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Big Bang energy density

  1. Jul 31, 2004 #1

    marcus

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    the big bang has been studied by a number of people and found
    not to contain a singularity
    (the density does not go infinite but has a finite limit)

    a good recent paper is
    http://arxiv.org/gr-qc/0407074
    Genericity of the Big Bounce in isotropic loop quantum cosmology'
    Date and Hossain

    they calculate, among other things, the maximum energy density that occurred right at the crossover between contraction and the onset of expansion

    you can guess
    the energy density at the onset of expansion is bounded (Date and Hossain argue) by our old friend the planck energy density!

    So we can say, in joules per cubic meter, what is the mother of all energy densities.

    or if you prefer in kilograms per cubic meter---with the understanding that it is kilograms of mass-energy---using mass to measure equivalent energy content

    We can figure it out----the planck energy unit is 2 GJ------2E9 joules
    and the planck unit volume is 4.2E-105 cubic meter
    So just divide and it comes out around
    4.6E113 joules per cubic meter.

    divide by c2 if you want kilograms per cubic meter
    i guess that means divide be 9E16

    planck unit energy density may seem useless because so huge
    but it is actually an OK unit and its nice to know that it was back there
    at the bounce and so-to-say participated in bringing us into being
    and there it is: 4.6 x 10113 joules per cubic meter
     
    Last edited: Jul 31, 2004
  2. jcsd
  3. Jul 31, 2004 #2
    This only leaves the question of how everything got started still unanswered. You're "begging the question". You're stating in effect that there is no reason for the universe to even start, and thus even to exist at all. So in essence you are saying the the universe as a whole is illogical. There is no getting around it. You must answer how spacetime came into being from nothing to begin with, however long ago that was.
     
  4. Aug 1, 2004 #3

    marcus

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    Please do not put words in my mouth
    I AM NOT SAYING THE UNIVERSE AS A WHOLE IS ILLOGICAL
    on the contrary I think highly of the universe and am hopeful it be
    inherently logical.
    Or to turn it around, I have high expectations of human reason, that it will turn out equal to the task of finding the universe logical!
    for the universe is just as she is,neither logical nor illogical, and the challenge is whether our thought process is adequate to fathom her.

    why are you pressing me to answer some belief-type question?

    science is organized doubt, said Feynmann.


    The important thing is not to have beliefs, but to be able to reserve judgement when necessary

    In science i do not have to pretend to know what is not yet empirically established. If we do not know something, fine, maybe next year we will.

    It is in religion that they are always jumping the gun and believing some story because it sounds nice, or it appeals to their desire to feel secure and loved, or important.

    Wait. Bit by bit the universe is getting clearer.

    Dont you think it is wonderful that humans have already seen back before the big bang ex-singularity? Now the big bang has been gotten rid of, at least as some grand Where-it-all-began. Let's take the time to rejoice in that and hold off complaining that we still dont know everything.
     
  5. Aug 1, 2004 #4
    Personally I think singularities will only ever exist in mathematical voodoo but will never apply in reality. Have they had singualarities on star trek yet ?
    You think they would be good breakfast cerial ?
     
  6. Aug 1, 2004 #5

    Chronos

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    I endorse that concept. The Planck density is incomprehensible, yet finite. 10-94 is a pretty big number. The mere notion we can peek back into time as far as we have is no less than amazing. It is scary how smart some people have been, and are. I think they are aliens [see the push theory of gravity thread].

    Footnote: I entirely agree with you, Bozo. Singularities only exist mathmatically.
     
    Last edited: Aug 1, 2004
  7. Aug 1, 2004 #6

    Chronos

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    Well, that is a very good question. At least I think so. Consider this: A universe, such as ours, was not the first 'quantum fluctuation' to result in a 'universe'. Assuming 'nothing' is forbidden by quantum theory, a universe such as ours is the inevitable result.
     
