twin paradox

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Offline thebrain13

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twin paradox
« on: 15/06/2006 21:10:40 »
lets say there are two spaceships containing one pilot each, they are identical twins of course. We'll call them pilot a and pilot b. pilot b fires his engines and travels at 99 percent the speed of light away from pilot a for one year. Then turns around and comes back. Einstain says that from pilot a's perspective pilot b would have aged less than him. However Since velocity is relative to each observer, pilot b sees pilot a speeding away from him and then returning. So pilot b should see a younger pilot a. So my question is when the two meet each other after the trip which one is younger?

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another_someone

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Re: twin paradox
« Reply #1 on: 15/06/2006 21:57:34 »
Speed is relative, but acceleration is not.

When pilot b switches on hit rocket motors, he will feel a kick up the backside (and every other part of him touching his accelerating space ship), while pilot a will still be floating in zero gravity.



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Offline thebrain13

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Re: twin paradox
« Reply #2 on: 15/06/2006 22:43:26 »
Although i am not sure what you mean by your statement that acceleration is not relative, but doesnt that imply that there is some prefered speed of objects, or absolute motion? the way i understand it, you are saying that an object somehow keeps track of wether it has been accelerated for the entirety of its' lifespan, in order to make sure that pilot a is in fact older than pilot b. Are you saying that the twin paradox occurs only in the period in which an object is accelerated. so if an object accelerates for a period of one second, does that mean that is the maximum amount of time in which his time can be off for the twins? because once they stop accelerating all frames of reference are equal right?

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another_someone

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Re: twin paradox
« Reply #3 on: 16/06/2006 00:28:32 »
quote:
Originally posted by thebrain13
Although i am not sure what you mean by your statement that acceleration is not relative, but doesnt that imply that there is some prefered speed of objects, or absolute motion?



What I mean by acceleration is absolute is that: F=mA, where F = force, m = mass, and A = acceleration.

You can measure force without reference to any outside object (if you were blindfolded, you would still be able to know whether you were accelerating or remaining at a constant velocity, therefore acceleration must be absolute and not relative to something else).

quote:

 the way i understand it, you are saying that an object somehow keeps track of wether it has been accelerated for the entirety of its' lifespan, in order to make sure that pilot a is in fact older than pilot b. Are you saying that the twin paradox occurs only in the period in which an object is accelerated. so if an object accelerates for a period of one second, does that mean that is the maximum amount of time in which his time can be off for the twins? because once they stop accelerating all frames of reference are equal right?



In a sense, this must be so.

I don't know the exact ways it resolves itself, but what one can say is that pilots a and b do not, and cannot, exist in isolation, but exist within the context of the wider universe, which does influence the space within it, and so these pilots, in their space ships must have a motion relative to the motion of the total universe.



George

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Offline ukmicky

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Re: twin paradox
« Reply #4 on: 16/06/2006 01:21:15 »
http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_intro.html



http://www.weburbia.com/physics/acceleration.html

The "paradox" is only a conflict between reality and your feeling of what reality "ought to be". - Richard Feynman
Michael
« Last Edit: 16/06/2006 01:37:25 by ukmicky »

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Offline thebrain13

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Re: twin paradox
« Reply #5 on: 16/06/2006 02:09:34 »
i've read, the stella and terrance phenomena for an explanation of the twin paradox. And to me it seems like a way of masking the problem. Both points of view are still equally applicable, the article states that when stella is leaving terrance, terrance views a redshift when shes moving away and a blue shift when shes coming forth. BUT WHY DOESNT STELLA VIEW A REDSHIFT. The article doesn't say that in order for this to work terrance is the only one to observe the redshift. Are we now stating that if you were ACTUALLY accelerated, then you are free from observing the redshift and you are in fact, the actual, prefered, absolute, frame of reference?

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another_someone

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Re: twin paradox
« Reply #6 on: 17/06/2006 01:35:09 »
quote:
Originally posted by thebrain13

i've read, the stella and terrance phenomena for an explanation of the twin paradox. And to me it seems like a way of masking the problem. Both points of view are still equally applicable, the article states that when stella is leaving terrance, terrance views a redshift when shes moving away and a blue shift when shes coming forth. BUT WHY DOESNT STELLA VIEW A REDSHIFT. The article doesn't say that in order for this to work terrance is the only one to observe the redshift. Are we now stating that if you were ACTUALLY accelerated, then you are free from observing the redshift and you are in fact, the actual, prefered, absolute, frame of reference?



In essence, that is the interpretation that I would read into the explanation (if not actually a case of not seeing the red shift, but merely seeing less of the red shift, while seeing more of the blue shift).

One consequence that appears to me to come from this is that if two objects are moving relative to each other in space,m one cannot tell what the relative time references (and thus the true red/blue shift) is of the two objects unless one knows the history of the object (i.e. which object accelerated away/towards which?).  This must have an inference for the astronomical observation of distance objects in the universe, objects that are assumed to be receding at very high velocities from us – but did we start moving away from it, or did it start moving away from us?



George

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Offline Roy P

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Re: twin paradox
« Reply #7 on: 17/06/2006 12:29:14 »
quote:
Originally posted by thebrain13
BUT WHY DOESNT STELLA VIEW A REDSHIFT.

I'm trying to get my head around this. How do we *know* Stella doesn't see a redshift?

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another_someone

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Re: twin paradox
« Reply #8 on: 17/06/2006 12:38:13 »
quote:
Originally posted by Roy P
How do we *know* Stella doesn't see a redshift?



