Gravity causes space-time to curve around massive objects Or, if the marble comes too close, then it might be drawn inexorably into the depression of the bowling ball, rolling in ever-decreasing circles until it joins the ball in its hollow. It might roll straight past the bowling ball, or it might be deflected a little (or a lot) as it follows the dip but then 'escapes' (similar to the idea of using gravity to deflect or brake or slingshot a spaceship around a planet's orbit). The ants might explain it by saying that the weight is exerting a force of attraction on them, but, from the elevated point of view of the third dimension, it is clear that the ants are merely following the curve of the trampoline and that no actual force is acting on them.Īn even better visual analogy might be if a marble is rolled along the trampoline surface. If a group of ants spend their entire lives on the essentially 2- dimensional surface of a trampoline, and a heavy weight like a bowling ball is placed in the middle of the trampoline, the ants will find their paths mysteriously bent towards the bowl-like depression in the trampoline. In fact, it turns out that gravity is nothing more than curved space, or, more specifically, the curvature or warpage of four- dimensional space-time.Ī geodesic is the shortest path between two points in curved spaceĪ simple analogy might help us to understand this notoriously hard-to-visualize concept.

If we combine this concept with Einstein's principle of equivalence, then it would appear that light in the presence of gravity follows a curved trajectory, or, put in another way, gravity bends the path of light. The only possible interpretation of the curving laser beam, then, is that the space inside the cabin is in some way curved. On a curved surface, the shortest distance between two points is actually a curve, technically known as a geodesic, which we can perhaps visualize when we think, for example, of a plane flying the shortest route between London and New York which, as travelers will know, follows a 'great circle' path over Newfoundland rather than what appears to be a more direct straight line on a flat map. However, a straight line is only the shortest distance between two points on a flat surface. Now, we know that light always takes the shortest path between two points, which we usually think of as a straight line. If we imagine again the astronaut in his accelerating spaceship cabin from the previous section, and imagine him pointing a laser horizontally across the cabin, the upward motion of the spacecraft would result in the path of the laser appearing to curve (very) slightly downwards as it crosses the cabin.

- Speed of Light and the Principle of Relativity.

- Special and General Relativity Introduction.Main Topics > Special and General Relativity > Curved Space Topic Index: A Few Random Facts Where in the universe is the Earth? How fast are we traveling through space? How fast does light travel? How far is it to space, the Moon, the Sun, the stars, etc? How many stars are there? How does the Sun shine? What different types of stars are there? What is the human body (and the Earth, the Sun, the Universe) made of? How many molecules/atoms are there in each cubic meter? What if the history of the universe were squeezed into the period of one year? What are the coldest and the hottest objects in the universe? What is the electromagnetic spectrum? What is a planet? What is a dwarf planet? Why do the planets orbit the Sun?

Light following a curved space