Today I want to talk about the claim that our universe is especially made for humans, or fine-tuned for life. According to this idea it’s extremely unlikely our universe would just happen to be the way it is by chance, and the fact that we nevertheless exist requires explanation. This argument is popular among some religious people who use it to claim that our universe needs a creator, and the same argument is used by physicists to pass off unscientific ideas like the multiverse or naturalness as science. In this video, I will explain what’s wrong with this argument, and why the observation that the universe is this way and not some other way, is evidence neither for nor against god or the multiverse.
Ok, so here is how the argument goes in a nutshell. The currently known laws of nature contain constants. Some of these constants are for example, the fine-structure constant that sets the strength of the electromagnetic force, Planck’s constant, Newton’s constant, the cosmological constant, the mass of the Higgs boson, and so on.
Now you can ask, what would a universe look like, in which one or several of these constants were a tiny little bit different. Turns out that for some changes to these constants, processes that are essential for life as we know it could not happen, and we could not exist. For example, if the cosmological constant was too large, then galaxies would never form. If the electromagnetic force was too strong, nuclear fusion could not light up stars. And so on. There’s a long list of calculations of this type, but they’re not the relevant part of the argument, so I don’t want to go through the whole list.
The relevant part of the argument goes like this: It’s extremely unlikely that these constants would happen to have just exactly the values that allow for our existence. Therefore, the universe as we observe it requires an explanation. And then that explanation may be god or the multiverse or whatever is your pet idea. Particle physicists use the same type of argument when they ask for a next larger particle collider. In that case, they claim it requires explanation why the mass of the Higgs boson happens to be what it is. This is called an argument from “naturalness”. I explained this in an earlier video.
What’s wrong with the argument? What’s wrong is the claim that the values of the constants of nature that we observe are unlikely. There is no way to ever quantify this probability because we will never measure a constant of nature that has a value other than the one it does have. If you want to quantify a probability you have to collect a sample of data. You could do that, for example, if you were throwing dice.Throw them often enough, and you get an empirically supported probability distribution.
But we do not have an empirically supported probability distribution for the constants of nature. And why is that. It’s because… they are constant. Saying that the only value we have ever observed is “unlikely” is a scientifically meaningless statement. We have no data, and will never have data, which allow us to quantify the probability of something we cannot observe. There’s nothing quantifiably unlikely, therefore, there’s nothing in need of explanation.
If you look at the published literature on the supposed “fine-tuning” of the constants of nature, the mistake is always the same. They just postulate a particular probability distribution. It’s this postulate that leads to their conclusion. This is one of the best known logical fallacies, called “begging the question” or “circular reasoning.” You assume what you need to show. And instead of showing that a value is unlikely, they pick a specific probability distribution that makes it unlikely. They could as well pick a probability distribution that would make the observed values *likely, just that this doesn’t give the result they want to have.
And, by the way, even if you could measure a probability distribution for the constants of nature, which you can’t, then the idea that our particular combination of constants is necessary for life would *still be wrong. There are several examples in the scientific literature for laws of nature with constants nothing like our own that, for all we can tell, allow for chemistry complex enough for life. Please check the info below the video for references.
Let me be clear though that finetuning arguments are not always unscientific. The best-known example of a good finetuning argument is a pen balanced on its tip. If you saw that, you’d be surprised. Because this is very unlikely to happen just by chance. You’d look for an explanation, a hidden mechanism. That sounds very similar to the argument for finetuning the constants of nature, but the balanced pen is a very different situation. The claim that the balanced pen is unlikely is based on data. You are surprised because you don’t normally encounter pens balanced on their tip.You have experience, meaning you have statistics. But it’s completely different if you talk about changing constants that cannot be changed by any physical process. Not only do we not have experience with that, we can never get any experience.
I should add there are theories in which the constants of nature are replaced with parameters that can change with time or place, but that’s a different story entirely and has nothing to do with the fine-tuning arguments. It’s an interesting idea though. Maybe I should talk about this some other time? Let me know in the comments.
And for the experts, yes, I have so far specifically referred to what’s known as the frequentist interpretation of probability. You can alternatively interpret the term “unlikely” using the Bayesian interpretation of probability. In the Bayesian sense, saying that something you observe was “unlikely”, means you didn’t expect it to happen. But with the Bayesian interpretation, the whole argument that the universe was especially made for us doesn’t work. That’s because in that case it’s easy enough to find reasons for why your probability assessment was just wrong and nothing’s in need of explaining.
Example: Did you expect a year ago that we’d spent much of 2020 in lockdown? Probably not. You probably considered that unlikely. But no one would claim that you need god to explain why it seemed unlikely.
What does this mean for the existence of god or the multiverse? Both are assumptions that are unnecessary additions to our theories of nature. In the first case, you say “the constants of nature in our universe are what we have measured, and god made them”, in the second case you say “the constants of nature in our universe are what we have measured, and there are infinitely many other unobservable universes with other constants of nature.” Neither addition does anything whatsoever to improve our theories of nature. But this does not mean god or the multiverse do not exist. It just means that evidence cannot tell us whether they do or do not exist. It means, god and the multiverse are not scientific ideas.
If you want to know more about fine-tuning, I have explained all this in great detail in my book Lost in Math.
In summary: Was the universe made for us? We have no evidence whatsoever that this is the case.
You can join the chat on this video today (Saturday, Jan 16) at 6pm CET/Eastern Time here.