Hello and welcome back to Life’s Biggest Questions, I’m Ron McKenzie-Lefurgey.
The universe is mysterious place.
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.
But does it, in fact, go on forever, or is there an outer edge that we simply haven’t
discovered yet?
Let’s explore what science has to say on the subject.
If you want more Science videos, check out our “Biggest Science Questions” playlist
on the channel.
Now get ready, it’s time to ask the question: Is the universe 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.
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
be considered infinite.
Cool!
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
will never be able to see from Earth, where the expansion is faster than the speed of
light.
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
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.
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.
Thankfully, while we remain somewhat uncertain, there is more consensus as to the shape of
the universe than its finiteness.
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.
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.
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.
Some believe that the density parameter is greater than one.
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 is because gravity causes expansion to slow and eventually stop, before contracting
back to a singularity.
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.
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.
A universe with negative curvature would be infinite, as it would be continuously moving
outwards and growing, forming a hyperbolic shape.
Finally, the majority of cosmologists subscribe to the view that the universe is flat, with
a density parameter of 1.
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.
It would have always been infinite, and expansion increases the distance between objects as
time goes on.
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
at least very very close to it.
This can be calculated in two ways.
First, you can add up all the mass-energy in the universe, average it out, and divide
it by the critical energy density.
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.
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.
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
is necessarily infinite.
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,
and has no definite end.
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.
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.
In cosmological terminology, this universe would be finite, but unbounded.
This isn't the only way in which our flat universe could be arranged.
There are 18 known configurations.
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.
It's important that these not have definite edges, as that tends to throw relatively for
a loop.
Unfortunately, however, in our current understanding of physics, there are no laws that predict
or restrict the topology.
So if we're trying to decide the topology of the universe, your guess is just about
as good as mine.
And now we return to our question: Is the universe infinite?
Sadly, as of now, we just aren't sure.
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.
It could be that it does, in fact, continue to expand for eternity, but it could be a
more finite shape, like a torus.
We don't know if the universe will eventually begin to collapse back on itself, or if it
will continue to expand forever.
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.
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.
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Until next time, I’m Ron McKenzie-Lefurgey with Life’s Biggest Questions, wishing you
the best of luck, on your quest for answers.