[alancalverd]

And my definition of synchronism is that A knows what time B is showing, just from observing his own clock and nothing else.

I am unaware of any other useful definition.

The best way of A knowing their relative velocity is to assume that their clocks are identical and measure the redshift of B's clock signals. Except that he doesn't know the gravitational potential difference between them....so as ES implies, it's better to forget about time and twins altogether!

[hamdani yusuf (OP)]

The paradox is why anyone thinks it is a paradox. And the answer is inertia and vanity.

Something is called a paradox if it seems like there's a contradiction, but a closer look can determine that there are errors in the line of thought leading to that contradiction.

On the other hand, if the contradiction is inherently within the described situation, and no error can be found in the reasoning, then the conclusion is to reject the proposition. It's called proof by contradiction.

Twin paradox is called paradox by those who accept STR. They think that it doesn't cause a real contradiction.

On the other hand, critics of STR think that twin paradox actually demonstrate a contradiction, instead of just a paradox. It causes them to reject STR.

[alancalverd]

Back to experiment. We know that identical clocks are not synchronised when there is relative motion between them, and however we calculate it, they can remain synchronised if v = 0.

Most human experience involves v << c, so we have a "good enough" and specific concept of "twins"  that actually has no general validity.

What paradox?

[alancalverd]

the coordination of something like video and its soundtrack

We use the clapper board to mark the beginning of a sequence, then set the studio metronome to ensure that the music reaches its climactic discord when the hero dies, or whatever, 28.4 seconds later. If the studio clock doesn't count at the same rate as the video clock, you rather lose the dramatic effect. Or to put it another way, if your downbeat coincides with the clapper, you should be able to tell the number on the video timestamp by just looking at the studio clock at any time thereafter.

According to Einstein and experiment, it doesn't work if the video was recorded in orbit, even if the spacecraft carried the actual studio clock.   

Studio band work is difficult enough when v_rel = 0, thank you.

[hamdani yusuf (OP)]

That would be a seeming paradox, not an actual paradox.

W. V. O. Quine (1962) distinguished between three classes of paradoxes.
https://en.m.wikipedia.org/wiki/Paradox

[alancalverd]

To some extent, this now runs parallel to the "virtual universe" thread.

Any model is a mapping, and the characteristic of mapping is loss of dimension.

Now we have an apparently  complete model of the behavior of clocks, twins, spectral lines or whatever, from relativity. If we map that behavior onto a model where v_rel << c we can, for most practical purposes, ignore the loss of synchronism (using my definition of that word).

But in cases where v_rel → c we cannot accurately construct the behavior of twins, clocks etc from observations made at  v_rel << c by assuming no loss of synchronism.

[hamdani yusuf (OP)]

My favorite are the articles claiming STR does not predict the Sagnac effect, and it's pretty trivial to spot the errors in these papers.  Why does light travel west faster than it does east? Can you explain that in STR terms without violating its premise about the constancy of light speed?

I asked Gemini. does light travel west faster than it does east?

No, the speed of light in a vacuum is constant regardless of the direction it travels, whether west, east, or any other direction. This is a fundamental principle of physics established by the theory of special relativity.

It's true that Earth rotates eastward, and objects on its surface, like airplanes, can travel faster eastward than westward due to this rotation. However, this doesn't affect the speed of light itself. Light travels independently of the motion of the source or observer.

There might be some confusion due to the Sagnac effect, which is a phenomenon observed in rotating reference frames. It predicts a minuscule difference in the travel time of light depending on its direction relative to the rotation. However, this effect is incredibly small and only significant in very precise measurements with extremely sensitive equipment.

For all practical purposes and everyday situations, the speed of light remains constant and independent of direction.

[Halc]

I asked Gemini. does light travel west faster than it does east?

Always a good place to find wrong answers that sound authoritative.

No, the speed of light in a vacuum is constant regardless of the direction it travels, whether west, east, or any other direction. This is a fundamental principle of physics established by the theory of special relativity.

This statement is wrong. The speed of light is posited to be constant only in an inertial frame in Minkowskian spacetime. In such a coordinate system, east is an undefined direction. If you disagree, then relative to the inertial frame of Earth, which direction is east? Why is no star labeled the east star?
'East' has meaning in a rotating reference frame, and Gemini eventually gets to that:

There might be some confusion due to the Sagnac effect, which is a phenomenon observed in rotating reference frames. It predicts a minuscule difference in the travel time of light depending on its direction relative to the rotation.

Confirming my statement. In a rotating frame, light travels west faster than it does east, and only in said rotating frame is east and west defined as a valid direction.

However, this effect is incredibly small and only significant in very precise measurements with extremely sensitive equipment.

With enough angular speed or large enough radius, the ratio of light travel speeds can be arbitrarily high.

For all practical purposes and everyday situations, the speed of light remains constant and independent of direction.

So usage of the effect in airplanes doesn't constitute a practical purpose, according to Gemini.

[hamdani yusuf (OP)]

Quote from: Gemini
For all practical purposes and everyday situations, the speed of light remains constant and independent of direction.

So usage of the effect in airplanes doesn't constitute a practical purpose, according to Gemini.

Is there any example where airplanes usage changes the speed of light?

[alancalverd]

Ring laser gyroscope.
From Wikipedia:

Many tens of thousands of RLGs are operating in inertial navigation systems and have established high accuracy, with better than 0.01?/hour bias uncertainty, and mean time between failures in excess of 60,000 hours.

