4 ms·

That’s just not true, it’s an artifact of the Bohr model of the atom which doesn’t take the wave-particle duality of the electron into account. The wavefunction

That’s just not true, it’s an artifact of the Bohr model of the atom which doesn’t take the wave-particle duality of the electron into account. The wavefunction of the electron is “smeared” around the atom, which is not empty. The black hole as dark matter theory is also largely discredited (MACHO theory for MAssive Compact Halo Object) because gravitational lensing studies don’t support it.

krastanov 8y ago
For those interested in more intuitive understanding of how the "smearing" breaks the meme about atoms being mostly empty space, check out these plots: https://en.wikipedia.org/wiki/Atomic_orbital#/media/File:Hydrogen_Density_Plots.png https://en.wikipedia.org/wiki/Atomic_orbital#/media/File:Hyd... While you can argue they are still flawed, they do clearly show that the electrons have fairly large probabilities of being observed pretty much anywhere inside the "radius" of the atom.
- RightMillennial 8y ago
  Those are simply the electron orbitals which describe the probability of finding the respective election at a given point. That doesn't imply "smearing" any more than a picture with a long exposure does. Atoms are still mostly empty space.
  - tzahola 8y ago
    Define “empty”.
  - krastanov 8y ago
    I am really confused by what you are saying. It sounds like you think that electrons are point particles with charge that have some position somewhere. This is frequently a convenient model, but the last 100 years have showed pretty convincingly that the "reality" is that electrons are wavefunctions (or if you want to be pedantic, excitations of a particular quantum field). At this point, arguing about "are atoms mostly empty space" becomes a futile semantic argument. The model you picked in order to defend this statement is indeed useful in some limits, but it has been proven wrong. Imagining electrons as clouds has proven to be much closer to reality.
    - contoraria 8y ago
      It's hard to abandon the old idea, when the new idea, I mean, it's there, everywhere and nowhere at the same time, if you don't look, isn't particularly convincing, and the retort that it doesn't need to be convincing if you (read: I) just aren't smart enough, because it's counterintuitive, then I have a counterintuitive disregard for your cleverness. I have to concede, though, that "empty" is not a particularly meaningful physical concept, quite the opposite. Disregarding the Aether theory, only to replace it with fields of potentials, that is kind of running in circles. A model is fundamentally wrong. That's what it means to have a model. At that "clouds" is no more helpful then "empty". The fact of the matter is that no one has ever seen these things, no nucleus, no electrons, as far as I know. Yet, you haven't pointed out what was actually wrong with "Those are simply the electron orbitals which describe the probability of finding the respective election at a given point". Edit: Perhaps you intended to imply that this description is overly idealized (not to say simple).
- metaobject 8y ago
  Regarding the "smearing" concept, how does that square with the formation of neutron stars and white dwarfs? Those objects are incredibly dense because they're composed mostly (?) of nuceei or neutrons, respectively.
  - krastanov 8y ago
    The plots I linked to are for a single atom. If you have many other atoms around it, the smearing becomes different. For instance, in metals some of the electrons are completely smeared over the whole macroscopic piece of metal (this is a bit handwavy, but not incorrect phrasing). Chemical bonds also happen due to deforming and sharing of those "smeared" clouds between neighboring atoms. If you have too much external pressure (gravity), those smeared electron clouds come too close to the nucleus, react with it, and the only thing left is neutrons.
credit_guy 8y ago
>gravitational lensing studies don’t support it As a non-astrophysicist, just scanning the wikipedia entry [1] it appears to me that gravitational microlensing studies must be fiendishly difficult, you probably need massive amounts of data and of compute power to get to highly confident conclusions. Is my impression accurate? If that is so, than the MACHO theory should not be discredited that quickly. It is after all the only theory that does not require any new physics in order to explain the missing mass. [1] https://en.m.wikipedia.org/wiki/Gravitational_microlensing https://en.m.wikipedia.org/wiki/Gravitational_microlensing
- Semirhage 8y ago
  It isn’t totally discredited, but the constraints on it make it exceedingly unlikely. Against it: No gamma ray signals as hoped/expected from evaporating PBH’s. LIGO is not seeing PBH mergers at a rate that would support the numbers required. Micro lensing studies don’t support it. Is it’s possible, but it’s much less likely than other theories which allow for less fine tuning of parameters. There’s a very good graphic that shows what I’m talking about. https://astrobites.org/wp-content/uploads/2017/08/constraintsPBH.png https://astrobites.org/wp-content/uploads/2017/08/constraint... From: https://astrobites.org/2017/08/31/could-dark-matter-be-black-holes/ https://astrobites.org/2017/08/31/could-dark-matter-be-black...
