Hey everyone! Today we're going to be seeing what would happen(Ready?)
if a white hole and a black hole collided
So I'm going to be showing you what a real white
hole would look like compared to a real black hole
what they would look like when they combine together and I'm
also going to be showing you a real experiment you can do that
will simulate this. Now if you solve Einstein's
field equations, you can predict black holes should
exist but you also predict another thing that
exists called white hole. White holes are similar
to black holes; there are different solutions to the field
equations, and they have some different
property. One of these properties is
that instead of nothing being able to escape
the event horizon like a black hole,
for a white hole, what it means is that nothing can
enter the event horizon, so nothing can actually go into
the white hole
whereas nothing can actually come out of a black hole
So a white hole and a black hole are actually very
similar; a white hole is just a time
reversed black hole. In Relativity
it's important to choose your coordinate system wisely because
time and space depends on gravity and
speed. The easiest way to understand
the difference between a white hole and a black hole
is to talk about coordinate system in which you're free-falling
in this coordinate system, a black hole
appears as though it is sucking in space-time
so space-time is ever flowing inward towards
the centre of the black hole. But for a white hole
space-time is always flowing outward, away
from the centre of the white hole. So remember that in a
free-falling coordinate system, black holes are
sucking in space-time, and white holes
spewing out space-time. Here's where it gets
interesting. So for a black hole
it's always sucking in space-time, and the closer
you get to the centre of the black hole the faster
it's sucking in space-time. So for example, picture a
drain with water flowing. As you're
further away the water is not flowing very fast but as it
gets closer and closer to the centre of the drain, speeds up
faster and faster until it gets extremely
fast right at the centre of the drain
At the very centre of the black hole there's a singularity
and at that point space-time is getting sucked
in at an infinite rate. But that's not
the interesting part. The interesting part is actually a little bit
away from the singularity called the event horizon
At the event horizon that is the point at which
space-time is flowing inward at
the speed of light. So that means exactly
at the event horizon light cannot escape
because space-time itself is being sucked inward
at the speed of light, and so photons can't go any faster
than that, so they're forever held at the event horizon
Now inside the event
horizon of a black hole space-time is actually
flowing faster than the speed of light, and so that's why nothing
can never escape from the black hole because inside
the event horizon space-time itself is moving faster
than light, and nothing can move faster than light or can never
escape it. This still doesn't violate
Einstein's law that says nothing can move faster than
the speed of light, because that law is talking
about objects in space-time
in reference to each other thay can't move faster
than the speed of light. But it's not talking about
space-time directly. Space-time itself, while
being sucked into the black hole, can move faster than the speed of light
So that's a black hole, but what about a white hole
Well, a white hole also has a singularity at the centre
it's made of mass, just like a black hole, so that
means that also has gravity as objects are
also attracted to it and get pulled towards it
But here's is when it gets interesting. When an object
gets pulled towards a white hole, the
object never goes into the white hole
even though it's attracted to it. Well remember I said
that the white holes, instead of sucking in space-time
they're spewing it out, it's flowing outward
from the white hole, and so that means as
an object gets closer and closer to the white hole
space-time is pushing out
So let's say you are moving at the speed of
light going towards a white hole, while
space-time itself is moving against you this time
so that means that you will just be completely stopped at the event
horizon at the white hole, and so nothing can ever move
faster than the speed of light, that means that nothing can actually
get into the white hole, because at the event horizon
space-time is moving at the speed of light and nothing
can go faster than it so nothing can get inside of it
Inside the event horizon, space-time is actually
moving faster than the speed of light going in the
opposite direction
So you can see that a black hole and a white hole are actually
really similar. The only difference between them
is the direction of flow of space-time
Previously I made a video about white holes
and in this video, I show you a real-life
experiment that scientists have actually used to make
predictions about white holes. It's actually a
pretty simple experiment. All you need to do is turn on your
kitchen sink
You may have overlooked this pattern. This pattern
shows up whenever you have a stream of water hitting a flat
surface below it. and this kind of this wall of
water then forms. So you can define this inner
circular area where I've taken a cross section over here
you can call the jump radius. So you can actually
show that anything within this jump radius, anything
within these walls of water, or this hydraulic
jump area, you can show that
the water is actually moving faster than the
speed of wave propagation. So what that means is that
if you're to make a little splash in the water; make a wave here,
the waves can propagate out
but if you made a little splash in the water here
the speed of this water is faster than
the speed of wave propagation in the water. And so
the wave itself can never get past this hydraulic
jump here. So now here is where the comparison
comes in. Anything that's inside of
this jump radius is the equivalent to anything
that's within a white hole. And the hydraulic
jump here is similar to the event
horizon of a white hole
So what that means is that once something
or some information leaves this hydraulic jump here
it can never come back in. Let's say this
food colouring represents information or some object
coming out of the white hole
You can see this something can come out of the white hole
so I start within the event horizon and a little
come out and it comes out quite easily
see it come out
But you can see that once it's out it can never come
back in. It tries to come back in but it can
never get back in
If I try to get anything in it, try really hard
it can never get back inside of it
What would a real white hole look like?
