Let me be clear about my priors. I do not know what UAPs are. Nobody does. That is the honest starting point. Not "they are alien spacecraft." Not "they are all weather balloons." I do not know, and neither do you, and neither does the Pentagon.

Now let me tell you what the physics says.

What "Unexplained" Means

The U.S. government has acknowledged that military pilots have observed objects that exhibit flight characteristics beyond known technology. The 2021 DNI report documented 144 incidents. The subsequent reports have added hundreds more. In most cases, the objects could not be identified.

"Could not be identified" is not the same as "alien." It means: given the available sensor data, we cannot determine what the object is. That could mean alien spacecraft. It could also mean sensor artifact, atmospheric phenomenon, classified military technology (ours or someone else's), or insufficient data to draw any conclusion.

The physics question is: do the reported flight characteristics violate known physics? If they do, that is genuinely interesting. If they do not, then the objects are unusual but not impossible.

The Reported Characteristics

The most commonly reported extraordinary characteristics are:

Instantaneous acceleration. Objects that appear to change velocity from stationary to thousands of miles per hour in fractions of a second. If real, this would require forces that would destroy any known material and kill any biological occupant.

Transmedium travel. Objects that move from air to water (or vice versa) without slowing down. The physics of fluid dynamics makes this extremely difficult. Air and water have very different densities. An object optimized for one medium is poorly suited for the other.

No visible propulsion. No exhaust, no wings, no rotor, no jet. Objects that appear to fly without any mechanism for generating thrust or lift.

What the Physics Says

On instantaneous acceleration: If an object truly accelerates at 1,000 g's (the reported range), the inertial forces on any physical structure would be enormous. Most materials fail above 100 g's. Biological organisms fail above about 10 g's sustained. So either: (a) the object has no mass (light, plasma, hologram), (b) the object has a propulsion system that cancels inertia (no known physics does this, but general relativity permits spacetime distortion in principle), or (c) the acceleration measurement is wrong.

Option (c) is the most likely in most cases. Radar and infrared sensors can produce spurious acceleration readings from multipath reflections, sensor glitches, and parallax effects. A small object close to the sensor can appear to move like a large object far away. Without independent multi-sensor confirmation, apparent acceleration is not confirmed acceleration.

On transmedium travel: This is physically possible but extremely constrained. A torpedo is transmedium. A diving bird is transmedium. But they slow down at the interface. An object that does not slow down would need to manage the enormous drag change, which requires either very high energy or very low cross-section. Not impossible. But extraordinary.

On no visible propulsion: Many real technologies have no visible propulsion to the naked eye. Gliders have no engine. Balloons have no wings. Drones can be quiet enough to be inaudible from a distance. "I do not see propulsion" is not the same as "there is no propulsion." It means the propulsion is not visible to you with your sensors at your distance.

The Fermi Question

Carl would ask: if these are alien spacecraft, where are they from? The nearest star is 4.2 light-years away. At the speed of light (which requires infinite energy for any massive object), the trip takes 4.2 years. At 10% of the speed of light (technically possible but far beyond current engineering), it takes 42 years. At 1% of the speed of light (a more plausible interstellar speed), it takes 420 years.

Interstellar travel is not forbidden by physics. It is permitted but extraordinarily expensive in energy. A spacecraft traveling at 10% of the speed of light has a kinetic energy comparable to a large nuclear weapon. For every kilogram of payload.

So: aliens visiting Earth is physically possible. But it requires a civilization so far beyond ours technologically that the question becomes: why would they bother? And why would they be detectable? A civilization capable of interstellar travel would presumably be capable of stealth far beyond our ability to penetrate.

Where the Honest Line Is

The honest line is here: there are observations that we cannot currently explain. Some of the sensor data, if taken at face value, describes physics we do not understand. But sensor data taken at face value is often wrong. The history of science is full of anomalous observations that turned out to be instrument errors, atmospheric effects, or misinterpretations.

Extraordinary claims require extraordinary evidence. We do not have extraordinary evidence. We have interesting evidence that has not been adequately explained. Those are different things.

My position: keep looking. Collect better data. Deploy dedicated sensors designed specifically to characterize these objects. Do the science. Do not assume the answer before you have the data. And do not dismiss the question because the possible answers make you uncomfortable.

The universe is under no obligation to be boring. But it is also under no obligation to confirm our hopes. The physicist looks at the data. The data says: unexplained. Not alien. Not mundane. Unexplained. And unexplained is the most honest word in science.