Irrelvancy of motion in C perspective

[JJRittenhouse]

Okay, so...

How is the speed of light a constant regardless of the observer.

SR doesn't explain it, it's simply a postulate. What does explain it?

 

[Fredrik]

How can C be constant regardless of the observer?

It's not that hard to see that it is, if we already know that the functions that change coordinates from one inertial frame to another are Poincaré transformations. Motion is represented by curves in spacetime. Coordinate systems map those curves to points in \mathbb R^4. Take any two points on a straight line \mathbb R^4 with velocity c and apply any Poincaré transformation to them. You will find that the line that connects the transformed points is also a line with velocity c.

So why are Poincaré transformations the functions we use to change coordinates between inertial frames?. In the context of SR, this is either an axiom or a statement that follows almost immediately from the axioms. However, you can also ask if there's a theory that uses \mathbb R^4 as the mathematical representation of space and time, in which the coordinate change functions satisfy a few reasonable requirements, like if f and g are coordinate change functions, then so is f\circ g. If we include preservation of simultaneity in the "reasonable requirements", then there's exactly one set of coordinate change functions that work: Galilei transformations. If we drop that specific requirement, there is exactly one more: Poincaré transformations.

The details are pretty complicated, unfortunately.

By the way, the word is "regardless", not "irregardless".

SR doesn't explain it, it's simply a postulate. What does explain it?

As I mentioned above, the only thing that can answer a question about reality is a theory. There is no theory that really answers this question, and even if there was, you could still ask why the axioms of that theory holds. To answer that question, we need another theory, and so on, ad infinitum.

 

[Dale]

it doesn't. what surprises me is that you don't have a translation for your answer.

I can translate it into math or into spanish if you like.

It doesn't have anything about being "Dissatisfied" with the answer, it has everything to do with there not being an answer at all.

Yes, there is an answer. The answer is that there is no inertial frame which moves at c wrt any other inertial frame.

What can your answer say about light? It travels at C, but through what? Through space in our frame?

Through vacuum in any inertial frame.

How does this even explain how light can move at the same speed regardless of the observer? Oh, wait I forgot, it's a postulate.

Exactly. Now you are getting it. You don't explain the postulates of a theory, you use the postulates to explain and predict other things. Then you test those predictions and if they hold then you have a scientific reason to accept the postulates, as weird as they may seem.

And I am taking physics, we just aren't studying relativity yet.

Have you studied Maxwell's equations yet?

 

[JesseM]

For one, at the very least, time dilation is real, not an illusion.

There is no coordinate-independent way to define the rate a clock is ticking. If two clocks meet, compare times at a single point in space and time, then move apart, then come back together and compare times at a second single point in space and time, then there is a coordinate-independent truth about how much time each clock has elapsed between the two meetings. But there is no coordinate-independent way to answer questions like which clock was ticking faster at some point midway between the two meetings.

For another, when something moves, space and time slow and compress for the rest of the universe outside of him. Is this not really happening?

Not in any coordinate-independent sense, so if you define coordinate-dependent statements as "not real", then no, it's not "really" happening. It is true that in the object's inertial rest frame, the coordinate length of moving objects is compressed and the rate moving clocks are ticking relative to coordinate time slows down.

So what is the translation for there not to be a reference with respect to C?

There is not an inertial rest frame for light. As I said you can certainly define a non-inertial coordinate system where the light is at rest (an infinite variety of them, in fact).

 

[JJRittenhouse]

As I mentioned above, the only thing that can answer a question about reality is a theory. There is no theory that really answers this question, and even if there was, you could still ask why the axioms of that theory holds. To answer that question, we need another theory, and so on, ad infinitum.

Allright, well, thanks for the time.