Here’s what you’ll learn when you read this story:
We interact with our environments every day. You might break your favorite coffee mug, stain your favorite sweater, or eat all the ice cream in your freezer. All of this makes it feel like we’re fundamentally shaping our reality—but what if it’s actually the other way around?
Popularizers of quantum physics often talk about the “observer effect,” or that quantum objects are usually in many places at once until we look at them. As soon as we make an observation, this quantum superposition of being everywhere at once “collapses” to a single location; an electron or a photon (a particle of light) is always detected in one well-defined position. Hence, the notion that observers affect and even create reality by looking at it; however, this is a superficial impression very far from what physics tells us reality really is.
As a teenager, I had a rock band, and we once got lucky enough to be invited to play a big gig in my hometown. I cranked my Marshall amp to 11, really wanting to blow away the audience with the guitar riff I had composed specially for that occasion. But my eagerness to impress the crowd caused a fuse in the amp to blow. My bandmates played on and completed a couple of songs without me, while I kept asking myself why I had ended up in this very unfortunate universe.
It was only years later, when I learned quantum physics properly, that I realized the way I had framed that very question was completely wrong. Even more amazingly, I also realized that the other reality—the one in which the amp didn’t blow up (and I received a standing ovation for my guitar virtuosity)—also exists and can ultimately affect the reality in which the amp had collapsed.
How can that possibly be? Well, let’s consider a simpler scenario than a big rock concert. Imagine instead that a photon strikes someone’s sunglasses—we’ll call him Bob. After interacting with the sunglasses’ surface, the photon is in a superposition of being transmitted and reflected away from the lens. That’s what quantum physics tells us. When transmitted, the photon enters Bob’s eye, thereby generating a nerve impulse that ultimately results in Bob seeing light. However, when reflected, the photon bounces away from Bob and doesn’t generate any neurological response in Bob’s brain, which leads to a different reality from the first.
According to quantum physics, Bob and the photon are entangled: in one branch, the photon passes through the glasses and stimulates something in Bob’s brain, whereas in the other branch, the photon is reflected and Bob is left unperturbed. Both realities exist simultaneously—though Bob only consciously experiences one.
In the first branch, Bob “knows” he has seen the photon, while in the second branch, he “knows” he hasn’t. The relationship between Bob and the photon, of course, is the good old Schrödinger’s cat state—or a state in which a cat exists, dead or alive, in two realities. Without too much exaggeration, it’s fair to say that all quantum experiments are really just more or less complicated versions of Schrödinger’s.
The Bob who sees the photon may ask why he ended up in that universe rather than the one where the photon bounced off (just as my teenage self asked why he was in the universe where the amp blew up). But that misses the point. The situation is actually the other way around; the photon that entered Bob’s eye led to Bob being that person, different from the Bob in the branch where the photon was reflected. It’s the observation of the photon that affects Bob, so it’s meaningless for either Bob to ask why he isn’t the other Bob. When we interact with the external world, which exists in a multitude of states, the crucial change is in us, not in the external world. In other words, reality affects you. But there’s more to this.
Outcomes in other realities can also affect Bob. For instance, if he sees the photon, he can still be affected by not seeing it in other branch states. The idea, as always, is to quantum interfere the two possibilities, or create a superposition and then reverse it. This is exceptionally difficult to achieve in practice; however, if quantum physics is universal, it ought to be possible with sufficient resources.
For this purpose, we imagine a physicist, Alice, who controls the experiment in which Bob and the photon become entangled. Alice now needs to reverse the entangling process that has resulted in Bob’s observation. If the process is perfectly reversed, then Bob and the photon are in their initial states, before the photon has interacted with the sunglasses and Bob has made any observation.
This means that both alternatives—either the photon reflecting off the lens or being transmitted—must have existed and were perfectly superposed in an entangled state, for otherwise the final state wouldn’t be the same as the initial one. This is what we mean by interference: a superposition is first created, only to be reversed. Likewise, the outcomes in both branches of reality must have existed within the entangled state of Bob and the photon. The elements of reality that are encoded into quantum objects are fundamental, and you—in this reality and others—are shaped each time you observe them.
Will the reality in which I played a successful gig as a teenager ever collide with my present reality to produce something surprising? Or will you ever collide with the version of yourself that won the lottery? It seems unlikely that the two events will ever quantum interfere given their complexity, though we can never rule such things out. But the question that still keeps me up at night is: How would you even know if this had happened? Maybe, just as in Bob’s case, my two realities have already merged, and many others keep colliding, but I am simply completely unaware of these extraordinary events. And maybe this is just as well, given that there are so many more ways in this universe in which things could go wrong for us instead of right.
Vlatko Vedral is a professor of physics at the University of Oxford, known for both his theoretical and experimental work on quantum information, including developing a novel way of quantifying entanglement and applying it to macroscopic physical systems. When not studying the fundamental nature of reality, Vlatko enjoys drawing, wakeboarding, and playing his electric guitar "up to 11." He is the author of the 2010 book Decoding Reality, as well as the latest "Portals to A New Reality." Born in Serbia, he now lives in Oxford.
此内容由惯性聚合(RSS阅读器)自动聚合整理，仅供阅读参考。 原文来自 — 版权归原作者所有。