快猫短视频

THREE years ago we discovered that the Universe is expanding at a faster and
faster rate. Now physicists say this might mean the Universe is littered with
invisible 鈥渁nti black holes鈥� that repel any matter that comes close.

The accelerating expansion of the Universe has been very difficult to
explain. Many theorists think its ballooning size is caused by an exotic
material called 鈥渜uintessence鈥�, a form of vacuum energy that pervades all of
space and exerts a negative, outwards pressure
(快猫短视频, 3 April 1999, p 28).
This is similar to the vacuum energy thought to have driven 鈥渋nflation鈥�,
the rapid expansion of the Universe just after the big bang.

But according to David Santiago of Stanford University in California, if
quintessence exists it might be 鈥渃lumpy鈥� on small scales, just like normal
matter. Although the Universe looks fairly smooth on large scales, planets,
stars and galaxies make it patchy on small scales. 鈥淚t鈥檚 certainly plausible
that quintessence has the same fingerprint,鈥� says Santiago.

Arthur Chernin of Moscow University and Oulu University in Finland, along
with Santiago and his Stanford colleague Alexander Silbergleit, decided to solve
the equations behind general relativity, Einstein鈥檚 theory of gravity, assuming
that clumpy quintessence exists. The results suggest the Universe might contain
a new class of object鈥攁nti black holes that repel matter rather than
sucking it in.

Like black holes, they would be 鈥渟ingularities鈥� exerting an infinite force on
matter. The force of the singularity鈥檚 antigravity would grow as you got closer,
becoming infinitely strong at its centre. So nothing could get too close. 鈥淪ome
of its properties are quite weird,鈥� says Santiago. 鈥淚f such an object exists, it
will be protected by this `force shield鈥� and the singularity will be
耻苍谤别补肠丑补产濒别.鈥�

Anti black holes鈥攊n common with normal black
holes鈥攚ould be invisible, but they might be detectable because their
gravity would make nearby matter and light move in unexpected ways. However,
Santiago says that they may never have formed in the first place because their
own antigravity might prevent them clumping together. 鈥淭hese objects very
probably are unstable,鈥� he says. 鈥淚t might depend on how strong their
antigravity is.鈥�

The team, which has submitted its results to Physics Letters A, is
now trying to work out whether or not the anti black holes can form. If they
can, they might be just one of a range of related exotic objects, including
stars and galaxies, made of quintessence. 鈥淥ne can let the imagination run wild
and imagine all sorts of interesting non-standard scenarios,鈥� says Santiago.

He admits, however, that these oddities might turn out to be
nothing more than a mathematical curiositiy. 鈥淥f all our results, this is
probably the most likely to be just of academic interest,鈥� he says. 鈥淚n order to
be more definitive about their importance, we have some homework to
do鈥攚e鈥檙e working on it.鈥