Anthropic principle?

Kamataat

Hi!

I don't really know if this is the right place to post this, but here's the question:

It says that the universe is tuned so that we can exist. So if it were any different, we wouldn't be here to observe it. But why? I mean, there could still be life, maybe even more intelligent than us (or not), if the universe was different. So what's so important about us and so not important about some possible alien race that might have inhabited the universe were it just a little bit different? And why do we assume, that there has to be anyone observing at all? So in essence, I'm asking why should we be considered important enough to have a universe designed for us and not someone else???

- Kamataat

marcus

the Anthropic principle (if you can call it that, and not just a fairytale) has some pretty effective critics. You might be interested in this article

Scientific Alternatives to the Anthropic Principle
http://arxiv.org/hep-th/0407213

when this comes up, click on "PDF" and you get a quick PDF download

It is a nice article. Came out this year and shows that you can get the desired results about the universe on other grounds WITHOUT invoking some vague idea of conscious life.

there are more material observable testable explanations, of why the basic physics numbers (mass of proton, mass of electron, strength of fundamental forces, etc.) might be what we see them to be

a theory that is impossible to prove wrong cannot be right either----it is predictively empty. A kinder way to say it might be to say that a theory doesnt risk being proven wrong, but which is so mushy it can accomodate any future observation whatever, belongs to Philosophy, not science.
Anthropism is saying the fundamental constants and proportions of physics are what they are "Because we're here".
That is impossible to deny or affirm---it is so mooshy it can accomodate whatever outcome of whatever future experiments---so it is vacuous, empty, not science.

And there are alternatives which are testable---or at least one such, as described in that article. So you might be interested in reading about it
and asking for more explanation----several of us at PF have been discussing this and might be able to respond to questions.

Hello Kamataat, I just saw your post right after this one and will reply here (in reverse order) to save space. Yes Smolin wrote that. I am glad you'v had a look at it. Yes Lubos is a strong and cogent opponent of Anthropery and I agree with him there (tho I think his criticism of LQG and CDT gravity is to some degree superficial and misleading---shows extreme bias towards his own specialty: string---he cant believe any other approach has merit). So although I disagree strongly with the Motl on many topics I strongly support him in his rejection of AP.

I think you have the right handle on it. there is an underlying religious urge or a poetic one. It is a Philosophical principle and it may be fairly common for some kinds of philosophy to have a spiritual motivation. I dont condemn this. I like some poetry a lot! But it is a threat when it begins to crowd into scientific investigations.

Kamataat

Was that written by Smolin? If it was, then I've read some of it and pretty much agreed with all what he said (taking into account that I'm only in highschool and thus don't know much about the subject).

It just seems weird to me that people even give time to thought that such a principle could exist. Especially if they're scientists, who normally oppose religious people on these issues. I mean, like Luboš wrote recently, the outcome is the same whether you call it "God" or "anthropic principle" or "chance".

And we don't even know enough about life or conciousness to say such things like the anthropic principle is saying. All we can say, is that we wouldn't exist, but that doesn't say anything about some other aliens. And if there was a God and if he had a reason to make us the way we are, then couldn't he have made us like this in ANY universe, no matter the fundamental constants? (Well, the last thing seems odd even to me, but do we know enought about this stuff to actually deny it?)

So basically I mean, physics should stay away form this stuff until we know more about life, because I think only then can we make such arguments concering the importance of life.

EDIT: Oh, sorry for the long rant. I didn't see that you edited your post already.

- Kamataat

Kamataat

But now I have another question. You said:

"a theory that is impossible to prove wrong cannot be right either...".

I guess I see your point in the usual sense, but let's assume for a moment that we already have an existing theory that is actually right. We might not know that it is, because we could never know whether the next experiment is going to agree with it or not. But let's assume that it IS right, even if we don't know that. Then, if it really IS fundamentally correct, then shouldn't it be impossible to prove it wrong? But wouldn't in that case the above philosophy fail, because if it can't be proven wrong then it can't be right (although, as we assumed earlier, it IS fundamentally right)?

I guess this question has no relation to the real world, becuase it leads to a contradiction that would never happen in reality, because we can never know whether the theory is fundamentally correct or not, but I figured it's a good thought experiment (and maybe someone smarter has a thing or two to say about it).

