The “sensible anthropic principle” says that certain apparently unusual features of our environment might be explained by selection effects governing the viability of life within a plethora of diverse possibilities, rather than being derived uniquely from simple dynamical principles. Here are some examples of that principle at work.
- Most of the planetary mass in the Solar System is in the form of gas giants. And yet, we live on a rocky planet.
- Most of the total mass in the Solar System is in the Sun. And yet, we live on a planet.
- Most of the volume in the Solar System is in interplanetary space. And yet, we live in an atmosphere.
- Most of the volume in the universe is in intergalactic space. And yet, we live in a galaxy.
- Most of the ordinary matter in the universe (by mass) consists of hydrogen and helium. And yet, we are made mostly of heavier elements.
- Most of the particles of ordinary matter in the universe are photons. And yet, we are made of baryons and electrons.
- Most of the matter in the universe (by mass) is dark matter. And yet, we are made of ordinary matter.
- Most of the energy in the universe is dark energy. And yet, we are made of matter.
- The post-Big-Bang lifespan of the universe is very plausibly infinite. And yet, we find ourselves living within the first few tens of billions of years (a finite interval) after the Bang.
That last one deserves more attention, I think.
the saga of the 2-dimensional Ardeans that had a rough time coping with their planar world
That would be because they couldn’t actually one another unless their 2D world extruded somewhat, anywhat, into the 3rd dimension. You’re a male square, say, and you’re trying to check out the hottie female square next to you, and you can’t see a thing unless the hottie square has some ‘thickness’ in a 3D way.
I think similarly our 3D world, to be detectable to us, must extrude into a 4th spacial dimension. Or maybe it’s merely confirmation that space is granular, and the 2D space the Ardeans live in, has a thickness of one, um, grain.
I know what I’m trying to say but maybe haven’t said it well. Wouldn’t be the first time.
B, Sean is probably thinking about the coincidence problem in cosmology. Namely that we happen to live in the exact time where matter and dark energy are roughly of the same order of magnitude.
In the far future, dark energy will completely dominate and black holes will be just about everywhere. Life has a very strict threshold of existence time in the infinite accelerating universe.
Anyway, I have no problem with the AP, except in so far as its predictions are tautological. Fred Hoyle’s ‘discovery’ should be viewed as a simple statement of observational science, not as verification of the predictive power of the AP
“It’s only with QM that outcomes of interactions/scattering are truly random and disable the possibility to trace the state back in time.”
I thought something like that until I read Albrecht’s paper. Do let us know what you think after you read it! MAybe you would like to write something in your own blog? Warning: reading that paper may have irreversible effects on your brain…..by the way, I should also have mentioned that you should look at the beautiful art-work in Penrose’s “The Road to Reality” — I mean in the chapter which he devotes to this very question. His explanation of course-graining is probably the clearest ever written.
Hi Dr. Who:
Will do… I think I have that book somewhere… Thanks, I will come back to the question. Might take some time.
Hi Haelfix:
I see – yes, that might be. What I dislike most about the AP is that it is called a ‘principle’. I’d prefer was it called the anthropic ‘constraint’. That’s essentially what I think it is. To everything we observe, we have an additional constraint following from the ‘observation’ that it must be possible for us to observe. This might be useful in some cases, but it shouldn’t be overemphasized and there’s nothing spiritual, religious or mysterious about it. I admittedly don’t see why all that discussion around something so obvious. Best,
B.
Let me suggest that the “sensible anthropic principle” does not explain “certain apparently unusual features of our environment” except in a very limited sense. That is, it explains why we find ourselves in or near such features, but not why such features exist in the first place. The danger is that people will think that anthropic principles are reasonable substitutes for the hard scientific work of explaining the latter.
For example:
Most of the planetary mass in the Solar System is in the form of gas giants. And yet, we live on a rocky planet.
Most of the total mass in the Solar System is in the Sun. And yet, we live on a planet.
The SAP may explain why we find ourselves on a planet, and a rocky one at that. But it does not explain why there are planets, or why some planets are rocky, or why our solar system has the particular set of rocky and non-rocky planets it does. And in fact these latter questions are things which can be (and have been) investigated by the normal processes of science, including the “starting from simple dynamical principles” bit.
If we had ample observational evidence for other universes with other sets of physical constants, some or many of which were probably inhospitable to life — as is the case for non-rocky planets, interplanetary and intergalactic space, etc. — then answering the question “Why do we happen to find ourselves in a universe with such-and-such a set of physical constants?” with the SAP might make sense.
