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A Celebration of Light
Our understanding of light comes from centuries of careful experimentation. Each experiment peeled back another layer of mystery.
1666
Isaac Newton showed white light contains all colors
A beam through glass revealed the spectrum hidden in sunlight
1801
Thomas Young proved light behaves as a wave
Light passing through two slits creates interference patterns
1905
Einstein showed light comes in packets (photons)
Light ejects electrons from metal, proving particle nature
1960
Theodore Maiman fired the first laser on May 16
Coherent light - the reason we celebrate this day
1887
The experiment that disproved the luminiferous aether
Light speed is constant regardless of Earth's motion
1849
First terrestrial measurement of light speed
A toothed wheel and a mirror 8 km away
1676
First estimate of light speed from Jupiter's moons
Light takes time to cross space - it isn't instantaneous
1862
Refined light speed measurement
299,796 km/s - remarkably close to modern value
On this date, physicist Theodore Maiman at Hughes Research Laboratories achieved what many thought impossible. His ruby laser produced coherent light — photons all traveling in the same direction with the same wavelength, in phase with each other.
The acronym LASER stands for Light Amplification by Stimulated Emission of Radiation. Einstein had predicted stimulated emission in 1917, but it took decades before anyone could build a working device.
Maiman's laser pulsed for only a few milliseconds, but it opened a new era. Today lasers read our music, carry our internet traffic, perform surgery, measure distances to the moon, and cut through steel. The International Day of Light (May 16) honors this breakthrough.