You
can say the past/present/future are all "happening at once" and that
there is no need to "move".

Jerry wrote:

Schoenfeld wrote:

Jerry wrote:

Schoenfeld wrote:

Jerry wrote:

Greysky wrote:

Name the experiment, Autymn. Just tell me where someone
measured the
gravitational mass of an anti-particle. Oh wait, you can't -
must be that
messy time of the month, eh?

Oh, come off it, Greysky. Photons are their own anti-particle,
and they most definitely fall DOWN. Or haven't you heard of
gravitational redshift?

Photons don't "fall down".

Are you saying then that light is not deflected as it grazes
the Sun? That all measurements of this phenomenon, from the
Eddington expedition to Hipparcos to VLBI measurements, are
wrong, perhaps even fraudulent?

In General Relativity, spacetime is modelled as a curved Lorentzian
manifold consisting of 4 dimensions. The curvature of this manifold
arises from the presence of energy, momentum and mass (i.e.
stress-energy).

Since this manifold is curved, defining the shortest distance between
two points is not a simple straight line in the usual Euclidean sense.
Another way to define the shortest path between two points, even in
classical physics, is to take the path that reads the longest proper
time (the time read by a clock in that moving frame).

You will recall that in Special Relativity that if you move very fast
you get time dialation (the travelling twin is younger than the
stay-at-home twin). But in General Relativity, the strong equivalence
principle implies that a stationary clock placed higher in a
gravitational field ticks faster relative to an observer lower in that
gravitational field.

So if you were tasked to leave a point at some signal and arrive at
another point at some other signal taking the shortest possible path
then you would need to take the path that reads the longest proper time
(i.e. the time your wrist watch reads). So to get more proper time on
your watch you would need to go up higher into the gravitational field
to get some of that effect. But if you go too high it means you need to
go very fast, and that means you get the time dialation predicted by
Special Relativity. So to get your watch to read the largest proper
time you need to go up a little bit, but not too high or too fast, then
come back down to arrive at the destination point at the destination
signal.

This type of motion is the "shortest path" but it turns out to be
parabolic in the Euclidean sense. This is exactly the gravitational
motion taken by bodies emersed within curved spacetime. These bodies
aren't "falling down" but are simply moving in a "straight line"
through curved spacetime. These straight lines are called geodesics.

More to the point, nothing "falls down" due to gravity in GR but rather
travels the inertial motion demanded by Newtons 1st Law. Light travels
through null geodesics and bodies generally fall through timelike
geodesics.

...and of course, GR predicts that matter and antimatter should
both fall identically in a gravitational field.

As always, however, you COMPLETELY miss the point. The point
is, that I was making a response to Greysky, who contends that
antimatter should exhibit a negative gravitational mass. A couple
of posts back, Greysky wrote:
How much will our knowledge be altered when the first
scientist drops a significant amount of antimater and watches
it fall in the wrong direction? It will, and no one will have
a clue because science has been blinded to the truth for the
last 4 decades...
Given what you have written above, you ought to be in complete
disagreement with Greysky. Instead, you quibble at an intentional
looseness in the language that I used in responding to Greysky,
and seize the opportunity to show off your knowledge of GR, making
a considerable number of elementary mistakes...

Sorry, you really don't impress anybody here.

I actually felt pitty for someone who says "fell down" so i took some
time to educate, my mistake.

Jerry

In message <BSO8e.2902$J12.1...@newssvr14.news.prodigy.com>, Greysky
<greyskynos...@sbcglobal.net> writes

When scientists eventually perform an honest experiment to
determine the gravitational polarity of antimatter created in the

will be proven correct.

Well, gravity doesn't have any "polarity", and this result would

show that it affects particles and antiparticles alike.

"The only direct experimental result on antimatter and gravity comes

Supernova 1987A. This supernova in the Large Magellanic
Cloud emitted both neutrinos and antineutrinos, some of which were
eventually detected on Earth. Those neutrinos and antineutrinos

160,000 years to reach Earth, and while travelling were bent from a
"straight line" path by the gravity from our own galaxy. The bending

gravity changed the time needed to reach Earth by about 5 months,

the neutrinos and the antineutrinos reached Earth at roughly the

(within the same 12 second interval). This shows that the neutrinos

antineutrinos "fell" similarly, to a very high level of precision

part in a million). [4] and [5] provide some background information

this.

[4] "Limits on CP invariance in general relativity," J.M. LoSecco,
Physics Review D, vol. 38, no. 10 pg 3313 (1988) -- Supernova
1987A.
[5] "New Precision Tests of the Einstein Equivalence Principle from
SN1987A," M. Longo, Physical Review Letters, vol. 60, no. 3
pg 173 (1988) -- Supernova 1987A."
<http://math.ucr.edu/home/baez/ physics/ParticleAndNuclear/ant