# Irrelevant to ask if speed of light changes?

1. Jan 11, 2006

### Anders Lundberg

This question has not rendered any respons at all in the forum for Astronomy & Cosmology. Maybe it is more relevant in this forum?
My question is: Would not a change of the speed of light (or rather; the speed that not light or gravity or any other fenomena can exceed), change the speed of all chemical reactions also? Would it not change every aspect of the universe? And would not that universal change "even out" the change of the speed of light so that we will never be able to notice it?
If eg an increased speed of light also makes clocks tick faster (or makes the space expand a bit?), then we may still measure the speed of light to be 299 792 458 m/. In other words, do we not chase our own tail here?

2. Jan 11, 2006

### nazgjunk

it wouldn't matter, if what you say is true, everything would "slow down" or "speed up" at the same rate, thereby eliminating the effective change. Oh, and the definition of a metre is linked to time, so yes.

3. Jan 12, 2006

### vanesch

Staff Emeritus
The reason is that the only constants that have true physical meaning, are dimensionless constants. When you alter a quantity with a dimension, you are in fact just redefining the unit system.

4. Jan 12, 2006

### rbj

take a look at:

http://en.wikipedia.org/wiki/Planck_units#Planck_units_and_the_invariant_scaling_of_nature

then take a look at the other side:

http://en.wikipedia.org/wiki/Variable_speed_of_light

including the talk page (where i have a "little" debate with the originator of the article):

http://en.wikipedia.org/wiki/Talk:Variable_speed_of_light

maybe take a look at the heavyweights cited: Paul Davies, John Moffat, João Magueijo, and "my guy" Michael Duff, and then decide for yourself. if you want some expert input, try posting to sci.physics.research and ask those guys.

5. Jan 17, 2006

### rbj

Another statement about this from John D. Barrow, ''The Constants of Nature; From Alpha to Omega - The Numbers that Encode the Deepest Secrets of the Universe'' (Pantheon 2002):
"[An] important lesson we learn from the way that pure numbers like $\alpha$ define the world is what it really means for worlds to be different. The pure number we call the fine structure constant and denote by $\alpha$ is a combination of the electron charge, $e$, the speed of light, $c$, and Planck's constant, $\hbar$. At first we might be tempted to think that a world in which the speed of light was slower would be a different world. But this would be a mistake. If $c$, $\hbar$, and $e$ were all changed so that the values they have in metric (or any other) units were different when we looked them up in our tables of physical constants, but the value of $\alpha$ remained the same, this new world would be observationally indistinguishable from our world. The only thing that counts in the definition of worlds are the values of the dimensionless constants of Nature. If all masses were doubled in value [including the Planck mass $m_P$ ] you cannot tell because all the pure numbers defined by the ratios of any pair of masses are unchanged."