Multiverse

I was browsing YouTube before going to sleep a few days ago and came across a really interesting physics video surrounding the "many-worlds" interpretation of quantum mechanics. I do plan to read more on this but for now here's why I find it so interesting.

Some background

From what I understand, "many-worlds" is another interpretation the math involved in quantum mechanics, ostensibly a more elegant one than the current interpretation most scientists use. To illustrate this interpretation, we can reference the famous Schrödinger's cat thought experiment.

In this thought experiment, Schrödinger imagined an opaque box with a contraption and a cat within it. The first component of this contraption involves a radioactive source, preferably one with a 50% chance of decaying, attached to a sensor. If the source decays, the sensor would detect this and activate the second component, which releases poisonous gas guaranteed to kill the cat. If the source doesn't decay, no poison is released and the cat remains alive. Once the box is closed, we are no longer able observe the cat and are thus unsure of whether the cat is dead or alive.

According the the interpretation of quantum mechanics used today, the radioactive source does not really exist in a state where it is either decayed or not decayed, but instead exists in a superposition in which it is both decayed and not decayed. Only when we measure its state do we force it into a state of either decayed or not decayed. However, since whether the cat is alive or dead is directly tied to whether the radioactive source has decayed, when the box is closed, we would have to conclude that the cat is simultaneously dead and alive. Only by opening the box do we force it into either state.

Okay I hope I explained that well enough. If not, there are some funnier explanations that make much more sense in Silicon Valley (the TV series).

The interpretation

So quantum mechanics is probabilistic. Particles exist in superpositions, and only by measuring these particles (or poisoning cats) can we figure out what their properties actually are. But doesn't this feel unsatisfying? What if there were a better way to understand this probabilistic nature of quantum mechanics that makes it feel much more elegant and beautiful?

That's what the "many-worlds" interpretation aims to do. Again, this is more easily illustrated with the Schrödinger's cat experiment. Instead of the cat being simultaneously dead and alive when we close the box, this interpretation posits that our universe "branches out" into two parallel worlds. In one world, the cat is dead while in the other, the cat is alive. The person that is opening the box also branches into two separate people, and since these parallel worlds can't interact, they'll never know this happened. In each parallel world, the cat is either dead or alive, and opening the box no longer forces the cat into a certain state.

I find this method of explaining the nature of quantum mechanics to be much more elegant, and much easier to grok for the uninitiated. And the math is the same, "many-worlds" is only an interpretation of the underlying math and provides us with a different way of "thinking about the math".

What now?

I've found some interesting explorations for the future after talking about this with my friend Sean and searching around on Google.

My conversation with Sean led to the topic of simulations and how eventually we could simulate the universe and effectively predict the future with the knowledge of every particle in existence. I realised that tied in to quantum mechanics: if quantum mechanics was probabilistic, could we ever really simulate the universe and predict the future? Again, the "many-worlds" interpretation came to the rescue. If the universe branched out every time something like Schrödinger's cat occurs, then the universe wouldn't be probabilistic, which meant that it could be simulated, as long as this branching was simulated as well. How cool is that?

There are some great Reddit discussions surrounding this topic here and here. But after some searching, I realised that most of the discussions I foud online are more on whether the many-world interpretation is even worth discussing or whether it should be relegated to philosophy or classified under metaphysics.

Regardless, I think "many-worlds" interpretation is a fascinating way of seeing the world. There's a certain beauty to how small the universe makes you feel, and having multiple universes intensifies that feeling.