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We're 156 Billion Light-years Wide?

  1. Jun 4, 2004 #1

    Math Is Hard

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    http://www.space.com/scienceastronomy/mystery_monday_040524.html

    "All the pieces add up to 78 billion-light-years. The light has not traveled that far, but "the starting point of a photon reaching us today after travelling for 13.7 billion years is now 78 billion light-years away," Cornish said. That would be the radius of the universe, and twice that -- 156 billion light-years -- is the diameter. That's based on a view going 90 percent of the way back in time, so it might be slightly larger."


    I found it quite interesting that he said even though nothing can travel faster than the speed of light - it's perfectly OK for space between two objects to expand at faster then light speed. Or rather for the distance to grow so quickly that they appear to be flying apart at faster than light speeds.

    But still -- 156 Billion LY? What do you think of that?
     
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  3. Jun 4, 2004 #2

    marcus

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    Cornish's research has a special definition of a size parameter.
    First thing to say is that in ordinary gardenvariety cosmology the "particle horizon" is about 46 billion LY

    A photon arriving today could theoretically (if it didnt get scattered along the way) be coming from an object which is NOW at a distance of 46 billion LY from us.

    That is old news and standard consensus cosmology---it is just because during the past 13.7 billion years distances have gotten expanded.

    EG go to Siobahn Morgan's calculator and put in redshift z = 10,000 and you will get about 46 billion LY for the current distance of the object.
    (Astronomy reference thread has a link to the calculator)
    or EG go to Ned Wright's cosmology tutorial, same story.

    but Cornish is doing something else he is trying to exclude the possibilities that the U has weird topology like a donut and weirder stuff.
    or like a huge ball. He also has a monkey for a pet that sits onhis shoulder and he used to be a postdoc with St. Hawking at Cambridge. he wants to say, like, well we cant PROVE it doesnt curve around on itself but if it does the radius of curvature is enormous and it MIGHT be a donut but the distance all the way around has to be AT LEAST this and this much.
    So he defines what he calls a "topological distance scale" and he says this is at least 78 billion LY. he proves it doing statistics on the CMB map.
    And intuitively, since it is a bit complicated, I think of this distance scale as halfway arouind the ball, if the U is a ball.

    So the upshot of Cornish work is, like the u looks flat and infinite in extent in all directions and NOT like a finite ball or donut. And almost all working cosmologists quietly assume it is flat and infinite. But IF by some weird joke it should be finite, like a ball or donut then Cornish tells us that the "halfway around" size of the mother is at least 78.
    And as more data comes in he hopes to jack that up higher and higher so that even tho we cannot exclude the case of being finite we can at least say that if it is finite it is damn big and almost like a flat infinite thing.

    If you want to see the picture of Neil with the monkey on his shoulder
    just say and I will get the link
     
  4. Jun 4, 2004 #3

    Math Is Hard

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    yes, please!

    and thanks for your reply :smile:
     
  5. Jun 4, 2004 #4

    marcus

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    Here is cornish snapshot and the orig. article in arxiv.


    http://www.physics.montana.edu/faculty/cornish/

    http://arxiv.org/abs/astro-ph/0310233


    Here is the abstract:
    "The first year data from the Wilkinson Microwave Anisotropy Probe are used to place stringent constraints on the topology of the Universe. We search for pairs of circles on the sky with similar temperature patterns along each circle. We restrict the search to back-to-back circle pairs, and to nearly back-to-back circle pairs, as this covers the majority of the topologies that one might hope to detect in a nearly flat universe. We do not find any matched circles with radius greater than 25 degrees. For a wide class of models, the non-detection rules out the possibility that we live in a universe with topology scale smaller than 24 Gpc."

    Notice that "topology scale" which cannot be smaller than 24 Gpc

    that is 24 billion "parsecs" which is StarTrek talk for 78 billion lightyears.
    Astronomers want to make it easy for you to understand so they
    express distances is "parsecs" abbr. pc, and a pc = around 3.15 LY.
    Arent they cute?

    ADVICE


    If you can, always go to the scientists website and his/her original articles in arxiv

    Because journalists can be very confusing.

    find out what the scientist really said
     
    Last edited: Jun 4, 2004
  6. Jun 4, 2004 #5

    hellfire

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    I do not understand this.

    After reading the article my impression is that they have search for patterns in the CMB data and came to the conclusion that the diameter of the observable universe should be at least 156 billion Lyr.

    But the diameter of the observable universe depends on its age and the underlying cosmological model. If I recall correctly, assuming the current concordance model the radius of the observable universe would be ca. 45 billion Lyr.

    So, since the age of the universe is not questioned in this article, shall I assume that they are considering a different cosmological model?

    Regards.

