What counts as "observation" in quantumn theory?

Submitted by Iron_Rod_Stewart t3_xy7u8l in askscience

I'm curious about the physical forces that act on a quantum particle that collapse it down to one state, and the relationship between these forces and the observers knowledge or measurement.

I assume it's possible for a person to subject particles to these forces so as to collapse the particle down to one state without gaining any knowledge about the particle. For example, by not looking at the monitor or not recording the measurement made by the device. Is that the case?

Is there any theoretical way of measuring these objects through different means which do not subject the particles to such forces?

Or is their state inextricably linked to an observer's knowledge about them?

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ass_bongos t1_iriunq0 wrote

To add to the good answers already posted, think of how you "observe" something in day-to-day life. When you see an object, you see it because a photon (or many photons) from some light source bounced off of it and went into your eye. In the quantum world, this bounce itself changes the object you're looking at. The electromagnetic interaction between the mystery particle and the photon puts the particle in a different state than it was before. This is generally what we mean when we say that observing a quantum state "changes the outcome".

There is definitely some additional nuance as other posters have remarked, and observation is not always as simple as bouncing a photon. The delayed choice quantum eraser is a fun experiment that shows you can actually wait to "choose" whether or not to "observe" a quantum event until after it happens! Quantum is weird.

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Kered13 t1_irlfube wrote

> The electromagnetic interaction between the mystery particle and the photon puts the particle in a different state than it was before. This is generally what we mean when we say that observing a quantum state "changes the outcome".

This is the observer effect, and while it is also an issue when trying to make very small or very precise measurements, it is unrelated to the quantum physics question of what exactly an "observation" is for the purposes of wavefunction collapse.

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Kered13 t1_irhqcaj wrote

There is no widely accepted answer. This is one of the big open questions that quantum mechanics is still trying to figure out, and different interpretations have put forward various answers.

https://en.wikipedia.org/wiki/Observer_(quantum_physics)

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RBUexiste-RBUya t1_irl21i2 wrote

Different interpretations have put forward various answers, even some people say that "the observer" is a guy called Francesc Satorra :-D

I'm noob here. There's no facts that explain the observer effect, but I suspect that it's only an interaction.

What I can't understand is the 'spooky action' of the works that have recently won a Nobel prize. It's very difficult to me to understand why quantum mechanics is like 'to play dice' https://www.nobelprize.org/prizes/physics/2022/popular-information/

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astrange t1_irr0xth wrote

The “spooky action” (instantaneous collapse of the waveform) is part of the Copenhagen interpretation of quantum physics, but isn’t proven to exist, as that’s just one interpretation.

There’s other interpretations that are still valid (many worlds, superdeterminism, pilot wave) and don’t include it, but of course many of those can’t be falsified.

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DerpSouls t1_irisdl1 wrote

We can over simplify it to anything that interacts with the quantum phenomenon as an observer. So any measuring apparatus becomes an observer.

This ignores any philosophical implications that may or may not be what you are looking for

To take a measurement of something we must physically interact with that thing in some capacity. Measuring acceleration or voltage or heat will always have some impact on the subject causing significant effects on quantum realm due to scale while not so significant on the macro world

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royalrange t1_irkozes wrote

It means measurement, although I have almost never seen "observation" used in scientific work other than when talking about the philosophy of quantum theory. A photodetector detecting a photon is a measurement, as an example.

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