Comments on: Gravity is an Important Force

By: Ellipsis

Ellipsis — Mon, 27 Oct 2008 02:50:12 +0000

It’s wonderful that an economist would ask such an insightful, superb, and fundamental physics question. It would be a great thing for academia if we could all be so inquisitive and interested in probing each other’s fields.

By: spyder

spyder — Mon, 27 Oct 2008 01:21:24 +0000

Just a shout out to all of you above for making this thread so approachable and educational for the layperson to comprehend. It is one of the reasons that i think Cosmic Variance is one of the very best blogs on the web.

By: Lawrence B. Crowell

Lawrence B. Crowell — Mon, 27 Oct 2008 00:24:46 +0000

The static gravity field will not act to decohere anything. If we think of electromagnetism the electronic states of an atom are held by a 1/r^2 force and there is no decoherence of any electron wave functions. Now if one of these electrons is in an excited state that state will decay with the emission of a photon. If that photon is in a high-Q cavity there will be an entanglement between the atom and the photon. There will then be a Rabi oscillation as a result, where the photon is reabsorbed by the atom and the electron restored to its excited state. The process will then repeat, as there is some periodic oscillation between the probability of a photon and the probability of the electron in an excited state oscillate with some frequency. However, if that photon leaves the system this is a spontaneous emission. The engtanglement between the atom and the photon is taken away by the environment or the vacuum occupation states the photon “fills up.” The first order theory for this is the Fermi Golden rule.

The point is that with any field there is no change in entanglement phases unless there is the emission of the gauge boson of that field. The same hold for gravity, though the quantum mechanics of gravity is less certain. Yet we can use some classical ideas. The quandrupole moment of a classical gravity wave will cause the body to periodically distend — squash along one direction and stretch along another, and then the opposite occurs. This is the basis for the Weber cylinders meant to detect gravity waves. This will then result in some bulk friction in the body. The temperature of will then increase and the phase space volume of that body’s dynamics. This is a measure for the removal of coherent phase which might be present in the body.

Now realistically a gravity wave will not do much. The decoherent activity of solar photons is far greater than what any gravity wave might produce. At least this is hoped! Any gravity wave the significantly heat up Hyperion would be devistating in general. For the gravity wave to have any detectable decoherence it must act on some body very very near absolute zero.

Lawrence B. Crowell

By: Sedigh

Sedigh — Sun, 26 Oct 2008 22:04:01 +0000

I’d like to ask the same question but from different prospective,
Do we really need Photons or Gravitons (or any external agent) to cause de-coherency in such a huge macroscopic system?!
More precisely my question is why we should believe that all the constituents particles of Hyperion are going to interact whit each other all at once? under what assumptions they came up with that 20 years criterion?!
suppose we have two entangled particles after an interaction the second one and a new third particle, all of them are entangled (am I right?!) then lets assume miraculously the third one happens to interact with the first one. I’m not sure but I think this scenario results in de-coherency (am I right or I should take QM course again?!)

By: sonic

sonic — Sun, 26 Oct 2008 21:59:41 +0000

James-
Actually I think your original post is appropriate.
How do you know there are gravitational waves?
Are you aware of the difficulty of measuring G (the constant in Einstein’s formulation of gravity) If G isn’t constant, then the prediction of gravitational waves is ???

Where do the findings of Gröblacher et al. fit into this discussion?

By: David McMahon

David McMahon — Sun, 26 Oct 2008 15:12:25 +0000

Gravitational waves have been inferred indirectly. They are detectable and there is an experiment underway to try and do that, although as far as I know they have not found one. Gravitons are way more hypothetical though. Physics would take an interesting turn if quantum theory didn’t apply to gravity at all. Although there are strong reasons to believe there is a quantum theory of gravity and some unified theory of physics (even if its not string theory) it is not out of the realm of possibility that gravity just doesn’t fit into that situation.

By: Lawrence B. Crowell

Lawrence B. Crowell — Sun, 26 Oct 2008 14:55:49 +0000

I meant to start that out by saying not a “coherent source,” but as a source of decoherence. — L. C.

By: Lawrence B. Crowell

Lawrence B. Crowell — Sun, 26 Oct 2008 14:54:02 +0000

Gravity could be a coherent source if the exciton of the field interacts with the moon. A classical analogue of this would be a gravity wave. This would cause the moon to exhibit quadrupole oscillations and some displacement of its bulk material. This would then heat the moon up slightly and that thermalization would have a decoherent effect.

Lawrence B. Crowell

By: Serge

Serge — Sun, 26 Oct 2008 06:03:27 +0000

I don’t think it’s exactly metaphysics. Macroscopic quantum objects is known to exists, like Bose–Einstein condensate, and it have some unusual mechanical properties. So why not entangled orientations ?

By: ObsessiveMathsFreak

ObsessiveMathsFreak — Sun, 26 Oct 2008 01:24:35 +0000

I think that this debate about the applicability of quantum mechanics to the motion of a moon leaves the realm of science and enters the realm of metaphysics, or quite possibly philosophy. The idea that the moon’s orientation will stop being classical due to quantum effects is inherently not testable. The orientation will stop being predicable due to the motions of dust, radiation, gravity from other planets in the solar system, and probably the motion of flies in the jungles of Russia, long before quantum mechanics plays its part.