THE WORLD THROUGH MICROWAVE EYES
It's a crystal clear night far away from the bright lights of a big city. A luminous full Moon is pulling itself free of the treetops. Against the velvet black sky stars are winking like diamonds.
But the night sky is not all it seems...
The visible light our eyes see makes up only a vanishingly small portion of all the light that is streaming through the Universe. Raining down on the Earth from space is a ceaseless torrent of invisible "light".
For most of human history we have been entirely blind to this light. But in recent years astronomers have opened up our eyes. New telescopes have been built which can see X-rays, infrared light, radio waves and every other kind of invisible light. Now, for the first time, we can behold the greater glories of the Universe.
Imagine that you can see what the astronomers see simply by putting on a pair of "magic" glasses. To "tune" them to different types of light you need only twiddle a nob on the frame. No longer are you almost blind. Now you can have infrared eyes, radio eyes, eyes that see ultraviolet light, gamma rays or X- rays.
Look up at the night sky and start tuning your magic glasses. What do you see?
At first, nothing appears to be changing. Then you realise that the Moon is fading. So, too, are most of the stars. Soon the Moon is hardly visible and the stars have begun to wink out one by one. But as the stars disappear new ones pop into view in places where no stars were visible before. Some of the new stars are shrouded in clouds of misty white nebulosity.
This is the ultraviolet sky. Your glasses are registering the kind of invisible light that causes sunburn when you lay too long on a beach. Only the very hottest stars shine brightly with ultraviolet light.
The stars change again. Now there are no familiar signposts in the heavens. The intensely bright pinpricks that dot the sky mark places where stars are cannibalising other stars and where blisteringly hot gas is plunging headlong into black holes. Wherever matter is heated to millions of degrees it shines brightly with X-rays.
Everything is fading now. We have come to gamma rays, the most energetic light in the Universe, created by the most violent events imaginable. Now the sky looks utterly black.
But wait! Over there! A tiny brilliant flash of light!
You turn your head to stare. But there is nothing to see. The black sky is utterly empty. Was it your imagination playing tricks?
No. If you were very patient indeed and watched the gamma ray sky for several days at a stretch you would see another brilliant flash from an entirely different place in the sky. And after a few more days you would see another. So what are these flashes? The answer is, nobody knows. Astronomers have called them "gamma ray bursters" and they are one of the great unsolved mysteries of the Universe.
There isn't anything more to see by twiddling any further-- except blackness and yet more blackness. Twiddle the nob back the other way. Zip back through the X-ray and ultraviolet skies to the familiar visible sky with its full Moon and well-known stars. But don't stop. Keep going. Keep twiddling.
You are now seeing infrared light. Rather than seeing hot bodies in the Universe you are seeing relatively cool ones. Even human beings give out infrared. It's the same kind of light earthquake rescue teams use to see people trapped beneath rubble.
The Moon has reappeared in the sky. But instead of shining brightly from reflected sunlight, it is glowing dully from its own meagre internal heat. The sky is full of unfamiliar stars. Cold stellar embers. There are bloated red giants in their death throes and stars so recently born that they are still swathed in shimmering gas out of which they formed.
But now you have left even the infrared sky behind. You are seeing microwaves, the same type of light used for radar and for heating food in microwave ovens. Wait! Something very odd is beginning to happen. The sky is lighting up. Not just a portion of it--all of it!
There must be something wrong. You take off the glasses and rub your eyes. You put the glasses back but nothing has changed. The whole sky, from horizon to horizon, is glowing a uniform pearly white. You twiddle further into the microwave region but the sky just gets brighter. The whole of space seems to be glowing. It's like you are inside a giant light bulb. It's overwhelming. You want to look away but there's nowhere you can look.
Are the glasses malfunctioning? No, they are perfectly okay. What you are seeing is quite real.
It's the relic of the Big Bang, the titanic fireball in which the Universe was born. Incredibly, it still permeates every pore of space 15 billion years after the event.
There is more energy tied up in this universal "cosmic microwave background" than there is in the visible light of all the stars put together. In fact, the Big Bang radiation makes up 99 per cent of all the light energy streaming through the Universe at this moment.