I suppose that until someone actually sends Stella out there at 99% the speed of light, we do not actually know, we merely predict that this is what would happen.  If it did happen, then we would simply have to ask Stella when she got back what it was she saw out of the window.



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Offline ukmicky

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Re: twin paradox
« Reply #9 on: 17/06/2006 13:18:31 »
Ok i'm not too up on this it can be very confusing.

but if stella is traveling at 99% of c wouldnt the space in front of her be Length Contracted shortening the wavelength of any photons in front of her, blue shifting everything.
Michael
« Last Edit: 17/06/2006 13:20:07 by ukmicky »

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Offline Roy P

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Re: twin paradox
« Reply #10 on: 17/06/2006 15:38:46 »
quote:
Originally posted by ukmicky
but if stella is traveling at 99% of c wouldnt the space in front of her be Length Contracted shortening the wavelength of any photons in front of her, blue shifting everything.

Now that's what I would have thought, but the theory says no. Well, no according to Stella's POV. It's why I have my doubts about 'redshift' overall when it comes to speed and its effects on light.

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« Last Edit: 17/06/2006 15:39:57 by Roy P »
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Offline ukmicky

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Re: twin paradox
« Reply #11 on: 17/06/2006 22:54:36 »
where's soul surfer when you need him  [:)]
Michael
« Last Edit: 19/06/2006 00:08:33 by ukmicky »

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Offline Solvay_1927

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Re: twin paradox
« Reply #12 on: 19/06/2006 02:22:28 »
I'm a little confused as to what the problem is here.

The theory (of Special Relativity) and the link (about Stella and Terrance) both say that Stella DOES see the light flashes (from Terrance’s clock) as being redshifted on the outward journey and blueshifted on the return journey.

Quoting from the link:
quote:
The regular pulses are redshifted to lower frequencies during the Outbound Leg, and blueshifted to higher frequencies during the Inbound Leg … And Stella computes the same for Terence … Stella sees what Terence sees: a slow clock on the Outbound Leg, a fast clock on the Inbound Leg.

Or have I misunderstood – is it some other part of the (Stella / Terra) link that’s confusing everybody?
 

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Offline thebrain13

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Re: twin paradox
« Reply #13 on: 19/06/2006 02:36:56 »
Okay, so if they both see redshifts on the outbound leg, and they both see blue shifts on the inbound leg, whys one older?

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another_someone

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Re: twin paradox
« Reply #14 on: 19/06/2006 02:55:59 »
quote:
Originally posted by thebrain13

Okay, so if they both see redshifts on the outbound leg, and they both see blue shifts on the inbound leg, whys one older?



I think the crucial bit the Paul (Solvay_1927) left out was:

http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_doppler.html
quote:

All well and good, but this discussion at first just seems to sharpen the paradox!  Stella sees what Terence sees: a slow clock on the Outbound Leg, a fast clock on the Inbound Leg.  Whence comes the asymmetry between Stella and Terence?
Answer: in the duration of the Inbound and Outbound Legs, as seen.  For Stella, each Leg takes about a year.  Terence maintains that Stella's Turnaround takes place at year 7 at a distance of nearly 7 light-years, so he won't see it until nearly year 14.  Terence sees an Outbound Leg of long duration, and an Inbound Leg of very short duration.
So there's the fundamental asymmetry: the switch from redshift to blueshift occurs at Stella's Turnaround.  Stella sees Terence's telescopic image age slowly on her Outbound Leg, but the image more than makes up for its dawdling on the Inbound Leg.  Terence sees Stella's image off to a slow start too, but here the image's final burst of rapid aging comes too late to win the race.





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Offline Solvay_1927

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Re: twin paradox
« Reply #15 on: 19/06/2006 02:59:20 »
To quote from the link again:
quote:
All well and good, but this discussion at first just seems to sharpen the paradox!  Stella sees what Terence sees: a slow clock on the Outbound Leg, a fast clock on the Inbound Leg.  Whence comes the asymmetry between Stella and Terence?

Answer: in the duration of the Inbound and Outbound Legs, as seen.  For Stella, each Leg takes about a year ... Terence sees an Outbound Leg of long duration, and an Inbound Leg of very short duration.

So there's the fundamental asymmetry: the switch from redshift to blueshift occurs at Stella's Turnaround.  Stella sees Terence's telescopic image age slowly on her Outbound Leg, but the image more than makes up for its dawdling on the Inbound Leg.  Terence sees Stella's image off to a slow start too, but here the image's final burst of rapid aging comes too late to win the race. [In other words, Terrance sees Stella's clock as not going fast enough on the return leg to catch up with the time on his own clock.]
 

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Offline Solvay_1927

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Re: twin paradox
« Reply #16 on: 19/06/2006 03:00:25 »
Oh.

Timing was never my strong point.
 

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Offline thebrain13

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Re: twin paradox
« Reply #17 on: 19/06/2006 03:55:14 »
history seems to be repeating itself, ive read multiple explanations on how stella is able to seperate her frame of reference from terrances', based on their relative velocities from one another. Too me it seems that all the explanations disguise the problem in a different way. first explanation, stella was accelerated. Second explanation, stella was redshifted. And lastly, stella was taking place in the turnaround event. All subtle ways to provide terrance with a superior frame of reference while keeping einsteins postulate that, there is no prefered intertial frame, intact(meaning all motion is relative) My rebuttle has been consistent.

