Armed Polite Society
Main Forums => The Roundtable => Topic started by: drewtam on August 14, 2012, 11:30:28 PM
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why does an electron and proton prefer to create a hydrogen atom, rather than diving right in to form a neutron?
why does an electron (a lepton with no quarks) interact at all with a proton (a hadron with inseparable quarks)? On the surface it makes sense, negative + positive = neutron. But the at the deeper quark vs lepton level, it doesn't seem to fit.
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Sounds like you need to brush up on your quantum string theory
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Or just connect the turboencabulator to the flux capacimator.
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Or just connect the turboencabulator to the flux capacimator.
You have to excommunicate the discombobulator first, or it'll never work.
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I don't know the answer to your question. My knowledge of how the world works ends at subatomic theory taught in chemistry.
I am curious what the answer is though!
ETA: This might help! http://www.physicsforums.com/showthread.php?t=5979
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(another "I'm wasted" post)
I think your too hung up on "charges". (I.E. +1 + -1 = 0)
The thing about sub, sub, atomic particles that they are just that, just another layer of building blocks. A lepton is a lepton, and a hadron is a hadron, charges are a resultant property.
(this post brought to you by Bacardi :angel: )
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why does an electron and proton prefer to create a hydrogen atom, rather than diving right in to form a neutron?
Because hydrogen is cool.....like fezs & bow ties.....
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Quantum mechanics and Neils Bohr to the rescue.
The electron can only exist at certain orbitals, which are not even really "orbits", like planets around stars, like we see in simplified atomic diagrams, more like spherical shells, torioids, blobs, or teardrop-shaped lobes of probability due to the Heisenberg uncertainty principle, but I digress... because of it's wave function. The electron has this wave function due to one of the other tenents of quantum physics, the wave/particle duality. Look up the famous "quantum two slit experiment" for an explanation of this. Well, not really an explanation as to why particle/wave duality exists, but convincing proof that it indeed does. [tinfoil]
One can even do this experiment at home with a laser pointer and some razor slits in cardboard if they want, and while that's exploring wave/particle duality for photons rather than electrons, the results if you set up a CRT tube with a metal plate with slits in between the electron gun and the phosphor screen end will also be the same...
Electrons don't "orbit" the nucleus in the way macro scale objects orbit under a balance of their gravity, and forward momentum in Newtonian physics, or how they really do, by following a shortest path through bent space-time on a like they do under Einstein. The oribtals the electron chooses correspond to certain multiples of the electron's natural wave function, and it can't exist around the proton at the Hydrogen atom's nucleus in any other place, which is what prevents it from crashing into the proton under the attraction of their charges. And this is why electrons also make quantum jumps instantaneously between their various allowed orbitals, absorbing, or giving off very specific quanta of light as they do so, because there's no complete multiple of their wave function that allows them to exist "in between", so they simply don't.
Just another example of how "rational" intuitive knowledge of Newtonian physics at the human macro-scale of how stuff moves and behaves is useless at the sub-atomic/quantum level. =D
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It CAN happen (inverse beta decay or electron capture). But if it's with a free electron, the cross section is REALLY small. Basically the issue is this, a proton with a bound electron is an energy minima (ie, capture of an electron to form a hydrogen atom is exothermic, the energy is released as a photon) while a proton capturing an electron to form a neutron is endothermic (and requires emission of a neutrino for spin and momentum conservation), which is why electron capture is a mode of radioactive decay (ie a higher energy nucleus decaying to a lower energy state). Since the electron needs to supply energy, it would thus have both energy and momentum (not to mention spin), both of which have to be dissapated in the reaction...since the only emission would be a neutrino and a photon, it's effectively prohibited and the cross section reflects that.
Since electron capture into an orbit is energetically beneficial, and doesn't require any nuclear emission or changes, that is what happens.
Also, there are exclusion principle effects at work, as it takes massive energy to force degeneracy and even more energy to force EC in stable isotopes. That being said, it DOES happen...that is how neutron stars are formed--the gravitational collapse puts in sufficient energy to force the degenerate matter of a white dwarf (a state reached only briefly and unstably in the collapse) to undergo nuclear collapse, and result in basically, one big nucleus. The reason the big ball of neutrons doesn't decay like a free neutron would is the same reason neutrons in a normal nucleus don't, it is energetically prohibited by gravity (neutron star) or strong plus EM force (normal nucleus).
Radioactive isotopes that are proton rich decay either through positron emission (turns a proton into a neutron) or electron capture (same result) and the split depends on the energetic and spin configuration of the nucleus. Neutron rich isotopes decay via beta decay (neutron turns into a proton) to seek an energetic minimum.
Explanation beyond that is extremely complex and actually beyond what I have in my head right now.
