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The Status of Cosmological Natural Selection (Smolin rebuts Vilenkin)

  1. Dec 18, 2006 #1


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    The status of cosmological natural selection
    Lee Smolin
    25 pages

    "The problem of making predictions from theories that have landscapes of possible low energy parameters is reviewed. Conditions for such a theory to yield falsifiable predictions for doable experiments are given. It is shown that the hypothesis of cosmological natural selection satisfies these conditions, thus showing that it is possible to continue to do physics on a landscape without invoking the anthropic principle. In particular, this is true whether or not the ensemble of universes generated by black holes bouncing is a sub-ensemble of a larger ensemble that might be generated by a random process such as eternal inflation.
    A recent criticism of cosmological natural selection made by Vilenkin in hep-th/0610051 is discussed. It is shown to rely on assumptions about both the infrared and ultraviolet behavior of quantum gravity that are very unlikely to be true."

    Last edited: Dec 18, 2006
  2. jcsd
  3. Dec 19, 2006 #2
    The rationale for the back-and-forth gets more absurd everyday. No matter how this whole mess ends up playing-out, there are going to be a lot of highly respected people who will score a new high in the crackpot index.

    And I say, good, they've earned it.
  4. Dec 21, 2006 #3


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    the issues around CNS are crisply and neatly delineated, as far as I can see.

    the main prediction, Smolin says, is that the observed parameters of cosmology and particle physics are approximately optimal for producing lots of astrophysical black holes.

    it is possible to test this observationally and the prediction has in effect been under test for over ten years.

    (it was made in various papers 1992-1994)

    In my judgment, VILENKIN GAINS stature and credibility as a scientist because he has attempted to seriously address CNS.

    It is remarkable that he was apparently UNABLE to propose a way of changing the parameters so as to increase abundance of astrophysical black holes----those made in the usual way by the condensation and eventual collapse of stars.

    I was fascinated to see that he apparently had to resort to a very speculative argument about non-astrophysical holes that he presumes might be produced (in some model or other) by "quantum fluctuation"----the theory of how that might happen, some form of QG theory----would have to be worked out in detail and tested before one could actually calculate how changing a parameter would increase the abundance of such "fluctuation" black holes.
    So his argument is really just pretense.

    But at least Vilenkin makes an effort and this is very much to his credit!
  5. Dec 21, 2006 #4
    It's really funny that you should mention that, because I held back from saying that there should be a rule that everybody has to keep unprovable speculation to themselves until and unless they can prove that they are necessary to the one true ToE, or at least a valid theory of quantum gravity.

    It seems to me though that his reaching speculation represents an effort to ignore and "explain-away" the obvious potential for identifying a stability mechanism from first principles that will be necessarily inherent to a system that is geared to maximize black hole production.

    What do black holes and intelligent life have in common?... other than the highly relevant and extremely limited ability to directly affect the symmetry of the universe, that is.

    So Lee's well-known contempt for the anthropic principle causes him to miss his own boat, as well, and round-n-round we go.

    Last edited: Dec 21, 2006
  6. Dec 22, 2006 #5


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    Why should that be a 'rule'? That approach seems to discourage anyone from promoting original ideas. Is that scientific? I think not.
  7. Dec 22, 2006 #6
    I could argue that it would prevent the promotion of crackpot ideas that aren't scientific if they aren't even real, and ask how can it possibly discourage the promotion of an original idea that can actually be qualified?

    It would elimnate the kind of flagerant rationale that is specifically designed to support some other unproven speculation, like we see in this case and many others on the cutting edge. I know that this is all too much to expect, but crazy ideas about the true nature of the universe become entrenched assumptions that are taken for granted as fact, far quicker than I ever would have believed possible... and I'm just sick of it, is all.

  8. Dec 22, 2006 #7


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    what Smolin calls the "CNS master prediction" has been encountering a test on another front just recently

    I will quote the central CNS prediction in a moment but first I want to get some links.

    On page 8, section 3.2, he says "Little early star formation."
    There is currently a controversy about this. If the people who claim to have observed early massive star formation happen to win the argument, that would tend to falsify CNS.

    In effect, CNS bets its existence on the people winning who challenge how these recent observations have been interpreted.

    These are observations in the infrared, around 4.5 microns, of a patch of sky about half as wide as the full moon. Some people claim to see massive stars which would be very old (from first billion years of expansion) because of the large redshift. Other people claim that what they are seeing is just the mottled warmth of gasclouds in nearby galaxies. What they think are extremely ancient stars are just nearby farts. Well, that's science folks.
    It makes a difference.

    I'll get some links to the controversy.

    BTW this is kind of a test to help you sort out whether your're bored by the actual nitty-grit of checking a scientific hypothesis, or not bored with empirical checks.

    I checked their article to see what wavelength infrared and on page 2
    "Here we concentrate on the interpretation of the data at 3.6 and 4.5 µm in terms of the luminosities,
    the epochs and the nature of the cosmological sources contributing to these fluctuations."

    they had data from 3.6 to 5.8 micron but it was polluted at the cooler end by intervening stuff. So they were looking at around 4.5 microns.
    That is a redshift of roughly EIGHT. That is a light travel time of THIRTEEN billion years, most of the age of the universe.

    There was a Spaceflight Now article
    posted 15 December and something in press at Astrophysical Journal Letters

    On the nature of the sources of the cosmic infrared background
    A. Kashlinsky, R. G. Arendt, J. Mather, S. H. Moseley
    Ap.J.Letters, in press

    "We discuss interpretation of the cosmic infrared background (CIB) anisotropies detected by us recently in the Spitzer IRAC based measurements. The fluctuations are approximately isotropic on the sky consistent with their cosmological origin. They remain after removal of fairly faint intervening sources and must arise from a population which has a strong CIB clustering component with only a small shot-noise level. We discuss the constraints the data place on the luminosities, epochs and mass-to-light ratios of the indvidual sources producing them. Assuming the concordance LambdaCDM cosmology the measurements imply that the luminous sources producing them lie at cosmic times < 1 Gyr and were individually much brighter per unit mass than the present stellar populations."

    They tried to remove the foreground stuff and thought they saw patterns in the infrared that was left.
    They thought they saw stars of about a THOUSAND SOLAR MASSES.

    That would have been bad for Smolin CNS, but then some other people challenged it.
    Last edited: Dec 22, 2006
  9. Dec 22, 2006 #8


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    The challenge was reported in New Scientist of 19 December

    "Earliest starlight detection disputed

    19 December 2006
    Maggie McKee

    Recent claims that the Spitzer Space Telescope has detected light from the universe's first stars or black holes have been met with scepticism by many astronomers. Instead, they say the light simply comes from faint, relatively nearby galaxies.

    On Monday, they reported finding the same signal in the new patches, arguing that it bolstered their claim of seeing objects from the first few hundred million years after the big bang. Watch a 592 kB Windows Media Player animation of the first stars lighting up after clumping together out of gas in the early universe (courtesy of NASA/JPL-Caltech/R. Hurt/SSC).


    Kashlinksy's team reached its conclusion by removing all of the stars and galaxies that Spitzer could resolve, then studying the remaining infrared glow, called the cosmic infrared background radiation. They attributed bright splotches of light to clusters of the first-ever stars – or to material heating up as it fell into the first black holes..."
    Last edited: Dec 22, 2006
  10. Dec 22, 2006 #9


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    Here's the CNS "master prediction" I said I'd copy in----from page 6 of the paper:

    "...ensemble will have the following property, which we may call the master prediction of CNS.

    M: ...almost no change in the parameters of the standard model
    from the present values will increase the numbers of black holes produced.

    the point about the early stars is that it predicts you don't see a lot of early stars EVEN THOUGH THE GASCLOUDS ARE THERE because there hasn't yet been produced enough CARBON AND OXYGEN and it is the CO molecule that is so good at absorbing energy from collisions and then wiggling and radiating the energy away as heat----which then allows these clouds to radiate off their excess energy efficiently so they can then condense into stars.

    Before slowly bootstrapping an adequate supply of C and O, the clouds are not very good at condensing and the whole process is slow. But after some massive stars form, they cook C and O by fusion, and then they blow up and seed the surrounding cloud with C and O.

    The carbon dust from exploded stars also helps new stars form by shielding condensing clouds from UV.

    the parameters of the STANDARD MODEL happen to be such that we get a large periodic table of stable elements, including C and O, and this promotes this process of stars fusing heavier elements and exploding and seeding surrounding cloud in a SELF-CATALYTIC star-formation feedback cycle.

    if it turned out that there was some ALTERNATIVE way for stars to form rapidly without this C and O bootstrapping, that would undermine CNS idea of one of the ways our Standard Model parameters are optimized for astrophysical black hole production.

