If you got into a spaceship,
and traveled long enough and fast enough,
could you eventually loop back
to where you started?
Assuming you don't accidentally collide
with another planet or star,
and no black hole
swallows you along the way.
We don't know much about the Universe.
We have no idea how big it is,
or where it starts or ends.
For years, scientists thought
the Universe was flat, like a piece of paper.
And that if you kept traveling
in a straight line through space,
you'd just sail off into infinity.
But a new study of cosmic microwave background, or CMB,
might have just ruined everything
we thought we knew about the Universe and its shape.
If the Universe is a loop,
it would mean that a kind of time travel
might just be possible.
Before we move on to the time travel,
let's get the theory out of the way.
I'll start with Albert Einstein's theory of relativity.
Einstein predicted that space
could bend in different ways,
meaning the Universe could be flat,
or curved, or closed.
The flat universe was the most likely shape of all.
And by that, I mean that it
fit our current understanding of physics.
But then researchers found something strange
in the cosmic microwave background.
Figuring out the shape of the Universe
isn't an easy task.
We've never sent a single space probe
to the outermost reaches of our Universe.
We don't even have spacecraft
that could possibly go that far.
And this is where the CMB comes in handy.
It's microwave radiation
that's spread throughout the Universe.
A relic from its very early ages.
Because it's so old, CMB serves
as the main source of data
about the Universe and its past.
And by measuring it, scientists can get
all kinds of cosmological information.
Now, this is the Planck mission satellite.
It was sent to measure temperatures in the CMB,
among other tasks.
But the data that this satellite brought back
didn't quite add up.
It suggested that gravity was bending the CMB
more than the researchers expected.
And this isn't something that
existing physics can explain.
Maybe, we were wrong about the shape of the Universe.
Maybe, it's closed,
like one huge, inflated balloon.
There is a way to test this theory,
although it's quite hypothetical.
So put your helmet on, and buckle up.
It's going to be a long ride.
And by the way, for this task,
you'd have to not age for billions of years.
You'd also need to build a spaceship
with warp drive technology.
Equipped with all that,
you'd begin your journey around the Universe.
Don't say I didn't warn you —
this one-way voyage would take you billions of years.
If the Universe is much, much larger
than what we can observe,
you might only get a third of the way.
But if the Universe is a loop,
that's less than 15 billion light-years in diameter,
you might return to your starting point.
That would be solid proof that
the Universe is, indeed, a loop, and that
physics, as we understand it, doesn't apply.
And what was I saying about time?
Oh, right. Albert Einstein suggested that
space and time are connected.
So, if the space of the Universe is looped,
could time be looped as well?
It might be.
The Universe could be repeating itself over and over again —
from the Big Bang to the Big Crunch.
That would explain how the galaxies, with their stars and planets,
came into being.
And if we live in a looped Universe with looped time,
maybe — just maybe —
one of those young galaxies
you can see out there
is actually an infant version of the Milky Way.
That may not be the kind of time travel you expected.
The thing is, the shape of the Universe
wouldn't have any effect on you, or the Earth,
or even the entire galaxy, but...
it might just give us a loophole
in covering the astronomical distances involved
in exploring the Universe.
If you really want to travel through time,
it would take more than just a different shape of the cosmos.
But that's a story for another WHAT IF.