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Space Science

Universe is Flat 41

Posted by michael from the elephants-all-the-way-down dept.
D Anderson n'Swaart writes: "BBC News is reporting that a recent experiment called Project Boomerang, conducted with a super-sensitive telescope suspended 40 km above Antarctica, has provided powerful new evidence to support the current trend in scientific thinking that the fabric of space is essentially flat, and not curved as Einstein postulated. The one billion measurements gathered took three weeks to analyse on a Cray T3E supercomputer, and have provided insights on the creation of the universe, and suggest that it will continue to expand indefinitely without collapsing in a Big Crunch."
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Universe is Flat

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  • John left out links to the papers he cited, try Adams and Laughlin [arxiv.org] first and foremost, and also Krauss and Starkman [arxiv.org].

    And you're right: no, we're not going to see a quark-gluon plasma emerge. You need very high temperatures to reach a phase transition. Confined quarks are the low energy state.

  • Misleading (Score:5)

    by Anonymous Coward on Saturday June 30, 2001 @12:37PM (#117959)
    ... the current trend in scientific thinking that the fabric of space is essentially flat, and not curved as Einstein postulated
    This seems to imply that scientific thinking is that Einstein's theory of gravity (general relativity) is wrong. That is not true.

    Rather, what it means is this: Einstein's theory predicts that spacetime is curved. However, some curved spacetimes can be sliced up into "space" and "time" in such a way that SPACE is flat. Current scientific thinking is that SPACE is flat in this way (or very close to it) -- spacetime is still curved and the curvature obey's Einstein's equation.

    Of course, it is true that Einstein personally favored a closed universe model in which space is hyperspherical and hence curved, so in that respect the above statement is correct. But Einstein's theory admits many other solutions and experiments favor near-flatness.

  • Elliot was always the better poet anyway.

    ( /me ducks the rain of tomatos )
  • GR is believed to be wrong. That's why we've been trying to discover the Higgs Scalar Boson, among other things, so we can figure out exactly how it is wrong and what should replace it.
    Steven E. Ehrbar
  • The gravity of the universe is just enough to make the universe flat. If there was more mass, the universe would be curved one way (closed), and with less mass, it would be curved the other (open).

    You are right, this is a universal flatness, not a local flatness.

  • Damn! (Score:3)

    by Black Parrot ( 19622 ) on Saturday June 30, 2001 @10:59AM (#117963)

    I got up this morning and discovered that my tire is flat, the coke I opened last night is already flat, my G/F is still flat, ... and now I hear that the whole d*mn*d universe is flat.

    I think I'll spend the day compiling kernels, just to take my mind off my troubles.

    --
  • I should have pointed out that IANAPBIASTBO (I am not a physicist, but I am studying to become one!). The info came from a paper I read recently ... don't recall where though - sorry.
  • With out a Big Crunsh, that means that the end of the Universe will be a cold one - eventually, all the stars will die out and the universe will eventually become a uniform plasma of quarks and electrons(this is dictated by the laws of Thermodynamics - the Universe is going towards a state of increased entropy - that means low energy - and a quark/electron plasma is thought to be at the lowest possible energy).
  • Yes, I agree.

    With the big crunch comes the possiblity for it
    to start all over again. Big bang, gravity,
    particles, planets, plants, animals, people,
    linux, FreeBSD, slashot.

    With the big crunch comes the possiblity of the
    bigger oscillation. (bang->crunch->bang->crunch)

    If the universe is flat it means every expanding,
    ever cooling, life dying out, empty space a very
    (relatively) few rocks laying about.

    I miss Douglas Adams. :(
  • A flat universe is flat in the absense of something that curves it, while a curved universe is curved even in such absense.

    You seem to be confusing two issues: (i) the 'average' flatness of the universe, and (ii) the cosmological constant.

    I was under the impression that the experiment did discuss the cosmological constant. From the BBC article [bbc.co.uk]:

    To astronomers, flat means that the usual rules of geometry are observed - light not being bent by gravity travels in straight lines, not curves.

    Unless the correspondent got this wrong, it appears that the experiment concluded that space is not curved in the absense of gravity, not that, taking all the gravity in the universe together, space still isn't curved all that much. Of course, the latter finding would support the comments on the Big Crunch more; like I said, perhaps the correspondent introduced this confusion.

  • Re:What is gravity then? (Score:3)

    by pubudu ( 67714 ) on Saturday June 30, 2001 @05:53PM (#117968)
    No, because as I noted elsewhere, it's possible for space to be flat while spacetime is still curved. Also, all that is established is that space is on average flat (or very close to it); locally, it is certainly curved (near concentrations of masses like stars and galaxies).

