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Finbar is offline
Dec30-11, 08:11 PM
P: 343
Quote Quote by suprised View Post
To make things easier, the electrons have an offset, or impact parameter, which is large, say 1km. Ordinarily one wouldnt expect that something would be peculiar or problematic.

But I didnt tell you that the kinetic energy of the electrons equals to the mass of a large star. A star with such a mass would form a black hole. So what's going to happen is that when the electrons are still, say 2km apart, a large black hole forms.

How can you be certain a black hole forms for the two electrons? This is not a kinematical regime that we have any experimental knowledge of and there is not an established theory at transplanckian energies. You cannot simply apply general relativity to two electrons with these energies.

It is a fact that one can only state when a black hole is formed with knowledge of the complete dynamical history of the spacetime. Yes it is true that initially when the two electrons are 2km apart that they should begin to collapse. But since they are transplanckian as they get closer to each other the quantum gravity effects will become important and it is possible that the collapse will cease to continue. So although an apparent horizon will form it is possible that once the electrons reach Planckian distances their coupling to the gravitational field will be vastly altered and a classical spacetime is unlikely to be a valid assumption.

To make rash statements about the formation of black holes one must at least take three quantities into account:

1) The total energy

2) The impact parameter

3) The number of degrees of freedom

The important thing in your example is the number of degrees of freedom is very small, just those of two electrons. Roughly speaking GR is only valid when the number of degrees of freedom is very large. So the normal hoop conjecture rational is good when we assume that there is a large number of degrees of freedom and so we only concern ourselves with 1) and 2). For a star this is fine but in your example it is clearly not.