Quantum leap of electrons...

[PaulMuaddib]

I'm not an expert in physics, but I was reading the "Dancing Wu Li Masters"
which discusses quantum physics....

 

I have a question about the quantum leap of electrons from one orbit (or
state) to another.

 

To quote an explanation off the web...

The "quantum". When the electron makes a quantum leap, it suddenlychanges not only its orbit, but also its energy. In doing that, it
Emits a burst of light. Technically speaking, it emists a packet of electromagnetic Waves. This packet, this burst, is called a "quantum." The
quantum of light is called a photon.

 

OK....so the electron emits a quantum packet of energy (a photon) when it
makes a quantum leap to a lower orbit, or absorbs it when it makes a leap to a
higher orbit (or a higher state of energy).

 

My question is this : if the electron is emitting/absorbing a quantum packet of energy as it moves from orbit to orbit.

 

This would seem to imply that the electron is not "moving" in the traditional sense, like a bowling bowl at the top of a hill, rolling down to the bottom.

 

It would seem to imply that it is disappearing from one orbit and reappearing elsewhere in another orbit, if it were transitioning like a bowling bowl at the
top of a hill to the bottom that would imply that the energy was also transitioning in a continuous (non-quantum) way as well, but this does not
happen with the energy released/absorbed.

 

It is released/absorbed in packets.....thus the movement of the electron is also quantumized.....which would mean it doesn't "move" in a continuous manner
from orbit to orbit but disappears from one orbit and re-appears in another orbit.

 

Is this correct?

 

In other words, it is not like when a satellite in a higher orbit dropping down (in a continious fashion) to a lower orbit, but it's more like a space station blinking out of a higher orbit into a lower orbit.

 

 

[elfmotat]

Your analysis is correct. Electrons are only "allowed" to occupy a discrete (i.e. not continuous) number of energy levels, E₁, E₂, E₃, etc. They aren't allowed to have energies in between any of those values. This is definitely very different from the way classical objects behave, like your bowling ball example.

[swansont]

You're also correct that there is no classical trajectory involved.

[PaulMuaddib]

I thougt maybe I was thinking about it wrong because it is so contrary to what we experience on the "macro" level of existance.

[swansont]

I thougt maybe I was thinking about it wrong because it is so contrary to what we experience on the "macro" level of existance.

 

One of the reasons quantum physics seems so strange is because many classical/macro notions don't apply.

[Enthalpy]

Your analysis is correct. Electrons are only "allowed" to occupy a discrete (i.e. not continuous) number of energy levels, E₁, E₂, E₃, etc. They aren't allowed to have energies in between any of those values. This is definitely very different from the way classical objects behave, like your bowling ball example.

Discrete energies are for the stationary (=non-evolving) states only.

 

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PaulMuaddib: "When the electron makes a quantum leap, it suddenly changes not only its orbit, but also its energy. In doing that, it emits a burst of light." [Emphasis by Enthalpy]

 

We have no means to know if the change is sudden. The (proton) transition that emits radiowaves at 21cm wavelengths to the delight of radioastronomers takes many years to happen. But if we try to determine if the emitting atom is in the old, the new or an intermediate state, we get a binary answer. As we observe many atoms, we get a statistical answer, hence the "many years". If we observe the emitted photons, we can detect them over a short time, but our receivers are more sensitive if observing them over hours. Other transitions take <1fs.

 

==========================================================================================

 

PaulMuaddib: "[it seems that the electron] is disappearing from one orbit and reappearing elsewhere in another orbit"

 

An electron is not "in" an orbit. An electron is a wave that occupies some volume, has some energy, momentum... This wave is called an orbital when the electron is trapped around a nucleus.

 

http://winter.group.shef.ac.uk/orbitron/

 

During a transition, the wave is a combination of the old and the new orbital. While the orbitals are stationary and don't emit light, their combination evolves over time, at a frequency equal to the difference of energy between the orbitals. Better: this evolution over time is a wobble of the charged electron, at the frequency of the might emitted or absorbed, which is perfectly similar to an antenna radiation.

 

The tricky part of the quantum process is that you can detect the emitted photon over a short time (though with a smaller probability) and it will have its full energy.

