Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Did cosmological natural selection get a reprieve?

  1. Apr 8, 2014 #1

    bcrowell

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The March 2014 issue of Physics Today has an article by Lee Smolin in which he argues that natural laws must change over time. As examples of such theories, he gives Penrose's CCC and his own cosmological natural selection (CNS):
    http://arxiv.org/abs/hep-th/0612185
    My understanding was that CNS had already been falsified in 2010 by the discovery of a 2-solar-mass pulsar:
    http://arxiv.org/abs/1010.5788
    But in the Physics Today article, Smolin says that CNS makes predictions and that, "The two main predictions,[4] first published in 1992, have survived despite several chances to falsify them since.[7] One of those is actually easy to state: The upper mass limit of neutron stars is at most two solar masses." The footnotes are:

    [4] L. Smolin, Class Quantum Grav 9, 173 (1992); The Life of the Cosmos, Oxford U Press, New York (1997)
    [7] L. Smolin, http://arxiv.org/abs/1201.2632 ; http://arxiv.org/abs/0803.2926 .

    The two arxiv papers are from 2012 and 2008, respectively. Their abstracts don't mention anything about empirical tests of the theory. I searched the text of the 2012 paper for the word "neutron," and found only one mention of neutron stars, which is in a reference to this 1997 paper: http://arxiv.org/abs/astro-ph/9712189 ; since it's from 1997, it's from before the discovery of the 2-solar-mass pulsar.

    What's up here? Did Smolin move the goalposts? Did he decide that the 2-solar-mass limit was fuzzy rather than sharp? Was the mass of this neutron star found to be a mistake? Are the error bars on its mass too big to allow it to falsify CNS?

    The article also describes Penrose's CCC as alive and kicking, whereas in fact I think it's clearly been dead for several years.
     
  2. jcsd
  3. Apr 8, 2014 #2
    First of all, I think this question should belong to the cosmology forum. However, I hardly ever visit the cosmology forum, so I couln't have answered you if you had put it there. I personally don't like CNS, and I can't offer you a proper answer about that. However, CCC apparently survived BICEP2 (or at least Prof. Dr. Sir Roger Penrose thinks so). See http://www.sciencefriday.com/segment...s-fantasy.html [Broken].
     
    Last edited by a moderator: May 6, 2017
  4. Apr 9, 2014 #3

    bcrowell

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The reason CCC has been long dead in my opinion is simply that it predicted certain things about particle physics, and those predictions were simply wrong. Specifically, it predicted the existence of massless charged particles, and although Penrose doesn't seem to have realized it for a long time, that's simply completely incompatible with observation.
     
  5. Apr 9, 2014 #4
    ... The major structure of the ccc doesn't (caution) match to our current observation (pointing towards some scalar fluctuations producing tiny variation in density across various scales). However, what's remarkable about the model is the inclusion of critical density suggesting a bounce which is a great 'flexible' mechanism that can hold pretty well to a/ny model especially with new and/or chaotic inflation. It will give some constraint on the large almost infinite value of inflation(assuming it will never end) unless some phase transition is present exceeding inflation IMO.
     
  6. Apr 9, 2014 #5

    martinbn

    User Avatar
    Science Advisor

    Where can I find this prediction? By the way this reason to think that ccc has been long dead applies to many other parts of physics, for example string theory, no?
     
  7. Apr 9, 2014 #6

    bcrowell

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Penrose unfortunately hasn't put any technical papers up on arxiv describing CCC (as far as I know). But he made this claim, for example, in a talk I saw online. The reason is pretty straightforward. To get CCC to work, you have to have astrophysical processes such that at some point in the distant future, *all* massive particles are converted into massless ones. Some of this can happen through formation of black holes followed by their evaporation into Hawking radiation, but not all matter ends up in black holes. Some electrons certainly end up isolated inside their own individual cosmological horizons and therefore can never undergo this process. The only way out is to propose that there are massless charged particles. Then an electron could decay into those.

    No, the reasoning is completely specific to CCC.
     
  8. Apr 9, 2014 #7

    martinbn

    User Avatar
    Science Advisor

    Ah, I see. If remember correctly, he writes in his book that perhaps massive particles aren't stable. Something to do with the fact the universe is not Minkowskian and the symmetry group is different.

    About the reasoning you say that ccc is dead because it predicts massless charged particles and no such particles have been observed. But doesn't string theory predict all kinds of superpartner particles and no such have been observed. How is that different?
     
  9. Apr 9, 2014 #8

    bcrowell

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    They're not analogous, but could we start a separate thread for the CCC stuff? I started this thread because I wanted to ask about the status of CNS.
     
  10. Apr 9, 2014 #9

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    Ben, I'm sympathetic to your wish to keep the focus on CNS (as per thread title!) I don't see that the paper you cite falsifies CNS so perhaps it is still alive and well, not needing a reprieve.
    If they keep finding neutron stars that are two or less, that would seem to support Smolin's upper bound. On the other hand they may have found SINCE 2010 some with masses definitely bigger. I don't know. I checked a while back and didn't find any reports of >2 that had narrow enough uncertainties or weren't in some sense preliminary still needing confirmation. But, you know CNS may have been falsified in the intervening years. I just don't know that it has been.

    The 2010 paper you cite gives the mass as 1.97 plus or minus a bit. It seems to me that wouldn't worry Smolin, he might even be happy with it :smile:

    http://arxiv.org/abs/1010.5788
    Shapiro delay measurement of a two solar mass neutron star
    Paul Demorest, Tim Pennucci, Scott Ransom, Mallory Roberts, Jason Hessels
    (Submitted on 27 Oct 2010)
    Neutron stars are composed of the densest form of matter known to exist in our universe, and thus provide a unique laboratory for exploring the properties of cold matter at super-nuclear density. Measurements of the masses or radii of these objects can strongly constrain the neutron-star matter equation of state, and consequently the interior composition of neutron stars. Neutron stars that are visible as millisecond radio pulsars are especially useful in this respect, as timing observations of the radio pulses provide an extremely precise probe of both the pulsar's motion and the surrounding space-time metric. In particular, for a pulsar in a binary system, detection of the general relativistic Shapiro delay allows us to infer the masses of both the neutron star and its binary companion to high precision. Here we present radio timing observations of the binary millisecond pulsar PSR J1614-2230, which show a strong Shapiro delay signature. The implied pulsar mass of 1.97 +/- 0.04 M_sun is by far the highest yet measured with such certainty, and effectively rules out the presence of hyperons, bosons, or free quarks at densities comparable to the nuclear saturation density.
    Originally submitted version. Final version appears in Nature (Oct 28, 2010)

    Do you know if the final version, published in Nature, said anything significantly different from the arxiv version? All I've seen is this version.
     
  11. Apr 9, 2014 #10
    Is there a concise argument for why a universe optimised for black hole production would have no neutron stars greater than mass 2?

    How does Smolin avoid an anthropic explanation for an optimum black hole count? For example, it would seem reasonable that a universe optimised for black hole production is also a universe optimised for galaxy formation and the greater the number of galaxies, the greater the probability of life. If such an argument were to hold, this would mean that any evidence would offer no support for his hypothesis.
     
    Last edited: Apr 9, 2014
  12. Apr 9, 2014 #11

    bcrowell

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    A star that's less than a certain critical mass will form a neutron star rather than a black hole. The boundary between these two depends on the the mass the strange quark, which is exactly the kind of arbitrary constant that is supposed to be heritable in Smolin's theory. So the theory makes the prediction that every physical constant, including the strength of nuclear forces, is optimized in order to maximize the production of black holes. If you had the freedom to make the strange quark mass whatever you liked, you could tune it up so that the maximum mass for a neutron star would be about 1.6 times the mass of the sun. When Smolin published his theory in 1992, he pointed this out, and said that therefore it was a prediction of his theory that no neutron star should exist with a mass of more than 1.6 times the mass of the sun. If a more massive neutron star was ever observed, it would show that our universe's natural laws were not tuned for maximum black hole production.
     
  13. Apr 9, 2014 #12

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    Exactly! In his picture conditions favorable to carbon-based life are merely BY-PRODUCTS of optimizing for BH production.

    Nature selects for a periodic table of elements with heavier elements like carbon and oxygen (rather than just a few light ones like hydrogen and helium)because molecules like CO and CO2 are good at radiating away heat.
    This makes it easier for gas clouds to condense, because they can radiate off excess energy as they contract.

    Having a richer chemistry makes it easier for stars to form.

    So the idea is that life is an inevitable SIDE-EFFECT of natural selection driven by the reproductive advantage of efficient production of stars from gas and then BH from stars.

    It is logically different from the anthropic principle, which says conditions are pure accident, nothing forcing them to be favorable, but because we're here the accidental conditions must have turned out favorable for us.

    CNS says conditions are NOT accidental, evolution DRIVES towards a set of physical constants which allow gas clouds to condense down to stars, easily, and allows stars to eventually collapse.
    There is no "because we're here, in this one out of a million lucky setup"

    IOW CNS says that if you pick BH formation as the REPRODUCTION MECHANISM then it HAS to be approximately this way, or at one of the evolutionary maxima (hilltops) that are good for reproduction.
    ===================

    Ben! Now I see your point. You did not mention 1.6 in your lead post. You were talking about 2 solar in the original post.
    So what you are talking about is the difference between 1.6 and 2.
    That makes sense all right! One can ask if that constitutes "moving the goal posts" from 1.6 to 2.
    Or is the whole thing considered too "fuzzy" or the uncertainties deemed too large, as you suggested.

    I had forgotten that back some years ago Smolin mentioned 1.6.

    ===================

    BTW check out Rovelli's "Planck Stars" paper (just google planck stars). If that model of BH is right then BH do not make daughter universes. they just do a slo-mo rebound in a Gammaray Burst, delayed for a long time by time dilation. So no "information loss" problem.

    One kind of has to choose. CNS and Planck Stars can't both be right.
     
    Last edited: Apr 10, 2014
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook