UPDATE I caused great confusion by putting the word “multiverse” in the title, when there is a whole other theory called “the” multiverse. Yet I did this because Hossenfelder herself, mainly in her prior book, Lost in Math: How Beauty Leads Physics Astray, did that. I was trying to keep with her terminology, to broaden the title. In the Many Worlds, which H called a kind of multiverse, the cloned or new universes are created at the instant of measurement. In “the” multiverse, these universes already exist for other reasons. My fault for being unclear.
This is a first of a number of posts as I review Sabine Hossenfelder’s new book Existential Physics, a book which is at turns infuriating, informative, and amusing. I thought it well to begin with agreement: Hossenfelder is as skeptical as I am about the Many Worlds theory(ies), but for different reasons than me.
Her objection, in brief, is that other “worlds” cannot be measured, and if it cannot be measured, it isn’t science. I agree with this, up to a point. More on that point in other posts.
I am not a (small-e) expert on Many Worlds, first proffered by Everett. So I am sure the objection to these theories given below must have been thought of by somebody else, but I have not been able to discover who or where.
I do know of a near criticism, called the problem of preferred bias, which is well known, and about which more in a moment. My objection carries the preferred bias objection through to its logical end, which, as I said, must have been done before.
What is Many Worlds? Quoting from the Stanford Plato link:
The fundamental idea of the MWI [many worlds interpretation], going back to Everett 1957, is that there are myriads of worlds in the Universe in addition to the world we are aware of. In particular, every time a quantum experiment with different possible outcomes is performed, all outcomes are obtained, each in a different newly created world, even if we are only aware of the world with the outcome we have seen. The reader can split the world right now using this interactive quantum world splitter. The creation of worlds takes place everywhere, not just in physics laboratories, for example, the explosion of a star during a supernova.
(I’m not here going to go over the background of quantum mechanics, and will assume you know it. If not, you can find out about anywhere.)
Suppose a Quantum System (QS) can take one of two measurements, 1 or 2. A function of the wave function of that QS gives the (conditional) probabilities of which state will be measured. For us, we do not care what these probabilities are, as long as they are not extreme (zero or one). We will make only one measurement in our universe, and suppose it turns out to be 1. That means, under MW, another universe sees the measurement 2.
Now comes the preferred bias objection, which notes the obvious: why did we get 1 and the other universe 2? Why not the other way around? This natural criticism does not appear to carry much force with believers in MW. After all, even if MW is false, there is no predicting with certainty which measurement we’ll get, so that we see 1 and the other universe sees 2 is just one more mystery.
And then there are similar things like the EPR “paradox” and entanglement, which nobody understands (it is said, but see Wolfgang Smith). An entangled pair of particles is let loose, one goes left, one right, and after a long time, long enough that the distance is so great the particles cannot communicate with each other, the left is measured spin up, and, voila, the right is spin down. How? Textbook quantum physics has no answer: it just accepts. So why complain about which universe gets which measurement?
That is where the preferred objection ends, and here is where mine begins.
It is not just that we see 1 and the other universe sees 2, it is that the other universe does not also see 1.
If we see 1, then according to MW, another universe must see 2. But that means there must be some greater cause, an Overseer, which ensures the second universe does not also see a 1. This is very similar to the EPR situation, where there must be some non-local cause ensuring one particle is spin up, the other spin down. But it’s not quite the same, as we now see.
The MW says there are different universes, not just different areas of space in one universe as in EPR, which makes non-locality even more puzzling. That Overseer must operate in such a way that every universe gets its own unique measurement, and that no other universe duplicates a measurement of any other universe.
What is this cause, this Overseer? A new force of the universe? We can wave our hands, as materialists do now with EPR and say “Who knows?” And so shrug this objection off.
But it’s much worse than it sounds. Much worse. For in some Quantum Systems we not only have the possibility of a finite number of measurements, as in our first example, but there are some measurements which might be any of an infinite number. So it’s not only 1 or 2, but it’s 1 or 2 or 3 or …, and so on forever.
This makes the Overseer’s job particularly difficult. Not just in sorting out which universe gets which measurement, but in making it so. Pause here. Think. The Overseer has to have infinite power to sort out the order, and he must create the proper order, according to MW, instantaneously.
So we not only require the Overseer to have infinite power to assign, in an instant, a unique measurement to each universe, but he must also have omniscience, he must be all-knowing, to sort out, in the instance of assignment, which universe gets which measurement so that there are no duplicates. Amazing.
That whole problem is made worse if, as some say, the infinity of possible measures is not just countable, but uncountable. If space is continuous, then a measurement of location is along the continuum, which is a much, much larger infinity than our countable infinity. The power and knowledge required of the Overseer is inconceivable greater here.
Whether or not that is so, countable or uncountable, the Overseer must be operating constantly, expending infinite amounts of energy every time a quantum measurement is made. And with no time off, or the multiverse comes to a halt.
Now it could be that the Overseer is God, who is both all powerful and omniscient. If that is so, then Many Worlds is not impossible. Or, rather, it does not seem impossible based on power considerations alone.
And if this Overseer is not God, and it just some new force, then there is no multiverse. For the Overseer’s actions tie all universes together, necessarily, because there are no duplicate measures in any individual universe. There must be a connection of all universes, at least through the Overseer. So it seems there is no multiverse at all, but one big universe, which can, and do, communicate with each other. Albeit through the Overseer. Who, or which, might be open to probing on questions of measurement decisions.
Incidentally, even in you ignore the infinities, and have only finite measurements, as with EPR, there still be something using a power to cause the measurements. That finishes my objection. If anybody has seen it before, please let me know.
This is one of the theories entertained by physicists who hold with an ontology that excludes potentiality as a form of existence. More on that in future posts.
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