The Electron's First Spin: An Overview

[faiziqb12]

Homework Statement

i was recently talking about uniform circular motion on the forum
and i got a question which i need not be solved using quantum mechanics and bla bla
but i just want an simple overview of it
my question is:
how did the electron the first time start spinning around an atom?
and if it does not spin then what it does? and how did it do the first time what it does?

 

[mfb]

An electron can be captured by an atom - it emits a photon ("light") and reaches a bound state in the atom. Understanding the details needs some knowledge of quantum mechanics.
The electrons do not "spin" in the classical sense. They are more like a static cloud around the nucleus.

 

[faiziqb12]

An electron can be captured by an atom - it emits a photon ("light") and reaches a bound state in the atom. Understanding the details needs some knowledge of quantum mechanics.
The electrons do not "spin" in the classical sense. They are more like a static cloud around the nucleus.

does it mean that they don't change their position

 

[faiziqb12]

and is there any uniform circular motion taking place inside the atom

 

[Nugatory]

and is there any uniform circular motion taking place inside the atom

There is not. The bound electron does not have even have a position (as we usually understand the word "position") so it makes no sense to talk of of it moving or not moving.

 

[faiziqb12]

does not have even have a position

yes i have heard from somewhere that a electron exists in more than one position at a time in quantum mechanics
is that true? if yes how is that possible?

 

[mfb]

"How" questions on a fundamental level cannot be answered. We can describe the universe with models like quantum mechanics, but this does not give a fundamental "explanation".

 

[Nugatory]

yes i have heard from somewhere that a electron exists in more than one position at a time in quantum mechanics
is that true?

No, the electron does not exist in more than one position at a time - that's a common but very misleading misdescription of what's going on..

The electron doesn't have any position at all except at the moment that we measure it, the same way that I don't have a fist except when I curl my fingers. It's not in several places at once, it's not in one place but we don't know where, it really has no position.

 

[faiziqb12]

"How" questions on a fundamental level cannot be answered. We can describe the universe with models like quantum mechanics, but this does not give a fundamental "explanation".

i don't want any fundamental explanation
u can use quantum mechanics or anything ..

 

[bhobba]

yes i have heard from somewhere that a electron exists in more than one position at a time in quantum mechanics
is that true? if yes how is that possible?

No - or rather that's one of a number of conjectures about it - but not one generally found in the professional literature.

Whenever it is observed it is only ever found in a single position. When not observed like bound to a hydrogen atom the theory is silent on it.

I think the following is the best way of looking at QM:
http://www.scottaaronson.com/democritus/lec9.html

If your math background makes that a bit difficult to follow don't worry - just try and get the gist.

Thanks
Bill

 

[faiziqb12]

it really has no position.

if it doesn't have a position then how does it exist

 

[bhobba]

if it doesn't have a position then how does it exist

That's the 64 million dollar question isn't it. To answer that you need to first be clear what exists mean. Philosophers argue about that sort of thing all the time and never reach a conclusion. Physics divorced itself from philosophy centuries ago without going into why. By forum rules we don't discuss philosophy here. These days its usual to take a very simple view - reality is what our theories describe. If its silent on position then its just the way nature is.

Thanks
Bill

 

[tms]

if it doesn't have a position then how does it exist

As you were told above, physics does not answer questions about how something happens.

When considering quantum phenomena, it is best to discard any and all expectations you have based on the macroscopic world you see around you. Trying to find everyday analogies for quantum phenomena will at best mislead you, and will probably totally confuse you. The rules of the quantum world are very different from the rules of the macroscopic world; the sooner you accept that, the better off you will be.

 

[faiziqb12]

As you were told above, physics does not answer questions about how something happens.
When considering quantum phenomena, it is best to discard any and all expectations you have based on the macroscopic world you see around you. Trying to find everyday analogies for quantum phenomena will at best mislead you, and will probably totally confuse you. The rules of the quantum world are very different from the rules of the macroscopic world; the sooner you accept that, the better off you will be.

well i have not reached quantum physics yet.
the way i will reach there i will inform you that yes evrerything can be understood to the deepest level..

