“Quite,” said Holmes. “Well, consider a different type of locked-room mystery, this one devised by an Austrian physicist named Erwin Schrödinger. Imagine a cat sealed in a box. The box is of such opaque material, and its walls are so well insulated, and the seal is so profound, that there is no way anyone can observe the cat once the box is closed.”
“Hardly seems cricket,” I said, “locking a poor cat in a box.”
“Watson, your delicate sensibilities are laudable, but please, man, attend to my point. Imagine further that inside this box is a triggering device that has exactly a fifty-fifty chance of being set off, and that this aforementioned trigger is rigged up to a cylinder of poison gas. If the trigger is tripped, the gas is released, and the cat dies.”
“Goodness!” said I. “How nefarious.”
“Now, Watson, tell me this: without opening the box, can you say whether the cat is alive or dead?”
“Well, if I understand you correctly, it depends on whether the trigger was tripped.”
“Precisely!”
“And so the cat is perhaps alive, and, yet again, perhaps it is dead.”
“Ah, my friend, I knew you would not fail me: the blindingly obvious interpretation. But it is wrong, dear Watson, totally wrong.”
“How do you mean?”
“I mean the cat is neither alive nor is it dead. It is a potential cat, an unresolved cat, a cat whose existence is nothing but a question of possibilities. It is neither alive nor dead, Watson—neither! Until some intelligent person opens the box and looks, the cat is unresolved. Only the act of looking forces a resolution of the possibilities. Once you crack the seal and peer within, the potential cat collapses into an actual cat. Its reality is a result of having been observed.”
“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 ça change, plus c’est la même 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 constitution 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 21st-century savant. Moments later, he was rewarded: the door to our rooms opened and in came the red-haired fellow.
“Hello, 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 recreated 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 micromanipulated 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 God, 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 recreation of the Switzerland of May 1891, to which we had originally fled to escape Professor Moriarty’s assassins. 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 assistance to me if you do exactly as you did before. There is no need, though, tor you to undertake the entire arduous hike to the Englischer Hof and back. Instead, simply head back to the point at which you pass 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.”