When observed, the electrons act as matter, but when not observed, they act as waves?
Obviously “observed” doesn’t mean recorded on an iPhone camera, but what does it mean? Is it like if we simply know the location or the velocity of the electrons, they behave differently?
The part I’m most not understanding is why the electrons behave differently. Certainly they aren’t capable of thought and recognizing they’re being observed lol
In: Physics
When you hear “observed”, think “measured”.
In order to measure something, you must *do* something to it. Even “just looking” means that photons bounced off of it then hit your eyes – which means those photons *did something* to it. In most cases, this is meaningless…but when you’re talking about measuring individual photons, then suddenly it matters a lot.
This is one of those situations where a specific field (Physics in this case) comes across something new that it needs to reference, and it ends up re-using an existing word, and that creates a bunch of confusion for everyone else.
In this situation, the word “observed” doesn’t mean that it’s being watched by some sort of aware being. The word has a different meaning in this specific context.
That being said, this is a part of quantum mechanics that is definitely not well understood. It’s often referred to as “the measurement problem”, and there are a bunch of different theories as to how a quantum system ‘collapses’ into a more classical system. It’s not really the kind of thing that’s easy to ELI5, because it’s something that even experts in Quantum Mechanics can’t come to much consensus on.
“Observed” means that you measure a property (like its position).
In classical systems measurement does not change anything on the object, you are measureing. If you measure the mass of an apple and then its color, it does not change anything on the apple itself. And it is also not matters, if you measure the mass or the color first for the results.
In quantum systems a measurement of a property changes the state of the system. There it becomes relevant if and in which order you measure properties.
If you have 1000 quantum apples, and you just measure the color, then you might find that you have 500 red and 500 green apples.
However if you repeat that and check if your quantum apples, have a mass greater than 20 grams, and then measure the color, then you might end up that all 1000 apples are red, as the mass measurements have forced the apple into the “red” state. (heavily simplified)
Something similar happens with the electrons. If you measure properties of them before they end up on the screen (which is a measurement too), you change their state and you get a different result in the second measurement (a different picture).
Being observed: You shoot photons. They interact with electrons. The electrons change the state and behavior, and don’t form the interference.
Being not observed: You leave the experiment untouched. Electrons make interference and obey wave function.
If you mean the quantum double slit experiment, then what happens is that if you send one photon at a time through the standard double slit setup and record where on the target sheet it strikes then over time it will build up an interference pattern on the sheet over time implying that it travelled through both and interfered with itself, but if you put in a method to *detect which of the two slits it travelled through* then the interference pattern disappears.
That’s the “observation” bit. Detecting which slit the photon passed through.
Why? I dunno. I cling to the famous Feynman phrase when this stuff comes up: “If you think you understand quantum physics, you don’t understand quantum physics”.
While it might be a tiny bit confusing, it’s simpler than people think.
The setup is analogous as for light, just with a screen able to detect electron hits and a different physical setup for the “slits”, because the one for light physically wouldn’t work for electrons.
Now, with two unobstructed “slits” the OVERALL IMAGE AFTER THOUSANDS OF EVENTS exhibits an interference pattern just like light. This is important, you won’t see the pattern with just one electron. It’s statistical. But it still exists if you fire them individually one after another, meaning they do interfere with themselves like a wave, before striking a specific place like a particle.
The issue starts if you try to in any way detect (“observe”) which path the electron goes through. This immediately destroys the interference pattern (because the condition for its formation were disrupted), and you’re left with what you’d expect from a pure particle. Again, that’s the same as for light.
> Is it like if we simply know the location or the velocity of the electrons, they behave differently?
What the observer effect actually means is that we **cannot** observe which path an electron took in the double slit experiment without interacting with the electron. We can’t detect its location without collapsing the wave function.
If you’ve seen a video on the double slit experiment, they probably lied to you that they put a detector in front of the slits to just passively “watch” which slit an electron took and that changed the electron’s behavior. But that’s not true. It’s a **thought experiment** that says no matter what kind of detector we would put there, it would **have to** interact with and thus affect the electron.
In quantum mechanics observation simply means interaction with the world e.g. when the electron hits the screen behind the slits, or hits the detector infront of the slits.
Where the particle is observed is probabilistic. The schrödinger equation, which evolves with time, tells you the probability of the particle being observed at a particular location. The waves you read about are probability waves. The function has crests and troughs, it has a wavy behavior, and you can calculate the probabilities from these.
When the position of electrons are being measured, they behave like particles with an exact location.
When the position of electrons are not being measured, their location takes on a fuzzy probability wave.
As to why, we have no definitive answer. One potentially compatible explanation is that we live in an efficient simulation – one that calculates exact particle locations only when that level of accuracy is needed, because they are being actively measured.
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