Hello and welcome back to Life’s Biggest Questions, I’m Ron McKenzie-Lefurgey.
Hello and welcome back to Life’s Biggest Questions, I’m Ron McKenzie-Lefurgey.

The universe is mysterious place.
The universe is mysterious place.

For millennia, humanity has looked to the skies and wondered just what was out there.
For millennia, humanity has looked to the skies and wondered just what was out there.

It seems that space goes on forever, with black as far as the eye can see.
It seems that space goes on forever, with black as far as the eye can see.

But does it, in fact, go on forever, or is there an outer edge that we simply haven’t
But does it, in fact, go on forever, or is there an outer edge that we simply haven’t

discovered yet?
discovered yet?

Let’s explore what science has to say on the subject.
Let’s explore what science has to say on the subject.

If you want more Science videos, check out our “Biggest Science Questions” playlist
If you want more Science videos, check out our “Biggest Science Questions” playlist

on the channel.
on the channel.

Now get ready, it’s time to ask the question: Is the universe infinite?
Now get ready, it’s time to ask the question: Is the universe infinite?

First let's discuss what we mean by infinite.
First let's discuss what we mean by infinite.

An infinite universe doesn't necessarily mean that it goes on forever at all times.
An infinite universe doesn't necessarily mean that it goes on forever at all times.

It can refer to one that is expanding so continually that it never ends, constantly getting larger.
It can refer to one that is expanding so continually that it never ends, constantly getting larger.

Thus, if a universe can expand indefinitely with nothing to stop the expansion, it can
Thus, if a universe can expand indefinitely with nothing to stop the expansion, it can

be considered infinite.
be considered infinite.

Cool!
Cool!

Now, in terms of what we can actually observe, the observable universe is not infinite.
Now, in terms of what we can actually observe, the observable universe is not infinite.

The theory of relatively states that there are certain regions of the universe that we
The theory of relatively states that there are certain regions of the universe that we

will never be able to see from Earth, where the expansion is faster than the speed of
will never be able to see from Earth, where the expansion is faster than the speed of

light.
light.

We can only see a universe with a radius of roughly 46 billion light years.
We can only see a universe with a radius of roughly 46 billion light years.

However, it's pretty darn unlikely that the universe ends right where we can no longer
However, it's pretty darn unlikely that the universe ends right where we can no longer

observe it; it's even possible that it has no end at all!
observe it; it's even possible that it has no end at all!

Let's see what the literature has to say about this scientific controversy.
Let's see what the literature has to say about this scientific controversy.

Before we can determine whether or not the universe is infinite, we should first discuss
Before we can determine whether or not the universe is infinite, we should first discuss

the shape of the universe, as that's quite important in determining its limits.
the shape of the universe, as that's quite important in determining its limits.

Thankfully, while we remain somewhat uncertain, there is more consensus as to the shape of
Thankfully, while we remain somewhat uncertain, there is more consensus as to the shape of

the universe than its finiteness.
the universe than its finiteness.

To understand this, we should first go over the Density parameter, which is represented
To understand this, we should first go over the Density parameter, which is represented

with Omega (?). This is used a good deal when determining the likely shape of the universe.
with Omega (?). This is used a good deal when determining the likely shape of the universe.

The Density Parameter compares the average density of matter and energy in the universe,
The Density Parameter compares the average density of matter and energy in the universe,

to the density at which the universe would only stop expanding after an infinite time.
to the density at which the universe would only stop expanding after an infinite time.

If the average density is higher than the critical density, then the universe will eventually
If the average density is higher than the critical density, then the universe will eventually

collapse back, and if it's lower, it will expand infinitely.
collapse back, and if it's lower, it will expand infinitely.

Some believe that the density parameter is greater than one.
Some believe that the density parameter is greater than one.

In this view, the universe would have a Positive Curvature.
In this view, the universe would have a Positive Curvature.

This universe would be spherical in shape, and is referred to as a closed universe.
This universe would be spherical in shape, and is referred to as a closed universe.

This is because gravity causes expansion to slow and eventually stop, before contracting
This is because gravity causes expansion to slow and eventually stop, before contracting

back to a singularity.
back to a singularity.

Others hold that the universe has a density parameter less than 1.
Others hold that the universe has a density parameter less than 1.

Here, the universe has a negative curvature, and would be classified an open universe.
Here, the universe has a negative curvature, and would be classified an open universe.

In this case, since the actual density is lower than the critical density, gravity is
In this case, since the actual density is lower than the critical density, gravity is

unable to take over and stop the expansion, so it continues to expand forever.
unable to take over and stop the expansion, so it continues to expand forever.

A universe with negative curvature would be infinite, as it would be continuously moving
A universe with negative curvature would be infinite, as it would be continuously moving

outwards and growing, forming a hyperbolic shape.
outwards and growing, forming a hyperbolic shape.

Finally, the majority of cosmologists subscribe to the view that the universe is flat, with
Finally, the majority of cosmologists subscribe to the view that the universe is flat, with

a density parameter of 1.
a density parameter of 1.

In this view, the universe could very well be infinite.
In this view, the universe could very well be infinite.

A simply connected flat universe is isotropic and homogenous, meaning it's the same everywhere.
A simply connected flat universe is isotropic and homogenous, meaning it's the same everywhere.

