Re: Are *observed* SR effects real?

On Jul 31, 6:52 pm, mluttg...@xxxxxxxxxx wrote:
On Aug 1, 1:21 am, PD <TheDraperFam...@xxxxxxxxx> wrote:



On Jul 31, 5:56 pm, mluttg...@xxxxxxxxxx wrote:

On Jul 31, 7:12 pm, PD <TheDraperFam...@xxxxxxxxx> wrote:

On Jul 31, 9:40 am, mluttg...@xxxxxxxxxx wrote:

On Jul 30, 11:19 pm, PD <TheDraperFam...@xxxxxxxxx> wrote:

On Jul 30, 2:50 pm, mluttg...@xxxxxxxxxx wrote:

I read:

"Of course, to Ginny, it's impossible for her to tell whether it's
her
that's approaching the beacon or the beacon is approaching Ginny. But
it doesn't matter. In the case of the Earth study I mentioned, it is
the Earth that is approaching the star and the Earth that is receding
from the star (by virtue of its orbit around the Sun), and there the
experimental answer is unambiguous: the motion of the observer does
not result in a change in the speed of light from the star."

Ok, case closed!

Marcel Luttgens

Until somebody runs an experiment that shows that there IS a
difference, and the experiment is repeated independently and confirms
the result, in which case there will undoubtedly be significant
celebration about something interesting having been found!

I asked you a question at the end of my last post, about seeing where
we are going next. I'd like to see if you'd like to attempt an answer
to that question before we go on. Care to give it a shot? Think about
where we've been so far.

PD

Is this your question? :

"By now you are surely wondering, "All these things I thought were
surely frame-independent you are telling me are frame-dependent. Are
there no physical quantities  left that are frame-independent??" And
the answer to that question is "Yes, just not the ones we at one time
thought." And we'll get there."

No, that isn't the question I had in mind. The one I was referring to
was the one here:
==============================
So if we use a light signal between the two clocks, then surely we
will have two clocks in different locations that are synchronized
(after any adjustments needed to make t3-t2 = t2-t1). What this
means,
of course, is that if one clock ticks 13:38:52, the other clock will
tick 13:38:52 *simultaneously*. This is, after all, what we *mean* by
clocks being synchronized.
Now, can you guess where we're going next?
PD

Sorry, I missed the question.

Logically, the next step would be to generalize the
procedure to moving clocks.

Marcel Luttgesn

Actually, the procedure works for moving clocks, by design.

Could you show how you get t2 - t1 = t3 - t2. when the
clocks are comoving at v. Imo, this is the first step
you should take. that's not difficult, think of the MMX.
Insted of using gammma, speak of a length contraction by
a factor f, which is some unknown function of v.
Afterwards, we could proceed further.

Sure. It actually doesn't have to do with gamma or contraction or
anything. It has to do with what it *means* for two clocks to be
synchronized.

Let's take two comoving clocks (which means basically, they stay a
fixed distance apart from each other). I propose to synchronize them
in the frame in which they are at rest. (If they are not at rest in
this frame, then I will move to the frame in which they are at rest
before synchronizing them.) We can then look at those clocks in
another frame if you want. So we have a frame B, with a bunch of
clocks at rest relative to that frame, and we want to synchronize two
of them, C1 and C2, that will be near the events E1 and E2.

So what I do is this:
1. Record the time t1 at C1.
2. Walk or send a signal from C1 to C2.
3. Record the time t2 at C2 upon arrival.
4. Walk or send a signal from C2 to C1.
5. Record the time t3 at C1 upon arrival.

We know that the distance covered in (2) and (4) is the same, since
the clocks are at rest in this frame, and the speed of transit in (2)
and (4) is the same, and so we expect that t3-t2 should be the same as
t2-t1 IF and ONLY IF the clocks C1 and C2 are synchronized. If they
are not synchronized, of course, then the way we will recognize that
fact is that t2-t1 =/= t3-t2. (And then of course we can adjust one of
the clocks forward or backward and redo this procedure until the
clocks ARE synchronized.) This is what we *mean* by synchronized
clocks, and how we can tell when we have them. If you think about it,
there's no other way (that isn't equivalent) to tell if two spatially
separated clocks are synchronized.

Now, what about the same two clocks C1 and C2 as seen in another frame
A? In this frame they are moving. We know already from our friends
Stan and Tom that if the clock ticks are simultaneous in B, then they
won't be simultaneous in A. But does A understand *why* they are not
synchronous in A? Of course! Watching the fella in B do the procedure,
it is still true that the speed of the signal transit from C1 to C2 is
the same as from C2 to C1 again, but now the distance isn't the same.
Because the clocks are moving in A, a signal has to travel further in
one direction than in the other, according to A. And so OF COURSE, the
clocks won't be synchronized because you don't expect t3-t2 to equal
t2-t1 in that circumstance, and setting the clocks SO THAT t3-t2 = t2-
t1 would result in unsynchronized clocks.

So the observer in B says he followed the procedure for
synchronization to the letter, and so he KNOWS the clocks are
synchronized, and the observer in A says the other observer did NOT
follow the procedure properly and so the clocks are NOT synchronized.

"Fine!" says the observer in B. "You do it. You synchronize your own
clocks."
And so A has his own set of clocks at rest in A and synchronizes two
of them near where E1 and E2 will happen, and he follows the *exact*
same procedure and declares them synchronized. Now, to the observer in
B, those clocks are moving. And so by the very same argument that was
made before, B says the clocks are NOT synchronized.

So the observer in A completely understands why the observer in B sees
A's synchronized clocks as unsynchronized, and the observer in B
completely understands why the observer in A see's B's synchronized
clocks as unsynchronized. There just isn't a way to determine who is
"right".

So we have two sets of clocks, both with a pair of clocks near events
E1 and E2. The observer in A says one clock pair is synchronized but
the other pair is not. The observer in B says the same thing but in
reverse. We need synchronized clocks to measure the time between E1
and E2. So obviously the synchronized set that each frame uses will be
different to measure that time, and each set of synchronized clocks
will come up with a different time between E1 and E2. And this is why
duration is frame-dependent, in much the same way that length is time
dependent.

Marcel, notice that in NONE of this discussion, including both the
frame dependence of length with Stan and Tom, and now with the frame
dependence of dilation, have we EVER had to invoke any gammas or
contraction or dilation or anything like that. All we have talked
about is what length *means* and what duration *means* and what
synchronization *means* and noticed that, experimentally, simultaneity
is frame-dependent -- and that frame-dependence of simultaneity is
expected from the laws of electrodynamics. I've done this on purpose
so that you can see where this frame dependence *comes from*. In a
little while, after we talk about frame-independent quantities, we can
bring up where those gammas and length contraction and time dilation
formulas come from.

PD



.

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