagnetism in which the photon has a mass and which is relativistically correct, the question of whether or not light propagates at `c' belongs in a theory of electromagnetism, not special relativity. The geometry of spacetime is what it is and the speed of light depends on the theory that describes electromagnetic phenomena in spacetime. The upper limit on the photon mass is so small that all you can say is that if it has a mass, it's too small to measure. It didn't have to be that way. In that sense, Einstein used physical insight to choose what he did as postulates, given what he knew and he was lucky that the photon is at least close enough to massless to make any difference from zero, irrelevant.
 abelian
Joined: 1/12/2008
Msg: 38
what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 2/21/2011 7:44:38 AM

Is that the particle that is far enough away from all other particles to be unentangled (if such a thing is possible - mach's principle better mach's law) and to move in uniform velocity would come to a complete halt and absolute rest it's energy and mass completely absorbed/ dissipated by antimatter until everything was was was reduced to a unmoving grist of particles at absolute rest.

In general and special relativity, there can be no absolute rest frame and entanglement has nothing to do with velocities or distances. In fact, velocities are not even quantum mechanical observables.
 abelian
Joined: 1/12/2008
Msg: 40
what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 2/21/2011 10:14:11 PM

well i read those theories contradict each other so one of those statements is probally incorrect.

Since qed which is a relativistic quantum field theory agrees with experimental data to 13 decimal places, making it the most precisely tested theory in human history, what you read was either wrong or you misunderstood what you read.

These make-up the so called "spooky actions"

There are no ``spooky actions.'' That comment (made 3/4 of a centuray ago) was due to not understanding quantum mechanics.
 abelian
Joined: 1/12/2008
Msg: 42
what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 2/22/2011 12:33:37 AM

I read it in Scientific American and several other places as well. and i didn't misunderstand. your beginning to spout nonsense. I'm talking about the general and special theories o f relativity. their wrong.

Feel free to post the parts of the derivations you think are incorrect and point out the mistakes in the equations.
 abelian
Joined: 1/12/2008
Msg: 44
what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 2/22/2011 9:08:10 AM
Einstein outlined his theories in plain English

Since the comments you've made don't give me the impression we are even reading the same articles, you can most easily avoid any discepancies from interpreting the plain English differently by sticking to the mathematics. The mathematics is the bottom line. The plain English is just there for pedagogical reasons. In this case, the pedagogical aspect seems to have confused you rather than helped you. If you don't understand the math, you don't understand the theory well enough to have an opinion about what the theory really means.

and they must follow logically and fit known science and they don't on either score.

On the contrary. Relativity does fit the data and follow logically from Einstein's arguments. His arguments are a little clumsy by today's standards, but since he wrote those papers a century ago, that's understandable.
 stargazer1000
Joined: 1/16/2008
Msg: 45
what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 2/22/2011 9:10:30 AM
while that sounds impressiveit's really a cheat of a reply. Einstein outlined his theories in plain English and they must follow logically and fit known science and they don't on either score.


He may have explained it in plain English but the backbone is mathematical. Hence, the equations like the one we see on the back of numerous t-shirts. You know the one. It describes energy and its relationship to matter?

I think abe's callenge was a "put up or shut up" one. If you can prove Einstein wrong, then do so. It's not a callenge of your rhetoric skills but of your maths. If all you have is the blanket assertion that "Einstein was wrong," you're the same as every other internet nut job with an axe to grind against the intellectual greats of the past century.

Just sayin'.
 abelian
Joined: 1/12/2008
Msg: 48
what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 2/22/2011 2:12:13 PM

ABE himself made the statement that according to quantum theory there was no uniform motion tobegin with.

No, what I said was that velocities are not quantum mechanical observables. You've just provided a perfect example of how you misinterpret the English and come up with something that makes no sense because you don't know that quantum mechanical observables are hermitian operators much less what that means physically.
 stargazer1000
Joined: 1/16/2008
Msg: 50
what happens to the general and special theory of relativity if light speed isnt a constant ?
Posted: 2/22/2011 3:55:27 PM
None of which changes the fact that, unless you got the math to back it up, you're talking out of your hat, mccullough. Time to get over it.
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