- Kamataat

marcus

Kamataat, pragmatically speaking what you are worrying about could only be a problem when we humans run out of ideas for experiments to do.
the truest most profoundly truly true true theory is still, in principle, FALSIFIABLE if there is still one experiment that we have not done yet where it predicts the outcome.

I dont admit the existence of an omniscient spectator who knows the outcome of future experiment that have not been performed. So I do not believe that we could ever know that a theory is absolutely true. We can only know that it has predicted right UP TO NOW. So even if an omniscient spectator if it existed might know that it is impossible to prove the theory false WE do not know the outcome of a test. And FOR US the theory is betting its life on the outcome of a future test of its validity. So for us, it is falsifiable. And that is what falsifiable means---or testable---or predictive.

Actually every physical theory that people have experienced so far has a LIMITED DOMAIN OF APPLICABILITY. there is always some range where it works, if it works at all, and outside that range the math breaks down, you get infinities, singularities, it just doesnt compute meaningful answers, or it computes wrong.

As long as that pattern persists, and as long as humans keep on thinking of new ways to put their theories on trial, then it looks to me like the culture of empiricism can continue. but a truly true absolutely true theory with unlimited applicability would finish us off, wouldnt it?

Kamataat

Would it? What if there are multiple ways to describe the universe? Then, in the future, we could use super-powerful computers to look for other TOEs besides the one we already have. I guess things like Ohm's Law and the really basic sutff would stay the same, but we could then find other ways to describe more advanced concepts. Maybe pick up some mid-20th century abondoned theory? I think that is what physicists will do in the future, because we can never know, if our theory is actually the one and only true theory. So they will start in the beginning again, unless of course in the case in which our TOE is so nice and easy to use that there's no point in looking for something different (although I hope that in even in a future like that, we will have people who'll do it just because the like and want to).

- Kamataat

marcus

I feel comfortable with the way you think. I wish you would have a look at
the Basic CDT papers thread, and skim the introduction and conclusion sections (the most accessible parts) of the two most recent. I'd like to know your reaction.

I think finally getting a quantum model of spacetime will provide a new place to do physics (fields and particles) and open up new possibilities for describing why the fields are how they are, how they arise, how they interact (maybe convert back and forth with) spatial geometry. So I (just a hunch really) think getting a good quantization of General Relativity is paramount---at the top of the agenda---and probably has to come before any substantial progress towards t's. of e.

so I am looking at these new candidates for backgroundindependent GenRel-type quantum gravity very carefully. And CDT looks very good right now to me.

they have some online animations of the geometry of lower-dimensional universes. i will hunt for those links and put them at the other thread when I find them.

anyway if you have anythoughts about those CDT papers Id appreciate hearing

Ontoplankton

Kamataat, the anthropic principle is something different from what you're describing. For a less biased, more informative view than Smolin's, see for example this paper:

http://anthropic-principle.com/prepr...smological.pdf

For a lot more information, see the other preprints at anthropic-principle.com:

http://www.anthropic-principle.com/preprints.html

Marcus, I still recommend that you look at some of this stuff as well. Also, look into Bayesian probability theory, which incorporates everything that is good about falsification but does not suffer from its problems (e.g. its inability to deal with probabilistic predictions).

marcus

Dear Ontoplankton, I have looked some of the stuff over. Have to say I was not impressed. From what I've seen, Nick B. is a charming writer in the Philosophy department but not much of a scientist. a bit vague, a bit naive.

Bayesian probablility and associated types of reasoning are familiar to me from grad school days. they are hardly new, it's just that at this point human scientists have no adequate grip on the Prior they would need to do bayesian cosmology inference with any confidence of being on the right track. Bayesian cosmology would produce much smoke and little light.
(Nick B is an example)

I was able to sample one article from his preprints, the top pick "recommended" article in his Cosmology section. If you have another Cosmology article by him that you'd recommend please let me know. This is the one he recommends himself and it's pretty bad

Self-Locating Belief in Big Worlds: Cosmology’s Missing Link to Observation

Nick is vague about the Big World he constantly invokes, and he cites people like Andrei Linde and Alexander Villenkin to the effect that the
"Big World" assumpion is popular. Popular maybe, but neither
clear or, in the physically real multiverse version, sound.
He doesnt make clear whether he means an infinite flat universe model (fairly common among working cosmologists) or one of the "multiverse" models. He says things that are wrong, depending on which assumption, and he mushes stuff together

I will give an illustration. here's the first paragraph of his Summary section at the end

----quote Nick B ---
Big World theories, popular in contemporary cosmology, engender a peculiar methodological problem: because they say the world is very big and somewhat stochastic, they imply (or make it highly probable) that every possible human observation is made. The difficulty is that it is unclear how we could ever have empirical reasons for preferring one such theory to another, since they all seem to fit equally well with whatever we observe. This skeptical threat is different from and much more radical than the problem of underdetermination of theory by data associated with Duhem and Quine. And if left unfixed, the broken connection between observation and theory spills over from cosmology into other domains.
---end quote---

this is wrong, as I will explain. The common cosmology model of a spatially flat infinite universe does NOT accomodate every possible observation, does NOT fit all future experimental outcomes "equally well" as he suggests! And indeed, if you go back to where he introduces the idea Big World you see he merges two very different pictures----the infinite spatially flat model which cosmologists find convenient and have been using for a long time----and also various Many Universe pictures (like from Linde and Villenkin) where there are different sets of fundamental constants.

The standard working model cosmology of an infinite spatially flat universe arising from a Big Bang, with the same fundamental constants throughout (alpha the same, proton mass the same, one speed of light etc.) does NOT lead to any strange new methodological problems.

The example he gives, of some creatures on another planet measuring the CMB temp to be 3.1 Kelvin and we here measure it as 2.7 Kelvin (he seems to think this causes some philosophical dilemma!) is not a problem because
CMB temp is just not a fundamental physics constant.
In the standard flat cosmology model it is the same all over the infinite universe at the same epoch in time, and it is gradually declining----she cools as she expands. If Nick's other creatures measure 3.1 Kelvin that just means they measured the temp earlier than us.

when the Univ. was 12.3 billion years old insted of 13.7 as it is now.

To illustrate how he goes wrong, this is from the very beginning!

---quote---

Space is big. It is very, very big. On the currently most favored cosmological theories, we are living in an infinite world, a world that contains an infinite number of planets, stars, galaxies, and black holes. This is an implication of most “multiverse theories”, according to which our universe is just one in a vast ensemble of physically real universes. But it is also a consequence of the standard Big Bang cosmology, if combined with the assumption that our universe is open or flat, as recent evidence suggests it is. An open or flat universe – assuming the simplest topology[1] – is spatially infinite at any time and contains infinitely many planets etc.[2]
....
....
Here I wish instead to address a more fundamental problem: How can vast-world cosmologies have any observational consequences at all? I will show that these cosmologies imply, or give a very high probability to, the proposition that every possible observation is in fact made. This creates a challenge: if a theory is such that for any possible human observation that we specify, the theory says that that observation will be made, then how do we test the theory? What could possibly count as negative evidence? And if all theories that share this feature are equally good at predicting the data we will get, then how can empirical evidence distinguish between them?

---end quote---

I am taking what are the most representative quotes from the article on cosmology he himself recommends. The first paragraph of the whole thing and the first paragraph of his "summary conclusions" section.

You see he merges the two assumptions (1. standard flat universe, 2. many physically real multiverses with different physical constants) and lumps them into his own Pop Philos. term "Big World", and draws a false conclusion.

It is evident he makes minor mistakes too, since right here in the first paragraph he is saying "OPEN OR FLAT, AS RECENT OBSERVATION SUGGESTS THAT IT IS"
In fact recent observation of Omega = 1.02 +/-.02
suggests that the universe is SPATIALLY FINITE OR FLAT

it is spatially finite if Omega is even slightly greather than 1.
Thus it is spatially finite in the central case 1.02
and also in the part of the error bar where it is 1.01 or 1.03
It is spatially infinite ONLY IN CASE omega is exactly 1.00

You can ask, why do astronomers even bother working with the model that the universe is spatially flat infinite? Well it is mathematically easy to use.
And since the real universe is NEARLY spatially flat you get essentially the same answers when you calculate.

Computationally you cant tell the difference. And assuming flat infinite does not get you the Philosophical Observational problems that Nick imagines. So why not.

