[General] [NEW] SRT twin Paradox

[Albrecht Giese]

Hi Grahame,

sorry, but I find a very fundamental error in your arguments: You 
describe a pair of twins which observe each other in a situation where 
they are permanently accelerated. And then you argue with dilation 
caused by gravity. But that does not fit the physical reality.

Gravity and acceleration are different regarding dilation. Gravity 
causes dilation, no question. But acceleration does not cause dilation. 
How can one know? 1) You find this in every textbook about special 
relativity; 2) it was experimentally proven in the Muon storage ring at 
CERN. The extension of the life time of the muons was only dependent on 
the actual speed of the particles, not on the very strong acceleration 
in the ring. If that would have been an effect according to an 
equivalent gravitational field, their lifetime would have to be extended 
by an additional factor of roughly 1000 compared to the results observed.


Am 27.08.2017 um 22:18 schrieb Dr Grahame Blackwell:
> Hi Albrecht,
> I'm afraid I have to disagree with you on a couple of points.
> First, I agree completely that gravitation doesn't come under SR.  
> However the concept of gravitation is essential to explanation of the 
> 'twins going in opposite directions around a circle and meeting on the 
> far side' (non-)paradox.  [It may be that in your view this scenario 
> cannot then be simply a playing-out of SR, it must be a GR issue?]
> Consider: Twin A and twin B each view themselves as being static, with 
> the other twin tracing out a path that takes them away and then brings 
> them back into proximity from a different direction, having formed a 
> loop of some kind; however, from the point of view of an observer 
> static with respect to the centre of a large circle, A and B have 
> started together at some point on the perimeter of that circle and 
> have each followed opposite halves of that circle to meet again on its 
> other side.  I.e. from the perspective of that observer the motions of 
> A and B are symmetric, so their clocks (synchronised at the start) 
> will still be synchronised when they meet again.  [We're assuming here 
> that this all takes place in deep space, far from any gravitational 
> influences.]
None of the twins can view himself as being static, because they are 
accelerated all the time and they will notice that. So the laws of SR 
are not applicable for this process in a simple way.
> From A's point of view, A has remained static and B has performed a 
> large loop in space, finally coming back alongside A.  According to 
> SR, therefore, A will observe a slowing-down of B's clock and so will 
> expect B's clock to have lost time, in real terms as measured in A's 
> frame (if it were an inertial frame).
No, it is not an inertial frame.
> [We can deal with the issue of A reading B's clock whilst B is on the 
> move by B digitally emitting their clock-time at intervals, to be 
> received by A who will assess those transmissions on the basis of 
> their crossing space at speed c across the distance that A measures B 
> to be from him at times of transmission - this could be done fairly 
> easily by A keeping a record of B's distance at all times as measured 
> on A's clock.]
Also this is not possible. A can receive signals from B, but he does not 
know the distance. According to SR this distance is not clearly defined 
because the assessment of any distance depends on the motion state of 
the observer. Which speed will A assume for himself? He cannot assume to 
be static as he notices to be accelerated.
> B will have a corresponding mirror-image experience of A's motion, and 
> so will expect A to have lost time in real (B-frame) terms.  This 
> appears to suggest that both A and B would each expect the other's 
> clock to have fallen behind their own - a paradox.
Also regarding time a similar problem like for distance is applicable. 
When are signals in different frames synchronised or when is time is 
running faster or slower? For any observer in different frames the 
result of this question may be different.
> However, our external observer will have seen A performing a circular 
> course - so A will inevitably have experienced a 'G-force' of some 
> kind (centripetal, from our observer's persective). Since A considers 
> him/herself to be static, he/she MUST attribute this to some 
> gravitational influence - indeed, from the SR/GR perspective there 
> must indeed be a gravitational influence in A's frame, from the 
> perspective of that frame; one just does not get G-force without 
> either acceleration or gravitation.  (Here, of course, Relativity 
> begins to become unravelled, as A is far from any massive body that 
> could give rise to a gravitational field - maybe they'll need to start 
> inventing their own local 'dark matter').  Note that the scenario 
> being considered - A and B traversing opposite sides of a circle - 
> involves NO gravitational fields - BUT A and B would HAVE TO PRESUME 
> the existence of such a field in their reference frame if they are to 
> reconcile a force they're experiencing with their assumption that they 
> are static (a totally valid assumption, in Relativity terms).
As said above, even if both, A and B, attribute the force of 
acceleration to gravity, they are in error; and it does anyway not help 
the situation. For your consideration they need a gravitational field 
for dilation, but this does not exist, and acceleration does not replace it.
> Resolution of this (apparent) paradox, as I said before, rests on A 
> (and likewise B) considering themselves to have been subject to a 
> gravitational field - and experiment shows us that gravitational 
> fields slow time - so their own clock will have slowed as well as the 
> others.  So they will both expect their clocks to be synchronised on 
> re-meeting.
That is anyway true also in the absence of dilation.
> As I say, this is where Relativity begins to become unravelled: A and 
> B will either each have to acknowledge that they are NOT in fact 
> static, or they will have to invent a convincing explanation for a 
> gravitational effect in the absence of any 'ponderous mass' (to use 
> Einstein's term).  But given that, synchronisation of clocks is not an 
> issue - as long as we allow A and B to each presume existence of a 
> gravitational field in their frame (which, as you say, takes it into 
> the sphere of GR).
Not applicable as mentioned above.
> Second point: in your case of the travelling-twin versus the 
> stay-at-home twin, the traveller would again experience G-force, which 
> they could if they wish regard as a gravitational effect (since under 
> Relativity they are free to consider themselves as static). They would 
> therefore expect their clock (including biological clock) to have 
> slowed (Pound-Rebka again), and so know that they have actually been 
> travelling more than one year in 'objective' terms - whatever that 
> might mean in this context.
The twin travelling, B, cannot assume that he is static because he has 
to notice his acceleration. And that is different from gravity. And even 
if it could be identified with gravity this would not solve the example 
which I have given.
> But of course the reality is that slowing of time is NOT symmetric, 
> it's a consequence of motion with respect to the unique 
> objectively-static universal reference frame.  Only when serious 
> scientists start asking WHY Relativity does (or appears to do) what it 
> does will we make any progress on this issue.
Which progress to you expect? There is no symmetry in the case where 
twin B returns and so you cannot conclude anything from symmetry.
> I think we're agreed on the key issues.  Perhaps it's time to stop 
> discussing how a self-consistent mathematical system (which doesn't 
> happen to match true reality) copes with paradoxes of its own making!
> Best regards,
> Grahame
As I have mentioned in the other mail: It is in conflict with Einstein's 
relativity to compare clocks residing in different frames. The result of 
any comparison depends on the motion state of the observer. That is what 
Einstein says.

