Light Speed Not Constant: Impact on E=mc^2

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Discussion Overview

The discussion centers on the implications of a potentially non-constant speed of light on the equation E=mc² and the conservation of energy. Participants explore the theoretical ramifications of varying constants in physics, particularly in relation to quantum field theory and relativity.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation

Main Points Raised

  • Some participants suggest that if the speed of light is not constant, then E=mc² may not hold, raising questions about energy conservation and the validity of many theorems.
  • Others argue that even if c varies with time, the laws of physics could remain valid by assigning an 'epoch' to them, similar to astronomical practices.
  • One participant emphasizes that the meaningfulness of varying constants differs between dimensionful and dimensionless quantities, noting that measuring changes in dimensionful constants like c is more complex.
  • Another participant expresses skepticism about the likelihood of constants such as c, ħ, and e varying over billions of years while keeping dimensionless constants like α constant, suggesting that such speculations should be curtailed.
  • A later reply highlights the challenges in measuring changes in dimensionful constants and suggests that discussions about dimensionless constants may be more meaningful.

Areas of Agreement / Disagreement

Participants exhibit disagreement regarding the implications of a varying speed of light and the feasibility of measuring changes in fundamental constants. There is no consensus on whether such variations are plausible or what their consequences would be.

Contextual Notes

The discussion involves speculative reasoning about the nature of physical constants and their implications, with participants acknowledging the complexity and uncertainty surrounding these topics.

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

Daniel.
 
the varying constant-matter has been widely debated here :

https://www.physicsforums.com/showthread.php?t=71105

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
 
marlon said:
the varying constant-matter has been widely debated here ...

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 [itex]\alpha[/itex] 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 [itex]c[/itex] or [itex]G[/itex] or [itex]\hbar[/itex] varied in and of itself (all other quantities remaining contant), we could not know the difference. we could not measure it.

r b-j
 
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.
 
dextercioby said:
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,

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 [itex]\alpha[/itex] has changed. saying the latter actually means something. might not be true, we got to 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 [itex]\alpha[/itex] or [itex]\frac{m_p}{m_e}[/itex] can go a little farther before speculation gets clipped.

r b-j
 

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