Probably a stupid question, but what is the engine or mechanism that keeps an electron moving?
I’ve read that atoms are essentially forever, so I’m assuming so are their electrons. They have mass, so are the ones here on earth affected by gravity/friction?
We are taught in physics class that electrons and some other elementary particles have spin, but clearly they are not literally tiny tops that will eventually run down due to friction.
“What keeps them moving?” is the wrong question. The better question would be “what stops them?”, to which the answer is “nothing”. Since nothing stops them, they keep moving.
One possible response is indeed to say that this is a naive question, and you are taking the simplistic “orbiting electron” model of the atom too far - it just doesn’t work like this.
But a similar question was important in the history of the modern understanding of the atom. An early idea was that the speed of the electron exactly balances the attraction between the electron and the nucleus, so that it moves in an orbit - just like a satellite orbiting the Earth. But it was soon realized that this cannot be right, because when a charged particle is accelerated (as it would be constantly in an orbit) it emits electromagnetic radiation, thus losing energy. So under this model the electron would rapidly spiral into the nucleus.
This was one of the problems that ultimately led to the development of quantum mechanics.
Yep. Planetary orbits radiate gravitational waves, which also would lead to the orbit losing energy, but gravity is weak, and planets orbit slowly - for electrons, the collapse of orbits would take place almost instantly from a human point of view (less than a billionth of a second), while planetary orbits last a long long time from a human POV (much longer than a billion years)…
Worth mentioning to be really pedantic, you can get free electrons quite easily. These move about and are affected by external forces just like any other particle. Your old school TV or computer monitor operated with free electrons being accelerated by a mix of electrostatic and magnetic forces. Since electrons repel one another, getting a cloud of them in one place is painful, but they hang around if allowed to. In vacuum tubes they have a habit of doing so. Very slow moving electrons can form what was termed the space charge in the middle of the tube, disrupting operation. The Penning Trap can isolate a cloud of electrons. They are still moving about in the trap however.
With a bit of care you can take a free electron and drive it to a near stationary state in an optical trap. That is perhaps as close as one can get to a still electron.
As noted above, what stops electrons from stopping when part of an atom is quantum mechanics, and an inability to shed or gain energy in anything but defined lumps. Moreover they can’t shed energy to fall into a state occupied by another electron, so there are defined minimum energy states that they cannot lose energy from. So they continue to orbit.
You might be able to collect electrons in a mason jar. From a post I made several years ago:
Not a stupid question, but ambiguously posed. All the important details of what I’m now writing has already been mentioned in the thread, but I think a summary would be good.
All electrons are affected by gravity and by electromagnetic forces. “Friction” as we think of it at the macroscopic level doesn’t have much meaning at the levels of electrons, but electromagnetic forces between molecules are a big part of macroscopic friction, so sure, electrons are affected by friction.
The ambiguity of your question lies in whether you meant electrons in the air, in wires or “orbiting in an atom”. In general, though, electrons, like anything else, obey Newton’s second law of motion and keep moving at the same velocity except when a force (gravity or electromagnetism) works on them to cause acceleration.
The “exception” to this is for electrons orbiting in atoms. As Riemann pointed, our early models of the atom had the electron orbiting under electromagnetic force the same way planets do under gravity. This model predicted things like energy levels of the Hydrogen atom well, but required a “they just don’t” explanation for why the circling charges didn’t constantly radiate energy and spiral into the nucleus. And then quantum mechanics fixed this while at the same time making the behavior of electrons bound to atoms rather incomprehensible.
Move an electron through a vacuum or a rarefied gas though and it behaves just like any other particle with mass and charge.
AIUI even “free” electrons have intrinsic angular momentum. Even though eg the Stern–Gerlach experiment used atoms.
Okay, what starts them?
For atoms (which I think this question is about, as electricity, plasmas, etc… are very different). They get started same way planet orbits do.
Imagine you have an atomic nucleus and and electron placed some distance apart (larger than an orbit). Even if both are stationary (as much as this has meaning in quantum mechanics), they will be attracted and the electron will “fall” towards the nucleus and gain energy. The electron might bleed off energy by emitting light. If the electron looses enough energy it will wind up in orbit around the nucleus (in a quantum mechanical sense, not an actual orbit). If the electron were to loose ALL energy, it would come to a stop relative to the nucleus. However, solving Schrodinger equation shows that it is impossible for an electron to loose all its energy; there is a minimum non-zero sized orbit.
Energies were too high for electrons to even exist until about 1 second after the big bang. And energies were too high for the electrons to be bound to nuclei and form atoms until 379,000 years after the big bang. So given these starting conditions, it was really a question of how long it took electrons to “slow down” enough to form atoms. The evidence for all this is strong, we are very sure about everything that happened from a short time after the big bang.
Your question then reduces to - how did the big bang conditions come about. This we don’t know, but the consensus theory is cosmic inflation.
Inflation (cosmology) - Wikipedia
It becomes more difficult to offer any kind of satisfactory intuitive explanation here, but the usual explanation of “where the energy came from” is that the hypothesized inflaton field that drives cosmic inflation gives rise to a universe in which the positive energy of the contents of the universe is offset by negative gravitational potential energy, making the arithmetic of conservation of energy work out.
Thank you. Perhaps when I retire I’ll have time to read up on this stuff. It is really fascinating.
[Personally, I can’t even wrap my head around how a battery charger actually gets all the electrons to where they need to be]
AIUI, electrons have little cute propellers. The propellers are electric-powered, and since electrons have charge by definition, they never run out of power.
It might seem obvious to you, but as I hinted at in the OP, I’m a little ignorant on this subject.
If I throw a baseball while out in space, it goes on forever - there is nothing to stop it. But if I throw one here on earth it stops rather quickly. Partly, that is due to earth’s gravity. That is why I wondered if the mass of an electron is affected by earths gravity.
One of the things the SDMB has taught is “There is such a thing as a stupid question”. However, your question is definitely not one of them. More, I’m glad you asked it because reading this thread has been very educational. I don’t know as much about physics as I’d like or feel I should know. I’d also like to know a bunch more about electricity and electronics. I can make some minor repairs and use a multimeter a bit. I hunger to know more.
Francis_Vaughan I miss cathode ray tube displays. Sure, LED displays are more energy efficient, weigh a lot less, and take up less space. But, do they react to magnets in fun ways? No! Can you in actual practice crack iron lawn furniture with an LED screen without breaking the front of the screen? No! Can you get weird colors by adjusting dials inside an LED screen? No!
You can have my Cathode Ray Tube when you pry it from my cold, dead hands!
A baseball is made of electrons, protons & neutrons. They all have gravitational mass, although the electron is much lighter. I’m not quite sure what you’re asking here. When gravity acts on a baseball, it’s acting on all these constituent particles, and they are all accelerated together. But gravity has nothing to do with the structure of an atom.
I think I might actually be able to help. Newton’s laws work great- unless you get near light speed or get down to quantum scale. At light speed, relativity mostly explains things. At a quantum scale things just get very mathematical and confusing.
Nah, gravity has nothing to do with it. The problem is just friction, of various sorts. But friction is just the result of a whole bunch of microscopic forces added together. At the scale of a single electron, you don’t get that.
Well, it does in the sense that the ball hits the ground. But I’m not really sure what OP is asking here.