# Speed of light and chemical properties

1. Jun 24, 2011

### entropy1

If the speed of light were (slightly) different, how would that affect the chemical properties of atoms, if so?

Last edited: Jun 24, 2011
2. Jun 24, 2011

### mathman

Probably not very much. Photon transit time at the atomic level is essentially instantaneous.

3. Jun 24, 2011

### Staff: Mentor

If LIGHT traveled at a different speed? Or if the velocity known as "c" was different? (Maybe I'm being to detailed here, if so sorry)
Either way I don't think there would be a big difference as long as the change was very small.

4. Jun 24, 2011

### bcrowell

Staff Emeritus
It only makes sense to talk about changing a universal constant if the constant is unitless. (See the paper by Duff below.) The speed of light has a defined value in the SI, for example, so it's not possible to measure it. The relevant unitless parameter would be the fine structure constant. The FAQ below is about time-variation of the fine structure constant, but it also applies to the OP's question.

Essentially the answer to the OP's question is that the only change of this type that would have observable results would be a change in the fine structure constant. A change in the fine structure constant would change atomic energy levels and make chemistry different. Yes, it would change the behavior of chemical reactions.

FAQ: Has the fine structure constant changed over cosmological timescales?

It has been claimed based on astronomical observations that the unitless fine-structure constant alpha=e^2/hbar*c actually varies over time, rather than being fixed.[Webb 2001] This claim is probably wrong, since later attempts to reproduce the observations failed.[Chand 2004] Webb et al. responded with even more extraordinary claims that the fine structure constant varied over the celestial sphere.[Webb 2010] Extraordinary claims require extraordinary proof, and Webb et al. have not supplied that; their results are at the margins of statistical significance compared to their random and systematic errors.

Even if this claim it is correct, it is not evidence that c is changing, as is sometimes stated in the popular press. If an experiment is to test whether a fundamental constant is really constant, the constant must be unitless.[Duff 2002] If the fine-structure constant does vary, there is no empirical way to assign blame to c as opposed to hbar or e.

J.K. Webb et al., arxiv.org/abs/astro-ph/0012539v3

J.K. Webb et al., http://arxiv.org/abs/1008.3907

H. Chand et al., Astron. Astrophys. 417: 853

Duff, http://arxiv.org/abs/hep-th/0208093