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# Time and the 'Twin Paradox"

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Time and the twin paradox by Alan McDougall

Nothing is really as it seems to us and all things are subjective to the observer. Everything is relative to each person from the viewpoint.

Comparative readings, of two almost unimaginably accurate precision atomic clocks located on fast moving spacecraft and airplanes and on earth, have detected this strange skewing of time and proved Einstein’s theory of relativity to be fact.

Stop all the clocks in the universe and movement will continue unaffected.

Stop all movement and the illusion we call time will stop and nothing ever happen again.

As an object approached the speed of light it becomes more and compressed (It occupies less and less space), distorts the fabric of space time and time slows on the speeding object when compared to an object stationary state, it left at its source.

Let the Object equate to a spaceship if you like.

Time is much like an elastic string which can only be stretched in one direction namely; into the future.

The twin paradox describes what happens. Twins; One boards a spacecraft that accelerates to near light speed, on say a voyage to Alpha Centauri, some four light years from earth.

The other remains on the home planet. Ten years later the bother who went to Alpha Centauri returns having aged only "one subjective year" because time has moved slower for him, “relative” to his brother who remained on the home planet, where time moved at the "normal rate"

Why and how did this ageing difference happen?

Why has the spaceman one brother become twenty years younger than his brother who remained at home? Alternatively, the reverse if you like!

There is no absolute universal time, time moves differently from one object to the next and in one location to the next according to its "gravity mass and density" Condense the matter on an object, into smaller and "smaller volume" and you alter gravity and the flow of time on its surface. This is the reason that time stops in a black hole of infinite density

Note; this will really happen if we develop near light speed space vehicles

A year of subjective time has passed for the twin on the spaceship, when compared to twenty year older brother who has somehow aged at a 1/20 ratio. The brother who remained at home is a grey haired old man of say 65 and his returning brother just one year older at 26 years of age

An enigmatic paradox but absolutely true and real, an exciting, but far distant use of this effect is the real possibility of reaching nearly any moment in the future.

Given enough speed and enormous energy, one could reach the Olympic Games of the year C.E. 3108, in a matter of a few subjective days or even return a million years later only older be maybe a decade or so older.

Backward time travel to the past, is a fantasy and if this were possible, a person could do the impossible and go back and murder their younger self.

There is no universal now! Events are simply there, hanging in space-time Time cannot exist without space and space cannot exist without time.

We only conceive of time by the movement of an object through space, so space and time are different realities of the same thing and can only exist where movement is allowed. For example, stop all movement in the universe and you have stopped time, have you not? Therefore, there is really only one reality all bound up into and combined into what I call "spacetimemovement."

There is simply no universal now and each moment is unique to the observer

By Alan McDougall 29/8/2007

© Copyright Alan Grant McDougall 2013

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The "Twin Paradox" is a fallacy, as it presumes an objective frame of reference exists relative to both twins. This is not true.

The twin leaving Earth would, in his/her own frame of reference, appear to be at rest while the twin on Earth (and Earth) moved at relativistic speed. Thus we could calculate that this Earth-bound twin only aged one year during their separation.

The only way a paradox could exist would be within an environment which provided a common frame of reference without relative motion - such as a gravity well.

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For example, stop all movement in the universe and you have stopped time, have you not?

I think not. I think time would continue, there would just be no movement within the continuing elapsing of time.

The twin leaving Earth would, in his/her own frame of reference, appear to be at rest while the twin on Earth (and Earth) moved at relativistic speed. Thus we could calculate that this Earth-bound twin only aged one year during their separation.

Only in relative uniform motion will both observers observe each other's clocks to be ticking slower.

