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Re: [Phys-L] GR and Gravitons



On 11/18/2015 03:57 PM, Jeffrey Schnick wrote:

http://www.quantum-field-theory.net/einstein-didnt-say/
Is that page a bunch of nonsense?

In addition to my previous note: Here is one passage from
that paper:

Frank Wilczek put it this way:

“We can describe general relativity using either of two
mathematically equivalent ideas: curved space-time or metric field.
Mathematicians, mystics, and specialists in general relativity tend
to like the geometric view because of its elegance. Physicists
trained in the more empirical tradition of high-energy physics and
quantum field theory tend to prefer the field view… As you can
probably tell, I’m a field man.”

That strikes me as pretty far out on the nonsense scale.

Wilczek is a smart physicist, but he's more of a mathematician
and more of a mystic than most. I find it quite odd that he
would imply that people who do relativity for a living know
less about the subject than other physicists.

As for the idea that gravitation is like electromagnetism in the
sense that it is "just" a field as a function of position in some
pre-existing spacetime continuum ... that idea is definitely not
compatible with GR, or with observed reality.

In particular, imagine a bug living on a curved surface. The
curvature actually changes the actual distance between point
A and point B. So your notion of /position/ is affected by
the curvature. In GR the field is a function of position, and
the position is a function of the field ... which is every bit
as complicated as it sounds. It introduces both nonlinearity
and dispersion into the equations of motion.

For weak fields, to /first order/ the nonlinearities and the
dispersion don't matter. The earth's field is weak, so your
average pedestrian doesn't care about the messy details. There
are about a dozen different theories all of which give the
same answer for weak fields. Meanwhile, however, for strong
fields you do need to worry about details, and the spacetime-
curvature approach is the winner. In contrast, the idea of
a gravitational field riding on top of flat spacetime seems
superficially nice, but nobody's ever been able to make it
consistent with experiment (except for weak fields).

===========================

On 11/19/2015 08:50 AM, David Bowman said that the "Newtonian
acceleration field" is not one of the "physical fields".

That's true and important. It may sound insane to your average
high-school student, but it's the correct physics.

The idea is to focus on fields that you cannot get rid of simply
by changing reference frames.
-- By choosing a freely-falling frame, you can make the Newtonian
acceleration go away. A uniform acceleration tells you nothing
about the spacetime curvature, and vice versa.
-- What you /cannot/ make go away is the fact that the Newtonian
acceleration field on one side of the earth (Spain) is different
from the field on the opposite side (New Zealand). This is where
the curvature comes in.