how do we know electrons have different behaviours depending if they’re being observed or not? What are those behaviours?


how do we know electrons have different behaviours depending if they’re being observed or not? What are those behaviours?

In: 7

First think about what “observed” means.

We think about this as a passive activity – you don’t change the trajectory of a football by staring at it.

But on the subatomic level this isn’t true. You can’t “see” an electron, you can only measure its presence by interacting with it in some way. Prod it with a magnetic field. Bounce a photon off of it.

You can’t “observe” a subatomic system without touching it, and thus changing its behavior.

Unperturbed, an electron exists in a strange fuzzy wave state that has this bizarre ability to interfere with itself – as if it’s in two places at once.

When you touch it, this wave collapses and the electron is momentarily localized to wherever your observation point is. The self-interference disappears when you “watch”

Look into the double slit experiment.

When observed the detection of electron impacts act like they are traveling straight through one of the two slits.

When not observed the impacts form an interference pattern similar to wave interferences.

Keep in mind that for physics/quantum mechanics the term “obervation” doesn’t mean that a person is physically watching the experiment. It means that the physical properties of the items involved are being measured/detected as part of the experiment.

In this case the observation is measuring to determine which of the two slits the electron is going to pass through before it reaches them. Not observing doesn’t measure to determine which slit the electron passes through. Observing to determine which slit the electrons will travel through changes how they behave.

Here’s an experiment –

Make an electron machine gun and fire it at a piece of paper, what do you see? You basically see a bunch of “bullet holes” on the paper clustered around the target just like you would with a real machine gun.

Now put an electron proof shield between the gun and the target and cut a tiny, tiny little hole into it, what do you see? You see a tinier little cluster of bullet holes on the target, only in the place where an electron could have traveled through the hole.

Now cut a second, tiny tiny hole in the shield AND aim the machine gun directly between the two holes. In theory the only way a bullet can leave the gun, go on an angle and through the hole, and then on to the target would be for really errant shots off to the side. What do you see?

Suddenly you see a weird alternating series of bullet holes – no bullet holes – bullet holes – no bullet holes splayed left to right across the target. *None* of the bullet holes corresponds to a place where a bullet could physically have gone from gun, to hole, to target. WTF is happening?

Perhaps, you think, two bullets are somehow traveling through the holes at almost the same time, and somehow they are *hitting* each other an ricocheting into that pattern.

So you have an idea, you put a metal detector over the holes, if a bullet travels through the hole the detector goes off and you which hole has a bullet and when. The important thing is a metal detector has no effect on bullets, it doesn’t bend them or something, right?

You rig this up and turn it on, what happens? The moment you flip the switch the pattern on the target instantly reverts to the two small splotches of straight line fired bullets and the pattern disappears. What? You flip the switch back off and the alternating pattern instantly reappears, flip it on, back to two splotches.

This is called the double slip experiment, you can google it for more info.

Our current best model for interactions of small structures like electrons and photons characterizes them not as waves or particles but as probability functions.

Best example I can come up with offhand: Mario Kart item boxes. The single item boxes are all the same but they have the potential to become any item; you just don’t know what item it is until you hit the box and observe what is inside it. Before hitting the box, it has a probability function that defines how likely it is to contain any particular item but you don’t know what item it will be until you hit it. But by ‘observing’ the box, you have collapsed that probability function and revealed what the item it is.

Unlike Mario Kart item boxes, when you STOP observing what these small structures are doing, they revert back to probability functions. The instant the blue shell explodes, it turns back into an item box.

One of the ways this relates to electrons specifically: The Neil’s Bohr model for an atom (electrons as planets orbiting a nucleus like a sun) is vastly simplified because the electrons aren’t solely particles and only kind of orbit (not enough time to cover this). Each “orbit” is a cloud of electrical charge that the probability functions exists within. The ‘particle’ that is the electron could be anywhere in that cloud and the only way to find out is to observe it by having it interact with something or move to another electron orbit. But by interacting with it, you have changed it and thus don’t know where or what it is anymore, so it’s back to a probability function.

This is a really cool trick that allows things like magnetic fields and electrical charges to move at speeds that are WAY faster than a single electron can move. If you want to dive into this via the medium of high budget YouTube explainers, Veritasium did a couple of videos on this phenomenon: [The Big Misconception about Electricity]( and [How Electricity Actually Works](

edit: clarity and grammar

Hopefully this is helpful. I had the same question a week back and had a friend explain and send this to me