# Trying to understand The twin paradox for a year and a half

#### Alchemy One

Joined Oct 5, 2019
217
The following is the subject of moving frames at relativistic speed.

I am certain that most of serious science folks have heard of the whole thing about the Twin Paradox. So it is not necessary to describe what it is about so I will get to the meat of it.

The following reasons have been ruled out as to why one twin ages more than the other.

1. One was stationary and the other wasn't. Ruled out.
2. One was accelerating and the other wasn't. Ruled out.
3. One of them moved in two frames. Ruled out.
4. Doppler effect. Ruled out.
5. Depends on who is doing the measurment. Ruled out and out of context.

Explanation:
1. There are no preferred frame of reference as to who is stationary and who is moving. Everyone is stationary in their frame. Moving clocks runs slower, and therefore your clock always runs slower than mine even if you claim I am the one that is moving, well certainly you do. The traveling twin b begs to differe. He is stationary he claims and he has the right. I know you and I also don't agree with him, after all you and I are here stationary. Sure.

2. The traveling twin accelerted, decelerated twice, twice outward and twice inward. Acceleration has been fully debunked. You just have to google and read the twin paradox and all the rest along with all the experiments done.
3. The moving twin changed frames. It looks like it says something. It has no meaning. At which frame his clock began to run even more slow. It was moving slow from the moment he left according to the so called stationary twin. Accounting for 2 above also, to the traveling twin the stationary one changed frames. The first frame the earth was moving away and the second frame he was coming towards him. I.e. He saw earth moving away and coming towards him while he was stationary. Regardless of that changing frame is just that, something to say.

4. Doppler effect? The worse of all reasoning. It simply describes the objects direction with respect to the other and nothing else.

5. Who is doing the measurement...? someone was trying to pawn that off somewhere just to say something.

WHY DID THE TRAVELING TWIN UP ON RETURNING BACK TO EARTH AGED LESS?
Do you have another one you can throw in which I have not found anywhere yet? I have also read plenty other ones that make it look like they are saying something else other than what I have already covered. I am sorry, I have done plenty leg work and I will see through it and you should be glad that I do, so you can also toss it. It means someone pawned the wrong stuff just like they did me at least for awhile until I saw through it.
I have read the long long narrative on Wikipedia and elsewhere.... and you have to look very attentively to see that you are left empty handed and robbed of your time selling the appearanc of some goods. Just see if you are giving the above reasons but using different words... look closely.

[ I should throw this in just for the sake of being there to be read. It is sort of assumed subconsciously that when one hears this statement: " Moving clock runs slower" aside from seeing the other clock moving and not you because you of course don't see your clock run slow unless the battery is awfully low, the picture that comes to mind without consciously being aware is that the clock is moving away from you. No. no no. It is any clock that its position its distance changes from you no matter of the direction, so long as there is change in distance between you two, both see the other's clock run slower. And it is the other that is moving and not you].

[ Please make a note that the position of both twins are biased. Therefore neither one can draw worldline for the other. Therefore you can not draw worldline for them either. If you do then you have to explain where are you, what is your position, where are you looking from? who called on you to show each twin why you know more than they do?]

Last edited:

#### Ya’akov

Joined Jan 27, 2019
6,551
Here is an explanation, for what it is worth. It is hard to understand unless you abandon intuition since it is entirely non-intuit i’ve concerning our everyday conceptions of spacetime. I think the key bit is that relativity is relative but not symmetrical.

#### BobTPH

Joined Jun 5, 2013
5,743
Although I agree that acceleration is not the “explanation“ of the twin paradox, it is the explanation of why people think it is a paradox. The assumption is that the twins are equivalent and thus they should each see the events the same way. But that is not true. One is accelerated and the other is not. So the assumption that leads to the paradox is false.