YMMV on that explanation, but it's a combination of balance of energy, momentum, angular momentum, and energy levels (quantum states) of both the electron and nucleus.
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<Note to self. Don't read physics threads
so early in the day at all. You'll feel stupid.>
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^^Or anytime during the day or night, for any matter.
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Where is Mr. Spock when you need him? [tinfoil] [popcorn] [popcorn]
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Quantum mechanics and Neils Bohr to the rescue.
Now why would a radio talkshow host have a contribution to the discussion?
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Sheldon says you're all troglodyte dumbasses...
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It CAN happen (inverse beta decay or electron capture). But if it's with a free electron, the cross section is REALLY small. Basically the issue is this, a proton with a bound electron is an energy minima (ie, capture of an electron to form a hydrogen atom is exothermic, the energy is released as a photon) while a proton capturing an electron to form a neutron is endothermic (and requires emission of a neutrino for spin and momentum conservation), which is why electron capture is a mode of radioactive decay (ie a higher energy nucleus decaying to a lower energy state). Since the electron needs to supply energy, it would thus have both energy and momentum (not to mention spin), both of which have to be dissapated in the reaction...since the only emission would be a neutrino and a photon, it's effectively prohibited and the cross section reflects that.
Since electron capture into an orbit is energetically beneficial, and doesn't require any nuclear emission or changes, that is what happens.
Also, there are exclusion principle effects at work, as it takes massive energy to force degeneracy and even more energy to force EC in stable isotopes. That being said, it DOES happen...that is how neutron stars are formed--the gravitational collapse puts in sufficient energy to force the degenerate matter of a white dwarf (a state reached only briefly and unstably in the collapse) to undergo nuclear collapse, and result in basically, one big nucleus. The reason the big ball of neutrons doesn't decay like a free neutron would is the same reason neutrons in a normal nucleus don't, it is energetically prohibited by gravity (neutron star) or strong plus EM force (normal nucleus).
Radioactive isotopes that are proton rich decay either through positron emission (turns a proton into a neutron) or electron capture (same result) and the split depends on the energetic and spin configuration of the nucleus. Neutron rich isotopes decay via beta decay (neutron turns into a proton) to seek an energetic minimum.
Explanation beyond that is extremely complex and actually beyond what I have in my head right now.
YMMV on that explanation, but it's a combination of balance of energy, momentum, angular momentum, and energy levels (quantum states) of both the electron and nucleus.
If EC is "endothermic", what is the mechanism?
Typically, an energy gradient is associated with some kind of force. Is there an identified repulsive nuclear force at these scales, that is counteracting the electromagnetic attraction? Electro-Weak force? Strong force?
Please explain in more detail if you have the time.
Also, why is a lepton able to interact with a quark like this? Why is it able to change an "up" quark to a "down" quark at all?
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If EC is "endothermic", what is the mechanism?
Typically, an energy gradient is associated with some kind of force. Is there an identified repulsive nuclear force at these scales, that is counteracting the electromagnetic attraction? Electro-Weak force? Strong force?
Please explain in more detail if you have the time.
Also, why is a lepton able to interact with a quark like this? Why is it able to change an "up" quark to a "down" quark at all?
First question, what I mean by endothermic is the overall energy of the combined nucleus (proton rich) plus electron system is lower after EC than before, EC is effectively converting the excess energy of a nuclear excited state (excess energy which in this case due to EM force from the excess protons) into the higher rest mass of a neutron relative to a proton plus electron. Since the end state is at a lower energy than the start, the potential barrier that is between the electron's wave function before (barrier due to the prohibited intermediate states of an electron "between" an innermost orbital and being part of the nucleus) can be tunneled through--that is where the probabilistic nature of radioactive decay is from, in this case, it's the probability of the electron tunneling from its stable inner orbital state into the merged state with a proton. so the reaction in this case is governed by three forces, EM and weak force (the electron-proton interaction) and EM and strong force (which creates the high energy initial state due to EM force larger than strong force in the excess proton nucleus and low energy final state due to strong force over EM force in the balanced nucleus afterwards with the new neutron replacing the proton)
For the second question, I don't know how to explain the exact mechanism, but the most analogous example is the reverse reaction of beta decay where a down (-1/3 charge) quark is changed into an up (+2/3) to change a neutron into a proton--in at case (effectively the reverse reaction) e charge is conserved intrinsically and the spin is balanced by the emission of a neutrino.
In both cases, it's the weak force that is governing the electron reaction that is occurring IIRC
The neutrinos are the key in these reactions as they are the spin-balancers of the nuclear world, and being uncharged leptons (the uncharged counterparts to electrons), allow the reactions to balance--the spin of the emitted neutrino is the opposite of the electron involved in the reaction.
