Tell me more ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.
up vote 0 down vote favorite

We know light from the sun takes about 8 minutes to reach earth. Now let's imagine a reality where light is twice as fast so it takes 4 minutes to reach earth.

What would be our measure of lightspeed in such a reality?
Would it be 6*10^8 m/s ?

My guess is we'd still measure it at 3*10^8 because since light is faster then everything works faster as well, i.e. the clock used to measure the speed is going to run faster.
So even though light takes only half the time to reach earth, clocks run twice as fast so we would end up measuring the same 8 minutes.
Am I right?

EDIT:
Well I guess this is not really about physics, but meta-physics or something.
Speed of light is a constant of our reality (our universe or whatever bigger than that our reality is) and I was just wondering if there is any way that lightspeed could be any other number given the fact that the notion of speed depends on the notion of time and time depends on the speed of light.
It's like trying to define a word using other words whose meaning depend on the word we are trying to define.

share|improve this question
"Now let's imagine a reality where light is twice as fast so it takes 4 minutes to reach earth." The FAQ says that you should not ask questions about "fictional physics". That doesn't necessarily rule this question out, but you are going to have to be very clear about what you are supposing here. Various facts about chemistry, for instance, depend on the speed of light. Are you going to try to scale things to get those to be the same? – dmckee♦ Sep 24 '12 at 14:30
1  
I'm going to close this for the moment, but would be happy to re-open it once it is clarified. Use the "edit" button to work on it, then the "flag" button to get a moderators attention. – dmckee♦ Sep 24 '12 at 14:32
Actually, today's definition of meter makes the speed of light constant - even if it should change for weird reasons :) – Hagen von Eitzen Sep 24 '12 at 16:06
1  
It is certain that the numeric value assigned to the speed of light is arbitrary. Indeed, many physicists find it convenient to use a system of units in which $c$ is a dimensionless, unit constant. – dmckee♦ Sep 24 '12 at 17:39
@dmckee, that's somewhat the direction I was pointing to with this question and you enlightened me with that. Lightspeed is really the absolute point of reference and not the units it's expressed on. That's why you can't really measure it since the units themselves depend on it. – GetFree Sep 24 '12 at 19:58
show 1 more comment

closed as not a real question by dmckee♦ Sep 24 '12 at 14:31

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, see the FAQ.