ARE WE LIVING INSIDE A BLACK HOLE?
We are living inside what we call “Universe”. But if we look closer, it seems that there
are some connections between a Black Hole and our Universe.
So, is it possible that we are living inside a black hole?
This turns out to be a good question to answer, because there are so many people that,
in approaching Cosmology and Astrophysics for the first time,
found themselves with plenty of questions about the Universe we are living in.
We could say that everybody is interested in a mix of existential questions that turn out to
have both philosophic and scientific answers. This happens because we are humans, and we
stay up all night asking questions. One could drive himself nuts asking questions like that.
But don't worry: we are here for you, trying to help you.
Have the Universe and a Black Hole anything in common?
They seem so different, but are them?
Follow me on this journey through the Universe to find out more about the connection and
differences between Black Holes and the existence of the Universe, between Event
Horizon and Particle Horizon, between Black Hole singularity and Big Bang singularity.
A black hole cosmology (also called Schwarzschild cosmology or black hole cosmological model) is
a cosmological model in which the observable universe is the interior of a black hole.
Such models were originally proposed by theoretical physicist Raj Pathria and
concurrently by mathematician I. J. Good. Any such model requires that the Hubble
radius of the observable universe be equal to its Schwarzschild radius, that is,
the product of its mass and the Schwarzschild proportionality constant. This is indeed known to
be nearly the case; however, most cosmologists consider this close match a coincidence.
But let's take a step back and consider some connections between a Black Hole and our Universe.
First coincidence: Mass of the universe and size of a black hole.
There is this coincidence when we're looking at the universe
and we are comparing the universe to a black hole:
we look at the universe and we say: if there was a black hole the size of
the universe, how much mass would the black hole need to be the mass of the universe'?
It's a really simple equation, you plug it into Schrodinger equations and then...
you get the mass of the universe. This is a little bit interesting: if you
plug in the mass of the universe into the black hole equations, you get the size of the universe.
At first blush, the universe and black hole do seem to have some similarities.
Second coincidence: Event Horizon and Particle Horizon.
Event horizon, boundary marking the limits of a black hole.
At the event horizon, the escape velocity is equal to the speed of light. Since general
relativity states that nothing can travel faster than the speed of light, nothing inside the event
horizon can ever cross the boundary and escape beyond it, including light. Thus,
nothing that enters a black hole can get out or can be observed from outside the event horizon.
The particle horizon (also called the cosmological horizon, the comoving horizon,
or the cosmic light horizon) is the maximum distance from which light from particles could
have travelled to the observer in the age of the universe. It represents the boundary between the
observable and the unobservable regions of the universe, so its distance at the
present epoch defines the size of the observable universe. Due to the expansion of the universe,
it is not simply the age of the universe times the speed of light, as in the Hubble horizon,
but rather the speed of light multiplied by the conformal time. The existence, properties,
and significance of a cosmological horizon depend on the particular cosmological model.
Also, both the Big Bang and Black Holes do possess the concept of Singularity.
We can easily see that there are some connections to both the Event Horizon and Particle horizon.
We get caught by a black hole, and once we come in, we can't go out; we are inside the
Universe trying to get out, but we can't because there is a limit to how far we can travel...
but...is this enough to conclude that we are living inside a black hole?
Of course not.
Let's go on and now try to have a discussion on differences between a Black Hole and the Universe.
First difference.
The black hole singularity is actually different from the Big Bang Singularity.
In the centre of a black hole is a gravitational singularity,
a one-dimensional point which contains a huge mass in an infinitely small space,
where density and gravity become infinite and space-time curves infinitely,
and where the laws of physics as we know them to cease to operate. As the eminent American
physicist Kip Thorne describes it, it is "the point where all laws of physics break down".
Current theory suggests that, as an object falls into a black hole and approaches the singularity
at the centre, it will become stretched out or “spaghettified” due to the increasing differential
in gravitational attraction on different parts of it, before presumably losing dimensionality
completely and disappearing irrevocably into the singularity. An observer watching from a safe
distance outside, though, would have a different view of the event. According to relativity theory,
they would see the object moving slower and slower as it approaches the black hole until it
comes to a complete halt at the event horizon, never actually falling into the black hole.
Instead, the Big Bang singularity or the initial singularity is a singularity predicted
by some models of the Big Bang theory to have existed before the Big Bang[1] and
thought to have contained all the energy and spacetime of the Universe.[2] The
instant immediately following the initial singularity is part of the Planck epoch,
the earliest period of time in the history of the universe.
Black Hole singularity is just a piece of space. time embedded inside of a larger universe.
Instead, the Big Bang singularity is the whole universe, it is where all started.
Second Difference. When it comes to the Event Horizon,
we can say that a black hole's event horizon it's like a Bubble,
embedded again in the larger universe, and once you get in, you can't go out.
Whereas, in the Universe, no matter where you go, you are ALREADY in the bubble.
Third difference.
Furthermore, a black hole singularity is something that lies in the future:
if you entered a black hole, no matter where you move and how much you strive to get out, you will
be led to the singularity, you will always end up in that singularity. It is always in the future.
Instead, the Big Bang singularity is something that happened in the past.
If you go back in the past you will realize that you can't avoid that singularity,
but if you go into the future you can move everywhere you want,
in any direction without ending up in that singularity.
So. It seems we have learned something more.
But it isn't still enough. In fact, it seems that we
have added some new stuff, without ending up to a satisfying conclusion.
Our question is still unanswered. We learned that there are connections between
Black Holes and our Universe, but we learned that there are also some substantial differences.
What is the truth?
Well, it appears the truth does not lie in some physical reasons,
but in some mathematical constructions. Here's why.
We look at our reality, at our Universe, trough the eyes of Einstein's Relativity.
The fact that if you look at the universe and kind of play this pretend game that's a black hole,
it's just a coincidence. It is a result of the fact
that we are using the same equations to describe both our Universe and Black Holes.
We describe both of them using the General Relativity Theory set of equations.
A set of equations can be applied in many different scenarios.
In our case, it can be applied to a black hole as well as it can be applied
to the evolution of the universe. In both cases, once you have solved the
set of equations mathematically, you get a set of solutions that are pretty much similar, just
because they come from the same set of equations. Can you see the thin connection between the two?
We could say it is because of math, and not physics, that we get tricked.
Because of that, some coincidences pop up. There are of course some similarities
between a black hole and the universe, for example, the fact that both are thought to
have a symmetrical distribution, and this leads to similar solutions in terms of mathematics.
But we can ask a further question: even if it wasn't a mathematical coincidence,
and it turns out we actually live inside a black hole, so what?
Nothing would change. The equations that describe
our evolution of universe would be the same. All our knowledge of cosmology would be the same.
We would be still limited by the Particle constant:
we would not learn anything! We would not gain anything.
So even if there is this chance for us to be caught in a black hole,
our suggestion is, as Paul M. Sutter said:
“don't take that similarity too far! Sometimes a cigar is just a cigar and sometimes a set of
spherically symmetric solutions are just a set of spherically symmetric solutions.”
That's what we learned today. So we would like to give you a hint:
Keep dreaming, but keep in touch with reality. As Oscar Wilde said:
We are all in the gutter, but some of us are looking at the stars.
But we would like to say that, even if we are looking at the stars,
sometimes we need to remind you that we are all in the gutter.
Get your feet back upon the ground, because science is what pushes you to dream,
but it is made of real things, real bodies, science is concrete.
Do you think we could actually live inside a black hole?
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