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Name: Jan
Status: N/a
Age: N/A
Location: N/A
Country: N/A
Date: Around 1993

Once, when I studied math, I read about the diverse versions of the GUT. One thing that puzzled me was, that the theories seemed to talk about space-time being some kind of 'quantum foam', that as a consequence time would be 'broken up'; a state that should presumably have existed at a very early time, when the energy density was high enough. But how can one talk about time, when time is not well defined. Or did I just not understand it?

Well, I do not think anybody understands it yet - That is why there really is no theory right now. The problem basically is how to quantize gravity. Gravity is associated with the shape and actual fabric of space- time. From experience with the quantum versions of other forces, it is expected that at low energies, for long times and large distances (the realm of our normal experience) the laws of quantum gravity will reduce to the ordinary laws we know describe the universe pretty well - the "classical" version of gravity due to Einstein. It is also known from previous experience roughly where energies become "low", times become "long" and distances "large" for quantum gravity - these are the so-called Planck scales arrived at by combing Planck's constant h with the gravitational constant G and the speed of light. The energies at which the quantum nature of gravity become important are something like 10^16 times what particle accelerators can achieve, and the length scales and time scales are correspondingly shorter than anything we have investigated up to now. This puts it fairly well beyond experimental investigation for the foreseeable future. But theoretical speculation persists ence the quantum foam and other ideas. Basically we do not have a clue what space-time looks like at extremely short times and lengths, but we are pretty sure it is very strange. However, because regular laws are obeyed for longer times and lengths, the regular definition of time works fine for this.

A. Smith

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