Op vrijdag 8 april 2016 10:01:20 UTC+2 schreef Steven Carlip:
On 4/7/16 4:13 AM, Nicolaas Vroom wrote:
Op zondag 3 april 2016 23:33:21 UTC+2 schreef Steven Carlip:

We believe that matter in a pure quantum state can collapse
to form a black hole.

This is in a certain sense equivalent that a star collapses and becomes
a neutron star

Not really. A collapsing star is very unlikely to be in a pure
quantum state.

The whole question becomes: what is a pure quantum state versus
a non-pure (mixed?) quantum state.
Does it physical make sense to talk about a pure quantum state
except under laboratory conditions?

Such a black hole will then evaporate
by Hawking radiation, which is thermal.

This is in a certain sense equivalent that a star explodes and
becomes a super novae.

No. Here things are very different, because a black hole has an
event horizon.

Think of the first photon coming out of a supernova. etc

A black hole is different. The first photon of Hawking
radiation etc

IMO (here I have to be very carefull) the concept of correlation
is very difficult, because you have to define what you mean
in this specific context and how it is measured.

IMO the issue is much the type of particles or energy range of
photons that can be emitted from any object.
This diversity is a function of the processes that happen inside
an object.
How larger this diversity how more information is available.
How smaller this diversity it is the opposite.

The issue is if in either of these cases you can speak about
information loss?

In the first case, there's "coarse grained" information loss --
it's *hard* to recreate the state of the star by looking at the
correlations among the photons that come out. But it's not
impossible. In the second case, the conventional picture of
Hawking radiation implies that there is no correlation among
the photons, so the information is genuinely completely lost.

I agree with the conclusion but not with your reasoning.

To answer the questions you must have a clear definition of what
information means and what a pure and mixed quantum states are.

Yes, but this is standard quantum mechanics.
I agree for laboratory conditions.
The concepts are very tricky in reality, related to actual objects
in space.

My interpretation of a mixed state is that it has a structure.
For example in the Sun and in planets when you "travel" towards
the center the density changes.

This is also not what the term means. There's a nice explanation
in the Wikipedia page under "Density matrix." If you want to
talk about the black hole information paradox, you need to use
the correct definitions.

I fully agree with you.
The practical problem is what is the density matrix of a BH?
of a star, a sun, a planet

The issue is here how do we know that BH physical can evaporate and
change into a gaseous (visible?) state.

"Evaporation" here has nothing to do with "gaseous" -- it just means
that the mass of black hole is converted completely to Hawking
radiation.

How do we know this happens? By doing a computation in quantum
field theory to predict the evolution of a black hole. Now, the
answer to the paradox may be that we're doing the computation
wrong, but that's not a real answer unless you can say exactly
*where* the computation is going bad.

The real answer should be to make a prediction about the evolution
of an object (BH) which we should be able to verify
The problem is that that is very difficult for a BH.
For example it is impossible(?) to demonstrate that a BH has
evolved from something into "nothing" i.e. Hawking radiation
In practice this means that it is very difficult to claim that
the computation is right or wrong.

The problem only
appears quantum mechanically, when you allow black holes
to evaporate thermally via Hawking radiation.

The problem is much more a physical, chemical problem.

No, it's not. You are free to invent a different problem, but
that's not the one that's called the black hole information
paradox.

The evolution of a BH is a physical issue.
I do not see in principle any problem that a BH completely
evaporates. The problem starts, when it is possible to verify
such a process (sequence of events) that this should not be in
conflict with other laws.

Nicolaas Vroom