Well, we now know what a real black hole looks like
So first let's see a real black hole, and then I'll show
you what happens if that black hole were actually
a white hole how would look different
Here's a rendering of the black hole at the centre of our Milky
Way galaxy
The first thing that you'll notice is that it is not very
black at all. In fact, it is extremely bright
The reason it is so bright is
because it's constantly spewing out radiation, Hawking
radiation, and also because of the
accretion disc surrounding it
Now the accretion disc happens because as things
approach the black hole, they approach the speed of light
and as they approach the speed of light, their time
relative to our slows down. And so basically as
though they become frozen in time, eventually
they become red-shifted out of view
and we never actually see them enter the black hole
And so why you get around the black hole is basically this
frozen ring of light
And you'll notice that everything is "lensed" because
the black hole's gravity bends space-time
and so it's basically bending the light from the
stars behind it, and so it appears as though
as this giant lens
So here is what it looks like approaching the black hole at the centre
of our galaxy. Now the part of the black hole
that you can't see anything, that is the event horizon,
in which no light can escape at all
So you'll notice that as you gaze into the black hole
you can't see anything inside of it, because nothing can
escape it
Here's the interesting thing. Remember that I told
you a black hole and a white hole are different solutions
to the same problem. So what we can do in this simulation
is actually just flip the black hole to
a white hole
And so let me do that right now
OK, I'm gonna turn this giant black hole
into a white hole
and done
So the first thing you'll notice is that the accretion disc
disappears from the white hole. That's because
space-time itself is pushing things outward
and so in a free-falling coordinate system, you can't ever
stay around it, as it's always been pushed outward
You'll notice that this still has the ion jets coming out of it
But now let's fly in towards the centre of the white hole and
see what happens
So you'll notice as we get closer we still get the
gravitational lensing effect, but you'll notice that
there's no dark centre
You can actually see inside of the white hole
That's because any light that is coming from the centre of the
singularity of the white hole is still exiting. So
we can still see inside of it
So the inside of a white hole could be another
universe altogether or a different part of our own universe
You can see this a little bit clear when I put on this
grid pattern and then look at the white hole
So you'll notice that as I'm going towards the centre of the
white hole, now you can see that there's almost like an entire
universe inside the white hole
So now what would happen if a black hole and a
white hole were now to combine together. First let's
do an experiment to see what would happen
So if a white hole could be simulated by pouring a fluid
onto a flat plate, and having a flow outward,
then a black hole should be able to
be simulated by having a fluid sucked
into something. So basically this is a
really simple experiment to set up
If you turn on your water in your sink, that's the
white hole, and the drain is the black hole
So first let's see what happens when we combine these two together
in a real experiment and then let's do a simulation
of it and see what happens and what it looks like
OK, so you can see my white hole in the corner here
You can see there if I try to tap out a message
it can exit the white hole, but if I try to
tap in a message, no messages can get inside
of it. And if I try to tap information inside of
the black hole, nothing can get out of it
So now this is the easiest simulation you'll ever see.
What happens when a black hole and a white hole combine?
Well, you can see that the black hole just swallows
up the white hole(lol)
OK, now let's see what it would look like in real life
So, just like in the sink experiment, the black hole
basically swallows up the white hole
For a black hole that has more mass
than the white hole, it's easy to believe that it
would end up still being a black hole, meaning that
space-time is being sucked into it.
But what about if the white hole had a larger mass than the
black hole? Would it end up being a white hole?
Or what if a black hole and a white hole had the same
mass and they collided together? What would they end up
being? Well the heart of that question is the
relationship between black holes and white holes
Black holes and white holes might seem very different
but they're actually just two sides of the same coin
In fact, if you're going just based off of gravitational effects
there's absolutely no way you can
tell the difference between a black hole and a white hole. They
both act exactly in the same way. There's a lot of
theories surrounding black holes and white holes. Some of those
theories are that black holes can turn into white holes
and white holes actually can turn into black holes. And at
the creation of the singularity, a black hole and
a white hole are actually in a quantum superposition
of both of them, so it's a "black-white hole"
until eventually one of them emerges
And the reason you have to take into consideration
quantum effects, is because at the centre of the black
hole and a white hole is a singularity, so
something extremely small, smaller than an atom;
all that mass is contained in that single point, and so
quantum effects dominate. And so if you had a black hole and a
white hole of exactly the same mass that came together
I don't know whether they would be a black hole or a
white hole at the end of it. Everything I've just
shown you, keep in mind that white holes are
purely theoretical right now
There's a few problems with the existence of white holes
First, is that they don't obey the second law of thermodynamics
Einstein's theory of General Relativity doesn't
take into account thermodynamics, and so we can
have solutions to these equations that don't necessarily
have to obey the laws of thermodynamics
and white holes are one of those solutions
Another reason why white holes probably don't exist
is because their variance is stable
So you can show that white holes would extremely fast turn
right into a black hole, even if there's some way that
they can't be formed in the universe. But the mathematics
of Einstein's field equations, let us to understand
black holes before we even proved they existed
This could be the case for white holes, but we won't
know until further research is done
So thanks for watching another episode of "The Action Lab", I hope
you enjoyed it, If you did remember to hit the subscribe
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And thanks for watching and I'll see you next time.(The ebd)
*BYEBYEEEE