“Now we’re a good long jump ahead,” Albert said happily. “About half a million years have gone by. The temperature has gone way down. It’s only about four thousand Kelvin now-there are plenty of stars hotter than that, but of course we’re not talking about isolated points of heat here, we’re talking about the average temperature of the whole thing. Notice that it’s not quite as bright anymore? Up until now, Robin, the universe was ‘radiation-dominated.’ The dominant thing was photons. Now matter dominates radiation.”
“Because there aren’t so many photons anymore, right?”
“Wrong, I’m afraid,” Albert said apologetically. “There are still plenty of photons, but the overall temperature is lower which means the average energy per photon is lower. Therefore its mass is lower. From now on, matter outweighs radiation in the universe and-here we go-“The glob inflated and darkened. “Now we’re a couple hundred thousand years later and the temperature has dropped another thousand degrees. This is according to Weinberg’s Law: ‘The time it takes for the universe to cool from one temperature to another is proportional to the difference in the inverse squares of the temperatures.’ I don’t suppose you really need to understand that, Robin,” he added wistfully, “although there’s a really neat demonstration in ten-dimensional super-symmetry—”
“Cut it out, Albert! Why’s the damn thing so dark?”
“Ah,” he said, gratified, “that’s an interesting point. There are so many nuclear and electron-like particles now that they get in the way of the light. So the universe is opaque. But that will change. Up to now we’ve had electrons and we’ve had protons, but the universe was so hot that they just stayed that way. As free particles. They couldn’t combine. Or, rather, they kept combining all the time to make atoms, but the heat just blew them apart again. Now we roll the cameras”—and the glob enlarged itself again, and suddenly brightened-“and all of a sudden, look, Robin! The mixture has cleared! Light shines through! The electrons and protons have combined to make atoms, and the photons can move freely again!”
He paused. His shadowy face was beaming in pure pleasure.
I thought hard for a moment, staring at the glob. It was beginning to show-oh, no real structure, but at least hints that maybe something was happening somewhere inside there, like the planet Uranus seen from afar. “Albert?” I said. “That’s all fine, but, look, there are still plenty of photons, right? So why don’t they collide and make more particles to make it all opaque again?”
“Oh, Robin,” he said affectionately, “Sometimes I think you’re not really stupid, after all. I’ll give you the answer. Remember my famous e equals rn-c-squared? The photons have energy, e. If two of them collide and their combined energy equals the mass of any particle, m, times the square of the speed of light, then they can create that particle in their collision. When the universe was young-the threshold temperature is somewhere around ten-to-the-ninth Kelvin-they had plenty of energy and they could create hellish big particles. But it has cooled down. Now they can’t. They just don’t have it anymore, Robin.”
“Oh, wow,” I said. “You know? I almost have the illusion that I nearly understand!”
“Don’t put yourself down,” he chided-meaning, I supposed, that I should leave that sort of thing to him. He was silent for a moment, then he fretted, “I haven’t told you about the creation of quarks and hadrons. I haven’t even said anything about acceleration, and that’s important. You see, for the model to work, you have to account for the fact that at some point in the Big Bang the outward expansion got faster. I can give you an analogy. It’s as though you had an explosion that kept on exploding for a time, so instead of slowing down it expanded faster. The actual explanation is more complicated, and—”
“Albert! Do I have to know this?”
“Not really, Robin,” he said after a moment. His tone was wistful but not insistent.
“So why don’t you just roll the camera some more?”
“Oh, very well.”
I suppose every kid loves electric trains. Watching Albert’s model of the universe grow was almost like having the most hellishly huge set of trains to play with that any boy could imagine.
I couldn’t make them run, of course. But just watching was a lot of fun. The glob roiled and swirled and began to break up. Our “camera” zoomed in tight on one particular smudge in the swarm, and I saw that, too, breaking up into smaller blobs. Clusters and metagalaxies formed, and actual galaxies began to pinwheel into their familiar spiral forms. Individual points of light blew up and died; new ones formed in the center of clouds of gas.
“We have actual stars now, Robin,” Albert announced from beside me. “This is the first generation. Clouds of hydrogen and helium fall together and contract and start nuclear fusion in their interiors. That’s where they cook all the heavier elements, the ones your meat body was made of-carbon, nitrogen, oxygen, iron, all the elements higher than helium. Then, when they blow up as supernovae—” he pointed to one particular star, that obligingly exploded in a tiny torrent of light “—all those elements float around in space until they happen to contract into another star and its planets. And then they form other things. Like you, Robin.”
I yelped, “You mean all the atoms that make me up used to be in the core of a star?”
“That made up your meat body,” he corrected. “Yes, Robin. In fact, our own Galaxy is in there now. See if you can pick it out.”
He froze the expanding cloud so I could peer around. “They all look alike,” I complained.
“Most of them do, pretty much,” he conceded. “But there’s M-3 1, and there are the Magellanic Clouds. And that spiral there, that’s us.”
He was pointing to a glowing whirlpool of firefly light, surrounded by other firefly patches in a vast thinly sprinkled darkness. “I don’t see you and me anywhere in there,” I said, trying for a joke.
He took it seriously. He coughed. “I’m afraid I let it run a little past present time,” he apologized. “All of human history, including the formation of the solar system and the expansion of the sun into a red giant, has already taken place. You missed it.”
I turned to look at his shadowy face. “I don’t know if I want to hear this,” I said, and very nearly meant it.
He looked gently chiding. “But it’s only reality, Robin,” he said. “It’s a truth, whether you want to know it or not. I suppose that, in a sense, it might shake your notions of your own personal importance in the universe—”
“Damn right it does!”
“Well,” he said, “that’s not a bad thing. But don’t get too crushed. Remember, it is this-all of this-that the Foe are trying to change.”
“Oh, fine! Is that supposed to make me feel better?”
He studied me for a moment. “Not better, exactly, no. But more in touch with reality. After all, remember that you, and I, and all the rest of the human race and the Heechee and the machine intelligences have only two choices. We can let the Foe do what they’re doing. Or we can try to oppose them.”
“And how, exactly, are we supposed to do that?”
He looked thoughtfully at the frozen model. “Shall I run it a little further?” he asked.
“You’re changing the subject!”
“I know I am, Robin. I’m going to run the model. Perhaps if you understand what all this entails you may, in some way, contribute to the solution of this problem. Perhaps not. Perhaps it can’t be solved; but in any case I don’t see that we, or someone else sooner or later, have any choice but to try; and you can’t effectively even try without knowledge.”