Short answer — Nobody knows — and anyone who tells you otherwise has left the record. No engine, no wreckage, and no propulsion physics have ever been publicly documented.

What the reports describe — Objects with no visible engines, exhaust, or control surfaces; extreme acceleration and instant direction changes; and — in some official reports — movement against wind or between air and water.

What that would require — Accelerations described in Navy encounters imply forces far beyond what known aircraft or their crews could survive, and energy densities beyond any flight technology in the public record.

Status — Unexplained. The candidate explanations run from sensor artifacts and misperception to technology unknown — and the official reports decline to choose.

The ODNI's 2021 assessment put it in bureaucratic language that rewards a careful read: some UAP “appeared to remain stationary in winds aloft, move against the wind, maneuver abruptly, or move at considerable speed, without discernable means of propulsion.” The same paragraph adds the caveat this site always keeps attached: some of that may be sensor error, spoofing, or misperception.

The famous cases sharpen the question without answering it. The Nimitz aviators described a forty-foot object accelerating out of sight in roughly a second — under oath, in 2023, before Congress. Nothing in the public record of physics or aerospace engineering produces that performance with no visible means of doing it.

Everything beyond that — antigravity, exotic fusion, warped spacetime — is speculation, and we label it as such. The honest inventory is short: a documented performance gap, no documented machinery, and a file that stays open.

Sources

• ODNI, Preliminary Assessment: Unidentified Aerial Phenomena — June 25, 2021

• House Oversight hearing on UAP — sworn testimony, July 26, 2023

• DoD statement on the release of the Navy UAP videos — April 27, 2020