Happy Birthday Einstein! 100 years of General Relativity


On November 25, 1915, Albert Einstein finally announced the complete mathematical details of his General Relativity Theory in the last of a series of four papers, but gravity and the nature of space itself, remain as mysterious today as they were back then.

Distortion in spacetime caused by rotating Earth (Credit:NASA/GP-B)

By now, we have all become accustomed to hearing about how this theory describes gravity as a ‘warp in space’, and that general relativity has led to some sensational discoveries and explanations such as Big Bang cosmology, black holes and how clocks run slower under the influence of gravity. We have even heard about how, in the Lense-Thirring Effect predicted in 1918, that rotating bodies can ‘drag’ space itself and cause some remarkable, but very subtle changes in how spinning gyroscopes behave in a gravitational field. This bizarre phenomenon was studied in detail by NASA’s Gravity Probe B satellite.

If you want to learn more about general relativity there are hundreds of great resources across the internet to choose from these days. Despite this exciting progress, there are still some very thorny details that have yet to be worked out, or even observed!

Some Basic Ideas

Relativity theory is based upon the idea that space and time form a single physical entity called spacetime. Every time you try to describe what something is doing, you have to describe its effects not just in relationship to the 3-dimensions of space, but the fourth-dimension of time. They are intimately connected to each other, especially in the way that you mathematically describe physical processes. You cannot just travel from one point in space to another at a specific speed, but you have to allow for how that motion changes the idea of time along the journey. This is all pretty elementary stuff, —> Read More