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I've got asked by someone who just graduated school and is about to start studying physics, what exactly is an electron, if it is not "a small ball rotating around the core of an atom". I couldn't really break it down for him though, i guess he didn't understand my explanation. Do you have an explanation in "easy words" that is still physically correct?

Qmechanic
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    The physically correct description is completely at odds with the day to day experience of the world. You can't explain it to the layman in an elevator speech. Figure out which lies to children you can live with. – dmckee --- ex-moderator kitten Jul 10 '15 at 23:31
  • Somebody who is about to study physics doesn't need to be told lies to children (even though I love the link). They can be told that an electron is a state of a quantum field that, under suitable circumstances, can be described as a charged classical particle. If they can't live with that, they won't find physics much fun to begin with. – CuriousOne Jul 10 '15 at 23:39
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    u don't seem to understand the problem. if u don't know what a "state of a quantum field" is, how can u accept that to be an electron, that would be accepting "empty words" with no meaning to you. –  Jul 11 '15 at 00:06
  • One does not have to know what a quantum field is to know that quantum fields exists and are very important descriptions in modern physics. After all, most of the world knows that rockets exist and that they are the only way to get to space. Should we talk about "that long loud thing with the tail of fire" instead to everyone who is not a rocket scientist, already? – CuriousOne Jul 11 '15 at 01:29
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    @CuriousOne: Are you being serious? We can just say the word "rocket" precisely because everyone knows what a rocket is! Suppose a kid asked you what a rocket is. Would you say "You don't have to know what a rocket is to know that it exists and it gets people into space"? – Javier Jul 11 '15 at 01:58
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    Where would a secondary school graduate intend to study physics at a university but have no previous exposure to it even at an elementary level, or even in say chemistry? Or am I misinterpreting ? – paisanco Jul 11 '15 at 03:41
  • @Javier: The last week or so we had two people here who wanted to calculate a rocket engine with "1W of power", which is a 100% false notion of what a rocket is and how it works. In theory you are right, everybody thinks they know what a rocket is, in practice almost nobody does and it's much worse with quantum mechanical entities like electrons. – CuriousOne Jul 11 '15 at 08:21
  • @CuriousOne I haven't read your answer to the original question, I'd like to. – Agent Zebra May 14 '16 at 06:22
  • @AgentZebra: Which original question? The one about the rocket? Oh, my, that was some time ago... :-) – CuriousOne May 14 '16 at 06:33
  • @CuriousOne Ha no. How to explain what an electron is to someone new to physics? I think you begun an explanation this evening, below. – Agent Zebra May 14 '16 at 06:39

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Electron is a particle with mass and a certain probability of being found at a given distance around the nucleus of an atom at a certain time. It caries a negative charge which makes chemical reactions possible since chemical reactions are driven by the electrostatic forces between electrons and positively charged protons which reside in the nucleus of the atom along with neutrally charged neutrons. It also allows for the flow of electricity, since the flow of current is directly proportional to electron flow. However if current is flowing one way, then the electros are flowing the opposite way ie current is a measure of positive charge flow.

Stochastic13
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Here is a more complicated answer:

I am going to try my best, ok?

