Neil Turok
speaker
2,693 appearances
2 recordings
1 series
first heard Apr 2025
last heard 22 Jun
Neil Turok’s voice in public audio — every appearance, attributed to the second.
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That'll give exactly the same answers in normal quantum mechanics.
But the beauty is because now it involves projection operators, it gives sensible answers even in a crying space.
And what we've shown is that provided the S matrix or Hamiltonian of this theory has this symmetry, the one I mentioned, the answers you get are always positive and the probabilities always add up to one.
So we found that in dealing with theories which have four derivatives, we have to very slightly generalize the framework of quantum mechanics.
But essentially, it's a trivial change.
And then we find all the probabilities are positive.
So even though there are ghost states, you still trace over them.
You trace over everything.
So this is very exciting because now I have to say that there's a caveat, which is that we haven't solved quantum gravity yet, but we're halfway there.
That's optimistic, of course, but that's a nice way of saying it.
So when you look at this quadratic gravity action, there are two terms which are allowed.
That's all.
The symmetries of general relativity only allow two terms.
One is what's called the Ricci scalar squared, and the other one is the Weyl curvature squared.
And this is the most general action.
So there are two couplings you can play with.
What we've shown is that if you take a limit where one of those couplings is zero, that basically decouples the graviton and everything associated with the vial curvature.
You're left with the curvature scalar.
That action is renormalizable, asymptotically free, and gives positive probabilities.
So we claim we understand quantum gravity in a certain limit,
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