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Look Close! Something’s Strange in the Photo of the Universe

Astronomers love it when the cosmos throws them a curve ball. It’s all very well to peer deep into the universe and turn up just what you expect to find, but discovering something inexplicable is a whole lot more fun. That’s what happened in the 1970’s when observers found overwhelming evidence for the existence of mysterious (and still unexplained) dark matter, which invisibly holds the universe together; and again in late 1990’s when they learned that the expanding universe is speeding up, not slowing down, thanks in part to dark energy.

This being the case, you might think that the brand-new image of the early universe released by the European Planck satellite mission is something of a disappointment. It pretty much confirmed, with minor adjustments, what astronomers already know — that the cosmos is made mostly of dark matter and dark energy; that nearly 14 billion years have elapsed (13.8, to be exact) since the Big Bang; that during the very tiniest fraction of a second right at the beginning, the universe expanded at an incomprehensibly rapid rate—what physicists call the inflationary period. “It’s a confirmation of the most vanilla model of the universe,” says Rachel Bean, a Cornell astrophysicist.

It is up to a point, anyway. But Planck’s new image, which captures light dating from just a few hundred thousand years after the Big Bang also poses a mystery that could shake the foundations of cosmology. For decades, scientists have operated on the assumption that the universe should look the same, on average, in all directions—same number of galaxies, sprinkled about the sky in the same general pattern, no matter where you look. It’s a homogeneity which is in keeping with a birth blast that radiated out uniformly and at once.

The ancient, leftover light from the Big Bang, however, seems lopsided, with a huge swath of sky at a slightly cooler temperature than the rest. It could simply be a fluke, like getting 50 heads in a row in a coin toss. Or it could mean that the age-old assumption about cosmic uniformity is wrong. The chance is maybe one in a few hundred that this asymmetry could happen randomly, says Bean. “So is it really significant or not? It’s tantalizing.”

As with the overall age and composition of the universe, this isn’t an entirely new finding: it was reported a decade ago by NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) satellite. There was always a chance, though, that it was some sort of mistake—but not anymore. “Everything that WMAP saw, Planck sees,” says David Spergel, head of Princeton’s astrophysics department and a leader of the WMAP team.

If the cold spot does represent something more than just a random throw of the cosmic dice, it’s not clear what that something might be.

“It could suggest that the universe is rotating,” says Spergel. That would account for an uneven temperature distribution, but, Spergel adds, “that’s inconsistent with other data.” It could also suggest that the universe is finite in size, and perhaps not a lot bigger than what we can actually see from Earth, but that appears to be inconsistent as well.

At this point, says Spergel,  “I don’t know of any compelling idea that would explain it.” The anomaly isn’t so glaring that it threatens our larger grasp of the universe, he admits, but “we may need some sort of new theoretical understanding.”

Things might get clearer with the development of future telescopes, including the ground-based Large Synoptic Survey Telescope (LSST), which could go into operation in 2021, and the space-based Euclid mission, scheduled for launch in 2020. They will do a better job of studying the far smaller hot and cold spots that make up Planck’s pointillist picture of the young universe and are the seeds that eventually grew into the huge clusters of galaxies we see today and the voids that lie between.

If LSST and Euclid see the same sort of pattern Planck sees, that will be further evidence that the cosmos really is lopsided—and that in turn could mean that theorists have a major curve ball to deal with.



SOURCE: http://science.time.com/2013/03/28/look-close-somethings-strange-in...


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It sort of makes sense

“The radiation left over from the Big Bang is the same as that in your microwave oven but very much less powerful. It would heat your pizza only to -271.3°C, not much good for defrosting the pizza, let alone cooking it.” -Stephen Hawking

One of the most powerful predictions of the Big Bang — the fact that our cold, star-and-galaxy-rich, slowly-expanding Universe came from a hot, dense, much more homogeneous state — was the existence of a bath of leftover radiation that should be detectable, even today.

Image credit: Pearson / Addison Wesley, retrieved from Jill Bechtold.

Image credit: Pearson / Addison Wesley, retrieved from Jill Bechtold.

Back when the Universe was too hot to form neutral atoms, photons crashed into the other particles — mostly electrons with the occasional collision with an atomic nucleus — far too frequently for them to travel any appreciable distance. But when the Universe finally became cool enough to allow the formation of neutral atoms, the vast majority of photons will never interact with another atom, nucleus or electron ever again, and will simply stream in a straight line from the electron they last interacted with.

