How old is cosmic background radiation

The universe initially had radiation of an infinitely small wavelength, but the expansion has "stretched" the radiation out and we now see microwaves. This is another type of redshift. Thus, the remnant light from the big bang is called the cosmic microwave background radiation CMB. Theory predicts that the big bang would also have produced some simple elements; hydrogen, helium and deuterium being the most common, and these elements would have been produced in very specific ratios.

These ratios are also seen in various sky studies. Thus, the observed recession of the galaxies, the CMB and the abundance of certain light elements are the three so called pillars of big bang cosmology.

No other theory can explain these three observed phenomena as well as the big bang theory can, and this is why it is so widely accepted. Of the three pillars, the CMB encodes the most information about the nature of the universe that we live in, and hence it has become widely studied by many experimentalists, including us. The CMB is remarkable in that no matter which direction in the sky you look, it appears to be almost the same temperature.

This is called isotropy. If there were to be irregularities in the CMB, they could be seen as tiny hot and cold variations on the sky. In , the COBE research team announced that it had evidence that these hot and cold spots did exist, and they released the map below. One was the Steady State Theory, which held that the universe was homogenous in space and time and would remain so forever.

The more controversial theory sought to incorporate Edwin Hubble's discovery in that galaxies are moving away from one another at remarkable speeds. A handful of physicists led by George Gamow argued that the separation between galaxies must have been smaller in the past, which meant that at some point the universe had once been infinitely dense.

Everything in the universe had emerged from this incredibly dense and hot state in a cataclysmic explosion called "the Big Bang. Bell Labs had built a giant, foot horn-shaped antenna in Holmdel, NJ in as part of a very early satellite transmission system called Echo, but the launch of the Teslar satellite a few years later made the Echo system obsolete for its intended commercial application. Penzias and Wilson seized the opportunity to use the antenna as a radio telescope to amplify and measure radio signals from the spaces between galaxies.

To do so, they had to eliminate all recognizable interference from their receiver, removing the effects of radar and radio broadcasting and suppressing interference from the heart of the receiver itself by cooling it with liquid helium. However, when Penzias and Wilson reduced their data, they found an annoying background "noise", like static in a radio, that interfered with their observations. The noise was a uniform signal in the microwave range with a wavelength of 7. The CMB is brightest at a wavelength of around 2 mm, which is around times longer than the wavelength of the visible light we see with our eyes.

They saw a constant signal which washed out their view of the galaxy. The CMB is so bright at millimetre-wavelengths that if you de-tune an old analogue TV to show the snow-like static, a few percent of the signal your TV is picking up will have come from the start of the Universe. It helped establish several things. Firstly, the CMB is almost completely uniform, with an almost constant temperature over the whole sky. However, it is not completely constant.

The areas of higher energy are blue, while the areas of low energy are red. If this is a little confusing, try to imagine the colors in a campfire. The hottest and most energetic part of the fire is the blue flame, while the red flame is the coldest and least energetic part of the fire.

The same thing applies to this map of the CMB temperature anisotropies. The blue spots are hotter regions of more energy, and the red spots are colder regions of less energy. The strange thing is, the cold spots ie. Why, you ask? Well, these cold regions are what we call gravitational potential wells, so the photons are "pulled" in these regions by gravity, making them more dense. Originally, these regions would be hotter then the less dense regions because when you compress a gas for example, the temperature increases as more particles collide with each other.

However, it requires a lot of energy for the photons to overcome the gravitational pull and exit these potential wells, so these areas actually end up having less energy and are colder than the less dense regions. A Word of Caution Be careful when looking at these anisotropy maps!

They can be very misleading. First of all, the temperature variations in the CMB are very, very small, and the CMB is uniform up to about 1 part in ,