The speaker, Jonathan Oppenheim, a physicist at University College London, discusses the challenge of reconciling gravity with quantum theory. He proposes a theory where matter remains quantum but gravity is treated classically. This theory attempts to resolve the inconsistency between general relativity, a theory of space-time, and quantum mechanics.
Oppenheim explains that while the general consensus among physicists is that gravity should be quantized like other forces, gravity's simplicity and its role as the background in which matter moves present unique challenges. Quantizing space-time would mean quantizing the speed of time, which if done, would freeze time and halt evolution.
The speaker also touches on the black hole information paradox, a problem that arises due to Hawking's discovery that black holes appear to thermally radiate, seemingly destroying the information thrown into them. This paradox is only a problem if one believes in deterministic physics, the idea that everything can be predicted with certainty.
Oppenheim suggests that any consistent theory of coupling between classical degrees of freedom and quantum degrees of freedom has to be fundamentally stochastic, or random. He proposes experiments to test this theory, which could potentially resolve the longstanding problem of reconciling gravity and quantum theory.
1. The general feeling amongst business for the last hundred years is that we need to quantize space-time just as we quantize every other field.
2. Reconciling gravity with quantum theory is one of the great challenges of physics thus far.
3. The speaker, Jonathan Oppenheim, is a physicist at University College London.
4. Oppenheim and his students have proposed a theory of gravity where matter remains Quantum but gravity is treated classically.
5. This theory attempts to reconcile the fact that our current theory of gravity, general relativity, is inconsistent with quantum mechanics.
6. In physics, we have two frameworks: quantum mechanics and classical mechanics. All particles in all the fields and different forces obey quantum theory, but quantum theory doesn't describe gravity.
7. The theory of gravity's general relativity discovered by Einstein is a theory of space-time.
8. The general feeling amongst physicists for the last 100 years is that gravity is a force just like any other force and therefore should be quantized.
9. Gravity is very simple in some ways, with almost all of gravity being that clocks run at different speeds in different places.
10. The main problem when trying to quantize gravity is that if you quantize the speed of time, time becomes Frozen and things don't evolve at all.
11. The black hole information Paradox is a fascinating conundrum in physics and it somehow seems to hold the key to reconcile gravity and quantum theory.
12. The paradox comes about because of Hawking's Discovery that black holes appear to thermally radiate so if you throw a known Quantum State into a black hole then the black hole will just radiate it away thermally in a way that seems to completely destroy the information that was thrown into the black hole.
13. The idea that we can consistently couple Quantum systems and classical systems has been around since the 90s.
14. Any consistent theory of coupling between classical degrees of freedom and Quantum degrees of freedom has to be fundamentally stochastic.
15. The amount of Randomness you have to have is a lot, with an upper bound of 10 to the minus one and a lower bound of 10 to the minus 40.
16. Oppenheim and his team have proposed experiments looking for Randomness in a gravitational field, which are indirect tests of a quantum theory of gravity.
17. If Randomness and noise are not found in the gravitational field, then a classical theory of gravity can be ruled out.
18. The experiments proposed by Oppenheim and his team will measure the gravitational field produced by one kilogram mass and how much noise there is in a precision test of gravity.
19. They will also measure how long they can put a massive object in superposition, such as a gold atom. These two experiments will squeeze any theory in which gravity is treated fundamentally classically from two directions.
20. The outcome of these experiments will determine the solution to the problem of reconciling gravity with quantum theory, a problem that has been struggling for 100 years.