In my previous post I discussed cosmic habitability categories, which involve four possible types of universes: uninhabitable universes (in which life can't exist), barely habitable universes (in which it is very hard but just barely possible for intelligent life to exist), moderately habitable universes (offering more favorable conditions), and abundantly habitable universes (in which life might be able to evolve all over the universe, with many planets having life all over them, and intelligent life having great prospects for being able to survive for eons). It seems that our universe is the fourth type of universe, as it does not have any serious shortfall in regard to habitability.
Now let us consider two interesting questions: (1) which of these types of universes are the most likely and the second-most-likely to exist? (2) what type of prediction about the habitability of the universe is implied by scientific materialism?
In my previous post I described a group of habitability necessities that are required for any universe to be habitable, and I also listed a series of factors I called habitability boosters, each of which would increase the habitability of a universe (without being an absolutely necessary precondition for the habitability of a universe). I then used these factors to define the different habitability categories:
Uninhabitable universe: A universe in which intelligent life cannot evolve anywhere, because it is missing one or more of the habitability necessities.
Barely habitable universe: A universe that has all of the habitability necessities, but none or only one or two of the habitability boosters.
Moderately habitable universe: A universe that has all of the habitability necessities, and roughly half of the habitability boosters.
Abundantly habitable universe: A universe that has all of the habitability necessities, and all or almost all of the habitability boosters.
So to delve into the relative likelihood of these types of universes, we must consider first : what is the chance of the habitability necessities occurring? Then we can consider what is the chance of the habitability boosters occurring.
Why a Random Universe is Overwhelmingly Likely To Be Uninhabitable
The first habitability necessity I mentioned was stable atoms heavier than hydrogen. We take heavy elements such as carbon and oxygen for granted, but we shouldn't. We should not expect them to exist in more than a very tiny fraction of all random universes. You wouldn't have atoms other than hydrogen unless you have the strange convenience we call the strong nuclear force, which binds together nuclei together, overcoming the electromagnetic repulsion between protons. First such a force must exist. Second, it must have the right strength level (and it is actually the strongest known force). You must also have electromagnetism causing a force of attraction between protons and electrons, which keeps electrons in an atom. Then you need quantum mechanical laws that prevent such attraction from causing electrons to fall into the nucleus. Given all of the ways you can wrong, it seems the chance of atoms existing in a universe of random constants and forces is very low.
The second habitability necessity I mentioned was planets with a reasonable level of gravity. To meet this necessity a universe needs a universal force of gravitation that is attractive. The very existence of such a force would seem to be no more than a one-in-three likelihood, since we can imagine two other equally likely possibilities (a universe with no such force at all, and a universe with a force of repulsion between all particles). But the likelihood of habitable planets in a random universe is actually much, much smaller than that. For one thing, the strength level of gravitation (signified in our universe by the gravitational constant) must be within a quite narrow range of values. If gravitation is too weak, planets won't hold together. If gravitation is too large, then the gravity on all planets will so great that no animals will be able to move around on a planet (and there are also reasons why an expanding universe would have collapsed into black holes if gravitation had been much higher). There is also fine-tuning required in regard to the proton charge and the electron charge. For example, in our universe if the proton charge and the electron charge were not exactly the same, gravitation would not be enough to hold planets together (since the electromagnetic force is roughly a trillion trillion trillion times stronger than the gravitational force, even a relatively tiny difference in the proton charge and the electron charge would cause repulsive effects exceeding the attractive effects of gravitation in large bodies such as planets, preventing their existence, as mentioned by Greenstein here).
In short, while we take planets for granted (having lived on one all our lives), it seems that we should expect only a tiny fraction of random universes to have planets suitable for the existence of mobile living creatures
The likelihood of a random universe being habitable seems even smaller when we consider the third habitability necessity I mentioned, the necessity of having a relatively empty vacuum. The issue (discussed here) is that according to quantum mechanics, quantum fluctuations should cause the vacuum to be teeming with energy. This is the “vacuum catastrophe” problem or cosmological constant problem that is perhaps the biggest unsolved problem in physics. According to the predictions of quantum field theory, we should live in a vacuum that is at least 1060 times denser than the observed vacuum – so dense that a square meter of the vacuum should be denser than a square meter of steel. Pretty much the only idea physicists have as to why our vacuum is so relatively empty is that there was some fantastically improbable and coincidental “cancellation of contributions” leaving us with a nearly empty vacuum – something rather like the annual savings of Chinese citizens coincidentally matching the annual credit card charges of US citizens, with an exact match to the penny. The chance of such a thing in a random universes is very, very low.
