In 1965, two electrical engineers at Bell Labs made an extraordinary discovery. They found using a radio telescope a diffused signal of microwaves identical in intensity in every region of the sky. They had no idea how to explain this and were puzzled by it. Up the road at Princeton University, the physics group had learned of a model called the Big Bang model. That the universe had an early hot dense phase. They realized that model made a prediction that the relic radiation from the Big Bang should be visible in the present day universe as diffused low-energy microwaves. This was the radiation that Penzias and Wilson, had discovered. So for 50 years we've known that the universe is immersed in a bath of low energy radiation microwave photons. In the model of the expanding universe, this radiation originates when the universe was cool enough that stable atoms formed and radiation could travel freely without interacting in particular with electrons. So this radiation represents a baby picture of the infant universe in its very early hot phases. Without electrons to scatter them as the atoms became stable, the photons traveled freely through the universe. We see them now nearly 13.7 billion years later. This was the curtain raising of the universe when it became transparent for the first time. Its temperature when this radiation was emitted was about 3,000 degrees Kelvin and the universe has expanded a thousandfold since then stretching the radiation by a factor of 1000 in wavelength to become microwaves. Because the microwave background radiation as it's called is such a signature of the Big Bang. Enormous effort has been put into measuring it more precisely and understanding it in detail. The first map of the sky produced by Penzias and Wilson, showed a uniform signal of microwaves at a temperature just below three degrees Kelvin almost absolutely cold. Astronomers were motivated to learn more about the microwave background. In the late 1980's, NASA launched a satellite called the Cosmic Background Explorer, (COBE). COBE, produced a map of the microwaves that started to show detail. The central region of the map represents emission from the Milky Way. So that's approximate signal that gets subtracted out to analyze the universe as a whole. COBE data showed the hints of fluctuations in the microwaves that were assumed to be the seeds for galaxy formation. In breathless press releases of the time, people talked about discovering the fingerprints of God but COBE barely hinted at these fluctuations. So designs were made for a new satellite, WMAP, the Wilkinson Microwave Anisotropy Probe, that would explore this radiation with 10 or 20 times better signal to noise and resolution. WMAP operated for most of the first decade of the 21st century and produced exquisite detail of the microwave radiation, refining and honing our theory of the Big Bang. One thing these microwave satellites are able to do especially WMAP, is explore the nature of the angular fluctuations of the radiation. Now that we know the radiation is not completely isotropic or uniform, we can look at what spatial scales, or angular scales the radiation fluctuates. If you look at the WMAP picture, it has the illusion of speckling on a particular scale and that's not an illusion. Mathematics shows that there is a preferred angular scale for the variations. In these maps, color is code in temperature but those differences are tiny. Less than a 1,000 of a degree Kelvin. The angular fluctuation power spectrum or the amount of power in the microwaves on different angular scales shows a peak at about one degree. This is a characteristic of the physics of the very early universe and needs to be explained by the Big Bang model. There also is a second third peak at even smaller scales. This is also helping us understand the Big Bang better. This level of detail is unprecedented and came only with the WMAP mission. We can use a timeline analogy to realize how early a picture of the universe these microwave observations are giving us. The universe is 13.7 billion years old and the microwaves have helped tell us this age with precise detail perhaps an accuracy of three or four percent. But the microwaves were imprinted 380,000 years after the Big Bang. As a fraction of nearly 14 billion years, this is a tiny percentage. So when we look at the microwave sky, it's like looking at a picture of yourself when you were less than a day old or when running a marathon it's like being just a yard from the beginning of the race. This is an extraordinarily early picture of the universe and it's viewed with extraordinary detail. The universe was a very different place when these microwaves were created and released to travel freely through space. The temperature of the universe was 3,000 degrees Kelvin. If anyone had been present to witness this which of course they weren't they would have seen a dull red glow. Three thousand degrees is about the temperature of the photosphere of a cool red dwarf. In a sense the microwave background is very analogous to the photosphere of a star. We cannot see into a star because within a