Bad News for Cosmic Inflation

A paper released today after careful analysis of the CMB (cosmic microwave background) map captured by the Planck satellite have revealed that contrary to the claim by the BICEP2 telescope of polarisation in the photons from the CMB this could be purely due to unaccounted for galactic dust.

Gravitational waves

The original BICEP2 evidence released in support of polarisation in the CMB in support of cosmic inflation.

The BICEP2 team in March this year announced at an important press release that they had detected a 5-sigma detection of polarisation in the CMB which would confirm inflation and also fit nicely with the idea of primordial gravitational waves. It was an announcement that if proved true when tested by fellow physicists would change the face of cosmology forever.

However over the months since that announcement many people have had doubts with how the team dealt with the prediction of how much galactic dust lies between the telescope and the CMB. This dust can if not correctly accounted for produce a polarisation effect. The Planck team after analysis across the sky (and not just in one small spot like BICEP2) have released a paper which states that the signal is unfortunately most likely just an excess of galactic dust than was expected when the team were performing their study.

Although this is a setback for confirmation of cosmic inflation, it is not it’s doom. The BICEP2 mission is now collaborating with Planck to find regions of the sky in which the galactic dust column is much more sparse to continue further study.

The idea of cosmic inflation is currently the best theory we have for describing a few phenomena seen in the universe. It refers to a era just after the Big Bang in which some form of phase transition (maybe the decoupling of forces in a cooling universe) lead to a rapid expansion of the universes size. This can be then used to explain how when the CMB is observed we see an isotropic uniformity of temperature at 2.75K with fluctuations of 1 part in 10000. As well as the homogeneity on scales which would not have been possible without inflation we also have measured the geometry of the universe by observing the typical angular size of fluctuation patches on the CMB. If these are found to be 1 degree then this points to a flat geometry. When observed this is what is seen but what does it signify? One of two possibilities;

1. The universe has fine tuned constant which allow for a unstable completely flat geometry. But why should such fine-tuning exist?

2. The universe is not completely flat but cosmic inflation has caused the geometry to tend towards flat. Like the surface of a massive balloon. It may start of curved but blow it up to the size of the earth and the horizon will look flat.

Diagrams describing the 3 possible 4-dimensional geometries of the universe with the corresponding CMB signature angular scales.

Cosmic inflation is the favoured theory to explain these abnormalities in nature and it is imperative that further research be put into confirming or denying its validity. Whether further study by Planck or BICEP2 help or hinder the theory of cosmic inflation one things for sure, it will be an exciting time to be a cosmologist.



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