Thanks to The Ridge Wallet for sponsoring today’s video.
Is the universe inescapable?
If we were to conquer the limitations of light speed and were to travel to space’s furthest
edge, what might we find?
Just more space?
Infinite planets and planetary systems?
Or would we somehow come back to where we started?
Amazingly, according to scientists, all of these are possible, but which one is correct
comes down to the nature of that unseen world all around us.
I’m Alex McColgan, and you’re watching Astrum.
Join me today as we continue our series exploring the unseen world of 4D space and discuss possible
answers to the question: what is the shape of the universe itself?
But first, let’s begin by talking about infinity.
You likely are already familiar with infinity.
In maths, it is the concept of a number so large, it cannot possibly be beaten.
Of course, no such number exists – for any number you can name, I could come up with
a number that is at least 1 larger than it.
But in a way, that’s sort of the point.
In infinity, there is always another number.
And when it comes to our universe, we have so far discovered no edges.
There may always be another star or planet.
An infinite universe is a little mind-boggling for us.
We live in a very finite world, with edges and endings.
So, the idea that there might be literally infinite more planets out there is a little
bewildering.
However, as we develop more and more powerful telescopes and push back the darkness further
and further at the edges of what we can observe in our universe, all we are finding is that
even the darkest patches of the night sky are turning out to be brimming with stars.
So increasingly, an infinite universe might be something we are forced to contemplate.
But that is not to say that just because the universe is infinite, there are not a finite
number of things in it.
That may sound a little counterintuitive but let me show you what I mean.
Believe it or not, there are different kinds of infinity when it comes to our universe.
Three possible scenarios could be true: a flat universe, a spherical one, or a hyperbolic
universe.
Allow me to explain.
In a flat universe, if we were to form a grid to broadly represent reality, everything would
seem fairly standard.
All the lines would either be parallel to each other, or perpendicular.
An infinite universe of this variety would simply extend outwards in all directions forever
and ever.
This is a little boring, so I won’t spend too much time on it.
However, this is a lot like what we perceive the universe to be.
For the most part, all lines of direction appear straight to us.
We can distinctly see the planets and stars around us, and we notice no real curving or
warping.
However, this is not the only way that the lines can be drawn.
Consider for a moment a black hole.
You may immediately notice the strange rings that appear to run around its equator, as
well as across the top of it and along the bottom.
This is something of an illusion.
There are no rings across the top or bottom of this black hole.
What you are seeing is the equatorial ring that’s on the other side of the black hole.
However, due to the powerful gravity of the black hole, the light that is hitting it is
not bouncing off upwards or downwards into space.
Instead, the rays are curving towards us, as the black hole’s gravity pulls them in.
You are seeing the top and the bottom of that ring at the same time.
Light being bent by gravity…
what do I mean by that?
Actually, this is an excellent example of our second kind of universe.
In a flat universe, all the lines that make up reality are fairly straight.
But what if we were to come up with a rule – all the lines must instead curve towards
each other?
There is only one way such a universe could be drawn, and that is in a sphere.
Consider trying to draw two parallel lines on a sphere.
You might start off well, but would quicky realise that your task is impossible.
All lines would converge towards each other, intersecting at least twice, as they return
back to where they started.
What would a universe that was based on these kinds of lines look like?
Essentially, rather than going in the straight line you thought you were going in, you actually
would be travelling in a massive curve.
It’s a little bit like those computer games where you travel off one end of the screen
only to reappear from the other side.
In a spherical universe, you could try to travel infinitely, but ultimately, you would
only end up arriving back to where you started.
With a powerful enough telescope, and if light were to travel a whole lot faster all of a
sudden, it would be possible to look at the back of your own head.
This kind of universe contains a finite amount of things, but it appears infinite just because
you’d keep bumping into the same things infinite times.
Thanks to objects like black holes and powerful stars, we do indeed have evidence that our
reality sometimes is a curved, spherical one – at least near large bodies of mass.
The inside of a black hole’s event horizon is this kind of infinite space – no matter
what path you take, you can never get out of it.
