- We're not just looking for a time criminal.
We're looking for a Loki, a variation of this guy.
- [Narrator] In the Disney+ series "Loki",
the god of mischief is arrested for time crimes.
- Guilty of a crime against the sacred timeline?
Absolutely not, you have the wrong person.
- [Narrator] This confirms there's a multiverse
in the Marvel cinematic universe,
an idea that's been teased in previous movies.
The next "Doctor Strange" movie is even called
"The Multiverse of Madness",
but are there real scientific theories
behind this fictional multiverse?
- I'm Professor Michio Kaku,
Professor of Theoretical Physics.
Let's break down the Marvel multiverse.
[sci-fi whooshing]
- [Narrator] In the first episode of the series,
Loki goes to time jail and is subjected to this
adorable cartoon orientation video.
- [Female Narrator] Countless unique timelines
battled each other for supremacy.
But then the all-knowing timekeepers emerged,
bringing peace by reorganizing the multiverse
into a sacred timeline.
- When you watch this clip, you say to yourself,
"Aw, come on.
I mean this is just a cartoon, it's science fiction."
But believe it or not, elements of that
are actually encoded in the laws of physics.
We do believe that at the beginning of time,
there was chaos.
All of these whirl lines colliding,
quantum fluctuations taking place everywhere.
And out of that came our classical world.
Our Newtonian world.
Isaac Newton said that time is like an arrow.
It fires in one direction, never deviates.
Einstein comes along and says, "No.
The timeline is not an arrow, it's a river.
A river that can speed up and slow down."
The quantum theory says that river of time
can fork into many rivers to create parallel realities.
We branch off continually every time we make a motion,
every time we move.
There could be a universe where you have a twin brother
or a twin sister.
Another universe where you could be a billionaire.
Another universe where you could be a mass murderer.
And believe it or not, you can calculate that number
using quantum mechanics.
All we physicists can do is calculate the probabilities
that these universes can exist,
but our universe, the so-called sacred timeline,
is the common sense universe, the universe of Newton,
it is the dominant timeline
which is singled out in Marvel comics.
According to Marvel comics, a few of these variants
that deviate from our timeline can really mess things up
and create another Big Bang of some sort
where these multiverses collide.
- [Narrator] Right, but does the multiverse
really look like a bunch of squiggly lines?
- There's two ways of visualizing the multiverse.
One way is to look at this long timeline
where we have the past, the present, and the future,
and like a tree, branches keep coming off.
There's another way of looking at it
and Einstein says that are our universe is a bubble,
expanding that peels off a baby bubble
or perhaps two bubbles collide,
giving you a bigger bubble,
and we think that is the Big Bang.
Most of these bubbles pop into existence
and pop right back into the vacuum,
never to be seen again.
And so the vacuum that is the state of nothingness
is teeming with bubble universes being created
and destroyed and that's why Stephen Hawking called it,
"The Spacetime Foam".
Out of this spacetime foam,
the chaos of all these different timelines,
one bubble just kept on going and that is our universe,
or in the Marvel language, the sacred timeline,
the Newtonian world that we see around us.
- [Narrator] All right, so surprisingly
Marvel cinematic universe and contemporary physics theory
seem to align here,
but where do they deviate?
- It deviates on the question of the TVA.
- On behalf of the Time Variance Authority,
I hereby arrest you for crimes against the sacred timeline.
- The TVA are time cops.
They are the Time Variance Authorities.
They pick out variants who will create their own timeline
which will gum up the works
and create a collision between multiverses.
Well, to the best of our knowledge, there is no TVA.
- We are from the future, right?
What is the TVA, I mean, it's from the future.
It sounds from the future, it's pretty future-y.
- [Narrator] Right, so what about time travel then?
There's a lot of time travel happening in "Loki"
and in the Marvel movies.
Is it even possible?
- I have no idea, I mean,
we're talking about time travel here.
Either it's all a joke or none of it is.
- According to Einstein's general theory of relativity,
time travel is possible.
- We're good!
- And in fact, now we have scores of solutions
of Einstein's equations which allow for time travel.
So this is an active area of theoretical research.
