Cosmic mariners
“THERE’S NO SUCH THING AS A GRAVITATIONAL time machine!” belted out a voice across the hall. “You can’t just reverse gravity!”
One of us (NIL) was lecturing on work that we and our collaborators had been developing, in which we tried to answer two simple questions: How did the Milky Way form, and why does it look the way it does? Our approach was rooted in observations of what’s termed the local neighbourhood — the immediate (relatively speaking) vicinity of our galaxy, out to some 100 million light-years. But instead of using telescopes, we were building galaxies in computers and then running time forwards and backwards to see how their appearance changed.
The lecture was in Tallinn, Estonia, at a meeting dedicated to the 100th birthday of Yakov Zeldovich, a towering figure in 20th-century physics and astrophysics. Besides helping to develop the Katyusha rocket and being an instrumental player in the Soviet Union’s atomic bomb project, Zeldovich left an indelible mark on our understanding of the universe on its largest scales, including on how to map the cosmos. His school of thought produced some of the greatest luminaries in modern astrophysics, a number of whom are still active today, mostly spread across the Western world in a post-Soviet diaspora.
The voice berating our method came from Andrei Doroshkevich — a scion in the field who, now at more than
