Hubble adjusting the 100-inch telescope at the Mount Wilson Observatory in California
At the beginning, heat and pressure started the universe expanding. Edwin Powell Hubble (American astronomer, 1889–1953) discovered in 1929 that the universe is still expanding. Most galaxies or galaxy clusters are spreading out, moving away from each other. The farther they are from us, the faster they move away.
This movement must have started at some time in the relatively recent past. If it had always been going on, forever and ever in the past, then by now all the other galaxies would be infinitely far from us, and we couldn’t see any. But the sky is full of galaxies. Therefore we know that at a certain moment, not infinitely remote in the past, all the material and energy of the universe was close together. This moment marks the beginning of the universe, 13 820 million years ago.
This movement must have started at some time in the relatively recent past. If it had always been going on, forever and ever in the past, then by now all the other galaxies would be infinitely far from us, and we couldn’t see any. But the sky is full of galaxies. Therefore we know that at a certain moment, not infinitely remote in the past, all the material and energy of the universe was close together. This moment marks the beginning of the universe, 13 820 million years ago.
Einstein’s and Hubble’s discoveries, the materialization of energy and the expansion of the universe, lead to a working model of the beginnings of the universe. A fraction of a second after the beginning cosmic rays collided in the darkness, making a fiery mixture of particles and rays that expanded under tremendous pressure. Eventually the material, heat, and light separated from the darkness and formed the first stars and galaxies.
Hubble was working with the largest telescope of his day when he made his discovery. Even so he could not see very far into space. This meant that he could only observe conditions in the relatively recent past.
Light moves very fast, but still takes years to arrive even from the closest stars. We can never see how things are at the present moment in the heavens. What we see there is now past. The farther out one looks into space, the farther back in time one sees.
Telescopes gradually increased in size and performance. Nevertheless, they had to await the invention of electronic detector arrays to replace film before they could see very close to the beginning. Until then, theories based on Hubble’s discovery had to rely on indirect evidence for confirmation. By 1948 Ralph Asher Alpher (American physicist, 1921–), Robert Herman (American physicist and civil engineer, 1914–), and George Gamow (Russian-born American theoretical physicist, 1904–1968) had calculated that the original high temperature of the universe has dropped to about 5 kelvins at present in the coldest empty regions of space.
We now know the temperature more accurately. It is 2.735 kelvins.
Bright red coals or electrical heating elements have a temperature of 850º C to 950º C (1 562º F to 1 742º F). Some people can see incipient red heat beginning at temperatures as low as 500º C (932º F). Five kelvins is ‑268º C (‑450.4º F). This is far too cold to produce any detectable light.
Bright red coals or electrical heating elements have a temperature of 850º C to 950º C (1 562º F to 1 742º F). Some people can see incipient red heat beginning at temperatures as low as 500º C (932º F). Five kelvins is ‑268º C (‑450.4º F). This is far too cold to produce any detectable light.
The expansion of the universe makes the first light colder than that. Therefore no optical telescope can ever see the first light, no matter how far it can look. Only a radio telescope can detect the electromagnetic waves that correspond to so low a temperature.