Yet although the technology to detect microwaves was developed for radar during the Second World War, it was not until 1965 that anyone noticed this "afterglow of creation". And even then it was noticed only by accident.
The extraordinary story of the discovery of the relic radiation from the Big Bang forms the backbone of this book. With its tortuous twists and turns, accidents and missed opportunities, it reads more like a mystery novel than a story of scientific discover. But it provides a wonderful example of the way in which science is really carried out.
The cosmic microwave background is the oldest "fossil" in creation. It has come to us directly from the Big Bang and has been flying across space for an incredible 15 billion years.
The cosmic microwave background was given out by matter cooling in the fireball. So it carries with it an imprint of the Universe as it was soon after the Big Bang. When you look at the microwave sky you are seeing a snapshot of the Universe as it was 15 billion years ago!
The early Universe must have been an extremely boring place, you think. After all, there is not a single feature anywhere in the microwave sky. Everywhere is that uniform pearly glow. It makes your eyes go funny.
Well, yes, you may be right. But a boring universe is a lot easier for scientists to understand than a complicated one. You can't have everything.
The smoothness of the cosmic microwave background is telling us that matter in the early Universe must have also been spread amazingly smoothly throughout space. And herein lies a great puzzle. Today's Universe is anything but smooth. In fact, the Universe is full of stars and the stars are grouped together into galaxies and these galaxies in turn are linked into great chains and clusters which snake their way across space. And between these groupings of galaxies are great voids of utterly empty space. Far from being smooth, the luminous material in today's Universe has the appearance of Swiss cheese.
So how did such an uneven and complicated universe arise from such a smooth and simple beginning?
Clearly, at some point the stuff of the Universe must have begun to clump together, like milk curdling. So although the cosmic microwave background looks remarkably smooth, it cannot be dead smooth. If we we look closely at it we ought to be able to see signs of the first structures in the Universe beginning to clump under gravity soon after the Big Bang.
For more than twenty-five years years, since the discovery of the cosmic microwave background, astronomers have peered at it closely. But, try as they might, they have been unable to find any variation in the brightness of the microwave background. There were no signs of the lumps of matter which would later form galaxies like our own Milky Way. The evidence of the cosmic microwave background seemed be contradicting one of our most cherished ideas: the fact that we exist!
But in 1989, NASA launched an obscure satellite called COBE (pronounced co-bee) into an orbit just above the Earth. Until now, the fireball radiation had been difficult to study because the Earth's atmosphere glows brightly with microwaves.
COBE's sensitive instruments listened carefully for the faint whisper of the cosmic explosion which started the Universe's expansion 15 billion years ago. For more than two years it found nothing. There were mutterings among scientists. They were getting jittery.
But in April 1992, COBE hit the jackpot. It found "ripples in the cosmic background radiation". In some parts of the sky the cosmic microwave background was ever so slightly brighter than in others. It was a tiny effect. The "hotspots" in the sky were only a few parts in a million hotter than the "coldspots". But the outpouring of relief among scientists was unprecedented. "It's like seeing the face of God," declared one of the scientists on the COBE team. "It's the discovery of the century, if not of all time," declared the physicist Stephen Hawking.
Many thought these remarks a little extravagant but the fact remained that COBE had found the "seeds" of galaxies in the early Universe. Those regions that were ever so slightly denser than others would grow and grow as the Universe expanded in the aftermath of the Big Bang, getting bigger as their gravity pulled in more and more matter. They would eventually grow into the clusters of galaxies and superclusters of galaxies we see around us today. COBE had not quite seen the face of God but it had seen the largest and oldest structures in the Universe.
At the time of the discovery the media of the world went wild. The story was splashed across TV screens and newspapers across the planet. It is probably true that no other scientific story has received such blanket coverage in the media.
Why everyone went so wild over such an obscure and esoteric story is a bizarre tale in itself and one that I tell later in this book. But before you can understand what all the fuss was about, you need to know a little background to the cosmic background. In particular, you need to know about the Big Bang. But what exactly was the Big Bang? Where did it happen? And how have astronomers come to believe in such a ridiculous idea?
The story begins in the first decades of the twentieth century when a new generation of giant telescopes allowed astronomers to probe the remote depths of space and discover for the first time just what kind of Universe we were living in…