General Relativity

This slideshow is an introduction to general relativity.

Newton's law of gravity works well in low gravitational fields, but becomes inaccurate in stronger fields.

Einstein noted that the laws of physics seem to be the same where there in no gravity as where one is in freefall in a gravitational field, like when one is in the International Space Station. The Earth's gravitational field is almost as strong at the space station, but, because it is in freefall, it feels like there is no gravity.

From this, he came up with the Theory of General Relativity. This theory regards gravity as a curvature of space-time rather than an attractive force. Matter causes space-time to curve and the curvature of space-time tells matter how to move. The general relativity field equations can be used to calculate how matter moves in different situations, but the mathematics is very difficult.

Einstein's equations gave a different prediction from Newton's law of gravitation for light deflecting as it passes a massive body like the sun and a different prediction for the orbit of Mercury which is in quite an intense gravitational field courtesy of the sun.

Around 1920, both phenomena were observed with sufficient accuracy to show that Einstein's equations worked where Newton's didn't. From then on, Einstein became an international celbrity and, over 100 years later, no fault has been found in the theory.

Images: commons.wikimedia.org