Re: Stupid Relativity Question

From: Geraldine Hobba (g.hobba_at_optusnet.com.au)
Date: 03/04/05 

Date: Fri, 4 Mar 2005 14:44:50 -0800

"Young J. Putt" <j.putt@verizon.net> wrote in message
news:38q3lfF5ooor9U1@individual.net...
> Thanks for the references. I will check them out. Too many years in the
> non-scientific world have atrophied my math skills considerably, so it
> will
> take some work to get through that derivation.
>
> I hope you'll indulge my ignorance a little longer. See below:
>
>> > Since there is no preferred frame of reference, why is it that the
>> > traveling
>> > twin stays younger, and not the twin that remains on earth, since we
> could
>> > say that the twin on earth is also moving away from the traveling twin
> at
>> > close to C?
>>
>> Saying that the laws of physics should be put in a form that is frame
>> independant is not the same as saying all FOR's are equivalent. All
>> inertial frames are equivalent - but one can tell the difference between
>> inertial frame and frames accelerated wrt to inertial frames by the
> presence
>> of forces of acceleration. Thus the situation is not symmetrical - one
> twin
>> experiences forces of acceleration - the other does not.
>>
>
> Ah! The traveling twin experiences forces.

Yes - very important point.

> I've seen this explanation before
> as to why he gets to be younger. So it seems that it's the force and the
> acceleration that create the space/time dilation, NOT the relative
> velocities of the twins.

Be careful here - the forces of acceleration and the acceleration are
inseparable so it is not really meaningful to say what causes what. If you
have read about General Relativity (GR) and are thinking of the Einstein
Equivalence Principle (EEP) remember that principle applies locally. For
details see
http://nedwww.ipac.caltech.edu/level5/March01/Carroll3/Carroll_contents.html

> Is it the fact that I've been accelerated in a
> certain direction that makes the distance to my destination become
> smaller?

No - it is the fact that according to the Lorentz transform the distance is
measured smaller than if you were at rest.

> What would I percieve if I looked back towards earth?

You would see the earth receding from you.

> Would it be further
> away since I am accelerating away from it?

Of course the distance will be increasing because you are accelerating.

> Also, it would seem that the
> distance dilation would occur during the period of acceleration, then
> appear
> constant once I reached my top velocity. Right?

Think about the problem by considering the acceleration as a large number of
different velocities that exist for an infiintesimal amounts of time. Have
a look at the clock postulate in the FAQ's I linked you too and give it a
bit of thought. I am sure you will see what is going on.

> Why wouldn't the effect be
> reversed as I decelerate when I return to the earth?

I am not quite sure I understand what you mean.

>
> The concept is never presented that way (in terms of forces of
> acceleration)
> until someone asks my question about why time slows for the traveling
> twin,
> nor have a heard an explanation as to why accleration causes this effect.
> It's just sort of brushed over. Is there a way for a non-scientist to
> conceptualize this?

Have a look at the twin analysis in the FAQ's I linked you to.

>
> Would I be able to lenghten my lifespan by sleeping each night in room
> that
> is rotating very rapidly?
>

Yes - relative to someone who did not - but the effect would be exceedingly
small for realistic velocities. Also time for you will travel exactly as is
if you did not do it - you simply would be slightly younger than someone who
did not do it.

> It seems like once it got up to speed, it
> shouldn't bother me. Although I guess my boss might get a little upset
> when
> I don't show up for work for ten years while I get a good nights sleep!
>
>> >
>> > and
>> >
>> > As I understand it, the traveling twin could, by traveling nearer and
>> > nearer
>> > to the speed of light, perceive less and less time passing during his
>> > trip.
>> >
>>
>> The traveling twin perceives time flowing exactly the same as the
> stationary
>> twin - it is only when they are bought together that a difference is
>> noticed.
>>
>> > If he traveled fast enough, he could finish the trip in 5 minutes his
>> > time.
>>
>> Yes.
>>
>> > If he traveled, say, 10 light years in 5 minutes, didn't he just travel
>> > way
>> > faster than light?
>>
>> He could not travel 10 light years in 5 minutes as measured by the
>> stationary twin. But the twin can conceptually travel at any speed less
>> that the speed of light for any period at all.
>>
> So it seems to me that although I may not be able to travel faster than
> the
> speed of light as observed by me while I'm doing the traveling, I can
> still
> arrive at a destination that is many light years away in a few minutes.

Yes - that is one of the interesting conclusions of relativity.

> So
> as far as I am concerned, I can travel faster than light.
>

You can not travel faster than light. However by traveling very close to
the speed of light distances that would have previously been vast are now
much smaller (Lorentz contraction) and able to be traversed in much less
time according to you.

> I realize that
> perhaps the way I worded this isn't accurate, but if I don't care about
> the
> perceptions of people at either end of my journey, does what I'm saying
> make
> sense?

Yep. Keep thnking and post any further questions.

Thanks
Bill

>
> Thanks again for entertaining my questions!
>
>

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