# What if speed limit is slightly faster than light?

• thenewmans

#### thenewmans

Let’s say some reasonable scientist claims it turns out the speed limit of the universe is actually 8000 meters per second faster than the speed of light. That’s 0.0025% more. What experiment would disprove that? The only thing I know of is the Michelson–Morley style interferometer. I’m not sure what effect a slightly faster speed limit would have on the interference pattern. Besides, it still wouldn’t measure a preferred inertial frame of reference. There’s no reason to assume a preferred frame just because the speed limit turns out to be faster than light. (Right?) So I suspect it might have a very small effect. So what would it take to disprove such a claim?

If there were any kind of communication faster than the speed of light, then it will be possible to measure the one-way speed of light, which means that it will be possible to identfy an absolute rest state for the medium that propagates light and Einstein's second postulate will no longer be necessary. Don't worry, it ain't going to happen.

OK. But I'm not clear on how such an experiment would be done.

You need some underlying theory as to why that would be true...then you have some basis for developing an experiment to detect that phenomena based on your theory.

Suppose, for example, all mass was .0025 greater than we think? What experiment would prove or disprove that?? None...because stuff would still work the same as we have experimentally observed already.

Don't worry, it ain't going to happen.

We should maybe wait to see how the whole OPERA scenario plays out before we make such statements. Who knows, in a year from now you might be eating your own words. The problem I see right now, is that we are at a very critical moment in physics. We are running into the limits of the standard model (only one particle left to find), and some new theories have to be investigated, even ones that allow for FTL travel. We also know that Lorentz invariance must be broken if spacetime were truly discrete (which we don't know one way or the other yet), since the idea of a minimal length is not consistent with length contraction. One can also define a preferred reference frame (locally), and the natural choice in my opinion would be the frame at rest with respect to the cosmic microwave background. Though, I am just speculating of course, I wouldn't say that FTL travel isn't ever going to happen, and I leave an open mind to the issue until we get more experimental results.

Suppose, for example, all mass was .0025 greater than we think? What experiment would prove or disprove that?? None...because stuff would still work the same as we have experimentally observed already.

So I guess what you're saying is you don't know of such an experiment.

You need some underlying theory as to why that would be true...then you have some basis for developing an experiment to detect that phenomena based on your theory.

I appreciate your point but I don't have a theory. I'm just figuring somebody in here knows more than I about how the speed limit was determined. It makes complete sense to me that the speed limit is really close to the speed of light. I just don't know how that was determined. All I know of is the Michelson–Morley interferometer. But I don't even know if that is what was used to determine the speed limit. I don't even know if it can tell you the speed of light. All I know is that it can tell you that the speed doesn't change (much).

I guess the speed limit (rather than the speed of light) has been pretty well measured by the people at CERN and other particle acceleration facilities, where they see the asymptote in speed as they add more energy to their particles, which go to within a tiny percentage of the speed of light.

My understanding is that the highest precision measurements of c are based on its role as the invariant speed, not on the actual propagation of light. What we would observe in the opening description is photons moving slower than c. This happens in a refractive medium.

So far the two have been shown to be equivalent, as far as we can measure. Satellite communication time delays rule out the measure of uncertainty that you specify. Any difference, with photons slower than c, would be taken as evidence that photons have mass.

In fact, it is known that photons have $m<10^{−18}eV/c2$

If there were any kind of communication faster than the speed of light, then it will be possible to measure the one-way speed of light, which means that it will be possible to identfy an absolute rest state for the medium that propagates light and Einstein's second postulate will no longer be necessary. Don't worry, it ain't going to happen.

OK. But I'm not clear on how such an experiment would be done.
It's really very easy, in principle, to perform an experiment to see if anything is faster than light. You get yourself a long evacuated tube. You put a source of light and a source of your faster candidate at one end of the tube. You put detectors for each at the other end of the tube with electronic counters to measure the time interval between the detection of each signal. You simultaneously trigger both signal sources. You repeat the experiment in different orientations and different elevations and different lengths of tube. What you don't do is attempt to measure the one-way speed of your faster candidate with clocks that have not been calibrated with an actual one-way propagation of light in vacuum over the same path.

In other words, you have a race. You see which one wins the race. If you perform one half of a race with just one candidate and use clocks to measure the time and then you perform the other half of the race with the other candidate in a different location at a different time and a different distance and different clocks, then you haven't performed a fair race.