The interesting thing about trying to unravel
the laws of nature is that yes, we have found
some laws.
We understand gravity to some extent.
We understand the quantum world with some
extent.
But we don’t understand everything.
We know that there are some laws missing,
laws that we haven’t found yet.
Now what theoretical physicists do is the
following.
They try to learn what we know so far and
they try to see where the limits of today’s
knowledge lie and they try to go beyond.
They try to make one step beyond what is known.
And that is what is called theoretical physics.
Theoretical physics is trying to see a law
beyond the laws we have.
There are at least two places in our universe
where we know that we do not know what laws
apply.
Those two places are inside black holes and
at the big bang.
In both cases the conditions surrounding everything
are so extreme that the laws we know they
break down.
And that is why both these – that is one
reason why both these places are so interesting
to look at.
For a long time gravity has told us that nothing
can escape the gravitational grip of a black
hole.
But then in 1976 or 75 Professor Stephen Hawking
discovered that it was not the case.
That actually things could escape black holes.
How did that come about?
Picture yourself in outer space.
There is a black hole right in front of you.
You don’t see anything.
No light can come out of it.
So it’s like a dark patch that distorts
the stars that are around.
But there is this dark patch right in front
of you and you’re far away and you look
at it and it’s scary and you don’t want
to get closer which is normal.
But – and respectable.
But what you know is that gravity is not everything.
The matter that surrounds you, the light that
surrounds you obeys a different kind of law.
They obey quantum physics.
They obey the law of the quantum world.
And everything we had known about black holes
until the mid-1970s was only related to gravity.
Now what Hawking did at the mid-1970s is to
add some quantum aspects to all this.
He took a quantum particle and threw it in
his mind towards the black hole to see what
would happen to it.
And he found out that some part of that particle
was getting out of the black hole.
That the black hole was evaporating.
It was not the exact same particle he had
sent inside and that was, that’s what’s
tricky about this problem and that’s what’s
interesting about this problem.
He realized which is something that became
known as the black hole information paradox.
In a way that means that the information gets
bleached by a black hole.
Why is that?
You could imagine that it’s the same with
an encyclopedia that you would throw in the
fire.
You take an encyclopedia, you throw it in
the fire, it’s gone.
Well not quite.
If you could get back the ashes, if you could
collect all the lights that was shown during
the fire.
If you could get the heats and everything
you could build back the encyclopedia.
It’s not gone.
It’s just difficult to retrieve.
For a black hole it’s worse.
If you throw an encyclopedia inside what the
black hole will evaporate has nothing to do
with the encyclopedia whatsoever.
You could have thrown in something else.
So why is that a problem?
It is a problem because it means that our
universe has memory losses.
It means that whatever a black hole has swallowed
would get inside, never get back out and we
would never be able to understand the past
of our universe.
There’s some things that are not retrievable
at all.
Not just in practice but also in theory.
And as it evaporates the black hole eventually
disappears completely maybe.
And if it’s gone where did the information
go about the encyclopedia.
Where did it go?
We don’t know.
And that’s a problem because that’s called
non-unitarity.
That’s the technical term for it and it
means that you do not, you cannot use physics
to understand the history of what happened
before.
In a sense the information paradox says that
physics is not going to give you the history
of our universe.
And you can fairly easily understand that
scientists did not like that idea.
And people are still working today on the
way out of that problem.
There are some solutions that have been put
forward.
None that I believe is sufficiently convincing
mathematically to be considered a proof but
people have been working on that information
lost paradox problem since 1975-1976.
And in a sense maybe the answer to that question
will come from this theory of everything that
everybody is looking for.
