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Quantum Physics – A Walk Through

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Quantum Physics – A Walk Through

Quantum Physics is a curious topic for decades. Put simply, it’s the physics that explains how everything works: the simplest description we’ve of the character of the particles that structure matter and therefore the forces with which they interact.

What is quantum physics?

Quantum physics underlies how atoms work, then why chemistry and biology work as they are doing. You, me, and therefore the gatepost – at some level a minimum of, we’re all dancing to the quantum tune. If you would like to elucidate how electrons move through a computer chip, how photons of sunshine get turned to the electrical current during a solar array or amplify themselves during a laser, or maybe just how the sun keeps burning, you’ll get to use physics.

Quantum physics

The difficulty – and, for physicists, the fun – starts here. to start with, there’s no single scientific theory. There’s quantum physicsthe essential mathematical framework that underpins it all, which was first developed within the 1920s by Bohr, Werner Heisenberg, Erwin Schrödinger, et al. . It characterizes simple things like how the position or momentum of one particle or group of few particles changes over time.

But to know how things add to the important world, quantum physics must be combined with other elements of physics – principally, Albert Einstein’s special theory of relativity, which explains what happens when things move in no time – to make what is referred to as quantum field theories.

Three different quantum field theories affect three of the four fundamental forces by which matter interacts: electromagnetism, which explains how atoms hold together; the strong nuclear force, which explains the steadiness of the nucleus at the guts of the atom; and therefore the weak nuclear force, which explains why some atoms undergo decay.

For decades researchers have stalled at this apparent impasse. They can’t say exactly what a superposition is without watching it, but if they struggle to seem at it, it disappears. One potential solution—developed by Elitzur’s former mentor, Israeli physicist Yakir Aharonov, now at Chapman University, and his collaborators—suggests how to deduce something about quantum particles before measuring them.

Aharonov’s approach is named the two-state-vector formalism (TSVF) of quantum physics and postulates quantum events are in some sense determined by quantum states not just within the past—but also within the future. That is, the TSVF assumes quantum physics works an equivalent way both forward and backward in time. From this attitude, causes can seem to propagate backward in time, occurring after their effects: a phenomenon called retro causation.

But one needn’t take this strange notion literally. Rather within the TSVF, one can gain retrospective knowledge of what happened during a quantum system by selecting the outcome: rather than simply measuring where a particle finishes up, a researcher chooses a specific location during which to seem for it. This is often called postselection, and it supplies more information than any unconditional peek at outcomes ever could. This is often because the particle’s state at any instant is being evaluated retrospectively in light of its entire history, up to and including measurement.

The oddness comes in because it’s as if the researcher—simply by choosing to seem for a specific outcome—then causes that outcome to happen. But this is often a touch like concluding that if you switch on your television when your favorite program is scheduled, your action causes that program to be broadcast at that very moment. “It’s generally accepted that the TSVF is mathematically like standard quantum physics,” says David Wallace, a philosopher of science at the University of Southern California, who focuses on interpretations of quantum physics. “But it does cause seeing certain things one wouldn’t otherwise have seen.”

Take, as an example, a version of the double-slit experiment devised by Aharonov and his co-worker Lev Vaidman of Tel Aviv University in 2003, which they interpreted with the TSVF. The pair described (but didn’t build) an optical system during which one photon acts as a “shutter” that closes a slit by causing another “probe” photon approaching the slit to be reflected back the way it came. By applying post-selection to the measurements of the probe photon, Aharonov and Vaidman showed, one could discern a shutter photon during a superposition closing both (or indeed arbitrarily many) slits simultaneously.

In other words, this thought experiment would in theory allow one to mention confidently the shutter photon is both “here” and “there” directly. Although this example seems paradoxical from our everyday experience, it’s one well-studied aspect of the so-called nonlocal properties of quantum particles, where the entire notion of a well-defined location in space dissolves.