I think we can figure this one out in plain English.
A conscious observer finds itself alive in a universe, and learns enough physics to find out that 1) the physical constants of his universe look awfully fine tuned for life, and 2) life is otherwise exceedingly unlikely without fine-tuned constants. Is this evidence for a multiverse over a single lucky universe? As you explain, no. In a multiverse, living observers will see a fine-tuned universe around them; and in a single lucky universe, living observers (given that they exist) will equally see a fine-tuned universe around them. So no update.
But, by the same token, it's also not evidence for cosmic purpose. In a world with cosmic purpose, living observers will see a fine-tuned universe around them. In a world without cosmic purpose, living observers (given that they exist) will also see a fine-tuned universe around them. Similarly, no evidence either way.
So we have three theories: a single lucky universe, a huge multiverse, or cosmic purpose, and all three predict our observation equally well. Bummer.
But we still have the intuition that fine-tuning requires an explanation. Let's try to formalize that into a general principle, so that we can add it to our system and see if anything changes. I think a fair formulation is that we would like our basic theory to be as general as possible. The more arbitrarily precise or complicated elements a cosmological theory requires, we will give it a proportionally lower prior probability. Clearly "pick random constants" is much simpler than "pick constants within this narrow range".
A simple model would be that if a theory requires n bits for its formulation, we give it a prior probability of 2^-n. But that's too harsh. At the very least we need to discount the number of bits of theory needed to have any universe at all; if we call that N, then let's take 2^-(n-N) as our prior probability.
So let's see how our three main theories stack up:
1. There is a single universe, fine-tuned by brute fact, and we're in it. Here the entire fine-tuned values go into the initial theory, so we pay a heavy price by our principle. If we optimistically guesstimate only 40 bits of fine-tuning info, our lucky universe has a prior probability of only 2^-40, which is around 10^-12. Oof.
2. There is a multiverse process that creates universes with a wide variety of parameters. Maybe only the free constants vary, or maybe also the dimensions, or even the shape of the equations. In the most general case, every possible equation that would describe a viable universe, gets instantiated as one. There is very little extra information in this theory, just a few bits to describe "try everything". Equations that don't describe a universe don't even need to be excluded because they won't create one anyway. So if its prior is not 1, it's at worst an order of magnitude or two below. Nice.
3. There is a process that creates universes, and that process favors universes that can harbor life. This means that the basic theory must contain an approximate criterion for life in its formulation. The rules for Conway's game of life compress to ~20 bits of info (google gemini optimistic estimate), which sounds like less than the bare minimum to be able to distinguish life from non-life. So let's give it 2^-20, which is around 10^-6. It's still a heavy burden to carry a criterion for life around, but not quite as heavy as carrying its complete blueprint.
Clearly the multiverse wins by a large margin.
But there's one more thing to consider. Theory #1 creates just this universe, while #2 makes a huge amount of them, and #3 is somewhere in between. Given that we find ourselves in *this* universe specifically, should we also compare how likely that appears in each theory, and update accordingly?
I think not. Here on Earth we don't consider that it requires a cosmic explanation why "I" was born in Spain that day, and not in Botswana or somewhere else. I see the world from Spain, and another guy who was born in Belgium sees the world from Belgium, but it's still the same world, each of us is in the same situation, and there's nothing to explain about that.
Similarly, in a large multiverse teeming with intelligent life, people in this universe wonder how it came to be fine-tuned, and intelligent beings in other universes presumably do the same. So which one *we* happen to be doesn't change anything to our initial conundrum.
To me a universe fine-tuned for life would look a lot different than what we observe. Life is extremely rare, unable to survive in most of time/space, & constantly struggles for survival faced with numerous dangers. In my view fine-tuning would mean a universe optimized for life, not one where life could potentially emerge given the right circumstances & luck which is rarely seen. So the lack of optimization of the universe for life indicates that the universe is not Fine-Tuned for life but that life is a coincidence in nature. My view, laid out more in this paper, is that The Universe is not Fine-Tuned for Life;
In my experience the Fine-tuning argument has been conflated with a religious/creationist argument. In my paper I was replying to the argument from Timothy O'Connor
"According to the defender of the fine-tuning argument, we should infer that our universe is fine-tuned because it was created by an intelligent, powerful designer, who created the right elements in just the right initial conditions as to allow for the eventual emergence of intelligent and sentient life… The alternative hypothesis is that the one universe there happens to be exists as a brutely contingent fact. But this is overwhelmingly improbable."