  8. Aug 1, 2004 #7
    How it got started, where did it come from .. etc ?
    These types of questions are solved with an infinite everlasting universe
    as they become irrelevant.
     
  9. Aug 1, 2004 #8
    As I understand it, quantum fluctuations are something inherent to fields inside a larger space - a space that has the physical properties that accommodate quantum effects. These fluctuations presuppose a pre-existing background spacetime of some sort with these physical properties. So there is no indication that quantum effects have any influence over the creation of the background spacetime to begin with.
     
  10. Aug 1, 2004 #9

    That is the logical question that arises.

    The Question: Can you get something from nothing?

    Yes or No

    I know Marcus has not dealt with the very foundation that logically arises from the question above. You do not have to be religious, to ask this question. If you cnanot answer it logically what must you fall back on? Is there a a basis of the logic in how we must answer this?

    My take has been to assume, that there is a background and I am dependant on it, or I could not make sense. I have based it on that question. I have to believe that by answering the question as to something arising from nothing that this cannot be so. Maybe I have been wrong, to take this position?

    I look to LQG and how they deal with this. How would we answer the origins of the universe from the original question if we take this position? That somethng can? I am open to correction anywhere along this post.

    The example following, raises important issues about consistancy and logic. Can we see the totality of the universe in the varying actions within that universe. From a back ground dependency I see that we can, so how would Lqg do it? Pathway integrals plotted out in Feynmens toys models? How much more specific has they become when they look to Glast for a discritption of the early universe for comparison.

    Hopefully the question can be dealt with apporpriately first. I would not settle for a religious point of view but one with reason. So is there a reasonal explanation from the logical position?
     
    Last edited: Aug 1, 2004
  11. Aug 1, 2004 #10

    marcus

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    I'm totally clueless about where it all came from
    and like a bird with one note I keep saying
    "what does it predict?"

    if you can come up with a picture of where it all came from even if their are some vague or fuzzy steps in it but at least it plausibly seems to predict something, then it is meaningful in a way and might be tested.

    if physicists ever run out of things to predict, then physics-as-we-know-it will be out of gas and we will have to get out and walk to the next civilization. every theoretical advance depends on making and testing predictions

    the reason I find myself so completely at a loss is that I cannot conceive of how a theory of Where-it-all-came-from could predict something, which we arent yet sure about, which has the possibility of being found not so, and if it did not check out would refute the theory.

    if anyone here can it would be great
     
  12. Aug 1, 2004 #11

    marcus

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    Oh, it was Chronos I think who said the energy density at the bounce was around

    1094 tons per cubic meter

    or 1094 times the density of water

    (im not sure what exactly was meant but something like this probably)

    I think that is about right. Let's see.
    we are using the Planck energy density as a pretty good guess
    (being what Date and Hossain said, among other people)
    and I estimated that to be 4.6 E113 joule per cubic m.

    so you divide by the square of speed of light 9E16
    and you get 0.5E97 kilogram per cubic meter
    andthat is 0.5E94 tonne per cubic meter

    so about 94 orders magnitude more dense than water
    OK so the estimates agree (encouraging, I wasnt sure of mine)
     
  13. Aug 1, 2004 #12

    turbo

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    I think we are in this quandry because of a peculiar philosophical preference for closure. There is a 100% chance that the universe will exist, because here we are in it. That is not the same as saying that there is a 100% chance that the universe had a beginning. Many people, however, cannot philosophically tolerate a universe that did not "begin" and will not "end". The Big Bang faction of this group is the most powerful, vocal force in cosmology today. They insist that there was a beginning and can tell us authoritatively that the beginning was 13.7Gy ago. The science that they use to "prove" this is very accurate and predictive up to a point, BUT only because of all the assumptions and constants loaded onto the Standard Big Bang Theory to keep it in line.