Granted all frames of reference are equally valid

WHY WOULDN'T STELLA VIEW TERRANCE ACCELERATING?
WHY WOULDN'T STELLA VIEW TERRANCE REDSHIFTED?
WHY WOULDN'T STELLA VIEW TERRANCE'S TURNAROUND EVENT?

Anybody want to become part of the fourth bold statement?[8D]

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another_someone

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Re: twin paradox
« Reply #18 on: 19/06/2006 14:49:25 »
quote:
Originally posted by thebrain13
All subtle ways to provide terrance with a superior frame of reference while keeping einsteins postulate that, there is no prefered intertial frame, intact(meaning all motion is relative) My rebuttle has been consistent.

Granted all frames of reference are equally valid

WHY WOULDN'T STELLA VIEW TERRANCE ACCELERATING?
WHY WOULDN'T STELLA VIEW TERRANCE REDSHIFTED?
WHY WOULDN'T STELLA VIEW TERRANCE'S TURNAROUND EVENT?

Anybody want to become part of the fourth bold statement?[8D]



First correction, Special Relativity does not say all frames of reference are equal – you got it right the first time: all inertial frames of reference are equal.  An accelerating frame of reference is not an inertial frame of reference.

The point about “WHY WOULDN'T STELLA VIEW TERRANCE ACCELERATING?” rather misses the point.  You are only concentrating on the visual sense, and I agree that the visual sense cannot tell the two apart.  As a comparison, it is often the case that if you sit in a railway carriage, and look at an adjacent train begin moving past you in the opposite direction, it sometimes  takes a moment for you to work out whether it is your train that has started to move forward or the other train that has started moving in the opposite direction.  As you rightly surmise, visually the two experiences are identical.  On the other hand, if you close your eyes, you can sense whether your train is accelerating or not, and if your train is not accelerating, then it must be the other train that is accelerating.

As for  “WHY WOULDN'T STELLA VIEW TERRANCE REDSHIFTED? “ and “WHY WOULDN'T STELLA VIEW TERRANCE'S TURNAROUND EVENT?”, neither of these two questions are correct.  It is not the case of whether Stella will not see Terrance redshifted, because she will see Terrance redshifted – the question is, for how long will Terrance be redshifted.  Nor is it a question of whether Terrance will observe Stella to turnaround, but rather when will he see the turnaround event.

I totally accept your point that having 3 different explanations for the same supposed phenomenon does seem a bit of a fudge.  It might be easier to understand if we could actually perform the experiment; but alas we do not have the wherewithal to undertake such an experiment, so we seem to be left with a number of fudge solutions, with the argument being that in the physical world you cannot actually tell which is the right explanation because to the observers they would all look the same, even though the underlying explanation may be radically different.  It seems more a matter of pragmatic science than creating a unique model of events (I suppose one could argue the same problem between the particle/wave duality in a different scale in science, except that with the particle/wave duality, the two models do create different answers in some situations).



George

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Offline Soul Surfer

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Re: twin paradox
« Reply #19 on: 19/06/2006 19:15:38 »
I did not come into this argument because I thought that the first reply was adequate.  The initial question is also a bit ambiguous because it is not clear whether the one year journey is from pilot a's or pilot b's point of view although it seems most likely that it was pilot b's in which case the pilot that does not accelerate will experience a period of more than one year before pilot b returns.  On the practicalities of the experiment people are not like clocks and you can only tell age differences superficially if the are quite large their respective digital watches (which I presume they are carrying) will be a much more accurate measure of the difference in time experienced between them.  On a practical point human beings do not likeaccellerating much faster thane 1G and getting up to 99% of the speed of light takes quite a long time and then b has to take just as long to decelerate and acelerate and decelerate on the journey back.

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Offline thebrain13

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Re: twin paradox
« Reply #20 on: 29/06/2006 00:17:56 »
okay i've been away for a little while, where to start. first off, your initial rebutal says, acceleration is not relative, or you can tell that you are accelerating. This is simply not the case, you can only tell you are accelerating relative to another object. For example, if you are driving a car and you hit the gas, you consequently feel a push from the seat, this is not because YOU are accelerating but the car is, and is pushing you forward. So lets say you painted the windows black and you hit the gas again, this time some force from within your body is pushing you forward, so you and the car are accelerating equally. In this case, you dont feel any push, so how do you SENSE you are accelerating?

Secondly, lets not deflect attention to acceleration because although einstein does say, only inertial frames of reference are equal, einsteins' time dilation equation is not based on acceleration, it is based on relative velocities. And this phenomena does not soley exist in the moments an object is non inertial.

It seems like I still see the same mistakes I was talking about in my last post, with your rebuttal of my statement, why doesn't stella view a redshift. you say it is a question of how long terrance will be redshifted. So my fourth bold statement is,
WHY WOULDNT STELLA VIEW TERRANCE REDSHIFTED AS LONG?

You also state that it is not a question of wether terrance will view stella to turn around but when.
So my fifth bold statement is
WHY WOULDNT STELLA VIEW TERRANCE TURNING AROUND AT THE SAME TIME?
To get to the heart of my argument, how can you distinguish between two objects using relative motion, when both motions have to be exactly equal at all times?

you also say I am paying to much attention to the visual, I dont think so, all experiments are observed not sensed. Although im not sure where you were going with that.

Also, I just glanced over your second post, you say,I don't know the exact ways it resolves itself, but what one can say is that pilots a and b do not, and cannot, exist in isolation, but exist within the context of the wider universe, which does influence the space within it, and so these pilots, in their space ships must have a motion relative to the motion of the total universe.

