Directions : The passage below is accompanied by four questions. Based on the passage, choose the best answer for each question.
Sometime late this century, someone will push a button, unleashing a life force on the cosmos. Within 1,000 years, every star you can see at night will host intelligent life. In less than a million years, that life will saturate the entire Milky Way; in 20 million years - the local group of galaxies. In the fullness of cosmic time, thousands of superclusters of galaxies will be saturated in a forever-expanding sphere of influence, centred on Earth. This won't require exotic physics. The basic ingredients have been understood since the 1960s. What's needed is an automated spacecraft that can locate worlds on which to land, build infrastructure, and eventually make copies of itself. The copies are then sent forth to do likewise - in other words, they are von Neumann probes (VNPs). We'll stipulate a very fast one, travelling at a respectable fraction of the speed of light, with an extremely long range (able to coast between galaxies) and carrying an enormous trove of information. Ambitious, yes, but there's nothing deal-breaking there. Granted, I'm glossing over major problems and breakthroughs that will have to occur. But the engineering problems should be solvable. Super-sophisticated flying machines that locate resources to reproduce are not an abstract notion. I know the basic concept is practical because fragments of such machines - each one a miracle of nanotechnology - have to be scraped from the windshield of my car, periodically. Meanwhile, the tech to boost tiny spacecraft to a good fraction of the speed of light is in active development right now, with Breakthrough Starshot and NASA's Project Starlight. The hazards of high-speed intergalactic flight (gas, dust, and cosmic rays) are actually far less intense than the hazards of interstellar flight (also gas, dust and cosmic rays), but an intergalactic spacecraft is exposed to them for a lot more time - millions of years in a dormant 'coasting' stage of flight. It may be that more shielding will be required, and perhaps some periodic data scrubbing of the information payload. But there is nothing too exotic about that.
The biggest breakthroughs will come with the development of self-replicating machines, and artificial life. But those are not exactly new ideas either, and we're surrounded by an endless supply of proof of concept. These VNPs need not be massive, expensive things, or perfectly reliable machines. Small, cheap, and fallible is OK. Perhaps a small fraction of them will be lucky enough to survive an intergalactic journey and happen upon the right kind of world to land and reproduce. That's enough to enable exponential reproduction, which will, in time, take control of worlds, as numerous as the sand. Once the process really gets going, the geometry becomes simple - the net effect is an expanding sphere that overtakes and saturates millions of galaxies, over the course of cosmic time.
Since geometry is simplest at the largest scale (owing to a Universe that is basically the same in every direction), the easiest part of the story is the extremely long-term behaviour. If you launch today, the rate at which galaxies are consumed by life steadily increases (as the sphere of influence continues to grow) until about 19 billion years from now, when the Universe is a little over twice its current age. After that, galaxies are overtaken more and more slowly. And at some point, in the very distant future, the process ends. No matter how fast or how long it continues to expand, our sphere will never overtake another galaxy. If the probes can move truly fast - close to the speed of light - that last galaxy is about 16 billion light-years away, as of today (it will be much further away, by the time we reach it). Our telescopes can see galaxies further still, but they are not for us.