The Universe seems to be just as queer as we could have supposed, or maybe less queer. The results from PLANCK, which came out in their first ever press conference, 15.5 months after the probe was launched, speaks of a Universe described almost entirely by what is known to be the Standard Model of Cosmology. In other words, there is nothing that should startle us, but a lot that should be enlightening and, frankly, quite exciting.
For cosmology virgins, Planck is a space probe launched into an orbit around Earth designed to pick up the radio and microwave radiations from the whole Universe. By charting out the whole sky, it creates a unique map, a map of the Universe, as seen from the microwave frequency regime, and not the optical regime that we are so used to. The Universe is extremely different in these frequencies from the star-filled Universe we know and love. But these frequencies tell a different tale – one of the early universe and what imprints of that we can see today. The story of Cosmology starts right at the beginning of the Universe, or rather, more accurately 10-32 seconds after it. The Universe underwent a sudden expansion phase, called inflation, and then stabilized, while continuing to expand. The radiation from the inflationary era have got both diluted (i.e. reduced in intensity) and ‘stretched’ (i.e. their wavelengths have increased, leading to a decrease in their energy) due to the expansion of the Universe which is continuing to this very day. So ‘cold’ have these radiations become that we need specialized probes to catch them, their temperature being just 3 K (i.e. 3 Kelvin above absolute zero). The redeeming fact about these strange low-energy waves is that they are everywhere – all over the Universe. They form a kind of ‘background’ radiation and are thus called ‘Cosmic Microwave Background Radiation’ (CMBR), the name being self-explanatory.
The theory goes that there arose minute quantum fluctuations in the radiation soup right after the inflationary phase. As the Universe expanded, these expanded, then gravity took over and clumped matter in these pockets of disturbed equilibrium. These manifest as galaxies or clusters we see today – the tiny quantum fluctuations have grown to giant scale. The imprint of these early fluctuations will be found in the radiation seen by Planck.
The Age of the Universe
First big observation – the Universe seems to be just a bit older than we thought it to be – about 70 million years older. So the official age of the Universe become 13.82 billion years, raised from the 13.75 (or 13.77) billion it was assigned earlier.
The constituents of the Universe
It seems that the known constitution of the Universe has changed slightly from previous estimates. The matter percentage of the Universe is slightly higher than what we had known. The constitution of the Universe is mostly unknown to us and we can only put in some percentages on the amount we know and the part we are ignorant about. For example, we know that matter forms a very small percentage, followed by dark matter which forms a large chunk and that dark energy – a strange form of energy responsible for the accelerated expansion of the Universe currently – forms the largest chunk of the matter-energy pie. The earlier estimates have been bettered by Planck which quotes 4.9% ordinary matter, 26.8% dark matter and the rest 68.3% as dark energy. This is a decrease in the estimate for dark energy from previous estimates and an increase in the estimate of normal matter and dark matter. This implies that we know a bit more about the Universe (we only know about the ordinary matter part) and that the Universe is expanding at a slightly less accelerated rate than what we thought. Our ignorance about most of the Universe is only slightly abated.
Closely related to this is the value of the Hubble’s Constant which Planck calculates to be 67.3 +/- 1.2 km per second per megaparsec. This is a big surprise from the earlier value of the Hubble’s constant 71.0 +/- 2.5 km per second per megaparsec. The lower value of the Hubble’s constant means that the Universe is expanding slower than earlier thought.
CMB Spectrum: Cosmic Fingerprint
The whole Cosmic Microwave Spectrum as predicted by theory matches that seen by Planck to very high precision. We see the Universe at very high angular width as well as very narrow width. What Planck says is that at high multipoles, corresponding to very narrow angular width, the data matches experiment exactly. At low values of multipoles, the error bars are large, but Planck has seen as much as can be seen.
No probe in the future will be able to see at finer resolution, since the limit on resolution is not placed by the instrument anymore, rather by the Universe itself as a whole. Our Universe not only seems perfect, it seems good at hiding possible imperfections as well.
Asymmetry and Anisotropy
Planck gives an asymmetry in temperature over the two hemispheres of the Universe. This is a startling find, but nothing absolutely new. It’s just that Planck has confirmed – at high resolution – something that WMAP had already hinted at.
An important point to be made here: The distribution of the fluctuations are exactly random, even though we might not feel it to be so. They pass all tests of randomness. Just to emphasize, the angular distribution of the fluctuations is really exactly random. The fluctuations could have been anywhere and they just happen to be where they are! What is important is that the amplitudes of the fluctuations are not random. The amplitudes – i.e. the real temperature of the fluctuations – are not random and one hemisphere seems to be on the whole hotter than the other. This wasn’t expected! Note that a small patch of sky could’ve been warmer than the other, but this is seeing a whole trend in the temperature – one side is colder and the other hotter – and we have nothing to explain that. In fact, our cherished notions of isotropy of space (I.e. cosmological phenomena and features don’t have a preferred direction) contradict this finding. We have to wait for a verdict on this. There is also a cold spot detected in the Universe – a region of space considerably colder than the other parts. No one knows why this is the case – is it just random or is there some forces at play there?
Let’s look at a couple of more topics, both being a bit more technical.
Neutrino masses and the limit on them:
Planck puts a stern limit on the sum of the neutrino masses – a value of 0.23 eV. This is at a 95% Confidence level and this result is completely consistent with the neutrino mass being zero. However, the phenomenon of neutrino oscillation says that neutrino mass cannot be zero, no matter how small. Planck also says that the number of neutrino species is 3 and no more, well almost. This rules out those elusive sterile neutrinos, the possible fourth species of neutrinos which don’t even interact via weak interaction and their effect is felt only through the gravity that they exert.
Spectral Index and Inflationary Theories
Inflation as a theory receives a major boost from these results. The simplest inflationary models predict that knowing the two-point correlation function would be enough since the whole spectrum of the fluctuations right after inflation can be modelled by a Gaussian. Planck reinforces that. The models also say that spectrum is scale invariant (or ‘conformal’) and Planck shows slight deviation from that. A quantity called ‘spectral index’, ns, quantifies the scale invariance. If ns=1, then the scale invariance is perfect, otherwise there is deviation. Planck gives the value of ns = 0.9603 +/- 0.0073. So inflation is also nearly as simple as we can imagine and all ‘complicated’ models of inflation can be ruled out. So Planck reveals our Universe in details we have never seen before. However, even after looking at the Universe this closely, we find that the Universe is indeed plain vanilla, with a couple of chocolate chips thrown in. People are calling it the MBU or Maximally Boring Universe. Is the Universe really less queer than we thought?
[For more technical references, I refer you to the clutch of papers published by the Planck collaboration. They can be found here: