An alien civilization, existing for billions of years, will swiftly colonize every star in the galaxy shortly after developing (that is, swiftly compared to the amount of time that has already progressed). If an alien civilization has formed once, then its artifacts should already be here in our solar system.
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But is that all that they will do? Litter space with probes and garbage? But let’s try to consider what an alien species would really do during billions of years of time. Let us assume one thing: that an alien species, having evolved and survived the evolutionary process, will take steps to maintain and maximize their own survival.
In order to facilitate this, let’s imagine that it is us who are trying to maximize our survival. What can we do? How to we make it possible for our civilization to survive for the longest possible amount of time. Living forever is obviously impossible, but with a mindset for conservation, our civilization could probably survive far beyond the death of the sun, far beyond the end of the flickering out all the stars, even up to the point where matter itself will decay into subatomic particles.
How? The two deciding factors are how many resources we have, and how fast we use up those resources. Far in the future, the only real resource that will matter is energy. From a physical standpoint, you can keep recycling the same matter over and over, so long as you continually input energy to combat entropy. For example, you can burn gasoline to run an engine, then take all the exhaust and reverse the chemical reaction and literally turn smog back into gasoline. All that’s needed for the last part is an energy source and the know-how to do it.
Now, far in the future, we’ll likely be uploads living in virtual space. We likely won’t be using gasoline, and our impact on physical reality will be significantly reduced. All we’ll really need are computer systems and a power source, and computer hardware is extremely durable. Likely computers in the future, just like computers today, will have very few, if any, moving parts. Once the virtual space servers and systems are all set up, they will likely require very little maintenance for centuries.
All that leaves is energy. Our civilization’s survival becomes dependent on how much energy we have, and how fast we use it. To put some numbers to it, let’s assume that human civilization consists of ten billion uploaded people, who each consume, on average, on thousand watts. Power usage is clearly ten trillion watts, or ten terawatts, around 70% of humanity’s current power usage.
Next, we want to expand our energy reserve as much as possible. The most energetic object relatively close to us is the Sun. The Sun’s power output is some four hundred trillion trillion watts, or forty trillion times greater than our future needs. We could use only a small portion of that power, and just let the rest radiate away into space much as what happens today, or we could capture the entire solar output by enclosing the Sun with a Dyson swarm, and save it for later. Antimatter would do nicely for this. The Sun will only last the next five billion years or so. By using only a tiny fraction of its output and saving the rest, we could survive on its power output for forty trillion times longer than the rest of its lifetime, or 2 x 1023 years. This is from a single star.
Of course, the Sun is actually a pretty poor producer of energy per unit mass. It might be useful to actually mine hydrogen and helium from the surface of the Sun and burn it in our own fusion reactors. We can continue fusing the resulting nucleons into more massive elements (until you hit iron, which takes energy to fuse), and accounting for inefficiencies in the process, let’s estimate that we can tap fully 1% of the total mass-energy of the Sun. The total mass of the Sun in 1.989 x 1030 kg, so we will have on hand 1.989 x 1028 kg of energy, or 1.788 x 1045 J. At ten terawatts, our civilization could survive 1.788 x 1032 seconds, or about 5.676 x 1024 years.
This is an enormously long time. It is currently estimated that star formation won’t last much more than one hundred trillion (1015) years. But even after five trillion trillion years, the universe will still be quite habitable. Matter and energy will still exist, and if we take further steps, we can increase our civilization’s lifetime many orders of magnitude further.
So far, we have only exploited the resources of a single star. What if we expand the area from which we are gathering energy to include the entire galaxy? It is currently estimated that the Milky Way masses roughly 580 billion solar masses. By using all of that material, we would extend our survival by a factor of 580 billion, or 3.29 x 1036 years. We would do this by constructing Dyson swarms around every star in the galaxy, and gathering all extra interstellar material not already in stars. It’s quite a task but almost trivial considering we have hundreds of billions of years to figure out how to do it. And actually, it probably wouldn’t be all that hard. By sending out von Neumann probes, we would very quickly colonize the galaxy and begin autonomously constructing these Dyson swarms. All the stars in the galaxy would become covered by these swarms more or less simultaneously, and almost within the blink of an eye: a few million years, tops.
We could then go about colonizing and consuming other galaxies as well, but by now you should see the point. The logical consequence of wanting to survive for the longest possible time leads to having a large portion of the visible universe converted to, essentially, power generators and battery packs. And the sooner this process is started, the more energy we will have to live on. The Sun, and the galaxy, is blazing away far far more power than we actually need, and it’s being wasted by going out into empty space. Every year that we spend not mining the galaxy for energy costs us literally billions of trillions of years of time in the far future.
Of course, when we combine this plan with the possibility of alien intelligent the obvious question arises: why hasn’t this already happened? Why don’t we look up in the sky and see that the Earth is orbiting inside a giant opaque sphere? If aliens exist, and if they care about their own survival, why haven’t they figured this out? Everything that I have described requires a number of breakthroughs (interstellar travel, intelligent autonomous robotic probes, interplanetary-scale mega-construction, the social and political will to commit to projects lasting many millions of millennia, etc.), but none of them violate the laws of physics. It’s merely pushing survival instinct and technical know-how to their logical extreme. Any alien civilization that has evolved in the past several billion years will have both. So where are they?
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