Belief in infinite doppelgangers

I mentioned that Brian Greene is sympathetic to many-worlds theory without endorsing it, but he definitely believes in a multiverse that is almost as goofy:

Physicists Brian Greene and Max Tegmark both make variants of the claim that if the universe is infinite and matter is roughly uniformly distributed that there are infinitely many “people with the same appearance, name and memories as you, who play out every possible permutation of your life choices.”

Greene's 2011 book said:

“[I]f the universe is infinite there’s a breathtaking conclusion that has received relatively scant attention. In the far reaches of an infinite cosmos, there’s a galaxy that looks just like the Milky Way, with a solar system that’s the spitting image of ours, with a planet that’s a dead ringer for earth, with a house that’s indistinguishable from yours, inhabited by someone who looks just like you, who is right now reading this very book and imagining you, in a distant galaxy, just reaching the end of this sentence. And there’s not just one such copy. In an infinite universe, there are infinitely many. In some, your doppelgänger is now reading this sentence, along with you. In others, he or she has skipped ahead, or feels in need of a snack and has put the book down. In others still, he or she has, well, a less than felicitous disposition and is someone you’d rather not meet in a dark alley.”

I am not sure which is crazier, this, nonlocality, denial of free will, or many-worlds theory.

When some non-physicists like Deepak Chopra says stuff like this, they get mocked by physicists.

Greene would say that there is someone like in a distant universe, but he regularly blogs in favor of quantum computing instead of against it.

Why do physics professors like Greene and Tegmark get a free pass?

The above paper addresses several problems with the Greene-Tegmark view.

I think the problem is more basic. Once you start talking about infinities like that, you have left the realm of science. You as might as well be talking about angels dancing on the head of a pin.

You might be surprised that a mathematician like myself would be so hostile to infinities. After all, mathematicians use infinities all the time, and know how to deal with all the paradoxes. But the infinities are short-hands for logical arguments that make perfect sense.

What do you do with beliefs that you have no free will, and you have infinitely many copies of yourself in distant universes leading parallel lives? Or that what you think is a personal decision is really splitting yourself from an identical right here in this universe, but invisible? In some of these universes, bizarre things happen, like a tiger giving birth to a goat. But why don't we ever see such nonsense? You can say that those events are unlikely, but there are universes where they happen all the time. How do you know that we are not in one?

I am just scratching the surface of what a nonsensical world view this is.

Historians of science wonder how Galileo and Newton had such coldly rational views towards analyzing the mechanics of simple experiments or celestial observations, and yet they completely accepted all sorts of biblical religious that most scientists today say is just stupid mysticism. How is that possible?

Someday, Greene, Tegmark, and many other leading physicists will be seen similarly. They wrote some good scientific papers, but they also believed in total nonsense that a child could see was ridiculous.

Here are some mathematicians talking about infinities, from a recent podcast:

Dr. Garibaldi decided to talk about a theorem he calls the unknowability of irrational numbers. Many math enthusiasts are familiar with the idea of countable versus uncountable infinities. ...

The set of all real numbers—all points on the number line—is uncountable, as Georg Cantor proved using a beautiful argument called diagonalization. The basic idea is that any list of real numbers will be incomplete: if someone tells you they’ve listed the real numbers, you can cook up a number their list omits. ...

The end result is, in Dr. Garibaldi’s words, sort of hideous. Any classes of numbers you can describe explicitly end up being merely countably infinite. Even with heaping helpings of logarithms, trigonometry, and gumption, the number line is more unknown than known.

So all the real numbers we know anything about are countable. All our knowledge is countable. The reals are uncountable, so almost all real numbers are unknowable in some sense.

Mathematicians all understand this, and it is important in some mathematical arguments, but it doesn't really have any grand philosophical implications. Knowledge is countable because of they way knowledge is defined and accepted. Actual things are finite.

You could say that there is some real number that perfectly encodes your doppelganger, or records all your memories, or predicts all your future behavior, or any other weirdo fantasy you have. We cannot construct that real number, or say anything interesting about it.

You can fantasize all you want about alternate realities, but the physics and the math don't really add anything.