This is a blatant example of absolute motion. Given newtons third law, every action has an equal an opposite reaction, the overall motion of the universe has to remain constant, or absolute, you might say. so anything relative to the universe as a whole is as absolute a velocity as they come. Secondly, this is clearly not what einstein was saying, he says any non inertial frame of reference is equally valid, not just the frame of reference which is, the entire universe.
« Last Edit: 09/07/2006 22:48:41 by thebrain13 »

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Offline thebrain13

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Re: twin paradox
« Reply #21 on: 29/06/2006 00:17:56 »
okay i've been away for a little while, where to start. first off, your initial rebutal says, acceleration is not relative, or you can tell that you are accelerating. This is simply not the case, you can only tell you are accelerating relative to another object. For example, if you are driving a car and you hit the gas, you consequently feel a push from the seat, this is not because YOU are accelerating but the car is, and is pushing you forward. So lets say you painted the windows black and you hit the gas again, this time some force from within your body is pushing you forward, so you and the car are accelerating equally. In this case, you dont feel any push, so how do you SENSE you are accelerating?

Secondly, lets not deflect attention to acceleration because although einstein does say, only inertial frames of reference are equal, einsteins' time dilation equation is not based on acceleration, it is based on relative velocities. And this phenomena does not soley exist in the moments an object is non inertial.

It seems like I still see the same mistakes I was talking about in my last post, with your rebuttal of my statement, why doesn't stella view a redshift. you say it is a question of how long terrance will be redshifted. So my fourth bold statement is,
WHY WOULDNT STELLA VIEW TERRANCE REDSHIFTED AS LONG?

You also state that it is not a question of wether terrance will view stella to turn around but when.
So my fifth bold statement is
WHY WOULDNT STELLA VIEW TERRANCE TURNING AROUND AT THE SAME TIME?
To get to the heart of my argument, how can you distinguish between two objects using relative motion, when both motions have to be exactly equal at all times?

you also say I am paying to much attention to the visual, I dont think so, all experiments are observed not sensed. Although im not sure where you were going with that.

Also, I just glanced over your second post, you say,I don't know the exact ways it resolves itself, but what one can say is that pilots a and b do not, and cannot, exist in isolation, but exist within the context of the wider universe, which does influence the space within it, and so these pilots, in their space ships must have a motion relative to the motion of the total universe.

This is a blatant example of absolute motion. Given newtons third law, every action has an equal an opposite reaction, the overall motion of the universe has to remain constant, or absolute, you might say. so anything relative to the universe as a whole is as absolute a velocity as they come. Secondly, this is clearly not what einstein was saying, he says any non inertial frame of reference is equally valid, not just the frame of reference which is, the entire universe.
« Last Edit: 09/07/2006 22:48:41 by thebrain13 »

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Offline thebrain13

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Re: twin paradox
« Reply #22 on: 09/07/2006 22:49:23 »
Come on, you gonna let me get away with that?

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Offline ukmicky

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Re: twin paradox
« Reply #23 on: 10/07/2006 01:06:22 »
quote:
Originally posted by thebrain13

okay I've been away for a little while, where to start. first off, your initial rebuttal says, acceleration is not relative, or you can tell that you are accelerating. This is simply not the case, you can only tell you are accelerating relative to another object. For example, if you are driving a car and you hit the gas, you consequently feel a push from the seat, this is not because YOU are accelerating but the car is, and is pushing you forward. So lets say you painted the windows black and you hit the gas again, this time some force from within your body is pushing you forward, so you and the car are accelerating equally. In this case, you dont feel any push, so how do you SENSE you are accelerating?




But how would that force act equally on each individual molecule or atom of your body negating the sense of acceleration , and if you could provide that force as your in a non inertial environment all that force would do is move you towards the steering wheel.

And how can an internal force push you forward.

Michael

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Offline Solvay_1927

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Re: twin paradox
« Reply #24 on: 10/07/2006 01:15:04 »
Mr (or is it Ms?) Brain,

Does Newton’s 1st law help?  Every object remains in its inertial state (i.e. stationary or in uniform linear motion) unless (and only unless) acted upon by an external force.

So you know you’re accelerating because a force is acting on you.  And if there were NO force acting on you, you would NOT be accelerating.

For Stella to start moving away from Terrance, a force has to act on her. And for her motion to be changed again at the turnaround point, another force must act upon her.

But throughout this experiment there are NO forces acting on Terrance.

Stella may see Terrance receding away from her at an ever increasing rate (i.e. he “looks” like he’s accelerating), but the fact is that only Stella is experiencing a force being applied to her.

So acceleration is NOT relative.  Both Stella and Terrance may think that the other person “looks” like they’re accelerating away, but only one of them (Stella) really IS accelerating, as only one of them has a force acting on them.  This removes the symmetry in their situations, and explains why they don’t have symmetrical experiences (i.e. why they don’t measure the same passage of time).

As for the whole redshifting/blueshifting description in the above link, although I think it does give an explanation of the twin paradox, I don’t think it’s the best explanation (it’s a bit too easily confused and misunderstood).

Unfortunately, there aren’t really any easily understood explanations for the twin paradox.  Which is probably because, to fully understand the resolution to the paradox, you have to get your head around the fact that the whole concept of “simultaneity” is changed by relativity.

In case it’s of interest, here’s a link to another explanation of how relativity theory causes the breakdown of simultaneity:

http://www.incentre.net/tcantine/TP.html

Hope it helps. (Or maybe it will just make your brain whirl even more, as it does for me!)
 