[hamdani yusuf (OP)]

Ring laser gyroscope.
From Wikipedia:

Many tens of thousands of RLGs are operating in inertial navigation systems and have established high accuracy, with better than 0.01?/hour bias uncertainty, and mean time between failures in excess of 60,000 hours.

Does it confirm that speed of light isn't constant?

[alancalverd]

Depends on what you mean by speed of light! The RLG works on the basis that  the time taken for a photon to get from A back to A via a circular path depends on whether the path itself is rotating.

But the important point here is that, as usual, a chatbot is promulgating  a transparent untruth.

[hamdani yusuf (OP)]

Depends on what you mean by speed of light! The RLG works on the basis that  the time taken for a photon to get from A back to A via a circular path depends on whether the path itself is rotating.

So, in some definitions, speed of light is constant. While in some other definitions, it's not constant?

[hamdani yusuf (OP)]

But the important point here is that, as usual, a chatbot is promulgating  a transparent untruth.

What's usual now may no longer be usual later on.

Outputs of chatbots are determined by their training data. In this case, its mostly text books, and perhaps some encyclopedia.

[alancalverd]

from: alancalverd on 02/03/2024 11:39:39
But the important point here is that, as usual, a chatbot is promulgating  a transparent untruth.

What's usual now may no longer be usual later on.

There is no evidence of the gradual evolution of truth. Politics, religion, philosophy and every other evil known to Man rely on the growth of a convenient and locally profitable consensus that gradually smothers dissent and persuades people to ignore observation.  Goebbels was right.

[hamdani yusuf (OP)]

I'm glad you found one you like. No video is tagged with that name, but I'm guessing the one in post 184.

This one, I added his name in the post.

Why twin's paradox is NOT about acceleration?

Chapters:
00:00 What is the twin's paradox?
00:48 Why acceleration doesn't solve twin's paradox
2:24 Twin's paradox without acceleration (Earth's frame)
4:42 The traveling frame
7:13 My new website - floatheadphysics (ad)
8:48 Earth's frame again - with the flag
11:38 Travelling frame again - with the flag
13:30 The resolution!
14:45 Relativity of simultaneity
17:02 Isn't the root cause the acceleration?
18:20 What do they 'see'?

In this video, we'll intuitively resolve the twin's paradox. This version of the twin's paradox involves no acceleration. And no, you don't need equivalence principle, and you don't need general relativity to solve it. Twin's paradox can be completely solved using special theory of relativity and the correct usage of relativity of simultaneity.

Let's see if anyone has objection to the explanation given in this video, which is an improvement of previous video by the same author, Mahesh Shenoy from Floatheadphysics.

It should show my intention to learn, but somehow you can't see it.
On the other hand, if you are already convinced that your current explanation is the correct one, and the others are wrong, you won't be able to learn.

In the example in the video, the gamma factor is 2, which means the speed is around 0.866c.
In case of another twin travels with the same speed but opposite direction, the relative speed between them will be around 0.9897c, according to relativistic velocity addition. The gamma factor is around 7.

[hamdani yusuf (OP)]

In the comment section of the video, I asked

What if there is another twin travel to the opposite direction with the same speed? And another one in perpendicular direction?

Unfortunately no one has replied.

But there are some positive comments regarding the explanation in the video.

As a 60 year old physicist, I can say that this is the best demonstration of the twin's paradox I have seen, and I saw the first one when I was 15. I also love your enthusiasm. Bravo!

This is by far the best explanation for the twin paradox I?ve seen, and I have watched a lot of YouTube videos on this spanning close to a decade. This holds true for basically all of your videos. Thank you!!

Superb - I am a professor of geometry, and I never saw such a good explanation without drawing a space-time diagram.

Great video. Simultaneity in relativity is often overlooked. Nice explanation of why you can't ignore it. And it was great to highlight that what you measure using scientific apparatus, clocks, rulers etc is not the same thing as what you a see using your eyes or cameras. Nice.

That was such a good experience. I'm simultaneously Happy, impressed, dazzled, and awakened. I understand others comparing this to other explanations, but I want to say this is the first time it's ever really been explained. Your approach of having a conversation and asking all those questions is so incredibly effective. Thank you so much. Special relativity is itself an amazing leap of imagination. And then on top of that solving the paradoxes are a bunch of other giant leaps.

[alancalverd]

. And it was great to highlight that what you measure using scientific apparatus, clocks, rulers etc is not the same thing as what you a see using your eyes or cameras.

Absurd. When did a camera cease being a scientific instrument? How do you read a clock or a ruler without your eyes?

[alancalverd]

What if there is another twin travel to the opposite direction with the same speed? And another one in perpendicular direction?

Direction is irrelevant to time dilatation. What matters is relative velocity, i.e. the vector that describes their rate of separation.

[hamdani yusuf (OP)]

What if there is another twin travel to the opposite direction with the same speed? And another one in perpendicular direction?

Direction is irrelevant to time dilatation. What matters is relative velocity, i.e. the vector that describes their rate of separation.

What do you think about my calculation below?

In the example in the video, the gamma factor is 2, which means the speed is around 0.866c.
In case of another twin travels with the same speed but opposite direction, the relative speed between them will be around 0.9897c, according to relativistic velocity addition. The gamma factor is around 7.