I’ve been curious about how this limits us in the search for life. Suppose there is an extraterrestrial civilization on a planet near a star not far from us, and suppose there was a nuclear war there. Could we see it with our telescopes? Turns out that even with the most powerful of contemporary telescopes, we couldn’t see the flare.

However, there are ideas and techniques for detecting more subtle signatures — for example, radio signals.

YOU ONCE PUBLISHED A PAPER SUGGESTING THAT IF WE’RE SERIOUS ABOUT LOOKING FOR EXTRATERRESTRIAL LIFE, WE MIGHT SEEK OUT MARKERS OF INDUSTRIALIZATION, LIKE SMOG. SMOG?

Yes, smog might serve as a fingerprint of an industrial civilization. It’s always been thought that the way to detect life elsewhere was to look for signs of oxygen. But intelligent life could produce unnatural molecules. They might do that intentionally if their planet was too cold for life. Unnatural molecules might even show signs of a civilization that may not exist anymore because unnatural molecules can survive long after a civilization.

SOME OF YOUR WORK SOUNDS ALMOST LIKE SCIENCE FICTION. WHERE DO YOU DRAW THE LINE?

It’s not that. Nature has richness beyond our imagination. What I look for are interesting astrophysics questions that are provable. Though my research may ask unconventional questions, the answers are based on calculations, experiments and observations.

DID YOU ALWAYS WANT TO BE AN ASTROPHYSICIST?

At a young age, I was attracted to philosophy because it asked the most interesting questions. But then, at 18, I had to do my military service in Israel, where I grew up. After some testing, I was allowed to join a special program where you could work on projects useful for the defense of the country. I ended up doing research in plasma physics. And because of that, I was able to visit the United States in the 1980s.

During one of these trips, I visited the Institute for Advanced Study. A month later, I was offered the opportunity to do a postdoc there. There was one condition, though: I had to switch to astrophysics. That appealed because it was like returning to an old love — philosophy. In astrophysics, I could address very big questions about nature and life.