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Book suggestion in reply to question from oldman

  1. Jun 11, 2006 #1

    marcus

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    Oldman asked an interesting bunch of questions, which at the time i could not reply to because of the context

    Basically it was questions about the unlikelihood of life or more exactly our sort of life.

    the questions came up in the "Beyond" forum, relative to quantum gravity---various theories of what comprises space or spacetime and what underlies the fundamental constants.

    In a larger sense these questions are ones of COSMOLOGY and especially fall in the area of PHILOSOPHICAL ISSUES OF COSMOLOGY

    how improbable is it that the universe should be hospitable to our kind of life

    So last night I remembered an essay written by George Ellis (this is the GFR Ellis who was co-author with Stephen Hawking of a standard reference work "The Large Scale Structure of Space-Time")

    Ellis was invited to contribute the article on Philosophical Issues in Cosmology for the ENSEVELIER HANDBOOK IN PHILOSOPHY OF PHYSICS.

    fortunately his chapter is available online free for download.

    http://xxx.lanl.gov/abs/astro-ph/0602280
    http://arxiv.org/abs/astro-ph/0602280

    the thing is Ellis is a world-class cosmologist and also able to function as a philosopher (he also has religious views, he's a Quaker, but he keeps that separate so it does not intrude here).
    and this is one of the topics where it actually helps to have some philosophical depth!

    Issues in the Philosophy of Cosmology
    George F. R. Ellis
    To appear in the Handbook in Philosophy of Physics, Ed J Butterfield and J Earman (Elsevier, 2006).

    "After a survey of the present state of cosmological theory and observations, this article discusses a series of major themes underlying the relation of philosophy to cosmology. These are:
    A: The uniqueness of the universe;
    B: The large scale of the universe in space and time;
    C: The unbound energies in the early universe;
    D: Explaining the universe -- the question of origins;
    E: The universe as the background for existence;
    F: The explicit philosophical basis;
    G: The Anthropic question: fine tuning for life;
    H: The possible existence of multiverses;
    I: The natures of existence.

    Each of these themes is explored and related to a series of Theses that set out the major issues confronting cosmology in relation to philosophy."
     
    Last edited: Jun 11, 2006
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  3. Jun 12, 2006 #2
     
  4. Jun 12, 2006 #3

    marcus

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    I don't know anything about what's involved in a Quaker upbringing but I don't see any downside to it. In the US context i believe Quakers have acted constructively, with courage, and some intelligence.

    About the landscape of possibilities and the sense of stupendous preposterous improbability, my favorite parts of Ellis essay are pages 41 and 46.

    He has the guts to say, in a high-science establishment context, what I think is an obvious possibility to consider and one that people don't ordinarily discuss much at the present time.

    Admittedly it is without question possible that the universe is NOT optimized for life. Indeed we have no evidence that life is common----our immediate region is hardly swarming with aliens. Life can (obviously) occur, but we dont actually know for sure that it happens a lot.

    If the universe isn't optimized for life then it might still be optimized for SOMETHING ELSE.

    I.e. some unguided unintentional self-organizing process---analogous to biological evolution by natural selection---might be at work.

    One can MAKE TESTABLE HYPOTHESES about such things. Unlike with most "multiverse" scenarios, one can use an evolutionary model to MAKE PREDICTIONS allowing the model to be falsified.

    I find this very exciting----with some potential for a scientific revolution. For example AFAIK no one has yet shown that a small change in the 30-odd parameters of particle physics and cosmology would lead to a greater abundance of black holes. Our set of fundamental constants MIGHT be at a local optimum for black hole production.

    What I admire about Ellis is that he comes to grips with this. he does not talk about it much, but he clearly states the possibility. So far I havent seen other prominent physics and cosmology people doing that, as a rule. when they consider why and how our set of constants could turn out the way they are they tend to act as if there could be no simple mechanism and they often evoke notions of vast improbability and jillions of real other universes.

    if one actually wants to consider oneself a sublimely improbable accident then the evolutionary idea is a fly in that ointment.
    If our section of the universe is parameter-optimized for black hole abundance then MUCH OF THE REST of the universe could likewise be optimized and a great deal of it could have fundamental constants similar to ours (because they evolve that way)

    the image I have in mind is that if you ever did meet an alien it might have eyes----because cephalopods like squid and octopus have eyes rather like ours even though they evolved on a different track. So in a certain sense one could guess that EYES ARE NOT ALL THAT UNCOMMON. And what I am saying is that having a finestructure alpha that is around 1/137 might also be not all that uncommon.

    I think this is what Ellis is saying, if you read his page 41 and 46 closely, and I honor him for it.
    Ellis reference [205] is to
    L Smolin, “Did the universe evolve?” Class Qu Grav 9: 173-191 (1992)
     
    Last edited: Jun 12, 2006
  5. Jun 13, 2006 #4
    Taking the Gap

    Improbable accidents and evolutionary processes can and do co-exist happily. They both shape the world --- a point missed by many Blind-Watchmaker folk, Deists and some Darwinian folk who refute punctuated equilibrium. We and the universe around us are (at least) the result of both these processes. The sudden improbable accident that converted dinosaurs into birds and the slow evolution of African apes into the horde of hominids that now infest this planet were both crucial to you and I conducting this correspondence.

    It seems to me obvious that the name of the Universal Game (if such can be said to exist) is evolution, which brings order out of chaos in so many circumstances; in the physical world, in biology, with inventions like the bicycle, in physics, and in the development of software. And the essence of evolution is the auto-catalytic process --- success breeds success, or Take the Gap, as it were. Examples are the formation of rivers, the role of gravity in the genesis of stars, the development of biological camouflage and the rise and rise of Microsoft.

    Whether the constants of physics evolved in the manner envisaged by Smolin and discussed by Ellis, or in any other way, is a thought that fascinates many, I'm sure, but as you say:

    People are pragmatic and prejudiced about such matters. And the recognition of new kinds of auto-catalytic processes ain't easy --- let alone the making verifiable predictions.

    I haven't read about the reason why making lots of black holes could be an autocatalytic process. Perhaps you can alleviate my ignorance?
     
  6. Jun 13, 2006 #5

    marcus

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    I am not sure what you are asking. You may already understand what I'm about to explain and be familiar with the various points. I will lay out various ideas and references as for a general reader.

    First off, there are the recent papers by Ashtekar and Bojowald on BH and BB bounce.

    In the context of Loop Quantum Cosmology (LQC) the two leading authorities are Abhay Ashtekar and Martin Bojowald. They and collaborators have several papers resolving both the BH and BB classical singularities into a bounce. Gravity in LQG is repulsive at high density--the tentative conclusion is that spacetime does not terminate but, at least under certain simplifying symmetry assumptions, continues. Ashtekar and Bojowald are very cautious about drawing conclusions and they do not point to any explicit connection between their work and Smolin's hypothesis.

    for example
    http://arxiv.org/abs/gr-qc/0509075
    Quantum geometry and the Schwarzschild singularity
    Abhay Ashtekar, Martin Bojowald
    31 pages, 1 figure
    Class.Quant.Grav. 23 (2006) 391-411

    "In homogeneous cosmologies, quantum geometry effects lead to a resolution of the classical singularity without having to invoke special boundary conditions at the singularity or introduce ad-hoc elements such as unphysical matter..."
    page 25
    "For our quantum Einstein’s equation (55), this coefficient ... never vanishes. Therefore, the backward quantum evolution remains welldefined and determines the wave function not only for... In this precise sense, the classical black hole singularity can be traversed using quantum evolution and thus ceases to be a boundary of space-time."

    page 27 in the conclusions

    "Results of the last two sections support a general scenario that has emerged from the analysis of singularities in quantum cosmology. It suggests that the classical singularity does not represent a final frontier; the physical space-time does not end there. In the Planck regime, quantum fluctuations do indeed become so strong that the classical description breaks down. The space-time continuum of classical general relativity is replaced by discrete quantum geometry which remains regular during the transition through what was a classical singularity. Certain similarities between the Kantowski-Sachs model analyzed here and a cosmological model which has been studied in detail [10] suggest that there would be a quantum bounce to another large classical region. If this is borne out by detailed numerical calculations, one would conclude that quantum geometry in the Planck regime serves as a bridge between two large classical regions. Space-time may be much larger than general relativity has had us believe.

