Until the end of the universe, black holes
will be the longest living objects, but eventually
every black hole will die.
So today, we’re going to be discussing black
holes and explaining Hawking radiation.
We might as well begin with the parts of a
black hole.
At the very heart of all black holes lies
the singularity: a point where matter collapses
to infinite density, spacetime has infinite
curvature and the gravitational field strength
is infinitely strong.
The outer layer of a black hole is called
the event horizon: the imaginary boundary
of a black hole where the gravitational field
strength becomes so strong that nothing can
escape, not even light the fastest thing in
the universe.
You can think of the event horizon as a river,
which ends in a gigantic waterfall.
Further down the river and closer to the waterfall
you go, the stream becomes faster and faster.
Once you’re past the point of no return,
or in this case the waterfall, there’s no
going back.
No matter how fast you swim you can’t escape
the pull of the waterfall.
Nothing can escape the pull of a black hole,
if you get too close.
Unfortunately, we will never find out what
goes on inside black holes, past the event
horizon, however, we do have some ideas of
what occurs at the very edges.
Black holes evaporate their mass away.
All around us, virtual particles are constantly
popping into existence.
They come in pairs, a particle and an antiparticle.
After existing for an extremely short amount
of time, the two particles recombine and annihilate
each other.
If one of these particle pairs pops into existence
at the event horizon, one particle will fall
into the black hole but the other is able
to escape elsewhere.
And when particles escape, the black hole
loses an extremely tiny amount of its mass.
This is called Hawking radiation, a process
that's exceptionally slow.
Without a doubt, black holes will be the longest
living objects for the rest of the universe,
because of how slow they deteriorate.
However, if the black hole is consuming enough
matter, it can combat Hawking radiation so
that nothing happens or the black hole could
be consuming enough matter that it actually
gains mass.
In these circumstances, black holes are eternal,
assuming that they are always eating a constant
flow of matter.
It’s easy for more massive black holes to
combat Hawking radiation but for smaller black
holes, it’s not as easy.
Black holes emit Hawking radiation at a rate
inversely proportional to their mass.
So a small black hole evaporates very rapidly
and has an associated temperature that is
very high, whereas a massive black hole evaporates
much slower and has an associated temperature
that is very low.
Black holes at just the right mass, that formed
near the start of the universe, will be coming
to the end of their lives right now.
What happens when a black hole comes to the
end of its life?
We’re not entirely sure.
The best guess at the moment, is that the
black hole radiates out for the last time
and evaporates into nothing.
As mentioned, the smaller the black hole,
the quicker the process is.
So a black hole at the end of its life would
emit Hawking radiation faster than its ever
done before and evaporate into nothingness.
However, this is a problem because as the
black hole dies, the information it has gathered
over its lifetime also seems to die.
Information is what distinguishes one thing
from another; what makes one particle unique
from another.
It’s the mass, spin, position, temperature
and so on of any one particle.
According to the theory of quantum mechanics
information cannot be destroyed; it can be
changed but not destroyed.
This has created a paradox, because black
holes destroy information.
There are a few outcomes to the black hole
information paradox.
First, the information is hiding, in whatever
form it takes.
Perhaps black holes don’t disappear after
all and a small part of it remains.
Maybe the information is emitted before or
as the black hole evaporates into nothingness.
The information could separate into another
black hole, that we cannot access but it would
mean that the information is not lost and
our current laws of physics are not broken.
Second, we accept that information is lost.
The information would simply be irretrievable
and gone forever.
We would need to remove some current laws
of physics and rethink them.
And third, information is not lost.
When you put more material into a black hole,
the black hole becomes larger, to make room
for the new information.
When two black holes merge, the remaining
black hole has a combined mass of about the
sum of the two previous black holes.
More information translates into more surface
area.
The black hole could be storing the information
and release it on a later date.
Perhaps the information is conserved in parallel
universes.
One idea is that the information is converted
onto the surface of the black hole.
This is called the holographic principle.
If this is the case, and information is preserved
onto the edge of a black hole, then it’s
very possible that Hawking radiation could
read this information and take it away as
it’s emitted.
If all falling material has its information
preserved onto the event horizon, it’s a
bit like the information is going from three-dimensions
and then being stored onto a two-dimensional
surface; or in other words, a hologram.
Comment down below your thoughts on Hawking
radiation.
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