But the other solution is to follow the Lorentzian relativity. In that 
case the imagination becomes easy (in contrast to Einstein).

Greetings back
Albrecht.
> ----- Original Message -----
>
>     *From:* Albrecht Giese <mailto:phys at a-giese.de>
>     *To:* general at lists..natureoflightandparticles.org
>     <mailto:general at lists.natureoflightandparticles.org>
>     *Sent:* Sunday, August 27, 2017 7:48 PM
>     *Subject:* Re: [General] [NEW] SRT twin Paradox
>
>     Hi Grahame,
>
>     without going into details of this discussion I only want to point
>     to the following fact:
>
>     Whereas you are of course right that the twin situation is not a
>     paradox but logically clean, what we all as I think have
>     sufficiently discussed here, the following is not correct in my view:
>
>     The twin situation has absolutely NOTHING TO DO with gravity.
>
>     Two arguments for this:
>
>     o  The so called twin paradox  is purely Special Relativity.
>     Gravity on the other hand, is General Relativity. This is the
>     formal point.
>
>     o  From practical numbers it is visible that gravity cannot be an
>     explanation. Take the usual example saying that one twin stays at
>     home and the other one travels - as seen from the twin at home -
>     for twenty years away and then twenty years back. From the view of
>     the twin at home, at the other ones return 40 years have gone. For
>     the travelling twin only one year has gone (This case is
>     theoretically possible if the proper speed is taken, about
>     0.9997c)). Then the travelling twin would have saved 39 years of
>     life time. Now look at the possible influence of gravity: Assume
>     it takes the travelling twin  a year to change his speed from
>     almost c to almost - c , then, even if the speed of proper time
>     would decrease to zero, he would have saved only one year. But, in
>     this example, he has saved 39 years. How could this work? No one
>     in physics assumes that proper time can run inversely. So this is
>     no possible explanation.
>
>     How is it explained? I do not want to repeat again and again the
>     correct (but a bit lengthy) explanation, but I attempt to give a
>     short version: In Einstein's relativity the run of time in
>     different frames can  logically not be continuously compared, it
>     can only be compared at interaction points where two clocks (or
>     whatever) are at the same position. And the determination of the
>     situation at such common position has to be done by the Lorentz
>     transformation. And this determination works, as many times said
>     here, without logical conflicts.
>
>     If you solve this problem using the Lorentzian SRT, then the
>     result is the same but the argument is different, more
>     physics-related, and also better for the imagination. If wanted, I
>     can of course explain it.
>
>     Albrecht
>
>
>
>     Am 27.08.2017 um 01:13 schrieb Dr Grahame Blackwell:
>>     I'm sorry Wolf, but it seems that you're still not getting it.
>>     This situation can be explained fully logically WITHOUT either
>>     twin making any assumptions about SR or GR - simply from their
>>     own observations and from well-proven experimental findings.
>>     If we label the twins A and B, then their situations are
>>     effectively symmetric* - so we'll consider the scenario from the
>>     viewpoint of twin A.
>>     A considers him/herself static, and all motion to be attributable
>>     to twin B.  So - and this agrees with experimental observation of
>>     clocks at high speed (in planes and in GPS satellites) - twin A
>>     will observe twin B's clock running slow, if A's own clock is not
>>     upset by any effect. HOWEVER, since A is actually travelling in
>>     circular motion, (s)he will experience a centripetal force;
>>     assuming him/herself to be static, this will necessarily be
>>     attributed to gravitational effects - and it's well known from
>>     experiment (Pound-Rebka and successors) that gravitational fields
>>     cause time dilation - so A will expect their own clock to be
>>     running more slowly also due to that 'gravitational' effect (note
>>     that this is not any assumption of SR or GR, simply inference
>>     from proven experimental results) [and so also A's observation of
>>     B's clock, measured against A's own clock, will not fit the
>>     standard SR time-dilation model, for reasons that A will fully
>>     comprehend].  For A, the cumulative time-dilation for B's
>>     perceived relative speed and for A's own perceived
>>     'gravitational' effect exactly balance - so A will fully expect
>>     both clocks to coincide when the twins meet again (as B will also).
>>     No paradox.
>>     * It needs to be said that further study of causation of
>>     'relativistic time dilation' leads to the understanding that this
>>     is an objective effect due to travelling at speed relative to the
>>     unique objectively-static universal reference frame. So if the
>>     centre of the circle traced out by A and B is itself in motion
>>     relative to that reference frame then it cannot be assumed that
>>     A's and B's motions will be symmetric; in that case their clocks
>>     may well not be precisely synchronised on their meeting again. 
>>     This is an observation relating to physical reality, which in no
>>     way contradicts the self-consistency of SR (or GR) as a
>>     mathematical system.
>>     Best regards,
>>     Grahame
>
>
>
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