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Our future, our universe, and other weighty topics

Sunday, January 8, 2017

Pretzel Logic of the Multiverse Fantasists

Physicists who speculate about the multiverse (a vast collection of universes) are very good at math, but their essays are often shockingly poor at logic. An example is a recent essay by string theorist Tasneem Zehra Husain.

Husain states this early in the essay: “The same process that created our universe can also bring those other possibilities to life, creating an infinity of other universes where everything that can occur, does.” The origin of our universe in the supremely mysterious Big Bang is a total mystery. There is no understanding whatsoever of any natural or physical process that can create a universe or did create our universe. No physicist has any understanding whatsoever of a universe creation process. There is no evidence for any physical universe beyond our own. As for the notion of a universe-creating process creating not just one other universe but an infinity of them, that's just runaway speculation no more substantial than speculating about an infinity of unicorn kingdoms.

Husain spends most of her essay talking about how scientists “feel about the multiverse.” I guess that may be a good way to fill up a long essay when you have no evidence to back up your central claim (the idea of a multiverse, that there are countless other universes). Husain offers this reason for believing in the multiverse:

The multiverse explains how the constants in our equations acquire the values they do, without invoking either randomness or conscious design. If there are vast numbers of universes, embodying all possible laws of physics, we measure the values we do because that’s where our universe lies on the landscape. There’s no deeper explanation. That’s it. That’s the answer.

I give in this essay six reasons why the multiverse idea is quite worthless for explaining the fitness of our universe. To explain something means to discuss one or more causal factors that caused something or made that likely. You do not do any such thing if you say (as multiverse theorists do) “There are an infinity of universes, and our universe just got lucky.” It is also 100% superfluous to imagine the other universes in such a case, because you can just as easily say “Our universe just got lucky” when imagining that no more than one universe exists. You do not increase the likelihood of our particular universe getting lucky by imagining other universes (and, more generally, you do not increase the likelihood of success on any one particular random trial by imagining an increased number of random trials). So the fine-tuning of our universe (including its physical constants) does not provide any rationale for believing in a multiverse. The “why was our universe so lucky" question looms with equal weight, regardless of whether there is or is not a multiverse.

When used to explain cosmic fine-tuning, the multiverse idea therefore pulls quite the astonishing trick: it brings in infinite baggage, but with zero explanatory value. Imagine if some theorist were trying to explain the features of one rabbit by theorizing that there are an infinite number of rabbits. But suppose that such a theory did actually nothing to explain the features of that one rabbit. That would be kind of the ultimate “epic fail,” rather like some President paying all the money in his country to buy some contraption that didn't even work. Such is the epic fail of the multiverse theorist in this regard. 

Referring to some other thinker, Husain states the following:

The multiverse, he says, “could open up extremely satisfying, gratifying, and mind-opening possibilities.” Of all the pro-multiverse arguments I heard, this is the one that appeals to me the most.

Your reasoning is in very bad shape indeed if your best argument for the existence of something is that it opens up “satisfying” or “gratifying” possibilities. That reeks of some kind of wish-fulfillment fantasizing rather than hard thinking.

Husain also gives us this cringe-inducing howler: “Logically speaking, an infinity of universes is simpler than a single universe would be—there is less to explain.” No, very obviously an infinity of universes is infinitely less simple than a single universe, because it involves infinitely more to explain.

When our physicists give us this type of “black is white, squares are round” type of talk, this type of Orwellian doublespeak, I wonder whether we have ended up in some strange reality in which words may be used in exactly the opposite of their dictionary meaning. Faced with such absurdity, it is helpful to have a few reality checks such as the ones below.

  • There is no evidence for any physical universe beyond our own, nor can we can imagine any observations that we might ever have that would give us such evidence (anything we might observe would be part of our universe, not some other universe).
  • The idea that there are many universes beyond our own does nothing to explain the life-favorable characteristics of our universe.
  • The "cosmic inflation" theory of the exponential expansion of the universe during part of its first instant is not well supported by evidence, and does not intrinsically require any universe beyond our own.
  • We have no scientific understanding of what caused the beginning of our universe, nor is there any physical understanding of why the universe is so fine-tuned.
  • There is no evidence at all for string theory. String theory has thus far been pretty much a 35-year waste of time, the biggest flop in the history of modern physics. String theory is based on another theory called supersymmetry, which is rapidly dying, because experimental results from the Large Hadron Collider have all but closed the door on it (as discussed here).

From reading an essay such as Husain's, you might get the impression that the multiverse is some hot topic that is dominating the papers of theoretical physicists. But it isn't.

Below is a diagram from a scientific workshop. The line at the bottom represents the fraction of papers that have been written about the multiverse.

As we can see, it seems there are very few scientific papers actually being written about the multiverse.

There is a way for you to make your own graph similar to this graph, using the technique below.
  1. Go to the arXiv server for scientific papers, where copies of all physics and cosmology papers have been posted for the past twenty years.
  2. Click on the Advanced search link, taking you to this page.
  3. Type in a search topic, and limit the results to a particular year.
  4. Note how many papers appear in the search results, and add that number to a row on a spreadsheet.
  5. Graph the results.
Below is a graph I made using this technique. The number of papers on the supersymmetry theory (also called SUSY) should probably be twice as high, because I searched using only SUSY as a search string, without using “supersymmetry” as a search string. 


My graph above is consistent with the first graph. What we see is that the number of scientific papers written about a multiverse is only a tiny fraction of the papers written about other speculative topics such as string theory, cosmic inflation theory, and supersymmetry theory.

Here are some numbers from recent years.

2013 2014 2015 2016
String theory papers 365 419 377 295
Inflation theory papers 276 465 402 339
Multiverse papers 8 10 16 16
SUSY papers 105 104 114 71

Why are there so few papers written about the multiverse? Is it because physicists don't like to speculate? No, they love to speculate, as shown by the 1000+ speculative papers listed in the table above (string theory, cosmic inflation theory, and SUSY are all extremely speculative theories).

The reason so few papers have been written about the multiverse is pretty much that there's no factual basis on which to write a multiverse paper. There's no “there” there.

Don't let Husain fool you. The multiverse is just a “castle in the sky” that a few fantasist physicists are building, from a few gossamer threads of speculation. 

Postscript: See Peter Woit's post about "Fake Physics," with some relevant comments.