However, let’s consider our last example – the hyperbolic universe.
This one is the hardest to visualise, but the idea is simple.
Instead of having all lines remain parallel or move towards each other, every line must
move away.
From everything.
Drawing this is inherently tricky, because everything keeps getting wider exponentially.
The only way you can do that is to either buckle your nice flat disk until it becomes
something like this: Or warp what you are seeing like this: All of the objects in this
image are squares.
However, they are squares that are obeying our rule that all their lines must be diverging
away from each other.
This leads to the very strange situation where you can have 5 squares all meeting up at a
corner, instead of the usual 3 that is possible in normal 2D space.
All right, this seems a little confusing.
What does it mean if space is hyperbolic?
Well, let’s consider what it is we are curving around.
You might have noticed when we talked about our spherical shape that there must be something
we were curving around.
That direction of curvature is in regards to time.
Imagine if you will a series of timelines: We go a little more in depth with the interplay
between space and time in my last video, which I would really recommend you check out.
But for now, just remember for this model that objects in time move forward along their
timelines in the direction of “up”, or the future.
If they move left or right, they are moving through “space”, getting closer to each
other.
If we introduce a large mass into this model, it warps the timelines: Now, if you were a
small object travelling along one of those arrows that got too close to the mass, suddenly
your path of travel no longer goes directly up towards the future, it pulls you left or
right towards the mass.
There are reasons for this, but the essential thing to recognise here is that now, your
“straight” path towards the future pulls you in towards the planet, so you’ll have
to accelerate away from it just to stay on a straight path.
In a nutshell, you are experiencing gravitational pull.
Even the planet is effected by this – the atoms on either side of it are squeezed towards
the centre of mass, as if it were being forced down a narrow tube by giant, invisible hands.
Let’s get back to Hyperbolic space.
In this model, the opposite thing is happening.
All lines are moving away from each other.
We could represent this by curving space and letting our timelines be straight: which is
nice because it captures the idea that from your perspective, your time is always ticking
forward normally.
But let’s warp this slightly so that it’s space that is flat.
It’s all a matter of perspective, after all: Here, parallel lines are also impossible.
But this time, rather than converging, all parallel lines diverge more and more.
Everything moves further and further apart…
Hmm, why does that sound familiar?
It is because that is what the universe is doing.
This is not noticeable within a galaxy, where there is enough mass and gravity to keep everything
together.
However, from what we can see of the universe as a whole, every galaxy is moving away from
every other galaxy.
Scientists try to explain that with dark energy.
But maybe all that is happening is that the universe is just naturally hyperbolic in its
shape?
So what would that mean if the universe really was hyperbolic?
Well, for starters, it would mean that the universe was really infinite.
The flat space we looked at was infinite – for each light year you travelled out, you’d
discover another light year’s worth of space.
However, with hyperbolic space, you’d discover more than another light year’s worth of
space.
It’s like opening infinite doors, except inside each door are two new ones.
The possibilities would be far more endless, far more infinite, than in just regular flat-space
models.
But also, it means that, given enough time, the rest of the universe would drift away
from us until our galaxy was all that was left…
Scientists have looked out across the universe, however, and have not noticed this hyperbolic
space in action.
In fact, things all look pretty flat.
So perhaps flat space is the correct answer.
Yet, this still leaves room to me for hyperbolic space to be the default.
After all, if matter is curving space towards it, and the universe appears flat, it would
make sense that the universe was curved in the inverse, at least to some degree.
Perhaps all three models are true: Perhaps the universe is by default hyperbolic, but
mass brings it together in such a way that it perfectly offsets the inverse curves of
the universe to the point where everything appears flat?
There certainly seems to be some evidence that this is the case.
But it’s very difficult to know for sure.
Which model do you think is correct?
Or maybe you feel that we do not live in an infinite universe at all?
Please leave a comment down below to tell me what you think!
But for now, just remember – the unseen world might be a lot more influential on our
universe than we are currently aware of.
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Thanks for watching!
Do you enjoy the quirks of the universe?
Check out this playlist for more videos like this one.
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All the best, and see you next time.