Re: relativity: what if you can measure how far the light traveled?
- From: "Russell" <russell@xxxxxxxx>
- Date: 13 Feb 2007 11:25:07 -0800
Alen wrote:
On Feb 13, 12:16 pm, "Russell" <russ...@xxxxxxxx> wrote:
On Feb 12, 4:46 pm, "Alen" <a...@xxxxxxxxxxxxxxx> wrote:
On Feb 13, 1:49 am, "Dirk Van de moortel" <dirkvandemoor...@ThankS-NO-
SperM.hotmail.com> wrote:
"Alen" <a...@xxxxxxxxxxxxxxx> wrote in messagenews:1171288671.538626.223790@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I don't say there is a purely mathematical discrepancy. I do
say that the 4D spacetime geometry goes far beyond what the
original transformation equations actually say. They refer only
to time dilation and foreshortening.
No, that's incorrect, and you are repeating a common
misconception. The time-dilation and Lorentz-Fitzgerald
contraction equations are *consequences* of the Lorentz
transformation equations and refer to the *special cases*
of, respectively, constant x' and constant t. The LTE
themselves are more general, and they imply a third and
(IMHO) more fundamental result: relativity of simultaneity.
OK - that is an aspect of time dilation. But, the question
is: is that 'real' or only apparent. By apparent I mean that
what is observed is a distorted observation of a non-relative
or universal underlying reality. A purely 'real' relativity
of simultaneity does not make sense.
Well, simultaneity is a convention that we apply
to *clocks*. It isn't *real* to begin with. It's a
human invention.
There is of course a natural simultaneity that we
can apply to occurrences at a single event in
spacetime -- this bomb went off at exactly the
time when the clock next to it read 12:00. But
put the clock a mile away, and it becomes harder
to say what simultaneity "really" means then.
Given that, why in the world should it be a big
problem for you if we throw away the whole idea
of absolute simultaneity at a distance? It wasn't
real to begin with, and in practical terms it turns
out to be inconvenient.
They say nothing about
how this actually happens, and say nothing about something
like a 4D spacetime geometry.
On the contrary, that is exactly what they "say". The LTE
are mathematical equations, and mathematically they are
equivalent to a group structure on Minkowski spacetime.
Yes - but that doesn't mean that Minkowski spacetime is
as real as the space we can see when we look upwards
outdoors.
Look, I believe in a real world too, and I do believe
I am seeing real stars in real space when I look up.
But beyond that, I am not following you. Are you
saying that Euclid must hold *really* because that
is the impression you get when you look up at the
real stars? How are you so sure your impression
is not an illusion? Particularly when you do the
calculations and see that the differences between
Euclid and Minkowski are quite subtle and for the
most part imperceptible on the scale at which we
perceive things?
The point is that by assuming an underlying geometry
(Euclid) you are really no better off than the physicists
who use Minkowski. Indeed, even apart from questions
of which geometry is correct, I would say you are at a
psychological disadvantage because you seem to be
making *your* assumption without being aware of it.
Mindfulness is a good thing.
That is an interpretation imposed
on the equations. From a conceptual perspective, as
representing an underlying reality, as distinct from being
a purely mathematical representation, the 4D geometry
doesn't make sense.
I'm tempted to ask, doesn't make sense to *whom*, but
that would miss the more important point:
When you start worrying about the "underlying reality" --
that which cannot be observed -- you leave the realm of
physics. The LTE are part of physics because experience
has shown that they describe very well what can be
observed. You are free to put whatever conceptual
framework onto it that makes you happy, and if that leads
you to make predictions (ideally *new* ones) of things
that can be observed, then your new conceptions might
merit the term "physics". Not until then, though.
My impression is that Minkowski spacetime has been
already presented to the world as being the way reality
actually works. The question about underlying reality is
therefore not something I would accept as merely an
extraneous invention of my own.
Ok, I agree there may be too much of a tendency in
some presentations (particularly popular ones) to reify
spacetime. Some posters here -- Roberts in particular --
have come out explicitly against such a view; rather,
they point out correctly that spacetime is a *model*
and that the underlying reality, as you call it, is
unknown and, ultimately speaking, unknowable.
This is a bit of a subtle philosophical point, and it's
just not that interesting to most physists, since whether
you use spacetime believing it is real, or use it believing it
is a convenient illusion, you get exactly the same results
and those results turn out to be confirmed by experiment.
I can't see what meaning there could be in your phrase
"the way that reality actually works" other than that
experiments confirm and never falsify the theory. That's
as good as we can do.
Anyhow, going back to your original post where you
claimed that working with LTE's is somehow more "real"
than using spacetime diagrams, I hope you can agree
now that this was based on a misconception. If spacetime
diagrams someday turn out to be no good, the LTE's will
fail that very same day.
Hmm, maybe not that very same day everywhere in all
frames. ;-)
Alen
.
- Follow-Ups:
- References:
- Prev by Date: Re: if X observes a platform start moving, how can it appear contracted?
- Next by Date: Re: if X observes a platform start moving, how can it appear contracted?
- Previous by thread: Re: relativity: what if you can measure how far the light traveled?
- Next by thread: Re: relativity: what if you can measure how far the light traveled?
- Index(es):
Relevant Pages
|
