THE horizon of a black hole can either be smooth empty space or a blazing wall of fire. It all depends on your point of view.
The idea offers a potential resolution to a vexing paradox about whether black holes devour information.
In the 1970s, Stephen Hawking and Jacob Bekenstein showed that black holes emit radiation. Pairs of particles spontaneously form near the horizon 鈥� the point beyond which not even light can escape 鈥� and sometimes one falls into the black hole while the other flees, resulting in a slow stream of particles leaving the horizon.
Advertisement
This robs the black hole of mass and eventually it evaporates. But what happens to the information it contained? Quantum mechanics says that information cannot be destroyed, so physicists argued that it must come out in the so-called Hawking radiation.
In 2012, physicists realised this would lead to another problem: the black hole firewall paradox. If the radiation carries information, then any particle leaving must share a quantum connection called entanglement with its in-falling partner and all particles emitted earlier. Quantum mechanics doesn鈥檛 allow this: a particle can be fully entangled with only one other particle at a time. Breaking up the polygamous entanglement creates extreme energy at the horizon, forming a firewall 鈥� which is in turn forbidden by general relativity.
Now, of the University of Victoria in British Columbia, Canada, argue that you can see a firewall from near the horizon 鈥� but it鈥檚 caused by something completely different.
In order to stay put at a black hole鈥檚 horizon, you need to keep accelerating away from it. A phenomenon called the Unruh effect says that acceleration makes the empty space around you seem to heat up. Accelerating away from a solar mass black hole, this temperature can be as high as 1010 kelvin, says Israel.
鈥淵ou would feel as if you are engulfed in flames,鈥� he says. 鈥淭his is your personal firewall.鈥�
But to a distant observer, the Hawking radiation is of extremely low energy. Israel says this makes it impossible for the particles to be entangled in either case.
That means there is no threat to the monogamy of entanglement, says Israel. It also offers a partial solution to the information paradox: if you were to chuck matter at the black hole, it would be radiated back by your firewall. If no information enters the black hole, none is lost. Since the physics for nearby and distant observers should be the same, no information should be lost in either case, they say ().
of the University of California, Santa Barbara, says that standard quantum theory doesn鈥檛 support all of Israel鈥檚 claims. Instead, he thinks that quantum field theory may need tweaking to allow information to get out without creating firewalls. 鈥淲e have an indication that we need a new mechanism, a new ingredient to the story,鈥� he says.
This article appeared in print under the headline 鈥淏lack hole horizon is only fiery for you鈥�
