
A new Stephen Hawking presentation about black holes - ColinCochrane
http://www.washingtonpost.com/news/speaking-of-science/wp/2015/08/25/stephen-hawking-believes-hes-solved-a-huge-mystery-about-black-holes/?tid=sm_tw
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BjoernKW
I don't understand what's new about these theories. Both the holographic
principle and Hawking radiation have been known for years, decades even. If
there's something about those theories the article doesn't explain what it is
exactly.

~~~
keehun
"Nobel laureate Gerard t'Hooft, who was present for the discussion, has been
thinking about information loss in a similar way, and he cited several papers
he has published on the subject. It will take more discussion — and much
comparing of math equations — to establish what's new about Hawking's theories
in relation to t'Hooft's, and whether Hawking has overcome some of the issues
associated with earlier iterations of the idea."

~~~
nilkn
So is Hawking even claiming it's new or was he simply discussing the existing
theory but the article misconstrued that?

~~~
espadrine
As I understand it, he is redefining what is called the event horizon, because
it is a relativistic concept that doesn't work well with quantum mechanics.

One consequence of that redefinition is that humans could theoretically
survive crossing it, contrary to the firewall hypothesis (well, if they were
in a sustainable capsule with a large gene pool, and the hole was rotating
just right), by waiting long enough on top of it until the hole evaporates
(from the capsule's point of view).

Time would indefinitely slow down for them, so they would see the rest of the
universe speed up until the hole dies.

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aquadrop
I don't know if there's something new in there, but Leonard Susskind wrote a
book in 2008 exactly on that matter - "The Black Hole War" [0]. He describes
his "battle" with Hawking on whether the information is lost in the black
hole, and Susskind is the one who's against information disappearing.

[0]
[https://en.wikipedia.org/wiki/The_Black_Hole_War](https://en.wikipedia.org/wiki/The_Black_Hole_War)

~~~
mudil
I loved that book. One of the best books on cosmology/space-time/quantum-
general relativity. Susskind's thought experiments are mind boggling, and he
is a great writer, able to explain complicated physics in a clear and
thoughtful manner.

~~~
developer1
Is this a book that someone with no background in the sciences involved can
enjoy? Is it for the layman, or requires some knowledge of the facts involved
to appreciate enough to read?

~~~
aquadrop
It's written in pretty easy way, you just must be interested in this stuff,
then you'll enjoy it :)

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dysoco
Wait, hasn't this holographic theory been arround for years? What's new?

~~~
xlm1717
"It will take more discussion — and much comparing of math equations — to
establish what's new..."

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eykanal
I don't know a thing about black holes, but every time I see him I'm impressed
that someone with such severe disabilities is still able to accomplish so
much.

~~~
laumars
Not that I want to take anything away from his impressive achievements, but it
would only be fair to point out that he doesn't work solo on these theories.
Much of the maths is done by his team.

I can't even imagine how frustrating his condition must be for him though. To
have full mental capabilities but have so little (and slow!!) means of
communicating his ideas.

~~~
gizmo686
Beyond being slow at communicating his idea, he is also largely limited to his
working memory. I can't imagine doing any sort of serious intellectual work
without the assistance of paper (or similar technology) to augment my working
memory.

~~~
laumars
In fairness that is something you can get better at with practice.

In IT we tend to train our brains to commit processes (eg ways to research
information) rather than facts. But we also have the luxury of being able to
be lazy (internet, functioning limbs so can write notes, etc). Heck, before
IDEs and the internet I used to remember every function name and order of
parameters for any particular programming languages I was proficient in. These
days I just learn the function name and let the IDE remind me of the rest
(sometimes I don't even learn the function name and just search for it in the
package namespace).

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dasil003
And in our defense, I think this is the only sane way to go about programming
given that all the APIs and tools we use are just unfathomably deep layers of
human constructs. There's no real point in remembering so much detritus. It
naturally benefits from a completely different mindset to the problem of
studying the deepest mysteries of the universe.

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haberman
Does physics have some "conservation of information" laws that I missed the
memo about? Can anyone recommend some introductory reading about this?

~~~
danbruc
The laws of physics conserve information in that sense that two initially
distinct states will always remain, at least in principle, distinguishable for
all times, i.e. two distinguishable states A and B will never evolve into the
same state C. This is equivalent to the statement that the laws of physics are
time reversible, i.e. if you would end up in state C you could not tell
whether the system came from state A or B.

If you, for example, start a pendulum with different initial displacements the
pendulum will always end up at rest due to friction but if you could take into
account the exact states of all the molecules in the air and the joint and so
on you could in principle figure out in which exact positions you started the
pendulum.

You could actually just very precisely measure the temperature of a pendulum
in a box and infer the initial displacement from that because different
initial displacements imply different initial (potential) energies and
therefore different final temperatures after all the energy became thermal
energy and everything in the box had time to reach the equilibrium
temperature. You just couldn't figure out whether the pendulum was started to
the left or to the right of the rest position with this method.

~~~
haberman
Fascinating. Do physicists generally believe this? The idea that both the
infinite future and the infinite past are all encoded into any snapshot of the
universe is blowing my mind.

My layperson's understanding of QM always gave me the impression that it does
the opposite: that it gives non-determinism a place to "hide," so-to-speak. My
impression was that religious believers could use QM to argue that their
unseen God, for example, does actually have a physically plausible mechanism
by which he/it could intervene in the physical world. But if I'm understanding
this theory correctly, unless God is a physical thing, there is no way for God
or any other supernatural force to affect the physical world without itself
being physical.

This theory also would seem to deny the existence of free will.

~~~
solipsism
QM does away with any notion of conservation of information. Time
reversibility (T symmetry) is usually talked about at macro scales where QMs
effects are vanishingly small. IANAP

Regarding free will -- rigorously define it for us, without evoking the
supernatural, and as distinct from pure randomness and absolute determinism,
and it should be easy to tell whether the law of conservation of information
allows for it. Before spending too much time in e it, though, note that such a
definition is widely considered impossible. IANAP

~~~
haberman
To me, a lack of free will would mean that a mind's future state is entirely
determined by its current state. "Free will" would mean that its future state
can be altered by some nonphysical entity (whether you call that a soul,
consciousness, or whatever).

~~~
solipsism
I said _without_ evoking the supernatural. The concept of a soul is
supernatural. There's no reason to think consciousness is anything other than
physical in nature -- but to the extent that you mean it in some kind of
supernatural, extra-physical way, it's not part of this conversation.

By all means go on thinking there might be some supernatural thing called a
"free will" if you want. But if it's supernatural, then the utterly natural
laws of QM wouldn't have much to say about it.

~~~
haberman
> There's no reason to think consciousness is anything other than physical in
> nature

Consciousness is not the same thing as agency. It is possible that we are
conscious but do not actually have free will / agency.

> By all means go on thinking there might be some supernatural thing called a
> "free will" if you want. But if it's supernatural, then the utterly natural
> laws of QM wouldn't have much to say about it.

I am not sure I agree. If QM implies a strict determinism, to me that rules
out free will. For free will to be plausible, there has to be a place for non-
determinism to "hide." If QM can rule that out, to me that rules out free
will.

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boxcardavin
Something that is hard to mention but is worth knowing is that Hawking is not
at the leading edge of his field.

~~~
iso8859-1
How do you know this?

~~~
T-A
Maybe from the "Einstein index"? [1]

[1]
[http://www.science20.com/hammock_physicist/who_todays_einste...](http://www.science20.com/hammock_physicist/who_todays_einstein_exercise_ranking_scientists-75928)

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Steko
So top 7 =/= leading edge?

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T-A
Top 7 among those whom the author chose to compute his "Einstein index" for.

Something not accounted for by that illustration is age ~ proportion of
realized potential. Maldacena is 47, Randall 53; no longer promising
youngsters, but with decades of index-climbing potential left in them.
Weinberg and Glashow are both 82, and owe the bulk of their index position to
work done in the 60s and 70s. Witten is 64 and peaked in the 80s and early
90s. Polyakov is 69; for him it's 70s and 80s.

Hawking is 73. His index-driving contribution is black hole evaporation, from
1974. After that, he's mainly been a popularizer.

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guard-of-terra
It seems that matter usually doesn't fall through the event horizon: due to
time dilution it will take infinite time for matter to reach the horizon from
our point of view.

That's what I've got on Physics stack exchange. There's those collapsars that
look exactly like black holes but are made of matter around the event horizon,
infinitely falling in.

Is this right, wrong, or irrelevant?

~~~
DonGateley
That is correct. From the point of view of the infalling object, however,
nothing changes as he crosses it except his position in space.

I say who gives a shit about the point of view of the infalling object. :-)

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mc808
It seems to me, intuitively, that the infalling object should experience
inverse time dilation and extreme blue-shifting of the outside universe as it
approaches the event horizon. Due to length contraction, that energy would be
increasingly perpendicular to the object's trajectory, approaching a point
where it is bombarded with enough energy to either knock it off its trajectory
or "smear" its particles into orbit around the massive object (basically
another sort of firewall).

Presumably the mathematical descriptions tell a different story because I
never see it described like this.

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jbrooksuk
A video of Hawking's presentation is available at
[https://www.kth.se/en/aktuellt/nyheter/hawking-offers-new-
so...](https://www.kth.se/en/aktuellt/nyheter/hawking-offers-new-solution-to-
black-hole-mystery-1.586546)

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chrischen
How come quantum indeterminacy doesn't preclude information preservation?

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andrepd
All the information about the state of a particle is contained in its
wavefunction. The uncertainty comes from the fact that the wavefunction can
only tell you the probability of getting each value of a specific quantity
when you make a measurement of that quantity, which doesn't mean you lack
information about the state of the particle.

~~~
solipsism
_which doesn 't mean you lack information about the state of the particle._

Yes it does. Quantum observations (sometimes called "collapse of the wave
function") are not time symmetric. Once you've experienced one you can't
derive where you were before it. Otherwise you wouldn't be using the word
"probability".

This inability to recover a previous state is, by definition, the loss of
information.

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jdnier
"You wouldn't technically lose any information if you kept all of the ashes in
one place, but you'd have a hard time looking up the capital of Minnesota."

