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Space Science

Cosmic Microwave Background Leans To Inflation Theory 37

Posted by Hemos from the index-it-to-cpi dept.
Strigiform writes "Some of the questions about the early universe have been answered by the WMAP project as reported by New Scientist. The inflation theory of the early universe has been vindicated, as it correctly predicted the polarisation of microwaves observed. The earliest stars appeared only 200 million years after the Big Bang and the universe is about 13.7 billion years old"
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Cosmic Microwave Background Leans To Inflation Theory More

Cosmic Microwave Background Leans To Inflation Theory

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  • Pinning things down, sort of... (Score:4, Funny)

    by pphrdza ( 635063 ) on Monday February 17, 2003 @09:13AM (#5318588)
    Now MAP has pinned that down to 13.7 billion years, give or take 0.2 billion years.
    Well, it's nice to see we're getting close.

  • Up-to-date tutorials on CMB (Score:4, Informative)

    by RobotWisdom ( 25776 ) on Monday February 17, 2003 @09:54AM (#5318779) Homepage
    The AstroPic of the Day this morning includes links to Wayne Hu's accessible tutorials on the CMB: beginners [uchicago.edu] (12pp) and intermediate [uchicago.edu] (much longer, I think).

    Short version, as best I've understood so far:

    During the earliest expansion after the Big Bang, the attraction of gravity was counterbalanced by the pressure of photons, with slight fluctuations that echoed thru this superdense plasma as 'sound'.

    The resonant frequency of the sound was limited by the speed of gravity (ie, speed of light) and the spatial 'horizon' it could reach over the course of the universe's short life. (Harmonics also arose at some point.)

    When the plasma cooled enough for atoms to form, all the photons were released at once, in a pattern that retained the resonant-frequencies fluctuations, and that's what WMAP is measuring.

    • Re:Up-to-date tutorials on CMB (Score:5, Interesting)

      by KDan ( 90353 ) on Monday February 17, 2003 @10:48AM (#5319067) Homepage
      Umm... o_O... well, that's what I call "security by obfuscation" :-) (no offense meant).

      Simpler explanation for the people who want to understand it: (;-))

      The universe started as a (quasi-)infinitely dense point that expanded VERY fast. For a comparatively long time, the matter in the universe was opaque to the photons that bounced around it. So photons kept on being absorbed and re-emitted by electrons and such. While this was happening, the universe was expanding, and thus cooling. So the photons, as they kept on being absorbed and re-emitted, cooled with it. Then at one point the universe suddenly (ie not gradually) became mostly transparent to the photons (I believe it was when hydrogen formed but my memory is flaky here). That's what we call "decoupling" time in cosmology.

      Now after this, the photons kept on cooling due to the expansion of the universe, while the matter arranged itself in various heat-generating systems such as stars and so cooled off in a much more complex and separate way. So those photons kept on bouncing around the universe, and as the universe expanded their wavelength dropped (because space itself expanded). So now they're really cold, but they're still everywhere. What they provide is a snapshot of that "decoupling" time, of what the universe looked like back then.

      So historically, at first it was a big discovery and really surprising that the CMB was uniform - and that strongly supported the Big Bang theory. Next they discovered what is referred to as "anisotropies", ie differences in the CMB depending on where you look. First there's a big "dipole anisotropy", which is due to the motion of the Earth with respect to the "surface of decoupling" (ie the big big sphere which surrounds us at some 13 billion light years away, which is where the CMB we see now comes from). Then there's all sorts of other "powers" of the anisotropies, so that they go down to a very tiny level.

      Now if the universe was totally symmetric about the Big Bang, there wouldn't be anisotropies, either in the CMB or in the matter we see around us. In fact there wouldn't be clusters of galaxies, or galaxies, or planets or anything - just a great uniform mass of something (most likely hydrogen). What the anisotropies tell us is that the universe didn't just expand symmetrically after the Big Bang. So this begs the question: why not? What caused the anisotropies?

