Despite the obvious caveats, physicists are right to use fluids and other physical analogues to search for fresh insights about extreme cosmic phenomena, from black holes to the big bang.
ANALOGIES have always been helpful in our attempts to make sense of an enigmatic universe. Perhaps the best-known example is space-time, which is often likened to a malleable sheet underlying everything. Massive things like planets depress the sheet, such that less massive things – people, asteroids and so on – tend to fall inwards. It isn’t a perfect analogy, of course, but it allows those of us who can’t read the equations of general relativity to grasp the nature of reality.
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In recent years, researchers have been using fluids and collections of cold atoms as space-time equivalents. These aren’t just verbal analogies. They are physical imitations, or “analogues”, that purport to exhibit space-time phenomena in ways you can see and touch. Some of these phenomena – such as black holes and cosmic inflation, thought to have driven the exponential expansion of the universe after the big bang – have never been detected directly astronomically.
As we explore in our feature “Can recreating black holes in the lab solve the puzzles of space-time?”, the idea is that analogues can help us to better understand the behaviour of extreme objects or events we can never hope to directly observe. The question is, if you confirm a prediction in a laboratory analogue, are you also confirming it for the system the analogue is supposed to represent?
Many physicists think not. After all, an analogue black hole might consist of a few waves in a water tank, whereas a real black hole would rip you apart. They simply aren’t the same thing, and you can’t glean insights from one about the other.
What this view ignores is the surprising similarities between analogues and the real things they represent. At the very least, then, testing the strength of the relationship between analogue and real space-time could clarify how we think about hypothetical phenomena.
But some physicists believe that space-time has more in common with everyday stuff than we tend to assume. If so, the implications for our understanding of the cosmos could be vast – and the study of analogue cosmology entirely justified.
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