[hamdani yusuf (OP)]

No it doesn't.  In fact, it doesn't mention observation at all since there are no light lines in the picture. If the twin looks at Earth when turning around, he sees the same thing just before and just after the acceleration. The observation only changes in redshift, but no time jump is observed.  What is observed would be physical fact, and nobody regardless of where they are could contest it.

OK. I agree that this is not an observation, which should also consider light transit time. It's just a mental model of physical reality to calculate and predict the outcome. But if these time jumps are ignored, we get the wrong results.
Nevertheless, the reverse time jump is as real (or as unreal) as the forward time jump in the analysis of twin paradox using space-time diagram.

The Wikipedia article also shows some methods to determine how each twin observes the age of the other twin, like by sending signal at a constant interval, say once a year. For example, the journey takes ten years in earth frame, and the time dilation makes the travelling twin to age only eight years. The earth twin sends ten signals and receives only eight. While the travelling twin sends eight signals and receives ten.
This scenario unambiguously tells that travelling twin ages less than stationary twin, from the perspective of both twins. It doesn't matter how many times the travelling twin changes his reference frame, as long as he maintains his speed almost constant during the journey.
The stationary twin sends signals at the constant rate, but receives signals at different rate between outgoing and incoming legs of the journey.

[hamdani yusuf (OP)]

The Wikipedia article also shows some methods to determine how each twin observes the age of the other twin, like by sending signal at a constant interval, say once a year. For example, the journey takes ten years in earth frame, and the time dilation makes the travelling twin to age only eight years. The earth twin sends ten signals and receives only eight. While the travelling twin sends eight signals and receives ten.
This scenario unambiguously tells that travelling twin ages less than stationary twin, from the perspective of both twins. It doesn't matter how many times the travelling twin changes his reference frame, as long as he maintains his speed almost constant during the journey.
The stationary twin sends signals at the constant rate, but receives signals at different rate between outgoing and incoming legs of the journey.

This thought experiment can be used to distinguish between Einstein's theory of relativity and Lorentz' theory of relativity.
IMO, Lorentz' is easier to simulate. It doesn't involve any time jump. But being easier doesn't necessarily mean more accurate.

For time symmetry, let's make the stationary twin send signals to the travelling twin at t= 0.5, 1.5, 2.5, ..., 9.5 years in his frame of reference.
The traveling twin send signals to the stationary twin at t= 0.5, 1.5, 2.5, ..., 7.5 years in his own frame of reference, which is a journey of 10 years in earth time, but only 8 years in his frame of reference.
When does the twins receive the signals from the other twin?

[alancalverd]

It doesn't matter how many times the travelling twin changes his reference frame, as long as he maintains his speed almost constant during the journey.

Something of a selfcontradiction?

[hamdani yusuf (OP)]

It doesn't matter how many times the travelling twin changes his reference frame, as long as he maintains his speed almost constant during the journey.

Something of a selfcontradiction?

Which part contradicts which other parts?
Changing velocity without changing speed can be done by following a circular path, thus change the direction.

[alancalverd]

But that means he is changing from an inertial to an accelerated reference frame. Relativity applies to velocity, not speed.

[hamdani yusuf (OP)]

But that means he is changing from an inertial to an accelerated reference frame. Relativity applies to velocity, not speed.

In time dilation formula, the velocity is squared, which makes it indistinguishable from speed.
How do you think the acceleration affects the aging of the twins?
What's the quantitative difference between changing the direction once and twice?

[alancalverd]

How do you think the acceleration affects the aging of the twins?

If there was never any acceleration, either there is no relative velocity or they were never twins.

[hamdani yusuf (OP)]

How do you think the acceleration affects the aging of the twins?

If there was never any acceleration, either there is no relative velocity or they were never twins.

Does accelerating twin age slower than inertial twin? How much slower is it?

[alancalverd]

See Einstein, A: "On Relativity".

[hamdani yusuf (OP)]

I asked ChatGPT, According to Einstein's "On Relativity", does accelerating twin age slower than inertial twin? How much slower is it?

Yes, according to Einstein?s theory of relativity, the accelerating twin in the famous twin paradox ages more slowly than the inertial twin who stays on Earth. However, the precise calculation of how much slower the accelerating twin ages requires a proper relativistic treatment.

The acceleration during the turnaround does not directly cause time dilation but is necessary to change frames. During the turnaround, the traveling twin briefly exists in a non-inertial frame, which leads to an asymmetry in the twin paradox. However, the net effect on aging is still dominated by the time dilation from the high-speed travel phases.

Conclusion
The accelerating twin ages less than the inertial twin due to the relativistic time dilation effect. The exact amount of aging difference depends on the velocity and duration of the trip but follows the Lorentz factor formula.

It basically says that acceleration effect on aging is negligible compared to the effect from high speed travelling phase.  But in the twin paradox case, somehow it can reverse the effect of time dilation on the stationary twin when observed from the perspective of the travelling twin. In other words, it turns time dilation into time contraction.

[hamdani yusuf (OP)]

The Wikipedia article also shows some methods to determine how each twin observes the age of the other twin, like by sending signal at a constant interval, say once a year. For example, the journey takes ten years in earth frame, and the time dilation makes the travelling twin to age only eight years. The earth twin sends ten signals and receives only eight. While the travelling twin sends eight signals and receives ten.
This scenario unambiguously tells that travelling twin ages less than stationary twin, from the perspective of both twins. It doesn't matter how many times the travelling twin changes his reference frame, as long as he maintains his speed almost constant during the journey.
The stationary twin sends signals at the constant rate, but receives signals at different rate between outgoing and incoming legs of the journey.

This thought experiment can be used to distinguish between Einstein's theory of relativity and Lorentz' theory of relativity.
IMO, Lorentz' is easier to simulate. It doesn't involve any time jump. But being easier doesn't necessarily mean more accurate.

