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:
“I am not naturally ... A bag of wind; yet ... I mean deliberately and decidedly to cut in future all my old ideas on this head. I dont think modesty pays. It is a good quality in a family, it is a domestic virtue, it makes a home happy after you have got a home, but it is not potent in getting homes. It is not a money-maker, neither is it lucky in gaining a reputation. I am of the impression that gaseous bodies do better.”
—Rutherford Birchard Hayes (18221893)
“In any future great national trial, compared with the men of this, we shall have as weak, and as strong; as silly and as wise; as bad and good.”
—Abraham Lincoln (18091865)
“I would sum up my fear about the future in one word: boring. And thats my one fear: that everything has happened; nothing exciting or new or interesting is ever going to happen again ... the future is just going to be a vast, conforming suburb of the soul.”
—J.G. (James Graham)