#### WBahn

Joined Mar 31, 2012
27,389

#### dcbingaman

Joined Jun 30, 2021
720
I don't think we can ignore 'who is accelerating and who is not'. The effects of acceleration are very real and in an accelerating frame of reference; imagine playing tennis on a large interstellar space ship that is accelerating at say 1G, you cannot play the tennis game in that frame but in a constant velocity ship you can and you cannot even determine your velocity with any scientific experiment on the ship. I agree that at constant velocities of two bodies, there is no time or space warping between them except as what they experience when looking at the other ones clocks and lengths in the direction of travel both consider the other moving, this is not a contradiction because until they come back together at a common location they are both allowed to do this. But they cannot actually agree on the time/position until one of them (or both) changes that velocity allowing them to eventually share the same velocity and position. Until that point it is meaningless to discuss who is or is not 'moving'. But whoever experiences the acceleration effects is the one who is changing in velocity and is thus the one who will be considered 'moving with space and time dilation'. Thus there is no 'twin paradox' at all when viewed in this way.

Last edited:

#### dcbingaman

Joined Jun 30, 2021
720
This always raised the question in my mind: When you are 'accelerating' you know it is happening, you can feel the forces pushing you back into your seat as you accelerate that Ferrari from 0 to 120 in a few seconds. But how does the Ferrari and you 'know' that you are the one accelerating and not the rest of the universe in the opposite direction? Can't you just as easily think that the earth's surface is the one accelerating under the car away from you in the opposite direction is the one accelerating? It is a rhetorical question because physics informs you in no uncertain terms that you and the Ferrari are the ones accelerating.

#### dcbingaman

Joined Jun 30, 2021
720
Alchemy One
[ I should throw this in just for the sake of being there to be read. It is sort of assumed subconsciously that when one hears this statement: " Moving clock runs slower" aside from seeing the other clock moving and not you because you of course don't see your clock run slow unless the battery is awfully low, the picture that comes to mind without consciously being aware is that the clock is moving away from you. No. no no. It is any clock that its position its distance changes from you no matter of the direction, so long as there is change in distance between you two, both see the other's clock run slower. And it is the other that is moving and not you]

'Moving clocks run slower'. The statement is false, moving clocks do not run slower, they only appear to do so with respect to another observer. All we know is that two observers are moving at constant velocity and until one of them changes speed and direction and comes to 'rest' with respect to the other the time difference between their clocks is not relevant. But when they finally come together only then can they compare their clocks. Special relativity cannot exist in the absence of general relativity. Being that general relativity deals with gravitational fields and bodies changing speed and direction (velocity) (equivalent to a gravitational field), these are the only ones that experience such fields, there is no paradox.

#### WBahn

Joined Mar 31, 2012
27,389
This always raised the question in my mind: When you are 'accelerating' you know it is happening, you can feel the forces pushing you back into your seat as you accelerate that Ferrari from 0 to 120 in a few seconds. But how does the Ferrari and you 'know' that you are the one accelerating and not the rest of the universe in the opposite direction? Can't you just as easily think that the earth's surface is the one accelerating under the car away from you in the opposite direction is the one accelerating? It is a rhetorical question because physics informs you in no uncertain terms that you and the Ferrari are the ones accelerating.
Due to the equivalence principle, which says that inertial and gravitational masses are indistinguishable, a person in a car that is accelerating could claim that they are not accelerating, but merely that the gravitational field they are in has changed. Whichever they choose should have no effect on the results of any properly formed calculations.

In the classic twin paradox, that the situations are not truly symmetric is obvious. But what about a scenario in which the two situations are symmetric. Imagine two spaceships that are traveling in large circles in space at very high speed tangential to each other. One is traveling clockwise and the other counter-clockwise such that when they come together at the tangent point they have zero speed relative to each other and can briefly dock (or at least exchange information) and both be in the same intertial frame by briefly cutting their thrusters. Which one is traveling clockwise and which is traveling counter-clockwise is a meaningless distinction since it depends on the viewpoint of the observer. None-the-less, throughout much of the course of their travels the two spacecraft have very high relative velocities and thus the other craft's clock should run slower. But does not symmetry demand that, when they come together, that their clocks must agree? I've never see a treatment of this (though I'm sure it's been done). Since both are non-internal reference frames, I'm pretty sure that this problem is beyond special relativity and must be treated via general relativity.

