# Is there other intelligent life in our galaxy or an alternate universe?

Dec 14, 2017

A few thoughts...

#### Explanation:

Galaxies are not universes. They are gravitationally bound collections of stars with as few as ${10}^{8}$ or as many as ${10}^{14}$ stars. It is true that when we first found that there were other galaxies, they were dubbed "island universes", which is quite an attractive term, but the universe is everything that we know to exist: galaxies, clusters of galaxies, superclusters, the lot.

There are estimated to be somewhere between $2 \times {10}^{11}$ and $2 \times {10}^{12}$ (or possibly more) galaxies in the observable universe.

An "alternate universe" - if there is such a thing - is quite a different idea. For a start note that "universe" is supposed to mean "everything that exists". So by definition there is nothing else. Even if in a sense there "is" another universe, we need to think about the meaning of "is". If there is no interaction with our universe then there is no common frame of reference for time and so no meaning to "is".

If there is some kind of relationship with our universe then it could take the form of a branching of reality. For example, in the many worlds interpretation of quantum mechanics it is supposed that every possible transition actually occurs in some reality. This model gives rise to a ridiculously huge number of alternative universes, growing all of the "time". This seems to me to be a rather unattractive and counterintuitive model, but it can simplify some calculations.

Dec 14, 2017

Hmmm. That rather depends on your definition, and on how you interpret a rather troubling finding at the opposite end of physics (quantum theory.)

#### Explanation:

Firstly, let’s clarify a little. We suspect the galaxy we are in (the Milky Way) contains many (some would say many times many) intelligent life forms. The answer to this is given by solving the Drake equation and I would strongly encourage you to do this yourself (https://en.m.wikipedia.org/wiki/Drake_equation) It isn’t too scary, just guess a series of probabilities and multiply the total by the number of stars in the galaxy. Most people get between 1 and 10,000 intelligent civilisations currently existing in just our galaxy.

Next, your main question was about other universes. This is considerably more difficult to answer as, by definition, no energy (which includes information) can enter or leave our universe. That’s what ‘universe’ means. Thus we can only speculate? Well, yes and no. It all depends on how you interpret the results of a very simple, mind-blowing experiment in quantum physics called the diffraction of electrons.

In essence, a stream of electrons pass through one of two narrow slits. If you do this with light you get an interference pattern as predicted by wave theory. We do not expect that particles, like electrons would do this too, but the weirdness of that branch of physics was only just becoming apparent.

If you repeat the experiment with just one electron at a time it also builds up the same pattern over time. It’s as if either the electrons interfere with each other in the past/future or a single electron passes simultaneously through both slits. Both are impossible to our understanding of particles in space and time as we know them.

We needed a new view of very very small things and this is what quantum physics provides. Importantly, if you cover one slit the pattern disappears, and if you “peek” to see where it goes, the pattern also disappears and the electrons behave like “normal” particles, passing through one slit or other but never both.

When the “probability function” collapses to form an ‘outcome’ in our universe some propose that our universe splits into two. One where the electron went through the right hand slit, and one where it passed through the left hand slit. This implies that every event or choice in our universe causes it to split in two, yielding a ‘multiple universe’ or multiverse.

Sorry for the long, long answer .... great question :D