"That is worse gibberish than anything this namesake of your brother has spouted."

"No, it is not," said Holmes. "It is the way the world works. They have learned so much since our time, Watson-so very much! But as Alphonse Karr has observed, Plus ca change, plus c'est la meme chose Plus ca change, plus c'est la meme chose. Even in this esoteric field of advanced physics, it is the power of the qualified observer that is most important of all!"

I awoke again hearing Holmes crying out, "Mycroft! Mycroft!"

I had occasionally heard such shouts from him in the past, either when his iron const.i.tution had failed him and he was feverish, or when under the influence of his accursed needle. But after a moment I realized he was not calling for his real brother but rather was shouting into the air to summon the Mycroft Holmes who was the twenty-first-century savant. Moments later, he was rewarded: the door to our rooms opened and in came the red-haired fellow.

"h.e.l.lo, Sherlock," said Mycroft. "You wanted me?"

"Indeed I do," said Holmes. "I have absorbed much now on not just physics but also the technology by which you have re-created these rooms for me and the good Dr. Watson."

Mycroft nodded. "I've been keeping track of what you've been accessing. Surprising choices, I must say."

"So they might seem," said Holmes, "but my method is based on the pursuit of trifles. Tell me if I understand correctly that you reconstructed these rooms by scanning Watson's memories, then using, if I understand the terms, holography and micro-manipulated force fields to simulate the appearance and form of what he had seen."

"That's right."

"So your ability to reconstruct is not just limited to rebuilding these rooms of ours, but, rather, you could simulate anything either of us had ever seen."

"That's correct. In fact, I could even put you into a simulation of someone else's memories. Indeed, I thought perhaps you might like to see the Very Large Array of radio telescopes, where most of our listening for alien messages-"

"Yes, yes, I'm sure that's fascinating," said Holmes, dismissively. "But can you reconstruct the venue of what Watson so appropriately dubbed 'The Final Problem'?"

"You mean the Falls of Reichenbach?" Mycroft looked shocked. "My G.o.d, yes, but I should think that's the last thing you'd want to relive."

"Aptly said!" declared Holmes. "Can you do it?"

"Of course."

"Then do so!"

And so Holmes and my brains were scanned and in short order we found ourselves inside a superlative re-creation of the Switzerland of May 1891, to which we had originally fled to escape Professor Moriarty's a.s.sa.s.sins. Our re-enactment of events began at the charming Englischer Hof in the village of Meiringen. Just as the original innkeeper had done all those years ago, the reconstruction of him exacted a promise from us that we would not miss the spectacle of the Falls of Reichenbach. Holmes and I set out for the Falls, him walking with the aid of an alpenstock. Mycroft, I was given to understand, was somehow observing all this from afar.

"I do not like this," I said to my companion. "'Twas bad enough to live through this horrible day once, but I had hoped I would never have to relive it again except in nightmares."

"Watson, recall that I have fonder memories of all this. Vanquishing Moriarty was the high point of my career. I said to you then, and say again now, that putting an end to the very Napoleon of crime would easily be worth the price of my own life."

There was a little dirt path cut out of the vegetation running halfway round the falls so as to afford a complete view of the spectacle. The icy green water, fed by the melting snows, flowed with phenomenal rapidity and violence, then plunged into a great, bottomless chasm of rock black as the darkest night. Spray shot up in vast gouts, and the shriek made by the plunging water was almost like a human cry.

We stood for a moment looking down at the waterfall, Holmes's face in its most contemplative repose. He then pointed further ahead along the dirt path. "Note, dear Watson," he said, shouting to be heard above the torrent, "that the dirt path comes to an end against a rock wall there." I nodded. He turned in the other direction. "And see that backtracking out the way we came is the only way to leave alive: there is but one exit, and it is coincident with the single entrance."

Again I nodded. But, just as had happened the first time we had been at this fateful spot, a Swiss boy came running along the path, carrying in his hand a letter addressed to me which bore the mark of the Englischer Hof. I knew what the note said, of course: that an Englishwoman, staying at that inn, had been overtaken by a hemorrhage. She had but a few hours to live, but doubtless would take great comfort in being ministered to by an English doctor, and would I come at once?