Even without experimental knowledge of other universes, we can still make statements using the anthropic principle regarding the physical constants within our own universe. It’s really, really difficult to do. But it is, in principle, possible.
The first thing one needs to calculate is the probability of intelligent life given a set of physical constants (P(IL|C)). This is, unfortunately, an exceedingly difficult thing to calculate. But at least we can obtain some order-of-magnitude estimates fairly easily.
Then, once we have at least a rough estimate of P(IL|C), we can go about examining various theories that would give rise to the physical constants, to give us an estimate of P(C). Comparing the two, we can obtain information as to whether or not it is likely that our theory for generating P(C) is accurate.
For example, let’s imagine that upon examining physical constant X, we find that it can potentially be much larger (let’s say, a hundred to a thousand times), and we still might have life, but it can’t get much smaller than it is. In this situation, we expect that our theory-derived P(C) must provide us with an estimate that shows that low values of X are more likely than high values. If, instead, the theory predicts we should see high values of X preferentially, then we can rule out this theory as describing reality with high confidence.
Haelfix said:
Anyway, I have no problem with the AP, except in so far as its predictions are tautological.
That depends on how you apply the physics, and to what. For example, the goldilocks enigma predicts that life, past or present, will not be foud on Mars nor Venus, due to the runaway effects that they are subject to that anthropically balanced planets don’t succumb to. Approximately 9 mos from now this prediction will be tested, yet again.
B says:
I see – yes, that might be. What I dislike most about the AP is that it is called a ‘principle’.
Maybe the one that you follow isn’t a “principle”… but the one that I follow is an energy conservation law, and it damned sure is a very strong cosmological principle.
All this talk about deterministic QM makes me think of ‘t Hooft. He also knows where the real problem is… which is the missed interpretation of the negative energy solutions.
The SAP may explain why we find ourselves on a planet, and a rocky one at that. But it does not explain why there are planets, or why some planets are rocky, or why our solar system has the particular set of rocky and non-rocky planets it does…
Wait a minute here… Brandon Carter said that this “line of thought requires further development”, and I interpret this to mean that you have to complete the principle before you can answer this.
Have you done what Carter said needs to be done… first?
Jason,
The situation you describe holds precisely for the string theory landscape and the proton decay rate. Experimentally, it is at least something like twenty orders of magnitude lower than the anthropic upper bound, and, within the string theory landscape framework there is no known reason for P(C) to be concentrated at such exponentially low values. So, according to you ” we can rule out this theory as describing reality with high confidence”. Any idea why people are still promoting the string theory landscape despite this? Do you think it might be because this field has become a pseudo-science, abandoning standard ideas about how to evaluate a theory, because following standard scientific practice would require an admission of failure that people would rather avoid?
Jason (#56),
Leaving aside the issue of string theory/landscape/etc. — what you describe, especially in your last paragraph, doesn’t need the anthropic principle. If the theory predicts large values of X, but we observe (in our Universe) a small value of X, then we can rule out the theory on the usual scientific basis of agreement or disagreement with the evidence. Whether or not low values of X make life more likely is irrelevant.
“i” wrote:
‘t Hooft. He also knows where the real problem is… which is the missed interpretation of the negative energy solutions.
Carroll orignally said:
Most of the energy in the universe is dark energy. And yet, we are made of matter.
Not if dark energy is rarefied mass energy, baby.. because then they are equal.
The “extra” 1/2 in the eigenvalues of the harmonic oscillator Hamiltonian can be thought of as having a phase factor of -1, which represents vacuum energy as being equal to matter.
“vacuum energy” 1/2?, which equates to negative pressure, (-0.5*rho(matter)*c^2), necessarily arises if we require that e-iHT=?1.
This doesn’t just happen to coincidentally fit perfectly with Einstein’s finite static model.
I’d say… “go figure”… but I already know that nobody will… 😉
Peter Woit,
Well, as far as I know, you can only ever rule out a very specific class of theories with very specific dynamics. If we show that our theory doesn’t fit the anthropic bounds, then that doesn’t necessarily mean that we should throw out our theory entirely. Yes, it means that this specific incarnation of the theory is almost certainly incorrect, but it doesn’t mean that any potential modification of the theory is.
I will admit that I don’t know a whole lot about the string theory landscape. I like the principle of the idea, in that I think it’s the sort of idea that can one day successfully explain our observable region of the universe, but I don’t know enough about the details to comment on the merits (or lack thereof) of the string theory landscape.
