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Thursday
May192011

Before the Big Bang?

So we are all familiar with the Big Bang. The story goes, "Once upon a time, all the matter and energy in the universe were in one spot, and then that spot banged, bigly, and all the E=mc2 flew outward, and space itself expanded and has continued to expand. And it all lived happily ever after. Or at least 'ever after.'"

Part of the evidence for the Big Bang is the cosmic microwave background (CMB) radiation, which is a 2.73 Kelvin "glow" we see no matter which direction we look in space. It, like love and the Matrix, is everywhere. At the beginning of the universe (soon after the Big Bang, since that is when time began), the universe was way hotter and way smaller than it is now. As the universe continued to expand, its temperature dropped, and atoms could form. These atoms were stable and didn't want to catch the photons that were streaming past them, so the photons passed on through, which is the point at which the universe can be observed. This is called the Epoch of Reionization, and if you need a review, I wrote about it fairly extensively here.

The photons that existed at this time of "first light" have been hanging out ever since, although their radiation has become dimmer and lower in energy (since they once only had to fill a small universe and are now spread throughout our huge one). And, ta-da, we have the cold, faint, microwave-wavelength radiation whose hiss confused Penzias and Wilson as they tried out the first communcations satellite.

The CMB is the universe's embarrassing naked baby photo: it shows us what the universe looked like at its beginning, before it was potty-trained.

In a simpler, less interesting place, the CMB would be uniform, since it all came from the same place at the same point in time and has been spread through space in the same way ever since. However, the CMB is slightly different in some places than in others--slightly cooler, slightly hotter. These differences in temperature are usually called "anisotropies" or "fluctuations."

The fluctuations, while tiny in the CMB, grew as the universe progressed: they were the "seeds" of large-scale structure in the universe and are ultimately responsible for things like galaxy clusters, galaxies, you, and me.

The most famous students of the CMB anisotropies were COBE and WMAP, both satellite telescopes.
WMAP: Naked baby photos for the twenty-first centu
Now, these famous fluctuations are becoming infamous as they spark a fierce debate (or maybe the debate will be resolved quietly and with dignity, but I kind of like a good fight). If I get my wish, this debate will be in good company: "Does the sun orbit the earth, or does the earth orbit the sun?" "Is that a fuzzy nebula within our galaxy, or is that a whole other galaxy?" "Is Pluto a planet, or does it have to be taken out of that mnemonic device?"

Here's a court summary, so you can take your side:

The fluctuations are not random. They, in fact, sometimes present as concentric circles around which adjacent spots are more similar to each other than (to) spots not on the circles. Notice the grammatical double-meaning my strategically placed parentheses give. In other words, the circles have "anomalously low temperature variance."


How they interpreted it:
"Those circles are sure signs of pre-Big Bang activity." The team suggest that if supermassive black holes collided in the time before the Big Bang (an idea that kind of "blows" the "mind"), the energy generated by those collisions would have caused perturbations the initial state of the universe. The black hole collisions would have generated gravitational waves, which would travel uniformly outward, just like they do (we suspect) now. Those waves would have propagated through the post-Big Bang universe, leaving (through topological-type theories that, to be honest, don't totally understand) concentric circles on the CMB.

How the other side interprets it:
Doubting what admittedly sounds a bit like fringe science, Wehus and Eriksen decided that they would try to disprove Penrose and Gurzadyan. So they redid the analysis of the WMAP data and, to their surprise, also found the concentric circles. So did Moss, Scott, and Zibin. Both Wehus&Eriksen and Moss, et al., however, interpreted the circles differently. Running simulations based on standard cosmological assumptions, both groups found that the circles emerged naturally without aeon-before-the-epoch black hole crashes.

Moss's paper, speaking with a mighty fiery tone for a scientific abstract, said, "Properly simulated Gaussian CMB data contain just the sorts of variations claimed. Gurzadyan & Penrose have not found evidence for pre-Big Bang phenomena, but have simply re-discovered that the CMB contains structure." Zing.

Simulated differences
P&G's simulations used a white noise model to set the noise level (in this case, the average level of fluctuation), while W&E&M&S&Z used cosmological laws to determine what the average fluctuation would be.

What this debate tells us so far:
1. The same results can, gasp, be interpreted multiple ways. Though they may not have told you this during your ninth-grade titration experiment, you've probably figured it out by now.
2. A sensational interpretation can generate more fame than a more conservative, institutionally backed interpretation. While P&G's paper was only self-published on the arXiv and never by a peer-reviewed journal, it was picked up by mainstream science media outlets.
3. Arriving at a conclusion in a logically flawed way does not necessarily mean that the conclusion is wrong. There might well have been an (a)eon (as they say in the paper) before the Big Bang. Does that mean the concentric circles prove it's true? No. Does that mean they prove it's false? No. But that's science for you.


References

ResearchBlogging.org

V. G. Gurzadyan, & R. Penrose (2010). Concentric circles in WMAP data may provide evidence of violent pre-Big-Bang activity arXiv arXiv: 1011.3706v1

Moss, A., Scott, D., & Zibin, J. (2011). No evidence for anomalously low variance circles on the sky Journal of Cosmology and Astroparticle Physics, 2011 (04), 33-33 DOI: 10.1088/1475-7516/2011/04/033

Wehus, I., & Eriksen, H. (2011). A SEARCH FOR CONCENTRIC CIRCLES IN THE 7 YEAR TEMPERATURE SKY MAPS
The Astrophysical Journal, 733 (2) DOI: 10.1088/2041-8205/733/2/L29

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Reader Comments (4)

I have questions:

1. What starts the temperature fluctuations or anisotropies in the CMB?

2. Have collision of supermassive blackholes happened after the big bang? What do you think that would look like? Do you think we could see it? WHy hasn't Muse written a song about it yet?

3. Could these concentric circles be a by-product of the method they're using to look at this event?

3. Why do people think the Big Bang didn't happen? If so, what do they think actually happened?

May 20, 2011 | Unregistered CommenterBrooke N.

What about my Muse question?

May 23, 2011 | Unregistered CommenterBrooke N.

Because they haven't asked me to write it for them.

May 23, 2011 | Unregistered CommenterSarah Scoles

Sarah Scoles said...
1. They could be caused by gravitational waves, like these researchers suggested. Mostly, the fluctuations appear to be acoustic, meaning caused by pressure variations in the early universe. Fluid matter fell into gravitational potential wells, and pressure pushed in the opposite direction, sending an acoustic wave through the fluid.

2. To my knowledge, this is the only potential one: http://arstechnica.com/science/news/2009/03/supermassive-black-hole-binary-spiraling-towards-collision.ars . We haven't been able to prove the existence of even regular black holes for very many years, though, so it wouldn't surprise me if we're able to find evidence of more like this soon. We'd most likely see the collision as gravitational waves warping spacetime. Of course, you wouldn't see that, but telescopes might.

3. That's what the other, competing researchers thought, which is why they redid the analysis a different way. But the circles showed up in three independent analyses.

January 9, 2012 | Unregistered CommenterSarah Scoles

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