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Our future, our universe, and other weighty topics


Wednesday, March 2, 2016

The Dart of the Vacuum Miracle Hit the Distant Bullseye

Perhaps the biggest mystery in physics is why the vacuum of space has so little energy in it. Although it may seem intuitive to think of the vacuum of space as empty, quantum mechanics predicts that it should be something very different: something incredibly packed with energy, a dark energy caused by all kinds of quantum fluctuations. In a TED talk a physicist discussed this:

Now, if you use good old quantum mechanics to work out how strong dark energy should be, you get an absolutely astonishing result. You find that dark energy should be 10 to the power of 120 times stronger than the value we observe from astronomy. That's one with 120 zeroes after it. This is a number so mind-bogglingly huge that it's impossible to get your head around. We often use the word "astronomical" when we're talking about big numbers. Well, even that one won't do here. This number is bigger than any number in astronomy. It's a thousand trillion trillion trillion times bigger than the number of atoms in the entire universe.

Instead of the vacuum of space being filled with this kind of energy (which would give each square meter of empty space far more density than steel), we have a vacuum of space that is almost entirely empty of matter and energy. This discrepancy between reality and prediction is sometimes called the vacuum catastrophe. But for reasons I discuss here, it really should be called instead the vacuum miracle. Having a vacuum that is relatively empty is both exceptionally improbable and very fortunate in allowing our existence. The common term used for an extremely unlikely but highly fortunate event is the term “miracle,” as in: It was a miracle that she fell onto an open truck carrying pillows when she jumped off the high bridge.

The vacuum miracle is something that bothers many scientists, who would prefer to believe that the universe is not so well-arranged to favor creatures like us. One way they have tried to ease this discomfort is to suggest that perhaps there is some unknown reason why the vacuum of space has to be empty, resulting in a zero cosmological constant, or zero dark energy. But such reasoning doesn't work, because in the late 1990's it was discovered that the expansion of the universe is accelerating. This can only be true if there is a very small cosmological constant, which basically means that each square meter of the vacuum of space has a little bit of energy. Collectively this energy (the same as dark energy or the cosmological constant) is causing the expansion of the universe to accelerate.

A recent paper by five scientists suggests that a cosmological constant just like we have is actually necessary for the eventual appearance of creatures such as us. The paper states: “We find that we seem to live in a favorable point in this parameter space that minimizes the exposure to cosmic explosions, yet maximizes the number of main sequence (hydrogen-burning) stars around which advanced life forms can exist.”

The paper is discussed by this article in the journal Science, which states:

As it turns out, our universe seems to get it just about right. The existing cosmological constant means the rate of expansion is large enough that it minimizes planets’ exposure to gamma ray bursts, but small enough to form lots of hydrogen-burning stars around which life can exist. (A faster expansion rate would make it hard for gas clouds to collapse into stars.)

We can use the common phrase “threading the needle” to describe this type of fine-tuning. Or you might compare it to landing the golf ball in the golf hole, or hitting the distant bullseye target with an arrow. And given all the random quantum contributions to the vacuum, this should have been as improbable as a drunk blindfolded archer hitting the very distant target bullseye with his arrow.

But the journal Science is written for scientists, so it was quite predictable that the article author would try to ease the discomfort of any scientists who might be made uncomfortable by this extreme example of cosmic fine-tuning. This was in accordance with the standard principle that our scientists must be kept in carefully filtered information bubbles, like 1980 Moscow bureaucrats who would get all their news from Pravda. Heaven forbid that the tender ears of our scientists should ever be offended by something that does not match their expectations.

So the Science article cites a statement by physicist Lee Smolin:

However, he adds, all truly anthropic arguments to date fall back on fallacies or circular reasoning. For example, many tend to cherry-pick by looking only at one variable in the development of life at a time; looking at several variables at once could lead to a different conclusion.

It certainly is not true that “all truly anthropic arguments to date fall back on fallacies or circular reasoning,” a claim which is just a lazy kind of dismissal similar to statements such as “all Republican arguments use fallacies” or “all Democratic arguments rely on logic errors.” In fact, the particular example given does not hold up as an example of a fallacy.

Let's imagine if you found a case in which one cosmic parameter seemed to be extremely fine-tuned for life. Would it be wrong to form an opinion based on that parameter, without considering all other parameters? It might be if you were examining some external universe, and you didn't know whether life existed in it. Because the overall situation might be like this:

1 parameter with just the right value for life to exist
5 parameters inconsistent with the existence of life

But we know that no such situation can exist in our universe, because we know that life does exist in our universe. So given the discovery of a single parameter that seems to be fine-tuned for life, the worst situation that could exist is:

1 parameter with just the right value for life to exist
All other parameters consistent with the existence of life

Even if you found such a situation, the evidence would still be pointing to a fine-tuned universe. You would have one “thumbs up,” and zero “thumbs down.”

In fact, we know the situation is much better than that. We know that there are quite a few parameters and fundamental constants which are fine-tuned for life, as discussed here and here. So we know that the situation is really: lots of thumbs up, and no thumbs down (if there were any thumbs down, we wouldn't exist). We know of lots of parameters that are very fine-tuned, and there is no chance that we will discover some other parameter that will cancel out such evidence (because if such a parameter existed we could not). The darts of nature known as the universe's fundamental constants have most improbably hit not just one distant bullseye, but lots of them.

Cosmic fine-tuning

So Smolin's reasoning here has no weight. In fact, Smolin himself showed that he is extremely impressed by the evidence that the universe is fine-tuned. This is because Smolin wrote a whole book called The Life of the Cosmos in which he advanced an elaborate theory designed to explain the fine-tuned features of the universe. It was a pretty goofy theory, involving the idea that universes magically pop into existence whenever black holes collapse. But at least it showed that Smolin thought that cosmic fine-tuning is something very important we need to explain.

In general, we should not pay particular attention when physicists lecture us about errors in logic, as physicists have no training in logic. You can get a PhD in physics without ever taking an introductory course in logic.

Far from involving some fallacy, the fact that our universe is incredibly fine-tuned is one of the most important things discovered by science in the past hundred years. If your philosophy doesn't mesh with such a fact, your philosophy needs to be revised. 

Postscript: This post included this snarky comment: "This was in accordance with the standard principle that our scientists must be kept in carefully filtered information bubbles, like 1980 Moscow bureaucrats who would get all their news from Pravda." I didn't expect to see another example of that so quickly. Shortly thereafter news arrived that a flood of complaints by scientists caused the PLOS One journal to retract a scientific paper dealing with the great amount of coordination in the human hand -- solely because the authors made three one-sentence references to "the Creator" -- for example, "The explicit functional link indicates that the biomechanical characteristic of tendinous connective architecture between muscles and articulations is the proper design by the Creator to perform a multitude of daily tasks in a comfortable way." Again, we see the Pravda principle at work -- the tender ears of our scientists must not be offended, the information bubble must be carefully filtered from contaminating deviations of thought, and the sociological taboos of the tribe must be rigidly enforced.