It has always been a thankless thing to estimate the minds of creators on an individual (human) scale-although we have always been happy about it. Scientists need to rely on facts to speak, science fiction writers have the right to fully open their brains, but these still seem to be too conservative in the face of the real universe. We have not yet detected the boundary of the universe, and naturally, it is impossible to judge whether it has a boundary.
But if the boundary really exists, what is outside the boundary?
As an astrophysicist, I am always in shock: even the biggest sci-fi stories are always inseparable from human beings. No matter how strange it is, or how unusual scientific concepts are, in the end, most science fiction novels will return to typical human (or human-like) interactions, problems, difficulties, and challenges. This is what we need to deal with and understand best. Most science fiction novels nowadays take place in a relatively reliable setting on a certain planet or a certain spacecraft. But the real challenge is not only to tie the story with human emotion, scale and time scale but also to incorporate the infinite scale of the universe itself into the story.
The true size of the universe has always been a big problem that plagues all mankind. We say that the observable universe lasts for tens of billions of light-years. If humans want to truly understand this, they have to break things down into a series of steps. The only way is to understand the size of the earth. The direct flight from Dubai to San Francisco is about 8,000 miles (12,875 kilometres) long-the diameter of the earth. The sun is bigger, its diameter is more than 100 times larger than the diameter of the earth. The distance between the sun and the earth is about 100 times the diameter of the sun, about 100 million miles (160,934,400 kilometres). The orbital radius of the earth’s revolution around the sun is a basic unit of measurement in astronomy, called the astronomical unit, abbreviated as AU. For example, Voyager 1 launched in 1977, which flew at a speed of 11 miles (18 kilometres) per second, and now has a distance of 137 AU from the sun.
But other stars are farther away. The closest star to the earth is called Proxima Centauri, which is about 270,000 AU away, or 4.25 light-years. You must line up 30 million suns to bridge the «gulf» between the sun and Proxima Centauri. In Douglas Adams’s «The Hitchhiker’s Guide to the Galaxy» (1979), the extraterrestrial Vogons did not go to the galaxy where Proxima Centauri is located and could not see Earth’s demolition announcement was extremely shocked. The funny thing is: how far is the distance between the earth and Proxima Centauri.
The average distance between stars in the Milky Way is 4 light-years, and the sun is also a member of the Milky Way. There is an infinite, empty «star» space here! There are about 300 billion stars in the Milky Way, all of which are contained in the huge frame of the Milky Way, with a diameter of about 100,000 light-years. In the past 20 years, mankind has ushered in a truly exciting discovery: our sun is not a unique star; evidence shows that most sun-like stars in the Milky Way galaxy are surrounded by planets, the size of many planets and The distance between the parent stars gives them the possibility of gestating life.
Wanting to reach these planets is another matter: If Voyager 1 maintains the correct flight direction, it will reach Proxima Centauri in 75,000 years-but now, it has deviated from the correct direction. Science fiction writers use various techniques to try to cross these interstellar distances: keeping astronauts in suspended animation during long-distance flights, or flying at speeds close to the speed of light (using the time dilation predicted by Einstein’s special theory of relativity). They also use warp engines (a super-light-speed propulsion system that allows people to travel freely among the stars), wormholes, or other undiscovered phenomena.
A century ago, astronomers made the first authoritative measurement of the size of the Milky Way, and they were shocked by the size of the universe they mapped. At first, people suspected that the so-called «vortex nebula» in the deep sky photos was actually a «cosmic island»-a structure as large as the Milky Way galaxy, farther away. Although the vast majority of science fiction stories are confined to the Milky Way, most of the astronomy stories in the past 100 years have been the discovery of a larger universe. We are about 2 million light-years away from our nearest neighbour galaxy. When we see the light from the most distant galaxy in the telescope, the elapsed time of this light is almost the same as the age of the entire universe-about 13 billion years.
In the 1920s, we discovered that the universe after the Big Bang continued to expand. But about 20 years ago, astronomers discovered that this expansion is accelerating under the drive of a certain force. The physical properties of this force are incomprehensible, but we call it «dark energy» for the time being. Dark energy has an impact on the length and time scale of the entire universe: how do we describe such a concept in science fiction?
The story does not stop there. We can’t see some galaxies in the universe because they haven’t had enough time for their light to reach the earth after the Big Bang. What is outside the observable range of the universe? The simplest model of the universe shows that the universe is unified at its largest scale and is always expanding. Another view is that the Big Bang gave birth to the universe, but it is just one of many such explosions (there may be infinitely many). The extent of the «multiverse» created by the Big Bang is far beyond our comprehension.
American astronomer Neil de Grasse Tyson once said: «The universe has no obligation to make sense to you.» Similarly, the miracles of the universe have no obligation to allow science fiction writers to easily tell their stories. In this vast universe, there is mostly no «star» space; the distance between stars in each galaxy and the distance between each galaxy in the universe is incomprehensible on a human scale. Although it is connected in some way with human effort and emotion. For any science fiction writer, capturing the true scale of the universe is a daunting challenge. Olaf Stapledon accepted this challenge in his novel Star Maker (1937). The stars, nebulae, and the universe in the novel are whole and conscious. Standing in front of the boundless universe, how small human beings are, but our brains can understand how big the universe is to a certain extent. There is still hope for everything. Caleb Scharf, an astrophysicist at Columbia University, said: “In a finite world, to see the universe is not a luxury, but a necessity.” Passing ideas to the public is the real challenge for astronomers and science fiction writers.