This result appears puzzling because each twin sees the other twin as moving, and so, according to an incorrect naive application of time dilation and the principle of relativity, each should paradoxically find the other to have aged more slowly. However, this scenario can be resolved within the standard framework of special relativity: the travelling twin's trajectory involves two different inertial frames, one for the outbound journey and one for the inbound journey, and so there is no symmetry between the spacetime paths of the two twins.
The twin paradox has been verified experimentally by precise measurements of atomic clocks flown in aircraft and satellites. For example, gravitational time dilation and special relativity together have been used to explain the Hafele–Keating experiment.[A 1][A 2] It was also confirmed in particle accelerators by measuring time dilation of circulating particle beams.[A 3]

http://en.wikipedia.org/wiki/Twin_paradox

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Only in relative uniform motion will both observers observe each other's clocks to be ticking slower.

So, according to Wiki which twin is "the travelling twin"?

Because, in accordance with relativity and each twin's unique frame of reference both are.

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So, according to Wiki which twin is "the travelling twin"?

Because, in accordance with relativity and each twin's unique frame of reference both are.

The twin in the space ship is the travelling twin.

Max von Laue argued in 1913 that since the traveling twin must be in two separate inertial frames, one on the way out and another on the way back, this frame switch is the reason for the aging difference, not the acceleration per se.

http://en.wikipedia.org/wiki/Twin_paradox#Difference_in_elapsed_time_as_a_result_of_differences_in_twins.27_spacetime_paths

It can't be argued that the twins paradox is not a real phenomena. See my second quote from Wiki in my post #3.

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The "Twin Paradox" is a fallacy, as it presumes an objective frame of reference exists relative to both twins. This is not true.

The twin leaving Earth would, in his/her own frame of reference, appear to be at rest while the twin on Earth (and Earth) moved at relativistic speed. Thus we could calculate that this Earth-bound twin only aged one year during their separation.

The only way a paradox could exist would be within an environment which provided a common frame of reference without relative motion - such as a gravity well.

The twin paradox is not a fallacy, but a true concept of how time differs between objects receding from each other at close to C.You can take any one of the two objects (Planet Earth or Spacecraft) as reference points relative to the other. Any movement between two objects , such as one approaching the other, with one relatively stationary, alters the rate of linear time flow on the moving objects.

Take this example, stand stationary with your body held fastened to a wall, so that it cannot move. Then ask a friend to run towards you or away from you say from a 100 yards or so. Time in his frame of reference will flow slightly slower than it does from your stationary frame of reference. Thus your friend becomes a tiny bit younger than you albeit almost infinitesimal. But this sums up the truth of the twin paradox and one can extrapolate that to a spacecraft leaving earth at a colossal speed near as damn to C and the clocks on earth and in the spacecraft will immediately begin to record time at different rates.

I am aware of the fact hat everything in the universe moves relative to everything else, but this fact does not make the twin paradox a fallacy.

Please give me scientific citation proving

the twin paradox to be a fallacy.

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The basis of the apparent paradox are calculations such as the length contraction observed of objects in motion relative to the observer. The usual explanation given is that the twin in the spaceship travelling at a % of c perceives the target at a distance calculated by using the length contraction formula, as opposed to the 'real' distance observed by the Earth-bound twin. The time differential is then based on this apparent difference. However, that formula (the length contraction formula of special relativity) is used to measure the apparent size of objects, as measured along the direction of motion, relative to the stationary observer (the twin in the spaceship is considered 'at rest within his/her own inertial frame of reference.)

Space is not an object, nor is space moving relative to the twin in the spaceship. Other objects within space will be 'moving' relative to that observer, but not space itself. Therefore the distance to the target object does not 'shorten' and the time differential between the twins does not exist.

Edited by Leonardo

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Let me see if this is correct.

Making the twins paradox really simple, look at it this way. Say A is on earth and B is in the space ship. Still on earth, B wants to travel 10 light years away from earth to X and then return. Because of time dilation on the space ship (B's clock runs 1/2 slower relative to A's clock), for B it only takes 5 years to reach X and 5 years to return to earth.

For A, it's taken 10 years for B to travel to X and 10 years for B to return to earth. But for B it has taken 5 years to travel to X and 5 years to return.So when B returns to earth, for A 20 years have elapsed, but for B 10 years have elapsed.

Only for relative uniform motion do both A and B observe each other's clocks to be symetrically dialated. In other words, both A and B's time frame of reference are symmetrical relative to each other. Because B has traveled away from earth to X, turn around and traveled back to earth, this reference frame symmetry is broken. A and B are in different relative reference frames that are no longer symmetrical to each other.

This is why we can tell A has not moved in space-time and B has moved in space-time relative to A. The other reason we can tell that A has not moved and B has is because A is 10 years older than B when B arrives back on earth.

What do you think of this explanation?

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Let me see if this is correct.

Making the twins paradox really simple, look at it this way. Say A is on earth and B is in the space ship. Still on earth, B wants to travel 10 light years away from earth to X and then return. Because of time dilation on the space ship (B's clock runs 1/2 slower relative to A's clock), for B it only takes 5 years to reach X and 5 years to return to earth.

For A, it's taken 10 years for B to travel to X and 10 years for B to return to earth. But for B it has taken 5 years to travel to X and 5 years to return.So when B returns to earth, for A 20 years have elapsed, but for B 10 years have elapsed.

Only for relative uniform motion do both A and B observe each other's clocks to be symetrically dialated. In other words, both A and B's time frame of reference are symmetrical relative to each other. Because B has traveled away from earth to X, turn around and traveled back to earth, this reference frame symmetry is broken. A and B are in different relative reference frames that are no longer symmetrical to each other.

This is why we can tell A has not moved in space-time and B has moved in space-time relative to A. The other reason we can tell that A has not moved and B has is because A is 10 years older than B when B arrives back on earth.

What do you think of this explanation?

False.

Time dilation happens for each twin, in this scenario, since their only frame of reference is themselves. Thus no objective time dilation occurs for either twin.

As I stated in a previous post, the only way for a 'paradox' to occur is when you introduce a third, objective frame of reference - that being a gravity well. In that scenario you can have objects without relative motion to the objective frame of reference (using, perhaps, an orbital motion) undergoing time dilation with respect each other (one stationary in the gravity well, one orbiting it).

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So you have twins in separate spaceships, one says put and the other zooms away at close to the speed of light and then returns, they will both age the same (since in fact relative to the one who zooms away it was in fact the one who stayed put that zoomed away).

I think not; one undergoes acceleration, the other doesn't. One creates in effect its own gravity well by overcoming its inertia and zooming, the other doesn't.

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So you have twins in separate spaceships, one says put and the other zooms away at close to the speed of light and then returns, they will both age the same (since in fact relative to the one who zooms away it was in fact the one who stayed put that zoomed away).

I think not; one undergoes acceleration, the other doesn't. One creates in effect its own gravity well by overcoming its inertia and zooming, the other doesn't.

Acceleration alone cannot produce the "paradox effect", what you need is an absolutely objective frame of reference from which to measure the relativistic effects of motion - and it is this that a gravity well provides (the centre of gravity).

As framed, the "Twins Paradox" is not a paradox, but if you were to include a gravity well (Earth) as the objective frame of reference (not use the frame of reference of either of the twins) then you can establish a relativistic difference in ageing due to time dilation. But, because it is observed from this objective frame of reference, it is still not a 'paradox'.

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Is there even an argument here?

From what I can tell, Leonardo is arguing that the ``twin paradox'' is fallacious because it is not a paradox.

Alan McDougall, on the other hand, is arguing that the ``twin paradox'' is a real effect; it is possible to slow aging through relativistic motion.

Both arguments are correct and accepted by the scientific mainstream.

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False.

Time dilation happens for each twin, in this scenario, since their only frame of reference is themselves. Thus no objective time dilation occurs for either twin.

As I stated in a previous post, the only way for a 'paradox' to occur is when you introduce a third, objective frame of reference - that being a gravity well. In that scenario you can have objects without relative motion to the objective frame of reference (using, perhaps, an orbital motion) undergoing time dilation with respect each other (one stationary in the gravity well, one orbiting it).

