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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Recordings per month over the last 12 months — 1 in all, peaking in Jun 2026 with 1.

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The potential energy of a bound system has positive kinetic energy at the bottom, but gravity energy is negative.

So already when we deal with gravity, we're somehow used to the fact that, no, the energy isn't positive, right?

Potential energy is not positive.

And it's more than that.

observations show us that the universe is expanding exponentially now.

It doesn't sound like a very stable system, right?

Gravity has this weird property, if we believe in the cosmological constant, that the universe is going to expand exponentially forever.

That sounds awfully like an instability.

When we've studied this four-derivative theory of gravity, we show that the Ostrogradsky instability is nothing but normal gravitational expansion.

And if we analyze the expanding solution in just the same way that we do with Einstein's theory, we discover it's absolutely stable.

So the Ostrogradsky instability went away just by reinterpreting the theory as a gravitational theory.

Yes.

It's called a Krein space.

Pseudo-Hilbert spaces.

Let's call it Krein.

So, again, my student, Sam Bateman, has this...

deep interest in the mathematical literature, mathematical physics literature, and he's just been exploring.

And of course the internet is very helpful, and even AI can find papers.

So somehow Sam came across this notion of the Krine space, which is not generally known to physicists.

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