Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Dave Thacker on 21/08/2013 17:35:42
-
How is it the sustained Orbit of an electron around a neutron does not violate conservation of energy?
Dave in Dayton Ohio.
-
How is it the sustained Orbit of an electron around a neutron does not violate conservation of energy?
Dave in Dayton Ohio.
This so-called orbit is more like a cloud of negative energy we call the electron. To describe it as an orbit is inaccurate.
-
It's not my point to make a statement. If it's a cloud and it's moving, it seems it cannot do this without consuming energy. Is there a decay process? I wish to understand. If this can go on indefinitely without decay, where is the energy coming from to sustain it?
-
There is no friction to slow the electron down, so no energy input is required to keep it moving. An object in motion will continue its motion until an external force is applied. It's analogous to a hypothetical perfectly elastic spring floating in a vacuum. If you tap the spring to get it vibrating, it will vibrate for ever. If something bumps into the vibrating spring the energy may be transferred. The total energy remains constant (unless you change the frame of reference in which the energy is measured).
The energy of photon may be absorbed by an electron, raising the electron to a higher orbital. Later, the electron may fall to a lower orbital releasing the same amount of energy that it had absorbed. If the atom absorbs more or less energy than it releases, the difference may take the form of a temperature change.
In nuclear reactions, it is conservation of mass-energy. Mass is captive energy. When energy is converted to mass, it still exists, and it may be released later in the exact same quantity. So the total of mass plus energy remains constant.
-
There is one thing though, assuming a electron would have a orbit, then it also must be accelerating, as it won't be traveling a linear path (geodesic), having one direction and a speed. And so it not only would 'not lose energy', assuming this orbit to be stable, it somehow would have to constantly gain energy as it seems to me, just to keep that stable orbit.
Quantum mechanically it is something different though. Instead of a orbit it then is called a orbital, a representation of its 'probable orbit', when thought of as a single object.
"The picture you often see of electrons as small objects circling a nucleus in well defined "orbits" is actually quite wrong. As we now understand it, the electrons aren't really at any one place at any time at all. Instead they exist as a sort of cloud. The cloud can compress to a very small space briefly if you probe it in the right way, but before that it really acts like a spread-out cloud. For example, the electron in a hydrogen atom likes to occupy a spherical volume surrounding the proton. If you think of the proton as the size of a grain of salt, then the electron cloud would have about a ten foot radius. If you probe, you'll probably find the electron somewhere in that region.
The weird thing about that cloud is that its spread in space is related to the spread of possible momenta (or velocities) of the electron. So here's the key point, which we won't pretend to explain here. The more squashed in the cloud gets, the more spread-out the range of momenta has to get. That's called Heisenberg's uncertainty principle. It could quit moving if it spread out more, but that would mean not being as near the nucleus, and having higher potential energy. Big momenta mean big kinetic energies. So the cloud can lower its potential energy by squishing in closer to the nucleus, but when it squishes in too far its kinetic energy goes up more than its potential energy goes down. So it settles at a happy medium, with the lowest possible energy, and that gives the cloud and thus the atom its size." http://van.physics.illinois.edu/qa/listing.php?id=21425
And that cloud isn't really propagating, maybe one could call that a field too.
==
The real point to me with all such descriptions is the emphasis it puts on 'probing'. We have this saying 'if a tree falls in a forrest and nobody is there to see it, did it?"
That fits the idea behind probing something very well, quantum mechanically. Before probing no one is 'there', you have only this theoretical probability of something existing, but that probability is also what guarantees that when you probe, something will be there.´A probability comes from the statistics you have on a phenomena as I think, then there are also 'laws' that you can puzzle out from that statistic you gather, but they are specific to the 'very small'.
don't seem QM use our type of 'motion' that much, as I think then. And if you think of a entanglement you find a same proposition, forget macroscopic motion for it. The weirdest thing is how to understand how a logical system avoiding our macroscopic definitions of 'motion' can create it? That one I would like to know.
-
Thank you for the wonderful replies.
If the electron (or the electron cloud) has mass, it's not in an orbit, and it's constantly moving within a range of the nucleus, it must also be changing direction. Wouldn't energy be consumed in the change of direction?
Perhaps the statement that there is no orbit in reality, only probably of location has me visualizing a paddle as the nucleus with an elastic band as the force holding them within range and a ball as the electron.
I'm quite sure I'm out of my element. ;-)
-
The Law of Conservation of energy must always take into account the elapse of time generated thru all motions. Take for example the photon. A photon of light will continue in motion eternally until it is absorbed by matter in it's pathway. However, because light travels at 186,282 miles per sec., from it's frame of reference, no time will elapse from the moment of it's creation until it becomes absorbed. No energy will be lost because; For the photon, no time has passed. It will therefore continue, in our frame of reference to move at c from one side of the universe to the other without losing energy.
Time and motion are inextricably tied one to the other. So one must ask; If no time has elapsed for the photon, has the photon really moved from point A to point B, or has the space between point A and B only collapsed.
Very curious indeed!
-
If an electron accelerates, it must absorb or emit radiation. So clearly the electrons in an unexcited atom aren't actually moving in an orbit or anything else. The orbit description gives us a mathematical handle on some of the properties of an atom but an atom is not a macroscopic, classical, Newtonian entity.
A lot of confusion arises when people assume that a useful model of one property can be accurately extrapolated to other properties. Hence the "wave/particle duality" problem: light is not a wave or a particle, but can be best modelled as one or the other according to the interaction we are trying to analyse. For most purposes a free electron is best modelled as a particle since it has mass, charge, momentum, and all the rest, but the position of a bound electron is best modelled as a wave function that describes the probability density of the electron in space. Just to make it more complicated, of course, the binding energy is quantised so the orbital "cloud", although it looks like a continuum, isn't!
The "paddle and ball" model is interesting but it suggests that the electron can collide with the nucleus. Obviously if that happened, the atom would collapse. The fact that atoms have a finite radius is all down to the most fundamental property of all - the indeterminacy (I dislike the word uncertainty - all sorts of wrong implications) principle that asserts that a particle cannot have a definite position and momentum at the same time.
-
So sweet and logical Alan :)
"If an electron accelerates, it must absorb or emit radiation. So clearly the electrons in an unexcited atom aren't actually moving in an orbit or anything else."
That one is a pearl.
-
Yeah, indeterminacy. The word that really means something.. It's what I believe QM is about. And it's a 'law' not an idea.
-
If you cool an atom to almost absolute zero, the electron(s) fall into the "ground state (http://en.wikipedia.org/wiki/Electron_configuration#Energy_.E2.80.94_ground_state_and_excited_states)", which is the state of lowest energy. Quantum theory doesn't permit the electrons to get into a lower energy state, so they remain in the ground state, and energy is conserved.
One quantum oddity is that no two electrons can share the same orbital state, which in an isolated atom, means that additional electrons must stack up in higher orbitals. In a solid, this extends to all electrons in the object, so in this environment, electrons don't have a specific energy, but a range of energies. This is due to the Pauli exclusion principle (http://en.wikipedia.org/wiki/Pauli_exclusion_principle#Solid_state_properties_and_the_Pauli_principle).
-
"Time and motion are inextricably tied one to the other. So one must ask; If no time has elapsed for the photon, has the photon really moved from point A to point B, or has the space between point A and B only collapsed. "
Can the existence of a photon be measured without hindering it's passage? If not I wouldn't it be possible the photon is information existing only at the point of emission and absorption?
Ok, I'm sure I've fallen out of the boat now.
Dave
-
Can the existence of a photon be measured without hindering it's passage?
From all the information I've ever seen,...............No.