Future
Mathematicians and astronomers (such as Laplace, Lagrange, Gauss, Poincaré, Kolmogorov, Vladimir Arnold, and Jürgen Moser) have searched for evidence for the stability of the planetary motions, and this quest led to many mathematical developments, and several successive 'proofs' of stability for the solar system. By most predictions, Earth's orbit will be relatively stable over long periods.
In 1989, Jacques Laskar's work showed that the Earth's orbit (as well as the orbits of all the inner planets) is chaotic and that an error as small as 15 metres in measuring the initial position of the Earth today would make it impossible to predict where the Earth would be in its orbit in just over 100 million years' time. Modeling the solar system is subject to the n-body problem.
The angle of the Earth's tilt is relatively stable over long periods. However, the tilt does undergo a slight, irregular motion (known as nutation) with a main period of 18.6 years. The orientation (rather than the angle) of the Earth's axis also changes over time, precessing around in a complete circle over each 25,800 year cycle; this precession is the reason for the difference between a sidereal year and a tropical year. Both of these motions are caused by the varying attraction of the Sun and Moon on the Earth's equatorial bulge. From the perspective of the Earth, the poles also migrate a few meters across the surface. This polar motion has multiple, cyclical components, which collectively are termed quasiperiodic motion. In addition to an annual component to this motion, there is a 14-month cycle called the Chandler wobble. The rotational velocity of the Earth also varies in a phenomenon known as length-of-day variation.
Read more about this topic: Earth's Orbit
Famous quotes containing the word future:
“To believe in something not yet proved and to underwrite it with our lives: it is the only way we can leave the future open. Man, surrounded by facts, permitting himself no surmise, no intuitive flash, no great hypothesis, no risk, is in a locked cell. Ignorance cannot seal the mind and imagination more surely.”
—Lillian Smith (1897–1966)
“Our Last Will and Testament, providing for the only future of which we can be reasonably certain, namely our own death, shows that the Will’s need to will is no less strong than Reason’s need to think; in both instances the mind transcends its own natural limitations, either by asking unanswerable questions or by projecting itself into a future which, for the willing subject, will never be.”
—Hannah Arendt (1906–1975)
“The planet’s survival has become so uncertain that any effort, any thought that presupposes an assured future amounts to a mad gamble.”
—Elias Canetti (b. 1905)