This firewall paradox theory seems to be only recently theorised.

As far as I can understand from reading about it on the internet, there should be a firewall on the event horizon of blackholes, which should break the quantum entanglement of particles.

Now I don't understand what is the paradox here, what does firewall stands for (no oxygen in space)? Which particles need to have their entanglement broken and how and why?

Please help me understand these without the use of intimidating mathematics, I understand the language of science shows like cosmos and how the universe works.


1 Answer 1


The word firewall does not involve a fire such as here on Earth, (no oxygen is required) rather it refers to a lot of energy being released. See the picture below,

There are three physics concepts involved here.

The first is based on the Equivalence Principle of General Relativity. Because an observer is in free fall as they cross the black hole's event horizon, the equivalence principle says that there is no detectable difference between free fall and inertial motion, the observer shouldn’t feel extreme effects of gravity. The equivalence principle is only applicable in small region, tidal effects can also occur.

The second concept is based around quantum mechanics, and is called Unitarity, which conjectures that information that falls into a black hole is not irretrievably lost.

Finally, there is the assumption that the physics far away from a black hole obeys the same laws as here on earth. The laws may fail near the event horizon, or if not there, at the singularity itself. Obviously, we have problems testing this, but it is generally regarded as an inevitable consequence if you describe the universe using GR.

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Joseph Polchinski has put forward the idea that the simplest solution is that the equivalence principle breaks down at the event horizon, thereby giving rise to a firewall.

If his theory is wrong, it may help to resolve the problems in reconciling GR and QM into a theory of Quantum Gravity, which still to be unequivocally formulated, and aspects of which have yet to be experimentally tested in any way.

Black holes are involved because they represent the meeting of GR and QM, as both theories can apply in those regions.

A large part of the firewall paradox argument is based around the notion of monogamous quantum entanglement: that is, you can only have one kind of entanglement at a time. Polchinski and others argue that two different kinds of entanglement are needed in order for all three postulates listed above to be true. Since the rules of quantum mechanics don’t allow you to have both entanglements, one of the three postulates must be sacrificed.

From Firewall Paradox Scientific American which you should read, as this short summary of the above article can't contain all the details.

Entanglement — which Albert Einstein ridiculed as “spooky action at a distance” — is a well-known feature of quantum mechanics. When subatomic particles collide, they can become invisibly connected, though they may be physically separated. Even at a distance, they are inextricably interlinked and act like a single object. So knowledge about one partner can instantly reveal knowledge about the other. The catch is that you can only have one entanglement at a time.

From Wikipedia Firewalls And Black Holes

According to quantum field theory in curved spacetime, a single emission of Hawking radiation involves two mutually entangled particles. The outgoing particle escapes and is emitted as a quantum of Hawking radiation; the infalling particle is swallowed by the black hole. Assume a black hole formed a finite time in the past and will fully evaporate away in some finite time in the future. Then, it will only emit a finite amount of information encoded within its Hawking radiation. Assume that at time T, more than half of the information had already been emitted. According to some theorists, an outgoing particle emitted at time T must be entangled with all the Hawking radiation the black hole has previously emitted. This creates a paradox: a principle called "monogamy of entanglement" requires that, like any quantum system, the outgoing particle cannot be fully entangled with two independent systems at the same time; yet here the outgoing particle appears to be entangled with both the infalling particle and, independently, with past Hawking radiation.

In order to resolve the paradox, physicists may eventually be forced to give up one of three time-tested theories: Einstein's equivalence principle, unitarity, or existing quantum field theory.


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