Universe

Physicists Propose Solution to Black Hole Information Paradox

January 4, 2016 | Joanne Kennell

kaleidoscope effect, abstract image of black hole surrounded by colour
Photo credit: geralt/Pixabay (CC0)

It involves quantum particles existing near a black hole’s event horizon.

It is believed that once something enters a black hole, whether it be light or information, it is trapped or lost forever — at least until the black hole evaporates as it shrinks in size.  While that currently may be true practically, it turns out it is not true theoretically.

Back in 1974, Stephen Hawking suggested that if a pair of quantum particles from a vacuum popped into existence near a black hole’s boundary (event horizon), one particle would fall into the black hole, while the other would fly into space — carrying energy away from the black hole, known as Hawking radiation.  The exit of radiation causes not only the black hole to slowly evaporate, it also contains encoded information from the black hole.

Physicists Aidan Chatwin-Davies, Adam Jermyn, and Sean Carroll of the California Institute of Technology in Pasadena have found a way to retrieve information from one of these quantum particles lost in a black hole, using Hawking radiation and a concept known as quantum teleportation.

Quantum teleportation states that, given two particles, one can transfer its quantum state, such as an electron, to the other.  However, this state cannot be measured or it will collapse, removing all information.  The information has to be sent intact, without any tampering.

To do this, these particles must also share a pair of electrons connected by quantum entanglement.  So what we have is a particle that wants to teleport its state and also has half of an entangled pair — now how the heck does this quantum teleportation work?

SEE ALSO: You’ve Heard of Black Holes, But What About White Holes?

By projecting two unentangled electrons onto the entangled pair — which breaks the entanglement between the two particles — the receiving particle’s electron will change state to reflect whatever state the donor electron was originally set to.  And voila!  It has been teleported.

It is definitely not a practical or even testable theory since it would require the donor particle to instantly measure the spin of a black hole.  It is also very complicated and has two major limitations.  First, it only works for one quantum particle, not for two or three.  Second, most of the questions scientists have about black holes is about their complicated internal workings, and this theory would not account for states of the mysterious interior of black holes.  

“Unfortunately, all of the big questions we have about black holes are precisely about these internal workings,” said Stefan Leichenauer, a theorist at the University of California, Berkeley.  “So, this protocol, though interesting in its own right, will probably not teach us much about the black hole information problem in general.”

Although this theory is only a hypothesis and has been met with skepticism, it may provide a starting point that helps researchers better understand black holes.  “It could be that the information is preserved in the state of the leftover Hawking radiation, albeit highly scrambled and difficult to distinguish from a thermal state,” explained lead researcher Aidan Chatwin-Davies at the Preposterous Universe blog.  “Under very modest and special circumstances, you can toss one qubit into a black hole and then recover its state, and hence the information that it carried.”

Either way, it is no doubt an exciting research opportunity.

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