[Yahya (OP)]

is the twin paradox real ? is there any experiment of two twins one traveling at high speed and one on earth at rest aging differently ?

[Demolitiondaley]

is the twin paradox real ? is there any experiment of two twins one traveling at high speed and one on earth at rest aging differently ?

This has never been experimented in real life, we don't have the technology to put a person in a craft that would reach the near to speed of light necessary to observe a difference in ageing of the twins.

[geordief]

[quote author=Yahya A. Sharif


This has never been experimented in real life, we don't have the technology to put a person in a craft that would reach the near to speed of light necessary to observe a difference in ageing of the twins.

How would one verify quantitatively that one twin had indeed aged more than the other?

Would it not be enough to simply stipulate that each twin carry a clock?

Comparing clocks would show that one had aged more than the other?

I think this has been done routinely with astronauts in the Space Station.

One of the astronauts might have a twin on the ground if that made the experiment seem more convincing

[Colin2B]

Experiments have been done with moving atomic clocks.

[evan_au]

We often think of the twin paradox as a result of special relativity, where one twin accelerates for a long time, then turns around and comes back, reaching very high speeds in between (close to the speed of light).

However, there is another twin paradox that comes about through general relativity, where one twin climbs farther out of a gravitational well, and then returns. This experiment has been done with very accurate aluminium-ion clocks at NIST.

See: https://www.nist.gov/news-events/news/2010/09/nist-pair-aluminum-atomic-clocks-reveal-einsteins-relativity-personal-scale

[PhysBang]

Not a paradox

[hamdani yusuf]

[quote author=Yahya A. Sharif


This has never been experimented in real life, we don't have the technology to put a person in a craft that would reach the near to speed of light necessary to observe a difference in ageing of the twins.

How would one verify quantitatively that one twin had indeed aged more than the other?

Would it not be enough to simply stipulate that each twin carry a clock?

Comparing clocks would show that one had aged more than the other?

I think this has been done routinely with astronauts in the Space Station.

One of the astronauts might have a twin on the ground if that made the experiment seem more convincing

An astronaut actually has a twin stay on earth.
https://en.wikipedia.org/wiki/Scott_Kelly_(astronaut)
https://en.wikipedia.org/wiki/Mark_Kelly

[geordief]

[quote author=Yahya A. Sharif


This has never been experimented in real life, we don't have the technology to put a person in a craft that would reach the near to speed of light necessary to observe a difference in ageing of the twins.

How would one verify quantitatively that one twin had indeed aged more than the other?

Would it not be enough to simply stipulate that each twin carry a clock?

Comparing clocks would show that one had aged more than the other?

I think this has been done routinely with astronauts in the Space Station.

One of the astronauts might have a twin on the ground if that made the experiment seem more convincing

An astronaut actually has a twin stay on earth.
https://en.wikipedia.org/wiki/Scott_Kelly_(astronaut)
https://en.wikipedia.org/wiki/Mark_Kelly

Very good 

[CPT ArkAngel]

Within special relativity, it is a paradox. All explanations within the frame of SR alone are wrong because there is no key to differentiate the twins. The change is associated to the twin in the rocket by a purely arbitrary a priori choice. There are no explanations concerning acceleration and inertia in SR. It is a postulate (a choice, a belief). With GR, the twin feeling the acceleration of its inertial frame is linked to the increase in gravity potential and gives a first confirmation beyond the basic postulate of SR with the Equivalence principle. In Special Relativity, the acceleration is entirely reciprocal for both twins. Any explanation stating it is a matter of coordinates just differentiates artificially the twins from the beginning...

[evan_au]

I was listening to a podcast Introduction to Relativity with Anthony Aguirre. He had an interesting analogy on the twin paradox, that went something like this:

The twin paradox is like going to the gym. You can slow down aging, but you have to work really hard - accelerate quickly and move at high speeds. Your twin who just stays at home and sits on the lounge ages faster.

http://7thavenueproject.com/post/110697301080/general-relativity-introduction-pt1
I've downloaded part 2 to listen later...

[Yahya (OP)]

I was listening to a podcast Introduction to Relativity with Anthony Aguirre. He had an interesting analogy on the twin paradox, that went something like this:
The twin paradox is like going to the gym. You can slow down aging, but you have to work really hard - accelerate quickly and move at high speeds. Your twin who just stays at home and sits on the lounge ages faster.

I do not think it's useful . if my body is capable to age a certain degree each year  ,and I spend 10 years  it will age this certain degree everywhere when these ten years elapse , if the other twin spent 40 years it just  means  he spent most of his lifetime! and does not mean you slow down aging , the traveling twin will come to find his on -earth twin had his grandchildren while he only just got married! and enjoyed  40 years  while he only enjoyed 10 years supposing he had everything he needed in his spaceship.

[PhysBang]

Within special relativity, it is a paradox.

No. Anyone who says this merely fails to understand special relativity.

All explanations within the frame of SR alone are wrong because there is no key to differentiate the twins.

Except that there is: one twin remains at rest in a single system of coordinates that is an inertial reference frame that covers all events and another twin can only be described using a series of at least two systems of coordinates that are inertial reference frame and this series either does not cover all events or covers events in multiple ways that are inconsistent with the final system of coordinates. This is explained very well in most introductory textbooks on contemporary relativity theory. For example, see Bernard Schutz's textbook.

The change is associated to the twin in the rocket by a purely arbitrary a priori choice. There are no explanations concerning acceleration and inertia in SR.

Except that there are: the frame of reference of SR is an inertial frame of reference, i.e. a frame of reference in which Newtonian Mechanics holds to a first approximation.

With GR, the twin feeling the acceleration of its inertial frame is linked to the increase in gravity potential and gives a first confirmation beyond the basic postulate of SR with the Equivalence principle.

You are welcome to calculate the amount of this that effects the twin, it will not match that found from purely SR effects.

In Special Relativity, the acceleration is entirely reciprocal for both twins. Any explanation stating it is a matter of coordinates just differentiates artificially the twins from the beginning...

The twins are differentiated from the beginning because of what is given in the scenario: one turns around. In order to describe this in SR, one has to use momentarily co-moving reference frames to describe reference frames that co-move with that twin, just like one would do for any object that changes course in elementary SR.

[CPT ArkAngel]

You fell in the trap. SR is not just an add on to Newtonian mechanics, it is the start of a new theory. The choice is arbitrary because there is no explanation, it is just an a priori convention. With SR alone, you cannot really explain why the accelerating frame will have a slower time. This is a mathematical artefact due to the choice of coordinates based on a postulate. It is not because it is a right guess that it is not a guess, even though it made sense... Without an explanation of inertia (which is leading to gravity), you are stuck with a postulate... This is why Einstein worked so hard on GR after SR.

Einstein could have chosen the twin in the rocket to age faster than the other twin and it would have made perfect mathematical sense in the context of the speed limit of C. But evidently, he chose the non accelerating twin to have a constant time rate because it was intuitively right.

[PhysBang]

You fell in the trap.

Yes, the trap of reading textbooks on this subject that go into this in great detail. If you want to call that a "trap" then I recommend that you avoid all reading.

SR is not just an add on to Newtonian mechanics, it is the start of a new theory.

At this point I will point readers who do not worry about falling into a "trap" to take a look at the actual theory of SR. Einstein wrote as the very first step of SR: "Let us take a system of co-ordinates in which the equations of Newtonian mechanics hold good." (Note the footnote, too.)

http://www.fourmilab.ch/etexts/einstein/specrel/www/

The choice is arbitrary because there is no explanation, it is just an a priori convention. With SR alone, you cannot really explain why the accelerating frame will have a slower time. This is a mathematical artefact due to the choice of coordinates based on a postulate. It is not because it is a right guess that it is not a guess, even though it made sense... Without an explanation of inertia (which is leading to gravity), you are stuck with a postulate... This is why Einstein worked so hard on GR after SR.

While this may have been a motivation for EInstein (citation?) it doesn't change the fact that there is a reason for the difference in SR: there is no one inertial reference frame in which one of the twins can be described as being at rest.

Einstein could have chosen the twin in the rocket to age faster than the other twin and it would have made perfect mathematical sense in the context of the speed limit of C. But evidently, he chose the non accelerating twin to have a constant time rate because it was intuitively right.

No, there is no choice here because the mathematics are quite strict. Only if one ignores the mathematics of SR can one imagine that there is some sort of choice.

[hamdani yusuf]

What do you think about this explanation?

[PhysBang]

Excellent video.

[CPT ArkAngel]

You totally missed my point. SR is born out of two new paradigms: there is no ether and an there is an absolute speed limit. All this in regards to principles of relativity. This breaks Newtonian mechanics.

I`ve been reading about this for more than 30 years... The proof offered is a circular reasoning, they just forget to look for their tail, even though they are chasing it. The only thing separating the twins is the acceleration, not the coordinates. The coordinates are chosen in regards of the acceleration, nothing else. Thus, the key is in the acceleration as Einstein pointed out! There is nothing preventing you to switch your choice of coordinates on the accelerating frame and making total abstraction of who is feeling the acceleration. This is my point. (unless you can explain how the acceleration produces a variable relative time rate!)

[yor_on]

Nist clocks can do a 'Twin experiment' using elevations and gravity. Starting by two atomic clocks being synchronized (same time) at a same elevation (gravitational potential) to then lifting up one of the clock, later returning it to a same position as it was before lifted up. The clocks will now no longer be synchronized..

[yor_on]

Sorry Colin, missed your comment, but you're your level headed usual :) And as most times we seem to be in agreement. And PhysBang, good to have you back here, we do need you.

[guest4091]

You totally missed my point. SR is born out of two new paradigms: there is no ether and an there is an absolute speed limit. All this in regards to principles of relativity. This breaks Newtonian mechanics.

I`ve been reading about this for more than 30 years... The proof offered is a circular reasoning, they just forget to look for their tail, even though they are chasing it. The only thing separating the twins is the acceleration, not the coordinates. The coordinates are chosen in regards of the acceleration, nothing else. Thus, the key is in the acceleration as Einstein pointed out! There is nothing preventing you to switch your choice of coordinates on the accelerating frame and making total abstraction of who is feeling the acceleration. This is my point. (unless you can explain how the acceleration produces a variable relative time rate!)

Here is an example with both twins changing course. Acceleration does not determine who is younger. Notice the gamma factor is a function of speed, v/c!
https://app.box.com/s/c8yshj90l3c2eixu13cpkge8w53304cm