Throughout the universe, things spin around. Planets rotate on their axes and orbit around stars. Entire galaxies spin. It’s such a common feature of everything that we tend not to think much about it. But it can lead to significant findings in science – for example, the peculiar way in which galaxies rotate is suggested to be the best evidence so far for the existence of dark matter.
In Rotation in Space, a 2012 Gresham College lecture, Professor Carolin Crawford tackled the question of why rotation is so ubiquitous. She explained what we can learn from the processes behind it, and from the outcome seen in objects such as neutron stars where massive gravitational collapse can, through conservation of angular momentum, produce spin rates of over 700 times per second. And this leads to the conclusion that more massive stars could collapse even beyond the point where neutron stars would form, creating black holes which themselves would spin.
In his 1977 book The Iron Sun: Crossing the Universe Through Black Holes, Adrian Berry, the long term science correspondent for the Daily Telegraph and Fellow of the BIS, provided an imaginative account of how black holes might provide a route for interstellar travel. A key development was the solution to Einstein’s field equations – the equations that describe gravitation as a result of spacetime being curved according to the general theory of relativity – as provided by mathematician Roy Kerr in 1963. This solution led to a model of the gravitational field outside a rotating black hole.
The Kerr solution gave rise to the possibility of Einstein-Rosen bridges connecting one part of the universe to another through systems linking black holes to distant “white holes”. These might “be regarded as the actual navigable gateways through which spaceships in future centuries will be able to make instantaneous journeys to other parts of the Galaxy.” And astronomical observations since then have suggested that there is evidence for the actual existence of rotating Kerr black holes.
Using such wormholes in this way has been a regular feature of science fiction. The 1979 film The Black Hole uses the idea to suggest a means of performing a journey which is largely unintentional through some highly surreal landscapes. On the other hand, the Star Trek spin-off series Deep Space Nine in the 1990s takes place around a space station which is strategically located near the entrance to an Einstein-Rosen bridge connecting remote areas within the Galaxy, and which could provide a convenient route for invading aliens.
So strange things might happen around a rotating object in space. But what if the whole universe itself was rotating? (One might wonder what would be the medium in which the universe was rotating, and hence what the rotation could be measured against, but that’s a different question.)
In 1949, the mathematician Kurt Gödel provided an unexpected solution to Einstein’s field equations such that closed timelike curves would permit time travel in certain universes – provided they were spinning rather than expanding. Our own universe, as we know, is not one of them. In his 2005 book The Infinite Book: A Short Guide to the Boundless, Timeless and Endless, John Barrow commented on the speculation “that Gödel found time travel an appealing feature of a universe because of his paranoid fears about death. He saw a means by which it might be possible for him to live on in some strange way.”
But that’s all part of the speculation from observing rotating things. It prompts imagination, much like Alan Bergman and Marilyn Bergman’s famous song The Windmills of Your Mind: “Round like a circle in a spiral, like a wheel within a wheel/Never ending or beginning on an ever-spinning reel…”
Richard Hayes, Assistant Editor (Odyssey)