Imagine a world in which you’re going out with Margot Robbie, everyone wants you, Michael Phelps takes home a bronze medal (let’s be honest, even writing such a thing is ridiculous), Zayn never left 1D, and the iPhone didn’t really catch on. In our last post, we stressed how vast the universe actually is, (See : The Fermi paradox- why haven’t aliens contacted us yet?), but now we’re taking you one step further, what if there isn’t only one universe? What if there are actually multiple universes out there? If you were feeling small and insignificant earlier, trust us, you’re going to feel a whole lot smaller.

We know what you’re thinking – the existence of multiple universes sounds awfully like science fiction, but we kid you not – this is something physicists have come up with *when sober and perfectly serious*. It all boils down to the fascinating field of *Quantum Mechanics*. (Read: What is a Quantum Computer?– in case you want to brush up on the basic ideas)

**Quantum Mechanics challenged the world view of the time**

Quantum mechanics is hard. Even the best of scientists find it hard. When Quantum Mechanics was first formulated, it went against some absolutely fundamental intuitions of physicists at the time. This is because it replaced deterministic predictability with probabilistic laws, implying that the outcome of fundamental processes can be **completely up to chance. **

So whilst George Lucas may have sounded dramatic, empowering and motivating when says “There’s no such thing as luck,” perhaps a more accurate comment is that of Robert A Heinlein who noted “There is no such thing as luck; only adequate or inadequate preparation to cope with a statistical universe.”

The major problem with Quantum Theory is that whilst we know how to use the mathematical language of Quantum Mechanics to obtain *meaningful results*, a “physical interpretation” is not so clear. Scientists in the past have tried to come of up with all kinds of possible interpretations for what really lies behind the crazy chance-dictated theory – out of which the standard interpretation nowadays is the** Copenhagen Interpretation.** (Don’t worry, we’ll come back to this later)

Not everybody buys the Copenhagen Interpretation, however. In 1957 the PhD student **Hugh Everett, **over a sherry with some friends (this could quite possibly be the most life changing drinking session of all time ) came up with the ** Many Worlds Interpretation of Quantum Mechanics**. According to him, we are living in a

*multiverse of many different universes, each containing a different copy of us*.

**Okay, rewind – Why is Quantum Mechanics so uncertain?**

The basic idea of Quantum Mechanics is that physical systems can exist in a *superposition of different states* – in a way existing in different states at the same time. A famous example of this is **Schrödingers Cat**, a thought experiment where a cat is simultaneously dead and alive. To end up with this crazy situation, a cat is locked into a box and a dose of poison is connected to a quantum experiment in the same box. Depending on the outcome of the quantum process, the poison is released and the cat is killed. Since the quantum process is random, we cannot predict its outcome – meaning that we can’t predict the state of cat without looking at it.

Now as long as we don’t look at the cat, it could be either poisoned and dead, or still happily sat in the cage. We simply have no way of telling what state it will be in, leading to the notion of a superposition of the states ‘dead’ and ‘alive’.

However, when we look inside the box, we will know with certainty how the cat is doing. This ‘measurement’ of the state of the cat destroys the superposition – a process called *the collapse of the wave-function. *This is the core idea of the **Copenhagen Interpretation**, which suggests that every measurement destroys some of the possible paths our universe could have taken.

**What about all the other possibilities that are not realised?**

Everett asked himself the question – what happens with all the possible outcomes of such measurements that are never realised in our universe? If I decide to look in Schrödinger’s cat box, and see that it is happily alive – could there not be another universe, completely separate to ours, that will go on evolving from the other possibility, where the cat has been poisoned?

His theory suggests that at every point a quantum measurement is performed, the universe splits into two (or how ever many possible outcomes there are), giving all possible outcomes of the quantum process a stage to unfold their implications. This leads to the universe branching into a number of possible universes, with our own consciousness taking a particular path through this branching structure. Other copies of our consciousness (i.e. other versions of us) are then present in the other branches.

*Source: wikipedia *

This is shown in the picture above: at the point, where the measurement occurs, the universe branches into two, with the two outcomes of the process (dead and alive) realised in each.

