The big news overnight for science was the best measurement yet of the Cosmic Microwave Background [CMB], by the Planck Satellite. The CMB consists of microwave photons (particles of light with microwave wavelengths) that are the tell-tale leftover glow from the universe’s hot period, the Big Bang. These photons are almost entirely uniform across the sky, and consistent with a glowing object of temperature 2.7 degrees
Kelvin (or Centigrade) [poorly written] above absolute zero, the temperature where everything moves as slowly as allowed by quantum mechanics. (Note added: A change of 1 degree Kelvin is the same as a change of 1 degree Centigrade, but absolute zero is 0° Kelvin and -273.15° Centigrade. Centigrade and Celsius are the same.) But they aren’t quite uniform! And those slight non-uniformities, which speak volumes about the universe, have now been read with the greatest precision ever achieved.
Today my chores prevent my writing a proper post, and it doesn’t help that Planck released over a dozen papers overnight… it will take a while to sift through this. But the bullet points that everyone is talking about are
- On small angular scales, the universe looks about as simple and as consistent with current understanding as you could ask for (or not ask for). Many speculative notions about how the universe might have developed in its earliest stages are now out of the question. The detailed measurements of the basic properties of the universe are slightly changed, but the overall picture is evolutionary, not revolutionary. It’s a universe with a lot of “dark energy”, a lot of dark matter, some ordinary matter including three lightweight types of neutrinos… just as we thought before. Kind of a weird universe, but not new.
- The idea that cosmic inflation (a period where the universe was cold and expanding at a spectacular rate, following which the hot dense period we usually think of as the classic “Big Bang” began) may have occurred, making the universe so large and uniform, is unchallenged (one might even say supported) by the data at small and medium angular scales. Inflation could have been caused in many different ways; some of those options are now excluded or disfavored by the data.
- Planck’s predecessor, the WMAP satellite, found that there are some funny non-uniformities, a bit larger than you’d expect, at very large angular scales — and Planck sees them too, confirming their existence and allowing more precise study of them. (
The photons are a bit hotter[NO! Careless of me! “The temperature fluctuates more”] in half the sky than in the other half, and there’s a cold spot, and some sign of alignment of large-scale distortions that were expected to be randomly distributed.) But interpreting something like this is tricky — it could just be a statistical fluke, and since there’s only one universe, you don’t get to improve your statistics with better measurements. (That last point is called the problem of “cosmic variance”.) So if something interesting is going on in the overall shape or structure of the universe, I suspect we’re going to need an additional and different type of measurement to convince ourselves. And I’m not sure what that would be.
Since the last point is the one that’s the most curious, I suspect it will draw most of the discussion and speculation over the next months — and certainly the headlines today. (I also suspect the spin being put on it by the Planck collaboration — suggesting strongly that a rethink of the universe is necessary — is justified more by hope than by data.) Meanwhile, perhaps there are more things that I missed that are hidden in those many papers…