Image credit: Jodrell Bank Centre for Astrophysics, University of Manchester.

Image credit: Jodrell Bank Centre for Astrophysics, University of Manchester.

This is quite a prediction, because — since the Universe was in this hot, dense, expanding stateeverywhere — it means that we should see this radiation coming uniformly from all directions in space! And, because the Universe is no longer just a few hundred thousand years old (which is when this last-scattering occurred), but many billions of years old, this means that the Universe has expanded a tremendous amount.

And as the Universe expands, the wavelength of the photons in it get stretched along with the expansion of spacetime, meaning that this radiation should be very cool: just a few degrees above absolute zero.

Image credit: Addison Wesley.

Image credit: Addison Wesley.

So that’s the first prediction of the Big Bang about this radiation: it should be uniform in Temperature, just a few degrees above absolute zero, and should come equally from all directions in space. Additionally, it should also follow a blackbody spectrum, in accordance with the way thermodynamics works in an expanding Universe under the laws of General Relativity.

Image credit: LIFE magazine.

Image credit: LIFE magazine.

That’s exactly what Arno Penzias and Bob Wilson discovered back in 1965, using the Holmdel Horn Antenna, shown above. They saw a uniform amount of microwave radiation coming from all directions in the sky, hovering right around 3 Kelvin, with no apparent changes in different directions.

It was later confirmed (by the COBE satellite) that the spectrum of these fluctuations did in fact match the blackbody predictions, to unprecedented accuracy!

Image credit: COBE / FIRAS, George Smoot's group at LBL.

Image credit: COBE / FIRAS, George Smoot’s group at LBL.

But if everything were perfectly uniform, and there were absolutely no temperature fluctuations, then we never would have formed stars, galaxies, or clusters of galaxies in the Universe. The Universe needs imperfections to serve as the seeds for which — under the influence of gravity and millions (and billions) of years of time — structure on both large and small scales will form.

Image credit: Max Camenzind @ CamSoft, University of Heidelberg.

Image credit: Max Camenzind @ CamSoft, University of Heidelberg.

So it was a little surprising when we measured the temperature to be 3 Kelvin, and didn’t find any fluctuations.

And then we got more accurate, and found it to be 2.7 Kelvin, and still no fluctuations.

And then a little more, and found it to be 2.73 Kelvin, and — again — still no fluctuations.

Image credit: DMR, COBE, NASA, Four-Year Sky Map.

Image credit: DMR, COBE, NASA, Four-Year Sky Map.

Finally, it was discovered (see here for the history) that one side of the sky is slightly hotter than average by about 3.3 milliKelvin, while the opposite side is slightly colder by the same amount. This tells us that we’re in motion with respect to the rest-frame of the cosmic microwave background by a few hundred kilometers per second, totally in line with what we know about the typical peculiar motions of galaxies in the Universe.

But this isn’t a primordial fluctuation; this is merely an effect of our motion through space! If we want to find a primordial fluctuation, we need to measure things much more accurately, and that means on smaller scales, and down to microKelvin temperature fluctuations. This was done very famously — and very recently — by Planck, to the best precision of all time.

Image credit: NASA / JPL-Caltech / ESA.

Image credit: NASA / JPL-Caltech / ESA.

Whereas COBE managed to measure these fluctuations down to a resolution of about 7 degrees, and WMAP managed to go down to about 0.5 degrees, Planck has a resolution better than 0.1 degrees, and can measure temperature fluctuations down to a millionth of a Kelvin. The Planck map of the entire sky looks like this.

Image credit: ESA and the Planck Collaboration.

Image credit: ESA and the Planck Collaboration.

Now, what do we do with a map like this? Well, according to our theory, there are a few ingredients we can put into our Universe to get different patterns of fluctuations out. These ingredients include the following:

  • Normal, atomic-based matter,
  • Photons,
  • Neutrinos,
  • Dark Matter,
  • Cosmic Strings,
  • Domain Walls,
  • and a Cosmological Constant, among other possibilities.

The way we figure out what the Universe is made out of is that, on different angular scales, the Universe should exhibit different magnitudes and distributions of fluctuations. We break the sky up in different ways — into smaller and smaller chunks — to measure these fluctuations.

Image credit: Clem Pryke of University of Chicago.

