# Physics of Electron Probability Clouds

• nuby
In summary, the conversation discusses the concept of the electron "smear" or probability cloud and its physical meaning. The probability cloud refers to the probability density of measuring the electron's position at a specific time, and does not indicate its motion. The idea of an electron traveling faster than time or through time differently than regular matter is considered meaningless and inaccurate. The concept of an electron being in multiple locations at once is also not an accurate description. The conversation also touches on the difficulty of picturing the motion of an electron and how it is modeled in different contexts, such as in particle accelerators or in quantum mechanics.
nuby
Is there a physical meaning to the electron "smear" or probability cloud? If an object (electron) was to somehow travel faster than time, wouldn't it appear in multiple locations at once or as a "smear"?

Traveling "faster than time" is meaningless.

Ok, switch "faster than time" with "through time differently than regular matter".

That makes even less sense.

That makes even less sense.
C'mon.. Is my question that hard to comprehend?

Yes, it is, because it really doesn't make sense.

The probability "cloud" you speak of refers to the probability density of measuring the electron's position to be at that point, at a specific time. There is no reference to its motion.

What does "faster than time" or "through time differently than regular matter" mean? Seriously?

nuby said:
Ok, switch "faster than time" with "through time differently than regular matter".

What do you think "regular matter" is made from? :)

Yes, it is, because it really doesn't make sense.

The probability "cloud" you speak of refers to the probability density of measuring the electron's position to be at that point, at a specific time. There is no reference to its motion.

What does "faster than time" or "through time differently than regular matter" mean? Seriously?

I was referring to the concept that an electron (singularity) within a atomic orbit is "everywhere at once" around the nucleus. Is this not correct?

Dmitry67 said:
What do you think "regular matter" is made from? :)
I guess I should have said composite particles. But those are probably just as irregular as electrons.

I don't know if an electron in orbit is considered "everywhere at once". I think what is meant that, if you would measure the position of the electron, you could find it anywhere (even on the moon), but the chance of finding it near the atom it's orbiting around is much much much larger. The 'electron smear' is just the probability wavefunction that tells you the chance of finding an electron at a certain position. Where it was before you measured it isn't really a sensical question, because you would have to measure it to know where it was before you measured it, so you have to measure it before you measure it before you ... etc :p

So considering an electron in multiple locations at once isn't an accurate description of the actual electron/shell.

By "the electron traveling faster than light" do you mean that the expectation value of the electrons position, according to the underlying probability distribution function (PDF), is moving faster than light? Or are you thinking of the electron as really just non quantum mechanical object shaking and moving around in circles, ... at very high speeds > c and trying to use that as a way to interpret quantum mechanical (statistical) effects?

nuby said:
So considering an electron in multiple locations at once isn't an accurate description of the actual electron/shell.

I don't see why that wouldn't be a good way to look upon it ? (at least, that's how I look upon it)

Hi Peeps,
I'm new to this forum and self study QM. This thread raises an interesting question for me. How does science picture say an electron traveling in a straight line. The prob. amplitude wavepacket travels wth the velocity of the electron.! When we make make a measurement of its position , we have the probality of that result... psi ^2.! But how do we picture the electron smear traveling .? Do we picture an electron cloud with the ghostly electron smeared in it traveling withh velocity v and if so, how do we picture what happens when we measure it's position.?
I know the answer will probably be.. we can't!
BUT IT STILL PUZZLES ME ?
tHANKS!

enomanus said:
Hi Peeps,
I'm new to this forum and self study QM. This thread raises an interesting question for me. How does science picture say an electron traveling in a straight line. The prob. amplitude wavepacket travels wth the velocity of the electron.! When we make make a measurement of its position , we have the probality of that result... psi ^2.! But how do we picture the electron smear traveling .? Do we picture an electron cloud with the ghostly electron smeared in it traveling withh velocity v and if so, how do we picture what happens when we measure it's position.?
I know the answer will probably be.. we can't!
BUT IT STILL PUZZLES ME ?
tHANKS!

I work at a linear electron particle accelerator, and we model such electrons classically. All our particle tracking codes that we use to study the beam dynamics are all classical (relativistic) Maxwell equations acting on classical particles. And it WORKS!

Zz.

ZapperZ said:
I work at a linear electron particle accelerator, and we model such electrons classically. All our particle tracking codes that we use to study the beam dynamics are all classical (relativistic) Maxwell equations acting on classical particles. And it WORKS!

