What has happened at CERN?
Scientists say they have clocked neutrinos – tiny particles smaller than atoms – travelling at 300,006 kilometres per second, slightly faster than the speed of light.
What does that mean?
Einstein's theory of special relativity says nothing can travel faster than the speed of light in a vacuum, because photons – light particles – have no mass.
Proof that neutrinos, mysterious subatomic particles which have a tiny amount of mass, can travel faster would be inconsistent with Einstein's theory.
What are the knock-on effects?
Einstein's theory is critical to the Standard Model of physics that helps explain everything we know about how the universe works, from black holes to the big bang.
If it is shown to be flawed, virtually everything in modern physics and the fundamental laws of nature would have to be rethought.
Have the results been proven?
The findings were such a shock that CERN's scientists spent months checking their data before making their announcement. But they have asked American and Japanese teams to confirm the results before they are declared an actual discovery.
The data will also be put online overnight so that it can be scrutinised by experts across the world.
Does this mean E does not equal MC squared?
The theory of special relativity was used to spawn the theory that energy is equal to mass multiplied by the speed of light squared.
It is premature to discount the most famous equation of all time, but the latest discovery suggests one key assumption it relies on – that nothing can accelerate faster than light – may not be wholly accurate.