Cosmic TV

Let's start at the beginning. Well not quite the beginning, as that gets into the realm of philosophy and religion, but say a short time after the big bang. Space was very compact and as time went on it stretched. Quite quickly too. Still, with only a limited amount of space for all the matter in the Universe, things were a bit hot and crowded. It was so hot that atoms like hydrogen, oxygen, lead and the rest were unable to exist. Instead, the constituent parts - the electrons and protons - were spread all over the place as a sea of plasma.

Now, photons of light don't get too far in a dense plasma because they keep stopping to interact with the charged particles. This meant that the Universe was more opaque than a sheet of lead. However, space was still expanding and things were cooling down - allowing the first atoms to form as the Universe reached a temperature about the same as the Sun's surface. Once the electrons and protons had joined together to make electrically neutral atoms, about 300,000 years after the big bang, the photons were free to head off on their own.

Noise on a TV set

The CMB makes up a percent or so of the white noise on my TV set.


That light, from 13.7 billion years ago, has been stretched as the Universe has continued to expand - in much the same way as pictures on balloons get stretched as they are inflated. When the wavelength of light gets stretched, the amount of energy it has is reduced. Those very high energy photons from the year 300,000 are now in the less energetic, microwave, part of the electromagnetic spectrum. They were first accidentally observed by Arno Penzias and Robert Wilson of Bell Labs in 1965 using a microwave antenna in New Jersey although their existence had been suggested by people like George Gamow. The microwaves could be seen coming from every direction in the sky and the name Cosmic Microwave Background (CMB) was coined. The CMB is now extremely cold - it has a temperature of about 2.727 Kelvin (minus 270.425 degrees Celcius or minus 454.765 degrees Farenheit).

In recent years there have been a whole host of space, balloon and ground based instruments doing amazingly precise measurements of the tiny fluctuations in that temperature from one point on the sky to another. Although these are all very expensive, you don't need lots of money to detect the CMB. You just need a TV set.

Just tune your TV set between channels so that you see the 'snow' or white noise. This noise is mainly due to the components in your TV set which is at a temperature of about 300 Kelvin (room temperature). However, about one percent or so of that noise is actually due to microwaves from the Cosmic Microwave Background. Now that is cool.

Posted in astro blog by Stuart on Wednesday 10th Aug 2005 (16:11 UTC) | Permalink
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