    I think the discovery can be put more precisely without too much confusion. I don't doubt that you understand all that is meant by the universe being "on overage" flat, but the experiment has broader implications than this post makes clear.

    A flat universe is flat in the absense of something that curves it, while a curved universe is curved even in such absense. That is, mass is responsible for all (?) of the curvature (one effect of which is gravity) which we see, in a flat universe. In a curved universe, space is warped even in the absense of a mass (travelling objects appear to be deflected by the gravity of a mass which isn't there).

    We've of course already heard this news about a year ago when the most powerful instruments we had at the time said that the curvature was as close to zero as we could measure. This experiment uses more powerful instruments, confirming that the curvature is even closer to zero than we could accurately say before.

    This is actually one of the few experiments which says that the universe is not as wierd as the wierdest imaginable possibility. A flat universe is what most people expect: things go in straight lines unless something (in this case, gravity) interferes with them. If any of the wierdness that Einstein proposed (trajectories bent by nothing but space itself) actually occurs, it is too small for us to measure.

  • From the BBC article:
    To astronomers, flat means that the usual rules of geometry are observed - light not being bent by gravity travels in straight lines, not curves.

    Yes, the article was misleading on this point.

    A corrected version of the BBC sentence would be:

    "light not being bent more than an average amount by gravity travels in straight lines, not curves."

    The experiment was about real light, not light in some hypothetical 'empty' space.

    For astronomers, a flat universe also means that the negative curvature of geodesics being pulled apart by the expansion is exactly balanced by the positive curvature from gravitational attraction (and the expansion continues forever, but with no exponential runaway).

    You might like to look at this press release from Berkeley:

    Alternatively search google for "Boomerang Cosmological Constant flat".
  • By itself Boomerang says very little about the value of the cosmological constant Lambda; but as this diagram [ucsb.edu] shows, with its accompanying caption here [ucsb.edu] (second box from the bottom), when combined with data from supernovas it suggests that the vacuum energy density ("dark energy") accounts for about two-thirds of the total mass-energy of the universe.

    Such "dark energy" acts as a source for gravitational attraction and lensing, but it also exerts an outward pressure similar to the Caisimir effect, which accelerates the expansion.

  • Good try, but wrong (Score:4)

    by JPMH ( 100614 ) on Sunday July 01, 2001 @06:00AM (#117971)
    A flat universe is flat in the absense of something that curves it, while a curved universe is curved even in such absense

    You seem to be confusing two issues: (i) the 'average' flatness of the universe, and (ii) the cosmological constant.

    The question of the flatness of the universe question is basically this: if you defined a triangle of geodesics, would the angles in the corners add up to more than 180 degrees (positive curvature: a 2d analogy would be the surface of a sphere); less than 180 degrees (negative curvature, cf the 2d surface of a saddle); or exactly 180 degress (like a 2d sheet of paper).

    It turns out, when you do the sums, that an 'empty' expanding universe would not be flat, but would have negative curvature: two geodesics emerging from a point are pulled away from each other. For an expanding universe to be flat, there has to be enough gravitation attraction to balance this pulling apart. If the average energy density is a little higher, the attraction becomes more important than the divergence, leading to positive curvature and a closed universe.

    These latest results confirm that the universe appears to be either exactly or very nearly flat. This implies that the average energy density is either exactly or very nearly at the critical value. But the amount of visible matter seems to be too small to account for this. So it has been suggested that there is either more mass in the universe than we can see - "dark matter" - or that empty space itself has an energy density (like a quantum particle's zero-point energy). The present results, by indicating that space is flat, tend to support this idea of a missing energy density. This leads to an extra term in the equations, the Cosmological Constant (Lambda), which appears in addition to the energy density terms arising from visible matter and radiation. A flat universe suggests that Lambda is not zero.

    "on average" flat

    Strictly speaking, the discussion above assumes a Friedmann model of the universe. This is a simplified model which assumes that the universe is and remains homogeneous -- the same everywhere, with the same density at every point. Normally in relativity there is no way to say whether events in different places are happening at the same time; but in the Friedmann universe one can use the local density of matter (which is the same everywhere) to define a universal "proper time" co-ordinate. Having nailed down the co-ordinate system, one can then separate the spatial and the temporal aspects of the equations.

