Unlocking the secrets of the universe

How do astronomers learn about the Big Bang? By studying fossilised photons in light left over from the origin of the Universe...
13 March 2015

Interview with 

Professor Anthony Lasenby, University of Cambridge


There's a vast amount of light we can't see. In fact, visible light only makes up a Spacetiny proportion of the total light spectrum. X-rays, gamma rays and radio waves are all examples of light we can't see. Since the 1930s, astronomers have known that the secrets of the Universe could be revealed with these types of invisible light. Graihagh Jackson spoke to cosmologist Anthony Lasenby about a particular kind of light emitted at the beginning of time...

Graihagh - A few kilometres west of Cambridge sits Mullard Radio Astronomy Observatory, a collection of what looks like huge satellite dishes that stare at the sky day in and day out. They're on the hunt for a different kind of light though - a type of light we can't see and that's radio waves.

Anthony - I started working on radio waves in 1978 and then I moved to Cambridge in 1984, been working here ever since.

Graihagh - That's Dr. Anthony Lasenby, a cosmologist at Cambridge University and that buzzing noise you can hear is AMI.

Anthony - The whole telescope we're standing in is called AMI and that's for arcminute microkelvin imager. So that noise we just heard is AMI moving to another source in the sky.

Graihagh - If we were to put on some magic glasses that enabled me to see radio waves, just like AMI can and I look up at the sky today, what would I see?

Anthony - Well, you'd see some really bright sources. The sun emits strongly and there's lots of individual radio sources which are being studied here for many years. But the thing that's behind them all would be a sort of pattern of stipples and little knots of what we call fluctuations in the background. You get hotter bits of the sky, less hot bits of the sky, and these are randomly arranged around us.

Graihagh - What would these blotches be?

Anthony - These are basically fossils. The actual photons we see today were emitted about 400,000 years after the big bang. They're extremely important because if you look at their properties, you can infer lots of extremely interesting things about the universe.

Graihagh - These fossilised photons were emitted shortly after the Big Bang and cosmologists refer to them collectively as the cosmic microwave background. But on discovery, Arno Penzias and Robert Wilson of the telecommunications company Bell Labs initially thought it was something rather different.

Anthony - They were at Bell telephone labs and Bell were interested in understanding whether sort of the cosmic dyes were possibly going to affect radio communication on Earth. And so, an experiment was set up to basically monitor and measure these cosmic sources of noise. One of the possible explanations for this noise was that it was much nearer to home. It was actually pigeon droppings in the antenna that they were using to look at the sky, because anything locally which is warm will emit radiation and be like some universal source of noise if it's sufficiently close to you. But they eliminated that. They moved the pigeons out of their nest.

Graihagh - And I'm imagining scraped all the pigeon poo off with it.

Anthony - Exactly and after that, they were put in touch with theorists at Princeton University and they could tell from their observations that it really was intrinsic, coming from the whole sky. At that moment then the microwave background had been discovered.

Graihagh - Given that this was discovered in '60s then why are we still looking at the cosmic microwave background today?

Anthony - Because it's got this amazing information imprinted on it. But to find that information, you have to study it at much higher resolution that was possible initially.

Graihagh - When Bell's team looked out to the universe, measurements of the cosmic background radiation were uniform across the sky. There were no hot patches or cold patches and this was strange because the universe today as we see it isn't one smooth temperature. It's full of stars and galaxies, what cosmologists refer to as structures. Bell's team should have been able to see footprints of these structures when they were first developing. AKA, they should've been able to see hotter patches and cooler patches imprinted on the sky. Baffling as this was, it turns out, it was just a matter of making our telescope see in higher resolution. In 1992, a satellite called COBE hit the jackpot. It found these imprints, these ripples, everyone had been searching for. But COBE followed by subsequent satellites like WMAP and Planck were only just beginning to uncover the secrets of the universe. And even today, there's still much more to be understood.

Anthony - What proportion is there a dark energy, how much dark matter is there, how much ordinary matter is there, is the universe open or closed or flat? All these things you can read off in great detail if you can get really precise measurements in the microwave background.

Graihagh - So the quest continues with AMI and other satellites across the world.

Anthony - Well with AMI, certainly, the quest continues. Satellites, that's another issue because Planck finished about 2 years ago and we don't have another satellite at the moment. Everyone is extremely keen that we have another mission which can map the whole sky which only a satellite can do. Continuing the study of the microwave background is incredibly important for moving our physics theory. So, we are hopeful that there will be another satellite but there isn't one yet.


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