Discover Magazine has an interesting article up discussing a perennial favorite: the fine-tuning of the universe for life. I got a bit nervous when I saw the title:
Science’s Alternative to an Intelligent Creator: the Multiverse Theory
That makes it sound like scientists devised the multiverse idea strictly as a desperation move to counter all that annoying God-talk. In reality physicists have been seriously discussing the idea of a multiverse for decades, and quite a lot of work in physics is pointing in that direction. The multiverse does seem to follow naturally both from recent work in string theory as well as the inflationary Big Bang theory. This is a considerable improvement over the nothing at all on which the God hypothesis rests.
The article’s beginning sadly plays up the desperation theme:
Call it a fluke, a mystery, a miracle. Or call it the biggest problem in physics. Short of invoking a benevolent creator, many physicists see only one possible explanation: Our universe may be but one of perhaps infinitely many universes in an inconceivably vast multi verse. Most of those universes are barren, but some, like ours, have conditions suitable for life.
The idea is controversial. Critics say it doesn’t even qualify as a scientific theory because the existence of other universes cannot be proved or disproved. Advocates argue that, like it or not, the multiverse may well be the only viable non religious explanation for what is often called the “fine-tuning problem”–the baffling observation that the laws of the universe seem custom-tailored to favor the emergence of life.
This is a common trope in discussions of this subject, but it seems a bit off to me. Surveying what we know of our universe, it seems that the vast, vast majority of it is not hospitable to life. In the incredible vastness of space we know of one little planet that can sustain life over part of its surface some of the time. That doesn’t look like a universe primed for life. It looks like a universe where life won the lottery.
Happily, from here the article actually gets quite good.
Linde has spent much of the past 20 years refining that idea, showing that each new universe is likely to have laws of physics that are completely different from our own. The latest iteration of his theory provides a natural explanation for the anthropic principle. If there are vast numbers of other universes, all with different properties, by pure odds at least one of them ought to have the right combination of conditions to bring forth stars, planets, and living things.
“In some other universe, people there will see different laws of physics,” Linde says. “They will not see our universe. They will see only theirs. They will look around and say, ‘Here is our universe, and we must construct a theory that uniquely predicts that our universe must be the way we see it, because otherwise it is not a complete physics.’ Well, this would be a wrong track because they are in that universe by chance.”
Most physicists demurred. There wasn’t any good reason to believe in the reality of other universes–at least not until near the beginning of the new millennium, when astronomers made one of the most remarkable discoveries in the history of science.
Fascinating stuff. The article goes on to discuss the discovery of dark energy and recent work in string theory. Eventually we come to this:
When I ask Linde whether physicists will ever be able to prove that the multiverse is real, he has a simple answer. “Nothing else fits the data,” he tells me. “We don’t have any alternative explanation for the dark energy; we don’t have any alternative explanation for the smallness of the mass of the electron; we don’t have any alternative explanation for many properties of particles.
“What I am saying is, look at it with open eyes. These are experimental facts, and these facts fit one theory: the multiverse theory. They do not fit any other theory so far. I’m not saying these properties necessarily imply the multiverse theory is right, but you asked me if there is any experimental evidence, and the answer is yes. It was Arthur Conan Doyle who said, ‘When you have eliminated the impossible, whatever remains, however improbable, must be the truth.’?”
Quite right. The hypothesis of a multiverse explains a lot of data, and is strongly suggested by the best physical theories we have. I can understand why it is a bit frustrating as an hypothesis, since the best we can hope for is indirect evidence that it is correct. But what, exactly, is the reason for rejecting it? Is there any particular reason for thinking that the forces that created our own universe did not also create other universes at the same time? The multiverse hypothesizes more of the same. The God hypothesis hypothesizes something wildly and flamboyantly at odds with everything we know about the universe.
But some demur:
For many physicists, the multiverse remains a desperate measure, ruled out by the impossibility of confirmation. Critics see the anthropic principle as a step backward, a return to a human-centered way of looking at the universe that Copernicus discredited five centuries ago. They complain that using the anthropic principle to explain the properties of the universe is like saying that ships were created so that barnacles could stick to them.
“If you allow yourself to hypothesize an almost unlimited portfolio of different worlds, you can explain anything,” says John Polkinghorne, formerly a theoretical particle physicist at Cambridge University and, for the past 26 years, an ordained Anglican priest. If a theory allows anything to be possible, it explains nothing; a theory of anything is not the same as a theory of everything, he adds.
This is a bit rich coming from Polkinghorne, given that he has written several books arguing that it is the most natural thing in the world to believe in the Christian God. Talk about an hypothesis that allows you to explain anything!
But his comment is incorrect anyway. The multiverse hypothesis is not some all-purpose explanation for any current mystery of physics. It explains a very specific mystery, the illusion of fine-tuning, and does so with a very simple hypothesis that is strongly suggested by current theorizing.
As the article suggests, it is conceivable that we will someday obtain strong indirect evidence for the multiverse, but it is likely always to be speculative. It seems to me that in pondering these questions we are simply coming to the end of what physics can tell us. At some point the data runs out, and we must simply be content with a certain amount of mystery in our lives. I have no problem with that.
But I do have a problem with those who hypothesize into existence an all-loving, all-powerful God as a solution to any small mystery of life turning around and giving lectures on what is and is not a desperation move.
So let me close with a few words in defense of the multiverse:
Supporters of the multiverse theory say that critics are on the wrong side of history. “Throughout the history of science, the universe has always gotten bigger,” Carr says. “We’ve gone from geocentric to heliocentric to galactocentric. Then in the 1920s there was this huge shift when we realized that our galaxy wasn’t the universe. I just see this as one more step in the progression. Every time this expansion has occurred, the more conservative scientists have said, ‘This isn’t science.’ This is just the same process repeating itself.”
Take that anti-multiversers!