More on Einstein’s Theory of Relativity

Formulated by Albert Einstein in 1905, the theory of relativity is the notion that the laws of physics are the same everywhere. The theory explains the behavior of objects in space and time, and it can be used to predict everything from the existence of black holes, to light bending due to gravity, to the behavior of the planet Mercury in its orbit.

The theory is deceptively simple. First, there is no “absolute” frame of reference. Every time you measure an object’s velocity, or its momentum, or how it experiences time, it’s always in relation to something else. Second, the speed of light is the same no matter who measures it or how fast the person measuring it is going. Third, nothing can go faster than light.

The implications of Einstein’s most famous theory are profound. If the speed of light is always the same, it means that an astronaut going very fast relative to the Earth will measure the seconds ticking by slower than an Earthbound observer will — time essentially slows down for the astronaut, a phenomenon called time dilation.

Any object in a big gravity field is accelerating, so it will also experience time dilation. Meanwhile, the astronaut’s spaceship will experience length contraction, which means that if you took a picture of the spacecraft as it flew by, it would look as though it were “squished” in the direction of motion. To the astronaut on board, however, all would seem normal. In addition, the mass of the spaceship would appear to increase from the point of view of people on Earth.

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