In Netflix’s 3 Body Problem – based on Liu Cixin’s sci-fi novels – the drama is inspired by a real-life scientific puzzle in astronomy. Mathematician Kit Yates explains, in a text for the BBC.
What’s the connection between Sir Isaac Newton, alien solar systems and a new multi-million dollar TV show on Netflix?
The answer is the “three-body problem”: a puzzle in astronomy and mathematics that describes why it is often difficult to predict the long-term trajectories of planets, satellites and stars.
So what exactly is the problem? And how did it end up being the title of a Netflix TV series?
To understand, you must first know a little about the context of the TV series and its premise. The story is based on Liu Cixin’s epic science fiction trilogy, Remembering Earth’s Past, of which The Three-body Problem is the first book. The original trilogy is characterized by the author’s attention to scientific details. The adaptation is less careful, but is still full of scientific ideas.
The TV series focuses on the “Oxford Five”, who all studied under the same professor at the University of Oxford. Some became scientists themselves (a postdoctoral researcher in physics, a founder and scientific director of a nanotechnology company, and an academic in theoretical physics), one became a school physics teacher, while the fifth is now an entrepreneur in the field of snack foods. Scientific credentials abound.
The heart of the story is that an alien race – called the Trisolarians or San-Ti Ren – is heading to Earth to colonize it. Through intergalactic communication, these travelers attempt to intimidate human scientists into slowing down our rapid technological advance, which makes Earth easier to conquer.
But why are these aliens so determined to conquer our planet in the first place? This is where the three-body problem comes in.
In this context, “bodies” is a scientific term for planets, moons, suns, or any other massive astronomical object. The home planet of the aliens is located in a solar system with three suns, hence their name in the English translation of the book – the Trisolarians. This three-sun system can be extremely unstable, making conditions difficult for life, hence the desire to travel across the Universe to inhabit our relatively stable solar system. We only have one Sun, so Earth’s future is relatively predictable—at least for the next few million years.
We know this because of Sir Isaac Newton’s Universal Law of Gravitation, published in 1687, which describes the gravitational forces exerted by one body on another. Its simple equation allowed astronomers to model the relationship between two large bodies such as the Earth and the Sun. The Earth has a regular orbital period of about 365.24 days – one solar year. Similarly, the Moon orbits the Earth approximately every 27.3 days – another seemingly stable two-body system. In theory, Newton, armed with his two-body solution, could predict the positions of planets, satellites, and comets in the solar system long into the future.
In reality, Newton’s two-body solution was always only an approximation of the actual solar system. In general, the influence of smaller bodies – such as moons or other planets – on larger ones cannot be completely ignored. Instead of a two-body problem, our solar system instead contains what is called an n-body problem. Such problems cannot generally be solved using traditional mathematical techniques to provide exact answers. Worse, the trajectories predicted by such systems allow for chaos.
Chaos, in the mathematical sense, does not refer to its usual usage of “disorder and disorganization.” Instead, it is often characterized by what mathematicians call sensitive dependence on initial conditions. This means that the behavior of two otherwise identical chaotic systems, initiated with extremely similar (but not exactly identical) initial conditions, will eventually become extremely different from each other.
Although Newton’s laws may provide seemingly accurate predictions of the future configuration of our solar system, the movements of the celestial bodies within it are actually chaotic, because in reality there are more than two bodies. This planetary chaos occurs over long time scales – a chaos horizon of the order of tens or hundreds of millions of years. So, eventually, a planet could be found on the opposite side of the solar system from where today’s calculations locate it. This is not due to the random dynamics of the planets – Newton’s laws describe their motion well – but is the result of the fact that the motion of three or more celestial bodies can be a chaotic system.
In the TV series, the bodies in question are three relatively massive suns of a trisolar system – the original home of the San Ti Ren (which means “three-bodied people” in Mandarin). And the chaos is much more obvious. In their corner of the Universe, the movement of planets is inherently chaotic and unstable, meaning they face the prospect of being swallowed up by one of them or spit out of the system altogether.
To communicate this complex scientific idea, two of the Oxford Five scientists play a hyper-realistic virtual reality video game. Participants transform into various historical human civilizations that appear to be subject to the whims of a trisolar system. As the game progresses, some of history’s most famous scientists take on the challenge of preparing political and religious leaders for chaos.
In one level of the game, Newton teams up with computer scientist Alan Turing to solve Newton’s Universal Law of Gravitation on a human realization of one of Turing’s computing machines. Unfortunately, their predictions are wrong, leading to their deaths and the sudden end of the entire simulated civilization.
Realizing that the San-Ti will never be able to predict or control the chaotic trajectories of their planet, the Oxford Five finally realize that the aliens must abandon their home to save their people.
The issue of the three bodies is therefore the root cause of all the drama that unfolds throughout the rest of the series and potentially the next two series that the show’s creators have planned.
How will the story end? You could try to look ahead by reading the books, but the makers of the TV series may have other ideas. As with the planets and the sun, when there is a third party involved, there is always room for the unpredictable.
Source: BBC
Tags: body problem Chaotic Cosmic Mathematics Netflix Series
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