DO BLACK holes spit out particles that move faster than light and travel
backwards in time? Two physicists in New Jersey say that particles with these
bizarre properties could come to the rescue of a promising theory about what
happens in the heart of a black hole.
The world of very massive objects is ruled by general relativity theory,
while quantum mechanics governs the realm of very small scales. Black
holes鈥攅normous stars crushed into no space at all鈥攆all into both
categories, as they are both massive and tiny. Much to the chagrin of
physicists, general relativity and quantum mechanics appear incompatible, so
nobody is sure what equations hold true at the centre of a black hole.
But in the past few decades, a new set of theories has raised the hopes of
physicists struggling to understand the interior of these bodies. String
theories, for instance, portray black holes and particles as wiggling strings.
The disappearance of a particle into a black hole would simply be the result of
two different strings being spliced together.
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What鈥檚 even more exciting is that physicists are combining these theories
into one large 鈥淢-theory鈥�, which explains a lot about the interior of black
hole. But there is still a flaw: although black holes seem to devour everything
that comes their way, this cannot happen under the rules of M-theory. Just as
oil and water refuse to mix, so energetic particles cannot merge with black
holes, according to the theory.
鈥淚f you send a particle in towards the black hole, and it gets sufficiently
close, it needs some mechanism to be absorbed,鈥� says Daniel Kabat, a physicist
at the Institute for Advanced Study in Princeton, New Jersey. 鈥淥nce it gets too
close to the black hole, it becomes unstable.鈥� Without some way of getting rid
of that instability, the black hole would spit out the particle鈥攕omething
that doesn鈥檛 happen in nature.
But now Kabat and Princeton University鈥檚 Gilad Lifschytz believe they have
figured out how to keep M-theory intact, while at the same time explaining how a
black hole can keep down its lunch. The answer lies in tachyons. These are
particles with imaginary mass that can be thought of as travelling backwards in
time. They move faster than light, and slowing down to the speed of light would
be as impossible for them as it is for us to accelerate to light speed.
Physicists also use the term 鈥渢achyon鈥� for a whole family of instabilities that
quickly decay.
Though nobody has ever seen one, the researchers have shown that tachyons
might get rid of a particle鈥檚 excess energy, making it palatable to the black
hole. In an article due to appear in The Journal of High Energy Physics,
they suggest that particles spit out tachyons as they merge with a black hole.
鈥淭hese tachyons would be important for the dynamics inside the black hole, but I
don鈥檛 think an observer outside the black hole would be able to see them,鈥� says
Kabat.
If tachyons really do solve M-theory鈥檚 problem, physicists may at last have a
way to build up a coherent picture of what happens inside a black hole. 鈥淵ou鈥檙e
able to do precise calculations, and such calculations are hard to come by,鈥�
says Kabat. 鈥淚t鈥檚 a pretty compelling picture of a black hole.鈥�
鈥淭his paper is very interesting, and it鈥檚 potentially important,鈥� comments
Michael Douglas, a physicist at Rutgers University in New Brunswick, New Jersey.
鈥淚t poses a lot of ideas.鈥