This week, scientists affiliated with the European Space Agency’s Planck observatory announced several discoveries from the first 15 months of Planck observations. Planck observes the cosmic microwave background (CMB) radiation. The CMB is the oldest light we can observe in the universe (from about 380,000 years after the Big Bang), because it comes from the time when neutral atoms finally formed and stabilized and photons were no longer constantly absorbed by free electrons and protons. Because of it’s age, studying the CMB enables astronomers and cosmologists to look at the early structure of the universe.
The newly released Planck data contains a few surprises, some vindications of previous work, and many things that are a mix of both. One of the things I found most interesting was the newly calculated age of the universe. Based on the Planck observations alone, the team predicts the age of the universe to be about 13.82 billion years. What’s great about this is that it falls exactly within the resolution of the previously predicted age of the universe by NASA’s WMAP data, 13.73 billion years +/- 0.12 billion. The error bars on the WMAP data mean that anything within 0.12 billion (120 million) years of each other is pretty much indistinguishable from each other. That the Planck data falls within in it means our observations and models seem to be very good at describing the universe.
What’s even more interesting (at least to me), is the stuff that doesn’t entirely jibe with our understanding of the universe. Sure, the age is a bit different because of a change in when dark energy is believed to kick in (the force that is causing the accelerating expansion of the universe that was discovered in the late 90s), but the slight change is practically bookkeeping compared to the other things. When discussing fundamental physics, I mentioned one major kink in our theories is that there seem to “preferred” directions for giant globs of stuff to clump together in the universe. The Planck data shows many deviations from randomness that WMAP found still hold and weren’t just caused by limits in WMAP’s data.
So what do we have? The big deal is that the universe seems to be off-balance. If you look at the image below, comparing Planck’s data to the model, the left and right side seem to have different brightness. Since the brightness of the CMB is related to where mass would accumulate, this would also mean there’s more stuff in one half of the universe than the other, based on what we can see. It’s also worth noting that Plait says the distribution of hot and cold spots still seems random; it’s just the intensity that isn’t.
Another quirk is the so-called CMB cold spot, a region initially found in WMAP data that was both larger and colder than expected for a random distribution. In recent years, some people challenged its existence and said its uniqueness might be due to how WMAP’s data was analyzed, but it still holds up in the Planck data release (although I can’t find out if the Planck team used the same statistical analysis as WMAP, so the Michigan scientists might still have a point).
So what do these mean? Well, a popular theory for each of these that these are “imprints” from another universe. If you’ve heard anything about string theory, you probably know that it requires the existence of many other dimensions (10 or 11, typically, depending on the exact form). In some versions of string theory, our 4D (3D-space + 1D time) universe can move around in this higher-dimensional space called the bulk and it could also potentially interact with other universes.
This’ll be an exciting time for cosmologists and physicists as they try to reconcile their theories with the new observations.
PS: I can’t find if Planck shows anything about the “axis of evil” alignment or dark flow, which are other interesting structural observations. But both of them depend on large scale surveys like Planck (and dark flow was specifically based on CMB data), so I could see these being looked as people have more time to process the released data.