For several decades scientists have discovered more and more examples suggesting our universe is seemingly tailor-made for life. A list of many examples is discussed here. One dramatic example is the fact that even though each proton in our universe has a mass 1836 times greater than the mass of each electron, the electric charge of each proton matches the electric charge of each electron exactly, to twenty decimal places (the only difference being that one is positive, the other negative). Were it not for this amazing coincidence, our very planet would not hold together. But scientists have no explanation for this coincidence which seems to require luck with a probability of 1 in 100,000,000,000,000,000,000. As wikipedia states, “The fact that the electric charges of electrons and protons seem to cancel each other exactly to extreme precision is essential for the existence of the macroscopic world as we know it, but this important property of elementary particles is not explained in the Standard Model of particle physics.”
Wishing to cleanse their minds of any suspicions that our universe may not be the purely accidental thing they imagine it to be, quite a few materialists have adopted the theory of a multiverse. This is the idea that there are a vast collection of universes, each very different from the other. The reasoning is that if there were to be, say, an infinite number of universes, each with different laws and properties, then we would expect that at least one of them would have the properties necessary for intelligent life, no matter how improbable it may be that such properties would exist.
But there are many problems with trying to use a multiverse to explain cosmic fitness, or to explain anything at all. Let me list some of them.
1. A multiverse explanation is the worst imaginable violation of Occam's Razor
The first reason is that a multiverse violates to the most extreme degree imaginable the long-standing principle of Occam's Razor, which has been evoked by many a scientist over the centuries. Occam's Razor is the principle that “entities should not be multiplied beyond necessity” when explaining things, or that we should prefer to explain things as simply as possible. A multiverse is the greatest imaginable violation of the principle of Occam's Razor. A multiverse is what you might propose if you were following the exact opposite principle, a principle of “entities should be multiplied to the greatest number possible” when trying to explain something (a demented principle we might call “Anti-Occam's Razor”).
2. A theory of a multiverse is unverifiable metaphysics that can never be confirmed by observations
Although often made within scientific discussions, the theory of a multiverse is a metaphysical theory which can never be confirmed through scientific observations (despite insinuations to the contrary by multiverse proponents). Contrary to what some have claimed, looking for evidence of some unusual “flow” in some part of our universe could never confirm a theory of a multiverse, nor could any observations of early universe conditions. Such observations would at best imply that there was something that we did not understand about our universe, or that perhaps there was some “sister universe'' next to our universe (although such an area should more properly just be considered an unobserved part of our universe). We could never make any observations from our universe that would confirm that there are a vast number of other universes with different characteristics.
3. A theory of a multiverse makes one believe in the exact opposite of what our observations tell us --- that the laws and properties of nature are the same everywhere
An additional problem with the multiverse is that it leads one to believe in something that is 100% contrary to what our observations tell us. All observations made by physicists and astronomers support the idea that the universe is incredibly uniform. By comparing observations made by pointing telescopes in opposite directions of the sky, astronomers can compare one section of the universe with other sections on the opposite side of the observable universe. When they do this, they find a picture of incredible uniformity. The cosmic background radiation, for example, is uniform to within 1 part in 100,000. The laws of nature seem to be the same everywhere. The universe looks the same in all different directions. We have no good evidence that the laws of nature and the universe's fundamental constants have varied across the observable universe during the past ten billion years. If they had, the universe would not look as it does to astronomers.
So nature is screaming at us: uniformity, uniformity, uniformity. But the multiverse theory paints the exact opposite picture, a picture in which there is nothing like uniformity (with each universe having different characteristics). To believe such a theory, we must ignore the message that nature is shouting at us, and believe in some other imagined reality that is the exact opposite of what we observe. In a very real sense, therefore, the theory of a multiverse is counter-observational. Believing in an infinite variety of universes each with very different properties is rather like believing that the sun cycles through an infinite variety of different shapes – an interesting idea, and perhaps possible, but one that is completely at odds with what our observations tell us.
4. A multiverse explanation “proves” the wrong thing – that some universe would be habitable (without increasing the chance that our universe would be habitable)
Another problem with the multiverse reasoning is that it “proves” the wrong thing. An effective theory of multiple universes would be one that showed a likelihood that our universe would have the characteristics necessary for life purely by chance. The multiverse theory does not claim to show that. Instead it claims to show that “some universe” would by chance have the properties necessary for life. Now you may say: “some universe” and “our universe” – so what, no big difference. But there actually is a gigantic difference between the two. Confusing “some universe” and “our universe” (thinking as if they were the same) is an error in logic, an example of careless, sloppy thinking.
I can best illustrate the point by mentioning the case of a lottery. The Powerball lottery is a lottery with an incredibly low chance of winning, and a gigantic jackpot. Each year they sell enough Powerball lottery tickets to make sure that at least one person will win, but the chance of any lottery ticket buyer winning is less than 1 in a million. So consider these odds (which might be pondered by a couple that purchased a ticket):
Chance of some ticket winning: 100%
Chance of our ticket winning: less than 1 in 1,000,000,000
So as we can see, there is a gigantic world of difference in this case between “some ticket” and “our ticket.” There is an equally gigantic world of difference between “some universe” and “our universe” when we consider universes. Showing that some universe (under a multiverse theory) would be successful does not show that our universe would be successful.
In fact, the multiverse scenario does absolutely nothing to make it more likely that our particular universe would by chance have the characteristics necessary for intelligent life. If the chance of our universe being successful were 1 in a billion trillion quadrillion before we assume the multiverse, that chance is exactly the same even after we assume a multiverse.
