Evidence for the Big Bang
The Big Bang theory isn't speculation. It's supported by multiple independent lines of evidence that all point to the same conclusion.
1. The Expanding Universe
In 1929, Edwin Hubble discovered that distant galaxies are moving away from us. The farther away a galaxy, the faster it recedes.
Hubble's Law: velocity = H₀ × distance
If galaxies are flying apart today, running time backward shows they were once together. This expansion was the Big Bang's first major evidence.
2. Cosmic Microwave Background (CMB)
Predicted in 1948, accidentally discovered in 1965.
380,000 years after the Big Bang, the universe cooled enough for light to travel freely. That ancient light still fills space, cooled to -270°C (just 2.7 degrees above absolute zero).
The CMB is the same temperature in all directions (to one part in 100,000), exactly as the Big Bang predicts. Its tiny fluctuations match theoretical models precisely.
3. Abundance of Light Elements
The Big Bang predicts specific ratios: ~75% hydrogen, ~25% helium, traces of lithium and deuterium.
When we measure the oldest stars and gas clouds, we find exactly these ratios. No other theory explains this.
4. Galaxy Evolution
Looking at distant galaxies is looking back in time (light takes time to travel).
Distant galaxies look different — younger, smaller, more chaotic. We see the universe evolving exactly as Big Bang cosmology predicts.
5. Time Dilation in Supernovae
Distant supernovae appear to brighten and fade slower than nearby ones. This is because time itself is stretched by cosmic expansion — another Big Bang prediction confirmed.
What About Alternative Theories?
Steady State Theory (universe is eternal, new matter constantly created) failed to explain the CMB and element abundances.
Tired Light (light loses energy over distance) doesn't explain time dilation.
No alternative matches the evidence as well as the Big Bang.
Related Reading
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