And some day there may be an improved WMAP satellite that says
that Omega is, instead, 1.02 +/- 0.01
That is often how science goes. they build a better instrument and shrink the error bar down---less observational uncertainty.

If it goes this way then this will make very little practical difference. the universe will be considered spatially FINITE and just slightly positive curved. And the calculations will look pretty much the same.

And philosophers will have to stop lumping together the spatial flat case with the Physically Real Multiverses picture.

=========
If you try to repair Nick mistakes by restricting everything he says to apply to where you assume at the outset that you have
a Physically Real variety of universes, with all different sets of fundamental constants, then his paper gets kind of vacuous.

Concordance model cosmology runs on Universe (not multiverse) models where the universal constants are the same thruout and it is either spatially flat infinite or what is pragmatically the same: slightly positive curved finite.

There aint no physical evidence or even any solid theoretical grounds for assuming such a Physically Real variety. That is for string theorists to talk about, or people like Andrei Linde.

Linde-type "multiverse" daydreams is what some Inflation theorists invented as a rug under which to sweep some tuning problems with their inflation theory.
But Linde is getting old and his Inflation will, I expect, get replaced by some other inflation that doesnt have those problems.
And then that particular "multiverse" dreamed up by inflation theorists will go away.

LQG already has derived a robust inflation that is generic to Loop cosmology and does not need fine tuning. So that shift is already in progress---already less need for the Multiverse Rug.

Multiverses is what people with intractable problems dream up to get out of problems. Like the string theory landscape debacle. "Hey your theory is supposed to predict how things are and it doesnt! It predicts a huge variety of possibilities!" "Oh that's OK, just suppose all those various universes are real."

but the scientific enterprise keeps on chugging, some give up and some dont. possibly before too long a theory arises that actually predicts why some more constants are what they are

When that happens, I hear people saying: chuck the multiverse rug! those various other universes ARENT real after all. We dont need them to solve our tuning problems because there isnt any.

And the cosmological constant actually comes up in Ambjorn Loll CDT, it looks to me like they have a handle and may be able to say why it is.
or if not them, some other quantum gravity people. the CC is a quantum gravity thing, that you'd expect any decent theory to give a grip on

(string theory seems to want to say it is negative, or a huge variety, which flustered some people, but that is just string and that particular nervousness will, i suppose, pass)

BTW Onto, you said something about Smolin essay "Scientific Alternatives" being biased! I did not notice where he was being biased. Please cite a paragraph.

Cheers,

m

Garth

I believe Smolin is "biased". His own evolutionary universe is invoked to explain the very coincidences that the Anthropic Principle recognises. Yet it depends on the 'fact' that those conditions that maximise the number of black holes in a particular universe are also those that are propitious for life. Yet he does not recognise that this is itself rather a 'coincidence'.
There are many different possible universes, and to evolve any kind of complexity, chemical or biological, there has to be some pretty tight constraints. The universe has to last long enough to allow life to evolve for example. The weak form of the A.P., that this unverse has to be compatible with life is self evident. The prediction it makes, such as the resonance in the nucleosynthesis of carbon from berylium for example, are certain because we do exist.

Ontoplankton

(EDIT: I had some messy text here about your criticisms of Bostrom's "big worlds" paper. I cut it for now, because I don't think you've understood Bostrom's argument why all humanly possible observations will be made. It's true that there is always only one set of physical parameters and laws involved; but e.g. black holes can spit out any sort of brain with any sort of input. Bostrom doesn't require (at first) that the observations are "veridical": black holes can even spit out observers with such environments that they have the exact experiences that they would expect to have if the basic laws were different from what they actually are. Please go over the reasoning in the paper again, carefully: all your criticism is already answered there.)

(EDIT: I cut most of the rest of my post as well, because it wasn't that interesting, and I prefer to make sure we agree on the point above first.)

I made some specific points against the reasoning in Smolin's paper in earlier threads. As for "bias", it's hard to point to any specific paragraph to show that; I just got the idea from his article that he's very angry about these things and thinks recent ideas in string theory should be kicked out of science for blaspheming against his interpretation of Holy Popper. I think his paper represents a very specific opinion and isn't a good neutral introduction for someone new to these things.

