What if ?

1. Jul 26, 2004

shintashi

I would like to start a thread where the key theme, and asumption is

"the speed of light is no longer constant"

I would like to see how many things would change in the laws of physics, and how many crazy theories would crop up. Note the topic isn't "lets prove why the speed of light is, or is not constant" the topic is WHAT IF.

- Shin

2. Jul 26, 2004

urtalkinstupid

If c weren't constant, many things would change. For one, special and general relativity would be debunked. Object could travel faster than the speed of light. Photons could oscillate, resulting in them having a rest mass. I dunno...more stuff.

3. Jul 27, 2004

Antonio Lao

Contrary to accepted beliefs, the human thoughts travel faster than light. I can think of being at Andromeda galaxy this instant but my thinking cannot influence anything there such as applying a force to change the course of an object's motion at one of the planets around a star similar to the sun.

The speed of light is really the effect of an underlaying constant force. If c is not constant, then all the other constants of nature become varying quantties and anything is possible. The earth can suddenly stop moving, the sun can disappear, the CMBR can abruptly increase to 10 degrees without a moment notice, the sky can turn to the color of green, and there will be no air to inhale because gravity vanishes.

Last edited: Jul 27, 2004
4. Jul 29, 2004

shintashi

patience is a virtue

:rofl:

I've noticed a lot of physicists tend to feel that way, without the constant speed of light, their whole world crumbles. Its the "god" of the 21st century. Yet, I've observed plenty of people in history without any discouragement about the arrangement of the universe completely devoid of a constant speed of light, doing just fine, working out the various laws of physics.

Lord Kelvin didn't seem upset, nor did Newton, nor did Tesla.

So let us ask the next question, assuming that there was a luminferous aether, what would be the laws of phyiscs, then ? Would particles exist at all ? or be merely bubbles in the flow of the soup ?

5. Jul 29, 2004

Antonio Lao

The modern view of aether is that of spacetime continuum. This spacetime aether is dynamic. It is expanding and what more, expanding greater than light speed. But the speed of light still the same constant even though its energy is less when the source is receding.

6. Jul 29, 2004

Olias

The speed of light does vary?..send light through a matter medium and it slows a little as it interacts, it bends slightly!

Now the Vacuum which has a minimum light, such as hv-photon, produces the constancy with measurement, there is little "other" matter in which to 'bend' light, therefore its speed matches the observed and registered value recorded by the Vacuum set-up.

One can state that the intervening matter which slows down the effective "speed of light", has by its very nature a contanimated Vacuum presence.

I like to think of it this way: The more Matter light encounters, the less of a Vacuum is present, which can reduce its speed. The less Matter light encounters, the more pure a Vacuum, which increases the speed at which a Photon can spread out unhindered.

The speed of light is only constant because of the 'constant' Vacuum it is immersed within during measuring.

7. Jul 30, 2004

Chronos

What constant would you prefer, other than c? Aether? I prefer c because it is background independent... ie, is the same for all observers. As an added benefit, it has passed every valid experimental test ever devised.

8. Aug 1, 2004

anti_crank

Since you have quite explicitly stated that you don't want the thread to have any connection to reality, I am utterly powerless to mock it. You have to be commended on that; it's not that often something like this comes along.

That having been said, the number of theories we can write are literally endless. Since we're not relying on experimental facts to determine which are right, I must then ask you limit the possibilities somehow. Is the space-time galilean? (ie time is absolute, frames are converted by high school formulae, causal signals propagate at infinite speed? If you drop your hammer on your toe, someone on Mars can be immediately aware of it?) This is simply everything you can call "classical physics", minus one thing: Maxwell's EM must be drastically modified, since it requires relativity to work.

To make any further speculation, I must ask you to give the formulas to convert from one frame of reference to another (ie if one inertial observer measures an event at coordinates x,y,z and time t, what are the coordinates that a second observer would assign to that event, assuming that both observers were at the origin x=y=z=0 at time t=0 and the second observer has been moving with constant speed v in the positive x direction). Otherwise, we can write almost anything. (In fact, you might find a very interesting read in Godel's universe, a totally bizarre solution to the GR equations for spacetime. As far as we can tell, we could even be living in one!) There is really no point to speculate which theories are invalidated, unless you want to know just how much relativity is meshed into the fabric of modern physics. (Hint: a helluva lot)

Olias: even in matter, the speed of light is never anything other than c. Its *effective* speed is smaller because the light is constantly absorbed and re-emitted by whatever matter it interacts with (mostly electrons). There are slight delays and changes of trajectory caused by these processes which account for phenomena like reflection, refraction, and the reduced effective speed. There are plenty of threads in this forum about it.