    I think that from a scientific standpoint it doesn't matter what people in their wisdom think is likely or unlikely, because that usually has very little to do with what turns out in the future. What is expected is that we take seriously the business of testing this central prediction---that you can't find a way to adjust the parameters so as to make much of an increase in astrophysical black holes.

    It would be really amazing if the universe turned out to be optimized for astro black holes-----and the odd thing is that this challenge has stood for over 10 years and hasn't yet been overturned by observations.
    Last edited: Dec 22, 2006
  11. Dec 24, 2006 #10


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    I think CNS still has a few issues . . . like maximum neutron star mass:
    A 2.1 Solar Mass Pulsar Measured by Relativistic Orbital Decay
    Authors: David J. Nice, Eric M. Splaver (Princeton), Ingrid H. Stairs (UBC), Oliver Loehmer, Axel Jessner (MPIfR), Michael Kramer (Jodrell Bank), James M. Cordes (Cornell)
    Comments: 9 pages, Submitted to ApJ

    PSR J0751+1807 is a millisecond pulsar in a circular 6 hr binary system with a helium white dwarf secondary. Through high precision pulse timing measurements with the Arecibo and Effelsberg radio telescopes, we have detected the decay of its orbit due to emission of gravitational radiation. This is the first detection of the relativistic orbital decay of a low-mass, circular binary pulsar system. The measured rate of change in orbital period, corrected for acceleration biases, is dP_b/dt=(-6.4+-0.9)x10^-14. Interpreted in the context of general relativity, and combined with measurement of Shapiro delay, it implies a pulsar mass of 2.1+-0.2 solar masses, the most massive pulsar measured. This adds to the emerging trend toward relatively high neutron star masses in neutron star--white dwarf binaries. Additionally, there is some evidence for an inverse correlation between pulsar mass and orbital period in these systems. We consider alternatives to the general relativistic analysis of the data, and we use the pulsar timing data to place limits on violations of the strong equivalence principle.

    http://www.arxiv.org/abs/astro-ph/0510380 :
    Title: Double Neutron Star Binaries: Implications for LIGO
    Authors: Chang-Hwan Lee, Gerald E. Brown

    The NS mass in the helium white-dwarf, NS binary
    J0751?1807 is quoted as 2.1±0.20M? [15]. The NS mass
    in J0751?1807 is measured from the period change due to
    gravitational wave emission. The companion white dwarf
    mass is constrained by a marginal detection of Shapiro
    delay. Although the observational indication of high NS
    mass is strong, this mass would be brought down with
    the 4/3 power of white dwarf mass if the latter were in-
    creased, and still fit the same period change. Thus, we
    believe the case for such a massive NS to only be settled
    with a sufficiently accurate measurement of the Shapiro
    decay which pins down the white dwarf mass. It should
    be noted that just in the evolution of NS, white-dwarf
    binaries there is ample possibility for substantial accre-
    tion from the evolving progenitor of the white-dwarf, so
    these binaries are the place to look if one wants to find a
    high-mass NS.
    Last edited: Dec 24, 2006
  12. Dec 24, 2006 #11


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    That paper by Lee and Brown is a good find!
    I gather Gerald Brown is an expert about this. Smolin has cited several of Brown's papers. Quite likely Chang-Hwan Lee as well because he and Brown collaborate quite a bit.

    I spent a while last night reading this paper you linked to. I gather that they are dubious of the 2.1 solarmass figure. Their concern is to anticipate what kind of gravitywave signals one should look for with gravitywave detectors like LIGO. So they have to form reasonable probability estimates of various events to look for in the data.

    Through much of the paper, IIRC, they are promoting the idea that we probably arent going to see NS masses > 1.5 solar
    and that would in fact MAKE SMOLIN RIGHT! It would serve to confirm CNS rather than falsify it.

    but it certainly still is a live issue. Based on observation so far they don't expect to find NS mass > 1.5 solar. And that isolated case of 2.1, Brown and Lee say could be an artifact of mistaken measurement of the dwarf companion, so they cast doubt on it.

    But it still could happen that someone finds an unambiguous case of > 1.5 and that would discredit Smolin CNS. It is a serious prediction and the jury's still out.

    I'm glad you follow this part of it, Chronos. I hadnt registered that paper. thanks.
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