Cosmic Microwave Background (CMB)
Interactive IGCSE Physics Explainer
The Cosmic Microwave Background (CMB) is the thermal radiation leftover from the early universe, serving as key observational proof for the Big Bang theory.
Current Temperature
2.7 Kelvin (-270.45 °C)
EM Spectrum Region
Microwave Range
Uniformity
Isotropic (All Directions)
Originally emitted as high-energy gamma/ultraviolet radiation when the universe was hot and dense, these electromagnetic waves have stretched over 13.8 billion years due to space expansion.
Use the slider below to simulate cosmic expansion. Watch how expanding space stretches high-frequency waves into longer, lower-frequency microwaves.
Radiation Type: Microwave (CMB Today)
Temperature: 2.7 K
Early Universe
Present Universe
Why the CMB confirms the Big Bang theory for IGCSE Physics Paper 4:
- Universal Presence: CMB radiation is detected with equal intensity from all directions in space (isotropic).
- Cosmological Redshift: As space expanded, original high-energy radiation stretched into longer microwave wavelengths.
- Thermal Cooling: Predicts that an expanding universe cools down; the current 2.7 K temperature matches Big Bang mathematical models precisely.
- Flaw in Steady State Model: Alternative theories cannot explain the existence or uniform temperature of this background radiation.