by No matter what stock market analysts, political pollsters and astrologers say, we cannot predict the future. In fact, we cannot even predict the past.
So much for the work of Pierre-Simon Laplace, the French mathematician, philosopher and decisive king. In 1814, LaPlace declared that if it were possible to know the velocity and position of every particle in the universe at a given moment — and all the forces acting upon them — “with such intelligence nothing would be uncertain, and the future. , just as in the past, as a gift to him.”
Laplace’s dream remains unsatisfied because we cannot measure things with infinite precision, so small errors multiply and accumulate over time, leading to greater uncertainty. As a result, in the 1980s, astronomers including Jaques Laskar of the Paris Observatory concluded that computer simulations of planetary motions when applied more than 100 million years into the past could not be trusted. or in the future. For comparison, the universe is 14 billion years old, and the solar system is about 5 billion years old.
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“You can’t cast an accurate horoscope for a dinosaur,” Scott Tremaine, an orbital dynamics expert at the Institute for Advanced Study in Princeton, New Jersey, said in a recent email.
The ancient astrological chart is now more obscure. A new set of computer simulations, which take into account the effects of stars moving across our solar system, have reduced scientists’ ability to look back or forward by another 10 million years. Previous simulations considered the solar system as a discrete system, a clockwork cosmos where the main concerns were inner planetary orbits, resulting from asteroids.
“The stars don’t matter,” said Nathan Kaib, a senior scientist at the Planetary Science Institute in Tucson, Arizona. He and Sean Raymond from the University of Oklahoma published their findings in Astrophysical Journal Letters in late February.
The researchers found that a sun-like star called HD 7977, which currently lies 247 light-years away in the constellation Cassiopeia, may have passed close to the sun about 2.8 million years ago to give way to the planets vibrates more in its orbit.
That added uncertainty makes it even more difficult for astronomers to predict more than 50 million years into the past, to correlate temperature anomalies in the geological record with possible changes in Earth’s orbit. That information would be useful as we try to understand the climate changes that are taking place today. About 56 million years ago, Kaib said, Earth apparently went 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.
Did some change in the Earth’s orbit around the sun trigger this warm spell? We may never know.
“So I’m no expert, but I think that’s the hottest period in the last 100 million years,” Kaib said. “And it’s almost certainly not due to the Earth’s orbit itself. But we know that long-term climate fluctuations are linked to Earth’s orbital fluctuations. And so if you want to figure out climate anomalies, it helps to be confident about what’s going on in Earth’s orbit.”
Tremaine noted, “The simulations are done carefully, and I believe the conclusion is correct.” He added, “This is a relatively small change in our understanding of Earth’s orbital history, but it is an important conceptual change.”
The really interesting story, he said, is how chaos in the Earth’s orbit could leave a mark in the paleoclimate record.
The European Space Agency’s Gaia spacecraft, which has been mapping the locations, movements and other properties of 2 billion stars since its launch in 2013, has greatly improved the ability to track the motions of stars just outside the solar system.
“For the first time we can see individual stars,” Kaib said, “take them back in time or forward, and find out which stars are close to the sun and which ones aren’t, which is true -cool.”
According to his calculations, about 20 stars come within 1 parsec (about 3.26 light years) every million years. HD 7977 could come as close as 4 billion miles from the sun — about the distance to the Oort cloud, a vast reservoir of frozen comets at the edge of the solar system — or remain a thousand times farther away. Gravitational effects from the closer encounter could have eroded the orbits of the outer giant planets, potentially eroding the inner planets like Earth.
“That could be powerful enough to change the predictions of the Earth’s orbit simulations about 50 million years ago,” Kaib said.
As a result, he said, almost anything is statistically possible if you look far enough ahead. “So you find, for example, if you go forward billions of years, not all the planets are necessarily stable. In reality there is about a 1% chance that Mercury will hit the sun or Venus in the next 5 billion years.”
Whatever happens, chances are we won’t be around to see it. Stranded in the present, we do not know for sure where we came from or where we are going; the future and the past disappear into myth and hope. However we press on trying to look at our area of interest in terms of time and space. As F. Scott Fitzgerald wrote in “The Great Gatsby”: “So we met, boats against the current, that turned back endlessly in the past.”
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