eh

This thread is continued from a discussion in the philosophy form with Bob K over the nature of space. Since that thread went off topic and was locked, this seems like the appropriate place to continue it. I posted reasons why the classic atomists vision of the void is not quite correct in modern physics, so post here if there is something else to add.

Ensign Steve

Do you have a link to the original thread? The topic sounds fascinating, but I don't know what your position is.

I think space is curved, and most of it is a vacuum. But I'm not a cosmologist; I'm an accountant who watches too much Star Trek.

Dan<Devil>

I thought the Uncertainty Principle, forbids voids to be realy void. You must have some vacuum oscilations. A link to your discusion with Bob K is more than welcomed.

Arthwollipot

Quantum uncertainty does indeed forbid a vacuum. Extrapolation of Heisenberg's Uncertainty Principle shows that at all times, at all points in space, particle-antiparticle pairs are appearing and annihilating each other before the Universe has time to notice. This is a prediction of quantum mechanics.

Any theory which includes the Graviton as the messenger particle of the gravitational force must also include a 'background' of gravitons in a similar way to the Cosmic Microwave Background of photons (electromagnetic force). The Strong and Weak Nuclear forces do not include this background field as they are short-ranged forces.

There is an essential conflict when you bring up Einstein's smoothly curving General Relativistic model of space against Heisenberg's roiling quantum foam. Basically when you combine the two theories, well-formulated equations provide infinite answers. Essentially this means that both theories cannot possibly be entirely correct. This is one of the things that string theory was developed to address.

No, not a physicist, just a well-read layman.

Wounded King

If the casimr effect allows the establishment of a region with negative energy, due to restricting the possible states virtual particles in the field can adopt, how far can this be pushed? Is there any situation in which abosoloutely all the possible states could be denied and a true and absoloute vacuum would exist?

Is this theoretically possible even if practically impossible, I cant imagine a scenario where the gap between the two mirrors could be small enough in real life without imperfections in the mirror causing problems..

eh

The thread is at: http://www.iidb.org/vbb/showthread.p...5&pagenumber=2

Unbeliever

I've always been uncomfortable with the idea of gravitons. I don't understand why they are needed if gravity is just the curvature of space-time. It seems to me that Ockam's Razor would preclude the necessity of mediating particles when geometry is enough to explain the mechanism of gravity.

Answerer

General relativity breaks down at the quantum scale and this caused the physicists to believe that the spacetime might be quantized or even have a wavefunction. And since the strong, weak and electromagnetic force all have a mediating particle, the physicists believed that gravitional force has one such mediating particle as well.

Anyway, I believed that the existence of gravitons, if found, will explain mechanism behind the GR's first postulate of why light must be constant or the same in all reference frames.

Arthwollipot

The wavelengths of the virtual particles in the field could theoretically be arbitrarily small, down to the Planck length. At such small wavelengths, the total energy of the particles is necessarily extremely high, which would make the casimir effect stronger at smaller distances. I don't know to what 'smallness' this has been actually carried out.