Many physicists assume that we should live in a multiverse, but their basic calculations may be wrong

Many physicists assume that we should live in a multiverse, but their basic calculations may be wrong

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One of the most startling scientific discoveries of recent decades is that physics seems fine-tuned for life. This means that for life to be possible, certain numbers in physics must fall within a certain, very narrow range.

One example of fine-tuning that has puzzled physicists is the force of dark energy, the force that fuels the accelerating expansion of the universe. If that force were a little stronger, the matter would not be able to hold together. Two particles could never come together, which means no stars, planets, or any kind of structural complexity, and therefore no life.

If that force were much weaker, it would not be able to resist gravity. This means that the universe would have collapsed back on itself within the first fraction of a second, meaning once again there would be no stars, planets, or life. To allow life to be possible, the force of dark energy must, like Goldilocks’ porridge, be “just right.”

This is just one example, there are many others.

The most popular explanation for the fine-tuning of physics is that we live in one universe among multiple universes. If enough people buy lottery tickets, it’s likely that someone will have the correct numbers to win. Likewise, if there are enough universes, with different numbers in their physics, it is likely that some universes will have the right numbers for life.

For a long time, this seemed to me to be the most logical explanation for fine-tuning. However, experts in the mathematics of probability have identified that the inference from fine-tuning to the multiverse is an example of fallacious inference, something I explore in my new book, Why? The purpose of the universe. Specifically, the charge is that multiverse theorists commit what is called the reverse gambler’s fallacy.

Suppose Betty is the only person playing at her local bingo hall one night, and in an incredibly lucky event, all of her numbers come up in the first minute. Betty thinks to herself, “Wow, there must be a lot of people playing bingo in the other bingo halls tonight!” Her logic is: If there are a lot of people playing across the country, it is not unlikely that someone will be called with all their numbers in the first minute.

But this is an example of the reverse gambler’s fallacy. No matter how many people are or aren’t playing at other bingo halls around the country, probability theory says it’s unlikely that Betty herself would have such luck.

It’s like playing dice. If we get several sixes in a row, we mistakenly assume that we are unlikely to get a six on the next few throws. If we don’t get any sixes for a while, we mistakenly assume that there must have been a lot of sixes in the past. But in reality, every throw has an exact and equal probability of one in six of hitting 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 many other universes with the wrong numbers!” But that’s just like Betty thinking she can explain her lucky luck in terms of other people playing bingo. When this particular universe was created, like in Death Roll, it still had a low specific chance of getting the numbers right.

At this point, multiverse theorists introduce the “anthropic principle” — that given our existence, we cannot observe a universe that is incompatible with life. But this does not mean that such other universes do not exist.

Suppose there is a deranged sniper lurking in the back of the bingo hall, waiting to shoot Betty the moment a non-existent number appears on her bingo card. Now the situation was analogous to the real-world setting: Beatty could not have observed anything other than the correct numbers for win, just as we could not have observed a universe with the wrong numbers for life.

However, Betty may be wrong in concluding that many people play bingo. Likewise, multiverse theorists are wrong in their inference of the fine-tuning of many universes.

What about the multiverse?

Is there no scientific evidence that there are multiple universes? Yes and no. In my book, I explore the connections between the reverse gambler’s fallacy and the scientific state of the multiverse, something that has surprisingly not been done before.

The scientific theory of inflation—the idea that the early universe exploded in size—supports the multiverse. If inflation could happen all at once, it would likely happen in different regions of space, creating universes unto themselves. While this may give us tentative evidence of the existence 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 the total evidence requirement, which requires us to work with the most specific evidence available to us.

In terms of fine-tuning, the most definitive evidence that people who believe in the multiverse have is not just that the universe is “fine-tuned,” but that “this” universe is fine-tuned. If we believe that the constants of our universe are shaped by probabilistic processes — as multiverse explanations suggest — then it is incredibly unlikely that this particular universe is fine-tuned, unlike some other universe among millions. Once the evidence is properly formulated, the theory fails to explain it.

Conventional scientific wisdom is that these numbers have remained constant from the Big Bang onward. If this is true, we face a choice. Either it is an amazing coincidence that our universe has the right numbers. Or the numbers are what they are because nature is somehow driven or directed to develop complexity and life through an inbuilt invisible principle.

In my opinion, the first option is too unlikely to be taken seriously. My book presents the theory of the second option—cosmic purpose—and discusses its implications for human meaning and purpose.

This was not the way we expected science to turn out. It’s a bit like what happened in 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 picture of reality they were accustomed to no longer explained the data.

I think we’re in the same situation now in terms of fine-tuning. One day we may be surprised that we ignored for so long what was so obvious that the universe favors life.

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