    Of course, the universe is not homogeneous when you look at it closely -- every so often you come across a planet or a star or a black hole; and getting too close to the latter can bend geodesics a lot (gravitational lensing). Nobody is suggesting anything but that the universe is curved "up-close". But on a larger length scale the Friedmann approximation seems to work well: very few geodesics will actually pass close by a black hole; most will indeed experience an "average" amount of bending.

  • The best visual explanation of this is the expanding balloon analogy. Take a balloon of a certain size and put a bunch of dots on it with a magic marker. If you constrain yourself to the surface of the balloon (i.e., let the balloon be a 2-dimensional universe) and let the dots represent galaxies, then as you inflate the balloon you'll see that this universe expands and all the galaxies fly apart from each other. Note that no matter where you are on the balloon surface, all the galaxies are expanding away from each other, so there is no one spot on the balloon suface that is the "center" of this expansion. For the case of our universe our 4-dimensional (3 spatial and one temporal) spacetime is similarly expanding.

    There also is the issue of the shape of the universe, which is what this story addresses. The balloon analogy describes a closed and unbounded universe. There are also other types such as the closed and bounded (such as an expanding dinner plate) and an infinite universe.

    This all leads to some interesting questions such as what is this all expanding into? Is this 4-D space hung in a higher dimensional space, or is this all that there is? Some cosmologists look at possibilities such as whether our universe is just a local bubble and that there are other universes that are right next to us (and perhaps connected via black holes/quasars). Also, note that if the universe is as it is described above, then you should be able to set off in one direction and travel all the way around the universe and get back to your starting position, much like sailing around the Earth. However, with the rate of expansion of the universe, you would have to travel awfully fast. If the universe were not expanding and was closed (as with the balloon analogy) then if it were optically transparent and you had a big enough telescope, then you would be able to look far out and eventually see yourself.

    There are a number of good layman-targeted books on this subject. Two of the most popular have been Hawking's A Brief History of Time [fatbrain.com], and more recently Brian Greene's The Elegant Universe [fatbrain.com]. A very good book on the Big Bang itself is Steven Weinberg's The First Three Minutes [fatbrain.com].

  • You are asking a lot of very good questions, and you are correct that they have all been pretty much raised at one point or another. However, these questions really have not been answered. Basically we can only infer what we can from the universe by looking through telescopes, so the most you can ask of a certain cosmological model is that it be consistent with observation. These questions in particular are certainly not boring, and far from being resolved.

    The perception of time is an interesting topic because the "arrow of time" comes from thermodynamics (the second law in particular), and so some believe that it is independent of the expansion of the univese. However, some have entertained the possibility that if the universe were to contract, then time would reverse itself.

    In addition to the books I referenced previously, if you really want to exercise your brain, I highly recommend Barrow and Tipler's The Anthropic Cosmological Principle [fatbrain.com]. You might not agree with all that is in it, but it has some very nice historical chapters and discussions on the nature and fate of the universe.

  • But if it had to perish twice
    I think I know enough of hate
    To say that for destruction, ice
    Is also great
    And would suffice

    Anyway, a bang and a whimper are the same thing, observed as different on a subjective scale.
  • >One thing that puzzled me with this analogy is
    >that, for this to work, the galaxies had to be
    >taped-on solid items. If galaxies are just
    >collections of space (a bunch of dots) then why
    >wouldn't the dots inside the galaxy fly apart, too

    They are, but the force of gravity keeps them stuck together. In fact the planets are orbiting in stable orbits just slightly smaller (for their orbital velocity) than they would be if the universe wasn't expanding- the extra gravitation acceleration from being closer together cancels the expansion 'acceleration'.

    So the upshot is that things that aren't in orbit drift apart. Things that are in orbit stay stuck that way at the same distance.

  • Wait, sorry -- I thought it said the universe was PHAT.
  • On what do you base your opinion? In my opinion, the universe will end in a brilliant light show, and intelligent beings from other worlds will build a temporally isolated space restaurant to watch the show nightly. But, as noted, this is just my opinion.
  • A guy in Hoboken wednesday used a really nice level and determined that the earth is "essentially flat".

    So the universe is flat, is it level?

  • Um, could someone draw me a picture of what they're talking about? :-) Don't worry, take your time... And, are we talking more of a canvas, or light gingham?
  • Slashdot put a space in that URL... first time I looked at it, it appeared to be a link to the file relativity.h, and I wondered a) what the library did, and b) how it was relevant to this discussion...
  • Free quarks in a low-energy state? Where did you get this information?

    I was talking to a string theorist friend of mine about this final infinite period in the life of the universe, and we both agreed that all you'd have left is electrons and neutrinos (maybe also protons, but they might not ever decay).

