0 Members and 1 Guest are viewing this topic.
Well, under some specified conditions, not involving accelerations/decelerations it actually define it. When it comes to accelerations/decelerations you can still argue that the discrepancy you measure (from 'c') is a result of 'gravity', locally measured.
There are two sets of relativity, one being SR, the other involving gravity (GR). And using SR 'c' is a constant.
There are a sort of 'global definitions' in physics, as Lorentz transformations. Ways of knitting one frame of reference to another, what I measure to what you measure. They are expressions of a local logic applied on a universe we need to agree on. We can't agree though, not without introducing time dilations and length contractions, to get those different measurements to fit, unless we happen to be in a same frame of reference as we measure.. We've been in one for the longest time btw, it's called Earth. That's also why we found it so easy to agree on our observations. It's not until recently we've found out otherwise. But a 'time dilation' has nothing to do with your life span. It always stay the same. locally measured, as by your wristwatch. A 'time dilation' is a result of you measuring locally, using that wristwatch (and that measuring stick), relative some other celestial object (neutron star maybe?) for example. It doesn't change your clock, neither your meter stick. I better point out that it doesn't change your length either, Age does though =And all of this are general descriptions. Being in a same 'frame of reference' can also be seen as being scale dependent, depending on your type/choice of measurement, as shown by NIST experiments with atomic clocks.
It might be easier to see the difference if you make clear that local measurements are what we use. The universe you look out on is a result of your local 'measurement'. We haven't found any 'global truths' that I know of. What we call the 'universe' is always the result of you interacting locally with it, taking its 'measurement', as it might be expressed. It's a subtle thing to think about but it is true. And when it comes to relativity is actually accentuates the truth of this local interpretation, as it tells you that with different speeds, mass, etc, your experience/measurements will vary. Some things will still hold true though, no matter your speed or mass. Those include 'c', a meter, and a second.
The product of length times time is always the same for any particle. If it speed up its size will drop and its internal clock will slow. If it slows down its size will expand and its clock will speed up. The Earth is moving slowly relative to the speed of light C, so our differences in size and clock are very small.
I think you're mixing up some global definition, of your own choice, with a local? The local definition of 'c' fulfills all demands physics ask of it. what you do is to imagine a 'whole universe', yourself standing outside it, then saying that 'c' can't be 'c'. But it is, for you too. You're inside it, will never get outside it. That's the way the universe works.