Apologies if this is partially incorrect or muddy, it's been 14 years since my quantum classes. I'll think about it more and see if I can come up with a better explanation, but the fundamental basis is, as stated before, the electron has specific states that are energy minima (the "orbitals" the innermost of which is the lowest allowed potential energy state, so it can't move any further inward via normal (radiative emission of a photon, ie a pure EM interaction) modes, so there is a potential barrier to it moving into the nucleus. In a normal nucleus, the electron present there would be at a higher energy state than in the orbital, so it's transition there is prohibited. In a proton rich nucleus, that state is now a lower energy state, so there becomes a finite probability it will tunnel through the barrier and undergo capture.
In my previous example of degenerate matter and neutron stars, the electron states are modified by gravity to collapse inward, basically reducing the "radius" of the orbitals and allowing energy level degeneracy (gravity overcomes the exclusion forces preventing multiple electrons from occupying similar states), and when that gravitational force is high enough (again, think about it from an energy basis, the higher the density, the lower the energy state, so when there is enough gravitational force to overcome the exclusion forces, the defer ate states become allowed) the collapse goes further, and forces the electrons through the barrier to combine with the remaining protons and form all neutrons--a neutron star, which is, in effect, one big nucleus, where gravity (usually the weakest force, at least when it comes to nuclear interactions) is sufficient to dominate over the others and not only keep it together, but prevent neutron decay--a beta decay would require an neutron to form a proton and electron, and that would be a higher energy state, and thus prohibited.
Ugh.
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This is why i love conversations with Birdman
Birdman, you wanna come down to the house soon for BBQ and beers? We miss you. Brooklyn hasn't seen uncle marc in forever.
I'm wide open saturday evening.
Hell, you can even come to Busch Gardens with us on monday if you're hankerin for a break from work.
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This is why i love conversations with Birdman
Birdman, you wanna come down to the house soon for BBQ and beers? We miss you. Brooklyn hasn't seen uncle marc in forever.
I'm wide open saturday evening.
Hell, you can even come to Busch Gardens with us on monday if you're hankerin for a break from work.
Ironically, I have to work all weekend...getting ready for a startup pitch to some VC's :(
The next few months are going to be rough from a work perspective. Rougher than usual :(
That being said, I'll try. :)
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In my previous example of degenerate matter and neutron stars, the electron states are modified by gravity to collapse inward, basically reducing the "radius" of the orbitals and allowing energy level degeneracy (gravity overcomes the exclusion forces preventing multiple electrons from occupying similar states), and when that gravitational force is high enough (again, think about it from an energy basis, the higher the density, the lower the energy state, so when there is enough gravitational force to overcome the exclusion forces, the defer ate states become allowed) the collapse goes further, and forces the electrons through the barrier to combine with the remaining protons and form all neutrons--a neutron star, which is, in effect, one big nucleus, where gravity (usually the weakest force, at least when it comes to nuclear interactions) is sufficient to dominate over the others and not only keep it together, but prevent neutron decay--a beta decay would require an neutron to form a proton and electron, and that would be a higher energy state, and thus prohibited.
Ugh.
I wonder if the steep gravitational gradient means the difference in time from the reference frame of an external observer is such that it modifies the frequency of the wave function of the electron? Or maybe if because stuff is happening on the Planck time/length scale, that doesn't matter?
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I wonder if the steep gravitational gradient means the difference in time from the reference frame of an external observer is such that it modifies the frequency of the wave function of the electron? Or maybe if because stuff is happening on the Planck time/length scale, that doesn't matter?
Nope, while there are both special and general relativity effects that have to be accounted for, the actual effects that matter are energy based, which is why they occur even at dwarf star levels where while the density is high, it is insufficient to create significant relativistic effects
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Ironically, I have to work all weekend...getting ready for a startup pitch to some VC's :(
You're working for the Viet Cong?....
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You're working for the Viet Cong?....
Yes. They are in the trees.
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So an electron and a proton walk into a bar....
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Thoughts on someone successfully challenging a paternity suit based on the possibility that a sperm suffered spontaneous quantum teleportation?
I mean... it could happen. It's not impossible.
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So an electron and a proton walk into a bar....
The bartender said, "What is this, some kind of joke?"
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Thoughts on someone successfully challenging a paternity suit based on the possibility that a sperm suffered spontaneous quantum teleportation?
I mean... it could happen. It's not impossible.
Collections of particles cannot tunnel as their constituents have different quantum mechanical parameters, not to mention velocities and energies. Sorry.
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Collections of particles cannot tunnel as their constituents have different quantum mechanical parameters, not to mention velocities and energies. Sorry.
Ah, there is that. =(
Slight posting delay as I leave the country, and get set up in my new digs. Please don't be alarmed.