Here are some clues I use to update my personal credences. Plus/minus signs increase/decrease credence. The more signs, the more the increase/decrease. The list of options are not supposed to be exhaustive. The options are also not necessarily exclusive against each other. I hope to constantly update the clues as I learn.

Gravity

Foliation

Is there a common time foliation or not for spacetimes in superposition?

Framework

Which theoretical framework would the correct theory of gravity be based in?

• path integral
• Wheeler-DeWitt equation
• Schrödinger equation
• algebraic quantum theory
• not quantum theory

• • No difficulty for accommodating matter fields of the Standard Model. (+)
  • Works whether or not spacetimes in superposition follow a common time foliation. (+)
• • Seems impractical for accommodating matter fields of the Standard Model. (-)
  • How to extract empirical predictions from \(\psi\) that obeys the Wheeler-DeWitt equation? Converse, would the mathematical object actually useful for extracting empirical predictions obey the Wheeler-DeWitt equation? (- -)
  • The Wheeler-DeWitt equation would not hold if the lapse is positive for our universe (see, e.g., Section IV.A of Ref). (-)
• • Seems impractical for accommodating matter fields of the Standard Model. (-)
  • Still works if spacetimes in superposition do not follow a common time foliation? (- -)
• • What replaces the microcausality axiom when spacetimes are allowed in superposition? (- -)
• • Unclear if any non-quantum framework reproduces the success of the quantum framework for the Standard Model of particle physcics. (- -)

Description

How should gravity/spacetime be fundamentally described?

• metric field
• gauge field
• causal set
• extended objects
• holography
• emergence

• • Probably no measure factor subtleties in a sum over histories for causal sets. (+)
  • How to enforce dimension 4 in a sum over histories for causal sets? (- -)
  • How to incorporate fermionic matter in the absence of tangent spaces? (-)

Singularity

What’s the status of singularity in the correct theory of quantum gravity (if there is any)?

Information

What happens to quantum information in black holes?

Evidence

Where would theory-distinguishing empirical evidences come from?

Experience

Interior condition

History

Many-worlds

Boundary condition

Options

What should be the boundary condition of the universe?