Re: Are *observed* SR effects real?

On Jul 12, 4:09 am, mluttg...@xxxxxxxxxx wrote:
On Jul 11, 10:14 pm, PD <TheDraperFam...@xxxxxxxxx> wrote:



On Jul 11, 2:57 pm, mluttg...@xxxxxxxxxx wrote:

On Jul 11, 4:06 pm, PD <TheDraperFam...@xxxxxxxxx> wrote:

On Jul 11, 4:15 am, mluttg...@xxxxxxxxxx wrote:

On Jul 10, 9:09 pm, PD <TheDraperFam...@xxxxxxxxx> wrote:

OK, well I'm grateful that you are at least admitting there is
something you're just not getting about special relativity and you
would like the real answer. I'm happy to try to explain it to you. It
will be a circuitous route, though, for pedagogical reasons, and I
hope you'll stick with me. Here is the game plan:
1. I'll first show you why length contraction is real but is neither a
physical compression of an object nor an observational illusion.. This
will help set the frame for the similar statement regarding time
dilation, but it's easier to see with length.
2. To see what length contraction is, I'll have to show before that
that length *by definition* is inextricably linked to simultaneity.
3. We'll then show that simultaneity is realio-trulio frame-dependent.
Actually, what we'll say is what is seen in observation, which will
look odd, but then we'll show that it's not odd at all and is
completely consistent with the laws of physics.
4. Then, seeing that simultaneity is frame-dependent, and given
length's *definitional* dependence on simultaneity, it will be easy to
see what's going on when length contraction occurs.
5. Then we'll be able to find the analogous definitional dependency
for duration, and we'll quickly show the frame dependence of that
dependency, and from there it will be easy to see what's going on when
time dilation occurs.
6. The frame-dependence of some things we had assumed were frame-
independent will beg the question what frame-independent quantities
are left, and then we can get into spacetime interval and the
relationship with frame-dependent length and duration.

Do you see the plan? Is it dismaying that it's so elaborate?

PD

I would gratefully peruse your plan, after your
confirmation that in flight, the frequency of
the airborne clocks is not physically modified by their
velocity wrt the Earth clocks, even if, according
to H&K, those clocks, when brought back to Earth,
mark a different time than the Earth clocks.

Alright, then let's start with length and figure out what this word
means.
You could define it to be, say, the number of atoms lined up end-to-
end, but this leads to some dissatisfaction, because we know we can
compress a steel rod without changing the number of atoms from end-to-
end. Moreover, this presumes that we know, somehow and a priori, what
the dimensions of an atom are -- and we don't. Plus, we want to be
able to measure a length between any two events (an "event" is
something that happens at a particular location and at a particular
time, though of course the values of those coordinates will depend on
the coordinate system chosen) even if there is no material substance
between the two events.

A more sensible definition of length is by reference to some length
standard, which we'll call a "ruler". The length standard needs to be
reproducible and sturdy and accurate, and we'll further attach the
rule (for reasons that will be apparent in a bit) that the standard
ruler needs to be used at rest by the observer using it. Then, if we
want to measure a length between two events, then what we need to do
is make note of the mark on the ruler that is nearest one event and
the mark on the ruler that is nearest the other event, and then
subtract the numbers on those ruler marks. This gives us a length.

But it turns out to require more than that. What I've described above
works fine for something (where the events are the ends of that
something at the times those ends are looked at) that is at rest
relative to the ruler, because then I can take my time turning my eyes
from one end of the object and that mark, to the other end of the
object and the other mark.

But what if the object is moving relative to the ruler? Well, let's
suppose I wanted to measure the length of a passing Mercedes, bumper
to bumper. Suppose I laid the ruler on the ground and then, when the
Mercedes passed, I took note of the mark nearest the front bumper and
then walked quickly backwards and took note of the mark nearest the
back bumper. "Whoa, wait a minute," a bystander cries, "that doesn't
give you the length of the car! The car moved forward while you were
walking from the front of the car to the back of the car. It's no
wonder you came up with a number that is only 2 meters! If you measure
a car that way, you'll always come up with an answer that is smaller
than the number you get if the car were parked." (Do you see that?)

In the spirit of cooperation, you try again, this time marking the
rear bumper first and then walking forward to mark the front bumper..
"No! No!" says the bystander, "See, now you got 6 meters! If you do it
that way, then you always get a number that is bigger than than the
number you get if the car were parked." (Do you see that?)

A couple things dawn on you here. One is that nothing physically
happens to the car to make the number larger or smaller. It has to do
with your procedure that *defines* what the length of the car is. The
second thing is that you almost decide that the only thing you can
measure is the length of things that are at rest relative to you. But
that seems to be spectacularly useless; there must be something else
you can do.

So you redefine the procedure for measuring the length, this procedure
that *defines* physical length. What you have to do is mark the
locations of the bumpers *at the same time*. Maybe this will give you
the same number you would get if the car were parked. It seems like
the appropriate thing to do. It's not hard to do practically. There's
no rule that says that only one pair of eyes is available for the
measurement. So maybe you set up cameras along the ruler and you fire
them all from a common trigger through equal-length cables. Or maybe
you and a partner synchronize watches and then walk to opposite ends
of the ruler and agree to take a reading precisely at 12:43:18 when
the car rolls past.

And in fact, this kind of thing is the best procedure for *defining*
physical length: marking the locations of two events against a
standard ruler *simultaneously*. There is no better definition of
physical length between two events that has ever been found.

Notice three things:
1. The very meaning of physical length is inextricably entwined with
simultaneity.
2. The result of not following the simultaneity rule gives different
numbers for length, even though there is nothing that physically
happens to the car.
3. There is absolutely no concerns about optical propagation delay
time here. The ruler can be held close, or at least at common
distance, from the events being measured.

OK, comments or questions so far? Sorry for the long tortuous route,
but it really does work better this way.

PD

Before commenting, I would like a response to my
question:

Do you still claim that the frequency of the airborne
clocks is not physically modified by their
velocity wrt the Earth clocks, even if, according
to H&K, those clocks, when brought back to Earth,
mark a different time than the Earth clocks?

I think that is essentially right, although we need to be pretty
careful we're on the same page about what terms like "physically
modified" mean.

So, you claim that the frequency of the airborne
clocks is not physically modified by their
velocity wrt the Earth clocks.

However, according to H&K, those clocks, when
brought back to Earth, mark a different time than
the Earth clocks.

As the fact of bringing back the airborne clocks
to Earth can't noticeably modify their reading,
one should logically infer that in flight, those
clocks already showed approximately the same time
difference with the Earth clocks. And this means
physical, thus real, modifications, not only
of their frequency, but also at the level of their
electronic devices that count the minutes, hours,
days, etc...

This leads to a further question:

What is the airborne clocks' frequency in their
rest frame?

Marcel Luttgens

Marcel, I've offered to explain this to you according to a pretty well
defined plan, and you accepted this offer. Now you seem to be standing
well to one side of the path in the weeds. Do you want to pursue the
plan I laid out to you or not. I promise you that you will be given
the accounting of what's going on here, if you are willing and
patient.

PD




I believe this is what I told you in the first place.

Marcel Luttgens

.

Relevant Pages

  • Re: Are *observed* SR effects real?
    ... completely consistent with the laws of physics. ... mark a different time than the Earth clocks. ... ruler needs to be used at rest by the observer using it. ... The car moved forward while you were ...
    (sci.physics.relativity)
  • Re: Are *observed* SR effects real?
    ... completely consistent with the laws of physics. ... mark a different time than the Earth clocks. ... ruler needs to be used at rest by the observer using it. ... The car moved forward while you were ...
    (sci.physics.relativity)
  • Re: Are *observed* SR effects real?
    ... completely consistent with the laws of physics. ... mark a different time than the Earth clocks. ... ruler needs to be used at rest by the observer using it. ... The car moved forward while you were ...
    (sci.physics.relativity)
  • Re: Are *observed* SR effects real?
    ... completely consistent with the laws of physics. ... the airborne clocks is not physically modified by their ... mark a different time than the Earth clocks. ... The car moved forward while you were ...
    (sci.physics.relativity)
  • Re: Are *observed* SR effects real?
    ... completely consistent with the laws of physics. ... the airborne clocks is not physically modified by their ... mark a different time than the Earth clocks. ... The car moved forward while you were ...
    (sci.physics.relativity)