The discussion revolves around the nature of particles in and around an atom, specifically addressing the concept of an "atom's surface" and graphical representations of atoms. Participants explore theoretical and conceptual aspects of atomic structure, electron behavior, and the interpretation of atomic models.
Participants express differing views on whether the concept of electron movement is relevant to understanding atomic structure and probability distributions. There is no consensus on the interpretation of electron behavior in quantum mechanics, leading to ongoing debate.
Some participants highlight the limitations of classical models in explaining atomic structure and the necessity of quantum mechanics for a more accurate understanding. The discussion includes references to historical perspectives on atomic models and the evolution of thought regarding electron behavior.
tyogav said:What particles make up the surface of an atom?
tyogav said:When we see graphical illustrations of spherical atoms, what are we actually seeing?
You see a layer of (probably) graphene in green and some atoms are drawn as reflective spheres.tyogav said:Thank you! This is the illustration I was keeping in mind. Am I missing something fundamental? https://m.flickr.com/#/photos/uclmaps/8536981794/
tyogav said:There are many particles inside an atom.
What particles make up the surface of an atom? When we see graphical illustrations of spherical atoms, what are we actually seeing?
Delta² said:All the atoms consist of elementary particles, which elementary particles are (according to current theory) point particles, that is at a given time they occupy a single point in space. However these elementary point particles are in continuous movement, that's how we get the impression that they occupy some finite volume (like a spherical volume) in space.
ChrisVer said:It has nothing to do with motion of electrons around the atom. What they mainly show is the probability of an electron existing in some region. And the solution is static...
At low energies however, at which you can't see the structure of an atom [electrons' energy mainly], the atom can be assumed as a solid sphere... That's what people thought in the past [before rutherford's experiment]...
If the electrons didnt move at all and remain still then the probability to exist in some region would be zero except in a specific point where it would be 1.ChrisVer said:It has nothing to do with motion of electrons around the atom. What they mainly show is the probability of an electron existing in some region. And the solution is static...
Delta² said:If the electrons didnt move at all and remain still then the probability to exist in some region would be zero except in a specific point where it would be 1.
ChrisVer said:except for that is impossible [it would have definite position and momentum], I didn't say it doesn't move. I'm saying that the probability to be found in some region has nothing to do with the electron moving (which would need pictures of it for several times to cover the probability- however the probability is there at any given time... that's why I called it static)
This is an incredibly classical, and therefore incorrect, point of view. The electron's state is governed by quantum mechanics, which tells us that the electron is not occupying one position, then another. It is therefore meaningless to talk about the electron "moving." It is in a stationary state.Delta² said:How can you say "it has nothing to do with electron moving" if the electrons don't move, there is no meaning talking about the probability to be found in a region of space, the only probability tha there is , is zero everywhere except a specific point.
There is no meaning talking about uncertainty principle, wave function or probability clouds or whatever unless the electron is moving.
No, far from it. I'm talking specifically about electrons in a bound state in an atom.Delta² said:So you actually saying that particles in quantum mechanics never move?
Again, you are stuck on the idea of "moving". Teleporting would be the same as moving, but in discrete steps. What I am saying is that the electron is in many places at the same time, not jumping from one place to the next.Delta² said:They teleport from one position to another?
The thing is that an electron in an atom also doesn't have a definite momentum, it is also in a superposition of various "fast" and "slow".Delta² said:And what is the meaning of the momentum/velocity of the particle if they don't move??
ChrisVer said:You can try to calculate the "classicaly" behaved expectation value of the electron's momentum in Hydrogen atom's ground state. What you'll get will be zero... as someone expects from bound states (look at Dr Claude's post above, and the posts in the link below):
https://www.physicsforums.com/showthread.php?t=508528
DrClaude said:No, far from it. I'm talking specifically about electrons in a bound state in an atom.
Again, you are stuck on the idea of "moving". Teleporting would be the same as moving, but in discrete steps. What I am saying is that the electron is in many places at the same time, not jumping from one place to the next.
