Black holes in the laboratoryThe hierarchy problemLXD - Large Extra DimensionsThe LXDs explain the so-called hierarchy problem, presently one of the most prominent problems in physics. It is why first quantum effects of gravitation are to be expected at a length scale which lies far below the scale of the other interactions (the so-called Planck-length). So far below, that a consistent description is not possible without an explanation of this difference.
The LXD-models approach this problem by adding compactificated dimensions to space. Gravity, as a force which acts by geometry itself, can propagate into all dimensions. The other interactions remain constrained to our submanifold. The decay of a force with increasing distance to the source depends on the number of dimensions. The more dimensions, the more rapid the force lines thin and the more rapid the force decreases. Thus gravity first decreases considerably faster and becomes weaker. As the range approaches the length of the extra dimensions, compactification becomes important. The force lines cannot thin out further and on length scales, that are large compared to the length of the extra dimensions, our familiar law of gravity in three dimensions arises.
The rapid decay of the gravitational force at the beginning is here decisive. It explains why gravity is so much weaker on our submanifold and on large distances (always relative to the size of the extra dimensions) This was impossible to explain in earlier models with "small" extra dimensions which had a radius ouf approximately the Planck-length itself.
The modification of Newton's law and of the scale for gravity now has consequences on general relativity on small length scales. A black hole in our fourdimensional space has a radius -- the so-called Schwarzschild-radius -- which is proportional to its mass. It can be shown that this radius is comparatively diminutive. E.g. the Schwarzschild-radius of earth, if it would collapse, would lie in the range of millimeters. The Schwarzschild-radius of masses that can be created in accelerators is so small that it is illusory to focus these masses up to their Schwarzschild-radius to let them collapse.
Now it can be shown that this radius for black holes in a mass range which will soon be accessible by experiment, is considerably larger with extra dimensions. So large that black holes can be created in accelerators, as e.g. the LHC (Large Hadron Collider).
For heaven's sake, are we completely crazy? Now they make a black hole and, slurp, we're all doomed? Well, at last we know then what a black hole looks like from within. Haha, but let's stop joking. The mass of the hole is still exiguous and so is its gravitational force which it exerts on surrounding particles. The air in your mouth still weighs 1015 times more, even when it stands open. This applies at least to ordinary distances, i.e. those that are larger than the radius of the extra dimensions.
A particle therefore vanishes into the mini-hole only if it accidentally stumbles directly on it. And densities we usually have or which can be created on earth cannot feed the hole sufficiently to make it grow. Furthermore another factor gets important:
Black holes emit a radiation which is called "Hawking-radiation", named after Stephen Hawking, who calculated it first. This radiation leads to an energy loss of the black hole: it vaporises. It is a pity, because then it is gone. Our group has studied the properties of these black holes [7] and it was shown to our great pleasure that the presence of extra dimensions is conducive to the stabilisation of the black holes. They vaporise so slowly than one can call them quasi-stable. So we have time to examine their properties which pleases a phycisist's heart.
Our results are published in [5,6,7,8].