      That's when you get into fairly advanced theories like Inflation Theory, which explains the anisotropies in terms of a super-super-super-super fast expansion (we're talking about growing by a factor of 10^24 in about 10^-15 seconds... that's FAST++ ok?). According to Inflation Theory, then, the anisotropies (and the fact that they're pretty uniformly distributed and of all shapes and sizes) would be explained because as the universe expanded (FAST++) particles were still appearing spontaneously everywhere because of all the tension of spacetime, and as that was totally random AND discrete, they *grew* into the galaxies and stuff we see.

      Note that according to Inflation Theory, afai understood it, the visible universe (15 billion light years of it around us) is a tiny tiny tiny tiny fraction of the actual *existing* universe, which we'll never be able to reach because the expansion of the universe is accelerating, as highlighted in a previous /. article.

      Phew, hope this helps.

      Daniel
      • Umm... o_O... well, that's what I call "security by obfuscation" :-) (no offense meant).

        Some offense taken. >:^(

        You should really read the tutorial before spouting off what you think you know.

        Simpler explanation for the people who want to understand it

        Not simpler, and mostly unrelated to the tutorial I was trying to summarise. (I obviously wasn't trying to substitute for the tutorial, as you are, I was trying to suggest what was interesting about it, which you can't.)

        What caused the anisotropies?

        The whole point of the tutorial is explaining what regularities they're able to extract info from. You obviously don't know anything about that.

        • You should really read the tutorial before spouting off what you think you know.

          I don't think I know it, I know it. I've just finished a physics degree and my very last exam was a minor option paper on cosmology.

          Daniel
          • I don't think I know it, I know it.

            Well, aren't we special! (You were supposed to apologise for acting like a clumsy ego-geek.)

            What you don't know, but think you do, is Hu's main topic-- the anisotropies as reflecting the resonant frequencies of the 'primordial sound'.

    • The CMB aka the Cash Money Brothers were a pair of criminal types from New Jack City, a bad movie about Crack's appearance on the streets of NY.

  • Dupe- (Score:2)

    by Omkar ( 618823 )
    Dupe [slashdot.org]

    This is a big step forward, but even with inflation theory, where's all the antimatter?

    • Re:Dupe- (Score:3, Interesting)

      by KDan ( 90353 )
      See This Comment [slashdot.org] just above for the intro, but basically it could be that we just happen to be in a region of spacetime where there's only matter. Given that according to Inflation theory the visible universe is about as big compared to the "total" universe as an atom is compared to the visible universe, that leaves plenty of potential for antimatter elsewhere.

      Daniel
    • in the anti-universe. Antimatter immediately destroys matter, it's an exception to the law of conservation, so therefore if there actually were "anti-matter" in existence it would immediately blink out out existence along with an equal amount of matter, creating a temporary void, which would yes, be filled with virtual particles!
      • Anti-matter is not an exception to the law of conservation (I assume you mean conservation of energy). When anti-matter comes into contact with matter, they both convert each other into energy.

  • Q. Spherical expansion & Planet's Orbits (Score:4, Interesting)

    by UnknownSoldier ( 67820 ) on Monday February 17, 2003 @10:10AM (#5318837)
    Q1. If the universe is expanding, wouldn't it do so in roughly a spherical shape? Isn't there a "bulge" in the center of the universe?

    Q2. I'm curious if the orbits are always drawn as being 2D because they really are, or just because it's simpler to demonstrate. My encylopedia lists one factor in the orbit is the inclination, or tilt, of the orbital plane to the reference plance. But what is the reference plane? Why would our planets have an elliptical orbits that lie in the same plane if the universe is expanding? It seems strange that only Pluto and Neptunes orbit "cross". Anyone have any [links to] diagrams showing the realistic orbits?

