The cosmic catastrophe is a

thought experiment A thought experiment is a hypothetical situation in which a hypothesis, theory, or principle is laid out for the purpose of thinking through its consequences. History The ancient Greek ''deiknymi'' (), or thought experiment, "was the most anci ...

in which the sun were to instantaneously disappear. The question is what would then happen to the

earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

and the other planets

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

ing the sun. According to

Isaac Newton Sir Isaac Newton (25 December 1642 – 20 March 1726/27) was an English mathematician, physicist, astronomer, alchemist, theologian, and author (described in his time as a "natural philosopher"), widely recognised as one of the grea ...

's classical theory of

gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

, the planets would immediately cease to move in circular motion, and inertia would make them start traveling in a straight line.

Albert Einstein Albert Einstein ( ; ; 14 March 1879 – 18 April 1955) was a German-born theoretical physicist, widely acknowledged to be one of the greatest and most influential physicists of all time. Einstein is best known for developing the theory ...

saw a deficiency in Newton's theory. The finiteness of the

speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit ...

would mean that it would take a certain amount of time before the darkness from the sun's absence would reach the orbiting planet. Therefore, why would the planet instantaneously start traveling in a straight line before the arrival of information that the sun's disappearance has occurred? The cosmic catastrophe thought experiment led Einstein to the invention of the General Theory of Relativity and the creation of the concept of

spacetime In physics, spacetime is a mathematical model that combines the three dimensions of space and one dimension of time into a single four-dimensional manifold. Spacetime diagrams can be used to visualize relativistic effects, such as why differen ...

. Spacetime allowed Einstein to fix the deficiency in Newton's theory. In Einstein's spacetime model, the disappearance of the sun would create

gravitational wave Gravitational waves are waves of the intensity of gravity generated by the accelerated masses of an orbital binary system that propagate as waves outward from their source at the speed of light. They were first proposed by Oliver Heaviside in 1 ...

s in the spacetime. The gravitational waves travel at the speed of light, and an orbiting planet would not react to the sun's disappearance until after the gravitational wave has reached it. Only then, the planet would start to travel in a straight line.

External links

The elegant Universe
part 1 of a 3 part

Nova A nova (plural novae or novas) is a transient astronomical event that causes the sudden appearance of a bright, apparently "new" star (hence the name "nova", which is Latin for "new") that slowly fades over weeks or months. Causes of the dramati ...

mini-series (see details under the "transcript" tab). Based on a book of the same title by

Brian Greene Brian Randolph Greene (born February 9, 1963) is a American theoretical physicist, mathematician, and string theorist. Greene was a physics professor at Cornell University from 19901995, and has been a professor at Columbia University since 1 ...

. Theory of relativity Spacetime Thought experiments in physics {{relativity-stub