This deep dive covers Cosmic Microwave Background Radiation (CMBR) within Red Shift & Big Bang for GCSE Physics. Revise Red Shift & Big Bang in Space Physics for GCSE Physics with 13 exam-style questions and 12 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 5 of 14 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.

🚀 Cosmic Microwave Background Radiation (CMBR)

The second major piece of evidence for the Big Bang is the Cosmic Microwave Background Radiation (CMBR). This is faint microwave radiation that comes from every direction in space equally.

What the CMBR Is

About 380,000 years after the Big Bang, the universe had cooled enough for electrons to combine with atomic nuclei to form neutral atoms for the first time. Before this point, the universe was opaque — photons could not travel freely because they kept colliding with charged particles. When neutral atoms formed, photons were suddenly released to travel freely through space. These photons form the CMBR.

The universe has been expanding and cooling for 13.8 billion years since then, stretching these originally hot photons to much longer (cooler) wavelengths. What were originally high-energy photons are now detected as low-energy microwave radiation at a temperature of about 2.7 K (just above absolute zero).

Why the CMBR is Strong Evidence

The existence of the CMBR was predicted by Big Bang theory before it was discovered — this is very strong scientific evidence
It comes from all directions equally — consistent with a universe that began everywhere simultaneously
Its temperature (2.7 K) matches theoretical predictions almost exactly
It was discovered accidentally in 1965 by Arno Penzias and Robert Wilson, who initially thought it was interference from pigeon droppings in their antenna

Cosmic Microwave Background Radiation (CMBR)