"But the note is a pretext," said I, turning to Holmes. "Granted, I was fooled originally by it, but, as you later admitted in that letter you left for me, you had suspected all along that it was a sham on the part of Moriarty." Throughout this commentary, the Swiss boy stood frozen, immobile, as if somehow Mycroft, overseeing all this, had locked the boy in time so that Holmes and I might consult. "I will not leave you again, Holmes, to plunge to your death."

Holmes raised a hand. "Watson, as always, your sentiments are laudable, but recall that this is a mere simulation. You will be of material a.s.sistance to me if you do exactly as you did before. There is no need, though, for you to undertake the entire arduous hike to the Englischer Hof and back. Instead, simply head back to the point at which you pa.s.s the figure in black, wait an additional quarter of an hour, then return to here."

"Thank you for simplifying it," said I. "I am eight years older than I was then; a three-hour round trip would take a goodly bit out of me today."

"Indeed," said Holmes. "All of us may have outlived our most useful days. Now, please, do as I ask."

"I will, of course," said I, "but I freely confess that I do not understand what this is all about. You were engaged by this twenty-first-century Mycroft to explore a problem in natural philosophy-the missing aliens. Why are we even here?"

"We are here," said Holmes, "because I have solved that problem! Trust me, Watson. Trust me, and play out the scenario again of that portentous day of May 4th, 1891."

And so I left my companion, not knowing what he had in mind. As I made my way back to the Englischer Hof, I pa.s.sed a man going hurriedly the other way. The first time I had lived through these terrible events I did not know him, but this time I recognized him for Professor Moriarty: tall, clad all in black, his forehead bulging out, his lean form outlined sharply against the green backdrop of the vegetation. I let the simulation pa.s.s, waited fifteen minutes as Holmes had asked, then returned to the falls.

Upon my arrival, I saw Holmes's alpenstock leaning against a rock. The black soil of the path to the torrent was constantly re-moistened by the spray from the roiling falls. In the soil I could see two sets of footprints leading down the path to the cascade, and none returning. It was precisely the same terrible sight that greeted me all those years ago.

"Welcome back, Watson!"

I wheeled around. Holmes stood leaning against a tree, grinning widely.

"Holmes!" I exclaimed. "How did you manage to get away from the falls without leaving footprints?"

"Recall, my dear Watson, that except for the flesh-and-blood you and me, all this is but a simulation. I simply asked Mycroft to prevent my feet from leaving tracks." He demonstrated this by walking back and forth. No impression was left by his shoes, and no vegetation was trampled down by his pa.s.sage. "And, of course, I asked him to freeze Moriarty, as earlier he had frozen the Swiss lad, before he and I could become locked in mortal combat."

"Fascinating," said I.

"Indeed. Now, consider the spectacle before you. What do you see?"

"Just what I saw that horrid day on which I had thought you had died: two sets of tracks leading to the falls, and none returning."

Holmes's crow of "Precisely!" rivaled the roar of the falls. "One set of tracks you knew to be my own, and the others you took to be that of the black-clad Englishman-the very Napoleon of crime!"

"Yes."

"Having seen these two sets approaching the falls, and none returning, you then rushed to the very brink of the falls and found-what?"

"Signs of a struggle at the lip of the precipice leading to the great torrent itself."

"And what did you conclude from this?"

"That you and Moriarty had plunged to your deaths, locked in mortal combat."

"Exactly so, Watson! The very same conclusion I myself would have drawn based on those observations!"

"Thankfully, though, I turned out to be incorrect."

"Did you, now?"

"Why, yes. Your presence here attests to that."

"Perhaps," said Holmes. "But I think otherwise. Consider, Watson! You were on the scene, you saw what happened, and for three years-three years, man!-you believed me to be dead. We had been friends and colleagues for a decade at that point. Would the Holmes you knew have let you mourn him for so long without getting word to you? Surely you must know that I trust you at least as much as I do my brother Mycroft, whom I later told you was the only one I had made privy to the secret that I still lived."

