# C is not a constant

1. Apr 15, 2005

### lwymarie

recently many scientists think that light speed is not a constant. if it is true, then E=mc^2 does not hold because c is no longer a constant. Does it mean that E is not conserved? if yes, many theorems will be wrong...

2. Apr 15, 2005

### dextercioby

How about everything we know about particle phyiscs (which is based on QFT) and relativity (special & general).I think Newton wouldn't mind...

Daniel.

3. Apr 15, 2005

### marlon

the varying constant-matter has been widely debated here :

As to your original question. Suppose c varies with time, all laws will remain valid because we can assign an 'epoch' to them, just like we do in astronomy when describing the orbits and dynamics of celestial objects like planets. But in the end, all formula's in QM that we know of are completely correct. If you want proof, just look at every functioning electronics-device that you use every day. Ofcourse, certain changes will have to be made and this still is all very speculative. I my opinion, such notions are to some extent quite overblown

marlon

4. Apr 15, 2005

### rbj

that issue (at least as far as i can see) was more about the meaningfulness (from the POV of mortals) of a vaying dimensionful constant vs. the meaningfulness of a varying dimensionless "constant". i'm not saying that $\alpha$ has varied (i think not as likely) but if it did, we would know the difference. stuff, as we could measure it would be different. if $c$ or $G$ or $\hbar$ varied in and of itself (all other quantities remaining contant), we could not know the difference. we could not measure it.

r b-j

5. Apr 15, 2005

### dextercioby

It's very highly improbable that "c","hbar" and "e" to have varied over the billions of years in such way as to keep "alpha" constant...So how about quitting speculations???

Daniel.

6. Apr 15, 2005

### rbj

Daniel,

i do not at all take issue with you about whether or not these measurable universal constants have been changing. only to point out that when someone says that c has changed, they have a much more difficult metrological problem even stating such a proposition than if they say that $\alpha$ has changed. saying the latter actually means something. might not be true, we gotta measure it carefully, if we could conceivably measure such a change and that would mean something. since, in experiments and in our perception of reality, we only measure dimensionless quantities (we measure dimensionful quantites agaisnt a like dimensioned standard or "unit"), saying c has changed, in and of itself, means nothing. As Michael Duff pointed out, it is like saying that the number of pounds in a kilogram has changed.

so, with regard to changing dimensionful constants, i am trying to clip speculation at an even earlier point. changing $\alpha$ or $\frac{m_p}{m_e}$ can go a little farther before speculation gets clipped.

r b-j