    Cheers
    ~~
    Let me get this straight - I need to upgrade my video card to play UT2003 at the same frame rate as I did with UT on my older video card?
    - George Moeckel

    • Re:Q. Spherical expansion & Planet's Orbits (Score:5, Insightful)

      by Omkar ( 618823 ) on Monday February 17, 2003 @10:19AM (#5318888) Homepage Journal
      I'm not sure about relativistic orbits and stuff, but with Newtonian laws, you can prove orbits are planar (Kepler did this - orbit is an ellipse).

      Let r be the position vector of a planet, v=r' the velocity, and a=r'' be the acceleration.

      Now,
      a = GMr/|r|^3
      from Newton's Second Law and Newton's Law of Gravitation.

      So

      d(r X v/dt
      = r' X v + r X v'
      = r' X r' + r X a
      = 0 + r X GMr/|r|^3
      = 0
      ==> r X v = h, some vector constant ==> r and v are coplanar ==>The orbit of a planet is a plane curve

      Its fun and good practice to prove Kepler's Laws - my book outlines the proof. Try it.
      • How the hell does the above answer the parent's question? Man, you moderator people really ARE on crack. Of fucking course all orbits are planar, and you don't need Kepler's frickin' laws to prove it, just the fact that the only data defined in a planetary orbit are a point (center) and a vector (the velocity of the object) attached to the second point. All you can define with a point and a line in 3d space is a plane, hence orbits have to be planar.

        But the parent was asking how come ALL the planets are in the same plane, completely different question. If there's any sane mods out there, mod the parent down and mod my reply (below) up!

        Otherwise I think I will completely lose faith in any sort of /. moderation... i mean, wtf, if that's how ppl mod other stuff (where I don't know much about the subject) then it's fucking useless! Disinformation++!

        Daniel
        • You have three vectors - dispacement, velocity, and acceleration. They are not coplanar in general, but because of Newton's Law of Gravitation, they are in this case. That's what I showed, just with math (more rigorous). h becomes important in the proof of Kepler's other laws. BTW, the "definition" you cite follows from the law, so your reasoning is circular.
          • You can take a single point and write it as an addition of n vectors and say "oh, look, n vectors", but it's still just a point.

            The point (no pun intended) is that he didn't ask for "how did the fact that orbits are circular get proved by Kepler before Newton", and he didn't even ask "why are orbits circular" but "why are all the orbits more or less in the same plane". My definition follows from the law of gravitation, which is, I believe, fairly well accepted (anyone want to disagree? Sit down Albert!) - at least at the level/speeds of calculating planetary orbits.

            Daniel
        • Of fucking course all orbits are planar, and you don't need Kepler's frickin' laws to prove it, just the fact that the only data defined in a planetary orbit are a point (center) and a vector (the velocity of the object) attached to the second point. All you can define with a point and a line in 3d space is a plane, hence orbits have to be planar.

          You left out the acceleration, and the requirement that the force on the planet needs to be a central force from your origin where r=0.

    • Q1: It does, but it's a 4-dimensional sphere... little or nothing to do with a 3D sphere.

      Q2: The planets formed from a great big cloud of gas (a protostar) which also formed the sun. After the sun started 'emitting', there was still some leftovers. They turned into the planets. Now due to the facts that a) there's some residual magnetic field lines due to some other objects around the condensing protostar and b) it's easier to move without crossing magnetic field lines than to cross them (ie costs less energy) the circular motion in the direction that crosses field lines died down whereas the motion in the direction that doesn't cross field lines stayed. So that turned a ball of gas into a flattened disc of gas. Then the planets formed. That's why they're all in the same plane, more or less. See "Thin Accretion Discs" in your favourite physics library for more advanced info.

      Daniel
    • universal expansion is flat, not spherical. And truthfully there is no "realistic" orbit patterns, because it's not exactly a pattern. The closest we can come is predicting the orbit, but then again, that's pretty damn close.
    • Generally, when we're trying to visualize space expanding, we think of something like a balloon filled with matter that's being blown up. So from that picture, yes, you'd intuitively think that there should be a "center" with some identifiable property (like being more dense, as you suggest).

