The Big Bang theory

According to the Big Bang theory, about 13.8 billion years ago the whole Universe was a very small, extremely hot and dense region. From this tiny point, the whole Universe expanded outwards to what exists today.

Evidence of expansion

Scientists have discovered that red-shift data provides evidence that the Universe, including space itself, is expanding. Astronomers have also discovered a cosmic microwave background radiation (CMBR). This comes from all directions in space and has a temperature of about –270 °C. The CMBR is the remains of the thermal energy from the Big Bang, spread thinly across the whole Universe.

Professor Brian Cox explains how evidence for the Big Bang can be found by analysing the colour of starlight

Prediction from Big Bang theoryEvidence observed Does evidence support the Big Bang theory?
More distant galaxies should move away fasterMore distant galaxies have greater red-shiftYes
Initial heat from the Big Bang should now be thinly spread across the whole UniverseCMBR is everywhere at a temperature of about -270°C Yes
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