9. Aug 1, 2004

Janitor

A non-constant speed of light would seem to imply photons having nonvanishing mass. It seems like a theory of that sort was investigated by Proca. I think I have seen Proca's Lagrangian for massive spin-1 interactions, and it looked kind of like the Maxwell Lagrangian, but with an extra term involving mass and maybe the square of the Faraday tensor. I'm not sure about that, but somebody here will be able to say more.

10. Aug 1, 2004

anti_crank

I suppose the question is how much physics does one want to rewrite. If we keep SR as describing the spacetime background with a limit of signal propagation c (just that photons are massive and don't travel at c), then we can retain most of the QFT apparatus. In fact I suspect that we just need to throw in a Higgs coupling to the photon in such a way as to preserve the electroweak gauge invariance and we'd be done. On a more mundane level, the Coulomb potential would pick up an exponentially decaying factor, and Maxwell's equations would look quite different to produce a Proca wave equation for the photon.
The EM equations can in fact be fiddled with to produce an effectively massive photon in some circumstances; I don't have time to get into it now.

11. Aug 1, 2004

Janitor

Good points, Anti. Welcome to the Physics Forum!

12. Aug 1, 2004

Chronos

A clever argument, and a very good one. I kind of object to the loss of energy thing it implies, but, I am a self professed dummy. Would the energy density of space-time remain constant under those dynamics?

13. Aug 1, 2004

Antonio Lao

In quantum theory of radiation, the energy of a photon is given by $E = h \nu$ where $\nu$ is the frequency and h is Planck's constant. The Doppler red shift of photon indicates that the frequency is lower when a photon is farther away from us because of the increase in its wavelength and by the formula $c = \lambda \nu$ where c is constant.

According to Einstein's field equations, the energy-momentum tensor is what causes the spacetime structure to curve. Whether it's a constant, I have no clue. I am currently researching a relationship between mass/energy and density and volume and some of what I have hypothesized can be found in other posts of this forum.

Last edited: Aug 1, 2004
14. Aug 3, 2004

shintashi

i theorize that the array of light actually dilates, or better said, is dilated through the medium of local spacetime like glass, to some degree, getting "fatter" and slower. The total frequency and energy is the same, but it is covering more volume at a slower rate. As it reaches further into a more "crisp" space, the wave "thins" into a more beam-like structure, and picks up speed.

I hypothesize, that without signal degredation, the maximum velocity of this EM field is a function of its frequency, thus, oddly enough, a radio wave would be the slowest at maximum, while a gamma wave would be potentially extremely quick, in the perspective of, if nothing else, signal density.

15. Aug 4, 2004

anti_crank

I think I'm beginning to understand what you're doing. You had something very specific in mind when you started this thread, but you didn't want to say it outright. Instead, you decided to call for some open speculation in a potentially interesting manner, but without any intention of actually following through on it or bothering to reply. As much as I can see your method, the madness still escapes me, plus there's the fact that we were apparently tried on for fools, which I do not appreciate in the slightest.

As for the theory you propose: You still didn't decide whether SR describes the spacetime or not (taking the speed of light as no longer constant does not decide the issue since SR can exist in a universe without electromagnetism). This, however, isn't a problem as you can propose a formula for the wavelength, get two laser beams of different frequencies, measure their speeds and see what you get... personally my money is on "no difference in determined speed within experimental error"

16. Aug 4, 2004

Vern

What if !! the speed of light were not constant. According to Photon Theory, and in the real world, you would not be able to determine whether the speed of light were constant. No matter how it varied, it would always measure one constant value.

Now, if you mean what if the measured speed of light were not constant, then just about all theories break.

Interesting thought

Vern

17. Aug 4, 2004

Tom Mattson

Staff Emeritus
If the speed of light were not constant (invariant from one inertial frame to the next), then nonrelativistic dynamics would hold at all speeds, in its entirety.

The problem would be electromagnetism. It would be necessary to develop a replacement for Maxwell's equations that is covariant under Galilean transformations.

18. Aug 4, 2004

pervect

Staff Emeritus
This would have much the same effect as the age-old question

"What if the number of cm in an inch were no longer constant?"

We could have 2.5 cm/in on mondays, 2.6cm/in on tuesdays, etc. etc. With extra factors for how many cm there were in an inch if the moon was full, perhaps. But unless we actually change physics itself, changing the number of cm/in isn't going to do anything but cause confusion.

19. Aug 18, 2004

shintashi

I recently changed internet companies from cable to DSL, which is why I havn't posted much in the time. I come back and...

Hmnn.. there have been many changes in this place. I have been here obviously longer than anyone else (well probably not, but maybe, unless, you consider the 34 years it says i've had the same password, but its closer to 2-3) This bothers me. It is probably the last time I will be posting here, the Nepotism is exceedingly thick, and even this post itself may be locked and deleted shortly after it arrives.

- Shin, probably for the last time, saying farwell.

20. Aug 18, 2004

Prometheus

Would you still have the speed of light be perceived to be constant by observers, or would the speed of light be perceived to be inconstant?