The thing is that an electron in an atom also doesn't have a definite momentum, it is also in a superposition of various "fast" and "slow".
I don't want to derail this thread, so I won't go into more details, but it's one of the important conclusion of quantum mechanics. Electrons in an atom do not orbit around the nucleus, they are in diffuse orbitals, diffuse both from the point of view of regelar space and momentum space. It seems strange from the classical/macroscopic point of view, but this is what the theory, which is very well backed by experiments, tells us.
Google for "quantum tunneling" for one of the many reasons why this model is not tenable.Delta² said:No i strongly disagree, electron is a point particle, and at a given time it occupies a single point in space and it has a definite momentum. It is just that we don't have the technology to measure with infinite degree of accuracy its position or momentum,
You are right about that, but it's also going too far to assume that the electron has a definite position within the cloud, but we just don't know what it is. It's a natural assumption, it's an almost irresistible assumption if you're thinking of particles as if they were grains of sand except much smaller, but... It's just not the way world is.way too far ahead to assume that just because the theory give us a probability cloud, this means that actually (in the physical reality) the electron occupies simultaneously all those points in the theoretical probability cloud.
It is not a measurement issue, the uncertainty is an intrinsic property of the objects. There is no way to explain the quantum-mechanical effects with particles at specific positions.*Delta² said:No i strongly disagree, electron is a point particle, and at a given time it occupies a single point in space and it has a definite momentum. It is just that we don't have the technology to measure with infinite degree of accuracy its position or momentum , the current theory says that its impossible to measure with infinite degree both of them, and we also don't have the theory to predict exactly its position or momentum. The best current theory give us is a probability cloud in which the electron lies, but you are going way too far ahead to assume that just because the theory give us a probability cloud, this means that actually (in the physical reality) the electron occupies simultaneously all those points in the theoretical probability cloud.
mfb said:It is not a measurement issue, the uncertainty is an intrinsic property of the objects. There is no way to explain the quantum-mechanical effects with particles at specific positions.*
*technical detail: The de-Broglie-Bohm theory has specific positions, but those don't do anything, the physical interactions are done by the pilot waves.
The evolution of a quantum-mechanical system is always deterministic and there are even deterministic interpretations of the application of quantum mechanics to our everyday world, but that's not the point.Delta² said:Cant be explained if we assume that the motion of the particles is not deterministic, or speaking more generally that the time evolution of a system is not deterministic?
There is no well-defined "path" a particle takes.that is, given two time intervals [t1,t1+t] and [t2,t2+t] such that all the fields of interest take exactly the same values (that is for any field E, E(t1+x)=E(t2+x) 0<x<t) and the initial momentum of particle p(t1)=p(t2) yet the path the particle takes is not the same in the two time intervals.
Whenever we do a measurement, the particle seems to be at a specific position, i suppose if we could do measurements at a sequence of times t_n=t_0+n\epsilon with ε arbitrary small it would seem that the particle has a well defined path.mfb said:.
There is no well-defined "path" a particle takes.
No, that depends on the type of measurement you do. For other measurements, the particle might have a specific momentum (but not position), or specific polarization (but not position, or momentum), or whatever.Delta² said:Whenever we do a measurement, the particle seems to be at a specific position
Making ε small will lead to an observed pattern that has nothing to do with the initial propagation of an unobserved particle - for example, you won't observe the electron bound to an atom any more if you measure its position frequent enough (with suitable methods), or you don't get double-slit patterns and so on., i suppose if we could do measurements at a sequence of times t_n=t_0+n\epsilon with ε arbitrary small it would seem that the particle has a well defined path.
But this is exactly the case. Note that there are interpretations without wave function collapses.Is there something particular in the measurement process or the measurement device that causes the particle to take a well defined path? Dont tell me welcome to the big mystery of QM, the measurement process and the wave function collapse :D.