Zz.

enomanus said:
Hi Peeps,
I'm new to this forum and self study QM. This thread raises an interesting question for me. How does science picture say an electron traveling in a straight line. The prob. amplitude wavepacket travels wth the velocity of the electron.! When we make make a measurement of its position , we have the probality of that result... psi ^2.! But how do we picture the electron smear traveling .? Do we picture an electron cloud with the ghostly electron smeared in it traveling withh velocity v and if so, how do we picture what happens when we measure it's position.?
I know the answer will probably be.. we can't!
BUT IT STILL PUZZLES ME ?
tHANKS!

It smears in time yes. But the reason why you could look on it classically for particle accelerators (as Zz mention) is that the time is so short, since particles travels close to the speed of light (Or?).

Assume you have a Gaussian package at t0 with size a0 (standard deviation) which travels with some "average" speed v. For the free particle case the evolution of this package is easy to calculate.

$$\Psi_0=\exp\left(i\hbar k_0-(\frac{x-x_0}{a_0})^2\right)$$

the "size" a will increase in time roughly as (for more exact result use the free Green propagator):

$$a(t)=\sqrt{\frac{\hbar t}{m}-a_0^2}$$

using $$m\;v_0=\hbar k_0$$ and, total time T=L/v0, and wavelength $$\lambda=2\pi\hbar/mv_0$$ you could play around with what you get after distance L, with speed v0 and with initial smearing size a0.

Also the potentials involved in accelerators are macroscopic, i.e., the typical "size" of them are much larger than the wavelength and a0 of the electrons, so you could safely look on the electron as a point particle. But things changes if the electron hits a region with interaction distance similar to its wavelength (slit, or double-slit for example).

per.sundqvist said:
Also the potentials involved in accelerators are macroscopic, i.e., the typical "size" of them are much larger than the wavelength and a0 of the electrons, so you could safely look on the electron as a point particle. But things changes if the electron hits a region with interaction distance similar to its wavelength (slit, or double-slit for example).

Correct. Or the potential a "free electron" sees in a periodic crystal lattice. In such cases, then the classical electron model can easily break down.

Zz.

msumm21 said:
By "the electron traveling faster than light" do you mean that the expectation value of the electrons position, according to the underlying probability distribution function (PDF), is moving faster than light?

This is more relevant to what I was thinking/wonder about.

## 1. What is an electron probability cloud?

An electron probability cloud, also known as an electron orbital, is a visual representation of the likelihood of finding an electron at a specific location around the nucleus of an atom. It is a three-dimensional region of space where the electron is most likely to be found, based on its energy state.

## 2. How is the shape of an electron probability cloud determined?

The shape of an electron probability cloud is determined by the quantum numbers of the electron, which describe its energy level, orbital shape, and orientation in space. The Schrödinger equation is used to calculate the probability of finding an electron at a particular point in space, resulting in a specific shape for each orbital.

## 3. What is the significance of the electron probability cloud in chemical bonding?

The electron probability cloud is crucial in understanding chemical bonding because it determines the spatial distribution of electrons around the nucleus. As atoms come together to form molecules, their electron clouds overlap and interact, leading to the formation of chemical bonds.

## 4. Can an electron be located at any point within its probability cloud?

No, an electron cannot be located at any point within its probability cloud. The cloud represents the areas where the electron is most likely to be found, with higher probability regions being denser and lower probability regions being less dense. The exact location of an electron within its orbital cannot be determined due to the wave-like nature of electrons.

## 5. How does the electron probability cloud change with increasing energy levels?

The shape and size of the electron probability cloud change with increasing energy levels. As the energy level increases, the cloud becomes larger and more diffuse, leading to an increased probability of finding the electron further away from the nucleus. This is because higher energy levels allow the electron to occupy a larger region of space, resulting in a larger orbital.

• Quantum Physics
Replies
13
Views
2K
• Quantum Physics
Replies
21
Views
1K
• Quantum Physics
Replies
6
Views
2K
• Quantum Physics
Replies
19
Views
380
• Quantum Physics
Replies
10
Views
2K
• Quantum Physics
Replies
36
Views
2K
• Quantum Physics
Replies
4
Views
965
• Quantum Physics
Replies
14
Views
2K
• Quantum Physics
Replies
0
Views
320
• Quantum Physics
Replies
21
Views
1K