Astronomy
Baryon Acoustic Oscillations as a Cosmological Standard Ruler
Quick fact
The BAO scale is approximately 500 million light-years across, yet it has remained nearly constant since the universe was only 380,000 years old, making it one of the most reliable distance markers in cosmology.
Why this is interesting
If you could stretch a measuring tape across billions of light-years, what would it be made of? Surprisingly, the universe has its own ruler, etched sound waves from its infancy.