The likelihood of a random universe being habitable seems even smaller when we consider the fourth habitability necessity I mentioned, the necessity of having both carbon and oxygen in the universe. Scientists have discussed how if the strong nuclear force had been slightly weaker or slightly stronger, we would have been left with a universe that would have had either lots of carbon but no oxygen, or lots of oxygen but no carbon. Apparently getting both required a lot of luck that would be very unlikely in most random universes.
Based on these considerations (which do not at all discuss all of the habitability necessities of a habitable universe), we can conclude that uninhabitable universes are vastly more likely than habitable universes. Such a conclusion has been made by quite a few previous scientists. A recent article by physicist Luke Barnes has a relevant graph showing habitable universes as just a small portion of a parameter space that is much bigger (and there are lots of bulls-eyes that nature must hit for a universe to be habitable, not just the one illustrated here).
Why a Barely Habitable Universe Should Be Vastly More Likely Than a Moderately Habitable Universe Or an Abundantly Habitable Universe
The conclusion above has been made by many writers, but now let's look at a question rarely considered, but quite important: in the class of all habitable universes, what fraction should be we expect to be just barely habitable? In other words, should we expect that barely habitable universes are vastly more common than moderately habitable universes and abundantly habitable universes?
I will now argue that we should expect exactly that, mainly because the habitability boosters that I identified are unlikely to occur in random universes. Let's look at the first habitability booster I identified, the existence of radiant stars.
The likelihood of you getting radiant stars in a random universe is discussed in section 4.7 of the scientific paper here. The paper quotes a scientific paper by Adams mentioning a 1 in 4 chance of stars being possible if you allow the fine-structure constant and the gravitational constant to have values differing from their current values by ten times. But this is an example of “putting the camera near the needle hole in order to make the needle hole look big.” There's no reason why the the fine-structure constant and the gravitational constant could not have values a million times smaller or larger. When we properly consider that, we are then left with a probability of less than 1 in a million that a random universe would have radiant stars. See here for more on this issue. On page 40 of this paper, physicist Luke Barnes says, “We conclude that the existence of stable stars is indeed a fine-tuned property of our universe” – in other words, something that would be very unlikely to occur in a random universe.
Another habitability booster I mentioned is the existence of sun-like stars. A universe that has such stars will tend to be a lot more habitable than one merely having red stars (planets around red stars are predicted to be tidal-locked planets on which there is only a ring of habitability between the side facing the star and the opposite side). It turns out that the fine-tuning for sun-like stars is far greater than the fine-tuning needing for red stars. Below is a quote from page 73 of The Accidental Universe by physicist Paul Davies:
If gravity were very slightly weaker, or electromagnetism very slightly stronger, (or the electron slightly less massive relative to the proton), all stars would be red dwarfs. A correspondingly tiny change the other way, and they would all be blue giants.
It seems, therefore, that in random universes we are extremely unlikely to see sun-like stars, and that the requirements for such stars are much more special (much greater “long shots”) than the requirements for stars in general, just as the requirements for getting into Harvard are much harder-to-meet than the requirements for getting into “some type of college.”
Another habitability booster I mentioned is the existence of large amounts of both carbon and oxygen. Scientists have identified this as something that would not occur unless fundamental constants are fine-tuned. According to page 41 of this paper, a 1 part in 100,000 change in one fundamental constant would change things so that the main stellar process producing carbon and oxygen would produce either carbon or oxygen, but not both. That paper concludes, “The ability of stars in our universe to produce both carbon and oxygen seems to be a rare talent.” So we can conclude that this habitability booster (an abundance of both carbon and oxygen) is highly improbable in a random universe.
Another habitability booster I mentioned is low radioactivity. For simplicity let's just assume there is maybe 1 chance in 2 of such a condition. It would seem to be many times harder for a universe to have the last habitability booster I mentioned, that of low static electricity (so there are not all kinds of lethal static electricity amounts hanging around all over the place, ready to kill anyone who touches them). Low static electricity seems to require two different coincidences: the coincidence that the number of protons in a universe roughly equals the number of electrons (as it seems to do in our universe), and the coincidence that the proton charge equals the electron charge (as it does in our universe, to twenty decimal places). If you change those conditions just a little, you will be left with a universe in which there is so much free-floating static electricity (excess charges floating about) that life should be very rare, very short-lived or both (imagine a planet teeming with billions of “static electricity landmines” and you'll get the idea).
