Holy Mackerel its Tensor modes!!!

So today we saw announcement of the possible detection of tensor modes in the Cosmic Microwave Background radiation (CMB).


This is extremely significant as it gives us information which appears to be from closer to the big bang (time=zero, whatever you want to call it.  The bit we don’t understand.  I’m going to call it time zero) than anything else that has ever been observed.

So some background as to how this fits into our best guess of what is going on in the Early Universe – we think that at some very early time, some tiny fraction of a second after time zero the Universe expanded extremely rapidly during a period of Cosmological inflation.  Now there are many theories of inflation, the simplest ones happen over a period of about 10^-34 seconds but you could probably cook one up which took as long as 0.1 seconds if you were being really crazy and pushing everything to its limits.

What determines the timescale over which this happens depends upon the energy density during inflation, and you can’t tell what that is from the normal ripples in the CMB which give rise to galaxies etc.  However the energy density during inflation DOES lead to gravitational waves in the early Universe which affect the polarization of these microwave photons.  The new results from the BICEP 2 experiment shows that they can see this effect, or at least they seem to be able to see these gravitational wave effects, or tensor modes, or B-modes.

This is a bit strange because the Planck Satellite kind of ruled this out last April, so we need to think about this a bit more.  That might be telling us something about which models of inflation are OK and whether inflation itself really is a good match to the data.

Also, it could be inflation, or it could be something else, time will tell… but it’s very very significant and it is the beginning of a whole new story…

Taken at face value it tells us that we are seeing imprints of the very early stage of the Universe on the CMB, and that we have started to see signals from an epoch when the energy density was closer to the Planck scale than many of us, including myself, ever hoped to see.

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