Regardless of what political pollsters and astrologers say, we cannot predict the future. In fact, we can't even predict the past.
In 1814, Pierre-Simon Laplace—the French mathematician, philosopher, and king of determinism—said that if it were possible to know the speed and position of every particle in the universe at a particular moment, and all the forces acting on them, “ For such an intellect nothing would be uncertain and the future, like the past, would be the present for him.”
His dream remains unfulfilled because we cannot measure things with infinite precision, so small errors propagate and accumulate over time, generating greater and greater uncertainty. As a result, in the 1980s some astronomers concluded that computer simulations of planetary motions could not be trusted when applied more than 100 million years in the past or future. (The universe is 14 billion years old and the solar system is about 5 billion years old.)
“You can't put together an exact horoscope for a dinosaur,” Scott Tremaine, an expert in orbital dynamics at the Institute for Advanced Study, in Princeton, New Jersey, said recently.
The old birth chart has become even more blurred. New computer simulations, which take into account the effects of stars passing through our solar system, have effectively reduced scientists' ability to look back or forward another 10 million years. Previous simulations had considered the solar system as an isolated system, a mechanical cosmos in which the main perturbations to planetary orbits were internal, resulting from asteroids.
“Stars do matter,” said Nathan Kaib, a senior scientist at the Planetary Science Institute in Tucson, Arizona. He and Sean Raymond of the Laboratoire d'Astrophysique de Bordeaux in France published their results in the Astrophysical Journal Letters in February.
Researchers found that HD 7977, a Sun-like star that currently lies 247 light-years away in the Cassiopeia constellation, could have passed close enough to the Sun about 2.8 million years ago to shake the largest planets into existence. their orbits.
That additional uncertainty makes it even more difficult for astronomers to forecast beyond 50 million years into the past and correlate temperature anomalies with possible changes in Earth's orbit. That knowledge would be useful as we try to understand climate change. About 56 million years ago, Kaib said, the Earth evidently passed through the Paleocene-Eocene Thermal Maximum, a period lasting more than 100,000 years during which average global temperatures rose by up to 8 degrees Celsius.
Was this heat wave caused by some change in the Earth's orbit around the Sun? Maybe we will never know.
Kaib's calculations show that about 20 stars come within one parsec (about 3.26 light years) of the Sun every million years. HD 7977 could have come within 644 billion kilometers of the Sun, or remained a thousand times more distant. The gravitational effects of the closest encounter could have shaken the orbits of the outer giant planets, which in turn could have shaken the inner planets like Earth.
“That's potentially powerful enough to alter simulations' predictions of what Earth's orbit was like beyond about 50 million years,” Kaib said.
As a result, he added, almost anything is statistically possible if you look far enough in advance: “In fact, there is about a 1 percent chance that Mercury will collide with the Sun or Venus over the course of the next 5 billion years.” years”.
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