Planck supports inflation but confirms some strangeness

The European Space Agency (ESA) has just released the initial 15.5 months of data from the Planck mission that detects the relic radiation from the Big Bang when the universe was just 380 000 years old. The map of the Cosmic Microwave Background shows minute temperature fluctuations that correspond to regions of slightly different densities at a spatial resolution of 5 arcminutes. These regions evolved into the galaxies, clusters and
superclusters of today.

Anisotropies in the Cosmic Microwave Background (CMB) as observed by Planck. This CMB map, imprinted on the sky when the Universe was just 380,000 years old, shows tiny temperature fluctuations corresponding to regions of slightly different densities. These tiny overdensities represent the seeds of all structure we see in the present epoch. (Credit: ESA and the Planck Collaboration)

Planck’s new map provides an excellent confirmation of the standard model of cosmology, which is a 6 parameter, flat (Ωtotal = 1 exactly) Λ-CDM model, where Λ represents dark energy and CDM = cold dark matter. The universe appears flat to a level of 0.1%. The inferred amounts of normal matter, dark matter and dark energy are in
good agreement with previous results from WMAP (the Wilkinson Microwave Anisotropy Probe). The derived Hubble constant has decreased a little, meaning the universe is slightly older (by about 100 million years or so).

What is important is that Planck has confirmed some strange features initially suggested in the WMAP data. Planck’s map is at higher resolution and it reveals some peculiar unexplained features that may well require new physics to be invoked, or even new ways of thinking about the origin of the universe .

Here are some details from Planck:

  • The Universe is 13.82 billion years old (up from 13.77 billion years from WMAP)
  • The Universe is expanding a bit slower than we expected (H0 = 67 km/s/Mpc down from 69 km/s/Mpc from WMAP)
  • The Universe is 4.9% normal matter, 26.8% dark matter, and 68.3% dark energy (WMAP found 4.6%, 24.0% and 71% respectively)
  • The Universe is lopsided (hints of this were seen in the WMAP results)

It is the last item above that is of great interest, and has profound implications. Note that the Planck map shows temperature fluctuations just a bit stronger on the right hand side. Remember you are looking at the whole sky. It is a significant discrepancy of the CMB signal as observed in the two opposite hemispheres of the sky. Why would one part of the sky be showing this? Shouldn’t the whole map look the same? The possibilities are still being debated. The dark energy may not be constant with time. It could also be an “imprint” left over from the Big Bang. If so, this has huge ramifications for the
multiverse theory.

Sean Carroll has an excellent blog in which he discusses such a situation or as he calls it a “lopsided universe”. As you can see from his article from 5 years ago (June 2008) there were a few interesting yet speculative ideas that might be able to explain such a signature. Such proposed mechanisms may involve processes prior to Inflation.

If you navigate through the arXiv pre-print server and search the title field for “Planck 2013 results” you will find  twenty-nine — yes 29! — pre-prints uploaded by the Planck science team. Figures 11 and 37 of the Planck collaboration Paper XV shows the power spectra of the fluctuations. We reproduce the power spectra here:

Planck power spectrum. The largest angular scales are on the left side, whereas smaller and smaller scales are shown towards the right. The red dots are the Planck data. The green curve represents the best fit of the ‘standard model of cosmology’ to the Planck data. The pale green area around the curve shows the predictions of all the variations of the standard model that best agree with the data. (Credit: ESA and the Planck Collaboration)

The overwhelming response to the Planck results is one of wonder. Yes, the Λ-CDM model still looks the goods, inflation still looks valid, but the mission has thrown up new questions about the early universe, and perhaps even hinted at a multiverse. Future results from Planck will include polarisation data which will include the polarisation signal at large scales which relate to reionisation.

“The Universe seems to be simpler, but at the same time, also weirder than we ever thought. The anomalies in the CMB are telling us something fundamental: we do not know yet what this is, but we are eager to find out,” says  Jan Tauber, Planck Project Scientist at ESA.

For more details, see

[Glen Mackie]

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