    We must bear in mind that until Kepler discovered the elliptical nature of planetary orbits, Copernican cosmology was accurate and predictive. It was accurate and predictive, though, only because of all the epicycles that were tacked onto the theory to make it conform with observed planetary motion. Proponents of the SBB theory claim that it is provable, testable, consistent, etc, but it is obvious from the great many "epicycles" tacked onto SBB that it is in trouble. SBB cannot be true unless we accept the existence of Dark Matter, Dark Energy, early inflation, etc. In fact, our understanding of gravity is hobbled by the same type of problems. Gravity is proportional to mass, but we cannot predict the mass of an atom by adding the masses of its constituents, so we measure the shortfall and attribute the shortfall to theoretical Higgs particles (which have not been found at their predicted energies) acting across a theoretical Higgs field. We cannot explain the anomalous rotational rates of spiral galaxies except by positing the existence of a cloud of dark matter around each of them that is about 10x more massive than the galaxy AND distributed in a non-uniform manner that "fixes" the anomalous rotation. Gravity is a pretty darned basic force, and we don't have a sufficient grasp of it (or the mass from which it arises) to explain our universe without these "epicycles". We badly need a Kepler right now, but if he (or she) shows up, the priesthood of Big Bang orthodoxy will promptly excommunicate him and deny him any support or resources.
     
    Last edited: Aug 1, 2004
  14. Aug 1, 2004 #13

    marcus

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    I share some of your attitudes but you risk making a dogma of
    the fact that people are dogmatic

    I would like to know your reaction to this:
    it is an 18 page document and the pages are slides
    (only a few words per page, or a picture
    with some numbers)

    it is part of the movement in quantum cosmology to do away with dark matter

    (or at least do away with some of the dark matter, there probably is some matter we cant see that really is floating around out there, but some of what is posited to explain galaxy rotation curves might be just an "epicycle" as you suggested)

    this is slides of a talk Smolin gave in Poland in February 2004
    "Quantum gravity with a non-zero cosmological constant. Part III: Is there a new scale?"

    part of what I find impressive is the graphic presentation of some rotation curve data from individual galaxies.

    if you are thinking of Kepler, then the rotation curves are like the orbit of Mars was for JK. maybe.

    see if you can find this at the Polish Winterschool site

    http://ws2004.ift.uni.wroc.pl/html.html

    you will have to find where it says "lectures" and click on lectures and scroll down the list to smolin's three lectures and get the third

    what I am thinking is the real situation in cosmology may be more fluid and less locked-down than you think----it has an unsettled feel to me (even tho it is human nature to be dogmatic and all, as you rightly point out)
     
    Last edited: Aug 1, 2004
  15. Aug 1, 2004 #14
    It will always come back to one simple question.

    Did the universe begin from nothing?

    If you can't answer that, then you have to assume it always existed?

    This would govern your very principals and explorations?

    In my case, energy has always existed, because, I could not see something coming from nothing.

    Is this not logical?
     
  16. Aug 1, 2004 #15

    turbo

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    You are right. It is not true that all physicists are monolithic in their support for the SBB theory, nor did I mean to imply that, but we are truly in need of some fresh ideas. The universe is incredibly complex, but we know that complexity can arise from small pertubations in otherwise simple systems, and my gut feeling is that we need to find a way to make the modern "epicycles" go away.

    Thank you for the great link. I have bumped into Smolin on Wikipedia whle looking up Loop Quantum Gravity, but had not seen those slides. If the LQC people can manage to reconcile MOND to relativity, maybe the "epicycle" of dark matter to explain gravitational rotation will be dispensed with.

    One very interesting effect of LQG is the quantization of space-time. If space-time comes in discrete quanta, forming a Planck-scale "foam" of spin loops, then the propogation of light and other radiation through space can't be thought of as continuous, except at macro scales.
     
  17. Aug 1, 2004 #16

    marcus

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    I agree, that would really be fine.
    Especially if it can be done in a mathematically elegant way.

