The University of St Andrews is one of the best in the UK, and its Physics and Astronomy department, according to the Guardian, is the best physics department in the UK, so, of course, they wanted to hear about quantised inertia (QI) :)
I went up there by train on Monday and stayed with them for a couple of nights and gave a seminar on quantised inertia on Tuesday. The talk seemed to go well since there were quite a few questions at the end, and no-one stood up and threw general relativity textbooks at me.
The most useful and enjoyable activity was discussing things informally, and often with a beer :) and Indian food, with the Professor who invited me, and two keen young cosmology PhD students who made some very good points. In the first meeting they made a toast to quantised inertia, and then they started, as they should, to try to pull apart the theory. That is a extremely fruitful approach.
Their first criticism went something like this. It seems inconsistent that I model a star orbiting round a galaxy by using the very low acceleration of its galactic orbit (v^2/r) and saying that the inertial mass has dropped because of QI (and thereby explaining anomalous galactic rotation without dark matter), but the actual components of the stellar system, say the Sun and Jupiter show a much higher mutual acceleration, and the atoms in the Sun for example are zooming around at very high acceleration, so shouldn't the inertia of the system be normal in QI?
I gave an answer to that in this blog post. That is still valid and I explained it to them (they had some questions about whether Rindler horizons mask the cosmic ones), but a simpler way to say this is that in quantised inertia, inertia is not a property of an object, but is a property of an interaction between objects. This makes philosophical sense, since an object alone in an empty universe would not be able to have any meaningful inertia because it would have no way to know if it was accelerating or not. I agree with Mach and the early Einstein so I do not see space-time as something that one can determine one's motion relative to. This means that for Jupiter, when you work out its response, in QI, to the gravity from the galactic centre, the inertia needs to be reduced in line with its low acceleration relative to the galactic centre (the inertia of that interaction), but when you work out Jupiter's response to the gravity from the Sun, the acceleration is large so the inertial mass in QI is not reduced. This means that the theory predicts the behaviour of the atoms in the Sun, the Sun and Jupiter, and the whole galaxy in a self-consistent way. It also means that each object has more than one inertia. The challenge remains how to encode this in the maths, and that was their other criticism: that the maths for QI is not yet fully formed, and does not use the same symbols or metrics as the maths they use, and this is advisable if I want cosmologists to start modelling with it.
I thoroughly enjoyed my visit to St Andrews University. The town itself is very pleasant: they have a city wall, huge golf links (though I don't play) and a beach, but I did not see it this time. I was told, and I thought it was very Scottish, that as a mild 'test of courage' the University gets students to walk along the pier in their gowns. My impression of the people in the Physics and Astronomy department was good because the audience I had seemed curious and open-minded (they did not look at me as if I was a bug, as sometimes happens!) yet they were keen to try to identify any problem. I noticed that someone in the department was also bothering to leave interesting articles lying open on tables for students to read, and the academics pin up their papers outside their doors. There was a general attitude, not of looking efficient, but of genuine interest in what they were doing.