    [marcus: I did not read your posts before posting this, but, anyway, I do not understand it yet: how did they came to such a distance? I think they must have assumed a cosmological model giving distances between the CMB spots]
     
    Last edited: Jun 4, 2004
  7. Jun 4, 2004 #6

    marcus

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    they are not talking about the size of the observable
    the consensus is that the observable U extends out 46 bill. LY
    the current size, at this moment, of what we can receive light from at this moment, is radius= 46 billion LY

    that is called the "particle horizon"


    cosmologists tend to imagine U infinite because that simplifies things
    conceptually but no matter how much one would like to one cannot totally exclude the possibility that the U (NOT THE PART WE CAN SEE, not the currently observable, but the whole thing) is finite!
    The best we can do is to gradually exclude the possibility that it is finite by saying if it is finite then it must be at least X big
    and gradually as we get more data jack X up and exclude more and more
    of the suspicion of possible finiteness.

    Intuitively it it were finite, tho very large, then it would show some hint of curving around
    Cornish analyzes the data to a certain degree of precision and finds no hint.

    therefore he excludes finiteness out to a certain distance which depends on the precision of analysis.

    the real distance he is aiming at is infinity but his precision limits him to saying 78 billion LY.

    this is way out beyond the 46 billion radius of the observable and it depends on inference of distant geometry from what is closer

    I find his paper difficult and have to take it to some extent on faith that he and his co-authors have proven what they say they have proven. Cant help you understand it in detail, maybe someone else can
     
  8. Jun 4, 2004 #7

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    density

    I am curious as to what impact this has on current theories of the critical density of the universe. I am out of my depth here, but basically what I see is that we have a bigger number for the volume but not an increased value for the mass. What if the universe actually is finite, and his radius calculation is correct? What if the universe turns out to be more like whipped cream in density than Campbell's chunky soup? :smile:
    Do we have constantly increasing acceleration in its expansion? Or do we still have more "missing mass" to account for?
     
  9. Jun 4, 2004 #8

    marcus

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    bigger volume than what?
    in conventional cosmology there is no finite volume because the U is conventionally supposed to be infinite, or of very large unknown volume.

    the critical density is just a density----X amount per cubic km, but there can be infinitely many cubic km.
    -----------------------

    Neil Cornish and co-authors has not given us a "bigger volume" than we thought we had. We thought we had infinite volume, or damn near. There was no surprising
    "largeness" about his 78.

    Neil C's work helps to shake out the people who imagine the U to be finite, by giving them less and less ground to stand on. If one of them was thinking 60 he says no, Ive proved it has to be greater than 78.
    If one of them says 90 then next year Neil will up the number, with more data, and run over 90-----probably, there's no foreseeing the future, but I consider it good and likely.



    ------------------

    Math Is, you say: "What if the universe actually is finite, and his radius calculation is correct?"

    -------------

    He did not calculate the radius.
    he calculated a lower bound on this "topological scale" thingee, showing that the U may well be infinite but it must be at least this much.
    ------------------
    You say: " What if the universe turns out to be more like whipped cream in density than Campbell's chunky soup? :smile:"
    ------------------

    His calculation does not effect the estimated density.
    His calculation is consistent with assumed approximately flat U
    and approximate flatness implies a certain approximate density
    (regardless of finite or infinite, volume is irrelevant, density is what
    determines the curvature and expansion rate and all that.

    If it was like cobweb before Cornish paper then it is like the sameold
    cobweb after------you just arent permitted to imagine it smaller than a certain size but the density estimate is the same as always.

    Campbell's soup! I expect the planet Jupiter is about the density of Campbell's chunky soup-----Labguy would know since he knows all about soup and such not to mention stars.
     
  10. Jun 5, 2004 #9

    Chronos

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    amen, marcus. you cannot have a universe without causality.
     
  11. Jun 5, 2004 #10

    hellfire

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    Thanks marcus. I went shortly through the paper and, although I didnt understand the theoretical background, my impression is that you are correct. The mentioned distance is not of the observable universe and they are talking about the global geometry. But in this case I wonder how misleading the press article is...

    Regards.
     
  12. Jun 5, 2004 #11

    marcus

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    thanks to you all---Math Is, hellfire, Chronos---for a lively discussion.
    Math Is, your way of asking questions is provocative and enjoyable, I left out the smilies in my replies for conciseness but here they are :smile: :smile: :smile: :devil: :smile: :biggrin:
    to put back in wherever they belong like with the Campbell soup
    I am glad you spotted that Neil Cornish thing
    and hellfire dont worry about the journalist getting it wrong because
    its is really hard to get a complicated message right
    all you can ask is that the reporter gives you enough information to
    find the scientific article online
    As I said, I find the actual article pretty hard to understand and so
    cant go any further with it, from my viewpoint, someone with
    more expertise has to come in----or Math Is has to find another article about something else.
     
  13. Jun 5, 2004 #12

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    Thank you, Marcus. I enjoyed your insights on this. You have given me much to think about.

    (And I liked that picture of Neil with his monkey, too!)
     
  14. Jun 6, 2004 #13

    Chronos

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    i cannot accept a universe without causality.
     
  15. Jun 6, 2004 #14

    selfAdjoint

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    You and Einstein - and Schroedinger!
     
  16. Jun 7, 2004 #15

    Chronos

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    apologies if i came across as inflexible. i have a hard time letting go of classical physics sometimes. i believe SR is totally correct and GR is very nearly so. at least they provide testable solutions to real life consequences. my hard spot comes from trying to reconcile GR with quantum theory. i have a problem with solutions that are derived from unobservable regions of this universe. superdimensional strings are not very satisfying answers.
     