**Okay so then how many of me are there? And aren’t quantum processes really small?**

Remember, we didn’t say that *all* possible things are realised. Only the possible outcomes of *quantum processes *are realised in this multiverse, meaning that in order to make the assertion that a particular scenario (for example, you’re a billionaire after selling your startup and are happily dating your dream girl, living on a private island with 2 Lamborghinis and an Aston Martin parked out front that you don’t generally use because you prefer to travel in your private jet) is actually reality somewhere in the multiverse, you should be able to trace its origin back to at least *one quantum process*.

The foundation behind our ideal life scenario is that the macroscopic and quantum worlds *must be linked*. The trouble is that we do not know the connection between everyday macro-processes to the microscopic world of quantum mechanics. By this we mean that yes, we believe that falling in love is basically a biochemical response, whose interactions follow the laws of quantum mechanics – but we don’t know if quantum mechanics is directly responsible for it. On macro-scales, the probabilistic fluctuations of quantum processes tend to average out, so that we don’t know if its probabilistic nature is a requirement for our everyday phenomena, or whether they are separated by so many layers that any direct connection is impossible.

“Today we cannot see whether Quantum Mechanics contains frogs, musical composers, or morality – or whether it does not.” – Richard Feynman

**Are there other reasons for believing in the multiverse?**

The multiverse theory has been visited time and time again in science fiction. People have come up with a number of different explanations for why parallel universes exist, ranging from the downright bizarre to complicated physics ideas riddled with equations involving string theory. One theory suggests that if we define the ‘universe’ as only that part of space that we can observe, then it’s diameter is 13.7 billion light years. This is because the Big Bang happened 13.7 billion years ago, and in order to be able to observe the edge of the universe, the light emitted there must have reached us.

However, many scientists actually believe that the real extent of space and time is infinite. Now there is only a fixed number of ways in which all the atoms in our universe can be arranged. (A massively large number of ways, but still a finite number.) This means that at some point in this infinity, the universe will end up repeating itself – with other, slightly different versions of you walking around in a far away part of our space – effectively in another universe.

**So when can I start dating Emma Watson – Can we observe the multiverse?**

No. By definition, everything we can observe is part of our universe, so that anything splitting off our universe to form another separate universe can never be observed. This makes the theory untestable.

But you could try and imagine that beyond the stars and solar systems, orbiting around in their galaxies and galaxy clusters, there is structure even beyond our own universe, forming a bubbly foam of universes – the multiverse.

**Is the multiverse accepted by scientists?**

There are a lot of problems with the multiverse theory. First of all, in its formulation it doesn’t predict why some outcomes of quantum processes are more likely that others, since all are supposed to be realised in some universe. In our universe (in real life), we observe consistent probabilities for every given process, which can be predicted using other interpretations of quantum theory.

This would suggest that our consciousness takes some specially consistent path through the multiverse branching, which is not really satisfactory. The second big problem we already pointed out, is that unobservability lies at the very core of the multiverse theory, making any kind of verification or falsification impossible.

A large number of physicists at his time dismissed Everett’s theory, and he had to abridge his Ph.D. thesis on the topic to make it seem less controversial. Disgruntled, he even quit physics altogether and decided to work for the defence industry.

**What’s the point then?**

It’s a cool thought and makes for some good science fiction! Another interesting aspect of Everett’s idea is that it allows for all randomness to be removed from quantum theory, and hence, from all of physics.

Since it cannot be tested and hence falsified, there still exist a number of scientists who believe in Everett’s Many Worlds interpretation . Michael Nielsen observed: “at a quantum computing conference at Cambridge in 1998, a many-worlder surveyed the audience of approximately 200 people… Many-worlds did just fine, garnering support on a level comparable to, but somewhat below, Copenhagen and decoherence.” While Everett himself was scorned at, now, some 60 years later, Everett’s idea radical idea lives on among a small — but growing — subset of physicists.

*Writing an essay or want to learn more?*

*A fascinating book about the life of the man behind the theory: Peter Byrne’s book, The Many Worlds of Hugh Everett III*

*And the stellar award winning BBC documentary on his work called Parallel Worlds, Parallel Lives*

Great to read this #GPS http://bit.ly/2bytC2l