Chronos

I think it is fair to say that Smolin has objections to string. I don't think he goes on bashing binges, just points out differences compared to other approaches. Is that biased? I suppose, but like everything else, bias is not harmful when used in moderation. Frankly, I think a lot of people are frustrated, if not annoyed by the lack of progress [i.e., testable predictions] and some of the straw grasping [e.g., anthropery] that goes on in the increasingly obscure worlds according to string.

marcus

I found what you refer to at the bottom of page 3.
---quote from page 3---
Consider two rival theories about the local temperature of CMB. Let T1 be the theory we actually hold, claiming that CMB = 2.7K. Let T2 say that CMB = 3.1K. Now, suppose that the universe is infinitely large and contains an infinite number of stochastic processes of suitable kinds, such as radiating black holes. If for each such random process there is a finite, non-zero probability that it will produce an observer in any particular brain state (subjectively making an observation e), then, because there are infinitely many independent “trials”, the probability, for any given observation e, that e will be made by some observer somewhere in the universe is equal to 1...
---end quote---
I also found his discussion of black holes evaporating and spitting out objects like human astronomers convinced they had just observed or measured something.
---quote from Nick's "Self-locating" paper---
Consider a random phenomenon, for instance Hawking radiation. When black holes evaporate, they do so in a random manner such that for any given physical object there is a finite (although extremely small) probability that it will be emitted by any given black hole in a given time interval. Such things as boots, computers, or ecosystems have some finite probability of popping out from a black hole. The same holds true, of course, for human bodies and human brains in particular states.[7] Assuming that mental states supervene on brain states, there is thus a finite probability that a black hole will produce a brain in a state of making any given observation. Some of the observations made by such a brains will be illusory and some will be truthful. For example, some brains produced by black holes will have the illusory of experience of reading a measurement device that does not exist. Other brains, with the same experiences, will be making veridical observations – a measurement device may materialize together with the brain and may have caused the brain to make the observation. But the point that matters here is that any observation we could make has a finite probability of being produced by any given black hole.
---endquote---

Philosophers traditionally also have speculations about dream states. Perhaps i am just dreaming that the speed of light has been established at 3E8 meters per second and that the CMB is 2.7 kelvin. These things have worried Philosophers over the years but have not had much relevance to science.

Of course one has ways of reducing the probability of being fooled by dreams, if one is concerned by that possibility, by repeating the measurment, involving other instruments and people, making an illusion or a dream less and less likely----of reducing the chance that we are being fooled to smaller and smaller levels.

Now the evaporation of black holes (generally supposed to produce thermal radiation from its particle-output, which exists only briefly) is being invoked to play the same Philosophy tricks with and one used to play with dreams.
From the looks of it, black holes do not even work as well as dreams did.

=====
BTW, referring to that quote on page 3----As I'm used to hearing the word "theory" we would not "actually hold a theory claiming that the CMB equals 2.7 Kelvin". Nick sounds off-beat in his use of words. Instead,
that is a measurment of the radiation spectrum leading to an estimate of the temp parameter associated with that curve. A measurement not quite the same thing as a theory.
Neither the Hubble parameter (that you mention) nor the CMB temp are fundamental constants. Neither of them are "theories" except maybe in some unusual or personal fashion of speech.

Not sure that more discussion of Nick's writings would be helpful. I am going to try to respond to what Garth said.

marcus

Garth, I am puzzled by you this time. I often recognize your posts as on-target and knowledgeable (though I dont say it) But i do not see the point here. what does Life have to do with it?

Smolins CNS (cosmic nat. selection) says that universes reproduce, with gradual variation in their "genes" or fundamental physical constants, towards sets physical constants which favor black hole production.

I dont know if Smolin believes this, or wants to persuade anybody of it. he has offered it as a theory to be tested. I think it is a really constructive proposal. It CAN be tested, rather easily, by seeing if one can observe the constants of nature NOT favoring black hole production.

Any instance of that would make CNS seem unlikely to be true. And the more cases of it one could confirm, the more thoroughly it would be refuted.

I dont understand the words you have enclosed (oddly enough) in quotes.
His theory has nothing to do with life. So it does NOT "depend on the 'fact' that conditions promoting holes are also propitious for life". It is absurd to say this since Life does not enter the equation anywhere. And who calls that a "fact"? You do, right? Smolin CNS does not say anything about Life and doesnt claim anything about it----it just says "check this out, test to see if our universe is optimized to produce holes"

And you fault Smolin for not recognizing that this "fact" (which is not part of his theory and is irrelevant to it) is " itself rather a "coincidence"!
What do you mean by putting "coincidence" in quotes, I wonder?
the "fact" is not part of smolin CNS and neither is "coincidence". The theory is not about coincidences so much as a mechanism

a mechanism which may or may not be driving the set of fundamental physical constants into a configuration that favors black holes.

