Cosmic Microwave Background Leans To Inflation Theory

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"

Comments

Pinning things down, sort of...

[pphrdza]

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

[RobotWisdom]

The AstroPic of the Day this morning includes links to Wayne Hu's accessible tutorials on the CMB: beginners (12pp) and intermediate (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

[KDan]

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

Q. Spherical expansion & Planet's Orbits

[UnknownSoldier]

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

[Omkar]

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.

Re:Q. Spherical expansion & Planet's Orbits

[KDan]

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

Re:Dupe-

[KDan]

See This Comment 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