    On a side note, it was already known that the universe would never recollapse. Recent findings show that the expansion of the universe is accelerating, and there is no reason to believe that this acceleration will ever taper off.

    Here's a guy who really seems to know what he's talking about:

    http://math.ucr.edu/home/baez/end.html [ucr.edu]

  • and if I look far "back" in time enough, I would eventually see the "big bang" in a single place

    Unfortunately, we can not see the big bang, as the young universe was not transparent.

    The microwave background originates from the time when the universe is about 100 000 years old. In those early days, the universe was filled with hot gas and radiation. The gas was hot enough to be ionized, so it was very opaque. As the gas was getting gradually cooler, the electrons got bound with nuclei, forming neutral atoms and allowing the radiation to pass through. Now, this radiation has been doppler-shifted to the 3K blackbody we see. So, we can NOT see beyond the microwave background.

    or I have to be able to see it in EVERY direction I look

    At the moment of big bang the universe was point-like, or a singularity (Now I'm assuming this is the exact moment, ignoring all the stuff about Planck time etc.) I'm no expert in general relativity, but I think the concept of 'direction' can not be applied to singularities. The point of time at which the big bang happened is a point of time when the three spatial dimensions of the universe did not exist. No space, no directions.

    I hope this clarified things a little. However, I get the feeling I'm trying to explain a zen koan to someone.

  • I'm assuming you are talking about the black we see

    The 'black body' refers to the spectral distribution of the light energy (Planck's law), not colour of the radiation. For example, the Sun is a rough blackbody at 6000 Kelvin. The microwave background is a blackbody that was originally at a temperature of the order 10000 K, now redshifted to 2.73 K.

    how far are we looking back then?

    The exact distance depends heavily on the cosmological model used, and there is no consensus on which model to use. So the values I give may be different from what you see by an order of magnitude or even more. However, the universe was about 300.000 years old at that time, and the distance is a few tens of (American) billions of light-years.

    This seems to contrast the age of the Universe, (how can we see 20 billion light-years away when the light has travelled only 10 billion years?) but this is were the cosmological model (Hubble parameter, spacetime curvature etc.) steps in.

  • > If you constrain yourself to the surface of the
    > balloon...then as you inflate the balloon you'll
    > see that this universe expands and all the
    > galaxies fly apart from each other.

    One thing that puzzled me with this analogy is that, for this to work, the galaxies had to be taped-on solid items. If galaxies are just collections of space (a bunch of dots) then why wouldn't the dots inside the galaxy fly apart, too (and thus, to your viewpoint, the universe would stay constant w.r.t. the size of the galax.

    And if galaxy, why not your body?

    I do recall somewhere that galaxies rotated as if a solid disk, rather than as if a whirlpool, which would be the case if they were in orbits around a cenrtal area.

  • Cosmology and poetry (Score:3)

    by ryants ( 310088 ) on Saturday June 30, 2001 @07:53PM (#117985)
    Those who were leaning towards the Big Crunch favoured Robert Frost:
    Some say the world will end in fire,

    some say in ice.
    From what I've tasted of desire
    I hold with those who favor fire.
    Those who were leaning towards the "expands forever" idea favoured T. S. Elliot:
    This is the way the world ends

    Not with a bang but a whimper.
    Looks like the Elliot camp wins.

    Ryan T. Sammartino

  • Link is here: Plagarized Article [time.com]

    Or if you're lazy and want a quote from the article:

    "But a series of remarkable discoveries announced in quick succession starting this spring has gone a long way toward settling the question once and for all. Scientists who were betting on a Big Crunch liked to quote the poet Robert Frost: "Some say the world will end in fire,/ some say in ice./ From what I've tasted of desire/ I hold with those who favor fire." Those in the other camp preferred T.S. Eliot: "This is the way the world ends/ Not with a bang but a whimper." Now, using observations from the Sloan Digital Sky Survey in New Mexico, the orbiting Hubble Space Telescope, the mammoth Keck Telescope in Hawaii and sensitive radio detectors in Antarctica, the verdict is in: T.S. Eliot wins."

    Plagarist.

