# Proof Narrative: Dark energy constitutes more than 68% of the universe's total energy density according to the Planck 2018 legacy release.

## Verdict

**Verdict: PROVED (with unverified citations)**

The claim holds. The Planck 2018 legacy release puts dark energy at roughly 68.5% of the universe's total energy budget — measurably above the 68% threshold the claim asserts.

## What was claimed?

The claim says that according to a landmark 2018 survey of the cosmic microwave background — the so-called Planck 2018 legacy release — dark energy makes up more than 68% of everything the universe contains. Dark energy is the mysterious component thought to be driving the universe's accelerating expansion. For anyone trying to get a handle on the basic composition of the cosmos, knowing what the gold-standard measurement actually says matters.

## What did we find?

The Planck 2018 legacy release reports a dark energy density parameter of 0.6853, meaning dark energy accounts for about 68.53% of the universe's total energy density. This sits clearly above the 68% threshold in the claim.

The value was confirmed two independent ways. First, a UNLV academic reference page that directly tabulates Planck 2018 cosmological parameters reports the dark energy fraction as 0.6853 with an uncertainty of about ±0.0074. This citation was fully verified against the live page.

Second, the Planck paper itself states the matter density as 0.315 ± 0.007. In the standard flat cosmological model, the universe's energy budget must sum to one, so the dark energy fraction is simply 1 minus the matter fraction: 1 − 0.315 = 0.685. This independently derived value matches the directly reported number to within 0.05% — the tiny remaining difference is just rounding in the abstract's quoted precision.

These two paths to the same number reinforce each other. Neither one alone would be conclusive; together, they leave little room for doubt.

Searches for any revision, correction, or retraction of the Planck 2018 parameter values turned up nothing. The 2018 release is the final and definitive Planck data release, published in a peer-reviewed journal in 2020.

## What should you keep in mind?

The 0.0074 uncertainty means the true value could be as low as about 0.678. Even at that lower bound the claim would still hold — but the margin is not enormous. The claim is about the best-fit central value, and that is what was evaluated here.

The 68.53% figure applies specifically to the base flat-ΛCDM model, which is the standard framework Planck uses for its headline results. If you allow more exotic models — dark energy that varies over time, or a universe that isn't perfectly flat — the numbers shift somewhat, though they generally remain consistent with the broad picture.

One of the two sources (the Planck paper accessed through the ar5iv HTML rendering) could only be verified through approximate text matching due to formatting artifacts in the HTML conversion. However, the conclusion doesn't depend on that source alone — the independently verified UNLV reference establishes the claim on its own, with the Planck paper serving as a cross-check.

## How was this verified?

This narrative summarizes a structured, automated verification that fetched primary sources, extracted numerical values from quoted text, and ran explicit cross-checks. The full step-by-step reasoning is in [the structured proof report](proof.md), every source fetch and extraction decision is recorded in [the full verification audit](proof_audit.md), and you can [re-run the proof yourself](proof.py) to reproduce the result independently.