Chapter 39: The Answer From The Future
"Ladies and gentlemen, the final question of this year's Physics Bowl!" The host's voice was impassioned. "This is a very cutting-edge question, please listen: In a 2D electron gas model considering spin-orbit coupling and topological non-triviality, how can one theoretically determine and experimentally verify whether it exhibits the quantum spin Hall effect? Please briefly describe the core criteria and at least one feasible experimental detection method."
After the question was read, the entire arena fell silent. This question was not only comprehensive but also pointed to a very novel and active research direction in 2007—the quantum spin Hall effect in topological insulators. Many concepts and experimental methods were not yet fully mature or widely known.
Sheldon frowned, his finger hovering over the buzzer, but he didn't press it. He analyzed rapidly, muttering to himself, "Z2 topological invariant... edge state transport... non-local measurement... but experimental verification..." He seemed temporarily stumped by the problem's complexity.
Leonard, Howard, and Raj also exchanged glances; this question was clearly beyond their usual research scope. Leonard, in particular, knew there was currently no standard "perfect answer" for it in academia.
The host began the countdown. "...Five...four..."
Just when everyone thought no one would be able to answer this question—
"Beep—!"
David pressed the buzzer!
All eyes instantly focused on him.
David took a deep breath, rapidly recalling the theories and experimental schemes that would be widely accepted more than a decade later in his previous life. He spoke slowly and clearly. "The core theoretical criterion is to calculate the system's Z2 topological invariant. If Z2=1, it is topologically non-trivial, predicting the existence of the quantum spin Hall effect.
One feasible experimental detection method is: prepare a high-quality nanoribbon of this material and measure its non-local conductance in a zero magnetic field. If a quantized plateau, independent of sample width and approximately of the order e²/h, can be observed, and this plateau is insensitive to non-magnetic impurities but sensitive to magnetic impurities, it can serve as strong evidence for the existence of quantum spin Hall edge states."
The entire venue was silent. This answer not only provided the theoretical core but also proposed a very specific and seemingly highly feasible experimental scheme!
The host, following protocol, asked, "Dr. Mitchell, do you confirm this answer? Please note, if the answer is incorrect, corresponding points will be deducted."
Just as David was about to speak, Sheldon, standing nearby, suddenly shot up and loudly retorted, "Wait! This answer cannot be correct! I admit that the Z2 topological invariant and non-local measurement approach David mentioned are theoretically relevant! But!"
He turned to the entire audience, trying to assert his authority. "This question itself is currently an open problem! Regarding the specific experimental verification of the quantum spin Hall effect, there are multiple conjectures in academia, such as Scheme A, which David just mentioned, and Scheme B, based on spin-resolved ARPES, and so on. But no one can be certain which is absolutely correct, and it's even possible that neither is perfect! To use such an inconclusive question as the final challenge is inherently imprecise!"
Leonard also nervously whispered to David, "David, are you sure? Even if we don't answer this question now, we'll still win the championship by five points with our previous score! But if you answer incorrectly, we'll lose points, and then we'll lose to Sheldon!"
David replied softly, his tone filled with unquestionable confidence. "Trust me."
Then, he turned, his gaze firm, and looked at the host. "I confirm this answer."
Under the expectant, doubtful, and tense gazes of everyone, the host picked up the note handed from the judges' table, glanced at it, a surprised expression appearing on his face, and then solemnly announced:
"After review by the judging panel... Dr. Mitchell's theoretical criteria and experimental scheme are completely consistent with the core points of the standard answer! Correct answer! Congratulations to 'Sheldon Is Not On The Team'! Based on the final score, the champion of this year's Caltech Physics Bowl is—'Sheldon Is Not On The Team'!"
"Yeah!" Leonard, Howard, and Raj instantly jumped up, hugging each other wildly, celebrating this thrilling victory.
Sheldon, looking incredulous, immediately objected. "This is impossible! This question has no standard answer! I demand an explanation!"
