Fine Tuning and the Multiverse
The fine-tuning argument (FTA) is a popular one for theists wanting to prove God. Craig is a frequent proponent. Here is the Discovery Institute on the FTA, and here is CMI's take:
Neither really give a formal argument, so I will give one from here:
It also seems to be the case that not so many parameters need to be fine tuned as certain people would like you to think.
That is not to say there is no fine tuning. It is a thing, and it does need explaining.
X cannot be explained conventionally, therefore I get to insert my pet theory as the default.
Of course, science (and I hope philosophy!) is not like that. If X cannot be explained, then the only valid conclusion is that we do not know.
Even more importantly, there is an alternative explanation. Because the FTA is arguing by default, all we need to defeat it is a plausible explanation. It is not necessary to prove it is true, or even particularly likely. The mere existence of an alternative is enough, because the FTA is based on the implicit assumption that no other explanation is possible.
Fine-tuning occurs at at least three different levels, and the lowest is the easiest to understand and also to refute, so we will start there.
The chances of rolling double six on normal dice is pretty small (1 in 36), but if you keep rolling, you will do it eventually. If you make 10 tries, the chances of success are 1 in 4. Do it 100 times and the probability of failing to roll double six at least once is 1 in 17. The more tries you make, the greater the probability that you will have at least one success, and the chances of failing to do so head towards zero.
The chances of a planet being just right for life are small, but in a galaxy of 100 billion stars, there is going to be a lot of tries.
The last parameter offered by CMI:
And our galaxy is just one of billions, possibly one of an infinite number.
The probability of one planet being just right is so close to one it is almost a certainty.
Well, that is a certainty! If it did not sustain life, we would not be here. This is the anthropic principle: we must necessarily be on a planet that supports life in a universe that supports life.
A possible solution to this is to suppose numerous universes. This is exactly analogous to the planets previously; just as before we a huge number of tries to get to our ideal planet, if there are a huge number of universes, each is a different try to get the ideal one.
The idea that there are numerous universes is called the multiverse.
Admittedly the evidence that these universes exist is lacking, and we do not know what caused the multiverse to exist in the first place, but that puts the theory on the same level as the God-theory. Evidence for God is equally lacking, and we have no explanation for how God came to exist.
The density of matter and energy in the universe affects the curvature of space-time, with a very specific critical value being required for a flat universe - and a flat universe is what we observe. When a physicist talks about fine-tuning, it is probably this that he or she is talking about.
Inflation is a possible solution to the flatness problem, but one of its earliest proponents has since changed his position.
This gets quoted by proponents of FTA a lot, and gets more confusing because inflation is also a source of the multiverse; the process of inflation generates pocket universes. Note that this is a different sense of multiverse, one with the same physical laws in each universe.
When physicists talk about evidence for the multiverse I suspect they are talking about it in this sense.
The multiverse - in the earlier sense - is actually a possible solution.
This Wiki page gives an indication of the various types of multiverse.
Neither really give a formal argument, so I will give one from here:
- The fine-tuning of the universe to support life is either due to law, chance or design
- It is not due to law or chance
- Therefore, the fine-tuning is due to design
How Finely Tuned Exactly?
The argument is based on the claim that changing the nature of the universe even slightly would prevent intelligent life appearing. So far that has not been established - we just do not know what the effects would, or under what conditions life could form. Maybe not life as we know it, but how can we rule out life in an unimaginable form?It also seems to be the case that not so many parameters need to be fine tuned as certain people would like you to think.
That is not to say there is no fine tuning. It is a thing, and it does need explaining.
Argument by Default
Implicit in that argument is that there are no other explanations. As is usually the case, this is an argument by default:X cannot be explained conventionally, therefore I get to insert my pet theory as the default.
Of course, science (and I hope philosophy!) is not like that. If X cannot be explained, then the only valid conclusion is that we do not know.
Even more importantly, there is an alternative explanation. Because the FTA is arguing by default, all we need to defeat it is a plausible explanation. It is not necessary to prove it is true, or even particularly likely. The mere existence of an alternative is enough, because the FTA is based on the implicit assumption that no other explanation is possible.
