srp wrote:

Igor a écrit :

srp wrote:

Igor a écrit :

srp wrote:

Some physicists like to really complicate things for first contact
students.

In their explanation, they simply present the case as if
General Relativity spacetime curvature was a given in physical reality,
which is far from certain, and even disputed by a rather large segment
of the physics community.

On the contrary, GR has an entire mountain of evidence to support it.

Sure. So did CM before relativity became popular. So did geocentrism
before heliocentrism became popular. The list of past theories for
which there were mountains of evidence is endless... until more
data was gathered that couldn't be reconciled.

Name one observation that has contradicted GR?

Easy. I could name even two:

The "so-called" anomaly of the Pioneer 10 and 11 crafts on their
hyperbolic trajectories.

The "so-called" anomaly of the spin slowing down of both crafts
about their rotation axis.

I say "so-called" because obviously, there is an explanation, since
the real laws of nature are physically at play here.

Why is it just the Pioneers and not the outer planets that are
experiencing this effect?

Because the outer planets are not on hyperbolic escape trajectories,
the only type of inertial trajectories that could not be studied
before the space age.

To my knowledge both Pioneers are the only bodies in existence that
we weighed before launch that then were set on inertial hyperbolic
escape trajectories and from which we have for long periods been
able to Doppler analyze the trajectories.

This is the main reason that most consider this logisitical problems
with the spacecraft themselves.

I for one see a difference between the two types of trajectories.
One difference being that we currently have no way to directly weigh
the planets.

The way I understand it, some people have recently rescued the media
containing the Pioneer flight data just before it was about to be
destroyed. They want to reconstruct the flights to see exactly where
they started to deviate.

Interesting. I hope measures will now be taken for that data to be
preserved forever.

What would really be interesting is if they
are never able to determine any particular events on the spacecraft
that contributed.

Absolutely.

But the jury's still out on this one, as interesting as it might be.

Looking forward to the outcome.

The problem with GR in the first case is that no inertial hyperbolic
trajectories in a gravitational field had been observed prior to GR
being defined so its particulars could not have been taken account
of.

As for the second one, the problem runs even deeper. Related to
the centuries old strange notion that circular motion involves no
work (no expenditure of energy).

Why is it such a strange notion and how does it relate to GR?

Not related to GR really. Just came to mind since this is a second
"unexplained anomaly" related to the Pioneers.

It might be interesting philosophically, but work has a precise
physical definition. No real mystery there.

It has a precise CM definition yes. Conceived of considering macroscopic
bodie as being solid. The fact being that any body mechanically set in
rotating motion is made up of elementary particles animated with
uncompensated circular change in trajectories.

Strange in my view that no energy would be used up to actualize that
change. Contrary to 2nd law of Thermo in my view.

No energy is necessary to maintain an elliptical orbit, either.

Although a finite expenditure is usually necessary to get there.

Or name just one physicist out of that so-called "rather large
segment" that disputes it?

Easy also, there is even one on this ng. His name is Gisse if I
recall, so feel free to argue the point with him at will. Many others
have recently aired reservation on this very ng. Almost every month,
magazine articles and books come out talking of the dead end physics
has been in for decades.

Simple logic shows that if it couldn't be reconciled with QM at any
level despite the best efforts of countless leading edge physicists
for the past 80 years, there is bound to be something amiss with it,
since QM is definitely unassailable even as it stands.

I would be the last to argue that GR was complete as a scientific
theory. Far from it. But I was talking about disputing the theory on
the grounds that there are observations that contradict it. Everytime
you turn around, someone is claiming that new observations contradict
relativity, when in reality they don't.

Well, the Pioneer case certainly seems a very consistant prod in GR's
ribs, no?

Personally, I'm not sure there's actually a problem. But if there is,
then it's something that reflects not just on GR, but classical
Newtonian gravity as well, since this is occuring far from the sun
where GR has long ago melded into classical theory.