Mainstream Media Muddled Multiverse Mishmash

I have no problem with the title of the recent BBC article on the multiverse. It is “Why there might be many more universes beside our own.” Sure, there might be – anything's possible. My problem is with the subtitle of the article, which is: “The idea of parallel universes may seem bizarre, but physics has found all sorts of reasons why they should exist.” This is not accurate, and the article fails to provide any reasons why “parallel universes” should exist.

The first reason the article gives for thinking that there might be multiple universes is that our universe might have an infinite amount of matter, and if so, there might be duplication – such as some other galaxy exactly like our galaxy in all respects (including a double of you). But that's not really imagining another universe – it's imagining an infinite universe with large-scale duplication. There is no possibility that we could ever verify that such a large-scale duplication is likely, because we have no prospect of ever verifying that the universe does have an infinite amount of matter. Whatever observations we make in a finite span of time, they will never be able to justify a conclusion that the amount of matter in the universe is infinite. Even if you verified the existence of a trillion trillion trillion trillion galaxies, you would have no basis for assuming that there was more than a trillion trillion trillion trillion trillion galaxies. So the very idea of a universe with infinite matter is not provable, and not scientific. It certainly does not count as a “physics reason” for believing in a multiverse.

The article then describes the cosmic inflation theory, which is actually a large group of theories with a few similarities. Exaggerating the case for this theory (as many scientists do whenever discussing a theory that fits their ideological inclinations), the article claims that the match between predicted variations in the cosmic background radiation and those predicted by the inflationary theory are “almost unbelievably good,” suggesting that the theory is correct.

But that's misleading. Cosmic inflation theory (not to be confused with the more general Big Bang theory) started out around 1980, when we already knew pretty much how small the variations in the cosmic background radiation were. During the past 35 years (as our knowledge of such variations has slightly increased) physicists have continually fiddled with different varieties of the cosmic inflation theory, trying to get some version that matches observations. Most versions of the cosmic inflation theory do not match observations, and any that do are those that have been fiddled with and tweaked to try to match observations as those observations came in. Given such a situation, the evidence value of such a match between “prediction” and observation is minimal. We do not at all have a situation where the theory predicted something very surprising, which was much later confirmed to be exactly true.

In fact, there are many problems with the cosmic inflation theory, such as its excessive requirements for fine-tuning (the theory was created to help get rid of some fine-tuning, but may require more fine-tuning than it gets rid of). Far from predicting the cosmic background radiation variations exactly, as the BBC article suggests, the theory actually is hard to reconcile with one of those variations – the feature known as the Cold Spot. A cosmologist quoted here puts it this way:

[The inflationary model] “predicts that today’s universe should appear uniform at the largest scales in all directions. That uniformity should also characterize the distribution of fluctuations at the largest scales. But these anomalies, which Planck confirmed, such as the cold spot, suggest that this isn’t the case… This is very strange. And I think that if there really is anything to this, you have to question how that fits in with inflation…. It’s really puzzling.

The BBC article then tries to make the leap from the general idea of the cosmic inflation theory to a particular variation of that theory called the eternal inflation theory, which imagines many bubble universes. This eternal inflation theory is not at all verified nor well supported, so such an idea does not qualify as a “physics reason” for believing in a multiverse. We have zero evidence for the existence of any other “bubble universe” outside of our own (or any type of universe outside our own).

The BBC article then attempts to blend from an inflationary multiverse (the idea of lots of little bubble universes) to what is called the string theory landscape – the completely speculative idea that there are many different universes which each have a different version of string theory physics. There is no factual basis for such a leap, as there is currently no evidence that string theory is a correct theory. 

 Strange galaxy in an alternate universe 

The article implies that such an idea of a multiverse consisting of many universes may be helpful in explaining the fine-tuned features of our universe. But it isn't. This is because one does not increase the likelihood of success on any one trial by increasing the number of trials. If a universe as fine-tuned as ours is a zillion-to-one shot, it's still exactly the same zillion-to-one shot if you assume there are a zillion other universes. Increasing the number of universes may increase the chance that some universe may be accidentally habitable, but we are not interested in the probability of some universe being accidentally habitable. We are interested in the probability of our universe being accidentally habitable. That probability is not increased by even 1 percent by assuming other universes.

As physicist V. Palonen states in this scientific paper:

The overall result is that, because multiverse hypotheses do not predict the fine-tuning for this universe any better than a single universe hypothesis, the multiverse hypotheses fail as explanations for cosmic fine-tuning. Conversely, the fine-tuning data does not support the multiverse hypotheses.

Next the BBC article touches on Lee Smolin's theory of cosmological natural selection. The article describes it like this:

This suggested to Smolin that a black hole could become a Big Bang, spawning an entire new universe within itself. If that is so, then the new universe might have slightly different physical properties from the one that made the black hole. This is like the random genetic mutations that mean baby organisms are different from their parents.

The theory in question is a heap of crazy speculations. We have no basis for concluding that black hole collapses lead to new universes, nor is there any basis for concluding that such a new universe would have different laws and physical constants from our universe. Even if such a theory were true, it would not at all explain our universe's fine-tuning, contrary to Smolin's claims. This is because in order for you to have a universe in which black holes are forming in the first place, a universe needs to already have an incredible amount of fine-tuning – the fine tuning needed for atoms and for stars (the predecessors of black holes) to exist. There are specific reasons why we should not expect stars to exist in a millionth of universes with random laws and fundamental constants. You can't explain the universe's fine-tuning if you start out with a universe that is fine-tuned in the first place.  See here for some other reasons for rejecting Smolin's theory.
 

The BBC article then touches on M-theory, a version of string theory. This is also speculation for which there is no evidence. Its main purpose currently seems to be to create busy work for mathematicians who can play around with speculative equations because they can't think of something more productive to do.

Finally, as if building up to some muddling climax of confusion, the BBC article touches on the “many worlds” theory of parallel universes. This is the crazy idea that all physically possible realities are actualized – so there must be some universe in which your dog is the ruler of America. Thankfully there is not the slightest evidence for this morally ruinous theory, which tells us that any absurdity you can imagine is just as real as the news you watch on television (an idea that is a perfect prescription for moral indifference).

In short, the BBC article fails to provide any substantiation for its subtitle claim: “The idea of parallel universes may seem bizarre, but physics has found all sorts of reasons why they should exist.” The article fails to produce a single physics reason why they “should exist.” The article tacitly admits such a thing near its end, when it says “these ideas lie on the border of physics and metaphysics” and then attempts to rank the plausibility of multiverse scenarios “in the absence of any evidence.” Yes, we finally have a confession that we are in the realm of groundless speculation – drifting off into metaphysics “in the absence of any evidence.” So why did the article appear in the Science section? 

Postscript: See page 39 of this paper for a discussion of how only a certain small range of the fundamental constants will allow for the existence of stars.  If we assume that the gravitational force can have any value between its current value and a value as strong as the strong nuclear force, then "the stable star-permitting region" of parameter space occupies less than a trillionth of a trillionth of a trillionth of the total parameter space.