      Unfortunately, this picture isn't quite right. The problem comes from us trying to project this three-dimensional expansion (just think of spatial dimentions) into the two dimensions that we're used to dealing with. So to fix the analogy, think of the matter and energy as being distributed on the surface of the sphere (so draw dots on the balloon with a magic marker, for example). Then blow up the balloon as you did before. You will see that every dot moves away from other dots around it, and dots further away move away faster (this is what Hubble observed, the dots being galaxies). So the expansion isn't "away from a point", really. It's the space itself (the rubber of the balloon) that expands. The air inside the balloon is sort of meaningless here; it's just the surface that you observe.

    • You've asked some questions that sound simple, but are really complex.

      1: As far as the shape of the universe and whether there is a center bulge... general relativity tells us that there is no "ultimate" reference frame, so there should be no "center" of the universe. Our observations actually support this, the universe doesn't look like it's expanding like an explosion (from a point), everything is expanding in every direction at once. We don't know even if the universe has an "edge" or if it wraps around on itself, or what.

      2: Orbits can be approximated using Kepler and Newton to be planar. Remember though, those guys lived a long time ago. If we want to look at physics that is newer than 350 years old, we see something really different. The question of predicting orbits spawned the field of chaos theory. Orbits are generally planar and regular, but are easily "perturbed" into strange shapes. Most of the time, the reference plane which is used is "the elliptic". That would be just the plane defined by the earth's orbit. What you're used to seeing with just Neptune and Pluto noticably out of "the elliptic" is generally right.

      I'm studying for a PhD in physics, and part of the reason I'm doing that is for answers to those type of questions. I figured someone would eventually tell me or show me how to figure it out, but really... not a lot of people know this. For all the stuff we do know, you'd be surprised at the stuff we don't.
      • I'm studying for a PhD in physics, and part of the reason I'm doing that is for answers to those type of questions. I figured someone would eventually tell me or show me how to figure it out, but really... not a lot of people know this. For all the stuff we do know, you'd be surprised at the stuff we don't.

        Damn straight. Still, what you know after a physics degree is a damn sight better than before :-)

        Daniel

    • A1. The CMB dipole shows that there is a center and that we're moving away from it at roughly 600 km/s, but that center isn't in any way special. More information here [astro.ubc.ca]. There is no bulge because everything is expanding in an uniform way (gravity interactions notwhitstanding).

      A2. I don't know, sorry. Anyway, the expansion of the Universe would account for a really tiny variation in the size and shape of the orbits; the effects of solar wind and interactions between the planets themselves are much more significant.


  • I hope they figure out some experiment for determining a little bit more about the dark matter and the dark energy (which I hadn't heard about before).

    According to the article, they can place more accurate estimates on the proportions of dark matter and dark energy relative to what we can see, but it still begs the question of exactly what this stuff is.

    • there's any number of good journals that have bunches of new information on dark energy/matter. I guess the most interesting one is the fairly certain prediction that dark matter seems to "halo" galaxies, clusters of galaxies, and superclusters of galaxies. Oh, one more thing, you can be sure it is still relatively unknown, because it's still called dark matter, the moment we know what it is it technically isn't "dark" anymore :)

      • Thanks for the update.

        Last I heard, neutrinoes represented the best bet for dark matter, but measurements didn't seem to collect as many as were thought should be captured.

        • Dark matter comes in two varieties: "cold dark matter" and "hot dark matter". Neutrinos are examples of "hot" dark matter because their speeds are close to c.

          The observed mass distributions of galaxies implies that there is some stuff that gathers in clumps to form walls, voids, etc. So it must be "cold", because if it were composed of "hot" fast-moving particles, these structures would have dissipated by now.
          Neutrinos contribute to the overall mass of the universe (if they have mass), but they have been ruled out as cold dark matter candidates.

      • Too bad we can't just turn the universe upside down and peek at the answers.

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