#### Alchemy One

Joined Oct 5, 2019
217
Alchemy One
[ I should throw this in just for the sake of being there to be read. It is sort of assumed subconsciously that when one hears this statement: " Moving clock runs slower" aside from seeing the other clock moving and not you because you of course don't see your clock run slow unless the battery is awfully low, the picture that comes to mind without consciously being aware is that the clock is moving away from you. No. no no. It is any clock that its position its distance changes from you no matter of the direction, so long as there is change in distance between you two, both see the other's clock run slower. And it is the other that is moving and not you]

'Moving clocks run slower'. The statement is false, moving clocks do not run slower, they only appear to do so with respect to another observer. All we know is that two observers are moving at constant velocity and until one of them changes speed and direction and comes to 'rest' with respect to the other the time difference between their clocks is not relevant. But when they finally come together only then can they compare their clocks. Special relativity cannot exist in the absence of general relativity. Being that general relativity deals with gravitational fields and bodies changing speed and direction (velocity) (equivalent to a gravitational field), these are the only ones that experience such fields, there is no paradox.
========================
You as an observer is not needed to say it appears to run slower.
Time doesn't appear to slow down or stop in black hole. Moving clock ticks slower is not a relationship to other objects. Other objects just seem to notice and their perception therefore is false and that is obvious. Interesting?

Lets make it better.
Since nobody goes here, I guess someone someday just might so I will volunteer to bring it up.
Lets do it, two more scienarios.
1. Moving twin age the same amount as the stationary one.
2. Moving twin age more than the stationary one.

#### Alchemy One

Joined Oct 5, 2019
217
Although I agree that acceleration is not the “explanation“ of the twin paradox, it is the explanation of why people think it is a paradox. The assumption is that the twins are equivalent and thus they should each see the events the same way. But that is not true. One is accelerated and the other is not. So the assumption that leads to the paradox is false.
=========================
Lets do it, two more scienarios.
1. Moving twin age the same amount as the stationary one.
2. Moving twin age more than the stationary one.

#### Alchemy One

Joined Oct 5, 2019
217
Here is an explanation, for what it is worth. It is hard to understand unless you abandon intuition since it is entirely non-intuit i’ve concerning our everyday conceptions of spacetime. I think the key bit is that relativity is relative but not symmetrical.
==============================
May I?
Lets do it, two more scienarios.
1. Moving twin age the same amount as the stationary one.
2. Moving twin age more than the stationary one.

#### dcbingaman

Joined Jun 30, 2021
720
========================
You as an observer is not needed to say it appears to run slower.
Time doesn't appear to slow down or stop in black hole. Moving clock ticks slower is not a relationship to other objects. Other objects just seem to notice and their perception therefore is false and that is obvious. Interesting?

Lets make it better.
Since nobody goes here, I guess someone someday just might so I will volunteer to bring it up.
Lets do it, two more scienarios.
1. Moving twin age the same amount as the stationary one.
2. Moving twin age more than the stationary one.
'You as an observer is not needed to say it appears to run slower.'

Experiments require observers. How can we say that another clock is running slower if we don't have an observer to observe it?

'Moving clock ticks slower is not a relationship to other objects.'

Every clock's accuracy is measured with respect to another clock in order to verify if it is running 'faster' or 'slower'. I do this all the time with clocks in my house, I compare them to say the GPS time, to correct them if they are running to fast or to slow.

If it is not a relationship to other objects (observers) then what is the meaning of a clock running slower? It reminds me of saying that 'all the clocks in the entire universe are running twice as fast as what they where yesterday'. Where a 'clock' in this case is any physical experiment you can do on any system that results in a time passage measurement?
There is no experiment you could do to 'verify' that all the clocks in the universe are running faster say than a day ago.
If I can't perform an experiment to verify something, how can I even know that it is true?

I appreciate your response. Not trying to hammer it, just trying to understand what you are saying.