Fine-tuning occurs at at least three different levels, and the lowest is the easiest to understand and also to refute, so we will start there.
A Planet Suitable for Life
The CMI webpage linked above gives eight parameters, three of which are these:- Our sun is the right colour. If it was redder or bluer, photosynthetic response would be weaker.
- Our sun is also the right mass. If it was larger, its brightness would change too quickly and there would be too much high energy radiation. If it was smaller, the range of planetary distances able to support life would be too narrow; the right distance would be so close to the star that tidal forces would disrupt the planet’s rotational period. UV radiation would also be inadequate for photosynthesis.
- The earth’s distance from the sun is crucial for a stable water cycle. Too far away, and most water would freeze; too close and most water would boil.
The chances of rolling double six on normal dice is pretty small (1 in 36), but if you keep rolling, you will do it eventually. If you make 10 tries, the chances of success are 1 in 4. Do it 100 times and the probability of failing to roll double six at least once is 1 in 17. The more tries you make, the greater the probability that you will have at least one success, and the chances of failing to do so head towards zero.
The chances of a planet being just right for life are small, but in a galaxy of 100 billion stars, there is going to be a lot of tries.
The last parameter offered by CMI:
- The earth’s gravity, axial tilt, rotation period, magnetic field, crust thickness, oxygen/nitrogen ratio, carbon dioxide, water vapour and ozone levels are just right.
And our galaxy is just one of billions, possibly one of an infinite number.
The probability of one planet being just right is so close to one it is almost a certainty.
The Anthropic Principle
Okay, so given all those stars, what are the odds that we should happen to be in orbit around one that sustains life?Well, that is a certainty! If it did not sustain life, we would not be here. This is the anthropic principle: we must necessarily be on a planet that supports life in a universe that supports life.
A Universe Suitable for Life
These are the first four parameters CMI offer:- The electromagnetic coupling constant binds electrons to protons in atoms. If it was smaller, fewer electrons could be held. If it was larger, electrons would be held too tightly to bond with other atoms.
- Ratio of electron to proton mass (1:1836). Again, if this was larger or smaller, molecules could not form.
- Carbon and oxygen nuclei have finely tuned energy levels.
- Electromagnetic and gravitational forces are finely tuned, so the right kind of star can be stable.
A possible solution to this is to suppose numerous universes. This is exactly analogous to the planets previously; just as before we a huge number of tries to get to our ideal planet, if there are a huge number of universes, each is a different try to get the ideal one.
The idea that there are numerous universes is called the multiverse.
Admittedly the evidence that these universes exist is lacking, and we do not know what caused the multiverse to exist in the first place, but that puts the theory on the same level as the God-theory. Evidence for God is equally lacking, and we have no explanation for how God came to exist.
The Flatness Problem
Muddying the waters is that there is more than one fine-tuning problem and more than one multiverse.The density of matter and energy in the universe affects the curvature of space-time, with a very specific critical value being required for a flat universe - and a flat universe is what we observe. When a physicist talks about fine-tuning, it is probably this that he or she is talking about.
Inflation is a possible solution to the flatness problem, but one of its earliest proponents has since changed his position.
This gets quoted by proponents of FTA a lot, and gets more confusing because inflation is also a source of the multiverse; the process of inflation generates pocket universes. Note that this is a different sense of multiverse, one with the same physical laws in each universe.
When physicists talk about evidence for the multiverse I suspect they are talking about it in this sense.
The multiverse - in the earlier sense - is actually a possible solution.
This Wiki page gives an indication of the various types of multiverse.
Summary
The multiverse is a defeater to the FTA, as it offers an alternative plausible explanation for fine tuning. It does not matter that the multiverse (in this sense) is speculative, because the FTA is an argument by default. Any plausible alternative refutes it.Addendum, 21/Feb/24:
Turns out fine-tuning is not as restrictive as some claim,
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