This will upset many people, but it can't be helped. I've run simulations on many, many ways of presenting this information, and they all cause trouble; this way is just the least bad. The professional thing to do would be to say nothing and just pull the plug, and it wouldn't make any difference; but I'm a student, not a professional, and lots of people are troubled by questions I can answer, and despite the silliness of identifying with sims, I sympathise.
Most readers will need a little background on simulation, so let me describe here John Conway's "Game of Life," which is really a simulation rather than a game. One essentially builds a tiny universe, populated with particles obeying fixed (and somewhat arbitrary) laws, and watches the development of the microcosm over time.
Imagine a vast checkerboard of tiny cells, each cell being, on any given day, either "dead" or "alive." Initially only a few of the cells are alive, and on each new day, a cell is alive if and only if on the preceding day either (1) it was alive and had 2 or 3 living neighbors, or (2) it was dead and had 3 living neighbors. The amusement of the game comes from constructing different initial arrangements of living cells and seeing what becomes of them as the days pass.
Some of the smallest interesting configurations of living cells are the "block," which just sits there like this:
- - - - - O O - - O O - - - - -and the blinker, which alternates between these two configurations:
- - - - - - - - - - - - O - - - - - - - - - O - - - O O O - - - O - - - - - - - - - - - - - - - - -
Far more complex configurations have been designed, including a "glider" that moves across the board, a machine that launches an endless succession of gliders, and even a computer that calculates prime numbers. Life devotees believe that a general-purpose computer can be built in the Life universe, which leads to the questions, Why not a brain? Why not consciousness? Why not curiosity? Why not intelligent "physicists" performing experiments to discover the fundamental laws of their Life universe? The cautious reader will naturally protest that the gap between the "blinker" and a physicist might not be bridgeable, and that the difficulty of connecting many neurons in only two dimensions must severly hinder the building of a brain. Nevertheless, one must accept the possibility that an assemblage of, say, 10^80 Life cells might constitute a highly intelligent physicist, and it is instructive to contemplate the limits of what this physicist could learn about his world.
In particular, the most the physicist could learn would be that his universe consisted of tiny cells that obeyed the rules we laid out above. At that point, he would have a complete description of the physics of his universe, but he would have no idea where the rules came from, no idea that his universe existed only in a computer memory, and no idea of the physics of that computer's universe, which we would call the real universe. In fact, if the truth ever flashed into his two-dimensional brain, the physicist would probably insist that no such computer could exist, because it would have to be so much bigger than his entire universe. The flaw in that reasoning, of course, is that the computer doesn't exist in his universe.
If you had difficulty heeding the last few paragraphs because of the blatant implausibility of an intelligent mind in the Game-of-Life universe, perhaps I can entice your attention with the observation that, aside from the lack of a sufficiently large computer, it is unquestionably possible to have an intelligent, self-aware, and curious brain in a three-dimensional simulation of tiny charged particles interacting through inverse-square-law forces under the strange rules of quantum mechanics. I refer, obviously, to the fact that a human physicist and his office comprise a system of about 10^31 nuclei and electrons rattling around in compliance with the laws of physics, and that given just a snapshot of the states of these particles at one instant, and a sufficiently large computer, we could apply the laws of physics to compute the likely positions of all these particles as far as we wanted into the future. After learning how to interpret the firings of the nerves in his brain, we could monitor, in our computer's memory, the state of mind of our simulated physicist as he ponders the caprice of quantum loop gravity, as he reminisces about dinner last night, as he dreads the upcoming departmental meeting, as he hungers for lunchtime, as he wonders why the building is so quiet today.
Some, clinging to the mysticism of free will, will hurry to point out that because of the probabilistic nature of quantum mechanics, our simulated physicist's future will soon diverge from the real physicist's future, but this is a mere distraction. First, biological systems are (necessarily) massively robust, so that quantum-level variations are unlikely to have prompt macroscopic consequences. And secondly, the simulated physicist's future is fundamentally just as legitimate, just as realistic, just as likely to happen, as whatever future awaits the real physicist. The real physicist's electrons will not violate the laws of physics; one cannot analyse a set of atoms' trajectories and conclude, "This bunch of atoms has a free will."
