Quantum mechanics rule life; double slit confusion (Introduction)

by David Turell , Saturday, December 14, 2019, 19:49 (1586 days ago) @ David Turell

The double slit experiment is still not explained satisfactorily:

https://aeon.co/essays/the-elegant-physics-experiment-to-decode-the-nature-of-reality?u...

Note the title of this long essay:
"How a sunbeam split in two became physics’ most elegant experiment, shedding light on the underlying nature of reality."

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"In its simplest form, the experiment involves sending individual particles such as photons or electrons, one at a time, through two openings or slits cut into an otherwise opaque barrier. The particle lands on an observation screen on the other side of the barrier. If you look to see which slit the particle goes through (our intuition, honed by living in the world we do, says it must go through one or the other), the particle behaves like, well, a particle, and takes one of the two possible paths. But if one merely monitors the particle landing on the screen after its journey through the slits, the photon or electron seems to behave like a wave, ostensibly going through both slits at once.

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"In the mid-1920s, a few fabulously talented physicists, among them Heisenberg, Pascual Jordan, Max Born and Paul Dirac in one group, and Erwin Schrödinger on his own, developed two ways of mathematically depicting the behaviour of the quantum underworld. These two ways turned out to be equivalent. It boils down to this: the state of any quantum system is represented by a mathematical abstraction called a wavefunction. There is a single equation – called the Schrödinger equation – which tells us how this wavefunction, and hence the state of the quantum system, changes with time. This is what allows physicists to predict the probabilities of experiment outcomes.

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"Did the photon go through both slits at once? Does the photon have a trajectory, as it leaves the source and is eventually detected at the photographic plate? And given that the mathematics says that there are many regions where the photon can be found with a non-zero probability, why does it end up in one of those regions and not others? Finally, if the photon didn’t go through both slits, but rather the wavefunction did, is the wavefunction real?

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"For any given photon, you can never predict with certainty where it will be found: all you can say is that it will be found in region A with probability X, or in region B with probability Y, and so on. These probabilities are born out when you do the experiment numerous times with identical photons, but the precise destiny of an individual photon is not for us to know. Nature at its most fundamental seems indeterminate, random.

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"The opposite of locality – nonlocality – gets highlighted by something as simple as the double-slit experiment. When the photon’s wavefunction nears the photographic plate, the photon is in a quantum superposition of being in many places at once (this is not to say that the photon actually is in these places simultaneously, it’s just a way of talking about the mathematics; the photon itself is not yet ascribed reality in the standard way of thinking about it). Upon observation, the wavefunction is said to collapse, in that its value peaks at one location and goes to near-zero elsewhere. The photon is localised – and thus found to be at one of its many possible locations.

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"But our classical minds rebel. We cannot disregard the conviction that the photon has to go through one slit or the other. So we put detectors next to the slits (let’s assume that our detectors work without destroying the photons). Something weird happens. The photons will now go through one or the other slit. Curiously, this time they will not form an interference pattern. They act like particles and they will go to those regions on the photographic plate that they shunned when acting like a wave.

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"It was clear that whether a photon behaves like a wave or a particle depends on the choice of the experimental setup

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"Experimentalists have also combined delayed-choice and quantum-erasure experiments into one mind-boggling delayed-choice quantum-erasure experiment – in which you not only delay the choice of what to see (particle or wave nature), but you can also randomly erase this choice. Again, the photon or any quantum system will show you only one face or the other – and what it reveals depends on the final state of the experimental apparatus.

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"Even more enigmatically, does collapse ultimately need observation by a conscious human being? (To be clear, almost no physicist today thinks that this is the case.)

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"physics has yet to successfully explain the double-slit experiment. The case remains unsolved."

Comment: And this is the basis of reality! We can't seem to out-think God. Worth reading it all.