Q & A: Why don’t electrons fall into the nucleus?

Electrons are not little balls that can fall into the nucleus under electrostatic attraction. Rather, electrons are quantized wavefunctions that spread out in space and can sometimes act like particles in limited ways. An electron in an atom spreads out according to its energy.

How Electrons Orbiting the Nucleus Never Fall Into the Nucleus?

Follow-Up #1: Does the electron have a position?Q:But if we are saying that there is a probability of finding something here or there, this means that it must be somewhere at a definite place, it is just that we do not have the means to know without errors where is it. So if the position is definied but cant be determined, then how actually is the motion of the electron. I dont want to determine where it is, what is its momentum etc. – Amol Bhave (age 16) Jabalpur, Madhya Pradesh, IndiaA:Your interpretation is what common sense would initially lead us to believe. However, we know that it isn’t true. The electron is truly spread out. If these quantum variables (such as the electron position) that seem to be spread out had actual hidden values, then a set of experimental predictions known as the Bell Inequalities would be obeyed. In actual experiments the Bell Inequalities are consistently violated. Therefore the spread-out variables really are spread out. The process of interacting with a large apparatus that’s sensitive to where the electron is causes the formation of a state in which the electron’s cloud has much less spread. This occurs via a quantum process called decoherence. There’s no consensus about whether a single such state arises or a collection of states covering the whole range of possibilities. Mike W.

The electron is present as a cloud. Averaged over the cloud, the positive kinetic energy is half as big as the negative potential energy.

More importantly, the cloud really is the state of the electron. Its not a picture of where some dot-like particle probably is. It isnt anywhere in particular. It also doesnt have any particular velocity. In a hydrogen atom, its certainly not going in a circle. The cloud doesnt go anywhere at all. Theres no reason for it to radiate.

The world at a small scale cannot be put together out of anything like the pictures were used to at a large scale.

Follow-Up #3: what are electrons doing?Q:I want to ask about the electron. I love quantum mechanic and astrophysics. I’ve heard about this electron cloud and I google it for a while. I think I get the message, that is – At any given moment electron can be found at random place in the electron cloud (described with the wave function). What I don’t understand is how you can see the electron and determine his position? And if you take snapshot how can you be sure that the electron doesn’t move around this cloud? I mean, the electron must be moving in some pattern way but I think that he is so fast that we think that he is at many places at the same time or he simply disappear on one place and show up at another. Can this be true? Can you tell me the cutting edge, there must be something more than just saying that the electron can be everywhere and nowhere. Thank you! – Alexander (age 21) SkopjeA:

Alexander- Your question has a lot in common with many others, so Ive put it in a thread.

There are a variety of ways that an electron, which is always a spread-out wave, can be found to be in a smaller-than-usual region. Maybe it bumps into a piece of film, which localizes the wave to the region of one little bit of silver. Maybe the electron just got emitted from the fine tip of a needle, so you know its very close to that tip. Maybe a high-energy gamma ray bounces off of it, so that the position of the electron can be nearly determined from the gamma ray position and direction.

As we discuss at numerous points (search for “Bell Inequality”) the ranges of positions and of velocities are not due to our ignorance of some fast rattling around, but are a description of what the electron wave actually is. Its not that it is “in” the cloud, it is the cloud. Once the electron cloud has a small size than you can be sure that the electron is rapidly moving, in a broad range of directions, so that cloud will start to spread out. If the cloud is already highly spread out, the electron may not be moving much. This relation is called the Heisenberg Uncertainty Principle. Things people wrote about it before the Bell Inequality violations were established are generally outdated. They are still usually repeated in popular presentations and in some textbooks.

Follow-Up #4: particle cloudsQ:So from reading your thread where you answer several questions relating to the position of the electron in which you say that the electron has no defined measureable location but intstead exists as a wave probability function a set of positions in space where you might find the electron each position with a certain probability and that the electron doesn’t exist, even from an absolute perspective, at any one of these points at any given moment but as all of these points at once in a sort of cloud. This much I understand but what I don’t understand is why, why is it that an electron has this cloud like existance instead of a definite location I heard you mention the Heisenberg uncertainty principal that the more you know about a particles velocity the less you know about its position or visa versa but why is this that an electron exists as a cloud whereas on a macroscopic scale I have certainty of position and velocity, why is an electron a quantum wave probability function cloud thingy? – Eric Fernandez (age 16) Helena, MT, United StatesA:

We dont really know why the world is made up of quantum waves rather than of little dot-like things, or some other possibility. Thats just how it is. The Heisenberg uncertainty principle isnt really the reason for the quantum form of things, just one of the many mathematical consequences.

The thing that has to be explained, in a world made of quantum objects, is not why little things are fuzzy. Thats just part of the basic description. What we have to explain is why we experience a world where big things have fairly definite positions. They do still have, so far as we can tell, a little quantum fuzz, but it just isnt very noticeable on a big scale. What we have trouble talking about is why we see no Schrödinger cats that are both alive and dead. Thats the issue addressed, more or less, by various interpretations of quantum mechanics.

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