[paul cotter]

"Time contraction"? Where did you get this from?

[alancalverd]

Same place as he got "paradox" and "time jump", I think.

[hamdani yusuf (OP)]

"Time contraction"? Where did you get this from?

In standard explanation for the twin paradox, the stationary twin observes the travelling twin ages less than himself. He perceives that travelling twin experiences time dilation.
On the other hand, the travelling twin observes the stationary twin ages more than himself. He perceives that stationary twin experiences time contraction. It's simply the antonym for dilation. Do you have a better terminology?

[hamdani yusuf (OP)]

Same place as he got "paradox" and "time jump", I think.

You can find them in Wikipedia and YouTube videos, including from those who are considered mainstream scientists.
Wikipedia called it as "the plane of simultaneity jump".

[alancalverd]

In standard explanation for the twin paradox, the stationary twin observes the travelling twin ages less than himself. He perceives that travelling twin experiences time dilation.
On the other hand, the travelling twin observes the stationary twin ages more than himself. He perceives that stationary twin experiences time contraction. It's simply the antonym for dilation. Do you have a better terminology?

OK, that makes sense.

BUT the fact that  A thinks B has undergone an expansion and B thinks A has undergone a contraction is very, very significant!  It means that you can't base any explanation on "a continuously travelling" twin, i.e. a situation in which the relative velocity has "always existed", because if there  is nothing in their motion history to distinguish between the twins, the effects must be symmetrical.

Therefore the "travelling twin" must have undergone an acceleration since their clocks were synchronised.

Once again, the "paradox" only exists if you think there is (or should be) such a thing as absolute velocity, i.e you are trying to derive an observed relativistic effect from a classical axiom. Physics doesn't work that way. So your "mainstream" physicists are not worthy of the title.

[paul cotter]

In special relativity there is time dilation and length contraction. There is neither time contraction nor length dilation.

[alancalverd]

Because everything is related to the "moving" twin or body, when the correct adjective is "previously accelerated".

[Halc]

In special relativity there is time dilation and length contraction. There is neither time contraction nor length dilation.

There is also relativity of simultaneity. I see almost no mention of it anywhere, and yet this accounts for all of the stuff that Hamdani finds so confusing, and finds so many unofficial terms for in various pop sites.

Here's the space-time diagram of this signal exchange between stationary twin and travelling twin, according to Lorentz' theory of relativity.

Actually, the picture you post illustrates relativity theory, not LET theory, for three or four reasons:
1) There is no spacetime under LET. It is a theory used for 3D space existing in time (presentism), not 4D spacetime.
2) The picture presumes that the Earth people can determine that they are stationary. There is no way to determine that, so the presumption is unwarranted.
3) There are red lines of simultaneity in the picture. Lines of simultaneity are always horizontal under LET.
4) The universe of LET can have no gravity, so it is not a model of reality. Lorentz never came up with a model that included gravity, which is good because if he did, there's be no way to tell actual time even if you magically knew which clock was stationary.

Under LET, many coordinate effects (the ones Paul mentions above, the RoS, mass, etc. all become real. But so many things that are real under relativity (what clocks measure, what rulers measure) all become coordinate things. Translation: you cannot measure anything at all under LET because none of your tools work, and all the things that are real are undetectable.  So why defend this? I know two reasons why, but I've only mentioned the one.

[hamdani yusuf (OP)]

Actually, the picture you post illustrates relativity theory, not LET theory, for three or four reasons:
1) There is no spacetime under LET. It is a theory used for 3D space existing in time (presentism), not 4D spacetime.

It's a picture of 1D space against 1 D time. Just like classical mechanics in uniform straight motion.

[hamdani yusuf (OP)]

2) The picture presumes that the Earth people can determine that they are stationary. There is no way to determine that, so the presumption is unwarranted.

It was assumed to have something to calculate.

[hamdani yusuf (OP)]

3) There are red lines of simultaneity in the picture. Lines of simultaneity are always horizontal under LET.

They're not lines of simultaneity. They're laser signal trajectory.