Not false but perhaps the word paradox is wrong and I should have used "Time Dilation instead.

I suppose the term twin paradox came about due to one twin seemingly becoming much much biologically older than the other, due to the time dilation effect of near C. Of course in reality there is no paradox just an odd quirk allowed general relativity!

Lets us change it to a thought experiment, where you remove everything from the universe, except the earth, the twins, the spaceship and the infinite void in which the earth floats. One twin aged 20 years takes the spaceship and leaves the earth at an enormous speed, relative to the earth from which it has just departed outward into and through of the infinite void of he fabric of space time.

Of course the other twin who remains on earth it at the moment of the departure of his brother, the exact same biological age namely 20 years old.

The twin in the spaceship which reaches the almost impossible sped of 99.99999999% of the speed of light journeys outward for 10 years relative time, according to the atomic clock in his spacecraft. Ignore the time and effort needed to stop turn around, assume he somehow stopped and does the same thing on his return trip to the earth , he left behind, this again takes him 10 years relative time to get back to earth.

Are you going to tell me that his twin that remained on earth (of course if he still exists) would be the same biological age as his twin who traveled into via his spacecraft out into the void of space-time, for twenty years relative to his spaceship clock , would still be the same biological age as his twin brother who remained on earth?

I don't know how to calculate the time dilation effect between the twins, but the one who remained on earth would be very very old indeed and might even be just be an ancient memory, while his brother who journeyed in the spacecraft on his return, would be only 20 biological years older. Remember this is thought experiment, but the physics behind it are sound.

Remember the spacecraft would be travelling through the fabric of space-time and as it increased its speed and approached closer and closer to that of C, its mass and the mass of the twin inside of it would have increased hugely. The more massive an object the slower time moves on its clock, The object or twin who remained on earth,would retain his original mass While his twin in the spacecraft at near C would have become unimaginably massive and subsequently time would flow at a snails pace relative to his very much less massive twin on earth.

Indeed all the energy of the entire universe could not propel any object, up to any object, be it just a fundamental particle or a colossal object like a huge mountain. At the the speed of light, the mass of both of them would become infinite, it is all about a matter of diminishing returns.

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How about this as an explanation: I don't know why we're still discussing this twins not-paradox, as it has been proved to be correct.

The twin paradox has been verified experimentally by precise measurements of atomic clocks flown in aircraft and satellites. For example, gravitational time dilation and special relativity together have been used to explain the Hafele–Keating experiment.[A 1][A 2] It was also confirmed in particle accelerators by measureing time dilation of circulating particle beams.

http://en.wikipedia.org/wiki/Twin_paradox

[media=]

[/media] Edited by StarMountainKid

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Not false but not fully explained as this odd quirk of special relativity can become very difficult to explain, it is a complicated issue that cannot be explained.

Time is flexible and varies from place to place and is not one of the fundamental constants of the universe

Lets call the one "traveler" "the traveler" a the other "the home Body"

Lets us change it to a thought experiment, where you remove everything from the universe, except the earth, the "traveler's, the spaceship his twin brother "the homebody" and the infinite void of space-time, in which the earth floats. The traveler" aged 20 years takes the spaceship and leaves the earth at an enormous speed, relative to the earth from which he has just departed, outward into and through of the infinite void of he fabric of space time.

The asymmetry in the paradox is that the traveler leaves the earth's reference frame and comes back, whereas the homebody never leaves the earth. It is also an asymmetry that the traveler and the homebody agree with the reading on the traveler's clock at each event, but not vice versa. It is "the traveler's actions' that define the events.

I suppose the term paradox came about due to one "traveler" seemingly becoming much biologically older than the other, due to the time dilation effect of near C. Of course in reality there is no paradox just an odd quirk allowed by proved physics of Einstein's General and Special Relativity!

