# Doubling the Speed of Light [closed]

What would happen in a universe where c was double what it is in ours? Based on the constants in our universe that allow life to exist on Earth in its current form/s (you can change a few if this is necessary), could Earth-based lifeforms exist? Of course this will involve changing at least one law of physics. I'm not inquiring about changing any particular law. Ex. It would affect maximum rate of transfer of energy/information, which would increase the rate of osmosis, probably increase maximum rates of metabolism, which would increase maximum size of insects at our current oxygen levels, etc.

• I'm not a physicists but I don't think you could do that. c has nothing to do with light but it's a speed of causality. If you keep fundamental constants same as ours, then by using Lorentz transformation c must be same as now. If you change them its anybody's guess life might not even exist youtube.com/watch?v=msVuCEs8Ydo – slobodan.blazeski Dec 24 '16 at 18:22
• If the constant c was doubleed in your universe, and all physics remained the same, scientists would quickly find that the speed of light is c /2 – Aify Dec 24 '16 at 18:23
• The trouble is that the speed of light is linked with the elementary electric charge e (the charge of the electron), the electric constant ε₀ (the permittivity of the vacuum), the Planck constant ħ (the quantum of action) and the fine-structure constant α by the equation: = 4παε₀ ħc. You cannot change only one of those; you must change at least two. – AlexP Dec 24 '16 at 18:58
• – JDługosz Dec 24 '16 at 19:04
• @a4android your remark to Aify above can’t work. c is the only speed that is lorentz invarient. The appearance of c in various physics formulas is an artefact of our units and dimensional analysis, and is commonly 1 in “natural units” systems. You could not make light or anything else travel at twice that speed. – JDługosz Dec 25 '16 at 18:46

I know this has been explained at length before but I can’t find just where right now (update: Separatrix notes Can I keep our universe, but without the speed limit (of light)? and What if the speed of light were 100 times higher?)

The speed of light is not simply a setting that can be changed. It relates to everything so for example electron orbitals would be different, bond strengths would be different, etc. If you adjust other things as well to get the fine structure constant to still be the same, you find that everything is exactly the same! Atoms are bigger and chemical reactions are slower, so all you did was change the scale of the universe.

So, in a universe where the speed of light was double, you would not have the same kind of atoms. You would not have the same stuff (stars, planets, galaxies), if you had rich structure at all. So no, Earth based lifeforms could not exist.

• I can only think of these two immediately – Separatrix Dec 24 '16 at 20:19
• This depends on what anyone means by Earth-based lifeforms. if the alternative universe in question permitted complex structures, then convergent evolution might, I say might, because nothing in this scenario is wholly certain, produce lifeforms resembling Earth-based organisms. Even their atoms are bigger and chemical reactions are slower. – a4android Dec 25 '16 at 13:15
• Bigger/slower illustrates how nothing really changed: that is a different point. If you just change one or more things so α is different, then you will not have stars, planets, atoms as we understand them. My review is brief because this has been explained at-length elsewhere. – JDługosz Dec 25 '16 at 20:40

There's no real answer to this because we don't know what is required for life. Our sample size is 1. We do some extrapolation, but that's all we can do. The thing is, we disagree on how to extrapolate. Some argue that there are constants in the universe which, if they were different by a tiny fraction (I've heard one-part-per-million for some atomic forces), then the universe could not form atoms. Others argue that life is a pattern which occurs in limitless variety, and that while the life may appear alien to us, it would crop up no matter how far the constants are from ours.

There's also an open question as to whether we are unique or not. For all we know, you could restart the universe with exactly the same rules, but have the other team win a coin toss at the beginning of the universe and we find that tiny change lead in a direction which prevented life. Or, for all we know, the humanoid lifeform pattern may truly be a eigenvector of how the universe functions, and we will end up with a new Earth for any initial state!

If you wanted to explore this further, my recommendation would be to look at the relationships with other key constants. The constants in physics form a dense web of interconnections based on symmetries and other laws. For example, Maxwell's equations for electromagnetic radiation show that $c=\frac{1}{\sqrt{\epsilon_0\mu_0}}$, tying the speed of light to the permittivity and permeability of the vacuum. If the speed of light changes, so must one or both of these terms. Since you're building the universe, you can choose how that change got distributed between those two terms, and look at their side effects. Changing the permittivity, for instance, will likely affect the ability for air to act as an insulator, changing how lightning strikes. Given that the some of the best theories for abiogenesis suggest life may have started when lighting struck the primordial soup, anything which changes the behavior of lightning has a change of affecting life as a whole!

• Changing ε₀ will have massive effects on chemistry, for example -- all chemical forces are electric forces. – AlexP Dec 24 '16 at 19:00
• This is explained in more detail in this answer by celtschk. – JDługosz Dec 26 '16 at 6:14

Everything else fixed, one immediate consequence is that a fine structure constant becomes twice as small. No carbon, no life as we know it.

• Thank you, this answers my question, I think everyone was thinking too in-depth. – Harlemme Dec 25 '16 at 2:45
• Glad to see someone read the question and instead of flapdoodling around actually answered it. Plus one. – a4android Dec 25 '16 at 13:06