#### dcbingaman

Joined Jun 30, 2021
720
=========================
Lets do it, two more scienarios.
1. Moving twin age the same amount as the stationary one.
2. Moving twin age more than the stationary one.
In both these scenarios we are violating Relativity. It is only the accelerating object that has the higher speed and has a slower running clock with respect to someone who is 'not moving'. The twin in the spaceship has a powerful rocket engine that is causing him to increase his velocity along with his total energy and then has to use the same rocket engine to slow down his pace and stop back at the earth after his trip. The twin on earth feels none of these forces or changes in total energy.
A good example is particle accelerators where we can increase the life time of a given 'particle' by accelerating it up to close to c. It is always the particle that experiences the acceleration and thus has a slower clock than the scientist sitting in the lab observing it and the particle is the one who's lifetime increases by the factor
1/sqrt(1-v^2/c^2). This makes sense from General relativity, it is the particle that feels the acceleration and as WBhan pointed out, can consider it the same as being in a strong gravitational field (equivalency principle). It is not the scientist running the particle accelerator?

Another way of saying it: It is the particle that experiences the 'force' of the magnetic/electric field and gains energy from it that is the one who is accelerating being work is just Force applied over a distance.

Last edited:

#### dcbingaman

Joined Jun 30, 2021
720
Due to the equivalence principle, which says that inertial and gravitational masses are indistinguishable, a person in a car that is accelerating could claim that they are not accelerating, but merely that the gravitational field they are in has changed. Whichever they choose should have no effect on the results of any properly formed calculations.

In the classic twin paradox, that the situations are not truly symmetric is obvious. But what about a scenario in which the two situations are symmetric. Imagine two spaceships that are traveling in large circles in space at very high speed tangential to each other. One is traveling clockwise and the other counter-clockwise such that when they come together at the tangent point they have zero speed relative to each other and can briefly dock (or at least exchange information) and both be in the same intertial frame by briefly cutting their thrusters. Which one is traveling clockwise and which is traveling counter-clockwise is a meaningless distinction since it depends on the viewpoint of the observer. None-the-less, throughout much of the course of their travels the two spacecraft have very high relative velocities and thus the other craft's clock should run slower. But does not symmetry demand that, when they come together, that their clocks must agree? I've never see a treatment of this (though I'm sure it's been done). Since both are non-internal reference frames, I'm pretty sure that this problem is beyond special relativity and must be treated via general relativity.
That is an interesting question. Personally I feel if both spaceships experience the same acceleration forces (or gravity equivalences) for the same 'duration' of time (this seems like an oxymoron as I am trying to measure distance and time (the two entities that are changing) the two entities that are already not stable (grr), when they come back together to measure their clocks, they will still be synchronized in this case. I don't feel the direction of the acceleration is of any importance but only the magnitudes involved. But acceleration is nothing more than how much the distance is covered per unit of time per unit of time but that involves both distance and time which are themselves changing! It seems like a reference back to itself being the things we are trying to find the difference of are based themselves on the same quantities! What a dilemma!

Last edited:

#### dcbingaman

Joined Jun 30, 2021
720
Due to the equivalence principle, which says that inertial and gravitational masses are indistinguishable, a person in a car that is accelerating could claim that they are not accelerating, but merely that the gravitational field they are in has changed. Whichever they choose should have no effect on the results of any properly formed calculations.

In the classic twin paradox, that the situations are not truly symmetric is obvious. But what about a scenario in which the two situations are symmetric. Imagine two spaceships that are traveling in large circles in space at very high speed tangential to each other. One is traveling clockwise and the other counter-clockwise such that when they come together at the tangent point they have zero speed relative to each other and can briefly dock (or at least exchange information) and both be in the same intertial frame by briefly cutting their thrusters. Which one is traveling clockwise and which is traveling counter-clockwise is a meaningless distinction since it depends on the viewpoint of the observer. None-the-less, throughout much of the course of their travels the two spacecraft have very high relative velocities and thus the other craft's clock should run slower. But does not symmetry demand that, when they come together, that their clocks must agree? I've never see a treatment of this (though I'm sure it's been done). Since both are non-internal reference frames, I'm pretty sure that this problem is beyond special relativity and must be treated via general relativity.
Maybe a better way to measure space/time effects on both ships would be to measure how much energy is expended by the rockets and thrusters that are keeping them on these non-constant velocity paths. Assume for argument both ships have identical rockets and both ships have 100% efficient rockets and that both ships do not enter any substantial gravitational fields (with the exception of the ones self generated). If the energy consumption of the two rockets is identical when they come back together, then the space/time dilations should also be the same? I am stating it as a question because at this point I am definitely not sure of my own answer.

