What preceded the Big Bang / what state was the universe in?

The question

What was the state of matter "before" (or at the instant of) the Big Bang, when all the energy of the observable universe was in a subatomic volume — and what, if anything, was it "in"? michelle-thaller: "No astronomer thinks the Big Bang came from nothing," but "we have no description of what that state of matter would be."

Why it matters

It is the same class of gap as neutron-stars and black-holes interiors: regimes of extreme density and gravity where general relativity and quantum mechanics both apply and don't yet combine. Resolving it likely requires a new physics of high-density gravity.

What we currently believe

• The observable universe was once in a very small, hot, dense volume (supported by the cosmic-microwave-background and the expanding-universe picture).
• This does not imply the whole universe was small — it could already have been infinite.
• Sub-second early-universe accounts (Planck epoch, force unification, inflation) are best-effort extrapolations of current physics; Thaller takes them "with a big chunk of salt."

Evidence we have

• michelle-thaller in 2026-05-28-youtube-powerfuljre-joe-rogan-experience-2506-michelle-thaller: "The idea of what was that state of matter before that expansion, we have no description of yet. I think we will someday."
• CMB uniformity; CERN / Large Hadron Collider can recreate conditions to ~a millionth of a second after, but not before.

Evidence we need

• A working theory of gravity at extreme density (quantum gravity); experimental handles on pre-/early-Big-Bang conditions (possibly via primordial gravitational waves — see ligo).

How to resolve

• Progress in quantum gravity; gravitational-wave cosmology that sees past the cosmic-microwave-background opacity limit.

Related

• expanding-universe
• cosmic-microwave-background
• neutron-stars
• limits-of-science
• ligo
• michelle-thaller