ralfcis:

I've explained this many times. Brehme used "your space in my time" without objection from relativists so it is appropriate to mix any perspective with any clock.

This is the first time you've mentioned "Brehme" to me. I don't know who that is, or why he is authoritative. Regardless, I don't see why we need to rely on his authority.

If you randomly mix space and time measurements made in different frames, you can certainly calculate some numbers, but they are unlikely to relate to anything that's meaningful physically.

Yv is Alice using her on-board clock, the only measurement device she has access to, to measure the time it took her to cross Bob's proper space.

Alice and Bob are both in the same position as regards measuring devices and the like. You can't privilege one over the other. Whatever measuring devices Bob has, we can assume Alice has identical ones available to her. There are no preferred reference frames in relativity, so you can't even say that Bob was the one who was "really" stationary and Alice was the one who "really" moved.

So what? Yv isn't physically meaningful. What is it the velocity of? Nothing, as far as I can tell.

Alice cannot use the parallax distance measurement technique while she is travelling because it would take 2 ships.

If Bob wants to use parallax, he needs to observe from two different locations in his frame. Similarly, if Alice wants to use parallax, she needs to observe from two different locations in her frame. They are on an equal footing. It is absurd to say that Alice can't use parallax but Bob can.

She could remap the entire universe from her 3/5c perspective but that is not practical because it would have to be done for all velocities.

If she can't do it, nobody can do it. Is Bob, sitting on Earth, absolutely stationary? No. Earth moves around the Sun. The Sun moves around the galaxy. The galaxy moves relative to other galaxies. And so on and so forth. You're essentially claiming that nobody anywhere can make a map.

So long as relative velocity is depicted correctly, you can have your choice of all other valid depictions and you choose the easiest and one that makes physical sense.

All of them make physical sense.

You don't choose the perspective that you're stationary to an entire universe moving past you (no rule against that) just as you could choose the sun orbits the earth but why choose impractical perspectives that don't reflect reality?

They do reflect reality. There are no preferred reference frames in relativity. Alice's frame, in which the Earth moves away from her and Proxima Centauri approaches her, is just as valid a Bob's frame, in which Alice moves between a "stationary" Earth and Proxima Centauri.

I choose to ignore the existence of length contraction for the reasons I gave.

When you ignore it, you get wrong answers, like those speeds of light that you obtain that are greater than or less than c.

It's redundant so it means special relativity is not the simplest theory to explain the physics.

Your theory fails to accurately describe reality. SR succeeds where you fail.

You should state your postulates. SR only has two, and I've given them to you. Everything else is derived from those. So, what is your alternative theory derived from?

They're using clocks that suffer from relativity of simultaneity to measure length so of course their length measurements are different.

Try to be consistent, at least. Just above, you said you "ignore" length contraction, but here you admit that "of course their lengths measurements are different".

Can you see that you can't acknowledge that length measurements are different in different frames and, at the same time, expect to get correct answers if you ignore that?

Assuming length contraction allows the math used for relativity to work.

It's not assumed; it's derived from the postulates.

I assume you're read up on relativity. You will have seen how length contraction is derived. Right?

I mean, if you're going to criticise a theory, the first step is to make sure you fully understand it. Have you done that?

I explain the same physics with different math th\at also allows me to predict extra measurable physical phenomena that relativity cannot.

So far, I have pointed out a number of errors in your calculations, but you have not responded.

Which "extra physical phenomena" can you predict, that relativity cannot? Please give one example, at least.

So the two agree but relativity calls certain scenarios indeterminate that my math is able to determine.

Please give one example of something that relativity calls "indeterminate" but your math is able to determine. Be sure to choose something that is physically testable, at least in principle.

It is physically measuring a velocity using your own clock, without the need for clock sync or referring to the other clock, and using proper time star charts from a common stationary perspective such as the earth, to understand why you seemed to cross those distances in less time than your relative velocity v would indicate.

To measure a velocity, one needs two things: a measurement of distance and a measurement of elapsed time. It is impossible to measure a velocity using a clock by itself.

You are yet to define "proper time" or "proper distance", as you understand them, and I won't be commenting on those until you do.

Have you not heard of people able to cross the universe in a very short amount of their time if their v is close enough to c? Relativity explains this using length contraction. I use Yv and the Brehme perspective of your space in my time.

You're not being very specific about reference frames and the like in what you've written here, so for now I'm not going to try to unpack this.

The question you should have asked is why is v a relative velocity and Yv is not. Bob's not going anywhere but his relative velocity to Alice is x/t = 3/5c. Alice's relative velocity to Bob is also 3/5 from her DSR reading. But she is going somewhere, 3ly as measured by her clock in 4 yrs.

Her clock can't measure the distance. Clocks only measure time. She needs some rulers if she wants to measure the distance she travels.

This is her Yv=x/t'=3/4c which Bob has no access to seeing.

That is an error. In Alice's frame, Bob travels at -3/5c, while she stays still. In Bob's frame, Alice travels at 3/5c, while Bob stays still. Neither of them measure anything as travelling at 3/4c.

He sees Alice's clock ticking at half of his so he can't see her Yv.

Yv is just a randomly calculated quantity. It is not physically meaningful.