It would have always been infinite, and expansion increases the distance between objects as
It would have always been infinite, and expansion increases the distance between objects as

time goes on.
time goes on.

Of these three, the flat universe is by far the most commonly held position, because as
Of these three, the flat universe is by far the most commonly held position, because as

far as most scientists are concerned, the density parameter of the universe IS 1, or
far as most scientists are concerned, the density parameter of the universe IS 1, or

at least very very close to it.
at least very very close to it.

This can be calculated in two ways.
This can be calculated in two ways.

First, you can add up all the mass-energy in the universe, average it out, and divide
First, you can add up all the mass-energy in the universe, average it out, and divide

it by the critical energy density.
it by the critical energy density.

When this is done, using data obtained from the Wilkonson Microwave Anisotropy Probe and
When this is done, using data obtained from the Wilkonson Microwave Anisotropy Probe and

the Planck spacecraft, we find a density parameter of 1, plus or minus 0.02.
the Planck spacecraft, we find a density parameter of 1, plus or minus 0.02.

It can also be measure geometrically, looking at angles across the universe, which finds
It can also be measure geometrically, looking at angles across the universe, which finds

that the density parmeter is 1, plus or minus 0.12.
that the density parmeter is 1, plus or minus 0.12.

Editors, the calculations are on this page if you want to include them:
Editors, the calculations are on this page if you want to include them:

However, just because it seems that the universe seems to be flat, that doesn't mean that it
However, just because it seems that the universe seems to be flat, that doesn't mean that it

is necessarily infinite.
is necessarily infinite.

To demonstrate this, imagine the universe as a flat piece of paper that expands forever.
To demonstrate this, imagine the universe as a flat piece of paper that expands forever.

This could be seen as the infinite model, where it can continue to expand infinitely,
This could be seen as the infinite model, where it can continue to expand infinitely,

and has no definite end.
and has no definite end.

However, if we were to imagine folding the paper into a cyllinder, then joining the ends
However, if we were to imagine folding the paper into a cyllinder, then joining the ends

of the cyllinder, we would have a flat, finite universe, in a torus or donut shape.
of the cyllinder, we would have a flat, finite universe, in a torus or donut shape.

The multiple connections of this shape allow it to be finite, and the lack of true edges
The multiple connections of this shape allow it to be finite, and the lack of true edges

means that we're able to deal with it mathematically and conceptually.
means that we're able to deal with it mathematically and conceptually.

In cosmological terminology, this universe would be finite, but unbounded.
In cosmological terminology, this universe would be finite, but unbounded.

This isn't the only way in which our flat universe could be arranged.
This isn't the only way in which our flat universe could be arranged.

There are 18 known configurations.
There are 18 known configurations.

For example, it could take the shape of Klein bottles or Mobius strips, where traveling
For example, it could take the shape of Klein bottles or Mobius strips, where traveling

far enough in one direction brings you right back where you started.
far enough in one direction brings you right back where you started.

It's important that these not have definite edges, as that tends to throw relatively for
It's important that these not have definite edges, as that tends to throw relatively for

a loop.
a loop.

Unfortunately, however, in our current understanding of physics, there are no laws that predict
Unfortunately, however, in our current understanding of physics, there are no laws that predict

or restrict the topology.
or restrict the topology.

So if we're trying to decide the topology of the universe, your guess is just about
So if we're trying to decide the topology of the universe, your guess is just about

as good as mine.
as good as mine.

And now we return to our question: Is the universe infinite?
And now we return to our question: Is the universe infinite?

Sadly, as of now, we just aren't sure.
Sadly, as of now, we just aren't sure.

We're pretty sure the universe is flat, based on our current understanding of cosmology,
We're pretty sure the universe is flat, based on our current understanding of cosmology,

but science has yet to come to a consensus as to what kind of flat universe it is.
but science has yet to come to a consensus as to what kind of flat universe it is.

It could be that it does, in fact, continue to expand for eternity, but it could be a
It could be that it does, in fact, continue to expand for eternity, but it could be a

more finite shape, like a torus.
more finite shape, like a torus.

We don't know if the universe will eventually begin to collapse back on itself, or if it
We don't know if the universe will eventually begin to collapse back on itself, or if it

will continue to expand forever.
will continue to expand forever.

As of now, we simply lack the information to come to a definite conclusion, so we'll
As of now, we simply lack the information to come to a definite conclusion, so we'll

have to wait and see what science will come up with next.
have to wait and see what science will come up with next.

Thank you for watching Life’s Biggest Questions, I hope this was interesting and informative,
Thank you for watching Life’s Biggest Questions, I hope this was interesting and informative,

and maybe even inspired you to look into it further on your own.
and maybe even inspired you to look into it further on your own.

If you liked this video, please thumbs up and subscribe to the channel down below.
If you liked this video, please thumbs up and subscribe to the channel down below.

While you’re down there, let me know your thoughts on this question, as well as any
While you’re down there, let me know your thoughts on this question, as well as any

other science-related questions you’d like us to answer.
other science-related questions you’d like us to answer.

Until next time, I’m Ron McKenzie-Lefurgey with Life’s Biggest Questions, wishing you
Until next time, I’m Ron McKenzie-Lefurgey with Life’s Biggest Questions, wishing you

the best of luck, on your quest for answers.
the best of luck, on your quest for answers.