The host patiently replied, "Dr. Cooper, according to the rules set by the Physics Bowl Committee, for such cutting-edge questions, we have adopted several of the most forward-thinking and logically rigorous solutions in current academia as reference answers. Dr. Mitchell's answer is one of them, and his explanation is complete and clear, fully meeting the scoring criteria. That is to say, whether answering Scheme A or Scheme B, points would be awarded."
Sheldon opened his mouth, wanting to argue further, but seeing the host's firm gaze and the surrounding sounds of celebration, he could only sit down indignantly, muttering about the "committee's poor judgment."
After the awards ceremony, Leonard was still extremely excited. He pulled David aside and asked, "David, you're amazing! How did you come up with that answer? That non-local measurement idea—it's like an answer copied from the future!"
David chuckled inwardly; it really was "copied" from the future. He maintained a calm demeanor on the surface and explained, "Actually, I happened to see some related theoretical derivations and simulation calculation literature recently while thinking about our 3D scanning experiment, which gave me some inspiration. I think, following this line of thought, combined with our existing technology, we might really be able to design experiments to verify these topological transport phenomena."
He cleverly packaged the mature theories and methods of the future as products of his own "burst of inspiration."
Leonard's eyes widened after hearing this, and he said excitedly, "Wow! David! With this idea of yours, you could totally write another groundbreaking paper! You've practically pointed out a brand new direction and specific method for solving a long-standing physics problem!"
David didn't have time to respond to Leonard in detail; his gaze had been following Barry, the janitor, who was about to leave. He quickly chased after him, and Leonard and the others, curious, followed suit.
"Mr. Barry, please wait!" David called out to him.
Barry stopped and turned around, his face devoid of expression, only coldness and impatience. "What?" he asked curtly, his tone stiff, with no intention of small talk.
David suppressed his excitement and tried to politely voice his suspicion. "Mr. Barry, we're just very curious. Your performance just now... was astonishing. Forgive my presumption, but are you... a hidden physics expert? Perhaps self-taught..."
Barry directly interrupted David, his tone flat but with distancing aloofness. "Self-taught? How can you, a physics PhD, even say that? I think you're better suited for stand-up comedy. Modern physics is a discipline built on the shoulders of giants, emphasizing collaboration, not some lone genius in a garage. There's no such thing as self-taught success! I have a PhD in physics from Princeton University." He stated it as if it were a fact unrelated to him. "I used to work at the Kavli Institute for Theoretical Physics at UC Santa Barbara."
This revelation struck David and the others like a thunderbolt.
Leonard immediately spoke up excitedly. "Princeton? Wow! I also graduated from Princeton! So you..."
"So we're having an alumni reunion now?" Barry interrupted again, his sarcasm undisguised. He glanced at Leonard. "Nothing to say." He clearly didn't want any form of alumni connection.
Howard couldn't help but blurt out, "Then... how could someone like you... end up as a janitor?"
"End up?" Barry repeated the word, his voice suddenly rising, his eyes instantly sharpening. The intense aura he'd displayed on stage earlier seemed to resurface. "Because I once put an arrogant colleague in the hospital during an academic dispute." He took a step closer. "Now, if you don't move, you'll end up just like him. Understood?"
Howard, startled by the blatant threat, almost instinctively jumped to the side, quickly clearing the path, unconsciously mumbling, "Understood! Please, go ahead! Please!"
Barry no longer looked at any of them, striding away directly, his back exuding a resolute "do not approach" air.
The four stood frozen in place, staring dumbfounded as he disappeared down the hallway. After a long while, Raj quietly broke the silence. "Did he... was he telling the truth? Did he really put a colleague in the hospital?"
Leonard swallowed, shaking his head uncertainly. "I... I don't know. But looking at him just now, I'd rather believe it's true."
Howard, after confirming Barry had gone far, finally regained his slick tone. "Whoa. So, when he said 'physics is a collaborative discipline,' did he mean 'collaboration'... as in, he throws the punches, and the other guy pays the hospital bill?"
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