It was hot when it was young
The most widely accepted cosmological model is that of the Big Bang. This was proven since the discovery of the cosmic microwave background radiation or CMBR. Although, strictly speaking, no one knows exactly what ‘banged’, we know from extrapolation that the Universe was infinitely hot at birth, cooling down as it expanded.
In fact, even only within minutes of expansion, scientists predict its temperature to have been about a billion Kelvin. Moving backward to 1 second, it is said to have been at 10 billion Kelvin. For comparison, today’s universe is found to have an average temperature of only 2.725 Kelvin.
It will be cold when it grows old
Observations made especially on galaxies farthest from us show that the Universe is expanding at an accelerated rate. This, and data that show that the Universe is cooling allows us to believe that the most probable ending for our universe is that of a Big Freeze.
That is, it will be devoid of any usable heat (energy). It is due to this prediction that the Big Freeze is also known as the Heat Death.Accurate measurements made by the Wilkinson Microwave Anisotropy Probe (WMAP) on the current geometry and density of the Universe favor such an ending.
The Universe spans a diameter of over 150 billion light years
Current estimates as with regards to the size of the Universe pegs it at a width of 150 billion light years. Although it may seem peculiarly inconsistent with the age of the Universe, which you’ll read about next, this value is easily understood once you consider the fact that the Universe is expanding at an accelerated rate.
The Universe is 13.7 billion years old
If you think that is amazing, perhaps equally remarkable is the fact that we know this to better than 1% precision. Credit goes to the WMAP team for gathering all the information needed to come up with this number. The information is based on measurements made on the CMBR.
Older methods which have contributed to confirming this value include measurements of the abundances of certain radioactive nuclei. Observations made on globular clusters, which contain the oldest stars, have also pointed to values close to this.
The Earth is not flat – but the Universe is
Based on Einstein’s Theory of General Relativity, there are three possible shapes that the Universe may take: open, closed, and flat. Once again, measurements by WMAP on the CMBR have revealed a monumental confirmation – the Universe is flat.
Combining this geometry and the idea of an invisible entity known as dark energy coincides with the widely accepted ultimate fate of our universe, which as stated earlier, is a Big Freeze.