    However, as indicated at the end of section IVB significant numerical work is still needed before one can be certain that this scenario is really borne out in the model. Moreover, this is a highly simplified model. It is important to check if the qualitative conclusions remain robust as more and more realistic features are introduced. First, one should extend the analysis so that the space-time region outside the horizon is also covered. A second and much more important challenge is incorporation of an infinite number of degrees of freedom by coupling the model, e.g., to a spherically symmetric scalar field. First steps along these lines have been taken [39, 40] and one can see that the evolution still extends beyond the classical singularity [41]. But a comprehensive treatment still remains a distant goal."

    several papers have appeared since then reporting numerical results. Bojowald has moved from Germany to join Ashtekar's group at Penn State. Several of the postdocs there are helping and they seem to have a focus on this now at Penn State.

    catchall link for Ashtekar papers (most recent half dozen about this)
    http://arxiv.org/find/grp_physics/1/au:+ashtekar/0/1/0/all/0/1

    Bojowald papers
    http://arxiv.org/find/grp_physics/1/au:+Bojowald/0/1/0/all/0/1
    (64 papers mostly in Loop Quantum Cosmology but recently also applying LQG to BH)
     
    Last edited: Jun 13, 2006
  7. Jun 13, 2006 #6

    marcus

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    one thing I'm not sure is how you mean "auto-catalytic". I think it means "self-promoting" but in this context could correspond to what i've heard people call "self-organizing".

    I think the general idea is to have some way of understanding how a system can develop complexity, "by itself". Actually Ellis (pages 41 and 46) is so clear on this that I fear my trying to paraphrase will only muddy up the water.
    =================================

    what Smolin adds to the discussion is an hypothesis leading to falsifiable predictions

    he proposes several empirical observations (notably one about neutron stars) which he says would falsify his hypothesis.

    the hypothesis has a clear operational formulation in the form of a challenge

    YOU CANNOT FIND A CONTINUOUS MODIFICATION OF THE STANDARD MODEL PARAMETERS WHICH WOULD LEAD TO A MONOTONE INCREASE IN BH ABUNDANCE.

    he is talking about standard models of cosmology and particle physics---some 30-odd numbers.
    he is using some vagueness about BH abundance---he really means stellar mass BH resulting from gravitational collapse and is not talking about microscopic BH (which we dont know very much about or even under what conditions they might exist)---he might fudge and say he means a "significant" increase in BH abundance.

    But his challenge boils down to the above. Show me that the 30-odd parameters we have are NOT optimal for stellarcollapse BH production.

    He says for example, that finding a neutron star of 3 solarmass or more would allow for the topquark mass to be adjusted so that such a thing would collapse to hole. That would show that the topquark mass is NOT optimized for BH abundance, because a small change in it would cause there to be more BHs.

    Several predictions like this are discussed in
    http://arxiv.org/abs/hep-th/0407213
    Scientific alternatives to the anthropic principle
    Lee Smolin
    Contribution to "Universe or Multiverse", ed. by Bernard Carr et. al., to be published by Cambridge University Press.
     
    Last edited: Jun 13, 2006
  8. Jun 13, 2006 #7

    marcus

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    if nobody can find a small change in the 30-odd parameters with the desired effect, then we will have to consider the possibility that our standard model parameters are at a LOCAL MAXIMUM in parameter space, for BH production.

    Personally, I think that would be an interesting situation to contemplate. If that were the case, people would naturally want to know WHY.

    The work on resolving BH and BB singularities in quantum gravity context (Ashtekar and Bojowald although they do not talk about Smolin's idea) certainly suggests a possible mechanism

    with BH stellar collapse as reproduction and the 30-odd parameters as "genes", most of the universe would consist of regions where the parameters are near local optima.

    But the BH-BB "bounce" mechanism is secondary, in my view. The first thing on the agenda is to TEST THE HYPOTHESIS that the standard models' parameters are at a local maximum. This should be falsified, if possible. As I say, Smolin discusses several ways to do this.

