Re: HOCUS POCUS
- From: "PD" <TheDraperFamily@xxxxxxxxx>
- Date: 14 Sep 2006 07:11:41 -0700
mluttgens@xxxxxxxxxx wrote:
PD wrote:
mluttgens@xxxxxxxxxx wrote:
PD wrote:
mluttgens@xxxxxxxxxx wrote:
HOCUS POCUS
Two electrons E1 and E2 are ejected along a straight line with
opposite velocities v1 and v2 from a device stationary in S,
at t=0 according to S clock.
Assuming that v1 = -0.6 c and v2 = 0.8 c, what is the relative
velocity between E1 and E2 ?
After a time interval t measured on his clock, S will conclude
that the distance separating E1 from E2 is (0.6 + 0.8) ct = 1.4 ct,
hence that E2 is moving away from E1 at V = 1.4 c, or that E1 is
moving away from E2 at V = 1.4 c, meaning that the relative velocity
between E1 and E2 exceeds c.
Yes, and there is nothing wrong with that.
Ein Zwei Ein Stein HOCUS POCUS
E1 = S',
V = (.8 c-(-0.6c))/(1+0.8*0.6) = 1.40/1.48 c = ~.9459 c
E2 moves at 1.4/1.48 c relative to S'
E2 moves at 1.4/1.48 c relative to E1
ABRACADABRA
420000 = ~283784
By assimilating E1 to a frame S' moving away at -0.6 c from a frame S,
Srists claim that the electron E2, which had a velocity V = 1.4 c
wrt E1 measured in S, has only a velocity V' = ~0.9459 c measured in
S'.
Yes.
But the electrons don't bother about which name they are given, nor
does their relative velocity V depend on their velocity wrt the device
by which they have been emitted. Such device -the frame S according
to SRists- should be ignored after their emission, it belongs to
history.
Not at all. You seem to think that relative velocity between two
objects should be a frame-independent quantity. It's not. I don't know
why you think it should be.
I am skeptical about the physical validity of a formula (the
relativistic addition of velocities), which gives an infinity of
solutions for a same velocity V between to objects, for instance
1.4 c, measured in one frame (S in my example).
Well, there is one way to resolve matters of skepticism and that's to
make *measurements* and see if one should be skeptical or not.
You seem, however, to object to it on general principles, thinking
perhaps that relative velocity between two objects OUGHT to be
something that is observer-independent. I'd like to know on what basis
you have decided which physically meausurable quantities OUGHT to be
observer-independent and which ought to be observer-dependent. Surely
you do not believe that all physically measurable quantities are
observer-independent; consider momentum and kinetic energy, which are
clearly observer-dependent. So then, what is your criterion? How do you
know, without consulting experiment, which parameters OUGHT to be
observer-independent?
No, I don't claim that relative velocity is observer-independent, I
only
demonstrated (once more) that the Lorentz transformations lead to
contradictory results, see my today answer to Randy Poe.
Well, you said, " I am skeptical about the physical validity of a
formula (the relativistic addition of velocities), which gives an
infinity of solutions for a same velocity V between to objects, for
instance 1.4 c, measured in one frame (S in my example)." The infinity
of solutions is precisely the observer dependence of relative speed
between two objects.
As I commented in your response to Randy, the assumption that the ratio
of spacing intervals should be observer-independent is equivalent to
the assumption that relative velocities should be observer-independent.
Same assumption, just in different form.
PD
Marcel Luttgens
Let's consider a planet inhabited by advanced ET's, situated at
x billions light-years from the Earth. Their physicists, from the
redshift of the Earth galaxy A and the Hubble constant, calculate that
the Earth is moving away from them at -0.7 c. Opposite the Earth,
they observe another galaxy B, whose velocity relative to them is
+0.7c.
They conclude, in accordance with the cosmic expansion, that such
galaxy has a velocity 1.4 c relative to the Earth.
OK.
As they have mastered FTL communication,
Why would they need FTL communication to send a signal to Earth which
is receding from them at 0.7c?
they transmit those data to
the Earth SRists, who calculate that B is in fact moving away from
them at 0.7c + 0.7c / 1 + 0.7*0.7 =~ 0.94 c, forgetting that it is
impossible to observe a galaxy moving away at 1.4 c.
But you're assuming that the ET's would conclude that Earth observers
wouldn't be able to observe the other galaxy, simply because the ET's
measure the relative speed to be 1.4c. That would be idiotic of those
ETs, because they clearly are making the wrong conclusion.
Forget the ETs. Here on Earth, we can observe a galaxy G receding from
us in one direction at 0.6c and in the opposite direction another
galaxy H receding from us at 0.7c. However, it would be idiotic for us
to conclude that galaxy G cannot observe galaxy H. Of *course* galaxy G
can observe galaxy H. The relative velocity that G sees H receding is
not larger than c. The *idiotic* conclusion that G could not see H
would only come from an assumption that if we see the relative velocity
between G and H to be greater than c, then G and H will also see the
same relative velocity. That assumption, of course, is precisely what's
wrong and what makes the conclusion idiotic.
PD
For instance, E1 could have been emitted at -0.5 c, and E2 at 0.9c,
hence their relative velocity V remains 1.4 c.
But, according to SRists, V' is then
(0.9 c-(-0.5c))/(1+0.9*0.5) = 1.40/1.45 c, which is different from
1.40/1.48 c!
Marcel Luttgens
.
- References:
- HOCUS POCUS
- From: mluttgens
- Re: HOCUS POCUS
- From: PD
- Re: HOCUS POCUS
- From: mluttgens
- Re: HOCUS POCUS
- From: PD
- Re: HOCUS POCUS
- From: mluttgens
- HOCUS POCUS
- Prev by Date: A clown with fixed ideas : Ajay Sharma
- Next by Date: Re: HOCUS POCUS
- Previous by thread: Re: HOCUS POCUS
- Next by thread: Re: HOCUS POCUS
- Index(es):
Relevant Pages
|