    Smolin is a risk-taker
    he is suggesting that the U has this additional length scale L
    that shows up in various ways
    the cosmological constant is the curvature quantity: 1/L2

    the acceleration scale in the mond-phenomenon is
    the acceleration quantity: c2/L

    the anonmalous pioneer accelerations is c2/L

    he says some or all of these things can be unrelated accidents, mere coincidence, and on the other hand one or more might be pointing to a fundamental length scale

    maybe it was a very low frequency wave or fluctuation that our U got early in its life and is a constant of nature-----or maybe it doesnt exist

    but he is willing to contemplate the idea that there is this additional very long length L, on the order of 10 billion lightyears that is a built in scale, like some other things are built in (speed of light, planck mass)

    it strikes me as worth watching.....might go away, and might not.

    (also I have a high esteem for Etera Livine, who has picked up on this "third scale" possibility, so it isnt just Smolin, other people are wondering about it too)
     
  18. Aug 1, 2004 #17

    turbo

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    http://xxx.lanl.gov/abs/astro-ph/0204521

    Here is a really nice overview paper on MOND. The authors freely admit that the modification of Newtonian dynamics was ad-hoc. They offer the compelling argument, though, that it predicts the rotation curves of large and small galaxies very well with one free variable - the mass-to-light ratio of the visible portion of the galaxy. On the surface, MOND looks like another "epicycle", but it's predictive powers are impressive. Someday, we may find out why that ad-hoc modification works - what deficiency in our understanding of gravity are we rectifying with that patch?

    About the anomalous Pioneer acceleration: what if L is not invariant, but can be variable with differences between gravitationally-induced curvature in space-time and "flat" gravitationally balanced areas far from gravity wells. If space-time is quantized, could the apparent acelleration of the probe be a relativistic effect caused by the differences in L between the space-time occupied by the probe and that occupied by our Earth-bound receiver?
     
    Last edited: Aug 1, 2004
  19. Aug 1, 2004 #18

    jcsd

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    Actually a relativistic version of MOND has already been formulated by Bekenstein.
     
  20. Aug 1, 2004 #19

    turbo

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    Thank you for the reference. I read the paper and I appreciate the thrust of the paper, but just can't follow the math. Here's why:
    I started college expecting to pursue Chemical Engineering at the University of Maine, but they gave some of us high-SAT-score geeks to a Professor Emeritus for a little polishing (Cecil Rhodes - a wonderful and brilliant man, and a very good chess-player!) and he turned me to the dark side of the force. I left engineering and jumped to English Literature with a specialty in the poetry of the Romantic Movement (Coleridge, Byron, Keates, Shelly....go figure). Shortly after, I managed to get a 15-minute lunch-time appointment with the head of the Philosophy department (Erling Skorpen) to see if he would allow me to audit his course on Meta-ethics (seniors and graduate students only) for no credit. About 3 hours of animated conversation later, I was admitted into the course for full credit and never had to take an low-level course in Philosophy at that university. I got a great education, worked my tail off, and enjoyed it immensely.

    My problem: No physics professor at UMO took the time to tell me (a green freshman) that physics was addressing the REAL basic philosophical questions facing us, and the teachers at my high school either just didn't know or just didn't care. I would have stuck with the physics and math (K+E slide rules, jot pads for orders of magnitude, and all) for years had I known that I could have eventually been working on cosmology, but the prospect seemed so remote that I didn't make the effort. Oh, well...

    Moral: We need programs in our high schools and grammar schools that lay out some of the cosmological questions facing us, so kids know that there is some seriously important work to be done. There is some killer talent out there - we just need to provide the motivation and the educational resources to draw them to the field, educate them, and let them go. And we need to demand better performance of our science teachers and the schools that produce them. Throwing salary money at the existing teachers is probably not going to produce any more budding physicists, just newer Saabs in the teachers' driveways. :wink:
     
  21. Aug 2, 2004 #20

    Chronos

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    Excellent, Turbo. I am a big fan of LQG for much the same reasons you mention. That may not be a good sign because I have been known to be wrong about a lot of things.
     
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