[TallTroll]

Tee-hee-hee, cool thread! To throw another twist in, did you know that is it perfectly possible (at least theoretically) to make minute BHs?

A BH forms when the gravitational forces in a region of space become so large that the energy required for anything to escape becomes infinite.

Normally, the only way to do that is to pile so much mass up in a small volume that gravitational collapse results (ie big stars going nova, then collapsing back all the way)

But...on totally the other end of the scale, hands up those who know which parameter of a photon is inversely related to its energy?...Yes, you boy

Please Sir, wavelength!

Correct, boy! So, as wavelegth decreases, energy increases. As e=mc^2, we see that a photon of a given energy can be said to possess the equivalence of a certain amount of mass (as well as a tiny amount of "real" mass - thats why solar wind works).

A photon can also be said to occupy (on average) a small, finite volume of space at any time. It therefore possesses a calculable "density" (mass/volume=density, e=mc^2, =>(e/c2)/volume=density).

If its wavelength can be sufficiently reduced, and its energy thus increased to the point where that density is high enough to cause gravitational collapse, voila, a microscopic BH!

In case you are wondering, yes photons DO undergo gravitational interactions, hence the already referred-to "gravitational lensing" effect, so this is (sort of!) feasible

I seem to remember reading that the particle accelerator that could actually get a photon up to the required speeds would need to stretch out about as far as the orbit of Pluto... so no worries just yet!