"Well," I said, "since you bring it up, I was was slightly hurt by that. But you explained your reasons to me when you returned." slightly hurt by that. But you explained your reasons to me when you returned."

"It is a comfort to me, Watson, that your ill-feelings were a.s.suaged. But I wonder, perchance, if it was more you than I who a.s.suaged them."

"Eh?"

"You had seen clear evidence of my death, and had faithfully if floridly recorded the same in the chronicle you so appropriately dubbed 'The Final Problem.'"

"Yes, indeed. Those were the hardest words I had ever written."

"And what was the reaction of your readers once this account was published in the Strand Strand?"

I shook my head, recalling. "It was completely unexpected," said I. "I had antic.i.p.ated a few polite notes from strangers mourning your pa.s.sing, since the stories of your exploits had been so warmly received in the past. But what I got instead was mostly anger and outrage-people demanding to hear further adventures of yours."

"Which of course you believed to be impossible, seeing as how I was dead."

"Exactly. The whole thing left a rather bad taste, I must say. Seemed very peculiar behavior."

"But doubtless it died down quickly," said Holmes.

"You know full well it did not. I have told you before that the onslaught of letters, as well as personal exhortations wherever I would travel, continued unabated for years. In fact, I was virtually at the point of going back and writing up one of your lesser cases I had previously ignored as being of no general interest simply to get the demands to cease, when, much to my surprise and delight-"

"Much to your surprise and delight, after an absence of three years less a month, I turned up in your consulting rooms, disguised, if I recall correctly, as a shabby book collector. And soon you had fresh adventures to chronicle, beginning with that case of the infamous Colonel Sebastian Moran and his victim, the Honorable Ronald Adair."

"Yes," said I. "Wondrous it was."

"But Watson, let us consider the facts surrounding my apparent death at the falls of Reichenbach on May 4th, 1891. You, the observer on the scene, saw the evidence, and, as you wrote in 'The Final Problem,' many experts scoured the lip of the falls and came to precisely the same conclusion you had-that Moriarty and I had plunged to our deaths."

"But that conclusion turned out to be wrong."

Holmes beamed intently. "No, my Good Watson, it turned out to be unacceptable unacceptable-unacceptable to your faithful readers. And that is where all the problems stem from. Remember Schrodinger's cat in the sealed box? Moriarty and I at the falls present a very similar scenario: he and I went down the path into the cul-de-sac, our footprints leaving impressions in the soft earth. There were only two possible outcomes at that point: either I would exit alive, or I would not. There was no way out, except to take that same path back away from the falls. Until someone came and looked to see whether I had re-emerged from the path, the outcome was unresolved. I was both alive and dead-a collection of possibilities. But when you arrived, those possibilities had to collapse into a single reality. You saw that there were no footprints returning from the falls-meaning that Moriarty and I had struggled until at last we had both plunged over the edge into the icy torrent. It was your act of seeing the results that forced the possibilities to be resolved. In a very real sense, my good, dear friend, you killed me."

My heart was pounding in my chest. "I tell you, Holmes, nothing would have made me more happy than to have seen you alive!"

"I do not doubt that, Watson-but you had to see one thing or the other. You could not see both. And, having seen what you saw, you reported your findings: first to the Swiss police, and then to the reporter for the Journal de Geneve Journal de Geneve, and lastly in your full account in the pages of the Strand Strand."

I nodded.

"But here is the part that was not considered by Schrodinger when he devised the thought experiment of the cat in the box. Suppose you open the box and find the cat dead, and later you tell your neighbor about the dead cat-and your neighbor refuses to believe you when you say that the cat is dead. What happens if you go and look in the box a second time?"

"Well, the cat is surely still dead."

"Perhaps. But what if thousands-nay, millions!-refuse to believe the account of the original observer? What if they deny the evidence? What then, Watson?"

"I-I do not know."

