Re: On research into gravitons
- From: Gerry Quinn <gerryq@xxxxxxxxxxxxxxxxxxx>
- Date: Sun, 10 Dec 2006 20:54:24 +0000 (UTC)
In article <iCnNKfGcpReFFwrf@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
NotI@xxxxxxxxxxxxxxxxxxxxxxxxxxxx says...
In general relativity geometry plays rather a different role. Instead of
describing matter and its interactions by first defining a background
geometry, we now have a structure in which matter and geometry appear
are equally fundamental, the one affecting the other and the other
affecting the one. Gravity is described naturally within this structure,
as a manifestation of the geometry. The fact that we have this structure
is due to the very deep insights, not just of Einstein, but of two of
the greatest mathematicians in history - in my view the two greatest,
Gauss and Riemann, who recognised that, a priore, there is no reason for
thinking that space should be flat in the first place, and also to the
insights of two more greats, Descartes and Leibniz, who pointed out,
from observational evidence, that measurement of space is actually
illusory - measurement is always a comparison between matter and matter.
Space itself cannot be measured. Even Newton recognised that his notion
of absolute space is not subject to observation or measurement, but has
to be inferred from the success of the results of a theory incorporating
it. Ultimately, therefore, space and space-time exist in physical theory
as metaphysical, not empirical concepts.
We can easily imagine a universe made up entirely of black holes (apart
from a sprinkling of whatever gravitational waves and other random
stuff they and their interactions emit). It seems like GR doesn't
really depend on mass/energy as such - you could have a perfectly
plausible GR universe that is constructed essentially out of
'curvature' alone. Admittedly the question of initial conditions could
be raised in objection to this argument. But if that objection is left
aside, the implication is that either (1) curvature is something
physical, or (2) there must be something physical other than curvature
and mass/energy, or (3) the mass/energy is really still present in some
sense, even if it all appears to have fallen into black holes. None of
these notions seems entirely compatible with what you propose.
Considering all these arguments, it seems to me that to postulate an
exchange particle for gravity is a retrograde step, which overlooks the
very deep insights which lead to the formulation of general relativity,
and which shows gravity to be a manifestation of geometry. There simply
is no logical reason to turn back our thought on the matter, and attempt
to reformulate physics with a flat background, and considerable reason
to think that a theory of quantum gravity should dispense with the
notion of background altogether. Perhaps such a theory is not easy to
conceptualise, but what does seem to me clear is that it would not be
expected to follow the pattern of the quantisation of the e.m. field.
Certainly there is no reason to suppose that physics should be a
particular way just because of limitations in our thinking.
I agree that geometry must be something constructed by more fundamental
entities of the universe. But I remain rather doubtful about whether
general relativity is their starting point. One issue I find
particularly problematic is that of the thermodynamics of the causally
disconnected 'pocket universes' inside GR black holes. Seemingly the
arrow of time (whether or not it is re-labelled as space) proceeds as
normal for objects that have fallen in, leading towards a high-entropy
central singularity.
If this central singularity exists and is really utterly disconnected
from our universe in every way, how do the boundary conditions between
the pocket universe and our own get to match up perfectly? We cannot
simply say that the matter in the pocket universe just evolves
classically over time from the point at which it fell in, because the
geometry in which it evolves is created in part by it.
So I take the view that every universe must end in a single future,
instead of a multitude of disconnected ones; and consequently there
must be a useful level of physical description in which the end of our
universe is in the future of all matter within it. And that
proposition is a good deal more in tune with conventional quantum
theory than with GR.
- Gerry Quinn
.
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- On research into gravitons
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