asked
How do we know the speed of light is the same for everyone?
This is the assertion behind the theory of special relativity – and it’s not obvious. The speed of a train may be 200km/h to a stationary observer, but 400km/h relative to a train coming the other way. einstein’s claim that the speed of light is the same for everyone, regardless of how they’re moving, was confirmed by experiments at CERN in Geneva. Subatomic particles were accelerated to 99.975 per cent of the speed of light, but when the speed of light they emitted was measured, it turned out to be 300,000km/s – the same as when the particles are stationary, as einstein predicted.