  17. Jun 7, 2004 #16

    selfAdjoint

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    believe SR is totally correct and GR is very nearly so.

    Shouldn't that be the other way around? SR is the geometry of the local tangent space of GR. So GR would be the deeper theory and SR the differential approximation.
     
  18. Jun 7, 2004 #17

    marcus

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    Maybe you can be all right with GR then.
    The theory was proposed in 1915 and tested experimentally in 1919
    It makes predictions and they are checked to increasing precision from time to time.
    I dont think it derives from unobservable regions or speculative facets of the universe, but mainly from what we see.

    IMHO the incompatibility between GR and customary quantum theory recipes will eventually be resolved-----possibly by making quantum theory background independent (like GR) which seems highly desirable if difficult.
    GR and QM are human inventions and their incompatibility is not forever, or so i think.

    GR doesnt derive from "superdimensional strings" so you should be OK with that---the vanilla GR is just 4D.

    SR to me seems problematical because it doesnt predict the bending of light as it passes the sun, which GR does. And all the usual SR stuff is included locally in GR, in the approximately flat neighborhood of a point.
    So if I had to choose i would pick GR for sure. Its a classic!

    BTW my chorus sang Brahm's req last night and it was a dynamite performance. people who heard us said things like they had a spiritual experience. We meant what we said.
     
    Last edited: Jun 7, 2004
  19. Jun 8, 2004 #18

    Jenab

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    It would certainly have been scattered. The first particles were all ions because the universe's temperature was too high for matter to be anything except plasma. The whole thing was like the inside of a star. In every direction the visibility was low because of scattering glow.

    It was only after the universe's temperature fell below 3000K that the glow faded and space became more or less transparent.

    I've heard that the distance in excess of 13.7 billion lightyears is the result of inflation chugging out more space right after the big bang, so that the separations of the material objects in different parts of the universe briefly increased superluminally, even though nowhere did any two bits of matter encounter each other at any superluminal speed.

    Jerry Abbott
     
  20. Jun 8, 2004 #19

    Jenab

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    As I'm only a hillbilly who plays a clarinet while sitting among my apple trees and watching my goats frolic in the pasture, take this with a grain of salt.

    I think that the way to reconcile general relativity and quantum mechanics is to generalize relativity further and then apply it on the quantum scale. GR has it that mass curves space and alters the perception of local time by distant observers. GR goes a bit further than this and includes, along with mass effects, those of momentum, angular momentum, and mass flow... derivatives of mass with respect to one thing or another.

    The more generalized GR will account for how energy (including mass), momentum, angular momentum, space, and time all effect each other - how a field of each must change when a field of another is changed - and this is the theory that will apply universally on all scales from the quantum to the cosmological. On the quantum scale, there will be quantum rules that will describe behavior that will converge statistically to general relativity at extremes of physical parameters (speed, temperature, gravitational field, etc.), and to which classical mechanics will remain a useful approximation on the laboratory scale, just as it is now.

    When we think about GR, we regard changes to the measurements of space or time as effects of a cause based in changes in gravitational field or speed. Are there any effects of gravity or acceleration on angular momentum? Does angular momentum have any on space?

    For that matter, why are space and time anything but psychological quantities, important to us as aids to discriminating among processes likely to benefit us or harm us? Can space and time be dispensed with, and theory be concerned only with mass, energy, momentum and fields? What is the distance between the first letter of this paragraph and the question mark at the end of this sentence - INSIDE YOUR COMPUTER?

    What are the differences between a joule of translational energy and a joule of rotational energy, in regard to measurements of space and time for an observer in an appropriate reference frame?

    Do some special effects require more than one contributing cause? Do some causes have several independent effects?

    Are there any reasons, other than entropy, for why some cause-and-effect processes can't be reversed in time?

    Are there any identities of which we are unaware; e.g., is space a medium through which gravity acts, or are space and the gravitation field one and the same thing?

    Jerry Abbott
     
    Last edited: Jun 8, 2004
  21. Jun 8, 2004 #20

    marcus

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    Have you downloaded Rovelli's book "Quantum Gravity"?
    If not please do, as it addresses this question. Don't print it
    out as only the philosophical non-mathematical parts of the book
    apply to your question. Just get it on your desktop, I will help you
    find the relevant pages. Rovelli is philosophically astute and aware
    that at certain points in the history of physics it has been necessary
    to address fundamental philosophical issues before breakthroughs
    could be made. Not always but sometimes---he has studied the history
    of science and discusses the cases where philosophical investigation
    has played a key role.

    The book is in press and scheduled to appear in print in October 2004. the December 2003 draft version is still available online.
    http://www.cpt.univ-mrs.fr/~rovelli/rovelli.html

    See especially chapter 2, around page 50-52, and the parable of the whale.

    I believe that by sitting among apple trees in the company of goats one does, on occasion, get it right. I make it a daily practice to sit among apple trees and listen to birds---there are no goats here.
     
    Last edited: Jun 8, 2004
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