Nello spazio più lontano

Astronomical evidence shows that the Universe is expanding, as if from a great explosion, the Big Bang, nearly 15 thousand million years ago. In the beginning, the Universe was unimaginably hot and dense, its whole size smaller than a single atom! Since then it has expanded, and cooled to only 3 degrees above the absolute zero of temperature.

When we look at distant stars and galaxies we are also looking back in time. Some of the mysterious objects called quasars are so far away that when we look at them we are seeing light that was emitted more than 10 thousand million years ago. (The quasars are more than 10 thousand million light years distant.)

The (Hubble) Deep Field - humanity's most distant yet optical view of the Universe

It might seem that by looking at objects even further away we could come close to observing the origin of the Universe in the Big Bang. However, the conditions in the early Universe prevent us from doing this.

Before the Universe was about 300,000 years old it was too hot for neutral atoms to exist. Instead the Universe would have been a hot plasma of freely moving charged particles - electrons and nuclei in the later stages, or more exotic mixes at earlier times. Light would then have been absorbed and re-emitted by the charged particles - in other words, the Universe would have been opaque. Only at an age of 300,000 years would the Universe have cooled sufficiently for electrons to bind to nuclei to form atoms. Only then would light begin to travel freely and the Universe become transparent.

The early opaqueness prevents astronomers from seeing directly back to the Big Bang, before the formation of atoms. To study the creation of matter itself requires high energy particle physics and experiments such as those at the LEP collider at CERN.