Twins paradox explained without forces

[Celeritas]

5 hours ago, md65536 said:

What's the definition of a clock's "existence" in another observer's frame?

I meant only that twin B maps the twin A clock in his own spacetime system, as he goes.  If he had a tracking console, it would be populated on the display because it's current location is being updated and calculated.

5 hours ago, md65536 said:

What if B doesn't know of relativity, and says "A's existence spans 2 of its years on my outbound journey, and 8 years on my inbound, and I've measured that to be true"? How can you prove to B that it's wrong and that your description of existence is the right one?

Can you convince it that what it measures (2 + 8 years observed) is wrong and your numbers (unmeasured, but later verified to be consistent with a particular definition of simultaneity) are the ONLY ones that can be real? And can you do this without relying on Einstein's definition of simultaneity or an equivalent?

You say B measured the current A clock location and readout as he goes.  But that's impossible.  He's remote from A, and must consider the light transit time, the speed of light, and determine the A velocity and A location (as he goes) per whatever model he uses.  One may be able to prove B wrong, depending on how he is figuring it all.  Maybe you can, maybe you can't ...

We might imagine other clocks crossing paths during B's roundtrip.  Does B predict the correct readout of those clocks when they intersect, or not?  The owners of those clocks could verify that.  Which theory predicts that accurately?  If both do, then I'd say there is no way to know (yet) if one theory matches reality and the other does not.  For example, assume for a moment that the 1-way = 2-way in nature.  If conventions using 1-way <> 2-way produce the same solns, then both theories are valid far as spacetime solns are concerned, however only 1 theory matches what is real. We cannot measure the 1-way speed of light, and so I figure we may never know the answer to that.  LET theory could be correct, or SR could be correct. There may well be various reasons though, for presuming one theory superior to the other, but there may be no known way to ever prove that.  Then, Occam's Razor says use the simplest theory, and that theory is the most likely to match mother nature (but not guaranteed to). 

 

5 hours ago, md65536 said:

Do you think that when Einstein defined simultaneity in such a way that real-world events could be tested against that definition to determine if they fit it or not, he actually did much more than that, and actually defined existence? Or could it be that his definition so perfectly aligns with your assumptions about reality, that you figure he is proving your assumptions correct simply by definition?

I think Einstein picked 1-way = 2-way because it produces the simplest derivation and the simplest transforms.  Also, since he was not commencing his derivation from a master frame, it seems to me that 1-way = 2-way would be the natural first choice.  It would always be the natural first choice, if starting from a master frame or not.  I figure he would not say that his convention was the most likely to match reality, as he could not prove it.

Best regards,

Celeritas

Edited February 24, 2020 by Celeritas

[md65536]

11 hours ago, Celeritas said:

I meant only that twin B maps the twin A clock in his own spacetime system, as he goes.  If he had a tracking console, it would be populated on the display because it's current location is being updated and calculated.

Populated with what? Measurements of A? Or a prediction, based on the LT or the underlying definition of simultaneity? If simultaneity was not defined, could B say what the time at A "really" was? Is there for B, a physical "now" at the distant location A independent of that definition? Would you say that Einstein was wrong in writing that such a definition is needed?

11 hours ago, Celeritas said:

You say B measured the current A clock location and readout as he goes.

I didn't say "current". I said B can measure the total ageing of A without ever considering what the "current" or "real" time at A might be. It can measure what the time at A appears to be, using only the local current time at B.

11 hours ago, Celeritas said:

He's remote from A, and must consider the light transit time, the speed of light, and determine the A velocity and A location (as he goes) per whatever model he uses.

Why? He didn't, and got the right answer, never assuming anything at all about simultaneity. You say the speed of light must be considered, but don't you mean the one-way speed of light? B only needs to care about incoming light from A, to determine everything it needs to know about A, right? What is the one-way speed of incoming light? How do you know that light takes time to arrive? I'll just tell you the answer: You know it because the time it takes incoming light to cross a fixed distance is defined to be the same as the time it takes outgoing light to cross the same distance.

You're wrong to say you "must" come to the same conclusion to be able to predict the ageing of A. I've just shown, B can predict the total ageing of A using only the relativistic Doppler effect, which is a real measurement that can be made without relying on any definition of simultaneity, and gives you the same answer regardless of how you define the "current time at a distant location."

11 hours ago, Celeritas said:

Which theory predicts that accurately?  If both do, then I'd say there is no way to know (yet) if one theory matches reality and the other does not.

I'll just assume you're still using your own meaning of the word 'theory'.

Both the LT and the relativistic Doppler effect can accurately let B predict the total ageing of A. Would you say there is no way to know which one matches reality?

11 hours ago, Celeritas said:

If conventions using 1-way <> 2-way produce the same solns, then both theories are valid far as spacetime solns are concerned, however only 1 theory matches what is real. We cannot measure the 1-way speed of light, and so I figure we may never know the answer to that.

So, accepting that you can't know the answer to the question, you conclude that it must be the answer most reasonable to you?

Can you conceive of the idea that the inability to measure the 1-way speed of light is the one "theory" that matches what is real??? It's not that a way to measure it hasn't been figured out yet, it's that there's no accepted theoretical way in which such a measure can meaningfully be made.

It's like saying "Measurements of the Ether are all consistent with the fact that it doesn't exist," and someone arguing "I agree. Even though it exists, we may never have the ability to detect it."

11 hours ago, Celeritas said:

I think Einstein picked 1-way = 2-way because it produces the simplest derivation and the simplest transforms.  Also, since he was not commencing his derivation from a master frame, it seems to me that 1-way = 2-way would be the natural first choice.  It would always be the natural first choice, if starting from a master frame or not.  I figure he would not say that his convention was the most likely to match reality, as he could not prove it.

I agree! Einstein in fact did say something along those lines. He said, "in reality it assumes absolutely nothing about light" as I've quoted. In his 1905 paper he wrote,

Quote

We might, of course, content ourselves with time values determined by an observer stationed together with the watch at the origin of the co-ordinates, and co-ordinating the corresponding positions of the hands with light signals, given out by every event to be timed, and reaching him through empty space. But this co-ordination has the disadvantage that it is not independent of the standpoint of the observer with the watch or clock, as we know from experience. We arrive at a much more practical determination along the following line of thought.

and then defined the equal timing of light signals in opposite directions. Thus he literally said that 1) we "might content ourselves" with an alternative, which I take to mean that it can provide workable solutions, and 2) a justification of the definition he used is that it is more practical.

He knew what he was doing and didn't get mired in trying to base the theory on what he thought to be "real", only what agrees with experience.

 

Edited February 24, 2020 by md65536