Image credit: Clem Pryke of University of Chicago.

So you compare the measured temperature breakdown of the sky on each of these different scales, and you can find the average amplitude of temperature fluctuations on each angular scale. For Planck, we can go all the way up to about l=2500 and still have reliable results. The best-fit curve to the data is shown below.

Image credit: Planck Collaboration: P. A. R. Ade et al., 2013, A&A Preprint.

Image credit: Planck Collaboration: P. A. R. Ade et al., 2013, A&A Preprint.

As you can see, the low multipoles (or large angular scales) don’t fit the curve very well, and have very large error bars.

This is normal. In fact, there’s an entire blog named after this phenomenon: cosmic variance. That curve, above, is what you’d get if you averaged together a large amount of data. But — for the large angles — that would require a large number of Universes, and we can only see one. For example, the l=2 point only averages 5 measurements! So — and remember, statistically, there’s only a 68% chance that a given measurement will lie within one standard deviation of the mean — it’s pretty likely that we’re going to be off in many of the points at the low end, and that’s what we’ve always seen.

But that best-fit curve tells us that the Universe appears to be made of:

  • about 4.9% normal, atomic-based matter,
  • about 0.01% photons,
  • around 0.1% neutrinos,
  • about 26.3% dark matter,
  • no cosmic strings,
  • no domain walls,
  • and 68.7% cosmological constant, with no evidence for dark energy being anything more exotic than this.

Which is in fantastic agreement with all other observations. I’ve seen a lot of stories around the web focus on the anomalies in the CMB, and I want to point out to you exactly what these are.

Image credit: ESA and the Planck Collaboration.

Image credit: ESA and the Planck Collaboration.

Yes, there appears to be some “extra” stuff that’s not on the line predicted by the best-fit parameters to our theory. In other words, these are the locations where — if we subtract out theexpected fluctuations from the expected best-fit — there’s a little bit of extra (or too little) power, or temperature fluctuations that are a little too big or a little too small.

If you show them on the “anomalies” chart, above, they look pretty menacing. And no doubt, there may be new physics there. But I can show this to you in a different way.

Image credit: Planck Collaboration: P. A. R. Ade et al., 2013, A&A Preprint, annotations by me.

Image credit: Planck Collaboration: P. A. R. Ade et al., 2013, A&A Preprint, annotations by me.

Other than the largest scales I already talked about, these are the temperature anomalies. That’s right, the amount that that one binned data point is “off” from the predicted line represents practically the entirety of the “anomaly.”

The odds that the Universe would have that particular anomaly? Small; less than 1%.

But if you remember your statistics, we normally require a much higher standard: 5-σ statistical significance; this effect is around 3-σ. It could be interesting, but it could also just be the Universe we have. It’s important to probe potential cracks in the theory; that’s often where the greatest progress can be made. But don’t you dare understate the successes of the current cosmological model; remember how mind-bogglingly hard we’ve had to look to find anydepartures at all from what was expected! The Universe is what we thought it was, and from where I’m sitting, our current understanding of it — including all the data from the CMB — looks pretty damned good to me!

He writes:

And as the Universe expands, the wavelength of the photons in it get stretched along with the expansion of spacetime,

I didn't know that!

Yep! One of the factors they have to taken in to account when they are working out the red shift of an astronomical body!


Watch Wu Tang's GZA Explain The Big Bang In A Rap

It's a preview of his upcoming album, Dark Matter, which is all about the creation of the universe, quantum physics, and the cosmos. GZAs also been working to encourage high school students to create their own science-based raps.posted on March 28, 2013 at 4:16pm EDT



Source: youtube.com

The GZA gave PBS News Hour a sneak peek of a verse off his upcoming album,Dark Matter, and its a poetic depiction of how the universe came into being:

"Everything we see around us: the sun, the moon, the stars,
Are millions of worlds that astound us
The universe in size was hard to fathom.
It was composed in a region small as a single atom,
Less than one-trillionth the size the point of a pen,
Microscopic but on a macro level within."

The rapper has also been using his love of science to inspire high school students. GZA has joined forces with Columbia University professor Christopher Emdin for a program called Science Genius B.A.T.T.L.E.S.. Students from ten New York City public schools will create science-based raps, and then participate in rap battles leading to an ultimate showdown with GZA acting as a judge for the finalists.

Aww, GZA. We heart you.

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