Wyman wrote:I have a question for someone who knows physics that this exchange reminded me of. I never completely understood the constancy of the propagation of light in relativity. I often think I understand it and then realize I probably don't. If a star is coming towards you at 1 million units per hour, then is the light propagating from the star in your direction going at c, or at c plus a million?
No the speeds are not additive the speed of any object relatively speaking is always less than c unless it is light then the speed is c in a relative frame, but it is undefined by special relativity per se, it's taken as a constant, the rest of the science just falls out if you use the speed of light which happens to be c.
Take two photons travelling at light speed moving towards each other because of the Lorentzian nature of the process, they are actually just travelling towards each other at c, if an object has mass though that is slightly different.
It's not that hard maths though so let me show you the equation and you can plug any mass into it and see the relative speed in comoving objects. By the way, you can put mass anywhere in the equation not everywhere although that would work too if the mass was x; it won't affect it, which is the beauty of the Lorentz mathematics.
ok and the variables are:
The above is just a time space transform by rotation of 90 degrees, about any axis, you can ignore it in 4 dimensions x,y,z and time, a rotation about 90 degrees in that circumstance leaves you in any other axes concern so it's kinda like revolving around a circle you revolve enough you are back at the start or in this case just talking about another axis in space-time.
Now look very carefully at the maths, and plug in some numbers. Velocity is v, and the speed of light is c. This applies to the photon primarily and as you can see in maths you have a square root of 1 with a photon and something less than 1 with a mass object.
In a mass object you have a square root that is not 0, stick mass in there and...
Co moving objects move at less than c and as they travel towards each other they are experiencing time and space dilation which means the speeds are not additive.
I have probably explained this very badly, but suffice to say time dilation and space dilation means that no objects are ever moving at c except photons, and no mass objects which are comoving even if it's two trains running at each other can ever reach c, all the rest of the maths is a result of that, and the fact it works as well, in all experiment the predictions match up, of course you will get the usual suspects saying the maths doesn't work or the science doesn't work, but they never do any experiment to disprove it, so it's just specious I don't like science, so I will talk around it, but there are plenty of forums that indulge in that so suffice to say you can find the utter bilge of the untrained physicist who is apparently smarter than all the best minds in the 19th to 21st century anywhere, without ever studying science or the maths or even knowing what the hell they are talking about.
End of the day and to sum it up it means things are experiencing a sort of time dilation as they approach c, and a space dilation to that limit all energy and matter to c as the speed limit of the universe. Why this happens is anyone's guess, in fact, it's an open question, suffice to say it seems by experiment that is the way reality works...