  • Other links (Score:5)

    by windows ( 452268 ) on Saturday June 30, 2001 @09:07AM (#117987)
    Other information on this project can be found here [roma1.infn.it], here (Caltech) [caltech.edu], or here [ucsb.edu]. This link [princeton.edu] to Princeton University seems to explain the project much better, at least to me.
  • Einstein, I think, said that gravity was the curvature of space-time. If the universe is flat, I guess that goes out the door. Of course, my perception of this may be completely wrong - if the universe as a whole is fairly flat, does it allow for variations near massive objects?
  • And you can't spell, stupid fuck. It's Plagiarist.
  • This information is a little bit out of date(about a year). Although its based on data collected so far up to the time it was published, there still needs to be more data collected to get a better picture of our universe before we come even close to figuiring out if its flat our not. One of the discoveries that might alter this is a mysterius force that sends our deep space probes off target. We have no clue how it works, and what its effects are on the universe on whole. Its my oppoin that we live in a hybrid universe that exibits flat properties but will still collaspe upon itself and be reborn do to properties unforseen and unpredicted yet. But as noted this is just my oppion.

    -------------------
  • I was basing it off the state of the universe before the expansion had to be achivied somehow. And I was thinking how it could be achieved if the universe was flat. But after further reading from a link posted by a person nicknamed Spiffy(Thanks) http://math.ucr.edu/home/baez/physics/relativity.h tml has led me access to this great archive of information. I am now thinking that my previos post doesn't make any sense :-). Well, hopefully more insight and better informed commmentary will follow.

    -------------------
  • I think it has to do with atomic forces are not expanding. This document might answer your question better then I could. http://math.ucr.edu/home/baez/physics/expanding_un iverse.html [ucr.edu]

    -------------------
  • Another point to be made in this whole issue, there other means to cause the apparent curvatures that are being dicused. For instance light can be bent by extreme EMI, which can be produced by many stellar objects.( Ie Stars.) Subatomic particles do not exhibt any gravitonic responses. Since, light has subatomic mass the effect of gravity shouldn't have much of an impact. Another possibility is of subatomic collisions, this can produce a combitination of transformations and redirections. All of this would logically occur closer to large stellar masses.
  • Yeah yeah, I could never handle the math, which is why I became a physician and not a physicist, hehe. This article reminded me of a burning question I have though, and maybe you guys can explain it to me. It goes like this: OK... if I look at the sky, I am looking back in time. The further I look, the further back in time I look. This article claims that these people were looking at the universe almost 12 billion years ago. Ok. Now, if I see this "image", while looking at a certain point in the sky, by definition, if I look at any other point in the sky I should see the exact same image, no? Otherwise how can I see "the universe" x years ago, and turn around 180 degrees and see the same universe, x years ago? If the universe is expanding, then logically it would have been "smaller" x years ago, and if I look far "back" in time enough, I would eventually see the "big bang" in a single place... it was a singularity, wasn't it? But either I can only see it if I look in one special place, which would mean that I am only looking back in time when I look THERE (where the hell am I looking if I look somewhere and DON'T see the Big Bang?)... or I have to be able to see it in EVERY direction I look. And if THIS is the case, then how can I say the universe is expanding (yeah yeah I know the bit about the Doppler shift, etc)if the "Big Bang" happened all around me? Before my simple brain goes "gurk" (thank you for that word, Douglas Adams), I hope you don't see this message as a troll. I'm just a simple doc who would like to hear stuff from real physics nerds :)
  • No... thanks a great deal... it DOES make sense since you spared me the no doubt intricate details and proofs involved hehe. OK. So if the dimensions of the universe didn't exist, it would be sort of hard to see an event happening at that time. Weird though how these dimensions work great for a certain distance X, which also happens to be historically back in time T, and then everything goes to the shitter but it doesn't matter, since we can't see through this background radiation. In fact this eerily reminds me of one of my first surgeries for some reason... Hehe thanks.
  • Thanks for reminding me of that analogy... If I am correct it was Hubble who thought that one up, right? OK. You say (and I will buy) that the universe is 4D... D4 being time. So the way we perceive time as moving inoxerably forward is tied up to this expansion? Which begs the question... is expansion uniform? Which leads one to think that, if it isn't, are there places where time stands still, or even moves backwards, as the universe "shrinks" in that little part? I assume all this has been discussed, addressed and dealt with in physics... just like most of the _burning_ questions I had about medicine are actually quite boring having been discussed and resolved decades ago... oh well, each to their own field I guess. It's still nice to peek over the fence once in a while tho :)
  • OK, but if everything is expanding, including our bodies, it wouldn't matter anyway, right? In fact, we wouldn't even notice, I'll bet. But this can't be the case, since it CAN be noticed. Of course I'm no physicist :)

    Calculus: something that is passively or actively removed from the human body

  • So here is a question, when we are looking at this black body (I'm assuming you are talking about the black we see), how far are we looking back then? And is there any idea as to what the distance would be?

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