Re: I don't get it

On Feb 16, 8:51 am, kenseto <kens...@xxxxxxxxxx> wrote:
On Feb 15, 12:54 pm, Randy Poe <poespam-t...@xxxxxxxxx> wrote:



On Feb 15, 12:29 pm, pete.ha...@xxxxxxxxxxxxxx wrote:

I've started the relativity module of my physics degree, and I'm
having some conceptual trouble with it.

I'm fine with the maths and I can do the questions - I got 100% in the
first long answer test. But I just don't *get* it.

Well, you've set yourself up for an interesting exercise
in critical thinking. This newsgroup has a lot of
anti-relativists, many of them practically foaming
at the mouth with their hatred of all things relativistic.

There are people with actual expertise, and people
who claim Ph.Ds and claim to be the world's best
physicists but give no evidence of having ever passed
a freshman course. And all you have to judge them by
is what they write.

Have fun trying to figure out who is who!

No explanation of the twins paradox makes much sense to me. Everyone
just points out to me that the travelling twin is accelerate, and that
makes them different. But the Lorentz transformation don't seem to say
anything about acceleration as far as I can make out, which would mean
that they don't agree with the conceptual part of relativity (or what,
I understand, has been observed experimentally).

But however you analyze it, there is a clear
asymmetry that must be represented in some way.
For instance, suppose the two twins emit continuous
radio signals at each other, at a fixed frequency.
As the traveling twin gets farther away, both twins
see the signals red-shifted. When the traveling twin
turns around, he immediately sees the earth signals
blue-shifted, as soon as he is moving back toward
earth.

This is not necessary true. It depends on how far away from earth the
traveling is when he turnaround. If the traveling twin is very far
away then the inverse square law kicks in and the traveling twin will
still see the earth signal to be red shifted.


WHAAAAATTT??? Seto launches another pumpkin.
1. The inverse square law applies close to the earth.
2. The inverse square law is not what is responsible for red shift, as
red shift also occurs in a uniform field.
3. The twin puzzle has nothing whatsoever to do with gravitational red
shift.

Geez, that one smelled bad from here, and I'm nowhere NEAR Ohio.


Ken Seto

But the earth-bound twin will not see the
change from red- to blue-shift until the signal has
had time to propagate from the traveler's turnaround
point.

I'm essentially giving the "Doppler shift explanation"
which is done better here:http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_...

Another way of looking at it is with world lines:http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_...

And here's the top-level page to examine more aspects
of the analysis:http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_...

It is also a little unclear to me why we see relativistic effects. One
minute I am told time dilation is a consequence of the speed of light
being the same in all reference frames, then someone starts talking
about the time it takes light signals to come from a clock. In the
latter case it would seem the dilation isn't 'real' at all, whereas in
the former case it is.

There seems to be confusion there between doppler shift
and relativistic time dilation. The relativistic doppler
equation includes both a time-dilation (direction-independent,
second-order) term, and a term due to travel distance
from a moving source (direction-dependent, first order,
looks like classical doppler for sound).

If you just talked about the time for signals to propagate,
you couldn't explain the "transverse doppler effect".

http://en.wikipedia.org/wiki/Transverse_Doppler_effecthttp://mysite.d...

- Randy

.

Relevant Pages

  • Re: I dont get it
    ... radio signals at each other, ... As the traveling twin gets farther away, ... he immediately sees the earth signals ... There seems to be confusion there between doppler shift ...
    (sci.physics.relativity)
  • Re: Circular motion in SR
    ... slower than an identical clock on earth. ... it is orbiting or moving in a straight line. ... precisely also why the traveling twin comes back younger. ...
    (sci.physics.relativity)
  • Re: I dont get it
    ... that they don't agree with the conceptual part of relativity (or what, ... radio signals at each other, ... As the traveling twin gets farther away, ... There seems to be confusion there between doppler shift ...
    (sci.physics.relativity)
  • Re: I dont get it
    ... As the traveling twin gets farther away, ... he immediately sees the earth signals ... red shift also occurs in a uniform field. ...
    (sci.physics.relativity)
  • Re: Simple question
    ... reference is moving relative to ours or is in a gravitational field. ... sister on earth. ... Is there anyway that way that we can see the other clock run faster? ... the traveling twin see the Earth's twin's age to be when the traveling ...
    (sci.physics.relativity)
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