No matter what stock market analysts, political pollsters, or astrologers say, we cannot predict the future. In fact, we can't even predict the past.
So much for the work of French mathematician, philosopher, and king of determinism, Pierre-Simon Laplace. In 1814, Laplace wrote that if one could know the velocity and position of every particle in the universe at a particular moment, and all the forces acting on them, “to such an intellect nothing would be uncertain; The future, like the past, will be the present.”
Laplace's dream remains unrealized because we cannot measure things with infinite precision, so small errors propagate and accumulate over time, creating more and more uncertainty. As a result, in the 1980s astronomers including Jacques Lasker of the Paris Observatory concluded that computer simulations of planetary motions were unreliable when applied over 100 million years in the past or into the future. For comparison, the universe was born 14 billion years ago, and the solar system was born about 5 billion years ago.
“We can't give exact horoscopes for dinosaurs,” Scott Tremaine, an expert on orbital mechanics at the Institute for Advanced Study in Princeton, New Jersey, recently commented in an email.
Ancient astrological charts are now even more obscure. A new set of computer simulations that takes into account the effects of stars passing through our solar system has effectively reduced scientists' ability to look back or forward another 10 million years. Previous simulations considered the solar system to be an isolated system, a clockwork universe with an interior in which the main perturbations to planetary orbits come from asteroids.
“Stars matter,” said Nathan Kaib, a senior scientist at the Planetary Science Institute in Tucson, Arizona. He and Sean Raymond of France's Institute of Astrophysics in Bordeaux published their results in the Astrophysical Journal Letters at the end of February.
Researchers have discovered that a Sun-like star called HD 7977, currently lurking 247 light-years away in the constellation Cassiopeia, was in its orbit enough to shake the largest planet around 2.8 million years ago. It was discovered that they may have come close.
This increased uncertainty makes it more difficult for astronomers to predict beyond 50 million years into the past and to correlate temperature anomalies in the geological record with possible changes in Earth's orbit. That knowledge will be useful when trying to understand the climate change that is occurring today. According to Dr. Kaib, about 56 million years ago, the Earth apparently experienced a thermal maximum between the Paleocene and Eocene epochs, a period that lasted more than 100,000 years, during which the average global temperature was The temperature has risen by 8 degrees.
Was this warm period caused by some change in Earth's orbit around the sun? We may never know.
“So, I'm no expert, but I think this is the warmest period in the last 100 million years or so,” Dr. Kaib said. “And it's almost certainly not caused by Earth's orbit itself. But we do know that long-term climate change is related to Earth's orbital variations. So if you want to understand climate anomalies, It helps to be sure of what the Earth’s orbit is doing.”
Dr Tremaine said: “The simulations have been carried out carefully and we believe the conclusions are correct.” He added: “This is a relatively small change in our understanding of Earth's orbital history, but conceptually it is an important one.”
The really interesting story, he said, is what kind of imprint the disruptions in Earth's orbit have left in the paleoclimatic record.
The ability to track the movement of stars just outside our solar system has been dramatically improved by the European Space Agency's Gaia spacecraft, which has mapped the position, movement, and other properties of 2 billion stars since its launch in 2013. did.
“For the first time, we can actually see individual stars,” Dr. Kaib said. “We can project them into the past or into the future and figure out which stars are close to the sun and which stars are not. That's really cool.”
According to his calculations, about 20 stars will come within 1 parsec (about 3.26 light-years) of the Sun every million years. HD 7977 may have come as close as 400 billion miles from the Sun (the distance to the Oort Cloud, a vast frozen comet reservoir at the edge of the solar system), or remained 1,000 times that far. there is. The gravitational effects of the close encounter may have wobbled the outer giant planet's orbit, which in turn may have wobbled the Earth-like inner planet as well.
“This could be powerful enough to change simulation predictions about Earth's orbit from about 50 million years ago onwards,” Dr Kaib said.
As a result, he said, statistically, almost anything is possible if you look far enough ahead. “So if we go forward billions of years, for example, we find that not all planets are necessarily stable. In fact, there's about a 1 percent chance that Mercury will collide with the Sun or Venus in the next 5 billion years. .”
Whatever happens, we probably won't be able to see it. Stuck in the present, we don't know for sure where we came from or where we're going. Both the future and the past retreat into myth and hope. Yet we move forward, trying to look beyond the horizons of time and space. As F. Scott Fitzgerald wrote in The Great Gatsby, “We sailed against the tide, perpetually sailing backwards.”