Probing the Origins of the Universe with CMBR
Ben - Astronomers and Cosmologists seek to understand the origins of the universe, but as this was billions of years ago, we're left with very few clues as to what actually happened. One of the big clues is the Cosmic Microwave Background Radiation, as Cambridge University's Professor George Efstathiou explained.
George - The Cosmic Microwave Background Radiation is the remnant radiation from the Big Bang. And as the universe has expanded, this radiation has cooled and is now observed as a background radiation with a very low temperature of 2.3 degrees above absolute zero.
Ben - So it pervades the entire universe and shows us that at some point in the history, the universe, it was very hot and very dense.
George - That's right. The discovery of the microwave background was discovered in 1965 and once that radiation was discovered, it was really incontrovertible proof that the universe started off with a very hot dense state.
Ben - And how do we study it?
George - We can study it by observing the radiation at microwave wavelengths. So there have been a range of experiments and missions since the discovery of the background radiation. But it was realized very early on, as soon as the radiation was discovered, that the structure that now produces galaxies and classes of galaxies that we see in the universe today would have imprinted tiny little temperature variations on the background radiation. And so, physicists and astronomers started a search to discover these fluctuations and they were discovered in 1990 by the COBE satellite. These fluctuations are very important because we see them at the time that the universe became neutral. This occurred when the temperature of the background radiation was around 10,000 degrees and the universe was only 400,000 years old. So we see the universe as it was 400,000 years after the Big Bang. But the fluctuations that we see are faithful representations of what happened 10-35 seconds after the Big Bang and that's the real interest that cosmologists have in studying these fluctuations because it tells us about conditions in the ultra, ultra early universe.
Ben - And so, can we use it to work out some of the physics that was going on back then?
George - That's right. By studying these fluctuations, we can probe physics at ultra high energies, 10 to 15 orders of magnitude higher than the energies achievable by the large hadron collider. The physics of those high energies is really not at all well understood and it could be very, very different to the sort of physics that we know about. And that's what makes it really fascinating because a theory like that would have maybe 9 or 10 spatial dimensions. And these dimensions that we currently don't see, at those very early times, would've opened up. And so, it's possible that we could see signatures of higher dimensional physics by studying the background radiation.
Ben - Relatively recently, the Planck mission has set out to try and study this in more detail. What are you hoping to use that for?
George - Planck was successfully launched last year and it is by far the most sensitive space probe designed to study these fluctuations. So we will get much, much better images, of a higher angular resolution with much higher sensitivity that have ever been achieved before. And we're also measuring the polarisation. In this background radiation, the fluctuations are slightly polarised. They're polarised at a few percent level and Planck has sensitivity to polarisation so we expect to create an accurate picture of not just the distribution of temperature but the distribution of polarisation. That's very important because gravitational waves generated in the very early universe can produce a specific type of polarisation pattern which we may detect.
Ben - So what's the really big question that we're trying to answer?
George - We know very little about the physics of these very early times. What we would like to know is what actually happened very, very close to the Big Bang, not just in a sort of conceptual way, but actually really probe the structure of the Big Bang. What we think happened is that very close to the Big Bang, the universe underwent a period where it effectively expanded faster than the speed of light. So we called this a period of inflation. It's a very attractive theory. It is not a well-founded theory in terms of physics yet, so we don't understand the mechanism, we don't understand any of the details. What we hope to do with Planck is to get enough information that we can actually get a handle on what actually happened. Did the universe really go through an inflationary phase of expansion? What was the physics responsible for inflation? How were the fluctuations generated? What was the energy scale of inflation? These are the sort of questions that we hope to answer.
Ben - George Efstathiou on how we can use the leftover radiation from the Big Bang to probe the early universe.