What If Gravity Isn't Quantum? New Experiments Examine
Summary
This episode explores experimental approaches to testing quantum gravity, contrasting the standard effort to quantize gravity with the alternative hypothesis that gravity remains classical and causes quantum wave function collapse. The discussion covers tabletop experiments designed to detect gravitational diffusion or limits on macroscopic superposition, which would support models like Diósi-Penrose or Oppenheim's post-quantum gravity.
Topics discussed
Introduction: The challenge of testing quantum gravity
The conflict between quantum mechanics and general relativity
Why quantizing gravity is difficult and the alternative approach
Classical gravity models: Oppenheim and Diósi-Penrose
Experimental tests: Distinguishing quantum vs classical gravity
How classical gravity causes wave function collapse
Testing gravitational diffusion and mass measurement limits
Constraints from large molecule superposition experiments
Quantum entanglement as a test for quantum gravity
The QGEM experiment proposal and Stern-Gerlach interferometer
Mechanics of the Stern-Gerlach spin superposition
Gravitational interaction between interferometers
Using nanodiamonds to detect gravitational entanglement
Implications of a positive QGEM result for spacetime
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