What was the universe like after the big bang

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If galaxies are moving away from us, reasoned Hubble, then at some time in the past, they must have been clustered close together. Subsequent calculations have dated this Big Bang to approximately In two teams of astronomers working independently at Berkeley, California observed that supernovae — exploding stars — were moving away from Earth at an accelerating rate. This earned them the Nobel prize in physics in Physicists had assumed that matter in the universe would slow its rate of expansion; gravity would eventually cause the universe to fall back on its centre.

Though the Big Bang theory cannot describe what the conditions were at the very beginning of the universe, it can help physicists describe the earliest moments after the start of the expansion.

In the first moments after the Big Bang, the universe was extremely hot and dense. As the universe cooled, conditions became just right to give rise to the building blocks of matter — the quarks and electrons of which we are all made. As the universe cooled, the four fundamental forces in nature emerged: gravity , the strong force , the weak force and the electromagnetic force. Protons and neutrons began to form. Electrons began to combine with hydrogen and helium nuclei. High energy photons from this period rushed outwards.

The early universe was so hot, that as it has expanded and cooled, the highly energetic photons from that time have had their wavelengths stretched tremendously. The cosmic microwave background we observe today is evidence of what the early universe was like. The temperature of the cosmic microwave background is now only a few degrees above absolute zero and radiation left over from this period has wavelengths of about 1 mm which is in the microwave range of the electromagnetic spectrum.

This cosmic microwave radiation is what astronomers study with telescopes like Planck and others.