THE BIG BANG AND THE EXPANSION OF THE UNIVERSE

The big explosion from which the Universe we live in originated happened 15-20 billion years ago, and left an echo in the form of a fossil radiation at -270 degrees centigrade, called "cosmic background radiation".

10-43 seconds (0.0000000000000000000000000000000000000000001 seconds) after the Big Bang. The Universe is very hot, 1032 degrees (100000000000000000000000000000000 degrees) and very small 10-33 cm (0.000000000000000000000000000000001 cm).
10-36 seconds after the Big Bang. The first particles are formed: quarks. The Universe is still very hot, 1030 degrees and measures 10-26 cm. The "violent" expansion of the Universe begins, an age known as "the age of inflation'.

10-4 seconds after the Big Bang. The quarks form protons and neutrons, the antiquarks form the antiprotons and antineutrons. The temperature of the Universe is 1,000 billion degrees.

1 second after the Big Bang: the first electrons appear.

3 minutes after the Big Bang: the Helium nuclei start to form.

300,000 years after the Big Bang the electrons bind the protons and the Helium nuclei forming Hydrogen and Helium atoms. 10 million years after the Big Bang the first galaxies are formed.

15 billion years after the Big Bang: the Universe in which we are living. 

According to the actual theories, none of the four fundamental forces existed in the original Universe, but only one. While the Universe expanded and got colder these forces evolved into the following: gravitational, electroweak, electromagnetic and strong.

The depths of the Universe and the dark matter

Edwin Hubble discovered, towards the end of the twenties, that the galaxies are moving away from each other, and that the longer their mutual distance, the faster the movement.
In the depths of the Universe the "quasars" can be found: these are still mysterious objects, probably active nuclei of galaxies very far in space and time, with black holes in their inner parts, the mass of which could be a billion times larger than that of the Sun.
But the matter that composes our bodies, the stars, the galaxies, is probably only 1% of the total. The remaining 99% is "invisible" matter, that escapes direct observation: the astronomers call it "dark matter". The nature of dark matter remains a mystery, but it makes itself "known" through its gravitational attraction.
  The expansion of the Universe. 
By using large telescopes we can explore the farther portions of the Universe, observing celestial objects that sent to us their light billions of years ago. We can therefore see them as they were, thus making a voyage in the past. (JPEG, 66 K) 
(Project: Michelangelo Miani) 
 
  This image, obtained by Hubble Space Telescope, represents the farthest portion of the Universe ever seen. The weakest galaxies, approximately 12 million light years far, show what the Universe was like when its age was less than 10% of the present age. Such galaxies are 4 million times weaker than the human eye limit. Each side of the image corresponds to 1,500,000 light years. The light coming from the farthest galaxies is equal to that emitted by a 100 Watt bulb at a distance of 16 million km.. (JPEG, 894 K) 
(NASA-STScI) 

Gravitational lenses

  The gravitational lens effect is a consequence of the fact that gravity can "bend" light, that is to deviate its rectilinear route. It can happen that the light sent by a very far quasar is deviated by the gravitational field of a galaxy interposed between the quasar and the observer. Thus different images of the far object are formed around the galaxy. (JPEG, 39 K) 
(Project: D.Berry, STScI) 
 
  The gravitational lens. 
The image of the quasar appears to the observer as being multiple, not single, as in this image of the Space Telescope, thus forming the so-called "Einstein's cross". (JPEG, 130 K) 
(NASA-STScI) 
 
 
 
 

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