Alex asked:

Some physicists are currently supporting a new theory that there exist an infinite number of parallel universes beyond our own, some of which contain an exact copy of you and me, with every action we will ever or have ever done. What does this mean for uniqueness and legacy? Can you offer some optimistic mindset for someone worried about retaining some degree of uniqueness? Thanks a lot!

Answer by Helier Robinson

The theory is not new: J.B.S. Haldane, in his book Possible Worlds considered it nearly a century ago. He pointed out that if there were an infinity of them then not only would there be another one exactly like ours in every respect, but there would be an infinity of them, and another infinity which differed from ours by one molecule being different, and another infinity in which every one of your wishes came true. An infinity of infinities of differences.

In fact the physicists you speak of do not suppose an infinity, just a very large number of them. They do this in order to explain the fact of cosmic coincidences. There are a number of things in physics and cosmology which are unexplained by modern theories: the values of the strengths of the four forces (gravitation, electromagnetism, the strong force, and the weak force) and their ratios, the masses of the numerous of wave particles, etc. They could all have been different, but if any of them were we could not exist because stars would not form, or they could form but be very short lived, or they live long but would never go supernova. In any of these situations heavier elements would never form and life would be impossible. But, seemingly by coincidences, the values are just right and so life formed on our planet (and presumably on billions of other planets) and we are here.

One explanation of these coincidences is that of a huge number of parallel universes, in each of which all of the values are randomly determined. In a few of them the values will be just right for life. Ours is one of them, because we are here. This is called the Anthropic Principle.

It’s a very bad theory, in my opinion, for two reasons. One is because it disobeys Occam’s Razor outrageously. Occam’s Razor is the principle, as William of Occam put it, Do not multiply entities beyond necessity; or, in modern terms, do not invent more theoretical entities than are needed to explain the empirical facts. A huge number of parallel universes is far, far too much multiplication of entities. Secondly, in science a theory must be either verifiable or falsifiable experimentally, and there is no way such universes, which do not interact with ours, could be; so they are at best unscientific, just bad metaphysics.

There are two other points I would like to make. One is that infinity is an incoherent concept, invented or used by people who, not knowing the limit of something, declare it to have no limit. It is like the concept of chance, announced by people who do not know the cause or causes of something. Secondly, there are no degrees of uniqueness: something is either unique or it is not. To speak of something being nearly unique is as meaningless as saying that it is nearly infinite. So your main questions are answered: there are nor parallel universes and you are unique.

And by the way, if you are curious about cosmic coincidences, look at Lee Smolin, The Life of the Cosmos, O.U.P. 1997. Or consider Leibniz’s claim that the world is the best of all possibles (in which the coincidences have to occur) and exists necessarily because it is the best, so no others exist.