It may be that some String or Eternal Inflation theorist considers the observed values of the fundamental constants to be a happy COINCIDENCE.
He may think of it this way because he has no testable mechanism in mind to drive them thru sucessive iterations to their observed values.
So then they are indeed a fortunate coincidence favorable to our type of sentient being, so that we were able to take root here.

I would say the key question is this: whether or not a theorist is ready to give up and consider, for instance, alpha to be a happy circumstance (for us) and stop looking for some mechanism that makes it be what it is,
or whether the theorist is NOT ready to give up.

Smolin says CNS is offered as an "existence proof", which it plainly is. It shows by explicit construction that there is at least one testable mechanism that fills the bill. the message is not that CNS itself is right, but that theorists dont have to give up on explaining the fundamental constants.

Garth

Smolin is alive, which would not be possible if the necessary anthropic coincidences were otherwise.

Yes it is possible to believe the Anthropic coincidences to be just a "happy coincidence".

Garth

marcus

we may have reached a point of no discussion.
I dont believe that the values of the fund. constants are just accidental circumstances which we should give up trying to explain

I dont believe their values have any obvious connection to life

If earth's was the only life in the universe and if the earth suffered a collision tomorrow that extinguished all life, I suspect that the fundamental constants would be unchanged

and whatever explanation for their values is valid today would still be valid

and that the Cosmic Nat. Selection theory would still be a testable theory for why they are what they are----maybe wrong, maybe right.

=========

by contrast you are raising issues like "Lee Smolin is alive" which I dont think are relevant

you refer to the set of values of the fundamental constants as "Anthropic Coincidences" which puts your own slant on it, but doesnt tell me anything about the fundamental constants

=========

Personally, i dont need to believe much. I dont have a pet theory. I doubt a lot.

But one thing I am very hopeful about is that there is a lot left to explain.
So that is a kind of belief

Indeed some of the basic parameters of physics MAY be mere accidents, determined at some value when she came into existence. I dont think we have a clue as to which they might be, if any, and as to how to explain the rest.

but at this level of ignorance it would be foolish to give up looking for rational mechanisms to explain the parameters of the models that appear to work

marcus

when people talk about "Anthropic Coincidences" it is not always clear that they have something definite in mind

John Baez has a famous online list of some 26 numbers that are independent parameters of the particle physics Standard Model----or maybe it is some other number besides 26----and there are roughly order 10 basic cosmology numbers.

so maybe there are some 36 numbers that go into the Standard Models of cosmology and particle physics.

As we get better at explaining why they are what they are, we will presumably boil it down to fewer and fewer inputs.

So, if humans dont just give up like..... and call them "Anthropic Coincidences" and stop trying to explain them....we will presumably get it down to a smaller number of inputs.

Just for definiteness, let's say what some of these 36-or-so numbers are, and give actual numerical estimates


[tex]\alpha \approx \frac{1}{137}[/tex]

[tex]\Lambda \approx 3.4 \times 10^{-122} [/tex]

[tex]mass_{\text{ proton}} \approx \frac {1}{13 \text { quintillion}} = \frac {1}{13 \times 10^{18}}[/tex]

[tex]\frac{mass_{\text{proton}}}{mass_{\text{electron}}} \approx 1836[/tex]


anybody have any other that occur to them to post?
there are arbitrary choices to make in presenting the basic constants: for instance the cosmological constant can appear as a curvature (in planck terms) or as an energy density (likewise in planck terms).
the energy density number, rho-sub-Lamda, is conventionally equal to
the number for Lambda, but divided by 8 pi:

[tex]\rho_\Lambda \approx 1.3 \times 10^{-123} [/tex]

It would be great if anyone wants to contribute to the list!

Here is an earlier thread about the fundamental constants. It seems like a bewildering job to list numerical values for all of them---at this point in the history of science we have so many!

http://physicsforums.com/showthread....245#post382245