Макс Тегмарк - Life 3.0 - Being Human in the Age of Artificial Intelligence

To figure out how efficient an actual sphalerizer would be, one needs to work out key practical details: for example, how large does it need to be to prevent a significant fraction of the photons and neutrinos from leaking out during the compression stage? What we can say for sure, however, is that the energy prospects for the future of life are dramatically better than our current technology allows. We haven’t even managed to build a fusion reactor, yet future technology should be able to do ten and perhaps even a hundred times better.

Building Better Computers

If eating dinner is 10 billion times worse than the physical limit on energy efficiency, then how efficient are today’s computers? Even worse than that dinner, as we’ll now see.

I often introduce my friend and colleague Seth Lloyd as the only person at MIT who’s arguably as crazy as I am. After doing pioneering work on quantum computers, he went on to write a book arguing that our entire Universe is a quantum computer. We often grab beer after work, and I’ve yet to discover a topic that he doesn’t have something interesting to say about. For example, as I mentioned in chapter 2, he has lots to say about the ultimate limits of computing. In a famous 2000 paper, he showed that computing speed is limited by energy: performing an elementary logical operation in time T requires an average energy of E = h ∕ 4 T, where h is the fundamental physics quantity known as Planck’s constant. This means that a 1 kg computer can perform at most 5 × 10 50operations per second—that’s a whopping 36 orders of magnitude more than the computer on which I’m typing these words. We’ll get there in a couple of centuries if computational power keeps doubling every couple of years, as we explored in chapter 2. He also showed that a 1 kg computer can store at most 10 31bits, which is about a billion billion times better than my laptop.

Seth is the first to admit that actually attaining these limits may be challenging even for superintelligent life, since the memory of that 1 kg ultimate “computer” would resemble a thermonuclear explosion or a little piece of our Big Bang. However, he’s optimistic that the practical limits aren’t that far from the ultimate ones. Indeed, existing quantum computer prototypes have already miniaturized their memory by storing one bit per atom, and scaling that up would allow storing about 10 25bits/kg—a trillion times better than my laptop. Moreover, using electromagnetic radiation to communicate between these atoms would permit about 5 × 10 40operations per second—31 orders of magnitude better than my CPU.

In summary, the potential for future life to compute and figure things out is truly mind-boggling: in terms of orders of magnitude, today’s best supercomputers are much further from the ultimate 1 kg computer than they are from the blinking turn signal on a car, a device that stores merely one bit of information, flipping it between on and off about once per second.

Other Resources

From a physics perspective, everything that future life may want to create—from habitats and machines to new life forms—is simply elementary particles arranged in some particular way. Just as a blue whale is rearranged krill and krill is rearranged plankton, our entire Solar System is simply hydrogen rearranged during 13.8 billion years of cosmic evolution: gravity rearranged hydrogen into stars which rearranged the hydrogen into heavier atoms, after which gravity rearranged such atoms into our planet where chemical and biological processes rearranged them into life.

Future life that has reached its technological limit can perform such particle rearrangements more rapidly and efficiently, by first using its computing power to figure out the most efficient method and then using its available energy to power the matter rearrangement process. We saw how matter can be converted into both computers and energy, so it’s in a sense the only fundamental resource needed. *7Once future life has bumped up against the physical limits on what it can do with its matter, there is only one way left for it to do more: by getting more matter. And the only way it can do this is by expanding into our Universe. Spaceward ho!

Gaining Resources Through Cosmic Settlement

Just how great is our cosmic endowment? Specifically, what upper limits do the laws of physics place on the amount of matter that life can ultimately make use of? Our cosmic endowment is mind-bogglingly large, of course, but how large, exactly? Table 6.2 lists some key numbers. Our planet is currently 99.999999% dead in the sense that this fraction of its matter isn’t part of our biosphere and is doing almost nothing useful for life other than providing gravitational pull and a magnetic field. This raises the potential of one day using a hundred million times more matter in active support of life. If we can put all of the matter in our Solar System (including the Sun) to optimal use, we’ll do another million times better. Settling our Galaxy would grow our resources another trillion times.

How Far Can You Go?

You might think that we can acquire unlimited resources by settling as many other galaxies as we want if we’re patient enough, but that’s not what modern cosmology suggests! Yes, space itself might be infinite, containing infinitely many galaxies, stars and planets—indeed, this is what’s predicted by the simplest versions of inflation, the currently most popular scientific paradigm for what created our Big Bang 13.8 billion years ago. However, even if there are infinitely many galaxies, it appears that we can see and reach only a finite number of them: we can see about 200 billion galaxies and settle in at most ten billion. Region ParticlesOur biosphere 10 43Our Planet 10 51Our Solar System 10 57Our Galaxy 10 69Our range traveling at half speed of light 10 75Our range traveling at speed of light 10 76Our Universe 10 78

Table 6.2: Approximate number of matter particles (protons and neutrons) that future life can aspire to make use of.

What limits us is the speed of light: one light-year (about ten trillion kilometers) per year. Figure 6.6 shows the part of space from which light has reached us so far during the 13.8 billion years since our Big Bang, a spherical region known as “our observable Universe” or simply “our Universe.” Even if space is infinite, our Universe is finite, containing “only” about 10 78atoms. Moreover, about 98% of our Universe is “see but not touch,” in the sense that we can see it but never reach it even if we travel at the speed of light forever. Why is this? After all, the limit to how far we can see comes simply from the fact that our Universe isn’t infinitely old, so that distant light hasn’t yet had time to reach us. So shouldn’t we be able to travel to arbitrarily distant galaxies if we have no limit on how much time we can spend en route?

Figure 6.6: Our Universe, i.e., the spherical region of space from which light has had time to reach us (at the center) during the 13.8 billion years since our Big Bang. The patterns show the baby pictures of our Universe taken by the Planck satellite, showing that when it was merely 400,000 years old, it consisted of hot plasma nearly as hot as the surface of the Sun. Space probably continues beyond this region, and new matter comes into view every year.

The first challenge is that our Universe is expanding, which means that almost all galaxies are flying away from us, so settling distant galaxies amounts to a game of catch-up. The second challenge is that this cosmic expansion is accelerating, due to the mysterious dark energy that makes up about 70% of our Universe. To understand how this causes trouble, imagine that you enter a train platform and see your train slowly accelerating away from you, but with a door left invitingly open. If you’re fast and foolhardy, can you catch the train? Since it will eventually go faster than you can run, the answer clearly depends on how far away from you the train is initially: if it’s beyond a certain critical distance, you’ll never catch up with it. We face the same situation trying to catch those distant galaxies that are accelerating away from us: even if we could travel at the speed of light, all galaxies beyond about 17 billion light-years remain forever out of reach—and that’s over 98% of the galaxies in our Universe.