I’ve heard that electrons behave differently when observed, but how do you actually observe an electron?
In: Physics
To observe something you have to interact with it.
When you see with your eyes, that’s light bouncing off surfaces and then into your eyes.
But why do we see different colours? Because some light is absorbed by the surface. Some photons (particles of light) hit the molecules of the surface and excite them. That’s why light is absorbed. It’s a transfer of energy. The molecule gains energy. It’s state has changed.
Think of it like feedback. You only know something is there if you interact with it. You can only see something if light interacts with it. You can only feel something if you touch it.
When physicists talk about “observing” something, they’re talking about interacting with it. Because you can’t observe something without interacting with it.
Back to seeing stuff, how does that even work? Well, a photon hits the back of your eyeball. The photon hits a molecule in your eye and triggers an electrical response. The photon is absorbed, it no longer exists.
When you want to observe something on the quantum level, you have to be careful so that your method of observation doesn’t interfere with what your trying to see. For example, it’s no good trying to observe a sandcastle blindfolded with a shovel. You’ll destroy the sandcastle and not know what it looked like.
This is the ‘observer effect’
Electrons are tiny, and exist as a wave as well as a particle. Because of this, it’s properties are constrained by the **Heisenberg Uncertainty Principle**. This principle basically says that more accurately we know one property of the particle, the less accurately we know it’s pair. If we accurately know the position of the electron, then we have no idea what it’s momentum is.
So we can’t completely describe the particle.
The observer effect is more of a practical limitation, while the Heisenberg Uncertainty Principle is more of a fundamental limit.
In quantum mechanics, the word “observation” has its own specific definitions. It’s easier to use the more objective word/concept “interaction” that comes to us from successful modern Quantum Field Theory (QFT). In other words, any time any particles *interact* with each other, regardless of any instrumentation or humans present.
For example, in the well-known double-slit experiment, the “observation” can refer to the particle *interaction* that caused a “dot” to appear at one specific location on the detector screen.
If the screen hadn’t been there, there’d be no “interaction”, and so the *position* of the particle wouldn’t be defined at that location, except in terms of a probability distribution. This is again easier to understand in the framework of Quantum Field Theory, where the word/concept “particle” is *redefined* to refer to an excitation in a fundamental fully-space-occupying field. That means our intuition is way off the mark if we imagine a “classical” particle like a little chunk of something zooming around.
Ah yeah, that’s actually a really confusing aspect of quantum mechanics. Even people with actual degrees in quantum mechanics get tripped up.
Essentially though electrons can either behave like waves/clouds or like particles. When you have a small number of subatomic particles that aren’t moving too fast all interacting with each other they can all act as one big mess of clouds.
But at some point when you get too many of those clouds acting together instead of acting as clouds they suddenly act as particles.
On a big human sized scale to look at an electron we need to interact with it. Maybe we throw a photon at it, or wait till a photon is emitted by the electron cloud naturally. Maybe we bounce a second electron off of it. Whatever process you use is observation. We tend to call this observation because whatever process you use you can never directly interact with that cloud. Every time you “see” an electron it seems to be a point particle. But you -can- see changes that are only explainable if the electron was acting as a cloud before you got your information.
And we have zero concrete idea as to what constitutes too many clouds or why this is the case. There are theories but they are currently fairly speculative. We just know that it’s not a lot, and the tools we use to detect electrons to take measurements be it your eyes or a camera are way way too big.
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