Now, then, if I take what you have said at face value, and assume that nobody has yet found a better solution within the string theory landscape, then we have the question as to where to go next: do we have another answer from some other theory that provides a better fit to observation? Or is this the best we have where a truly fundamental theory is concerned? If the string theory landscape, even if it is a really bad fit to the data right now, is the best fit we yet have, then that seems to be reason enough to examine the string theory landscape further. It might be interesting to see comparisons of other theories along anthropic bounds, to provide an argument for why theory X is preferable to pursue.
Peter Erwin,
Actually, we need the anthropic principle, because we need to know whether or not our value of X is large or small, and investigation into what sorts of universes can contain life can potentially tell us that.
Taking vacuum energy as an example, most theories would predict that our value for the vacuum energy is absurdly small. But what is it compared to the subset of universes that can contain life? Is our vacuum energy just barely small enough that life can form? Or could it have been a few orders of magnitude higher and still produce life? If it could have been a few orders of magnitude higher, then we need to find a theory that predicts a very small value for the vacuum energy. If we find that the vacuum energy could not have been much higher at all, then any theory that predicts a large value, as long as it allows the possibility of a small value, is just fine.
Hi Island,
Maybe the one that you follow isn’t a “principle”… but the one that I follow is an energy conservation law, and it damned sure is a very strong cosmological principle.
I’ve made very clear what I am talking about here:
Thoughts on the AP
And for me that’s it. I don’t think it deserves more thought. If you want to talk about the energy conservation law (not sure though which), why don’t you talk about the energy conservation law ?
All this talk about deterministic QM makes me think of ‘t Hooft. He also knows where the real problem is… which is the missed interpretation of the negative energy solutions.
Oh, really? That’s quite interesting, do you have a reference?
Best,
B.
Jason,
Before deciding that the string theory landscape is the “best fit we have”, and that you like the principle of the idea, I suggest you look into it a bit more closely. I think you’ll find that it’s a classic example of pseudo-science: carefully constructed so that it can’t be confronted with experiment, and, in the few cases when it appears that it can, it fails badly and its proponents start going on about “well, we’re going to ignore that, and hope that some fix will someday be found for that problem.”
No, it’s the tags!, I’m certain of it… heheh
Hi B,
http://arxiv.org/abs/0707.4568v1
The states with n for some reason. Of course, we also do not have the ‘vacuum energy’ 1/2 ? , which would have emerged if we would have required e-iHT = ?1 . This minus sign is as harmless as an overall addition of 1/2 ? to the hamiltonian, but perhaps it will mean something in a more complete theory; we will ignore it for the time being.”
Just like the WMAP anomalies… “for the time being” is infinite…
The disappearance of the negative energy modes is very troublesome, however. In a single oscillator, one might still say that energy is conserved, and once it is chosen to be positive, it will stay positive. However, when two or more of these systems interact, they might exchange energy, and we will have to explain why the real world appears to have interactions only in such a way that only positive energy states are occupied. This is a very difficult problem, and, disguised one way or another, it keeps popping up throughout our investigations. It still has not been solved in a completely satisfactory manner, but we can try to handle this difficulty, and one then reaches a number of quite interesting conclusions. In short, our problem is this: in a deterministic theory, one can reproduce quantum-like mathematics in a multitude of ways, but in many cases one encounters hamiltonian functions that are either periodic (in case time is taken to be discrete), or not bounded from below (when time is continuous). Can the real world nevertheless be approximated by, or rather exactly reproduced in, some deterministic model? What then causes the hamiltonian of the real world to be bounded below, with a very special lowest energy state, the ‘vacuum’, as a result? Without this positivity of H , we would not have thermodynamics. The hamiltonian is conjugated to time. Is there something about time that we are not handling correctly?
Bee said:
If you want to talk about the energy conservation law (not sure though which), why don’t you talk about the energy conservation law ?
The *necessarily inherent* prediction of any true anthropic cosmological principle is that there exists a mechanism that enables the universe to “leap”/Bang/evolve to higher orders of the same basic structure in order to preserve the second law and the arrow of time… INDEFINITELY.
This is also empirically evidenced by our leap from apes to harness fire… and beyond.
I don’t make *inherent* predictions… I simply don’t ignore the physics that makes them… 😉
Peter,
We could consider something like the landscape to be pseudoscience if it didn’t come from a well-motivated and consistent theory like string theory. Since the landscape does appear to be a feature of string theory, then we have to take it seriously since this is the best theory of quantum gravity around. We may not like the landscape and hope it turns out to not be true, but we can’t just dismiss it out of hand. The universe has no obligation to conform to our wishes.
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Eric,
Yes, the universe has no obligation to conform to our wishes, but we do have obligations as scientists, and these obligations include admitting that a theory is wrong when it implies things that are drastically different than what is observed. To the extent the string theory landscape makes any predictions at all, it makes one that protons will decay at a rate many orders of magnitude faster than observed. The universe has no obligation to conform to your wish that string theory is true, and it has spoken…
The landscape predicts that protons will decay at a rate many orders of magnitude faster than what’s observed? Maybe for specific vacua, but I don’t think you can claim this as a general statement. There are certainly many vacua with an MSSM-like particle content where the proton decay rate is within experimental bounds.
Peter Woit,
Bear in mind that I haven’t claimed or concluded that the string theory landscape is the best fit we have. Given my ignorance, it would be foolish to do so. It was more of a question, really, as to whether we had anything better.
My liking of the idea has little to do with the experimental validity, but rather more to do with the approach: string theory, it seems, is a theory that can describe a tremendous variety of potential low-energy physics. And yet we may have the potential of describing our own realization of low-energy physics as one of a small subset in which life can form. These properties alone are what make me think it a pleasing theory. I won’t claim that this offers the theory any merits, just that it seems to me an argument that it is something useful to investigate until something else comes up that can provide similar descriptions, but do so in a way that is more likely to describe our own region of the universe.
So, I guess my question would be: do you think there [i]is[/i] a theory that provides as fundamental a description of our universe, but offers predictions that are closer to observation?
And yes, I think one day I may educate myself more strongly in string theory, or perhaps some other theory attempting to describe some of the same things, but for the moment I have enough on my plate, and am content to just be a bit of an armchair physicist where this is concerned.
Eric,
I’m talking about the kind of statistical prediction that the anthropic landscape people push as the only kind of prediction you can get out of the landscape (the kind Jason was explaining). If you want to throw these out and say that any vacuum in the landscape is fine, no matter how statistically unlikely it is, then string theory inherently has no testable predictions at all, and you’re still doing pseudoscience.
Jason,
Asking for a theory with “predictions that are closer to observation” doesn’t really make any sense, since string theory essentially makes no predictions at all. Unfortunately you just can’t evaluate string theory at all on the basis of how close it is to observation. Which is why it is in danger of devolving into pseudo-science rather than science.
Neil B: … the saga of the 2-dimensional Ardeans that had a rough time coping with their planar world…
WhatMeWorry: That would be because they couldn’t actually one another unless their 2D world extruded somewhat, anywhat, into the 3rd dimension. You’re a male square, say, and you’re trying to check out the hottie female square next to you, and you can’t see a thing unless the hottie square has some ‘thickness’ in a 3D way.
I think similarly our 3D world, to be detectable to us, must extrude into a 4th spacial dimension. Or maybe it’s merely confirmation that space is granular, and the 2D space the Ardeans live in, has a thickness of one, um, grain.
No, there doesn’t need to be an extrusion into the 3D world – the 2D beings would see the world in front of them as a line, with brightness and maybe “2D” vision of relief front to back (not like seeing a plane!) if they had one eye above the other for 2-stereo vision! The idea of extrusion does have some interesting physical ramifications for curled up extra dimensions etc.
The real problem for the Ardeans is their physics, as I noted: With a 1/r consequence of the generalized Gauss law, the potential energy between charges and masses would be infinite. That should cause infinite inertia due to mass-energy equivalence at the crude classical level, but somehow the Planiverse enthusiasts didn’t note that.
BTW: I know, I may have bragged about being part of top Google search for “quantum measurement paradox” rather too much. Oddly: several days ago, the search results referencing me dropped from the top 2-4 lines consistently for years down all the way to #9, I mean almost overnight. Um, could someone have Googlewashed those links or Googlebombed upwards the competition or somesuch? Well, it would be hard and fratricidal to kick down lepp.cornell, but maybe kicking up the alternatives wouldn’t be so hard? It’s just interesting – someone/s going to all that trouble would be a spiteful bastard with no life. So really, did Google just change their way of rating pages? Thanks, the answer would be broadly interesting in any case.
Let my mind light up your mind.
How can it be words combined from thousands of years ago still ignite