Thursday, February 12, 2015

A photograph from the abyss of time

The cosmic background radiation as detected by the Planck satellite telescope
When the space telescopes sent by NASA and the European Space Agency (COBE, WMAP, Planck) send us data on the cosmic background radiation, the corresponding images usually appear on the first page of high-diffusion newspapers, accompanied by headlines that are not always correct. Let's look at a few, published in Spanish newspapers:

  1. A radiation coming from infinity (La Vanguardia, April 28, 1992). This headline is clearly exaggerated, as the cosmic background radiation does not come from infinity, but from about 40,000 million light-years away.
  2. A telescope that gets back to the origin of the universe (El País, March 21, 2013). This is not true: when we measure the temperature of the cosmic background radiation, we are not getting back to the origin of the universe, but to a few hundred thousand years after that origin.
  3. The Planck space telescope reveals an older universe (, March 21, 2013). This is not accurate: the Planck telescope did not reveal an older universe than previous telescopes, just increased the precision with which the details of the cosmic background radiation are known, but the age of the detected signal was exactly the same.
  4. The Planck telescope shows the first lights at the origin of the universe (La Gaceta, March 21, 2013). This headline is almost right. If it had said The Planck telescope shows the first lights near the origin of the universe it would have been fully right.
  5. The Planck Space Telescope captured the first light of the universe (La Vanguardia, March 21, 2013, La Razón, March 22, 2013). This is the only right headline in this sample.
Wilson and Penzias near the radio-telescope antenna
Indeed, the cosmic background radiation is the residue, reduced by the expansion of the universe, of the first light that could go across the cosmos when it became transparent, several hundred thousand years after the Big Bang. The discovery of this radiation earned Arno Penzias and Robert Wilson the 1978 Nobel Prize in Physics and made the Big Bang the standard theory about the origin of the cosmos.
The existence of the cosmic background radiation was suggested in 1948 by Ralph Alpher and Robert Herman. After the Big Bang, while the temperature was above 3000K, electrons could not associate with protons to form hydrogen atoms. All matter was in the plasma state, the same as inside the sun. It was therefore opaque. When the temperature dropped below 3000K, atoms were formed, so matter passed to the gaseous state and became transparent. Since that time, the light from other parts of the universe can reach us.

The cosmic background radiation is the endpoint that our telescopes can reach. Beyond that we cannot see, because the universe becomes opaque and does not let the radiation through. To study the first half million years of the history of the universe (more or less), we may solve some mathematical equations and make predictions about processes that might have happened using particle physics, but we cannot see those processes directly, except by looking for traces of these phenomena in the cosmic background radiation.

The same post in Spanish
Manuel Alfonseca

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