Tag: quantum

Quantum Conservation Laws

Maybe energy can be created and destroyed, or maybe the notion doesn’t quite make sense. To reconcile quantum mechanics and general relativity will require a quantum theory of gravity. Physicists disagree vehemently on what such a theory will look like, but most agree on one thing: The notion of spacetime will disappear at the fundamental quantum-gravity level. In that case, conservation laws lose their relevance completely. How can you say a certain quantity does not change with time if there is no time at the fundamental level?

Super zoom

The classic short film Powers of 10 (1977) propelled viewers on a journey from a Chicago park into deep space and then back down to the scale of a single proton. In The Super Zoom, the Brazil-based graphic designer Pedro Machado’s visualisation dives even deeper into the realm of the subatomic and theoretical. While the original film by Charles and Ray Eames zoomed in to a scale of 10-16 m at most, Machado’s film draws on 40 years of quantum research – not to mention significant advances in 3D rendering technology – to drill down to the unfathomably small scale of 10-33 m, brushing up against the limits of human knowledge and imagination. The mind bending animation uses a framework of quantum gravity in which a gravitational field exists at these smallest conceivable scales.

Self-locating uncertainty

Self-locating uncertainty is a different kind of epistemic uncertainty from that featured in pilot-wave models. You can know everything there is to know about the universe, and there’s still something you’re uncertain about, namely where you personally are within it. Your uncertainty obeys the rules of ordinary probability, but it requires a bit of work to convince yourself that there’s a reasonable way to assign numbers to your belief. In one sense, all of these notions of probability can be thought of as versions of self-locating uncertainty. All we have to do is consider the set of all possible worlds — all the different versions of reality one could possibly conceive. Some such worlds obey the rules of dynamical-collapse theories, and each of these is distinguished by the actual sequence of outcomes for all the quantum measurements ever performed. Other worlds are described by pilot-wave theories, and in each one the hidden variables have different values. Still others are many-worlds realities, where agents are uncertain about which branch of the wave function they are on. We might think of the role of probability as expressing our personal credences about which of these possible worlds is the actual one.

Quantum Darwinism

One of the most remarkable ideas in this theoretical framework is that the definite properties of objects that we associate with classical physics are selected from a menu of quantum possibilities in a process loosely analogous to natural selection in evolution: The properties that survive are in some sense the “fittest.” As in natural selection, the survivors are those that make the most copies of themselves. This means that many independent observers can make measurements of a quantum system and agree on the outcome — a hallmark of classical behavior.

Quantum amplification

Their method achieves 50 times more precision than the previous best techniques, which also means that they can make measurements 50 times faster than before. Now they can narrow down the particle’s location to an atom-sized space in less than a second. The key to their method is to accept the noisiness decreed by the uncertainty principle, and control where it manifests itself. To measure the ion’s position, they basically transfer the uncertainty into its speed, a value they happen to care less about.

Continuous Quantum Leaps

By making a kind of high-speed movie of a quantum leap, the work reveals that the process is as gradual as the melting of a snowman in the sun. “If we can measure a quantum jump fast and efficiently enough, it is actually a continuous process.” But there’s more. With their high-speed monitoring system, the researchers could spot when a quantum jump was about to appear, “catch” it halfway through, and reverse it, sending the system back to the state in which it started. What seemed to be unavoidable randomness in the physical world is now shown to be amenable to control. We can take charge of the quantum.