One of the most surprising scientific discoveries of recent decades is that physics appears to be fine-tuned for life. This means that for life to be possible, certain numbers in physics had to fall within a 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 this force were a little stronger, matter would not be able to clump together. Two particles would never have combined, which means there would be no stars, planets or any kind of structural complexity and therefore no life.
If this force had been significantly weaker, it would not have counteracted gravity. This means that the universe would have collapsed in on itself in the first fraction of a second – again meaning there would be no stars, planets or life. To allow for the possibility of life, the strength of dark energy had to be, like Goldilocks’ porridge, “just right.”
This is just one example and there are many others.
The most popular explanation for the fine-tuning of physics is that we live in a universe among a multiverse.
If enough people buy lottery tickets, someone is likely to have the right numbers to win. Likewise, if there are enough universes, with different physical numbers, it becomes likely that some universe has the right numbers for life.
For a long time, this seemed to me the most plausible explanation for fine-tuning. However, experts in probability mathematics have identified the fine-tuning inference for a multiverse as an example of fallacious reasoning – something I explore in my new book, Why? The Purpose of the Universe.
Specifically, the accusation is that multiverse theorists commit what is called the inverse gambler’s fallacy.
Suppose Betty is the only person playing in her local bingo hall one night and, in an incredible stroke of luck, all her numbers come up in the first minute.
Betty thinks to herself, “Wow, there must be a lot of people playing bingo in other bingo halls tonight!”
His reasoning is: if there are a lot of people playing across the country, then it’s not that unlikely that someone will get all their numbers in the first minute.
But this is an example of the inverse gambler’s fallacy. No matter how many people are or are not playing in other bingo halls across the country, probability theory says that it is no longer likely that Betty herself will be so lucky.
It’s like playing dice. If we get several sixes in a row, we wrongly assume that we will be less likely to get sixes in the next few rolls. And if we don’t get any sixes for a while, we wrongly assume that there must have been a lot of sixes in the past.
But in reality, each roll has an exact and equal one-in-six probability of getting a specific number.
Multiverse theorists commit the same fallacy. They think, “Wow, how unlikely it is that our universe has the right numbers for life; there must be lots of other universes out there with the wrong numbers!”
But that’s just like Betty thinking she can explain her luck in terms of other people playing bingo. When this specific universe was created, like a roll of the dice, it still had a specific, low chance of getting the right numbers.
At this point, multiverse theorists bring up the “anthropic principle” – that because we exist, we could not have observed a universe incompatible with life. But that doesn’t mean these other universes don’t exist.
Suppose there is a sniper hiding in the back of the bingo room, waiting to shoot Betty the moment a number appears that is not on her bingo card. Now the situation is analogous to fine-tuning the real world: Betty could not have observed anything but the right numbers for winning, any more than we could 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 are wrong in inferring from fine-tuning for many universes.
And the multiverse?
Is there no scientific evidence for a multiverse? Yes and no. In my book, I explore the connections between the inverse gambler fallacy and the scientific case for the multiverse, something that has surprisingly never been done before.
The scientific theory of inflation – the idea that the early universe exploded enormously – supports the multiverse. If inflation can happen once, it is likely happening 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 proof 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 the total evidence requirement, which forces us to work with the most specific evidence we have.
In terms of fine-tuning, the most specific evidence that people who believe in the multiverse have is not just that The universe is well adjusted, but this that universe is adjusted. 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 particular universe, unlike some other among millions, would be precisely tuned. Once the evidence is correctly formulated, the theory cannot explain it.
Conventional scientific wisdom is that these numbers have remained fixed since the Big Bang. If this is correct, then we face a choice.
Or is it an incredible fluke that our universe has the right numbers. Or numbers are as they are because nature is somehow driven or directed to develop complexity and life by some invisible, built-in 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 happen. It’s a bit like the 16th century, when we started to get evidence that we weren’t at the center of the universe. Many found it difficult to accept that the image of reality they were accustomed to no longer explained the data.
I believe we are in the same situation now with fine tuning. We may one day be surprised that we ignored for so long what was plain to see – that the universe favors the existence of life.
Philip Goff, Associate Professor of Philosophy, Durham University.
This article is republished from The Conversation under a Creative Commons license. Read the original article.