[hamdani yusuf (OP)]

4) The universe of LET can have no gravity, so it is not a model of reality. Lorentz never came up with a model that included gravity, which is good because if he did, there's be no way to tell actual time even if you magically knew which clock was stationary.

Why not?
Lorentz didn't thought about it doesn't mean that someone else can't add it.
It's just a coincidence that general theory of relativity was written by the same person as special theory of relativity.

[hamdani yusuf (OP)]

Under LET, many coordinate effects (the ones Paul mentions above, the RoS, mass, etc. all become real. But so many things that are real under relativity (what clocks measure, what rulers measure) all become coordinate things. Translation: you cannot measure anything at all under LET because none of your tools work, and all the things that are real are undetectable.  So why defend this? I know two reasons why, but I've only mentioned the one.

I don't defend LET. I was comparing it's implications in contrast to STR to see which one is better for explaining the twin paradox.

[Halc]

They're not lines of simultaneity. They're laser signal trajectory.

So they are. My mistake.  From that standpoint, the picture works with either theory.

It was assumed to have something to calculate.

They can calculate, sure, but they've no way to measure anything, so any calculation is abstract.
Length of anything cannot be measured. Time cannot be measured, even if one has impossible access to knowledge of being stationary. Proper acceleration is real under relativity and abstract under LET. Coordinate acceleration can be computed from a chosen frame under relativity.  Acceleration under LET is absolute (real), and totally incalculable.from empirical measurements.

Lorentz didn't thought about it doesn't mean that someone else can't add it.

He did thought about it, and never completed the task. Yes, it was eventually done, but it took a century, and I suspect you don't know the name of the one that did it. Predictions from relativity go away, so no more black holes or big bang theory.  There is no absolute time, even if there somehow was a magical velocity meter and a magical objective gravitational potential meter.
The theory supports two new things, neither of which in any way can be measured at all. It is far more complicated, and I see it referenced only by other denialist papers.  But yes, it was eventually generalized.
The theory can be falsified by suicide, but the dead cannot publish the results.

I don't defend LET. I was comparing it's implications in contrast to STR to see which one is better for explaining the twin paradox.

And how is that going?  How does LET explain the scenario any better than the very first reply to the "What is the exact cause of the time dilation of the twin?" topic, which uses Einstein's theory?

Most topics are answered correctly within the first few replies. Ones that turn into blogs of hundreds of posts do not serve to answer any questions, and serve only to obfuscate any reasonable answers.  You for instance choose to rebut any good answer with some counter point rather than actually learn something from it. I cannot find a place in any of your topics where you actually appear to learn something not known at the start of the topic.
You will not learn anything from this post.  But I just have to butt in occasionally to remind the 3rd part reader what nonsense is being peddled in these blogs.

[hamdani yusuf (OP)]

The theory can be falsified by suicide,

Death of the author is independent from the falsification of their theory.
It can be falsified by showing contradictory implications of the theory, or showing some observation which is incompatible with the theory.

[hamdani yusuf (OP)]

I just found a question in Quora.

How does velocity time dilation work if two observers are both traveling at velocity v in the same direction and one of the observed slows down to 1/2v? Which of the two observers experiences time at a slower rate after the deceleration?

[alancalverd]

The question assumes the existence of absolute velocity.

[hamdani yusuf (OP)]

The question assumes the existence of absolute velocity.

It's not assumed by the question. It's assumed if you answer that the observer keep moving at v will experience time at a slower rate.

[alancalverd]

 

two observers are both traveling at velocity v in the same direction

is meaningless unless there is such a thing as absolute velocity, which there isn't, or a third observer, which isn't stated or relevant to the question.

The only fact is that one of the observers has undergone an acceleration from 0 to v/2 relative to the other.

[hamdani yusuf (OP)]

two observers are both traveling at velocity v in the same direction

is meaningless unless there is such a thing as absolute velocity, which there isn't, or a third observer, which isn't stated or relevant to the question.

The only fact is that one of the observers has undergone an acceleration from 0 to v/2 relative to the other.

It only means that their relative positions don't change with time. This can be determined even when there is no absolute velocity.