Re: Are *observed* SR effects real?

On Aug 22, 3:26 pm, PD <TheDraperFam...@xxxxxxxxx> wrote:
On Aug 21, 9:12 am, mluttg...@xxxxxxxxxx wrote:







This view is false, because it is physically
impossible that the distant star system
and the Earth  move at v relative to the ship.

If both frames were inertial, one could apply
the above relations tB = tA * sqrt(1-v^2/c^2)
and tA = tB * sqrt(1-v^2/c^2).
Then, tB/tA = tA/tB, tB^2=tA^2 and tB=tA,
which is only valid when v = 0.

In the scenario, as the spaceship B moves at
a big velocity v <> 0 relative to the Earth A,
one can rightly infer that tB = tA * sqrt(1-v^2/c^2)
= 0.500 × 10.28 years = 5.14 years.
But, in fact, the spaceship B moves at v
relative to an Earth that is almost "rest" in
the Universe (cf. its velocity wrt the CMBR).
Iow, the spaceship moves approximately at v
in the Universe, and this is the reason why its
clock reads tB = tU * sqrt(1-v^2/c^2), where
tU, the time marked by a clock almost at rest
in the Universe, is very close to tA.
On the other hand, as the Earth A can be considered
at rest in the Universe, i.e. vEarth =~ 0 wrt the
Universe, one gets tA =~ tU from tA =
tU * sqrt(1-vEarth^2/c^2).
So, in the so-called twin paradox", one is left with
tB =~  tA * sqrt(1-v^2/c^2) =~ 5.14 years
and tA = 10.28 years, meaning that when the twins
born on the day the ship leaves meet again,  the
traveler is 5.14 years old and the stay-at-home
twin is 10.28 years old.
There is no paradox at all!

SRists make the same mistake when they claim
that the Earth (and the distant star system (sic)!)
moves relative to cosmic muons, or that the
length of vacuum pipes where pions are accelerated
appears to be contracted, because of their velocity
relative to the pions. They forget that the pipes are
at rest in the lab, that the lab is situated on Earth,
and that the Earth itself is almost at rest in the Universe,
irrespective of SRists' imaginary world.

Several comments on an important point:
- First of all, you make the claim that the Earth itself is almost at
rest in the universe. This is demonstrably false. The speed of the
earth around the sun is 66,000 mph (that's just tangential speed in
the earth's orbit). The speed of the sun around the center of the
galaxy is about 4 times that. The speed of this galaxy with respect to
the other galaxies in the local cluster is about 5 times the previous.
And the speed of this galaxy with respect to more distant galaxies is
a significant fraction of c, as shown by "standard candles" in those
galaxies.

I claimed that the Earth is almost at rest
wrt the CMBR. This is certainly globally the
case. And the CMBR can be considered as the
rest frame of the Universe:

"There clearly is a frame where the CMB is
at rest, and so this is, in some sense, the
rest frame of the Universe."
(See http://www.astro.ubc.ca/people/scott/faq_basic.html )

About the global Earth velocity wrt the CMBR:

"We are moving at a velocity of 370.6
+/- 0.4 km/s towards galactic coordinates
(l,b)=(264.31+/-0.17,48.05+/-0.10)
which corresponds to RA=11h12m, Dec=-7.2.
These numbers are specifically for the
motion of the Sun relative to the CMBR.
Of course the Earth is in motion around
the Sun, and so there is an annual variation
in the Earth's motion relative to the background.
In fact COBE was sensitive enough that it
could detect the motion of the Earth by the
changing temperature pattern in the sky throughout
the year!"
(See http://www.astro.ubc.ca/people/scott/faq_email.html )

Notice that "COBE was sensitive enough that
it could detect the motion of the Earth <...>
throughout the year, but such motion doesn't
modify permanently its overall motion of
about 371 km/s.
Compared to the spaceship velocity of
v = 0.866c, which btw could in principle
be determined by the crew from the observation
of the CMBR, a velocity of 371 km/s is negligible.

Using SR theory, one can compare the ticking
rates of an Earth clock and a spaceship clock
to that of a clock at rest in the CMBR.