 

[bahamagreen]

if it doesn't have a position then how does it exist

That question is a "classical thinking" question asking about quantum thinking. Before people thought classically, there was mythical thinking, magical thinking, and someone asking a question from that perspective might not make enough sense to be answered from the classical perspective. Classical questions don't quite work with quantum answers.
The thinking of the modern physicists avoids unnecessary assumptions, especially the foundational assumptions of classical thinking (that things and their attributes exist independently, that the behaviors of these things are mechanical/dynamical, and that the relationships among these things are causal), and certainly avoids the mythical magical thinking of the old past.
The quantum account for these things (the math) seems to provide the predictions from experimental preparations quite happily without the classical concepts... which is fascinating and somewhat disorienting for the classically thinking world (still virtually everyone) learning that the casually observed world we know may be based on something entirely different.

 

[CWatters]

if it doesn't have a position then how does it exist

I can't really claim to be an expert on all things quantum but..

Electrons are quantum objects which are definitely weird. Normally if an object is moving it's no good just knowing it's position you also need to know when it was in that position and it's velocity so you can work out where it is "now". If you take a picture of a moving car at time T you only know where it was at time T not where it is "now". To know where it is "now" you also have to know how fast it was going and how long ago the picture was taken.

The problem with quantum objects is that the maths says you can't know both the objects position and velocity (actually momentum) exactly. The more you try and know it's position the more uncertainty there is over it's velocity/momentum. If the car was a quantum object the faster you set the shutter to try and "freeze frame" the position of the car the less accurately you would know it's velocity. That would make your calculation of it's position "now" even less accurate. At best you can draw a graph of the probability of it being in any particular position.

I might be wrong but I think it's even worse than that. It's not just that the position is unknown but that it can be in all positions under the graph at once.

 

[faiziqb12]

I can't really claim to be an expert on all things quantum but..

Electrons are quantum objects which are definitely weird. Normally if an object is moving it's no good just knowing it's position you also need to know when it was in that position and it's velocity so you can work out where it is "now". If you take a picture of a moving car at time T you only know where it was at time T not where it is "now". To know where it is "now" you also have to know how fast it was going and how long ago the picture was taken.

The problem with quantum objects is that the maths says you can't know both the objects position and velocity (actually momentum) exactly. The more you try and know it's position the more uncertainty there is over it's velocity/momentum. If the car was a quantum object the faster you set the shutter to try and "freeze frame" the position of the car the less accurately you would know it's velocity. That would make your calculation of it's position "now" even less accurate. At best you can draw a graph of the probability of it being in any particular position.

I might be wrong but I think it's even worse than that. It's not just that the position is unknown but that it can be in all positions under the graph at once.

i am not saying whether where is its position
i was asking if it had a position or not..
as nugatry said it had no position then how did it exist

 

[mfb]

It exists - obviously, we can detect it.
The question "where exactly is it" is meaningless. It is not a classical object. You can still say "it is bound to this atom", and give the probability density to measure it at some specific location if you measure the location.

 

[faiziqb12]

It exists - obviously, we can detect it.
The question "where exactly is it" is meaningless. It is not a classical object. You can still say "it is bound to this atom", and give the probability density to measure it at some specific location if you measure the location.

i agree but the thing that it exists and doesn't have any position is absolutely meaningless

 

[bhobba]

i agree but the thing that it exists and doesn't have any position is absolutely meaningless

That classical intuition you nave developed here in the classical world will hold you back in QM. Let go. Once you do that you will find progress in understanding QM will be swift. Until you do you will be mired in confusion. If you don't - and some people never do - then you will be like the promising student a professor asked about. He was told he wanted to sort QM out - all knew he was lost.

Thanks
Bill

 

[atyy]

i agree but the thing that it exists and doesn't have any position is absolutely meaningless

Yes, that is a good way to start (but not to end). One way to think about the wave function is that it is meaningless, and we just blindly use it to predict what we observe. We don't understand what reality it represents, but it works. As Niels Bohr said, "There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about Nature."

Ok, it works fantastically, But many physicists including some of the best like Dirac have said that this is not completely satisfactory. The first plausible attempt to explain the reality underlying quantum mechanics was Bohmian Mechanics, in which the electron does have a position. However, we don't know how to extend Bohmian Mechanics to cover all of quantum mechanics, so this is a matter of research at the moment. Another famous attempt is the Many-Worlds interpretation.

Edit: An amusing guest post by Anton Garrett at Peter Coles's blog: https://telescoper.wordpress.com/2015/08/03/guest-post-hidden-variables-just-a-little-shy/

 

[S.B]

An electron can be captured by an atom - it emits a photon ("light") and reaches a bound state in the atom. Understanding the details needs some knowledge of quantum mechanics.
The electrons do not "spin" in the classical sense. They are more like a static cloud around the nucleus.

absolute truth. nothing to cotradict. but the amazing part is that how electrons were created? waiting for the views

 

[bhobba]

absolute truth. nothing to cotradict. but the amazing part is that how electrons were created? waiting for the views

Electrons are excitations of the quantum electron field. So your question really is - why is there a quantum electron field. That we do not know.

Thanks
Bill

 

[David Welsh]

I favor the wave structure of matter theory, space being an active entity and not inert. What is a field?

 

[mfb]

I favor the wave structure of matter theory, space being an active entity and not inert. What is a field?

A concept in quantum field theory. A theory that makes thousands of testable predictions, all in agreement with experiments. This is not a matter of taste.

 

[tadchem]

The bane of theoretical physics is the equivocation that arises when we are trying to communicate novel ideas but the only words we have were coined for older ideas that may be similar, but not identical to the new ideas.
The electron is NOT a particle, nor a wave, nor a wave function. It is simply an electron.
By studying the electron we find that it interacts with other 'things' (electrons, protons, atoms, fields, etc.) in ways that we can describe mathematically using equations that are identical in form to equations we use to describe other things and their interactions.
When we say 'the electron is a particle' what we really mean is 'the electron is LIKE a particle.' We feel comfortable saying that because we can use the same mathematics to describe theoretical particles (the legendary spherical cow, for example) and to describe certain aspects of the ways the electron interacts with other things.
The 'properties' we ascribe to electrons (mass, spin, charge, magnetic moment, etc.) are things we feel competent to describe with mathematical exactness, even though they may be mutually incompatible (i.e. diameter and wavelength), that mimic what we observe in the interactions of the electron with other 'things'.
Never mistake your models for reality.
Analogies are like ropes, they tie things together reasonably well, but there are limits to how far you can push them.

 

[Feeble Wonk]

i agree but the thing that it exists and doesn't have any position is absolutely meaningless

This is exactly what your take away understanding from this should be faiziqb... The mental image that you have regarding physical "existence" is not accurate. The electron is not an incredibly small piece of something that has to have a location to exist. None of the fundamental particles are (unless we accept the Bohmian interpretation).

The electron is NOT a particle, nor a wave, nor a wave function. It is simply an electron.

Tadchem said it well. The electron is what it is. Physics can not tell you "what" it is, but it can give you a very good idea of what it's NOT... and it's NOT a hard little particle. The quarks that make up the protons and neutrons in the atomic nucleus are also NOT hard little particles. Physical existence, as a whole, is NOT a distribution of hard little particles flying around in a continuous fashion doing what they do.

You've got to let that general concept go.

 

[S.B]

Electrons are excitations of the quantum electron field. So your question really is - why is there a quantum electron field. That we do not know.

Thanks
Bill

true, and there exists the true toil of quantum physics.. we always lack the knowledge about self

 

[bhobba]

true, and there exists the true toil of quantum physics.. we always lack the knowledge about self

I have zero idea what self has to do with anything.

Thanks
Bill