An electron is a negative elementary charge subatomic particle of an atom. It was once known as a beta particle, but it is now an electron. It takes electromagnetic, gravity, and weak interactions into play. In Coulombs, it's charge is approximately $-1.6 * 10^{-19} C$ and it's mass in kilograms is approximately $9.1*10^{-31} kg$. It is said that the electron has no substructure, meaning there is no subparticle known that makes up the electrons. It was first discovered by J. J. Thomson in 1897 in an experiment to observe the straightness of a cathode ray (I think, someone correct me on that if I'm wrong), who also theorized that these particles existed like "blueberries in a muffin", meaning they were almost implanted on the surface of an atom. With the discovery of the nucleus of an atom (from an experiment which fired alpha particles through a slit and found that their paths were changed drastically), Rutherford said that electrons orbited the nucleus much like planets do around the sun. However, this model failed to explain the stability of the atoms (as since the electrons have to counteract the pull of charge and gravitation with centrifugal force and electromagnetic pulses), and also failed to explain the ray spectrums that were emitted from the gases when light was shown through them instead of a continuous spectrum. In comes the Bohr Model which apparently solves all those problems and more. The Bohr model states the quantum condition, $2\pi rmv = nh$, and the frequency condition, $hf = E_f - E_i$, this also used the proposition from french scientist de Boglie that all moving particles take the properties of a wave ( wave particle duality ). However, the Bohr model failed to explain many other Spectrum phenomena, but Schrodinger used his equations to create wave functions which explained many of them, and Heisenberg using quantum mechanics set forth the Uncertainty Principle, which was used to create the model of today, which includes an electron cloud where an electron could be theorized to be there in that area. The electron again, orbits the nucleus based on it's energy levels at different radii from the nucleus. This radii can be quantitized and used to explain the absorption and emission ray spectrums caused by the atoms. Basically, electrons have the tendency to "jump" between energy level orbits in an atom. Typically, the number of electrons in a specific elements valence shell determines it's ability to conduct electricity or form chemical reactions with other elements. It's transition to an atom's conduction band also allows the specific element to flow currents. The transition of electrons from one atom to another also causes electric fields to form, and either it's moving orbit or half-spin allows for magnetic fields to form as well.

Phew! Someone please tell me if I got something wrong and if you can edit it, but show the edits, I want to learn from my mistakes.

phi2k
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    Yep, that's a whole lot of confusion for the kid made form a hodgepodge of partly factual (and partly rather silly) explanation attempts made at different times in science history and it actually completely misses what an electron actually is. It's a very good example of how not to teach in the 21st century, though. – CuriousOne Jul 11 '15 at 01:38
  • It may be just me but I think it would have been better to just edit the original question – paisanco Jul 11 '15 at 04:08
  • I love how you say partly factual when all of the information I got is from what I learned from a well known textbook that I use for studying that's probably much more reliable than what you could come up with. Anyway, I find it quite hurtful that you are only seeming to look down on an explanation that I put effort into to become a good member of a community. If you have a problem, state it nicely, or just leave it to someone else to point it out. – phi2k Jul 11 '15 at 04:34
  • @PhyCS: That's not an explanation but an exorcism of bad habits brought on by tons of lies to kids in high school and beginners' college textbooks. An electron, for a kid, is just a unit of electric charge. If the kid wants to know more, then you say that it's complicated and he/she will have to wait for her second or third year in college to get the correct answer. Or tell him/her, that you can tell the usual ghost story of the little blue balls that are flying trough the air, but that you love them too much to lie to them in such a hideous way. :-) – CuriousOne May 14 '16 at 06:43
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Hmmm... I'll take a crack at it.

An electron is a negatively charged subatomic particle that orbits the nucleus of an atom, which contains a positively charged subatomic particle called a proton and a neutral subatomic particle called a neutron.

