Planck and Herschel Exclusive Interviews

Robert Wilson

Co-discoverer of the Cosmic Microwave Background (CMB) and

co-recipient of the 1978

Nobel Prize in Physics

Right: Astronomy Now Editor Keith Cooper with Robert Wilson at the IYA opening ceremony in Paris, January 2009.

When you first discovered the CMB and realized what it was, and in the years since then, how has it changed your own personal view of the Universe?

I actually liked the steady state better because of not having a beginning but especially because the Universe could then go on forever; I don’t like the idea that everything is eventually going to be destroyed. But unfortunately I had to change my ideas and so I certainly understand that it’s a big bang Universe and things will come to an end, and it will become harder and harder as things look now, but of course before that happens we have to watch out for the Sun but that’s billions of years off and we have much bigger problems to worry about now.

How do you think the discovery of the CMB has changed other people’s views in general?

Well I think the change is profound and probably most people didn't think that much about cosmology and what the Universe was like. There was a biblical story and various other stories that kept changing. Now we, for the last 30 years, have a unified story and it has gotten into the consciousness of the general public and this is the way it seems to be.

When you first saw the results from COBE [COsmic Background Explorer], what were your reactions?

My first reaction to COBE was splendor, it was a marvelous technical feat as well as really proving that this was radiation from the big bang or the very early Universe. The first measurement from COBE of the anisotropy was interesting and a relief in a way because there had been an effort over many years ever since the discovery to get to the point that we could see that. We knew that the Universe had to have some seed to the current structure, and early on theoreticians predicted a much larger anisotropy, and so experimentalists worked and ruled that out so the theorists would come back with a smaller one, and it was getting to the point there was nothing left to do to the theory, if this didn't work we’d have to change dramatically the theory of the whole Universe, but fortunately it worked and it all fits nicely!

WMAP allowed scientists to create the most detailed map of the CMB, revealing tiny temperature fluctuations in the 'left over' radiation of the big bang. Planck will study the CMB in even greater detail. Image: NASA/WMAP.

How and why are there fluctuations in the CMB?
We don’t necessarily know why they’re there there. The present explanation is that they come from quantum fluctuations during or prior to inflation. It’s very important that they are there, because if the Universe was completely uniform there never would have been stars or galaxies and we wouldn’t be here talking about it. It’s very important they are there, but the actual reason why they’re there is still perhaps up for grabs on some new theory. The present thought is that quantum fluctuation seems to work, it just isn’t proved.

We’ve already observed the CMB in remarkable detail but now we have the new mission Planck, what do think there is still left to learn about the CMB?

I think there’s still more to learn. Planck will go to higher frequencies it will look on the short wavelength side of thermal radiation and make sure that corresponds to what we’ve been seeing on the long wavelength side. From Planck’s point of view it’s a little unfortunate that WMAP [Wilkinson Microwave Anisotropy Probe] was so successful because the combination of ground based and WMAP has painted a pretty amazing picture. Planck, I suspect, will confirm that, but there’s a possibility it won't which will be even more interesting. I think that the thing to do, which Planck may or may not be able to do is the next form of polarization. Electromagnetic radiation comes in two polarizations. When sunlight is reflected form a water surface, if you used Polaroid glasses you can avoid the reflection by canceling the polarization which is reflected the most and looking at the other polarization. The same thing is true of radio waves that it can be polarized by reflection - and thats similar to what happened in the early Universe, but instead of having the dramatic effect if you turn your polaroid glasses, it’s an effect of less than a part per million. It can be seen but its still a predicted effect in the radiation that we should be able to see. There are two forms of polarization, called E-mode which doesn't really tell us much and about a tenth as much as the anisotropy, and B-mode, which is down another factor of several, which will give us new information about the Universe at the time of separation. It will tell us about gravitational waves at that time, but it is a very difficult measurement and Planck is on the edge of having the sensitivity of being able to do it.

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