The Big Bang

Cosmology is the search for origins. The origin of the universe remains one of the greatest questions in science.

According to the Big Bang theory, our Universe came into being as an infinitesimally small, infinitely hot, infinitely dense, something – a "singularity" around 13.7 billion years ago. Singularities are zones of infinite density that are thought to exist at the core of black holes, which are areas of intense gravitational pressure. In the first second after the Universe began, the surrounding temperature was about 5.5 billion Celsius. After its initial appearance, it apparently inflated (the "Big Bang"), expanded and cooled, going from very, very small and very, very hot, to the size and temperature of our current universe. It continues to expand and cool to this day and we are inside of it.

The Big Bang theory is the result of several important observations. In 1927, Edwin Hubble first observed that:

· The light from all the distant galaxies is red-shifted.

· The further away the galaxy the bigger the red-shift.

This means:

· All the distant galaxies are moving away from us.

· The further away the galaxy, the faster it is moving away.

We would not see these patterns in the red-shifts just because we, or the galaxies, are moving through space, but it is what we would see if space was expanding.
This is why scientists think we live in an expanding Universe. The Universe is everything that exists. There is nothing outside the Universe – not even empty space.

If the Universe is expanding, then one can assume that the galaxies that compose our Universe were once much closer together than they are now. By simply measuring how far apart galaxies are and how fast they are moving, we determine the Hubble Constant (estimates range from 50 to 100 km/s per kiloparsec*). The Hubble Law states that the recessional velocity** of a distant galaxy is proportional to its distance from us. It is very easy to determine the recessional velocity of galaxies; on the other hand, their current positions are difficult to measure. The distance to the galaxy is quite hard to measure, but can be estimated from its apparent angular size or by the brightness of objects in it such as supernovae.

If we run the expansion process backward, we get two results.

· The first is that it probably took approximately 15 billion years for the Universe to grow to its present size.

· Second, the Universe must have begun its expansion in an awesome event that astronomers call the Big Bang.

The Big Bang Theory started as a hypothesis – a suggested explanation created to account for the data. Scientists then used it to make a prediction. They said that the Big Bang would have produced radiation that, by now, would be found in the microwave region*** of the spectrum. It would come from all parts of the Universe. Scientists called this the cosmic microwave background radiation (CMBR). Scientists began searching for the CMBR and in 1965 two scientists, Arno Penzias and Robert Wilson, discovered it accidently. They were using a radio telescope and could not account for an annoying microwave signal that seemed to come equally from all directions. It was the CMBR. The Big Bang Theory was the only theory that could account for it, so this evidence led to the theory being accepted by most scientists.

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* A distance of 1000 parsecs (3262 light-years) is commonly denoted by the kiloparsec (kpc). Distances expressed in parsecs (pc) include distances between nearby stars.

** Recessional velocity can be calculated according to the formula:

where is the Hubble constant, is the distance, and is the recessional velocity, generally measured in km/s.

*** Microwave region - микроволновый диапазон, диапазон сверхвысоких частот

Дата добавления: 2014-12-23