    The hypothesis has stood for about 10 years now, since around 1994 when first published together with some predictions.

    What I like about Ellis is that he magisterially acknowledges that this hypothesis has some interest----deserves serious consideration by those doing fundamental physics and cosmology research.

    this will mean, I think, that people like Ashtekar and Bojowald will, in future, be able to point this out as a possible consequence of their work without having it seen as "fringe" or marginal of them to mention it. Both of them have a guarded mainstream demeanor---averse to speculation. Ellis helps to make the terrain a bit safer for everybody.
    Darwinian ideas are still revolutionary, still have some of the old unsettling dynamite in them, so recognizing the possibility of self-organization in fundamental parameters is a slow process.
     
    Last edited: Jun 13, 2006
  9. Jun 13, 2006 #8

    SpaceTiger

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    The word "improbable" in this context makes me cringe. Is it improbable that humans would take on the exact genetic configuration that they do? Of course, but that's very a posteriori and the wrong question to be asking. It's more interesting to ask how probable it is for any creature to develop intelligence such that they could question their existence. If it is in fact very improbable, then that suggests something about our origins -- either we are just one iteration of many evolutionary cycles or there was some kind of intelligent design involved.

    However, I'm not convinced we're capable of answering that question right now. Our understanding of evolutionary processes could be described as crude, at best. Similarly, I think we're still a good bit away from answering the related question -- how likely is it that we would live in a universe hospitable to life?
     
  10. Jun 15, 2006 #9
    What you have posted is just fine and helpful. I am indeed a general reader w.r.t. such matters.

    I mean that once an event has happened, it becomes easier or more likely for it to happen again. The name auto-catalaytic derives from another branch of physics. Examples are: once a dollop of water pouring down a featureless slope has displaced slope material, the next dollop is more likely to follow the same course. Hence an emergent property of chaotic hydrodynamic flow --- namely rivers, which (to be pompous) are auto-catalytic phenomena. Burglars follow the same recipe; once they have robbed a house they are likely to return again. I believe that such processes, although sometimes hard to identify, are the essence of evolution.

    Then about whether the present numbers of physics are parameters optimised for BH formation or constants: I can see that G and c will affect this process, but do you include e and h, for example? For me the idea is quite novel; I'm out of date and need to do some reading. Thanks for pointing me in useful directions.
     
  11. Jun 15, 2006 #10
    I must confess that any kind of statistically-flavoured reasoning makes me dizzy.

    An example is the conclusion that the very precise initial flatness of the Standard Model universe required to account for its present "nearly flat" geometry is "improbable". This was critically analysed in dizzying detail by Coles and Ellis in section 2.3.3 in their "Is the Universe Open or Closed?". Despite their statistical sophistry the simple label "improbable" has been vindicated by the agreement of the WMAP results with inflationary predictions of the power spectrum of CMB irregularities.
     
  12. Jun 16, 2006 #11

    marcus

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    interesting thought. not exactly the same as the natural selection idea.
    more compatible with the "co-evolution" picture. once a species STARTS evolving to fill a particular niche----the other species which serve to DEFINE that niche also begin to CO-evolve
    like the channel in the dirt where the water runs
    and so the niche evolves to fit the water, and the water, in turn, cuts the niche. I mean ditch. well something.

    so your plcture is a reminder that in the randomvariation-naturalselection model of evolution, the conditions are themselves dynamic. but I am not well read, hardly read at all, in that business. sitll I am glad to imagine your running water picture

    this is something I believe I know a little bit more about, oldman.
    the numbers (model parameters) inquestion are DIMENSIONLESS NUMBERS
    which in effect take G, c, hbar as GIVEN UNITS in which to express everything else.
    depending on convention also one could take the elementary charge e (that you mention) also as a unit.

    these things define the scale on which all else is quantified, in the standard models of particle physics and cosmology.

    there was an article by Max Tegmark and others (Wilczek, Aguirre, Rees) that listed these 30 odd dimensionless numbers and discussed them some
    I will see if I can find the link.

    http://arxiv.org/abs/astro-ph/0511774

    they dont talk about Smolin's idea of how the numbers could have evolved, but it is a useful background paper because it surveys the 30-odd numbers
     
  13. Jun 17, 2006 #12
    Thanks for the clarification and the reference, Marcus. Having looked at Tegmark et al. I see what is meant by dimensionless parameters. A nice sophisticated way of formulating the puzzle of what fixes the values of dimensional quantities like G, e, h and a host of others (apart from the arbitrary human choice of S.I. standards, such as the second, or similarly arbitrarily normalising them to unity).

