Compare · The Fate of the Universe

Classical Closed Recollapse vs Negative Cosmological Constant Recollapse

Recollapse and the Big Crunch· within family

	Classical Closed Recollapse Rejected	Negative Cosmological Constant Recollapse Speculative
Proposed	1922	2002
Key figures	Alexander Friedmann	Gary Felder, Andrei Frolov, Lev Kofman, Andrei Linde
In one sentence	Classical Closed Recollapse is the original Big Crunch, the closed Friedmann universe that dominated cosmology before dark energy was discovered. If the total density exceeds a critical value, space has positive curvature and is finite, and gravity eventually halts the expansion and pulls everything back into a hot, dense crunch. Current measurements of a flat universe with dark energy have made this the disfavoured route, but it remains the foundational picture of a recollapsing cosmos.	A Negative Cosmological Constant Recollapse is what happens if the vacuum energy is negative rather than positive. A negative cosmological constant produces an anti-de-Sitter-like spacetime that cannot expand forever: once it dominates, it halts the expansion and drives a collapse to a Big Crunch. Felder, Frolov, Kofman, and Linde 2002 analysed these futures, which matter because negative vacuum energy is the generic outcome in string theory while a positive one is notoriously hard to obtain.
Predictions	The total density exceeds the critical value, giving positive spatial curvature and a finite, closed universe Expansion reaches a maximum and reverses purely under gravity, with no dark energy required The contraction reverses cosmic history: blueshifted, reheating background radiation ending in a hot dense crunch A measurement of significantly positive spatial curvature would revive this route to a crunch	The vacuum energy is ultimately negative, so a negative cosmological constant comes to dominate the late universe Expansion halts and reverses into a Big Crunch regardless of whether space is flat, open, or closed The present acceleration is a transient phase of a field not yet settled into its true, negative-energy vacuum Evidence that the dark-energy density is decreasing over time would support an underlying negative vacuum energy
Where it breaks	Precision cosmological measurements are consistent with a spatially flat universe, removing the positive curvature this scenario requires A positive dark energy, which is observed, drives eternal expansion even in a closed universe, overriding the gravitational recollapse On current data this is not a viable future, which is why it carries historical status	Observations currently measure a positive dark-energy density, so any negative vacuum energy must be hidden behind a transient positive phase, which is an extra assumption The timing of the collapse depends on how the present field configuration relates to the true vacuum, which is unknown Whether the crunch is singular or bounces is, as always, undetermined by known physics
Key unresolved problem	The scenario needs a closed, super-critical universe, but the measured near-perfect flatness and the observed positive dark energy together leave it with no room in the current data.	The scenario needs today's clearly positive dark energy to be a passing phase over a hidden negative vacuum, and nothing measured tells us whether that hidden vacuum exists or when it would take over.
Reader vote	No votes yet	No votes yet

Classical Closed Recollapse

1922 · Rejected

Negative Cosmological Constant Recollapse

2002 · Speculative

Proposed

1922

2002

Key figures

Alexander Friedmann

Gary Felder, Andrei Frolov, Lev Kofman, Andrei Linde

In one sentence

Classical Closed Recollapse is the original Big Crunch, the closed Friedmann universe that dominated cosmology before dark energy was discovered. If the total density exceeds a critical value, space has positive curvature and is finite, and gravity eventually halts the expansion and pulls everything back into a hot, dense crunch. Current measurements of a flat universe with dark energy have made this the disfavoured route, but it remains the foundational picture of a recollapsing cosmos.

A Negative Cosmological Constant Recollapse is what happens if the vacuum energy is negative rather than positive. A negative cosmological constant produces an anti-de-Sitter-like spacetime that cannot expand forever: once it dominates, it halts the expansion and drives a collapse to a Big Crunch. Felder, Frolov, Kofman, and Linde 2002 analysed these futures, which matter because negative vacuum energy is the generic outcome in string theory while a positive one is notoriously hard to obtain.

Predictions

The total density exceeds the critical value, giving positive spatial curvature and a finite, closed universe
Expansion reaches a maximum and reverses purely under gravity, with no dark energy required
The contraction reverses cosmic history: blueshifted, reheating background radiation ending in a hot dense crunch
A measurement of significantly positive spatial curvature would revive this route to a crunch

The vacuum energy is ultimately negative, so a negative cosmological constant comes to dominate the late universe
Expansion halts and reverses into a Big Crunch regardless of whether space is flat, open, or closed
The present acceleration is a transient phase of a field not yet settled into its true, negative-energy vacuum
Evidence that the dark-energy density is decreasing over time would support an underlying negative vacuum energy

Where it breaks

Precision cosmological measurements are consistent with a spatially flat universe, removing the positive curvature this scenario requires
A positive dark energy, which is observed, drives eternal expansion even in a closed universe, overriding the gravitational recollapse
On current data this is not a viable future, which is why it carries historical status

Observations currently measure a positive dark-energy density, so any negative vacuum energy must be hidden behind a transient positive phase, which is an extra assumption
The timing of the collapse depends on how the present field configuration relates to the true vacuum, which is unknown
Whether the crunch is singular or bounces is, as always, undetermined by known physics

Key unresolved problem

The scenario needs a closed, super-critical universe, but the measured near-perfect flatness and the observed positive dark energy together leave it with no room in the current data.

The scenario needs today's clearly positive dark energy to be a passing phase over a hidden negative vacuum, and nothing measured tells us whether that hidden vacuum exists or when it would take over.

Reader vote

No votes yet