They are described by wave functions, and those wave functions can evolve into superpositions themselves.Īnd they not only can, they necessarily do, if you simply posit that everything obeys the Schrödinger equation, quantum mechanics' fundamental equation. Everett’s idea was to keep in mind that observers – whatever they may be, from people to video cameras – are quantum systems in their own right. These questions, collectively known as “the measurement problem” of quantum mechanics, bothered Hugh Everett, a graduate student at Princeton University in the 1950s. What do you mean by “measure”? Does it have to be a human being doing the measuring, or does any conscious creature count? Could it be a video camera? How quickly does it happen, and how does the system distinguish between measurements and any other kind of physical interaction? But when we measure the system, it’s wave function stops being a superposition, and suddenly “collapses” to some particular measurement outcome, like spin-up. That brings up a problem, namely, why do wave functions evolve differently when you’re looking at them and when you’re not? According to textbook quantum mechanics, a wave function by itself evolves according to a simple equation first written down by Erwin Schrödinger. It doesn’t just characterise our knowledge, it’s the real physical state of the electron.Īlbert Einstein believed the wave function represented a feature of the particle that hadn't yet been measured. But it hasn’t worked out that way the more we do experiments, and the more we understand the inner workings of quantum mechanics, the more it seems like the wave function really exists. That was the original hope of people like Albert Einstein. It’s natural to think that there really is some answer to how the electron is spinning, but we just don’t know what it is, and the wave function encapsulates our ignorance. We can use the wave function to calculate the probability of each measurement outcome. Physicists describe the state of the electron in terms of a “wave function,” which tells us how much of the state of the electron is spin-up, and how much is spin-down. We can prepare the electron in a “superposition” of spin-up and spin-down, such that there will be some probability of observing each outcome. That would be weird enough as it is – why only two possible answers? But even weirder is that we can’t always predict what that measurement outcome is going to be. When we measure its spin, we get only one of two possible answers: it’s spinning up or down, with respect to whatever axis we used to measure it. Consider an electron, which is an elementary particle that has a certain fixed amount of a quantity called spin. To see why, we have to think about how quantum mechanics works. (Not everyone agrees with me about this.) The many worlds of quantum mechanics, I would argue, are probably there. And they arise naturally from the simplest version of our most solidly tested physical theory, quantum mechanics. They are not far away – but only because they aren’t “located” anywhere at all. The multiple “worlds” of quantum mechanics are something else entirely. It may very well exist, but the only thing to say right now is that we don’t really know. But exactly because those ideas are themselves speculative, the cosmological multiverse should be thought of as speculative-squared. It arises naturally as a consequence of other speculative ideas, including string theory and cosmological inflation. The cosmological multiverse wasn’t invented because physicists thought it would be cool to have a bunch of universes out there. Dead and alive: why it's time to rethink quantum physics.Quantum field theory: "An unholy crossbreed between quantum physics in a bad mood and every button you never push on a calculator".
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |