Re: HOCUS POCUS


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).

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.
As they have mastered FTL communication, 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.

Marcel Luttgens




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

.

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