What about the gravitational field due to vacuum energy? Theoretically it acts as a source of gravity (i.e. cosmilogical constant).

I take it you mean Zero Point Energy. Granted the vacuum is not "empty space" but more a quantum foam, from whence ZPE is derived, but I for one would put this into speculative physics.

YelmalioM This has never been observed in real life. pmb What about the Casimir effect or the new experimental evidence of inflation and the accelerating expantion of the universe?

The Casimir is usually explained as a quantum effect visible in the macro-world. There is no need to invoke gravity to explain it.

The rapid inflation of the Universe is another story. As I have said previously here it is caused by a Higgs field that results in negative pressure-densities that power the inflation. In this persepective it is a type of anti-gravity, it pushes things apart. Chances are only the energies of the Big Bang are suffcient to produce a Higgs Field big enough to create false vacuums. Some theorists have speculated that the universe is a set of inter-connected bubbles of costantly inflating domains. This is purely speculative and not easy to experimentally verify.

We can use this mechanism iff a Higgs particle is found and relic Higgs particles can be created in a collider.

Evidence for an accelerating Universe (negative cosmological constant) is only based on high-z supernovae, IIRC. It's interesting but hardly qualifies as hard fact yet. The errors involved in measuring objects at cosmological distances tend to be large so the results obtained therefrom are subject to change without notice.

As I said elsewhere in this forum the majority of people who come here come to learn. It does no good confusing people by explaining that Relativity predicts such and such and then saying there is evidence against it. This leads people to think that any half-baked idea (if allowed in theory) could be true simply because it might be.

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Do you mean by this that it has never been directly observed or is not allowed/predicted within general relativity?

A lot of the Tensors and metrics used in GR are symmetrical so anti-gravity is permissible within the theory. I don't believe there is strong (or any) evidence for it's existence though. The Kerr-Newman metric allows for a symmetrical solution connected via an Einstein-Rosen bridge. There is no evidence (yet) for this so it remains of theoretical interest only.

There is something that is very important in cosmology nowadays. It's known as a vacuum domain wall. They may have existed in the early universe. These objects are like walls but they repell matter rather than attact matter.

These are artifacts from the Higgs mechanism, no? If they exist they do so at much larger distances than the currently observed Universe. It does not make them likely candidates for a viable anti-gravity device. Again, theoretically interesting but as yet no evidence. You also have a problem with the magnetic monopoles associated with them.

A cosmic string neither repells nor attracts objects (i.e. gravitational force = 0) but it does alter the space around it making it non-Euclidean. However for straight cosmic strings the spacetime is flat. Also the spacetime near a vacuum domain wall is flat, yet there is a gravitational field.

String and M-Brane theory is not my strong point. I stopped studying this stuff 10 yrs so have missed some of the devlopements in M-Branes and cosmological defects.

Seems to me though that if a cosmological string makes space non-euclidean than it produces a gravitational field under the equivalence principle. Open to correction here.

Yelmalio.

• Re: Anti gravitational force - Retraction - yelmalio/">yelmalio - February 17, 2000 - 08:33 UTC