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. What if we wanted to use the shape of space
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so definitely check out that link to find out more. Thanks for watching! Do you enjoy the quirks of the universe? Check out this playlist for more videos like
this one. A big thanks to my patrons and members. If you want your name added to this list,
check the links in the description. All the best, and see you next time.
