## Posts Tagged ‘**EPR paradox**’

## Wormhole entanglement solves black hole paradox

by **Jacob Aron**

WORMHOLES – tunnels through space-time that connect black holes – may be a consequence of the bizarre quantum property called entanglement. The redefinition would resolve a pressing paradox that you might be burned instead of crushed, should you fall into a black hole.

Knowing which hazard sign to erect outside a black hole isn’t exactly an everyday problem. For theoretical physicists, though, it reveals an inconsistency between quantum mechanics and general relativity. Solving this conundrum might lead to the sought-after quantum theory of gravity.

Relativity says if you fall into a black hole, you would die via “spaghettification” – a gradual stretching by ever-more intense gravitational forces. But last year, when Joseph Polchinski at the University of California in Santa Barbara and colleagues explored the quantum implications of black holes, they hit a problem. Black holes emit photons via something called Hawking radiation, and these are “entangled” with the interior of the black hole and also with each other. This breaks a quantum rule that particles can’t be entangled with two things at once.

To preserve quantum monogamy, Polchinski suggested last year that the black hole-photon entanglement breaks down. That causes a wall of energy at the black hole’s event horizon that wrecks relativity because anyone falling in would burn up rather turn to spaghetti. Welcome to the black hole firewall paradox.

Possible solutions abound but now two physics heavyweights, Juan Maldacena of the Institute for Advance Study in Princeton, and Leonard Susskind of Stanford University, California, have come up with the most audacious one yet: a new kind of wormhole that means the entanglement needn’t be broken in the first place.

First, the pair showed that these space-time tunnels, usually described by the maths of general relativity, also emerge from quantum theory, if two black holes are entangled. It’s as if the wormhole is the physical manifestation of entanglement.

The pair then extended this idea to a single black hole and its Hawking radiation, resulting in a new kind of wormhole (see diagram). Crucially, they suggest that this wormhole, which links a black hole and its Hawking radiation, may not be a problem for quantum monogamy in the way that normal entanglement is. As a result, the firewall needn’t appear, preserving relativity (arxiv.org/abs/1306.0533).

Patrick Hayden of McGill University in Montreal, Canada, finds the idea of wormholes from entangled black hole pairs convincing, but says more work is needed for the case of the black hole and a photon. Polchinski, meanwhile, is cautiously optimistic: “It certainly injects new ideas. But there is a lot that still needs to be filled in.”

There is still room for firewalls in the new wormhole definition. Maldacena and Susskind also outline how an observer outside the black hole could manipulate the Hawking radiation, creating a shock wave that travels down the wormhole and appears as a firewall. This may not screw up relativity because the firewall is optional, not intrinsic to the black hole. Maldacena hopes mulling these options will teach us about quantum gravity.

Read more at http://www.newscientist.com/article/mg21829224.200-wormhole-entanglement-solves-black-hole-paradox.html#.UcVGjjt7Lbw

## Cool horizons for entangled black holes

**Juan Maldacena, Leonard Susskind**

General relativity contains solutions in which two distant black holes are connected through the interior via a wormhole, or Einstein-Rosen bridge. These solutions can be interpreted as maximally entangled states of two black holes that form a complex EPR pair. We suggest that similar bridges might be present for more general entangled states.

In the case of entangled black holes one can formulate versions of the AMPS(S) paradoxes and resolve them. This suggests possible resolutions of the firewall paradoxes for more general situations.

Read more: http://arxiv.org/pdf/1306.0533v1.pdf

## EPR before EPR: a 1930 Einstein-Bohr thought experiment revisited

## Einstein’s “Spooky Action At a Distance” Paradox Older Than Thought

**Einstein’s famous critique of quantum mechanics first emerged in 1930, five years earlier than thought, according to a new analysis of his work
**

Einstein’s phrase “spooky action at a distance” has become synonymous with one of the most famous episodes in the history of physics–his battle with Bohr in the 1930s over the completeness of quantum mechanics.

Einstein’s weapons in this battle were thought experiments that he designed to highlight what he believed were the inadequacies of the new theory.

The most famous of these is the so-called EPR paradox, after its inventors Einstein himself, Boris Podolsky and Nathan Rosen, which they announced in 1935.

It involves a pair of particles linked by the strange quantum property of entanglement (a word coined much later). Entanglement occurs when two particles are so deeply linked that they share the same existence. In the language of quantum mechanics, they are described by the same mathematical relation known as a wavefunction.

Entanglement arises naturally when two particles are created at the same point and instant in space, for example.

Entangled particles can become widely separated in space. But even so, the mathematics implies that a measurement on one immediately influences the other, regardless of the distance between them.

Einstein and co pointed out that according to special relativity, this was impossible and therefore, quantum mechanics must be wrong, or at least incomplete. Einstein famously called it spooky action at a distance.

The EPR paradox stumped Bohr and was not resolved until 1964, long after Einstein’s death. The CERN physicist John Bell, resolved it by thinking of entanglement as an an entirely new kind of phenomenon, which he termed ‘nonlocal’.

The basic idea here is to think about the transfer of information. Entanglement allows one particle to instantaneously influence another but not in a way that allows classical information to travel faster than light. This resolved the paradox with special relativity but left much of the mystery intact. These days, the curious nature of entanglement is the subject of intense focus in labs around the world.

But that doesn’t tell the full story, says Hrvoje Nikoli at the Rudjer Boskovic Institute in Croatia. Today, he reveals that although history first records this paradox in 1935, Einstein unknowingly stumbled across it much earlier in 1930.

At this time, he was working on another paradox which he presented at the 6th Solvay Conference in Brussels in 1930. This problem focused on the Heisenberg uncertainty relation between energy and time which states that you cannot measure both with high accuracy.

To challenge this, Einstein came up with the following thought experiment. Imagine a box that can be opened and closed quickly and which contains an ensemble of photons. When open, the box emits a single photon.

The time of emission can be measured with arbitrary precision–its just the length of time for which the box was open. According to quantum mechanics, this limits the resolution with which you can measure the photon’s energy.

But Einstein pointed out that this too can be measured with arbitrary precision, not by measuring the photon but by measuring the change of energy of the box when the photon is emitted, which must be equal to the energy of the photon. Therefore, quantum mechanics is inconsistent, he said.

Einstein’s great rival, Bohr, puzzled long and hard over this but eventually came up with the following argument. He said that Einstein’s own theory of general relativity provided the answer.

Since the measurement of time takes place in a gravitational field, the lapse in time during which the box is open must also depend on the box’s position.

The uncertainty in position is an additional factor that Einstein had not taken into account and this, according to Bohr, resolved the paradox. Einstein was sent packing.

Of course, this not a very satisfactory answer to the modern eye. It implies, for one thing, that quantum mechanics requires general relativity to be consistent, an idea that modern physicists would roundly reject.

Nikoli says this problem has never been satisfactorily analysed from a modern perspective. Until now.

He says the proper resolution is to think of the total energy of the system, which is the energy of the box and the energy of the photon. The total energy is constant and governed by a single mathematical entity, even after the photon is emitted.

So the box and the photon must be entangled.

This immediately raises the problem that Einstein later hit on in the EPR paradox. A measurement on the box immediately influences the photon and vice versa–spooky action at a distance.

For this reason, the photon paradox is equivalent to the EPR paradox, says Nikoli. Had Einstein noticed it, he could have stopped Bohr in his tracks.

That’s an interesting historical footnote. Bohr’s triumph over Einstein on this occasion is widely thought to have been his greatest.

But now it’s easy to see that things could have been significantly different if Einstein had reformulated his his argument in terms of entanglement.

Thus is how history is forged!

Ref: arxiv.org/abs/1203.1139: EPR Before EPR: A 1930 Einstein-Bohr Thought Experiment Revisited

Read more: technologyreview.com

## Einstein Podolsky Rosen Paradox Resolved By Local Modal Realism

The Many Worlds Wiener Sausage is a very simple model that shows how the apparent non-locality in the infamous Einstein-Podolsky-Rosen paradox can arise simply by the world splitting into parallel universes. It can be understood by advanced high school students. But we saw that although it is a *many worlds*model, it is not a quantum world! Today we will make the model look like the great spaghetti monster. There are two aspects about this that I find amazing:

1) It can still be understood by high school students but is nevertheless correct quantum mechanics – not some cracked pot’s hidden variables nonsense.

2) It is one single and natural step that turns the model quantum, and this step has two important features:

– The step is obviously a *local* modification at one certain place of a classical and thus fundamentally *local* model, therefore the quantum model also still obeys Einstein locality! Since quantum physics cannot be both local and real, the “real” must have been modified. And it has.

– The crucial step obviously turns something that still can be described as a naïve direct realism into something that can no longer be so described, and again, not via philosophical sophistry or advanced math that rests more on authority than on what lay people can understand: After the crucial modification, a little arrow called “**DirectlyReal**”, short “**DR**”, is no longer able to point to the one real world it pointed to before….

Read more: http://www.science20.com