Of course the "the homebody" who remains on earth is at the moment of the departure of his brother "the traveler", are then at exact same biological age namely 20 years old.

The "traveler" in the spaceship which reaches the almost impossible speed of 99.99999999% of the speed of light, journeys outward for 10 years relative time, according to the atomic clock in his spacecraft. (Ignore the time and effort needed to stop turn around, assume he somehow stopped and does the same thing on his return trip to the earth ), he left behind, this again takes him 10 years relative time to get back to earth.

Are you going to tell me that the homebody" who remained on earth (of course if he still exists) would be the same biological age as his brother "the traveler" who accelerated, into via his spacecraft out into the void of space-time, for twenty years relative time accord to his frame of reference as reflected on his very accurate spaceship clock , would still be the same biological age as his "traveler" brother who remained on earth?

We can calculate the time dilation effect between the "homebody", who remained on earth would be extremely old indeed, relative to his "traveler brother" Indeed the "homebody might have died long ago due to old age and be just be an ancient memory, while his brother "the traveler" on return from his journey, would be only 20 biological years older. Remember this is thought experiment, but the physics behind it are sound.

The above is not an exact scenario it is just an illustration to simplify a complicated peace of physics

Remember the spacecraft would be accelerating through the fabric of space-time and as it increased its speed to approached closer and closer to that of C, its mass and the mass of the "traveler" inside of it would have increased hugely. The more massive an object the slower time moves on its clock, The object or "the homebody" who remained on earth, would retain his original mass While his "traveler" brother, in the spacecraft at near C would have become unimaginably massive and subsequently time would flow at a snails pace relative to his very much less massive "homebody" on earth.

Indeed all the energy of the entire universe could not propel any object, up to C, be they just a fundamental particle or a colossal object like a huge mountain. At the speed of light, the mass of both of them would become infinite, it is all about a matter of diminishing returns.

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Is there even an argument here?

From what I can tell, Leonardo is arguing that the ``twin paradox'' is fallacious because it is not a paradox.

Alan McDougall, on the other hand, is arguing that the ``twin paradox'' is a real effect; it is possible to slow aging through relativistic motion.

Both arguments are correct and accepted by the scientific mainstream.

Yes, I am arguing that it is not a paradox, but also that the "time dilation effect due to relativistic motion" only occurs when there is a separate, objective, frame of reference used in the scenario - and the only objective frame of reference available is a gravity well.

In the typical "Twin Paradox" scenario, if we remove the planet from being the location of the "at rest twin", and simply have that twin "at rest" in space, there is no objective frame of reference and hence no relativistic time dilation for either participant. What I am attempting to promote to people's understanding is that it is only through the inclusion of this objective frame of reference, from which both objects relativistic motions can be observed, do we see a difference in aging. The "time dilation effect" is not simply the result of an object moving at extremely high speed relative to another object, but the difference in motion of two objects relative to an independent, objective, frame of reference.

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Yes, I am arguing that it is not a paradox, but also that the "time dilation effect due to relativistic motion" only occurs when there is a separate, objective, frame of reference used in the scenario - and the only objective frame of reference available is a gravity well.

In the typical "Twin Paradox" scenario, if we remove the planet from being the location of the "at rest twin", and simply have that twin "at rest" in space, there is no objective frame of reference and hence no relativistic time dilation for either participant. What I am attempting to promote to people's understanding is that it is only through the inclusion of this objective frame of reference, from which both objects relativistic motions can be observed, do we see a difference in aging. The "time dilation effect" is not simply the result of an object moving at extremely high speed relative to another object, but the difference in motion of two objects relative to an independent, objective, frame of reference.

Ahh, now I understand. Thanks for explaining.

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Acceleration alone cannot produce the "paradox effect", what you need is an absolutely objective frame of reference from which to measure the relativistic effects of motion - and it is this that a gravity well provides (the centre of gravity).

As framed, the "Twins Paradox" is not a paradox, but if you were to include a gravity well (Earth) as the objective frame of reference (not use the frame of reference of either of the twins) then you can establish a relativistic difference in ageing due to time dilation. But, because it is observed from this objective frame of reference, it is still not a 'paradox'.

I'm not sure but I think I disagree; that the twin remaining "stationary" will age regardless of the presence of a gravity well. The objective frame of reference is what produces the inertia -- I suppose the overall frame of reference of the universe at large. You have to accelerate in order to transform space into time-like dimension.

Now I am going by stuff I learned ages ago, but I think I have a pretty good notion of it in my head.

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I'm not sure but I think I disagree; that the twin remaining "stationary" will age regardless of the presence of a gravity well. The objective frame of reference is what produces the inertia -- I suppose the overall frame of reference of the universe at large. You have to accelerate in order to transform space into time-like dimension.

Now I am going by stuff I learned ages ago, but I think I have a pretty good notion of it in my head.

Without the gravity well, which provides acceleration without motion relative to the frame of reference, neither object will experience any subjective motion. Without the gravity well, there is no objective frame of reference.

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I think there is. To change motion in space requires acceleration, which requires force. Two objects in space moving together will continue moving together, but if one takes a jaunt to another star and back, it is subjected to forces and experiences acceleration the other does not. Hence the clock on it will show less time has passed as that time was transformed to motion by the application of force.

Another way see it: in space/time everything always "moves" at the speed of light. Most of our motion seems to us to be in time, and when we accelerate in a non-time dimension some of this motion is transformed as slower time motion relative to others who do not so accelerate.

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I think there is. To change motion in space requires acceleration, which requires force. Two objects in space moving together will continue moving together, but if one takes a jaunt to another star and back, it is subjected to forces and experiences acceleration the other does not.

According to which object's frame of reference?

You are setting up a similar scenario to the Twin Paradox, which requires a third, objective, frame of reference from which to calculate any difference in relative motion. Without this independent FoR, neither object will experience any subjective acceleration and neither will experience time dilation relative to the other.

The Twin Paradox scenario is incorrectly framed because neither objects subjective FoR is applicable to calculate any relative motion from. The scenario requires an 'anchor' FoR - which has to be a gravity well.

Edited by Leonardo

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According to which object's frame of reference?

You are setting up a similar scenario to the Twin Paradox, which requires a third, objective, frame of reference from which to calculate any difference in relative motion. Without this independent FoR, neither object will experience any subjective acceleration and neither will experience time dilation relative to the other.

The Twin Paradox scenario is incorrectly framed because neither objects subjective FoR is applicable to calculate any relative motion from. The scenario requires an 'anchor' FoR - which has to be a gravity well.

To understand the twin paradox or the effect of near C related to time dilation, your frame of reference must always be the twin travelling in the hypothetical spaceship.

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According to which object's frame of reference?

You are setting up a similar scenario to the Twin Paradox, which requires a third, objective, frame of reference from which to calculate any difference in relative motion. Without this independent FoR, neither object will experience any subjective acceleration and neither will experience time dilation relative to the other.

The Twin Paradox scenario is incorrectly framed because neither objects subjective FoR is applicable to calculate any relative motion from. The scenario requires an 'anchor' FoR - which has to be a gravity well.

Either subjective frame of reference would be valid to calculate difference in motion. One doesn't experience time dilation. One experiences time flowing normally

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Either subjective frame of reference would be valid to calculate difference in motion. One doesn't experience time dilation. One experiences time flowing normally

The best way to look at the 'Twin Paradox" in particular, is from the reference frame of the traveller!

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Either subjective frame of reference would be valid to calculate difference in motion. One doesn't experience time dilation. One experiences time flowing normally

Which suggests there is no difference in the time elapsed for either twin in that scenario. The apparent difference is only an illusion brought about by the direction of travel of each with respect to the other.

The best way to look at the 'Twin Paradox" in particular, is from the reference frame of the traveller!

Without an 'anchor' (independent, objective) FoR, both are the 'traveller'.

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