Divining the CMB
What do you see in this pattern? Look very closely. The Cosmic Microwave Background (CMB) is a faint glow of electromagnetic radiation that pervades the universe. What it means is a matter of intense and sometimes bizarre speculation by cosmologists.
The spectrum of the CMB matches almost perfectly that of an ideal radiator, or blackbody, with a peak temperature of 2.7° Kelvin (graph) The spectrum is so smooth that it took years of analysis of the COBE satellite data to find any variations – inhomogeneities or anisotropies, as they are called. In 2001, the Wilkinson Microwave Anisotropy Probe teased out the variations to the highest resolution ever measured for a blackbody (picture). In the maps, the colors exaggerate the variations. They are exceedingly faint – on the order of 18 microkelvins, or parts per 100,000. They can be compared to tiny ripples on a calm sea. What does this imply? Does it shed light on the origin and nature of the universe?
Cosmologists advertise that the discovery of the CMB by Penzias and Wilson in 1965 (for which they received the Nobel Prize) was a confirmation of the Big Bang theory. It represents the cosmic afterglow of the primeval fireball, they said. Though such a glow had been predicted by George Gamow, Ralph Alpher and Robert Herman, the predicted value (28K) was higher than the measured value. Moreover, finding the spectrum to be so extremely smooth exacerbated the “lumpiness problem” in cosmology: if the universe began from a uniform explosion, where did the lumps come from? The universe is made up of lumpy aggregates of matter like galaxies and clusters of galaxies with near vacuums of empty space between them. The discovery of inhomogeneities, therefore, was latched onto quickly as an explanation: these tiny ripples grew into gravitational attractors for material that coalesced into the lumps. The discovery of the inhomogeneities won George Smoot the Nobel Prize in 2006.
Today, cosmologists continue to probe the CMB for clues to even grander visions. Here’s what some recent reports are claiming are visible in maps of the CMB that, to a layman, would look as meaningless as modern art.
- Donuts: The universe might be donut shaped. That’s what Nature News reported May 28, complete with a drawing. “Mmm… Universe,” teased the caption. “Calculations show it really might be shaped like the snack favourite.” How does one salivate over visions of donuts while looking at a CMB map? The vision lies in missing long wavelengths, which some cosmologists interpret as indicating the universe might be finite but non-spherical. Of the possible wrap-around shapes, a 3-torus seems to match the WMAP data best, they think. Yum.
- Treasure: The BBC News reported in March that the WMAP data constitutes a “treasure trove” of information about the universe – not only its age and early history, but its fate. A group from Oxford University believes that they see the faint glow of neutrinos in the map. Dr. Joanna Dunkley said, “We see patterns in light, light that has been travelling for billions of years, affected in the early infancy of the Universe by whatever the Universe was composed of at that point.”
This is more fun than an amusement park fortune-teller. Dr. Dunkley now sees “an impression of conditions billions of years ago” by inferring from the amount of helium today a “sea of neutrinos” that must have been given off early on by nuclear reactions, assuming it was built inside stars. Most neutrinos pass right through the earth without stopping. Very few are detected in the very few detectors built to look for them. There they are, right on the WMAP plot, staring us in the face. Don’t you see?
Dr. Dunkley also sees fog, but it clears up in her crystal ball. The dissipating fog reveals secrets about the first stars. “We basically have the first evidence that how the first stars switched on was a long, drawn-out process that took half a billion years,” she said. “We weren’t able to see that before.” Some of us are wondering how she sees it now.
- The Land Before Time: The familiar WMAP plot showed up in a story on the BBC News that suggested other universes are betraying their presence in the data. The possible observation of a slight asymmetry in the CMB from one direction to the other could clue us in that we inherited a structure from a parent universe, says a Caltech group. The fluctuations in the CMB are telling us that “new universes could be created spontaneously from apparently empty space.” If so, “From inside the parent universe, the event would be surprisingly unspectacular.” It’s just one of those ordinary things – everything from nothing, bubbling off in a flash from a previous universe that cannot be observed.
Sean Carroll (Caltech), who proposed the second idea, wants to convince his colleagues to think big. “We’re trained to say there was no time before the Big Bang, when we should say that we don’t know whether there was anything – or if there was, what it was.” Why say anything, then?
Carroll admits that we don’t know if universes can bud off from pre-existing ones. But if ours did, he thinks it would explain why time flows forward instead of backward in our universe. “Much work remains to be done on the theory:” the BBC said; “the researchers’ first priority will be to calculate the odds of a new universe appearing from a previous one.”
An untrained layman looking at the CMB would be astonished that such inferences could be conjured up out of faint color changes on a bland-looking map.
The know-nothings (02/22/2008 commentary) seem to know an awful lot (emphasis on awful). They have a lot to say about things they admit they can’t say. Did it occur to any of them that science was meant to be restricted to phenomena that are observable, testable and repeatable? Yes; tell us about the odds of getting a new universe from a previous one. Tell us all about it. Do a demo in the lab. Tell us about the infinite regress while you’re at it, and why there was something instead of nothing.
Today, we no longer need a calf liver, pendulum or water witch to play around with divination. We have trendier things with which the Babble-onions, Chaldeans and sooth-slayers can respectably practice their ancient Craft. The only thing they seem unable to divine is the Divine Nature (Romans 1). Odd; most of us lacking the divination tools can see it clearly all over the place.