Edited January 28, 2013 by Enthalpy

[swansont]

Discrete energies are for the stationary (=non-evolving) states only.

 

==========================================================================================

PaulMuaddib: "When the electron makes a quantum leap, it suddenly changes not only its orbit, but also its energy. In doing that, it emits a burst of light." [Emphasis by Enthalpy]

 

We have no means to know if the change is sudden. The (proton) transition that emits radiowaves at 21cm wavelengths to the delight of radioastronomers takes many years to happen. But if we try to determine if the emitting atom is in the old, the new or an intermediate state, we get a binary answer. As we observe many atoms, we get a statistical answer, hence the "many years". If we observe the emitted photons, we can detect them over a short time, but our receivers are more sensitive if observing them over hours. Other transitions take <1fs.

 

The lifetime of the state is not the same as the duration of the transition. As you say, if you probe the atom, you get one of two answers. But you can test to see how quickly the transition occurs. For the transition in Hydrogen you describe, you can induce this in a maser. That particular interaction cannot take years.

[Enthalpy]

The transition gets faster, and equivalently the excited state's lifetime shorter, because it's a maser, that is, a stimulated emission. Both the cavity and the number of coupled molecules reduce the time.

 

How would you tell the transition duration from the lifetime? I mean, between just two states, old and new. Being unable to tell better than "it's in the old state" or "it's in the new one" I can't imagine a way to distinguish both times.

[SamBridge]

I think the reason the change is sudden is because that's how it's mathematically modeled, or not to say math causes things itself, but it happens because it isn't a real movement, it's simply a correlation, and not a causation. There is nothing "causing" the electron to jump, as soon as it posses more energy, it's probability instantly correlates to different coordinates. If I say 1+1=2 that correlation is always true and it does not take time to be true, similarly it does not take time for the square of the probability amplitude of an electron to have the the probability they have at different distances from the nucleus, it's just a correlation that is true.

[swansont]

The transition gets faster, and equivalently the excited state's lifetime shorter, because it's a maser, that is, a stimulated emission. Both the cavity and the number of coupled molecules reduce the time.

 

How would you tell the transition duration from the lifetime? I mean, between just two states, old and new. Being unable to tell better than "it's in the old state" or "it's in the new one" I can't imagine a way to distinguish both times.

OK, simple absorption then. You can bombard the atoms with a pulse of radiation and subsequently measure that some are in the excited state. That transition cannot have taken longer than the time the atoms were exposed.

[Enthalpy]

In the absorption over a short time, it's the measure that lets atoms decide in which state they are.

 

I can' tell a means to distinguish a "transition" from the change between old and new state, and have no other means to tell a change has occurred than measuring it, then it determines itself.

 

The mathematical modelling of wave theory tells only a superposition of two states, with the probability varying over time from old to new, corresponding to a weighted sum of both waves. I see no reason to imagine a shorter transition between both, as this is not observable - or is it? Unless I get convinced with some means of observing it, I stick to weighted sum of waves.

 

The absorption of a short bunch of radiation is the same reason why photons were introduced: the observation is binary despite light being a wave, that is, a photon is absorbed or not.

[PaulMuaddib]

In the book it mentioned how an electron path through a photographic medium was not a continous line, but a series of dots....

 

This seems to indicate that the electron (wave/partilcle) has a discrete existance of sorts?

[SamBridge]

In the book it mentioned how an electron path through a photographic medium was not a continous line, but a series of dots....

 

This seems to indicate that the electron (wave/partilcle) has a discrete existance of sorts?

Well the electron path can be described of not as dots but as Feynman paths which involve a summation of the different phases an electron can posses, which are extrapolated by what you'd expect the particle to have in order to localize the probability to a region that travels over time. The dots most likely represent measurements of the particle and not the path.

Edited February 1, 2013 by SamBridge

[Enthalpy]

In the book it mentioned how an electron path through a photographic medium was not a continous line, but a series of dots....

 

This seems to indicate that the electron (wave/partilcle) has a discrete existance of sorts?

 

If the electron has a good energy, like a beta ray, it has a trajectory in the classical sense. Not a straight one because of shocks. The photo medium's behaviour can be to react only at some points.