Ask an Expert: What are the odds that aliens exist?

ALBANY, N.Y (April 7, 2026) — Physics Professor Kevin Knuth, whose research explores how scientists can better understand unidentified aerial phenomena (UAPs), answers today’s question: What are the odds that aliens exist? 

Knuth: This is a rather nuanced question. 

What might one consider to be alien? Does one mean an intelligent species, like us, or would microbes count? Could they live anywhere in the galaxy, or does one want to know if they could communicate with, or visit, Earth? 

One of the big problems is that we do not really have a good definition for life, and hence cannot always recognize it or differentiate it from things we consider not alive, like viruses. 

The more alien a life form is, the harder it may be to recognize as alive. If lifeforms were made of plasma, for example, there could be life on the surface of the Sun, and we might never recognize it! Because of this uncertainty, the question cannot be conclusively answered, so we usually limit ourselves to “life as we know it.”

Life as we know it depends on liquid water. For this reason, we focus on planets in the “habitable zone,” where temperatures allow liquid water to exist on the surface. Since roughly one out of five stars may host such a planet, and our galaxy contains about 300 billion stars, there could be around 60 billion planets capable of supporting water-dependent life. The Drake Equation attempts to quantify how many intelligent civilizations might exist by estimating the likelihood of life evolving. Its results vary widely.

Finally, one might ask whether we have detected an alien civilization or evidence that they have visited Earth. To date, there is no evidence either way. The Search for Extraterrestrial Intelligence project has yet to find radio signals. Some UFOs, now known as unidentified anomalous phenomena (UAP), have been studied by UAlbany Project X and others, but there is still no conclusive evidence that any UAP are alien in origin. 

If we ever obtain evidence that Earth has been visited by extraterrestrials, simulations suggest this would imply roughly one million space-faring civilizations in the galaxy, about 250,000 of which could achieve interstellar travel.