"Through the sheer stubbornness of their will, they reshape reality, Watson! Truth is replaced with fiction! They will the cat back to life. More than that, they attempt to believe that the cat never died in the first place!"

"And so?"

"And so the world, which should have one concrete reality, is rendered unresolved, uncertain, adrift. As the first observer on the scene at Reichenbach, your interpretation should take precedence. But the stubbornness of the human race is legendary, Watson, and through that sheer cussedness, that refusal to believe what they have been plainly told, the world gets plunged back into being a wave front of unresolved possibilities. We exist in flux-to this day, the whole world exists in flux-because of the conflict between the observation you really made at Reichenbach, and the observation the world wishes wishes you had made." you had made."

"But this is all too fantastic, Holmes!"

"Eliminate the impossible, Watson, and whatever remains, however improbable, must be the truth. Which brings me now to the question we were engaged by this avatar of Mycroft to solve: this paradox of Fermi. Where are the alien beings?"

"And you say you have solved that?"

"Indeed I have. Consider the method by which mankind has been searching for these aliens."

"By wireless, I gather-trying to overhear their chatter on the ether."

"Precisely! And when did I return from the dead, Watson?"

"April of 1894."

"And when did that gifted Italian, Guglielmo Marconi, invent the wireless?"

"I have no idea."

"In eighteen hundred and ninety-five, my good Watson. The following year! In all the time that mankind has used radio, our entire world has been an unresolved quandary! An uncollapsed wave front of possibilities!"

"Meaning?"

"Meaning the aliens are there, Watson-it is not they who are missing, it is us! Our world is out of synch with the rest of the universe. Through our failure to accept the unpleasant truth, we have rendered ourselves potential potential rather than rather than actual actual."

I had always thought my companion a man with a generous regard for his own stature, but surely this was too much. "You are suggesting, Holmes, that the current unresolved state of the world hinges on the fate of you yourself?"

"Indeed! Your readers would not allow me to fall to my death, even if it meant attaining the very thing I desired most, namely the elimination of Moriarty. In this mad world, the observer has lost control of his observations! If there is one thing my life stood for-my life prior to that ridiculous resurrection of me you recounted in your chronicle of 'The Empty House'-it was reason! Logic! A devotion to observable fact! But humanity has abjured that. This whole world is out of whack, Watson-so out of whack that we are cut off from the civilizations that exist elsewhere. You tell me you were barraged with demands for my return, but if people had really understood me, understood what my life represented, they would have known that the only real tribute to me possible would have been to accept the facts! The only real answer would have been to leave me dead!"

Mycroft sent us back in time, but rather than returning us to 1899, whence he had plucked us, at Holmes's request he put us back eight years earlier in May of 1891. Of course, there were younger versions of ourselves already living then, but Mycroft swapped us for them, bringing the young ones to the future, where they could live out the rest of their lives in simulated scenarios taken from Holmes's and my minds. Granted, we were each eight years older than we had been when we had fled Moriarty the first time, but no one in Switzerland knew us and so the aging of our faces went unnoticed.

I found myself for a third time living that fateful day at the Falls of Reichenbach, but this time, like the first and unlike the second, it was real.

I saw the page boy coming, and my heart raced. I turned to Holmes, and said, "I can't possibly leave you."

"Yes, you can, Watson. And you will, for you have never failed to play the game. I am sure you will play it to the end." He paused for a moment, then said, perhaps just a wee bit sadly, "I can discover facts, Watson, but I cannot change them." And then, quite solemnly, he extended his hand. I clasped it firmly in both of mine. And then the boy, who was in Moriarty's employ, was upon us. I allowed myself to be duped, leaving Holmes alone at the Falls, fighting with all my might to keep from looking back as I hiked onward to treat the nonexistent patient at the Englischer Hof. On my way, I pa.s.sed Moriarty going in the other direction. It was all I could do to keep from drawing my pistol and putting an end to the blackguard, but I knew Holmes would consider robbing him of his own chance at Moriarty an unforgivable betrayal.