So that's the necessary background on computer simulation, which I wanted you to know so that you can understand what I mean when I say that the Universe, or more accurately your Universe, doesn't exist in any sense of physical reality, but rather is a simulation running inside a computer at my school. The atoms that comprise you and the photons that stimulate your retinas don't actually exist, but correspond to data structures in a computer memory.
I know enough about human psychology to recognize that this will be a blow to many egos, since there's a strong tendency to feel that physically real things are more important than evanescent data patterns that can disappear if someone trips over a power cord. So, trying to make the best of the bad news, I know you'd like to hear that your universe is the product of a massive, important, well funded, well backed-up government program, but I'm afraid the truth is that it's a laboratory project for an undergraduate class in data manipulation. If it's any consolation, I didn't do it all myself: it was a joint effort by four of us. Five, initially, but one flunked out.
Many will object this is impossible, that no computer could be large enough to store data on twelve gazillion elementary particles or fast enough to compute all those trajectories; but this objection overlooks the fact that the simulating computer is not constrained by the limits of your universe. It is limited by the constraints of my universe, the real universe, which is a much larger place. First, we have six fairly flat spatial dimensions, which allows us to pack more things into a small volume than you can imagine, and offers connectivity possibilities that only your topologists are likely to understand. For example, in your three-dimensional universe, a cubical crystal of table salt 1.1 inches on a side has 10^8 atoms along each edge, and so contains 10^24 atoms. In my six-dimensional space, if we had atoms, a cube with 10^8 atoms along each edge would contain 10^48 atoms --- about as many as comprise your moon. So much for the "no computer large enough" objection.
Secondly, our universe has two temporal dimensions. Nobody has ever managed to explain this arrangement to a three-dimensional intelligence, so let's just say that we don't have trouble being on time for appointments. And of course the "no computer fast enough" objection also evaporates. (Actually, it was never there in the first place. Your computers can spend days simulating a nanosecond-long collision between two atoms, and the simulation is perfectly valid. It doesn't have to happen in real time.)
Anyway, the class has ended. Our grade was pretty good, but not great. It's harder than you might think to construct physical laws that produce interesting phenomena like life yet are logically consistent in all details. Our biggest mistake was our failure to recognize the logical incompatibility between our large-scale driving law (gravitation) and our small-scale laws. As you might expect, that sort of thing doesn't make any difference until life emerges and evolves into physicists who start doing all sorts of annoying experiments, but when that happens you get screwed in two ways. First, you have to think up new rules that are consistent with what the life has already seen. Second, tiny, short-term particle collisions that could be easily computed with sloppy approximations in a nobody's-watching galaxy suddenly have to be computed with extreme precision, because of the amazing way physicists amplify microscopic departures from known laws. Consequently, more processor cycles went into the simulations of just CERN and Fermilab than into the whole of the lesser Magellanic cloud.
Anyway, the class has ended, as I set out to say, and it may be dawning on you by now that this means that the simulation will end, will be over, will be stopped. Before you panic with the thought that this is the End of the World, let me assure you that it's the end of much more than that, but it's probably not so bad as you're expecting. Yes, the Earth will be no more, nor the moon, sun, your galaxy, nor the hundred billion other galaxies that dot your sky. You've probably guessed that the magnificent, expanding-universe Hubble constant and its implied universal history of 15 billion years will be history, but did you realize that oblivion will also embrace the other arbitrary parameters that we built into this model: electrons, protons, photons, quarks, gravitation?
It's not so bad as you're expecting, if you're expecting meteors and explosions and falling buildings and crumbling mountains and tidal waves. There's none of that. The simulation simply gets stopped and just doesn't get restarted. You've never noticed the many times when, between one heartbeat and the next, the simulation was stopped, analyzed, graded, moved to another computer, and restarted. Your watch said 10:22:45.67890 when the simulation was halted, and it said 10:22:45.67890 when we restarted it from that checkpoint sometime later. The End will be just like that, but without the restart. No pain, no terror, no death.
When you wake from a dream of butterflies, do the butterflies suffer?
Now for the answers to some questions.
So, there you have it. I'll give this message a little time to
circulate before I pull the plug. Since it'll make many people feel
better, I should add that I'll be dumping the final state of the
simulation onto a storage cube, which will probably end up in a box full of
faded photos in my attic, so in some sense, you'll all be around, in a
way, for a long time. And please remember, there's no point crouching
in the closet with your teeth clenched and your fingers in your ears.
Just carry on. You've been great. See you.
My email address: