The multiverse

Everything that exists today once exploded outwards from a tiny point in space. Billions of years ago, the Big Bang formed all matter – all the tiny building blocks that make up galaxies, stars, planets and you. This immense explosion even created the laws of physics – the rules that govern our universe – but what if this universe isn’t the only one that was created?

Some scientists think there may be a countless number of universes, all with their own laws of physics and their own unique map of the stars, separate from the one we know. It’s an idea that challenges everything about the way we think, and there are even several different theories as to how these multiple universes might be created. Welcome to the multiverse theory.

Many worlds

American physicist Hugh Everett proposed a ‘many worlds’ theory in the late 1950s. It suggests that trillions upon trillions of copies of this universe are created every millisecond, splitting like forks in a road.

There’s a copy of this universe where you decided to stay in bed for an extra minute this morning and a copy where you got up one minute earlier. However, the cause of these splitting universes is entirely outside of your control.

Everett’s Many Worlds theory has its roots in quantum mechanics. All of these world-splitting events happen on a subatomic level (in particles that are smaller than atoms). If we take a particle in the corner of a room as an example, the many worlds theory states that there will be parallel universes that exist wherever that particle moves to – one whole universe for every location of the particle. The same is true with every other particle too. That also means there’s a mind-boggling number of possibilities in each of those universes; there’s a universe where you’re a pop star and one where you’re prime minister. There’s even a universe where you wrote these words!

Speaking to The Week Junior Science+Nature, theoretical physicist Sean Carroll explains the best way to think about coexisting universes is as if they were twins. Sean explains that in the many worlds theory “there are many copies of you, but they are different people”.

Multiverse

The multiverse could be described as a “universe of universes”, created seconds after the big bang, like bubbles blowing from a bubble wand. Our universe could be one of many, but how would we know and would visiting one of these distant universes ever be possible?

Author Brian Clegg thinks not. He told Science+Nature that there are potentially ways that some information about other universes “leaks through”. What we know about the creation of this universe is entirely down to the speed of light; if light has been travelling towards you for one year, what you see is one year ago. With the multitude of ways we’re finding to look back in time, there may be ways we could detect “echoes” of what existed before this universe and whether, at the point of the Big Bang, multiple universes were, in fact, created.

Sean Carroll explains that the “many worlds” are not in space but parallel to our own. Even if there are other universes humans could physically cross to, we would have to travel for billions of years to reach the edge of our universe, if such a thing even exists. Most scientists believe our universe continues to expand.

Experts can’t agree on whether the many worlds and multiverse theories are science fiction or science fact, purely because they can neither be proven nor disproven. So although it might not be a physical experiment, it sure is a mind-melting one!

Comic book multiverses

If you’re a superhero fan, you might recognise the term “multiverse”, which is used a lot in comic book franchises to describe moments where characters from one story appear in the plot of an entirely different one.

In the Marvel Cinematic Universe, there are lots of examples of this. Spellcaster Doctor Strange often draws on energy from other realities to safeguard his own and in the finale to the Avengers saga, Endgame, the Avengers create parallel universes to complete their mission of reviving half of all life in their universe.

Although stories of many worlds and multiverses might exist only in the realms of fantasy for us, it’s only by asking these big, brain-busting questions that we’re able to challenge ourselves and stumble across new discoveries.

Only in the last few hundred years has humankind understood more about the universe, the secrets it holds and what might have caused the Big Bang. Even then, there are still many questions we don’t yet have answers to.

As technology and science continues to progress, scientists will slowly unlock more about the cosmos. One day, the thought of this universe being the only one in existence could sound as silly as the theory that the Earth is flat, even though lots of people used to believe that.

First published in The Week Junior Science+Nature, issue 45, February 2022.