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Re: twin paradox
« Reply #25 on: 10/07/2006 02:07:46 »
quote:
Originally posted by thebrain13
Come on, you gonna let me get away with that?



OK, this one slipped off my radar, but you're right, I'm not gonna let you get away with that [:)]

quote:
Originally posted by thebrain13
okay i've been away for a little while, where to start. first off, your initial rebutal says, acceleration is not relative, or you can tell that you are accelerating. This is simply not the case, you can only tell you are accelerating relative to another object. For example, if you are driving a car and you hit the gas, you consequently feel a push from the seat, this is not because YOU are accelerating but the car is, and is pushing you forward. So lets say you painted the windows black and you hit the gas again, this time some force from within your body is pushing you forward, so you and the car are accelerating equally. In this case, you dont feel any push, so how do you SENSE you are accelerating?



The problem here is that there is no such thing as a force from within your body, the force must always be from without.  Nothing, absolutely nothing, will accelerate unless it is subject to some external force (this was made clear in Newton's first law of motion, and remains true even in a relativistic world; Newtons second law of motion has had to be modified by relativity)..

quote:

Secondly, lets not deflect attention to acceleration because although einstein does say, only inertial frames of reference are equal, einsteins' time dilation equation is not based on acceleration, it is based on relative velocities. And this phenomena does not soley exist in the moments an object is non inertial.



Yes, the equations pertaining to special relativity only relate to relative velocity, but Einstein makes it clear that the equations are not valid for accelerating bodies, and so the fact that the equations do not address the issue of acceleration is not relevant.

If special relativity was pertinent to accelerating bodies, then Einstein would never had gone to the trouble of developing general relativity.  It is general relativity that pertains to accelerating bodies, but since the maths surrounding general relativity are considerably more complex than those pertaining to special relativity, I have never really got to grips with the mathematics of it.

In a sense, the difference between two bodies at constant velocity, and a body at accelerating velocity, is that: two bodies at constant velocities can only relate their velocities to each other; whereas a body that is accelerating can compare its present velocity to the velocity it had at an earlier time – so yes, it is relative, but relative to itself.

quote:

It seems like I still see the same mistakes I was talking about in my last post, with your rebuttal of my statement, why doesn't stella view a redshift. you say it is a question of how long terrance will be redshifted. So my fourth bold statement is,
WHY WOULDNT STELLA VIEW TERRANCE REDSHIFTED AS LONG?

You also state that it is not a question of wether terrance will view stella to turn around but when.
So my fifth bold statement is
WHY WOULDNT STELLA VIEW TERRANCE TURNING AROUND AT THE SAME TIME?
To get to the heart of my argument, how can you distinguish between two objects using relative motion, when both motions have to be exactly equal at all times?



The reason why they do not see things happening at the same time is because relativity causes a distortion of time.  It is even possible, in a relativistic world, to two observers to see the same thing happen, and yet one will swear that event A took place before event B, while the other will swear that even B took place before event A.

quote:

you also say I am paying to much attention to the visual, I dont think so, all experiments are observed not sensed. Although im not sure where you were going with that.



Are you telling me that a blind man cannot carry out experiments?

It is true that we are most used to carrying out experiments with visual instrumentation, because our visual senses tend to be the most precise; but we do actually have accelerometers that will measure acceleration, and provide a visual readout of how much a body is accelerating.  I was merely using the example of our own internal inertial sense as a way that you might have personal experience of the force associated with acceleration, but we also have electronic devices that can provide the same information in visual form.

quote:

Also, I just glanced over your second post, you say,I don't know the exact ways it resolves itself, but what one can say is that pilots a and b do not, and cannot, exist in isolation, but exist within the context of the wider universe, which does influence the space within it, and so these pilots, in their space ships must have a motion relative to the motion of the total universe.

This is a blatant example of absolute motion. Given newtons third law, every action has an equal an opposite reaction, the overall motion of the universe has to remain constant, or absolute, you might say. so anything relative to the universe as a whole is as absolute a velocity as they come. Secondly, this is clearly not what einstein was saying, he says any non inertial frame of reference is equally valid, not just the frame of reference which is, the entire universe.



There is nothing that I have said that violates Newtons third law.

As you say, in order for Stella to be able to accelerate, there must be a force acting upon her, and that force must create a reaction force on something else, thus the inertia of the universe is conserved.  This is the difference between Stella and Terrance, since Terrance is not accelerating, there is no force acting upon him, so there is no reaction force that must act upon something else.  But all of this pertains to acceleration, not to velocity.



George
« Last Edit: 10/07/2006 02:08:30 by another_someone »

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Offline thebrain13

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Re: twin paradox
« Reply #26 on: 10/07/2006 17:22:10 »
When I said, come on you gonna let me get away with that, I actually meant to post that on my other post, what is distance, since nobody was responding to it. Anyways it seems that since I implied that I obviously errored some place, it ignited a fire of posts, but I really didn't think I said anything false.

Okay so, when I said if a force was acting on your body and the car unifomly, I wasnt implying that I knew of machines that did so, Einstein didnt have to know how to make floating elevators in outer space and build trains that can approach the speed of light. And I didnt think that baseball players would be able to hit baseballs 99.999999999 percent the speed of light, I was assuming if you could.

If you need more examples, why dont you ask a goldfish? whose body is exactly the same density as water(in real life its just similar, were assuming here people) fill his fishbowl completely with water, so no air remains, and seal the top. Make sure you paint the bowl black so he can not see outside. Now accelerate the bowl all you want, in a perfectly controlled experiment he has no way of knowing how much he accelerated.