That's a very different argument than what you said though. With your definition Fine-tuning just means that life is possible though extraordinarily unlikely and if the universe were different life as we know it wouldn't exist. The O'Connor argument takes it far beyond that argument to assume we came about by design rather than chance because the universe could have possibly been different but it isn't.
Anyways, in that 2nd paper I talked about Charles Darwin's chapters in the Descent of Man called Comparison of the Mental Powers of Man and the Lower Animals in which he started the science of consciousness. What do you think of his framework and the subsequent scientific explanations of consciousness that have come about from his approach?
Copilot summed it up rather nicely: the anthropic principle contextualizes the fine-tuning argument within a framework that avoids the pitfalls of the inverse Gambler's Fallacy, making it a powerful tool for understanding our universe's apparent specialness.
I have done some modelling during my years as a research scientist. I usually found that when parameters need to be fine tuned, the models are not stable. Is it possible that the observed fine-tuning is an artifact of the models?
In our normal Bayesian ways of understanding evidence, this is evidence for goal-directedness towards life. Normally when something counts as evidence for something, we don't take them to show that something's gone wrong. I think the standard reaction here is rooted in cultural bias against teleological explanations.
I don't think you need to appeal to a multiverse to defeat the fine-tuning argument. The real problem is that fine-tuning proponents think that it is possible to model what the universe would be like if its physical constants were changed, and you can't do that. If alternate universes are unimaginable, then the fine-tuning argument can't get off the ground. https://open.substack.com/pub/eclecticinquiries/p/the-fine-tuning-argument-cant-get?r=4952v2&utm_campaign=post&utm_medium=web&showWelcomeOnShare=false
I think we can figure this one out in plain English.
A conscious observer finds itself alive in a universe, and learns enough physics to find out that 1) the physical constants of his universe look awfully fine tuned for life, and 2) life is otherwise exceedingly unlikely without fine-tuned constants. Is this evidence for a multiverse over a single lucky universe? As you explain, no. In a multiverse, living observers will see a fine-tuned universe around them; and in a single lucky universe, living observers (given that they exist) will equally see a fine-tuned universe around them. So no update.
But, by the same token, it's also not evidence for cosmic purpose. In a world with cosmic purpose, living observers will see a fine-tuned universe around them. In a world without cosmic purpose, living observers (given that they exist) will also see a fine-tuned universe around them. Similarly, no evidence either way.
So we have three theories: a single lucky universe, a huge multiverse, or cosmic purpose, and all three predict our observation equally well. Bummer.
But we still have the intuition that fine-tuning requires an explanation. Let's try to formalize that into a general principle, so that we can add it to our system and see if anything changes. I think a fair formulation is that we would like our basic theory to be as general as possible. The more arbitrarily precise or complicated elements a cosmological theory requires, we will give it a proportionally lower prior probability. Clearly "pick random constants" is much simpler than "pick constants within this narrow range".
A simple model would be that if a theory requires n bits for its formulation, we give it a prior probability of 2^-n. But that's too harsh. At the very least we need to discount the number of bits of theory needed to have any universe at all; if we call that N, then let's take 2^-(n-N) as our prior probability.
So let's see how our three main theories stack up:
1. There is a single universe, fine-tuned by brute fact, and we're in it. Here the entire fine-tuned values go into the initial theory, so we pay a heavy price by our principle. If we optimistically guesstimate only 40 bits of fine-tuning info, our lucky universe has a prior probability of only 2^-40, which is around 10^-12. Oof.
2. There is a multiverse process that creates universes with a wide variety of parameters. Maybe only the free constants vary, or maybe also the dimensions, or even the shape of the equations. In the most general case, every possible equation that would describe a viable universe, gets instantiated as one. There is very little extra information in this theory, just a few bits to describe "try everything". Equations that don't describe a universe don't even need to be excluded because they won't create one anyway. So if its prior is not 1, it's at worst an order of magnitude or two below. Nice.