phi2k
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    That's a great lie for children, but if you had told it to the theoretically oriented folks who were in my first semester with me, they would have identified you as the child and walked away bored. – CuriousOne Jul 10 '15 at 23:51
  • Alright, I'll buy that, so should I make a more complicated one? I could. The reason I tried to state it so simply is because his student apparently couldn't understand "a small ball rotating around the core of an atom", which sort of troubled me a bit. – phi2k Jul 11 '15 at 00:13
  • My point is that there is absolutely nothing complicated about talking in adult language. "state of a quantum field" is not some magical spell that we can only tell students after years of religious ceremonies that prepare them for reality, it's just a fact. So is the much more important recipe of science to have multiple layered explanations. If anything, a science student can't be taught early enough that the same phenomenon has multiple layers of technically useful models and we can tell them about the top level and the simplifications at the same time. – CuriousOne Jul 11 '15 at 01:22
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    Look, if you just have something against me, come clean, I won't mind, I deal with a lot of crap from a lot of people anyway. All I'm trying to say is I'm trying to put it in simplest terms possible. – phi2k Jul 11 '15 at 04:33
  • I also don't understand your logic: how can someone that can't grasp the concept of the existence of an electron even begin to consider "states of a quantum field"? – phi2k Jul 11 '15 at 04:47
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    Why are you taking this personally? All I am saying is that one can tell an 18 year old the facts. "An electron is a state of a quantum field. Now take a deep breath because it will take you four years to get to the point where you will have a chance to understand what that means in detail, but they will be the best four years of your life. Are you ready?". – CuriousOne Jul 11 '15 at 08:12
  • I never said I'm taking this personally, all I'm saying is that I find it a bit hurtful that you view my effort rather critically without offering any advice on improvements, which in my opinion, is a bad combination. – phi2k Jul 11 '15 at 18:00
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    I did offer my advice and not just to you. Stop scrapbooking random footnotes of mid 19th to mid 20th century physics and start with 21st century physics in a top-down approach. – CuriousOne Jul 11 '15 at 18:27
  • @CuriousOne can you try to explain for me "state of a quantum field" in a visual way, metaphoric? – Agent Zebra Jul 29 '15 at 06:16
  • @AgentZebra CuriousOne always say his words round and round, its hard to understand him at first look. But, he really says something more sensible, which you understand later. – Anubhav Goel May 13 '16 at 02:17
  • @CuriousOne Exactly which elements of 21st century physics in a top-down approach would you start with to explain what an electron is? – Agent Zebra May 14 '16 at 06:18
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    @AgentZebra: Start with the simple notion that nobody has ever seen an electron. The picture that electrons are tiny blue balls stems from poorly conceived textbook visualizations. The idea that electrons move from A to B along some well defined path is the next thing you have to get out of your mind. Nobody has seen that, either. What we are observing is similar to the behavior of a classical field, except that the smallest possible interactions conserve quantum numbers like electrical charge. That's a quantum and since no logical path leads from quanta to particles, stick with quanta. – CuriousOne May 14 '16 at 06:30
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How to explain what an electron is to someone new to physics?

I think you can come up with an easy-reading explanation that's physically correct. There's plenty of clues in the literature if you're willing to play detective. For example see pair production. We quite literally make an electron (and a positron) out of light. And then when we annihilate the electron and the positron, we get the light back. So:

1) The electron is quite literally made from light.

Then there's things like electron diffraction. We can diffract electrons, just like we can diffract light. We can also diffract neutrons, and buckyballs. We can also refract electrons, see The Refractive Index in Electron Optics and the Principles of Dynamics. That's the paper that predicted what's now known as the Aharonov-Bohm effect. The wave nature of matter is not in doubt. So:

2) The electron is definitely a wave.

After that we have things like Goudsmit and the discovery of electron spin: "But don't you see what this implies? It means that there is a fourth degree of freedom for the electron. It means that the electron has a spin, that it rotates". On top of that there's the Einstein-de Haas effect which " demonstrates that spin angular momentum is indeed of the same nature as the angular momentum of rotating bodies as conceived in classical mechanics". So:

3) The electron is an electromagnetic wave going round and round.

And then of course we talk about Dirac's belt wherein "a Möbius strip is reminiscent of spin-1/2 particles in quantum mechanics, since such particles must be rotated through two complete rotations in order to be restored to their original state". We also talk about spinors, which we similarly depict, with a chirality. And then in atomic orbitals the electrons "do not orbit the nucleus in the sense of a planet orbiting the sun, but instead exist as standing waves". And of course when we're referring to atomic orbitals we talk of spherical harmonics. And there's also topological quantum field theory which is related to knot theory. So:

4) The electron is a 511keV electromagnetic wave going round and round in a knot-like stable spherical spin-½ spinor configuration, such that the field-variation propagating at c now looks like an all-round standing field. Standing wave, standing field. In its simplest guise within an atom we call it an S-orbital, which is depicted below:

enter image description here © Copyright 2010 Encyclopaedia Britannica

It's important to note that a standing wave is a wave which appears to be motionless, when actually it isn't. If you have a standing wave in a cavity, when you "open the box" the wave is off like a shot from a standing start, because it wasn't really standing. It's the same for electron-positron annihilation to gamma photons. And to visualize the electron wave motion, see the "spindle sphere torus" below, courtesy of Adrian Rossiter's torus animations.

enter image description here

John Duffield
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