But what cannot be done in any sensible theory
is to believe, like a child, that the Earth
velocity wrt the CMBR becomes 0.866 c instead
of 0.0012 c, as soon as the crew imagines that
the Earth is moving at 0.866 c relative to
their ship. This would not only be wishful
thinking, it would be magical thinking. Alas,
SRists accept such wild imaginings.


- You have this apparent notion in your head that, if two objects are
in relative motion, then it is safe to presume that the more massive
one is moving comparatively slowly and the less massive one is moving
comparatively swiftly. I'm guessing that your mental process is that
you're clocking back to some acceleration process and asking how it is
that something massive could have acquired such a speed, and since
there is only a certain catalog of forces, then it is natural to
presume that the lighter one is the one that experience the higher
acceleration and therefore is the faster one today.

Not at all.

But there are problems with this scheme.
a) Problem 1: You are *presuming* that the pair started off at rest.
This is a poor presumption. An example is a satellite launch. While a
satellite may lift off the earth and acquire a relative speed of
19,000 mph, it is entirely possible that the direction was in the
direction opposite the earth's motion around the sun, and in this
case, the earth ends up with a speed of 66,000 mph relative to the
sun, and the satellite ends up with a speed of 47,000 mph relative to
the sun. Here the obviously *lighter* object ends up with the lower
speed. But note: NONE of the physics changes in the launch of the
satellite by virtue of this fact. What is still true is that the
*change* in the velocity of the satellite is larger than the *change*
in the velocity of the earth as a result of the launch (that is what
we'd expect from conservation of momentum), but this does NOT allow
you to conclude that the satellite ends up with the higher velocity.
b) Problem 2: When an asteroid collides with the earth on (thankfully
rare) occasion, it does so with relative speed of 65,000 mph
typically. Now, one is inclined to imagine that this is the result of
a fast-moving small object careening into a slow-moving massive
object. This, however is not the case. Usually the asteroid is
drifting at relatively low speed compared to the solar system and the
Earth smacks into the asteroid as it whizzes around the sun. Think of
a truck on the highway smacking into a flying bug, rather than a bug
flying into your forehead as you sit in a chair. Or.... is it? After
all, this description is only in the reference frame of the solar
system, and the solar system is itself moving around the galaxy and by
the time you fold that in, maybe it IS the asteroid that is moving
quickly and the earth slowly. The key thing is that, as far as the
physics is concerned, it doesn't matter *at all*.

Now, these two examples are not meant to represent anything in the
twin paradox per se. All it is intended to do is to disturb your
perception that it is obvious when you have a case of relative motion,
which one is moving faster and which one is not. And once that
perception is corrected, this allow you to check further and find that
the physics doesn't tell you *anything* about which object in a pair
has the higher velocity. The physics will *only* tell you what the
*relative* velocity is, and *relative* velocity is the only thing that
matters.

When a is moving at 60 mph relative to
a tree, nobody except a SRist would claim
that the tree is moving wrt the car.


Taking this one more conceptual step, there is an underlying aesthetic
in physics that abhors a "useless concept". That is, if absolute
velocity as a physical quantity is undetectable by any measurement,
and if the laws of physics neither involve nor allow you to deduce
anything about absolute velocity, then it is a useless concept. This
doesn't prove that absolute motion doesn't *exist* -- just that it's
useless. But from the perspective of *physics* (as a model of
explaining the universe), anything that is useless can be dismissed.

Think of the moving tree. You will never be
run over by a tree, but you could be knocked over
by a moving car. This is not a useless concept.

Marcel Luttgens


As another example, back in the days when it was thought that
neutrinos were massless and left-handed, the possibility was raised
that there could well be right-handed neutrinos. But massless
neutrinos ONLY interact via the weak interaction and the weak
interaction is *inherently* left-handed. Thus even if there were right-
handed neutrinos, they couldn't possibly interact with anything else.
Thus they would not only be undetectable, but they wouldn't even
influence the behavior of other particles. And thus, a right-handed
massless neutrino is a "useless particle". This is sufficient in
physics to say that, for all *physical* purposes, it doesn't exist.
This does not represent a *proof* that right-handed neutrinos don't
exist, any more than there is a physical *proof* that there aren't
invisible, winged pixies that never leave a trace.

PD- Hide quoted text -

- Show quoted text -

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