3. There is a process that creates universes, and that process favors universes that can harbor life. This means that the basic theory must contain an approximate criterion for life in its formulation. The rules for Conway's game of life compress to ~20 bits of info (google gemini optimistic estimate), which sounds like less than the bare minimum to be able to distinguish life from non-life. So let's give it 2^-20, which is around 10^-6. It's still a heavy burden to carry a criterion for life around, but not quite as heavy as carrying its complete blueprint.
Clearly the multiverse wins by a large margin.
But there's one more thing to consider. Theory #1 creates just this universe, while #2 makes a huge amount of them, and #3 is somewhere in between. Given that we find ourselves in *this* universe specifically, should we also compare how likely that appears in each theory, and update accordingly?
I think not. Here on Earth we don't consider that it requires a cosmic explanation why "I" was born in Spain that day, and not in Botswana or somewhere else. I see the world from Spain, and another guy who was born in Belgium sees the world from Belgium, but it's still the same world, each of us is in the same situation, and there's nothing to explain about that.
Similarly, in a large multiverse teeming with intelligent life, people in this universe wonder how it came to be fine-tuned, and intelligent beings in other universes presumably do the same. So which one *we* happen to be doesn't change anything to our initial conundrum.
So as far as I can tell, Mark is right.
To me a universe fine-tuned for life would look a lot different than what we observe. Life is extremely rare, unable to survive in most of time/space, & constantly struggles for survival faced with numerous dangers. In my view fine-tuning would mean a universe optimized for life, not one where life could potentially emerge given the right circumstances & luck which is rarely seen. So the lack of optimization of the universe for life indicates that the universe is not Fine-Tuned for life but that life is a coincidence in nature. My view, laid out more in this paper, is that The Universe is not Fine-Tuned for Life;
https://philosophicalrebellion.substack.com/p/the-universe-is-not-fine-tuned-for?r=211fuw
Also I'd like to get your feedback on this post of mine if you feel like it;
Charles Darwin & the Anti-Science of Consciousness
https://open.substack.com/pub/philosophicalrebellion/p/charles-darwin-and-the-anti-science?utm_source=share&utm_medium=android&r=211fuw
The standard use of 'fine-tuned for life' just means: for life to be possible, the numbers had to fall in a certain narrow range.
In my experience the Fine-tuning argument has been conflated with a religious/creationist argument. In my paper I was replying to the argument from Timothy O'Connor
"According to the defender of the fine-tuning argument, we should infer that our universe is fine-tuned because it was created by an intelligent, powerful designer, who created the right elements in just the right initial conditions as to allow for the eventual emergence of intelligent and sentient life… The alternative hypothesis is that the one universe there happens to be exists as a brutely contingent fact. But this is overwhelmingly improbable."
That's a very different argument than what you said though. With your definition Fine-tuning just means that life is possible though extraordinarily unlikely and if the universe were different life as we know it wouldn't exist. The O'Connor argument takes it far beyond that argument to assume we came about by design rather than chance because the universe could have possibly been different but it isn't.
Anyways, in that 2nd paper I talked about Charles Darwin's chapters in the Descent of Man called Comparison of the Mental Powers of Man and the Lower Animals in which he started the science of consciousness. What do you think of his framework and the subsequent scientific explanations of consciousness that have come about from his approach?
Copilot summed it up rather nicely: the anthropic principle contextualizes the fine-tuning argument within a framework that avoids the pitfalls of the inverse Gambler's Fallacy, making it a powerful tool for understanding our universe's apparent specialness.
I have done some modelling during my years as a research scientist. I usually found that when parameters need to be fine tuned, the models are not stable. Is it possible that the observed fine-tuning is an artifact of the models?
In our normal Bayesian ways of understanding evidence, this is evidence for goal-directedness towards life. Normally when something counts as evidence for something, we don't take them to show that something's gone wrong. I think the standard reaction here is rooted in cultural bias against teleological explanations.