But the quantum theory resolves the whole paradox question
of what happens if you alter the past
to make the future impossible?
The answer is you simply alter somebody else's universe.
If you go backwards in time to save Abraham Lincoln
from being assassinated at the Ford Theater,
you saved somebody else's Abraham Lincoln
who looks just like your Abraham Lincoln,
but your Lincoln died.
Your timeline is not altered.
You've altered somebody else's timeline,
because the river of time has forked into two rivers.
- [Narrator] So Marvel is taking some liberties
with the physics of time travel.
Let's take a step back and see how the multiverse idea
was first introduced early on in the MCU.
- Everything is connected, all nine realms.
All nine realms are passing through each other
and gravity, light, and even matter
is crashing from one world to the other.
- When you first see this scene out of the "Thor" movies,
you say to yourself, "Aw, come on, give me a break."
This is just gobbledygook
from some Hollywood script writer's imagination.
But actually, there's some physical basis to reality
in what he said.
In "Thor" comics, we have the nine realms, nine universes.
In physics, we have nine spatial dimensions
and one time dimension.
And so having nine realms in "Thor"
would correspond to the nine dimensions
of space in string theory.
According to Marvel comics,
one dimension has the Earth on it
and another dimension has Asgard.
And what connects the two is the Bifrost Bridge
is a tunnel connecting parallel universes.
It is the Einstein-Rosen bridge.
In 1935, Albert Einstein wrote a paper with his student,
Nathan Rosen, connecting two black holes together.
A black hole is like a funnel.
You take one funnel, take the other funnel upside-down,
join them together, and then you have a bridge
connecting two parallel universes.
- Any questions?
- Yeah, can I have my shoe back?
- [Narrator] In "Spider-Man: Far From Home",
Mysterio lies about being from another universe.
- There are multiple realities, Peter.
This is Earth, dimension 616.
- You're saying there's a multiverse?
- [Narrator] But Peter's mind is blown.
- If you read "Spider-Man" comics,
you know that Peter Parker is a nerd.
His true love is science and he uses science
to defeat his enemies.
- It completely changes how we understand
the initial singularity.
We're talking about an eternal inflation system
and how does that even work with all the quantum,
it's insane.
- [Narrator] Eternal inflation?
That's an actual theory in cosmology.
- The theory basically says
that Big Bangs happen all the time.
Even as we are speaking, multiverses are being created.
That's called eternal inflation.
Inflation is basically the creation of a baby universe,
but these baby universes are being created all the time
in this bubble bath of universes.
Each universe is perhaps with the laws of physics
slightly altered, with the flow of time slightly different.
You can go to any physics conference
where we have Nobel laureates,
directors of major laboratories
talking about cosmology and they'll say
that yes, eternal inflation, this multiverse idea
is the dominant theory in cosmology today.
- [Ancient One] This universe is only one
of an infinite number.
- [Narrator] You can't talk about the Marvel multiverse
without mentioning the Sorcerer Supreme.
- And here we have Doctor Strange hurled
through the Looking Glass,
hurled through the Einstein-Rosen bridge
to another reality.
- [Narrator] Could different universes
actually look like this?
Would the laws of physics be so different?
- The debate among physicists today is
can the laws of physics actually change
in another baby universe?
Stephen Hawking thought so
which means that are our familiar universe,
our benevolent universe that we know and love
may have different laws if you go through a wormhole
to a different universe.
Dark universes, universes of chaos,
universes where there's only darkness.
No stars, only blackness.
Stars do not ignite in these other universes.
Life as we know it cannot exist.
Only the chaos of randomness exist in these other universes.
Is that possible?
And the answer is yes.
- [Narrator] That's a scary thought,
but with new "Loki" episodes
plus the "Doctor Strange" sequel coming soon,
viewers will have the multiverse on their mind
for the foreseeable future.
- Young people know it's science fiction for the most part,
perhaps based on ideas from physics.
But as a consequence, they may decide
to make a career out of it and become a physicist.
That's how I got started.
So it helps to have young people being thrilled
by some of the ideas coming from science,
because they know at the back of the mind,
yes, it is science fiction after all.
But maybe, just maybe, there's a reality
that they can partake of.