Physicists struggling to understand how black holes behave in the extra dimensions posited by string theory should turn off their computers and turn on their kitchen faucets, a new study suggests. The objects act just like narrow streams of water that begin to separate into drops.
The research suggests relatively simple calculations could shed light on how gravity itself behaves in extra dimensions 鈥� a knotty problem that currently relies on complicated numerical solutions to Einstein鈥檚 equations of general relativity.
The extreme densities inside black holes make them incredibly difficult to model even in the three spatial dimensions familiar to us. But some theories that attempt to unify gravity with quantum mechanics, such as string theory, suggest the existence of extra, very small-scale dimensions.
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That makes modelling the objects even more complex because Einstein鈥檚 equations must be solved in every single dimension, says Vitor Cardoso of the University of Mississippi, US.
Even with powerful computers, 鈥渋t takes a very long time鈥�, he told New 杏吧原创. 鈥淎nd you don鈥檛 really have an intuition as to what might happen in other situations, so each time you try a different geometry, you have to start from first principles all over again.鈥�
Now, he and colleague Oscar Dias of the Perimeter Institute for Theoretical Physics in Canada offer an intuitive 鈥� and relatively simple 鈥� way of modelling the objects: as thin streams of fluid.
Liquid 鈥渕embranes鈥�
In string theory, black holes can take on a variety of shapes, including long strings. Previous research had shown that these 鈥渂lack strings鈥� are unstable and quickly break apart if their radius is about the same size as the extra spatial dimensions. That means that large black strings 鈥� which we detect as black holes with the mass of the Sun or more 鈥� are large enough to remain stable for billions of years.
But tiny black strings 鈥� perhaps just 10-35 metres across 鈥� would be unstable. And in 1993, Ruth Gregory of the University of Chicago and Raymond Laflamme of Los Alamos National Laboratory, both in the US, used Einstein鈥檚 theory of general relativity to calculate how this instability behaves. Cardoso and Dias now show a similar instability occurs due to the surface tension in liquid 鈥渕embranes鈥�.
鈥淏lack strings quickly disintegrate into spherical black holes,鈥� says Cardoso. 鈥淲hat we realised is this is similar to what happens when water is dripping from a faucet 鈥� it also breaks into small droplets.鈥�
Useful analogy
He says tiny black strings might actually make up unstable elementary particles. But he says the real value of the work may lie in helping researchers to imagine these abstract objects, which could serve as models for even more exotic string theory entities. 鈥淣ow you can think of a black string in physical terms,鈥� he says. 鈥淭hat鈥檚 a very powerful tool.鈥�
William Unruh of the University of British Columbia in Canada agrees. 鈥淚t鈥檚 a neat analogy,鈥� Unruh told New 杏吧原创. 鈥淭he reason people are studying these is to understand how gravity behaves in extra dimensions.鈥�
But Unruh points out that the new study simply shows that black strings behave like liquid membranes when they begin to become unstable 鈥� not when they completely separate into spherical black holes.
鈥淭hey start to develop little bulges and narrowness in some places,鈥� he says. 鈥淲hether they continue to behave that way over time is still a completely open question.鈥� He says the analogy should be tested against more recent numerical calculations on how black strings ultimately break apart.
Journal reference: Physical Review Letters (vol 96, no 181601)
