Bluffer’s Guide to Einstein’s theories of General and Special Relativity
When did Einstein make a breakthrough?
In 1905 Einstein published his theory of special relativity. It explained the relationship between space and time, based on the concept that light travels at a constant speed of 299,792 kilometres (186,000 miles) per second and that the laws of physics are the same for everyone. He figured that it would be possible for two people to witness two events occurring simultaneously yet see them at different times. Motion would affect how each person observed the events.
And what does that mean?
Einstein gave an example involving two people – one standing on a railway platform and another sitting at the exact midpoint on board a train travelling at a constant speed. As the train passes the platform and the midpoint aligns with the person there, lightning strikes both the front and back ends of the train. It could be assumed that both people believed the strikes took place simultaneously. This is indeed what happened. But the person sitting on the train will observe that the lightning struck the front of the train first. The movement of the train means the light from the rear would take that bit longer to reach the passenger’s eyes.
Sounds simple enough. Is that it?
There’s a bit more to it. The theory also uses the speed of light to define the relationship between energy and matter. Most people are familiar with one of the most famous equations ever created: E=mc2. It means energy is equal to mass times the speed of light squared – or that energy and mass are interchangeable under the right conditions. The equation can tell us exactly how much energy is obtained from converting mass. But it led Einstein to something even more complex.
Would that be general relativity?
Yes. After years of work, Einstein published his theory of general relativity, which enabled it to work when taking the effects of gravity into account. What we experience as gravity, he posed, was not an invisible force, but the result of massive objects curving space-time itself. It had been thought, for instance, that the Earth moved because of the force of gravity, but Einstein said our planet’s orbit was because curved space-time was forcing it along the shortest possible route around the Sun.
Mind-bending stuff
What’s more, this also led to the theory of black holes, where the curvature of space-time around extremely dense objects is infinite.
This forms a hole in the fabric of space-time. General relativity also showed that time can be dilated due to a difference in the strength of gravity – climb Everest and your clock will tick faster than that of a friend who decided to stay at the bottom. The theory also showed that the path of light can be bent by gravity so that the position of stars are false when viewed from Earth. It also led to the development of the Big Bang theory.