COSMIC RADIATION BACKGROUND This radiation was emitted approximately 300,000 years after the Big Bang, before which time space was so hot that protons and electrons existed only as free ions, making the universe opaque to radiation. It should be visible today because, after this time, when temperatures fell to below about 3,000°K, ionized hydrogen and helium atoms were able to capture electrons, thus neutralizing their electric charge (known as “recombination”), and the universe finally became transparent to light. In 1965, Arno Penzias and Robert Wilson, two young employees of Bell Telephone Laboratories in New Jersey, discovered, although totally by accident, exactly that. The mysterious microwave static they picked up on their microwave antenna seemed to be coming equally from every direction in the sky, and eventually they realized that this microwave radiation (which has a temperature of about -270°C, marginally above absolute zero, and the coldest thing found in nature) must indeed be the “afterglow” of the Big Bang. Penzias and Wilson received the 1978 Nobel Prize in Physics for their discovery (although, strangely, Gamow’s contribution was never recognized). It was later confirmed that the intensity of these microwaves at different wavelengths traces out a “black body” or “thermal” curve, consistent with radiation that has been brought into balance with its environment - just what would be expected if they were indeed a relic of an early hot “fireball” stage. This discovery, perhaps the most important cosmological discovery since Edwin Hubble had shown that we live in an expanding universe, was powerful evidence that our universe had indeed begun in a hot, dense state and had been growing and cooling ever since.
Posted on: Mon, 22 Dec 2014 16:26:57 +0000
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