Re: twin paradox, but a symmetric one

On Oct 26, 12:33 am, "Spaceman" <space...@xxxxxxxxxxxxxxxxxxxxxxxxxx>
wrote:
Uncle Ben wrote:
On Oct 24, 6:01 pm, "Spaceman" <space...@xxxxxxxxxxxxxxxxxxxxxxxxxx>
wrote:
Uncle Ben wrote:
On Oct 24, 4:18 pm, liketofindoutwhy <liketofindout...@xxxxxxxxx>
wrote:
On Oct 24, 6:17 am, "Dirk Van de moortel"

<dirkvandemoor...@xxxxxxxxxxxxxxxxxx> wrote:
PD <TheDraperFam...@xxxxxxxxx> wrote in message

e618e2a1-b23c-4a7e-acee-1edc654ed...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx

On Oct 24, 6:55 am, liketofindoutwhy <liketofindout...@xxxxxxxxx>
wrote:
On Oct 23, 8:00 am, PD <TheDraperFam...@xxxxxxxxx> wrote:

They will arrive with the same age.
The statement that "time dilation says A is older than B and B
is older than A" is an extravagant oversimplification of what
SR says, which is not uncommon for someone with a hobbyist's
contact -- and I'm not saying that condescendingly but rather
to incite you to find materials that will dig just a little
deeper, as it appears you want to do.

yes, by symmetry at least, they should arrive at the same age
(since by symmetry, A can't be older than B and B can't be older
than A, and therefore must be equal).

Now, note that in all 3 textbooks of Halliday, Serway, and
Hewitt, they say time dilation occurs when there is relative
velocity not equal to 0. That's it. There is no other
requirement.

And this bald oversimplification is symptomatic of the cursory
treatment that is given in a survey textbook intended for
freshmen, in a late chapter that is hardly ever covered in a
course because of time considerations. If you'd like a
considerably better book that doesn't do such a slap-dash job of
it, and is still aimed at the same level student, there are
several I can recommend:
Spacetime Physics, by Taylor and Wheeler
General Relativity, by Robert Geroch

I'd recommend the "GR from A to B" version here.
But definitely not for 10 years olds :-)

Dirk Vdm

Dirk, all you know is to type out "it is not for 10 year olds" in
every single post you write huh? if we just present a bunch of
formulas and ask a 10 year old to comprehend, I am sure it is quite
difficult. Just like calculus, if we throw out a bunch of
differentiations formulas, a bunch of integration methods, I am
sure a 10 year old will have a hard time understanding it. But, is
calculus so difficult that a 10 year old cannot understand it? I
think not. Differentiation explained as small change of y divide by
the small change of x to study the rate of changing at that moment,
is that so hard to understand? Integration explained as summing up
of many small parts, is it so hard to understand? I think we make
things hard to understand because we don't understand it very well
to begin with, and then we throw out formulas after formulas, and
it is going to confuse anybody at any age.- Hide quoted text -

- Show quoted text -

Dear liketofindoutwhy,

I like your first post -- the one that started this post. As a Ph.
D. physicist and teacher for many years, I think your questions in
that post deserve a considered answer:

You are exactly right that the usual language used in teaching
relativity encourages a hesitant mentality that is ambiguaous as to
whether the effects that "gaily mock at common sense" in the words
of one author are real or are onhy appearances or illusions.

The approach I prefer is to say that just as "left" or "right" are
directional terms defined relative to a person's stance, faster,
slower, longer, and shorter are terms that, Einstein discovered, are
defined only relative to a frame of reference. This is a shocking
concept, which is why so many in sci.physics.relativity spend their
pitiful lives trying to disprove it.

So I prefer to say that B's clock IS slower than A's clock with
respect to A's frame of reference. The same is true if you
interchange A and B.

Observation does not show such in a case where the observers
are heading towards each other.
Heading towards each, one sees the other as ticking faster.

The effects are not illusions or mere appearances. They are as real
as any other physical measurement, except that to be clear, one has
to identify the frame of reference one is supposing that the
measurements are referred to.

One observer is heading toward the clock,
one observer is heading away from the clock
The heading toward the clock sees the clock as faster,

No, slower,

No.
I did not say anything about an acceleration or change in g-force.
Doppler only will create the illusion of a faster clock.

The heading away from the clock sees the clock as slower.
The clock, has not changed it's physical rate at all.
Doppler explains it.

Doppler has nothing to do with time measurement.

Measurement of another clocks tick rate can not be determined without
including any doppler effect that is occuring between observer and
clock.
Again you seem to be ignoring such a fact instead of thinking about it.- Hide quoted text -

- Show quoted text -

In observing the Doppler Effect, one is not measuring the tick rate of
a clock. One is measuring the frequency or wavelenth of a received
light beam using one's own clock.

That is why I say that it has nothing to do with time dilation except
to remove the effect that one observes in the case of sound, that the
frequency shift is different for the case of the sender moving and the
receiver moving, both w.r.t. the medium. No medium, no difference.
.

Relevant Pages

  • Re: definition of a clock in relativity theory
    ... of relativity, ... So we "prove" that the hugely-accelerated clock still acts just like ... gravitational time dilation, and decide that the spacetime distortion ... accelerated clock behaves just like an inertial clock to an incredible ...
    (sci.physics.relativity)
  • Re: quibbles with special relativity
    ... >>let's stick to special relativity here.. ... >>supposedly time dilation takes effect when objects move period ... > observer are in relative motion. ... > You seem to imply that an observer moving with the clock itself would ...
    (sci.physics)
  • Re: Distance-dependent time contraction
    ... and relativity is about the relationship ... In this case, the observed, or measured time dilation could not be ... and you notice my clock is running slower than yours. ... So now I will immediatly observe your clock "rate" as going faster ...
    (sci.physics.relativity)
  • Re: A Speed Limit for Massive Particles?
    ... space based clock. ... relative speed) and gravitational time dilation. ... seem to have only a tenuous grasp on relativity. ... to a space observer a clock inside a Black Hole's ...
    (sci.physics.relativity)
  • Re: A Speed Limit for Massive Particles?
    ... change to the signals or to the clock. ... Time dilation increases with the mass of the massive object. ... Red/blueshift of a signal beamed from Earth to a space observer or visa ... Simultaneity is not a required component of such measurement. ...
    (sci.physics.relativity)