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Anthropic reasoning

polymath

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I think this is more philosophy than science&tech... Here's an article about the anthropic principle (from physorg.com):

http://www.physorg.com/news121691428.html

Anthropic reasoning is under debate in the scientific community, and is considered by some as a cop-out. It has now lost further ground as physicists show that anthropic conclusions mostly reflect our biases rather than our knowledge.

Anthropic reasoning uses the fact that the universe seems fine-tuned to support life as we know it in order to explain various physical phenomena that are otherwise unexplained. And why is the universe fine-tuned to support life like us? Because, if it were otherwise, we wouldn't be here to observe it.

Case Western Reserve University physicists Irit Maor, Lawrence Krauss, and Glenn Starkman find this explanation troubling. As they write in a recent issue of Physical Review Letters, the anthropic principle is "based fundamentally on ignorance rather than knowledge." So they have tested the robustness of the anthropic explanation, stripping it down to its simplest scientific elements in order to determine what it truly can tell us about the universe we live in.

“In our work, we have tried to point out the hidden assumptions of anthropic reasoning: in a sense, you need to assume what you are trying to prove,” the three scientists told PhysOrg.com. “Moreover, we have provided a quantitative understanding of this issue.”

Importantly, anthropic reasoning implies that intelligent life requires the precise conditions found in our universe. For example, one of these conditions is the dominant contribution of something that acts like a cosmological constant (CC) to the energy density of the universe. Scientists have observed the CC to be not too large or too small that the universe would collapse or rip apart, but about right to allow matter to form galaxies and planets – a habitat for Earthly life. The anthropic explanation usually claims that life could not exist in a universe with other conditions, and therefore we would not be able to observe a different universe. However, the claim that life could not exist in a different universe is based on the assumption that we are a typical life form.

Maor, Krauss, and Starkman quantify how strongly anthropic arguments rely on the assumption that we are a typical life form. The researchers define a parameter space (a mathematically quantified collection) made of all possible universes with different CCs, and then try to determine a probability for life (either as we know it, or as we don't know it) within this collection. The problem here, they explain, is that we don't know what we can't observe, which leads to a sampling bias.

"As we are the only life-form and this is the only Universe we know, we have no information whatsoever about how Life extends over the rest of the parameter space," the researchers explain in their study. "It might spread over a wide range, implying life can take many forms, or it might require exactly the parameter values which lead to our life-form. . . . However, our limited data set of a single sample of a single point does not probe much of parameter space."

They come to the conclusion that, without the assumption of typicality, the connection between the value of the CC and the existence of life cannot be established, and therefore the existence of life cannot explain the CC’s special value.

"We can say that our existence is a good indicator of the observed CC," they conclude, emphasizing that correlation is far from causation. "The correlations illuminated by our limited anthropic understanding imply that what we ultimately learn from these arguments is that the existence of us and the existence of the observed value of the CC do not contradict each other. That is nice, but hardly surprising."

One application of the anthropic principle is the conclusion that because it's improbable for a single universe to be 'fine-tuned' for life to exist, like our universe seems to be, there have to be multiple parallel universes. What is meant by fine-tuning is that if the values of fundamental physical constants like the planck constant or the electric charge of an electron were slightly different, there would be no stable nuclei or star formation in the universe and life could not exist.

Another example of an improbable occurrence is the fact that ice is less dense than liquid water (most substances are more dense in solid phase), which is necessary for life to exist in the form found on earth. Unfortunately the structure of water/ice is difficult to simulate quantum-mechanically with present-day computer technology, so it's difficult to estimate how small a difference in physical constants would make ice denser than water, making life as we know it impossible.

Anthropic reasoning can be criticised in many ways... For instance, a theory with multiple universes is not falsifiable (as required in Karl Popper's classical philosophy of science). In other words, you can't prove that there are no universes other than ours. Also, a theory with many universes seems unnecessarily complex and seems to be against the principle of Occam's razor, which states that of multiple theories compatible with observation, the simplest should be chosen to represent the truth.

Has anyone else been thinking about this subject?
 
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Has anyone else been thinking about this subject?

yes, i think about this subject and much of the details mentioned, often. maybe ill think about this subject for days on end, and after so much conclusion i think it is naive vein and narcissistic to actually believe we are all that exists in infinite...(lol) more importantly, my ultimate conclusion is what does it matter to us.?
seems just accepting such a thing as fact, will allow for that much more far-thinking-thoughts.

i like how they compare ice and water, ive drawn the same analogy going on about light in deep-space. it scares the crap out of me to think this sort of 'Anthorpic Reasoning' could be dismissed, the two need each other.
 
I think that anthropic reasoning is useful solely as a corrective for its near-inverse, the, "There is a fantastic set of circumstances tailored specifically to intelligent life, so there must be a fantastic, wide-sweeping cause at hand," argument. However, on its own, the anthropic principle does not present a fully fleshed out causal argument for such circumstances, and attaching this principle to fantastic explanations goes against its very reason for being.

Also, a theory with many universes seems unnecessarily complex and seems to be against the principle of Occam's razor, which states that of multiple theories compatible with observation, the simplest should be chosen to represent the truth.

I have two primary qualms with the application of Occam's Razor:
1. What qualifies as "the simplest" (ie, most parsimonious) argument cannot be defined logically rigorously, and thus often defaults to that which lies closest to anthropocentric common sense, and
2. there is no principle logically necessitating that Occam's Razor be true.

Still, as a heuristic, it 'seems to work'.

ebola
 
Since the Anthropic Principle exists to explain holes in the "near-inverse" Occam's Razor is not applicable to this scenario.

Anthropic Principle appears to be an instance of the Plenitude Principle.
 
Also, a theory with many universes seems unnecessarily complex and seems to be against the principle of Occam's razor, which states that of multiple theories compatible with observation, the simplest should be chosen to represent the truth.

that depends on what precisely the other universes offer you. if positing extra universes enables you to take your theory at face value, and not positing them requires you to add something to your ontology that both adds complexity and could be objected to on grounds of ad hocness, then adding universes isn't in clear violation of occams razor. i think there are cases where 'not multiplying entities beyond necessity' entails positing multiple universes, it obviously depends on what we take as entities though, and here i mean entities required in this universe to make our theories make sense.i agree with ebola in saying there isn't a unique way to define simplest, and the way we do so is often anthropocantric.

i always viewed the anthropic principle more as a sanity check on theories/calculations. the cosmologists version of checking probabilities sum to 1 or something. it is a fact that theories have to be consistent with us existing. i don't see how presupposing there to be some special reason for our universe being the way it is can be entertained as a serious assumption in science, it is not verifiable. life forms in other totally different universes could have exactly the same idea, so it doesn't appear to say anything unique about our universe anyway.
 
I'm not sure if people who are not scientists find this interesting, but a related thing is the 'cosmic large number coincidence'... The ratio of the universe's radius and the classical electron radius is about 10^40, and this dimensionless number also appears as the square root of the approximate number of charged particles in the universe, and as the ratio of the strengths of the electromagnetic and gravitational interactions between proton and electron. The number of occurrences of this curious number is just too large to be 'just a coincidence'. Another number that appears in many places is about 10^120.

The large-number coincidence can be explained either by an anthropic argument, i.e. the ratios etc must have this magnitude for us to be here observing them, or by saying that there must be some underlying unknown physical principle that makes these two large numbers 'special'. Of course people would primarily want to find an explanation involving new physics before using anthropic reasoning.

See also http://www.nature.com/news/2008/080220/full/news.2008.610.html
 
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