One of the most surprising scientific discoveries of recent decades is that physical He seems to be prepared for life. This means that for life to be possible, certain numbers in physics had to be within a certain, very narrow range.
One of the examples of fine tuning that has most baffled physicists is the force of dark energy, the force that drives the accelerated expansion of the universe. If that force had been a little stronger, the matter would not be able to clump together. No two particles would ever have combined, meaning there would be no stars, planets, or any kind of structural complexity, and therefore no life.
If that force had been significantly weaker, it would not have counteracted gravity. This means that the universe would have collapsed on itself in the first fraction of a second, that is, without stars, planets or life. To allow the possibility of life, the strength of dark energy had to be, like Goldilocks’ porridge, “perfect.”
This is just one example, there are many others.
The most popular explanation for the fine tuning of physics is that we live in a universe between a multiverse. If enough people buy lottery tickets, chances are someone will have the right numbers to win. Likewise, if there are enough universes, with different numbers in their physics, it is likely that some universe has the right numbers for life.
For a long time, this seemed to me the most plausible explanation for the adjustment. However, experts in probability mathematics have identified the fine-tuning inference of a multiverse as an example of fallacious reasoning, something I explore in my new book. Because? The purpose of the universe. Specifically, the accusation is that multiverse theorists commit what is called reverse gambler’s fallacy.
Suppose Betty is the only person playing at her local bingo hall one night and, in an incredible streak of luck, all of her numbers come up in the first minute. Betty thinks to herself, “Wow, there must be a lot of people playing bingo at other bingo halls tonight!” Her reasoning is: if there are a lot of people playing across the country, then it’s not that unlikely that someone will be told all of her numbers in the first minute.
But this is an example of the reverse gambler’s fallacy. No matter how many people do or don’t play at other bingo halls across the country, probability theory says that Betty herself is no more likely to have that lucky streak.
It’s like playing dice. If we hit several sixes in a row, we mistakenly assume that we are less likely to hit sixes on subsequent throws. And if we don’t get any sixes for a while, we mistakenly assume that there must have been many sixes in the past. But in reality, each toss has an exact and equal one in six chance of rolling a specific number.
Multiverse theorists commit the same fallacy. They think, “Wow, how unlikely that our universe has the right numbers for life; there must be many other universes with the wrong numbers!” But this is as if Betty thinks she can explain her lucky streak in terms of other people playing bingo. When this particular universe was created, like rolling a die, it still had a specific, low probability of getting the numbers right.
At this point, multiverse theorists introduce the “anthropic principle”: that, because we exist, we could not have observed a universe incompatible with life. But that doesn’t mean those other universes don’t exist.
Suppose there is a deranged sniper hiding in the back of the bingo hall, waiting to shoot Betty the moment she comes up with a number that is not on her bingo card. Now the situation is analogous to real-world fine-tuning: Betty could not have observed anything but the right numbers for winning, just as we could not have observed a universe with the wrong numbers for life.
Still, Betty would be wrong to infer that many people are playing bingo. Likewise, multiverse theorists mistakenly make inferences from the fine tuning of many universes.
What about the multiverse?
But is there no scientific evidence of a multiverse? Yes and no. In my book, I explore the connections between the reverse player fallacy and the scientific argument for the multiverse, something that has surprisingly not been done before.
the scientist inflation theory (the idea that the early universe increased enormously in size) supports the multiverse. If inflation can occur once, it is likely to occur in different areas of space, creating universes in their own right. While this may give us tentative evidence of some kind of multiverse, there is no evidence that different universes have different numbers in their local physics.
There is a deeper reason why the multiverse explanation fails. Probabilistic reasoning is governed by a principle known as total evidence requirementwhich forces us to work with the most specific evidence we have available.
In terms of fit, the most specific evidence that people who believe in the multiverse have is not simply that to The universe is fine-tuned, but that this The universe is tuned. If we hold that the constants of our universe were shaped by probabilistic processes (as multiverse explanations suggest), then it is incredibly unlikely that this specific universe, unlike some other among millions, is fine-tuned. Once we formulate the evidence correctly, the theory fails to explain it.
Conventional scientific wisdom is that these numbers have remained fixed from the beginning. big Bang forward. If this is correct, then we are faced with a choice. Or it’s an incredible coincidence that our universe had the right numbers. Or the numbers are the way they are because nature is somehow driven or directed to develop complexity and life by some invisible, embodied principle. In my opinion, the first option is too unlikely to be taken seriously. My book presents a theory of the second option (cosmic purpose) and discusses its implications for human meaning and purpose.
This is not how we expected science to turn out. It’s a bit like in the 16th century when we began to have evidence that we were not at the center of the universe. Many found it difficult to accept that the picture of reality to which they were accustomed no longer explained the data.
I think we are in the same situation now with the adjustment. One day we may be surprised to have ignored for so long what was plain to see: that the universe favors the existence of life.