So speaking very generally, not only are the habitability necessities rare strokes of luck that should be very unlikely to occur in a random universe, but also the habitability boosters are almost all rare strokes of luck that should be very unlikely to occur in a random universe. Consequently, barely habitable universes should be vastly more likely than moderately habitable universes or abundantly habitable universes. Barely habitable universes should be much more likely because they require much fewer “improbable strokes of luck” than moderately habitable and abundantly habitable universes.
The visual below illustrates this idea. This is a very schematic visual, and its proportions are not supposed to represent the actual ratio between different habitability categories. The visual refers merely to probabilities, not actualities. In the first bar we see something that represents very roughly a ratio between uninhabitable universes and habitable universes (although the actual fraction of habitable universes should be much smaller). The second bar is a closeup of the right edge of the first bar. When we zoom in and look at the habitable universes, we find that almost all of them are barely habitable universes, with a few (on the right side) being moderately habitable. The third bar is a closeup of the right edge of the second bar. When we zoom in and look at the universes that are better than barely habitable, we find that almost all of them are moderately habitable and only a tiny fraction are abundantly habitable. Although this visual is highly schematic, I think it gives a rough idea of the relative probabilities of a random universe being uninhabitable, barely habitable, moderately habitable or abundantly habitable.
What Prediction Does Scientific Materialism Make About Our Universe's Habitability?
Now let us consider: what type of prediction does scientific materialism make about the habitability of our universe? The answer is: it makes a prediction that could not be more wrong.
The actual prediction that scientific materialism makes about the habitability of universe is that our universe should be about the most uninhabitable universe imaginable. This is because of the long-standing problem in physics known as the cosmological constant problem or the vacuum catastrophe problem. Because of weird quantum mechanical considerations, physics predicts the vacuum of space should be seething with a very dense sea of virtual particles, particles that should cause each cubic meter of space to have more mass-energy than solid steel. Under such conditions, no type of life could exist for even an instant – it would be easier for life to exist in the middle of the sun.
So what we get from scientific materialism is the prediction that the universe should be as uninhabitable as anything we can imagine. But suppose we grant a special favor, and simply ignore the predictions of quantum mechanics. Suppose we pay no attention to the whole cosmological constant problem and vacuum catastrophe issue that physicists have been puzzled by for forty years. What type of universe does scientific materialism then predict? It then still predicts that our universe should be an uninhabitable universe. This is simply because an uninhabitable universe should be trillions of times more likely than any type of habitable universe. That's because of all the extremely improbable long shots and coincidences for a universe to meet the habitability necessities I have mentioned (and others I haven't mentioned).
But what if we grant a second special favor, and assume that observers must exist in a universe, perhaps by using some kind of dubious “selection effect” reasoning or “anthropic principle” reasoning. There is no sound basis for granting such a favor, but suppose we grant it anyway. What then does scientific materialism predict? It then predicts that our universe should only be a barely habitable universe. Why? Because, as we have seen, barely habitable universes should be vastly more likely than abundantly habitable universes like the one we live in. The list of long shots and coincidences that must be met in order to have a barely habitable universe is much shorter than the list of long shots and coincidences that must be met for moderately habitable universes or abundantly habitable universes.
So even if we grant two special favors, scientific materialism still makes the wrong prediction about what type of universe our universe should be. But what if we throw in a multiverse – the assumption that there are many universes? Does that help? No, it doesn't help at all. The habitability predictions of scientific materialism regarding our universe are not changed at all if we assume that there are many universes. It is a basic fact of probability math (ignored by multiverse enthusiasts) that you do not increase the chance of success on any one random trial by increasing the number of random trials.
The predictive failure of scientific materialism in this regard is very spectacular. It's a predictive failure far worse than has ever been made by any errant gypsy fortune teller or any misguided apocalyptic preacher. A failure this spectacular is a sure sign of underlying false assumptions. What we need is a worldview that predicts that our universe should be a type of universe like the type that it is, an abundantly habitable universe.