Humanity has long wondered whether other worlds have life intelligent enough to build advanced civilizations. The notion has not only inspired countless works of science fiction, but also dreams of space exploration beyond our solar system.

A study released last week by Oxford University’s Future of Humanity Institute examined the question and came to a depressing conclusion: It’s quite likely that humans are alone in the observable universe.

The study looked at the Fermi paradox – the apparent discrepancy between the seeming likelihood of alien life, given the billions of stars similar to our sun, and the scant evidence that such life actually exists. The paradox was named after physicist Enrico Fermi, who famously asked his colleagues at Los Alamos, N.M.. “Where Is Everyone?”

The study authors then examined various hypotheses and equations used to resolve the Fermi paradox. The results weren’t pretty:

Our main result is to show that proper treatment of scientific uncertainties dissolves the Fermi paradox by showing that it is not at all unlikely ex ante for us to be alone in the Milky Way, or in the observable universe.

Our second result is to show that, taking account of observational bounds on the prevalence of other civilizations, our updated probabilities suggest that there is a substantial probability that we are alone.

One of the authors, Oxford researcher Anders Sandberg, told the science news blog Universal-Sci that by some measures “one can have a situation where the mean number of civilizations in the galaxy might be fairly high--say a hundred--and yet the probability that we are alone in the galaxy is 30%!”

Given the conditions necessary to foster intelligent life, Sandberg said, he and his co-authors concluded there is a “fairly high likelihood” humans are alone.

Despite those conclusions, the study argued against despairing against finding intelligence in the universe. “Note that this conclusion does not mean that we are alone (in our galaxy or observable universe), just that this is very scientifically plausible and should not surprise us. It is a statement about our state of knowledge, rather than a new measurement.”

Nonetheless, Tesla CEO Elon Musk, one of the more ardent champions of space exploration, noticed the Universal-Sci story on Twitter this weekend and replied, “so strange.”

Musk, who is also CEO of space cargo company SpaceX, then cited the study’s conclusions as an “added impetus” for humanity to become a spacefaring civilization capable of extending life beyond Earth.