If any object is accelerating uniformly with its surroundings, no experiment can be done to determine acceleration. Unless you fellas can think of one?

To solvay  your link, is probably the most confusing one i've ever read, that didn't make sense at all. He says, both trains are accelerated equally on parallel tracks from earth to alpha cenauri. Then he jumps right into saying that they both wont make it to earth at the same time. Why the hell not? Why he makes that jump, who knows. I'd be surprised if anybody understood that.

Both solvay and anothersomeones arguments, imply absolute motion to explain this paradox. And Einstein made it clear, there is no such thing. Solvay, your implying that merely by being accelerated that makes you the prefered reference frame, and by being this prefered reference frame, changes the outcome of a given experiment. That is contrary to what Einstein was saying and that is absolute motion. And anothersomeone, even being relative to where you were is an absolute quality. I also never said you were violating newton (newton believed in absolute motion) when I brought his third law up, I was just using it to show you that the universe(as a whole) never accelerates or decelerates, in any direction. Setting motion relative to an anchored object like, the entire universe, is also implying absolute motion. Einsteins relative motion means relative to one other, only one specific object. Setting yourself relative to many objects, screws everything up.

You guys need to break yourselves of always thinking of everything in absolute terms, or you will never understand special relativity. Special relativity works with every object, relative to every other object. If you need to bring in more than one reference frame to explain this phenomema, then you are contradicting Einstein.

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Re: twin paradox
« Reply #27 on: 11/07/2006 01:55:07 »
quote:
Originally posted by thebrain13
Okay so, when I said if a force was acting on your body and the car unifomly, I wasnt implying that I knew of machines that did so, Einstein didnt have to know how to make floating elevators in outer space and build trains that can approach the speed of light. And I didnt think that baseball players would be able to hit baseballs 99.999999999 percent the speed of light, I was assuming if you could.

If you need more examples, why dont you ask a goldfish? whose body is exactly the same density as water(in real life its just similar, were assuming here people) fill his fishbowl completely with water, so no air remains, and seal the top. Make sure you paint the bowl black so he can not see outside. Now accelerate the bowl all you want, in a perfectly controlled experiment he has no way of knowing how much he accelerated.



But you are missing the point, the very point that you yourself raised, Newtons first law of motion, that each and every force has an equal an opposite force  applied to something else (i.e. that a force does not act upon an isolated object, but that a force operated between two separate objects).  This is what is different between a constant velocity, that does not require any force acting upon it (in fact, it must not have a force acting upon it – Newton's first of motion), and an accelerating body that must have a force applied in order to make it accelerate (Newton's first and second laws of motion).

quote:

If any object is accelerating uniformly with its surroundings, no experiment can be done to determine acceleration. Unless you fellas can think of one?



This is not true.  Even if you have a solid lump of iron, and that lump of iron is being uniformly  accelerated by a magnetic field, you can still attach an accelerometer to the lump of iron in order to measure its acceleration.

Even if you had not yet invented accelerometers, you could determine that the lump of iron is being pulled by the magnet by looking at the reaction in the magnet itself (Newton's third law, that every force must have an equal and opposite, and the force applied to the lump of iron will have an equal and opposite force measurably applied to the magnet itself.

quote:

You guys need to break yourselves of always thinking of everything in absolute terms, or you will never understand special relativity. Special relativity works with every object, relative to every other object. If you need to bring in more than one reference frame to explain this phenomema, then you are contradicting Einstein.



This is where we started out, and what you say is categorically wrong, all that special relativity pertains to is inertial systems.

http://en.wikipedia.org/wiki/Special_relativity
quote:

The theory was called "special" because it applies the principle of relativity only to inertial frames.



http://en.wikipedia.org/wiki/Inertial_frames#Equivalence_of_inertial_reference_frames
quote:

A fundamental principle of all physics is the equivalence of inertial reference frames. In practical terms, this equivalence means that scientists living inside an enclosed box moving uniformly cannot detect their motion by any experiment done exclusively inside the box.
By contrast, bodies are subject to so-called fictitious forces in non-inertial reference frames; that is, forces that result from the acceleration of the reference frame itself and not from any physical force acting on the body. Examples of fictitious forces are the centrifugal force and the Coriolis force in rotating reference frames. Therefore, scientists living inside a box that is being rotated or otherwise accelerated can measure their acceleration by observing the fictitious forces on bodies inside the box.






George

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another_someone

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Re: twin paradox
« Reply #28 on: 11/07/2006 02:24:36 »
quote:
Originally posted by thebrain13
You also state that it is not a question of wether terrance will view stella to turn around but when.
So my fifth bold statement is
WHY WOULDNT STELLA VIEW TERRANCE TURNING AROUND AT THE SAME TIME?



http://en.wikipedia.org/wiki/Relativity_of_simultaneity
quote:

Relativity of simultaneity means that events that are considered to be simultaneous in one reference frame are not simultaneous in another reference frame moving with respect to the first. For example imagine there were volcanoes located on Mars and Venus. We on earth may see these two volcanoes on the different planets erupt and conclude (after appropriate corrections for light travel) that the eruptions were simultaneous; we could calculate the Greenwich Mean Time at which the eruptions occurred. The inhabitants of a distant galaxy, travelling away from ours at a great speed, may one day observe these same eruptions and find that they were not simultaneous, that one occurred before the other. The concept of “simultaneous” or “simultaneity” is not an absolute, but a relative property – it depends on one’s frame of reference.
In Einstein’s Special Theory of Relativity, relative simultaneity seems to be inextricably linked with the (logically) separate phenomenon of time dilation, which concerns the different rates at which time passes (or identical clocks tick) in two different reference frames. However these two different things are not necessarily linked. For example, Einstein’s (1960) demonstration of relativity of simultaneity (lightning strikes both ends of a moving train, seen as simultaneous on the embankment but not on the train) makes no reference to clocks or the rates at which they are running. No conclusions need be drawn about the rate of moving clocks from this example alone.





