# Proof Narrative: The mean neutron lifetime measured in beam experiments is more than 1 second shorter than the lifetime obtained from ultracold-neutron bottle experiments.

## Verdict

**Verdict: DISPROVED**

This claim has the direction of a real physics mystery exactly backwards — and the reversal matters.

## What was claimed?

The claim says that when physicists measure how long a neutron lives before decaying, the "beam" method produces a result that is more than a second shorter than the "bottle" method. You might encounter this claim because there genuinely is a famous disagreement between these two experimental approaches — the so-called neutron lifetime puzzle — and someone may have mixed up which method gives the longer number.

## What did we find?

There are two main ways physicists measure the neutron lifetime. In beam experiments, scientists fire a stream of cold neutrons through a detector and count the protons produced when neutrons decay. In bottle experiments, ultracold neutrons are trapped inside a magnetic or material container and the survivors are counted after a set time. Both methods should yield the same answer if our physics is right — but they don't, and that discrepancy is genuinely puzzling to researchers.

The U.S. Department of Energy reports the beam method produces a world-average lifetime of about 887.7 seconds, while the bottle method gives approximately 878.5 seconds. That means beam experiments produce a longer measured lifetime, not a shorter one. The beam result exceeds the bottle result by roughly 9.2 seconds.

This is independently confirmed by science reporting that describes the gap as "nine seconds" — with beam on the longer side. The two sources agree within a fraction of a second, leaving no ambiguity about the direction.

The claim requires beam to come in more than one second below bottle. The actual difference is nearly ten seconds in the opposite direction. It is not a close call.

## What should you keep in mind?

The neutron lifetime puzzle is real: the two methods genuinely disagree by about nine seconds, and physicists don't fully understand why. Proposed explanations range from experimental systematic errors to exotic physics involving dark matter or new particles. So there is something genuinely strange here — just not what the claim describes.

The nine-second discrepancy has been stable for years. No beam experiment has ever measured a neutron lifetime below the bottle average. The most recent dedicated beam measurement dates to 2013; an updated experiment at NIST is underway but has not published a result that changes this picture.

One of the two sources used here is Quanta Magazine, a science journalism outlet rather than a primary research paper. However, the disproof rests entirely on the DOE source, which directly quotes both experimental values. The Quanta figure is corroborating, not foundational.

## How was this verified?

This narrative presents findings from a structured computational proof that extracted numerical values directly from source quotes, computed the beam-minus-bottle difference, and tested it against the claim's threshold. Full details of the methodology, sources, and computation traces are in [the structured proof report](proof.md) and [the full verification audit](proof_audit.md). If you want to reproduce the result yourself, you can [re-run the proof yourself](proof.py).