Sub-millimeter gravity
Today's colloquium was given by Eric Adelberger from University of Washington on their experiments for small scale gravity. They are using an extremely sensitive torsional pendulum apparatus coupled gravitationally by two rotating discs. All of them have holes so that 1/r^2 effect of two discs are cancelled and there is only non standard effects left at the first order. There are many checks of course. For example they discovered micron level non-smoothness of the inner surfaces of the holes by gravitation before the microscope!!! I think this is enough reason to trust them. Their conclusion so far is that there is nothing new down to 0.1 mm. But things get interesting at that scale because that is the length scale corresponding to measured dark energy. And as rumored by Lubos some time ago there seems to be something interesting around there. Data they have so far is not clean enough but seems to eye that the observed force is a little bit less than the theory. Since it is at the limits of their instrument, you should not get excited right now. He thinks that they can have enough tests in a few months to figure out whether it is some systematics or real signal. It seems that they are well away from the theoretical limits of the instrument design and currently limited by how fine they can manufacture their parts. We can expect much more accuracy in the following few years. Fingers crossed and waiting.
