Imagine yourself in a world not much different from Earth, orbiting a star not much different from our Sun. Temperature and atmosphere are ideal for liquid water to exist on the surface, and the mixture of oceans and continents ensures that life has stable conditions to thrive for billions of years. Evolutionary processes have also increased the complexity and level of differentiation of organisms in this world. Through a combination of random mutations and the pressure of natural selection, some of the species in this world have become intelligent, conscious and have reached unprecedented levels of dominance over nature.
As technology developed, this species began to think about other civilizations near other stars. And then, from a distant, faint point of light in their sky, the first attack came, blowing a hole in the planet at relativistic speed. It was not a meteor, an asteroid, or a comet; it was humanity.
Here on Earth, our dreams of interstellar travel have traditionally been divided into two categories:
- We travel slowly, rocket-powered, and our journey takes many lives.
- We set off quickly, using the best of science, to travel at relativistic (near light) speeds.
Even with unmanned travel, these two options seem to be the only options. Either we set off like Voyagers and it takes us thousands of years to travel even one light-year, or we are developing new technologies capable of accelerating the spacecraft to much higher speeds. The first option seems unacceptable; the second seems unrealistic.
Can we attack aliens?
But in 2010, something happened that could change the rules of the game. We've actually made a powerful technological leap forward that allows us to transfer a huge amount of energy to the apparatus over a relatively long time in order to accelerate it (in principle) to incredible speeds.
What is this leap? Laser physics. Lasers today are much more powerful and collimated than ever, which means that if we place a huge number of these powerful lasers in space, where they do not have to fight atmospheric scattering, they can illuminate a single target for a long time, transmitting energy and momentum until accelerated to more than 10% the speed of light.
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In 2015, scientists wrote a white paper on how an advanced laser system could be combined with a solar sail concept to create a "laser sail" spacecraft. In theory, current technology and extremely lightweight ships ("star chips") could be used to reach nearby stars within a few decades.
The idea is simple: direct this powerful array of lasers at a reflective target, attach a small satellite to the sail, and accelerate it to its maximum speed. Small means very small. The very idea of a solar sail is very old and has existed since the Kepler telescope. But using a laser sail is actually a revolution.
The advantages of this installation over the others are simply incredible:
- Most of the energy used in this case does not come from a disposable rocket, but from lasers that can be recharged.
- The masses of "star chips" are very small, so they can be accelerated to very high speeds, close to light.
- With the advent of miniature electronics and ultra-strong, lightweight materials, we can build usable devices and ship them light years away.
- The idea itself is not new, but the emergence of new technologies - which are already available and will be available in the next twenty to thirty years - make this perspective realistic.
So what do we have. We are developing a suitable material that can reflect enough laser light to prevent it from burning the sails. We tune the lasers well enough and arrange them into a relatively large array to accelerate these "star chips" to 20% of the speed of light: 60,000 km / s. We then send them to a planet near a potentially habitable star such as Alpha Centauri A or Tau Ceti.
Perhaps we will send an array of starships into one system, in the hope of exploring it in full and getting as much information as possible. After all, the main goal of science is simply to collect data upon arrival and transmit it back. But there are three huge problems in this regard, and together they can amount to a declaration of interstellar war.
The first problem is that interstellar space is filled with particles, most of which move relatively slowly (several hundred kilometers per second) through the galaxy. When they collide with the spacecraft, they punch holes in it, turning it into Swiss cheese in no time.
The second problem is that there is no deceleration mechanism. When these spacecraft arrive at their destination, they continue to move at the speed they took off. There is no stopping to take data, or going into orbit. They just sweep at full speed.
The third problem is that it is almost impossible to achieve the accuracy required to approach (but not collide) with the target planet. The "cone of uncertainty" for any trajectory will include the planet we will be exploring.
What happens when we hit an inhabited planet? What will it look like?
60,000 km / s is thousands of times faster than the speed of any spacecraft that has ever entered our atmosphere. This is 1,000 times faster than the fastest meteors born in our solar system. It would take such a stellar chip only a few thousandths of a second to travel through the entire atmosphere, from space to the surface.
Speed and energy work wonders together. If you double the speed, the energy quadruples; kinetic energy is proportional to the square of the velocity. A huge stone weighing 1,000,000 kg, falling on the planet at a speed of 60 km / s, will cause some damage, but a stone weighing only 1 kg at a speed of 60,000 km / s will release the same amount of energy in the collision process.
Even if the mass is tiny, it will still do some damage. A planet hit by a 1-gram spacecraft at 60,000 km / s will experience the same catastrophic effects as a planet hit by a 1-ton asteroid at 60 km / s. On Earth, this happens once every ten years. Each impact will release about the same amount of energy as the Chelyabinsk meteorite: the most energetically powerful collision of the decade.
If you were an alien in this world that is bombarded by tiny fighters, what conclusion would you come to? You would know that they are too massive and too fast to be found in nature; they are created by an intelligent civilization. You would know that you are being attacked on purpose; space is too big to accidentally hit you. It will be worse if you suspect that this civilization has malicious intentions. No benevolent alien would launch something so reckless and careless if he knew the damage it could cause. If we are wise enough to send a spacecraft across the galaxy to another star, we must be wise enough to foresee the catastrophic consequences of this.
Stephen Hawking once warned:
However, if we calculate the consequences of our interstellar ambitions and technology, we will be the first in history to bombard one inhabited planet from another. And the fact that Stephen Hawking himself was a Breakthrough Starshot proponent presents a big cosmic mystery. Cautious when it comes to contact with aliens, he also had no problem advocating the launch of interstellar weapons.
Ilya Khel