#### WBahn

Joined Mar 31, 2012
27,389
Maybe a better way to measure space/time effects on both ships would be to measure how much energy is expended by the rockets and thrusters that are keeping them on these non-constant velocity paths. Assume for argument both ships have identical rockets and both ships have 100% efficient rockets and that both ships do not enter any substantial gravitational fields (with the exception of the ones self generated). If the energy consumption of the two rockets is identical when they come back together, then the space/time dilations should also be the same? I am stating it as a question because at this point I am definitely not sure of my own answer.
I don't think that is a safe assumption. Clearly the two ships could tie a string between them and then fly on identical profiles effectively as one ship and the two clocks would obviously be synched. But they could also fly radically different profiles and I don't think the argument total energy consumption somehow equates to degree of space/time dilation stands on its own. For instance, one could boost out in a straight line at high accel up to a high speed and then coast for a long time, then boost again at high speed to turn around, and then boost a final time to come to rest at the original location. The second could just boost continuously at low accel in a relatively small circle around the original location. The amount of time coasting is simply adjusted so that, when the first ship comes to rest relative to the second ship they have both used the same amount of fuel. This essentially reduces to the original twin paradox problem.

Last edited:

#### Alchemy One

Joined Oct 5, 2019
217
'You as an observer is not needed to say it appears to run slower.'

Experiments require observers. How can we say that another clock is running slower if we don't have an observer to observe it?

'Moving clock ticks slower is not a relationship to other objects.'

Every clock's accuracy is measured with respect to another clock in order to verify if it is running 'faster' or 'slower'. I do this all the time with clocks in my house, I compare them to say the GPS time, to correct them if they are running to fast or to slow.

If it is not a relationship to other objects (observers) then what is the meaning of a clock running slower? It reminds me of saying that 'all the clocks in the entire universe are running twice as fast as what they where yesterday'. Where a 'clock' in this case is any physical experiment you can do on any system that results in a time passage measurement?
There is no experiment you could do to 'verify' that all the clocks in the universe are running faster say than a day ago.
If I can't perform an experiment to verify something, how can I even know that it is true?

I appreciate your response. Not trying to hammer it, just trying to understand what you are saying.
===============================
The twin flying away sees the supposed stationary's clock of his twin on earth to run slower than his, no matter which direction he moves..... so why he is surprised when he arriving on earth finds out he was wrong. He is a nut first to question his own observation and worse yet finds out it is false and that it was his own clock that was running slower.
I agree with you.

#### BobTPH

Joined Jun 5, 2013
5,743
===============================
The twin flying away sees the supposed stationary's clock of his twin on earth to run slower than his, no matter which direction he moves..... so why he is surprised when he arriving on earth finds out he was wrong. He is a nut first to question his own observation and worse yet finds out it is false and that it was his own clock that was running slower.
I agree with you.
No, the twin flying away sees the other clock running slow, and when flying back he sees it running fast. This is why we have red shift and blue shift.

#### WBahn

Joined Mar 31, 2012
27,389
No, the twin flying away sees the other clock running slow, and when flying back he sees it running fast. This is why we have red shift and blue shift.
Red and blue shift are not due to relativity or relativistic effects. Time dilation doesn't matter whether the moving frame is moving toward you are away from you. The relevant factor is (v/c)^2,

#### BobTPH

Joined Jun 5, 2013
5,743
Neither did the statement I was responding to. It was about how one would observe a clock if moving relative to the the clock.