    I have also looked at the article by Smolin in which he discusses the possibility that new universes are generated from black holes. One feature of this idea has me puzzled:

    I gather from the WMAP results that our universe's geometry is closely Euclidean (because of the position of the first peak in the power spectrum?). I hope I'm correct in assuming that this is now an observationally proven fact, and that dark energy is now needed to make up most of the deficit of "critical density" for flatness, as required by the general relativistic Standard Model (irrespective of why the universe is flat).

    If our universe was one of those generated by the process Smolin envisages, perhaps involving some sort of time-reversed black hole collapse, how come it's now so flat? Black holes are anything but Euclidean, and I don't know whether a flattening-by-inflation mechanism fits into his picture or not.

    I'm more of a nuts-and-bolts person than a speculator about such matters, so please excuse such crude questions.
     
  14. Jun 17, 2006 #13

    SpaceTiger

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    You're right that the argument is similar, but it rests on the idea that a flat universe is "special" -- that is, physically significant. With no prior information, there is no reason to think that the universe couldn't take on any value of curvature. If we had found that the universe had [itex]\Omega_k\sim10^{-5}[/itex] (which is just as "improbable" as any other value), we wouldn't necessarily be making arguments about the need for a theory (like inflation) to explain it. However, a flat universe is a sort of limiting case in cosmology, with significance independent of our existence.

    Compare this to the events you were describing -- the evolution of dinosaurs into birds or apes into humans. It's not obvious to me how "special" these events are, other than the fact that they led to our being here. How do we know that intelligence couldn't have arisen from some other evolutionary process? What's so special about apes? Why is it so improbable that dinosaurs should lose their dominance?
     
  15. Jun 17, 2006 #14

    marcus

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    by my standards what you are asking is a good question, one of the best that could be asked (maybe I have crude standards:smile: )

    I believe it fits in very well. In the model that Bojowald and Ashtekar use, inflation is generic-----it comes free.

    curious thing about LQC is they did not put the "bounce" in by hand, they did not put in by hand that gravity becomes repulsive at very high density---it came out as a surprise.

    also they did not put inflation in by hand. it comes out of the LQC model without fine tuning anything

    an Indian by name of Dati or Date (two syllables like that) has a paper called "Genericness of Inflation in Loop Quantum Cosmology". I will look for the link. Also Bojowald had an earlier paper about that. I guess there have been a dozen or so papers about inflation in LQC since 2003 or so.

    here is Ganashyam Date (and his postdoc Gollam Hossain)
    http://arxiv.org/abs/gr-qc/0407069
    Genericness of inflation in isotropic loop quantum cosmology
    Ghanashyam Date, Golam Mortuza Hossain
    4 pages, revtex4, one figure. Final version to appear in Phys. Rev. Lett.
    Phys.Rev.Lett. 94 (2005) 011301

    "Non-perturbative corrections from loop quantum cosmology (LQC) to the scalar matter sector is already known to imply inflation. We prove that the LQC modified scalar field generates exponential inflation in the small scale factor regime, for all positive definite potentials, independent of initial conditions and independent of ambiguity parameters. For positive semi-definite potentials it is always possible to choose, without fine tuning, a value of one of the ambiguity parameters such that exponential inflation results, provided zeros of the potential are approached at most as a power law in the scale factor. In conjunction with generic occurrence of bounce at small volumes, particle horizon is absent thus eliminating the horizon problem of the standard Big Bang model."

    BTW while searching I found these 28 papers of Date
    http://arxiv.org/find/grp_physics/1/au:+Date_G/0/1/0/all/0/1
    I see he has co-authored with Bojowald quite a bit.

    I think when Smolin made this conjecture around 1994 (and predicted that the parameters would be at a local max for BH abundance, a scientific hypoth. that can be CHECKED regardless of details about inflation etc) he was essentially making a LEAP. because he did not know that the quantum gravity models of BH and BB would turn out to be similar, suggestive of a link. he did not know Bojowald's 2001 BOUNCE result. he did not know the GENERICITY OF INFLATION result.
    but he put out the prediction anyway

    it is something that can be tested, and perhaps even falsified, without reference to explanations of why it might be true. one can simply ask is, or is not, our point in paramter space AT a local max?

    but no, the near flatness of the universe does not stand in the way of the finiteness of the universe, inflation can take a spatially finite universe and stretch it nearly flat

    I think Smolin's original idea in 1994 or so was in the context that everybody was assuming near spatial flatness
     
    Last edited: Jun 17, 2006
  16. Jun 17, 2006 #15

    marcus

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    I found the original Inflation from LQC paper:

    http://arxiv.org/abs/gr-qc/0206054
    Inflation from Quantum Geometry
    Martin Bojowald
    4 pages, 3 figures
    Phys.Rev.Lett. 89 (2002) 261301
    "Quantum geometry predicts that a universe evolves through an inflationary phase at small volume before exiting gracefully into a standard Friedmann phase. This does not require the introduction of additional matter fields with ad hoc potentials; rather, it occurs because of a quantum gravity modification of the kinetic part of ordinary matter Hamiltonians. An application of the same mechanism can explain why the present-day cosmological acceleration is so tiny."
     
  17. Jun 18, 2006 #16
    It is a delight to discuss such matters with intelligent folk on this forum.

    I agree that a flat universe is a sort of limiting case in cosmology, and I think that it was sensible for some cosmologists to seek and find an explanation for this perceived oddness, namely inflation. But an easy way of putting the curvature situation is simply to say that flatness is “improbable”, even if this is not kosher by statistical standards. After all, cosmologists are used to describing change in the universe simply as “expansion”, which I believe is not kosher by any standards. But this is another matter.

    I also agree that speciation in evolution is nothing special (except for us products thereof!). I don’t believe that apes are special, or that there is some unique evolutionary path to such limited intelligence as we fancy we possess.

    But the demise of dinosaur dominance was improbable because it was caused by the kind of event that (happily for us) only occurs on
    average at intervals of some hundreds of millions of years. In this case there is an ensemble of such events to consider and improbable is “probably” the statistically correct term.
     
  18. Jun 18, 2006 #17
     
  19. Jun 18, 2006 #18

    SpaceTiger

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    In the case of the flat universe, I agree with you, despite the fact that it's a posteriori.


    What's improbable about it? The dinosaurs lasted some 150 million years and 65 million years ago an impact event occurred. For an event that occurs every few hundred million years (a rate that is not known very well), that's not very improbable at all, especially for an a posteriori statistic.
     
  20. Jun 18, 2006 #19

    Nereid

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    How long, the reign of 'the 30'?

    100 years ago, how many of 'the 30' were known? A thousand years ago?

    100 years from now, what will the status of 'the 30' be? A thousand year hence?

    Who can say whether 'the 30' will continue to be, from our best efforts to divine their provenance, improbably coincidentally made 'just for us'? Or whether they will go the way of the atomic weight of chlorine, sulphur, and the earth/fire/water/air composition of the smell of freshly baked bread?

    Haven't we yet learned that the correspondence between our dark cave philosophical musings and the working of the universe is little different from random chance?
     
  21. Jun 21, 2006 #20

    marcus

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    nice short essay Nereid
    on the other hand whatever "the 30" is, it always seems to explain the previous set of parameters

    like the present 30 parameters make some show of explaining the atomic weight of Chlorine

    and the periodic table of elements information makes some show of explaining the nature of fire, and air, ...water as well.

    so one hopes in the future when there is a new set of principles it will look back and clarify the 30-some parameters of the standard muddles.
     
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