Fine-Tuned Gravity: Don’t Touch That Dial

Question from Cedric:
Victor Stenger says supporters of the Fine Tuning argument make the mistake of holding all the parameters constant and varying just one. He says “changes to one parameter can be easily compensated for by changes to another, leaving the ingredients for life in place.”

“The ingredients for life” is a more complex case since it involves several parameters but if one were to examine a simpler case involving only one parameter then the legitimacy of Fine Tuning might be easier to discern.

Take the force of gravity. The Fine Tuning argument says it had to be precisely what it is in order for the universe to expand as it did after the Big Bang. Too strong and the universe would collapse back to a singularity. Too weak and the universe would expand too rapidly. This doesn’t seem to depend on other parameters. So doesn’t the exactness of gravity alone imply design?

Answer by SmartLX:
If you’re going to circumvent Stenger’s argument by focusing on a single value, gravity is the wrong one to pick because it didn’t have to be all that exact. In Martin Rees’ book Just Six Numbers he finds that the gravitational constant would have to increase by a factor of 3000 to preclude the formation of stars. (I’ve never seen anyone use the same approach on another constant, so I suspect none of the others have similarly obvious independent significance.)

Creationists and other apologists have not contradicted Rees; they’ve taken two other approaches to dismissing this inconvenient amount of leeway. Both are found in this article, which is typical of a fair few apologetic articles attacking Rees’ conclusion of a lack of fine tuning. (Their abundance suggests to me that Rees struck a nerve.)

1. If gravity were nearly 3000 times stronger, they say, stars wouldn’t last even a billion years and life wouldn’t have time to form, so the universe is still fine-tuned for the really important thing, life. Well, the fact that this aspect of the extreme case isn’t workable doesn’t negate the fact that gravity could change an awful lot before there was any real difficulty.

2. A factor of 3000, they say, is still tiny when you consider that the different forces in the universe differ by factors of up to 10^40. True, but it’s still 300,000% so it’s huge compared to the actual value, and there’s no evidence to suggest that gravitational forces in a fresh universe are even capable of reaching the levels of our universe’s strong nuclear force. There’s an underlying assumption that each of the constants was selected from the same huge or infinite range of possible numbers, and there’s no basis for that assumption.

Even if gravity had to be what it really is for life to form, to within a zillionth of a percent, it would not simply “imply design”. We don’t know nearly enough about what went into the physical “setting” of the constant to jump to that conclusion. Alternatives include but are not limited to the following:

– A huge or even infinite number of universes exist, each of them with different constants, such that the probability of one of them hitting the magic spot is really quite reasonable. Ridicule the multiverse hypothesis if you like, but evidence has emerged suggesting its likelihood. (Additional universes seem more likely to me than a god because we know there’s at least one universe. If your cabbage patch is destroyed and you find one little rabbit, you don’t imagine that Bigfoot did the rest; you wonder where the other rabbits are hiding.)
– The value of the gravitational constant is a result, not a parameter. When a Big Bang happens, gravity comes out at 6.673 because of how a Big Bang happens, or else the constant is dependent on the other constants. (Pi is a good analogue for this; the value near 3.14 results from the physical properties of a circle.)
– The gravitational constant might have started anywhere, but it varied before it reached a stable equilibrium at its current value. Something about 6.673 stops it from wanting to shift. (This is one possible explanation for cosmic inflation.)

Finally, if you disregard all of the above, we’re ultimately comparing the probability that a universe with incredibly fortunate physical qualities arose naturally to the probability that it was designed by an even more complex, exotic, powerful, hypothetical entity with no origin at all. That might be a contest if the existence of the other entity were assumed, but you can’t take that liberty when the whole point of the discussion is to establish that entity’s existence.