Controls
Drag the sliders to evolve the cosmos. Galaxies are massless tracers carried by the comoving grid. Set w below −1 to enter PHANTOM; raise Ωm for a RECOLLAPSE.
Diagnostics
Drag the dial
w = −1 is a true cosmological constant. Below −1 is phantom — the energy density actually grows with expansion, leading to a Big Rip. Above −1/3 expansion is no longer accelerating.
Regime map
w<−1 PHANTOM w=−1 Λ −1<w<−⅓ QUINTESSENCE w=0 DUST w=⅓ RADIATION w=1 STIFFPick a destiny
Heat Death (Big Freeze): Λ wins forever. Galaxies recede past the cosmic event horizon (~16 Glyr). By 10100 yr only Hawking-evaporating black hole remnants and a frozen photon bath remain.
Timeline
Potentials
A scalar field φ slow-rolls down its potential V(φ). When kinetic energy ≪ V, it mimics Λ. When V grows it looks phantom; when V flips negative, it can recollapse the universe — sometimes called a doomsday field.
CPL parameterisation
In April 2024 the DESI BAO release combined with CMB & SN suggested w(a) is not a constant — early-time phantom behaviour crossing the w=−1 line into a less-negative present. If real, this would falsify the cosmological constant. Watch for the phantom-divide crossing highlighted on the curve.
Two ladders disagree
The early-universe value (CMB sound horizon + ΛCDM) and the local distance ladder give different H₀. Possible cures rewrite either side of cosmic history.
Proposed cures
Early Dark Energy Decaying Dark Matter Varying αem Sound horizon shift New neutrino species Local void (KBC) Modified recombinationMeasured slice
The bound
The holographic principle says the entropy of any region is bounded by its area in Planck units, not its volume. Apply this to the entire observable universe and the maximum vacuum energy drops by ~10120 — solving the cosmological constant problem at the cost of a strange non-local definition.
A wild proposal
Farrah et al. (2023) suggested that supermassive black holes gain mass as the universe expands, with k≈3 reproducing the entire observed dark energy density. The interiors would then be dark energy: a GEODE (Generic Object of Dark Energy) instead of a true singularity.
What if Λ doesn't exist?
David Wiltshire's timescape model: clocks in cosmic voids tick faster than clocks bound in galactic walls. Averaging over a lumpy universe makes the expansion look accelerated to us, without any Λ. A 2024 reanalysis of Pantheon+ supernovae found timescape preferred over ΛCDM at modest significance.
Maybe Λ is illegal
String theorists conjecture that any potential consistent with quantum gravity must satisfy |∇V|/V ≥ c or −min(∇²V)/V ≥ c'. Both forbid a positive cosmological constant minimum — pure de Sitter lies in the swampland. Our universe must therefore be quintessence in disguise, slowly rolling.
The worst prediction in physics
Sum the zero-point energies of every quantum field up to the Planck scale and you get a vacuum energy 10¹²⁰ times larger than the observed Λ. Every honest cancellation must agree to 120 decimal places — the cosmological constant problem.
Proposed answers
Anthropic landscape Unimodular gravity Sequestering Causal patch Adjustment mechanism (no-go) Fluctuation-driven ΛNotation
Conventions
FLRW metric, signature (−,+,+,+); ℏ=c=1 unless noted; Ωi ≡ ρi/ρcrit at present; subscript 0 means today.