Re: Gravity Question

This exercise is theortical chestbeating after the meaningless
'definitional' victory is fine,thankfully I can highlight just how
vacuous your views actually are.

Even a simple astrophotographer could point out that the Earth's
planetary orbital motion is conditioned by the motion of the solar
system in one direction around the galactic axis hence it is reaaly
dumb to ignore that motion and play with words such as 'speed of
gravity'.

Albert's reason for 'curving space' was a lament that light leaving
stars would go to waste nut in truth he was just re-affirming Newton's
celestial sphere geometry.all the fancy linguistics that emerged to
make some of 'spacetime' more that it actually is looks more pathetic
than anything else.

Suffer to look at the original reason for 'curving space' -

"This conception is in itself not very satisfactory. It is still less
satisfactory because it leads to the result that the light emitted by
the stars and also individual stars of the stellar system are
perpetually passing out into infinite space, never to return, and
without ever again coming into interaction with other objects of
nature. Such a finite material universe would be destined to become
gradually but systematically impoverished."

http://www.bartleby.com/173/30.html

Albert's sentimental reasons never matched Newton's clever maneuvering
to create the AU out of celestial sphere geometry but as all now adopt
Newton's geometry and the nightmare of his calendrically driven
mechanical solar system I guess these tortured 'relativistic'
linguistics are more a cry of despair than anything else.



Martin Brown wrote:
OG wrote:
"Mark McIntyre" <markmcintyre@xxxxxxxxxxx> wrote in message
news:enl6f21njsb4a9qmg0h86g2to4td4dik47@xxxxxxxxxx
On Mon, 28 Aug 2006 20:03:29 GMT, in uk.sci.astronomy , "Pete"
<petenfay@xxxxxxxxxxxxxxxx> wrote:

Its a puzzle to me but I have to ask;
If the Sun vanished in an instant would all the orbiting objects instantly
fly off into the universe or would they fly off one by one starting with
the
nearest one to the Sun. Newtonian gravity or special relativity?

This seems to be an "is gravity instantaneous or constrained"
question. My understanding is that it is effectively instantaneous,
so everything would head off at a tangent to its orbit, as as the
moment that it became evident the sun had disappeared. The tricky part
would be confirming whether this actually happened or not.

I agree. Newtonian mechanics and special relativity do not mix well.
The crucial point here is that unless gravity acts instantaneously in
the Newtonian world view we would see the planets spiralling into the
sun since they would always feel a retarding force from the place where
the sun was a time R/c ago (where R is the planets orbital distance
from the sun). This is demonstrably not the case. The force or gravity
is always exactly a radial one.

SR is not sufficient to handle gravitation reliably.

Another point of view.
This seems to be an "is gravity instantaneous or constrained" question. My
understanding is that it is propagated at a maximum speed of c; so
everything would head off at a tangent to its orbit only as the information
that the Sun no longer existed reached them. i.e. their movement changed at
the moment that it became evident the sun had disappeared. The tricky part
would be confirming whether this actually happened or not.

We can rule this out because in Newtonian dynamics the planets behave
exactly as if the force of gravity is propogated instantaneously.

The GR interpretation is that space-time itself is curved so that
nothing moves between the sun and planet to acheive this result.
Planets follow a natural shortest path. If you were able to make the
sun disappear totally you would violate so many other laws of physics
that all bets are off. Quantum gravity interpretations remain more than
a bit hairy.

My hunch is that the disturbance would propogate outwards at c, but the
situation is non-physical for a host of other reasons. Matter cannot be
made to just disappear magically!

The best chance of detecting gravity waves propogating at the speed of
light comes from observing binary pulsars in tight decaying orbits.

Regards,
Martin Brown

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