When mathematicians talk about probability, they speak of a trial as being something that might produce a favorable outcome (examples are a roll of a dice, a dealing of 5 cards from a deck, or a purchase of a lottery ticket). But it is a general rule of probability that increasing the number of trials does not increase the chance of success of any one trial.
From a purely explanatory standpoint, a multiverse is therefore the ultimate absurdity: a theory that introduces infinite baggage that serves no explanatory purpose, because it does not increase the odds of our universe being successful. The thing that a multiverse “explains” (some universe being successful) is not what we need to have an explanation for (the fact that our universe was successful despite such enormous odds).
I can illustrate the futility of a multiverse explanation with the following lines of dialog:
John: It required so many improbable coincidences for our universe to have intelligent life – what could be the explanation?
James: A lucky “1 in a zillion” accident – pure blind luck.
John: That's too farfetched, because it would have required something like a 1 in a 1,000,000,000,000,000,000,000 shot.
James: Well, there could be a multiverse. Maybe there's an infinite number of universes. Some of them might have got lucky.
John: An interesting thought. But still, why was our particular universe so lucky?
James: A lucky “1 in a zillion” accident – pure blind luck.
Here James has introduced an extravagant theory that accomplishes nothing. Before introducing his multiverse theory, his explanation for the universe's habitability was a lucky 1 in a “zillion” accident, and he is still stuck with that explanation even after introducing the multiverse scenario. The multiverse theory accomplishes nothing for him.
5. There is no verified case of anything ever being successfully explained by a type of explanation like a multiverse explanation, nor can we plausibly imagine any such case ever being verified
The typical process of rational explanation can be described as follows: (a) examine some thing that needs to be explained; (b) select some type of explanation that has been proven successful for other cases; (c) apply such an explanation to explain the thing that needs to be explained.
For example, if we see something strange in the sky that is unexplained, we can try to explain it by selecting “weather phenomenon” as our type of explanation, because we know that numerous previous items have been successfully explained by postulating weather as the explanation (for example, the morning dew on the grass of your lawn). More adventurously, we can explain the strange thing in the sky as an alien spacecraft. While we do not have a verified case of anything being successfully explained by exactly postulating an extraterrestrial spacecraft, we do have numerous observations that we know have been successfully explained by advancing this type of explanation – numerous strange lights in the sky have been explained successfully by mentioning some type of spacecraft (earthly spacecraft).
But in the case of a multiverse, it is an entirely different story. We have not one single verified case of anything that has ever been successfully explained by advancing any theory like the theory of a multiverse. A multiverse explanation therefore has a singularly low credibility. One can compare it to a totally new type of machine that has never been proven to work before.
For the multiverse enthusiast, this is an insolvable dilemma. We can have no confidence in multiverse explanations until we can have a verified case of this type of explanation explaining something, but it is impossible to reasonably imagine anything ever getting a verified explanation through this type of explanation (whether it be our universe's fitness for life, or anything else).
6. A multiverse theory can “explain” any claim, no matter how absurd; as it can “explain” anything, it explains nothing
A multiverse theory is in fact a kind of inane all-purpose explanation engine. It can be used to “explain” almost any absurdity or any theory no matter how improbable.
Let's randomly imagine an absurd theory which I may call the alien deception theory. The theory is that evolution is false, and that all of the fossils we have found suggesting evolution were planted on our planet by aliens trying to fool us into believing that evolution occurred. A multiverse theory “proves” this alien deception theory to the exact same degree that it “proves” that our universe's favorable characteristics are due to an accident. Exactly the same reasoning may be given for both: even though it may seem very improbable that such a thing would occur, we would expect it to occur some times given a vast number of universes.
I could go on and on with similar examples. Basically whatever crazy theory you wish to believe in, you can justify with multiverse reasoning. Do you want to believe that underground is a vast kingdom of leprechauns, cute little people like those in Irish mythology? Do you want to believe that these little leprechauns are all riding along underground on little unicorns? You can get there with a multiverse. You simply reason that no matter how improbable such a thing may be, we would expect it to have occurred at least once if there are an infinite number of universes.
Similarly, whenever your eyes seem to tell you of some fact with great certainty, you can use multiverse reasoning to support the idea that what you are seeing is not really happening. If you are unlucky enough to walk up to your house and see it burning on fire, you can convince yourself that this is a hallucination. If you then think a normal person like yourself would never have such a hallucination, you can use multiverse reasoning to squash that objection. You simply reason that no matter how improbable it may be that a normal person would have such a hallucination, we would expect such a thing to occur many times if there are a vast collection of universes.
The graphic below visualizes my point that a multiverse can be used to “explain” any absurdity. A multiverse can be basically used to explain anything. That which explains anything explains nothing.
Postscript: See this paper by physicist V. Palonen. He makes the same point I made that the relevant consideration is the likelihood of this universe being habitable, not "some universe." Palonen writes:
It follows that because multiverse hypotheses do not predict fine-tuning for this particular universe any better than a single universe hypothesis, multiverse hypotheses are not adequate explanations for fine-tuning. Conversely, our data on cosmic fine-tuning does not lend support to the multiverse hypotheses. For physics in general, irrespective of whether there really is a multiverse or not, the common-sense result of the above discussion is that we
should prefer those theories which best predict (for this or any universe) the phenomena we observe in our universe.