Sean Carroll in his inaugural column at Discover:
Theoretical cosmologist isn’t one of the more hazardous occupations of the modern world. The big risks include jet lag, caffeine overdose, and possibly carpal tunnel syndrome. It wasn’t always so. On February 17, 1600, Giordano Bruno, a mathematician and Dominican friar, was stripped naked and driven through the streets of Rome. Then he was tied to a stake in the Campo de’ Fiori and burned to death. The records of Bruno’s long prosecution by the Inquisition have been lost, but one of his major heresies was cosmological. He advocated that other stars were like our sun, and that they could each support planets teeming with life. Orthodox thought of the time preferred to think that Earth and humanity were unique.
These days, cosmologists like me may be safer, but our ideas have grown only more radical. One of the most controversial but widely discussed concepts in the field resembles a hugely amplified version of Bruno’s cosmology: the idea that the thing we call “the universe” is just one of an infinite number of regions in a much larger universe of universes, or multiverse. A big focus of my own research asks whether a multiverse can help explain the arrow of time.
Also like Bruno, cosmologists are reaching far beyond what observational evidence can tell them. At the time of Bruno’s death, Galileo had not yet turned the very first telescope upward to the stars. Today, nobody has looked beyond the boundaries of the known universe. In fact, such a far-reaching vision seems impossible by definition.