Background on Post-Quantum Gravity Theory

• Jonathan Oppenheim's post-quantum gravity theory emerged last year as first new quantum gravity theory in decades
• Made it into presenter's best of 2024 summary
• Presenter now doubts theory's correctness based on new paper
• Theory addresses 100-year-old problem: quantum physics and gravity incompatibility
  • Quantum physics: non-deterministic, random element, built-in uncertainty, limits on knowledge
  • Gravity: non-quantum, deterministic, unpredictable only due to lack of information
• Challenge: quantum particles have gravitational pull, theories must cooperate somehow

Oppenheim's Approach vs Traditional Methods

• Traditional quantum gravity approaches: give quantum properties to gravity
• Oppenheim's approach: add randomness to gravity to match quantum physics randomness
• Gravitational randomness assumed as fundamental property of nature (like quantum mechanics randomness)
• Theory suggests randomness changes gravity law at large scales
• Could eliminate need for Dark Matter
• Testing proposed through small fluctuations in object masses
• Difficult to test due to gravity's weakness compared to other forces
• Advantage: changes both gravity AND quantum physics, latter easier to test

New Paper's Testing Method

• New paper appeared on archive showing how to test whether gravity remains non-quantum
• Key insight: if gravity stays non-quantum, uncertainty must increase for quantum physics compatibility
• This causes gravitational attraction to become "fuzzy"
• Effect: measurably increases quantum uncertainty of small objects

Proposed Experimental Setup

• Two pendulum masses hanging on strings
• Set one in motion, gravitational pull affects second mass
• Random gravity element leads to bigger spread in mass positions
• Prediction independent of model details
• Very small effect requiring control of intrinsic noise from atomic motions
• Requires objects cooled to very low temperatures
• Current technology insufficient but may be possible in near future
• Space mission suggested to avoid Earth's gravitational field uncertainty

Historical Context and Predictions

• Same research group previously tested Penrose's gravitationally induced collapse theory
• Ruled out Penrose's idea four years ago
• Mathematical theorems prove: leaving gravity classical disrupts quantum physics in testable ways
• Changing quantum physics much harder than changing gravity
• Most quantum gravity approaches modify gravity instead

Assessment and Outlook

• Post-quantum gravity not yet ruled out, but presenter expects it will be
• Acknowledges possibility of being wrong about Oppenheim being right
• Compares post-quantum gravity to postmodern art: "too random"
• Emphasizes difficulty of modifying quantum physics vs gravity