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Offline thebrain13

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Re: twin paradox
« Reply #29 on: 11/07/2006 19:17:44 »
how do you put links in posts?

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another_someone

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Re: twin paradox
« Reply #30 on: 11/07/2006 19:24:04 »
quote:
Originally posted by thebrain13
how do you put links in posts?



I suggest you read through: http://www.thenakedscientists.com/forum/faq.asp



George

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Offline thebrain13

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Re: twin paradox
« Reply #31 on: 11/07/2006 20:17:56 »
Um actually, I dont really feel like learning links right now, anyways I just did a little research on the "relativity of simultaneity" Google that in parenthesis and click on the first link. I think this is really the misundetstood part of relativity, this is what really makes everything work, but hardly anybody ever references. Including almost all explanations of relativity I've seen, who WRONGLY, explain something without referencing it, or at least use it to explain things like relative velocity.

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Re: twin paradox
« Reply #32 on: 11/07/2006 20:25:50 »
And to anothersomeone, your accelerometer would not work if it was accelerating uniformly with whatever it was measuring. Im not talking about accelerating it by pushing a side of the accelerometer. The meter has to be uniformly accelerating with its surroundings. Would your meter work free falling in a gravitational field? Key word, free falling. Also there is a big difference between using internal systems and using absolute motion.
« Last Edit: 26/07/2006 02:19:53 by thebrain13 »

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another_someone

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Re: twin paradox
« Reply #33 on: 11/07/2006 21:10:12 »
quote:
Originally posted by thebrain13
Um actually, I dont really feel like learning links right now



So why did you ask?

quote:
Originally posted by thebrain13
And to anothersomeone, your accelerometer would not work if it was accelerating uniformly with whatever it was measuring. Im not talking about accelerating it by pushing a side of the accelerometer. The meter has to be uniformly acclerating with its surroundings. Would your meter work free falling in a gravitational field? Key word, free falling. Also there is a big difference between using internal systems and using absolute motion.



Gravity is a whole different issue, which is where general relativity comes in.

What general relativity says is that if you are free-falling in a gravitational field, you are simply following the natural curve of space (in other words, it is the person who appears to be stationary who is actually accelerating in space, and the person who is free-falling is actually not accelerating at all – this is exactly what an accelerometer would tell you).

http://en.wikipedia.org/wiki/General_relativity
quote:

gravitation is not due to a force but rather is a manifestation of curved space and time, this curvature being produced by the mass-energy and momentum content of the spacetime


One of the defining features of general relativity is the idea that gravitational 'force' is replaced by geometry. In general relativity, phenomena that in classical mechanics are ascribed to the action of the force of gravity (such as free-fall, orbital motion, and spacecraft trajectories) are taken in general relativity to represent inertial motion in a curved spacetime. So what people standing on the surface of the Earth perceive as the 'force of gravity' is a result of their undergoing a continuous physical acceleration caused by the mechanical resistance of the surface on which they are standing.





George

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Offline thebrain13

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Re: twin paradox
« Reply #34 on: 11/07/2006 22:17:52 »
I knew I would get that response if I brought up gravity. That free falling accelerometers don't work because gravity doesn't "really" accelerate things. Regardless of that, if you accelerate an accelerometer, uniformly with its surroundings it still gets no reading. Even if you don't use gravity.

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Re: twin paradox
« Reply #35 on: 26/07/2006 02:27:55 »
quote:
Originally posted by thebrain13
I knew I would get that response if I brought up gravity. That free falling accelerometers don't work because gravity doesn't "really" accelerate things. Regardless of that, if you accelerate an accelerometer, uniformly with its surroundings it still gets no reading. Even if you don't use gravity.



So what force (or pseudo force) would you use that would equally accelerate all parts of the accelerometer.

Any force that would behave in this way would be so much like gravity as to be indistinguishable from gravity, and so why would you not call it gravity.

Every other force you care to name behaves differently upon different types of matter, and so you could always construct an accelerometer using whatever type of matter was not affected by this force.



George

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Offline thebrain13

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Re: twin paradox
« Reply #36 on: 26/07/2006 04:07:05 »
Einsteins equivalence principle explains that all uniform acceleration acts exactly the same as gravity, so of course my example would act like gravity, thats inevitable. And since you cant distinguish between the use of gravity and whatever force(s) I use, granted they are under uniform acceleration like I explained in my experiment, the use of gravity wont affect the experiment.

In otherwords einstein is saying your accelerometer wont read anything, regardless of if it is in freefall or under uniform acceleration.

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Re: twin paradox
« Reply #37 on: 26/07/2006 17:05:00 »
But you have said that your hypothetical force is like gravity, but it is not gravity – do you have the least evidence that such a force actually exists.  If such a force does not exist, then your scenario does not exist.

The only force that operates at large distance other than gravity is the electromagnetic force, but the electromagnetic force can easily be distinguished from gravity.  Are you saying that you have discovered another long range universal force?



