Cosmology is one of the hippest most active fields of physics these days, and this excitement has been reflected strongly in these monthly articles thus far. Other reasons for this trend in my coverage are that I currently have a pretty unique vantage point on the topic, and also that cosmology is nearly able hypnotize me. This month’s issue will continue in this fashion, but I will diverge a bit to discuss with you another aspect of my current interests in physics: levitating small animals–But first, I want to bring to your attention a mission that might just provide the next big bang in the field of cosmology: ESA’s Planck.

As a JPLer, I know next to nothing about what’s going on in the space industry in places on the Earth other than America (couldn’t be important), but awhile ago I started noticing all these signs around my lab that said “Planck Flight Hardware” and stickers in places to the same effect. It’s true that I didn’t think twice about not knowing what these pertained to for at least a month, when finally it all was packed up and taken away and its absence made me more curious about the matter. In fact, any noticeable action at JPL is considered a curiosity, despite the fact that the people I work with have built dozens–and are currently operating 17–spacecraft in the last three decades. Upon further research into this mystery, I found that my group at JPL was commissioned by ESA to build a cryocooler for Planck. It seems that this is what had been meandering about my lab.

The mission follows in the wake of COBE and WMAP and, fundamentally, the Nobel Prize winning accidental discovery made by Penzias and Wilson in 1963: bird sh** does not cause 2.7 x 10¹¹ Hz background noise in radio antennas. Regardless of how meticulously the antenna was cleaned of pigeon dung, the noise reading was persistent and also curiously independent of the position of the antenna. After consulting a theoretical cosmologist (practically lepers of the field of physics in the height of the quantum era) at Princeton, Robert Dicke, the mysterious background radiation was identified as the echo of the big bang, and had been predicted by Dicke’s group.

Almost overnight, cosmology, once viewed as a field for metaphysical outcasts of “real physics,” gained enormous prestige. The Cosmic Microwave Background (CMB), as it came to be called, was proof that there was once a huge and very uniform explosion that burped into existence the universe and everything that can possibly be conceived of. The big bang is the most perfect example of blackbody radiation, which was well understood at the time of the CMB discovery. The frequency of the cosmic background radiation corresponds to a blackbody temperature of 2.7 K. Remember that the universe itself is expanding, and therefore we have to consider a redshift when we study the frequency of the CMB today (T_CMB = T₀(1+z), z == redshift). This is good because it means that the temperature of the universe at the time of the big bang was (a lot) hotter than 2.7 degrees above absolute zero.

I mentioned that the radiation was uniform. Imagine an infinitely dense and uniform ball of quarks exploding. This ball of radiation has to cool a little before the quarks will drop to a lower energy state by forming electrons and protons, and lower still before those particles can form atoms (analogous to shooting a probe past a planet: if the probe has too much kinetic energy, it won’t be captured in orbit). Eventually you’ll get molecules and then we get into chemistry, so it gets boring and I’ll stop. But the mystery here is how–if everything is shot out uniformly–do we end up with structure in the universe? If you look into our sky, there are clusters of galaxies here and there, and empty space, and—bottom line—our universe is not uniform. This is where detail becomes important: there must have been some disturbance that broke the uniformity of the big bang and propagated to leave us with our clumpy cosmos. No theories or simulations can account well for the structure evident in our universe, and this is one of the most prominent problems in physics today.

The Cosmic Microwave Background is incredibly, but not entirely, uniform: there are very small fluctuations (1 part in 100,000) that represent how matter and energy were distributed when the universe was very young, and may provide us with a thread to follow back to the source of the universe’s structure. COBE, launched in 1989, was the first of the space-based instruments sent to study the CMB. It returned valuable images and data, but with insufficient accuracy to study the anisotropies. WMAP, the second mission sent to study the CMB, returned data with 45 times the sensitivity and 33 times the angular resolution of COBE.

ESA’s Planck (cool spacecraft model here!) will measure the CMB with resolutions of an unprecedented 10^-6 ΔT/T, providing us with the most detailed set of CMB data in existence, and hopefully the drastic improvements will lead to a better understanding of the causes and origins of the anisotropies of the early universe. By the way, most of the increased accuracy derives from having a very good cooling system to minimize stray radiation from the spacecraft itself. It should be clear from this that my group rocks. Now that you have a little background, and before I start rambling, I encourage you to read Planck’s (surprisingly concise) list of scientific objectives from ESA’s webiste.

I hope you’ve read to this point anticipating cruelty to small animals in dark magnets. This article became longer than expected, and the amount of energy I have left to spend on describing how a creature is levitated and what we learn from the experiment would not do justice to the topic. So I will leave you here, salivating with miniature images of violence flickering behind your eyeballs, and we shall move on to our physicist of the month (this monthly part of the article was entirely neglected last month), Robert Dicke. Elected to this status mostly because he has a very unfortunate name and that really shouldn’t be taken into consideration by the Nobel committee (tsk tsk), but also partly because his group set an upper limit on the temperature of the CMB, which has turned out to be one of the most important scientific discoveries of the 20th century.

Finally, I would like to point out that MOND was Slashdotted today and I provided you with extensive information on this in November. The attention was brought to Slashdot because of a theory that I don’t know much about, called scalar-tensor-vector gravity (STVG–terrible name), which is a spin-off of MOND and has been able to account for the huge (400,000 km) discrepancy in the position of NASA spacecraft Pioneer 10, among other discrepancies not able to be reconciled with dark matter theories, or raw general relatively, for that matter. Coincidentally, the most significant theoretical issue for all three of these theories of gravity and mass distribution is that none of them can account for the structure that we see in the universe. Planck will hopefully continue to bulldoze through this mystery, closely following the progress made by COBE and WMAP.

Errata: I imply that electrons are made up of quarks. As far as can be told at this time, electrons are in fact fundamental, indivisible particles (and waves). Thanks to rhollen for this insight.