Is Gravity RANDOM Not Quantum?

Summary

This episode explores the possibility of a classical theory of gravity compatible with quantum mechanics, challenging the quest for quantum gravity. Physicist Jonathan Oppenheim proposes 'post-quantum gravity,' suggesting gravity may be inherently random, not quantum. The theory addresses inconsistencies between general relativity and quantum mechanics, offering a new perspective on unifying these fundamental physics theories and their implications for quantum information and determinism.

Takeaways

• 🌌 The script discusses the ongoing quest for a unified theory in physics, specifically quantum gravity, questioning if gravity is inherently quantum or just appears messy or random.
• 🧠 It introduces the post-quantum gravity hypothesis by Jonathan Oppenheim, suggesting gravity might not be quantum but could be made compatible with quantum mechanics through the addition of randomness.
• 🔬 The script contrasts general relativity, which describes large-scale phenomena like gravity, with quantum mechanics, governing the small-scale behavior of matter and energy.
• 🔄 The conflict between these two theories is highlighted, as they are both verified to high precision but seem fundamentally incompatible, leading to the search for a theory of quantum gravity.
• 🤔 The possibility of a classical theory of gravity that works alongside quantum mechanics is explored, challenging the assumption that gravity must be quantized.
• 📚 Einstein's field equations of general relativity are explained, which equate the geometry of spacetime with the matter and energy within it.
• 🌐 The script delves into the complexities of coupling classical gravity with quantum theory, discussing the issues with semiclassical gravity and the expectation value of the stress-energy tensor.
• 🚀 The concept of a singular spacetime shaped by quantum superpositions of mass and energy is critiqued for its inconsistencies with quantum mechanics.
• 💥 The idea of adding noise to gravity itself to create a singular classical spacetime that allows quantum objects to behave quantumly is presented as a potential solution.
• 🔮 Oppenheim's theory of post-quantum gravity is described, which includes a fluctuating gravitational field that could resolve issues with the uncertainty principle and the measurement problem.
• 🎲 The script touches on the radical implications of post-quantum gravity, including the abandonment of determinism and the potential resolution of the black hole information paradox by allowing for the destruction of quantum information.

Q & A

What is the holy grail of theoretical physics?

The holy grail of theoretical physics is to find the long-sought theory of quantum gravity, which would unify the principles of quantum mechanics and general relativity.

What are the two great theories in physics that explain almost everything?

The two great theories are general relativity, which describes space, time, and gravity on the largest scales of the universe, and quantum mechanics, which describes atoms, matter, and the smallest scales.

Why do general relativity and quantum mechanics appear to contradict each other?

General relativity and quantum mechanics appear to contradict each other at the most fundamental level because they are each verified to astonishing precision but describe the universe in very different ways, with general relativity being a classical theory and quantum mechanics being inherently probabilistic.

What is the assumption hidden in the term 'quantum gravity'?

The term 'quantum gravity' assumes that the solution to unifying quantum mechanics and general relativity is to 'quantize' gravity, making it work correctly alongside quantum mechanics.

What is the post-quantum gravity hypothesis proposed by Jonathan Oppenheim?

The post-quantum gravity hypothesis suggests that gravity is not quantum but rather has an element of randomness or 'noise' that allows it to be compatible with quantum mechanics without needing to quantize spacetime itself.

What are the Einstein field equations?

The Einstein field equations are a set of 10 partial differential equations that equate the geometry of spacetime, described by the Einstein tensor, with the distribution of matter and energy, described by the stress-energy tensor.

How does the concept of semiclassical gravity relate to the discussion of quantum and classical gravity?

Semiclassical gravity is an approach where spacetime curvature is defined by the expectation value of the stress-energy tensor, allowing for quantum matter to influence a classical spacetime. It has been historically successful but faces issues when considering quantum superpositions.

What is the issue with using semiclassical gravity to describe a quantum object in superposition?

The issue with semiclassical gravity is that it leads to a singular spacetime geometry defined by the expectation value of the quantum object's location, which can result in odd behaviors, such as objects appearing to be attracted to nothing, and violates the uncertainty principle.

How does the addition of noise to gravity in post-quantum gravity resolve the issues with semiclassical gravity?

In post-quantum gravity, the addition of noise to the gravitational field allows for a probabilistic interaction between quantum objects and spacetime, preventing the violation of the uncertainty principle and allowing quantum objects to maintain their quantum behavior.

What is the radical aspect of Oppenheim's post-quantum gravity theory?

The radical aspect of Oppenheim's theory is that it introduces true randomness into the gravitational field, which has implications for the determinism of physics and the conservation of quantum information.

What is the potential consequence of allowing quantum information to be destroyed in post-quantum gravity?

Allowing quantum information to be destroyed by random fluctuations in the gravitational field could resolve paradoxes such as the black hole information paradox and provide a consistent way for classical spacetime to evolve with quantum matter.