George

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Offline thebrain13

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Re: twin paradox
« Reply #38 on: 26/07/2006 19:39:30 »
you can use multiple forces, in whatever magnitudes. Your argument is that it is impossible to accelerate an object uniformly without using gravity, that is not the case.

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Offline ukmicky

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Re: twin paradox
« Reply #39 on: 26/07/2006 22:30:20 »
quote:
Originally posted by thebrain13

you can use multiple forces, in whatever magnitudes. Your argument is that it is impossible to accelerate an object uniformly without using gravity, that is not the case.

What other forces  can act on and  accelerate  every single atom in a body equally or how would you use multiple forces to act on every atom equally

Michael
« Last Edit: 27/07/2006 00:41:39 by ukmicky »

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Offline thebrain13

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Re: twin paradox
« Reply #40 on: 27/07/2006 01:04:31 »
yes, use multiple forces to accelerate the atoms equally.

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another_someone

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Re: twin paradox
« Reply #41 on: 27/07/2006 01:23:44 »
quote:
Originally posted by thebrain13

yes, use multiple forces to accelerate the atoms equally.



But you have still evaded answering the question – what is the force, or what are the multiple forces, you would use.  To say there are more than one of them does not tell us what they are.



George

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Offline thebrain13

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Re: twin paradox
« Reply #42 on: 27/07/2006 01:28:18 »
electric charge

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another_someone

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Re: twin paradox
« Reply #43 on: 27/07/2006 01:57:38 »
But electric charge has no effect upon electrically neutral entities.

Electric charge has no effect upon a neutron at all.  Electric charge has an opposite effect upon the electrons and the protons within an atom, and so the overall effect upon an electrically neutral atom will be nothing at all.  Furthermore, electric charge, although it can have a polarising effect upon photons, it will not cause and attractive or repulsive force upon a photon, since a photon is also electrically neutral (and the red shift in a laser or radar beam could be used to construct an accelerometer).



George

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Offline thebrain13

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Re: twin paradox
« Reply #44 on: 27/07/2006 02:50:13 »
Then use Electric charge, and Nuclear strong force. Cant you just drop this argument? The only way you can win is if you prove that accelerating an object uniformly is impossible. Which makes einsteins equivalence principle meaningless. Im implying if you did, what would happen, I dont need to make the experiment.

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Re: twin paradox
« Reply #45 on: 27/07/2006 03:42:35 »
quote:
Originally posted by thebrain13
Then use Electric charge, and Nuclear strong force. Cant you just drop this argument? The only way you can win is if you prove that accelerating an object uniformly is impossible. Which makes einsteins equivalence principle meaningless. Im implying if you did, what would happen, I dont need to make the experiment.



Photons, neutrinos, and much else are effected by neither electric charge nor the strong nuclear force.

Protons are neutrons are effected by the strong nuclear force, but the range of the strong nuclear force is so short that it cannot be felt outside the nucleus of the nucleus of the atom, so there is no way of using it to effect a group of atoms.

Einstein only postulated two equivalences – that if inertial reference frames, which is not the case we are discussing; and that between uniform acceleration (caused by the curvature of space) and gravity.  He made no suggestion that anything but a curvature of space itself could cause the kind of equivalence that you suggest.



George

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Offline thebrain13

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Re: twin paradox
« Reply #46 on: 27/07/2006 03:53:01 »
yes he did. Why do you think he called it the equivalence principle?

Because gravity is equivalent to uniform acceleration.

What Einstein never says, is only gravity can create uniform acceleration. Unless you can find where he says that, in which case, I stand corrected.

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Re: twin paradox
« Reply #47 on: 27/07/2006 11:20:06 »
quote:
Originally posted by thebrain13

lets say there are two spaceships containing one pilot each, they are identical twins of course. We'll call them pilot a and pilot b. pilot b fires his engines and travels at 99 percent the speed of light away from pilot a for one year. Then turns around and comes back. Einstain says that from pilot a's perspective pilot b would have aged less than him. However Since velocity is relative to each observer, pilot b sees pilot a speeding away from him and then returning. So pilot b should see a younger pilot a. So my question is when the two meet each other after the trip which one is younger?



[:)]

Hi, Thebrain13.

I both pilot travells 1 earthyear then they both are same age. If hundred year then they are 100year. Still same age.

If travelling speed is different a and b, x m/s, still s is actual same both. Only m is different and changed.

Can use timeunit, earth s or "constant" s, still 1s is 1s. What else it can be? 1s cannot be 1/2s or 2s.

Therefore my answer to your question is that both space-traveller going do aged at same time. Of cource and because our body is like other mammals fir to earth nature through many and many generation it control that ageing-process and different speed on space can happend some genetical-cell basic changes and then other traveller can be little seems yonger, but still, earth-year-age is same.


[:)]
 

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Offline tarbag

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Re: twin paradox
« Reply #48 on: 27/07/2006 22:49:11 »
quote:
. Einstain says that from pilot a's perspective pilot b would have aged less than him.


According to the experiment of Michelson Morely we deduce that the theory of special relativity  is valid for the light signals or the  electromagnetic waves.Why thus apply it for material bodies. It is not  a confusion here.
Well cordially
 

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another_someone

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Re: twin paradox
« Reply #49 on: 26/07/2006 17:05:00 »
But you have said that your hypothetical force is like gravity, but it is not gravity – do you have the least evidence that such a force actually exists.  If such a force does not exist, then your scenario does not exist.

The only force that operates at large distance other than gravity is the electromagnetic force, but the electromagnetic force can easily be distinguished from gravity.  Are you saying that you have discovered another long range universal force?



George