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Posted by Bruce on May 23, 2001 19:21:06 UTC

A signal (by definition) transfers information. No experiment has been shown to transfer information that would have an acausal resultant. There are several experimenters who think they have shown this but they are met by the scepticism of their peers. Quantum mechanics and relativity are, most likely, incomplete theories. The issue that divides them is on scale less than the Planck length. Quantum mechanics models dimensionless (point) particles so their domain can be infinitely small. General Relativity maps spacetime geometry and the field intervals must remain continiuos. A discontinuity is a singularity. Quantum fluctuations of the parameters which determine the spacetime metric result in discontinuities when evaluating spacetimes less than the Planck length. So what is needed to resolve this dilemma is a theory of quantum gravity. The interesting idea is that point particles are not really dimensionless points but tiny vibrating one dimensional strings. In string theory the minimum scale for these strings is several magnitudes greater than the Planck length. In essence string theory says that scale less than the Planck length doesn't really exist and therefore General Relativity and Quantum String Theory become completely compatible. No spacetime intervals less than the Planck length result in no discontinuity to the invariant interval and no singularities. As we all know String Theory is a very difficult work in progress. Most likely any theory of Quantum Gravity will be completely consistent with QM, SR and GR in their present domains.

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