region where the plasma density gets high photons cannot travel freely. The edge of the red dwarf is where the photons start to travel freely. Similarly, with the universe as it cools it reaches a density where atoms recombine and radiation can travel freely and this corresponded to the time when the universe was as cool as a dwarf star. Since then, it has expanded 1,000 fold. By the cosmological redshift those dull red photons perhaps at the edge of the visible range have been stretched by a factor of 1000 to be the microwaves we observe with radio telescopes today. So quite literally the microwave background corresponds to the visible edge of the universe. Earlier than that it's a fog that we cannot penetrate with electromagnetic radiation. This is the earliest view we can actually get of the entire universe. Where is the Big Bang and where's this microwave radiation? It's everywhere. It fills space. The space between galaxies, spaces within the Milky Way, spaces around the earth, the room you're sitting in. The Big Bang is all around us because this radiation pervades the universe. The microwave radiation detection was the best evidence clinching the idea that the universe was hotter and denser in the distant past. It's extremely hard to explain this radiation any other way because remember there are about a billion of these microwave photons for every atom in the universe. Clever experiments have shown that the microwaves are not local. They do not emerge from our galaxy or the nearby region of the universe but they are pervasive cosmic source of radiation. There have even been measurements to show indirectly that those microwaves have changed their energy over cosmic time and they have indeed had shorter wavelengths back in the past. Every breath you take contains hundreds of thousands of photons from the Big Bang. Most people have plasma or LED TVs now. But if you can find an old fashioned electron gun or phosphor tube TV and you tune it between stations. It turns out that about one percent of the speckles correspond to interactions of the phosphor with microwaves from creation from the Big Bang. Whatever cable package you might have I can almost guarantee that watching the Big Bang is more entertaining than most of what you'll find on those hundreds of channels. So some evening just stay in and watch the Big Bang. So what do you in the mood for? Action or action adventure? Seriously can we ever watch something without an explosion every five minutes. What, I'm a guy. I like explosions. Cable is out. My digital box is lose you have to jiggle it or we could just watch the Big Bang? Yes. Wait what? The Big Bang. Whenever you see static on an analog TV like this a small part of that static is actually residual radiation from the Big Bang. I can watch that. We are not watching static. Trying something else. So this static is really from the Big Bang. Scientists discovered it in 1965, while using a radio receiver. At first they thought it was caused by bird poop on the receiver but they cleaned up the poop the static got worse and they realized it was 14 billion-year-old radiation. You should study this. That's why the European Space Agency was helping NASA create the Planck Space Observatory to help study the cosmic microwave background. What's Planck? I'm glad you asked. This sound was converted from data of Big Bang radiating by a university professor in Seattle. Yes. I can feel it. Okay, that's it give me the remote. No. I win. Fine we can watch the Big Bang but tomorrow I choose a show. You know I think this one's a repeat. A small percentage of aesthetic and all analogue TV sets is residual radiation from the Big Bang. However, with the conversion to digital TV set it will become increasingly harder for the general public to see it. If you still have an analog TV, be sure to check it out for yourself before this common window into our past disappears completely. Mark Whittle, at the University of Virginia has even managed to sonify the Big Bang or turn the astrophysics of the early universe into a sound analog. What you will hear is the first 10 million years of the universe compressed in time to about 10 seconds and taken up in frequency by 54 octaves into the audible range. Because most of these vibrations in the plasma were extremely low frequency. This is the sound of the Big Bang. The most dramatic evidence that the universe had an early hot dense phase and that the Big Bang actually occurred is the microwave background radiation discovered in 1965. Is an almost uniform signal of microwaves in every direction of the sky representing radiation released into the spaces between galaxy. The heat bath from the early hot Big Bang. The universe as it cooled formed stable atoms and at that point radiation could travel freely. So when we look at the microwave sky we're seeing an infant picture of the universe barely 400,000 years, after the Big Bang. In the universe, this is nearly 14 billion years old. This radiation has now been observed in exquisite detail by microwave satellites and we've learned a lot more about the Big Bang by studying this radiation.