For time symmetry, let's make the stationary twin send signals to the travelling twin at t= 0.5, 1.5, 2.5, ..., 9.5 years in his frame of reference.
The traveling twin send signals to the stationary twin at t= 0.5, 1.5, 2.5, ..., 7.5 years in his own frame of reference, which is a journey of 10 years in earth time, but only 8 years in his frame of reference.
When does the twins receive the signals from the other twin?

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



As usual, horizontal axis represents space while vertical axis represents time.
In left picture, the stationary twin sends light signal every year, starting from t=0.5y. He sends 10 signals in total. The travelling twin only receive 2 signal before he turns around. The other 8 are received during return journey.

In right picture, the travelling twin sends light signal every year in his reference frame, which corresponds to 1.25 years in earth reference because of time dilation. He sends 8 signals in total. The stationary twin only receive 2 signal before half time of the journey period, 1 right at half time, and the other 5 are received after that.

[alancalverd]

It basically says that acceleration effect on aging is negligible

No. It implies that acceleration is essential otherwise there cannot be a relative velocity between twins.

The traffic lights turn green. One car accelerates to a constant velocity, the other stays still. Obviously the distance between them increases with time, but only if the initial acceleration is not zero.

[hamdani yusuf (OP)]

It basically says that acceleration effect on aging is negligible

No. It implies that acceleration is essential otherwise there cannot be a relative velocity between twins.

Read this part.

However, the net effect on aging is still dominated by the time dilation from the high-speed travel phases.

[hamdani yusuf (OP)]

The traffic lights turn green. One car accelerates to a constant velocity, the other stays still. Obviously the distance between them increases with time, but only if the initial acceleration is not zero.

In some explanations, the need for acceleration were removed, and replaced with constantly moving ships, only synchronized their clocks when they are passing nearby.

[alancalverd]

You cannot, by definition, synchronise clocks that are in relative motion. You can set them both to zero as the ships pass, but neither can say that the other is ticking at the same rate, so they are not in sync.

[hamdani yusuf (OP)]

You cannot, by definition, synchronise clocks that are in relative motion. You can set them both to zero as the ships pass, but neither can say that the other is ticking at the same rate, so they are not in sync.

In Einstein's Special Theory of Relativity, each observer sees the other's clock ticks slower than their own.
They only tick at the same rate when they are in the same frame of reference. To avoid unnecessary complication, the clocks were built identically using precise mechanism, such as atomic clock. In the thought experiments, the effect of time dilation are usually chosen to be significantly larger than error margin of the clocks.

[alancalverd]

So no "paradox" if no acceleration. And thanks to Einstein's neat explanation, no paradox anyway.

[hamdani yusuf (OP)]

So no "paradox" if no acceleration. And thanks to Einstein's neat explanation, no paradox anyway.

Congratulation. You might just solved a problem that had caused disagreements among physicists for more than a century.

[hamdani yusuf (OP)]

The Wikipedia article also shows some methods to determine how each twin observes the age of the other twin, like by sending signal at a constant interval, say once a year. For example, the journey takes ten years in earth frame, and the time dilation makes the travelling twin to age only eight years. The earth twin sends ten signals and receives only eight. While the travelling twin sends eight signals and receives ten.
This scenario unambiguously tells that travelling twin ages less than stationary twin, from the perspective of both twins. It doesn't matter how many times the travelling twin changes his reference frame, as long as he maintains his speed almost constant during the journey.
The stationary twin sends signals at the constant rate, but receives signals at different rate between outgoing and incoming legs of the journey.

This thought experiment can be used to distinguish between Einstein's theory of relativity and Lorentz' theory of relativity.
IMO, Lorentz' is easier to simulate. It doesn't involve any time jump. But being easier doesn't necessarily mean more accurate.

For time symmetry, let's make the stationary twin send signals to the travelling twin at t= 0.5, 1.5, 2.5, ..., 9.5 years in his frame of reference.
The traveling twin send signals to the stationary twin at t= 0.5, 1.5, 2.5, ..., 7.5 years in his own frame of reference, which is a journey of 10 years in earth time, but only 8 years in his frame of reference.
When does the twins receive the signals from the other twin?

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



As usual, horizontal axis represents space while vertical axis represents time.
In left picture, the stationary twin sends light signal every year, starting from t=0.5y. He sends 10 signals in total. The travelling twin only receive 2 signal before he turns around. The other 8 are received during return journey.

In right picture, the travelling twin sends light signal every year in his reference frame, which corresponds to 1.25 years in earth reference because of time dilation. He sends 8 signals in total. The stationary twin only receive 2 signal before half time of the journey period, 1 right at half time, and the other 5 are received after that.

In Lorentz' theory of relativity shown by the diagrams, the stationary clock ticks faster than any other moving clocks, regardless of their directions. There is no constraints about symmetry, regarding the reference frame of the observers.
On the other hand, constraints about symmetry of relativistic effects between relatively moving observers is postulated in Einstein's Special Theory of Relativity. To produce asymmetric result like in the case of twin/clock paradox, there must be a symmetry breaker somewhere down the line of reasoning in the thought experiment. Currently mainstream physics explanation, like shown in Wikipedia article, introduces time jump during turn around period, which effectively reverse the effect of time dilation of stationary twin in the perspective of traveling twin into time contraction.
How can this model be demonstrated in space-time diagrams to show the sequence of events in relativistic journey of the travelling twin when it's tracked with signals exchange?

[alancalverd]

Congratulation. You might just solved a problem that had caused disagreements among physicists for more than a century.

God knows what they disagree about. The theory of relativity predicts a  phenomenon that is supported by measurement, which is the way of physics. Anything else is philosophy.