  - perl4ever 8y ago
    The articles I read about LIGO detecting collisions between black holes said they were medium sized, meaning several solar masses. I kind of assumed that they wouldn't be able to detect anything orders of magnitude less than solar mass. Is that not correct?
pvg 8y ago
it’s an artifact of the Bohr model of the atom which doesn’t take the wave-particle duality of the electron into account. It's the direct result of the Geiger–Marsden experiments.
- turndown 8y ago
  Isn't this misinterpreting the results of that experiment? The Geiger-Marsden experiments established that most of the mass in an atom is concentrated within the nucleus, where all positive charge is located. It does not try to establish whether or not the area outside the nucleus is empty or not.
  - pvg 8y ago
    The (oversimplified) notion that the matter we typically deal with is mostly empty space is a direct consequence of that experiment, not an artifact of the Bohr model.
danbruc 8y ago
The wavefunction of the electron is “smeared” around the atom, which is not empty. The wave function may be smeared out over space, but that does not mean that there is an electron everywhere. Electrons are never at two places, never has anyone looked and found the same electron at two different places at the same time. What happens if nobody looks is up for debate, whether you think the electron has no position, whether you think it is guided along its path by a pilot wave, whether you think it split into zillions of copies in different universes, or whatever. But the electron or many electrons filling out its entire orbit is not compatible with any of that or any experimental evidence. At least as far as I know, I am not a physicist.
- pvg 8y ago
  never has anyone looked and found the same electron at two different places at the same time. https://en.wikipedia.org/wiki/Double-slit_experiment https://en.wikipedia.org/wiki/Double-slit_experiment
  - danbruc 8y ago
    The photon - or electron or whatever - hits the screen in exactly one spot, not in several and not in any smeared out way.
    - pvg 8y ago
      I think the other comment addresses this somewhat and, of course, there is the endless verbiage online on all levels - you can't really explain the observed phenomena by treating the particle as little ball with a somewhat uncertain location.
- krastanov 8y ago
  > But the electron or many electrons filling out its entire orbit is not compatible with any of that or any experimental evidence. On the contrary, imagining the electron as a smeared cloud (a complex-valued wave function with a bunch of specific properties), is pretty much the only way to explain chemical bonds. The confusion stems from semantics. Sure, nobody claims that an electron has been detected at two spots simultaneously, not because it does not happen, rather because to say that you need the premise that the electron is a point particle with a position. Sure, it is useful to claim that the electron is a point particle - in plenty of circumstances it does look like one. But modern physics pretty conclusively has demonstrated that it is actually something described by a wave function, that is most certainly smeared over space. I am a physicist, so I will leave the discussion of whether "smeared" is a good word for it to the philosophers and linguists. It is a good enough word for me, when I try to derive properties of atoms.
perl4ever 8y ago
I've read this a lot about gravitational lensing, but I'm not clear on whether we would be seeing lensing if most black holes were sand-grain-sized or smaller.
- yk 8y ago
  It is actually when the primordial black holes are too large, that we can't find them with lensing, we know the mass density of dark matter and if the black holes are large on average, then we would not see them with lensing because lensing events would be too rare. If the black holes are smaller, then there are a lot of lensing events and we can detect them. At somewhat larger scales one expects to see black holes due to interactions with stars. That leaves a rather small window in between were black holes as dark matter works, but nobody has postulated a plausible mechanism to only generate black holes in a narrow mass range, so the idea can be made to work, but fell out of fashion because the wimp miracle looked theoretically more attractive.
oldandtired 8y ago
The wave function is a mathematical construct that doesn't actually have anything to say about the actually of a particle. It is, in essence, the probability of where you might find the entity if you make measurements. As such to say that the electron is "smeared" around the atom is not saying anything meaningful about the electron. All we can say is that we don't know where it is. To attribute a dispersal property to the electron (or any other particle for that matter) is not doing anything helpful to discover or understand what an electron is.

krastanov 8y ago

For those interested in more intuitive understanding of how the "smearing" breaks the meme about atoms being mostly empty space, check out these plots: https://en.wikipedia.org/wiki/Atomic_orbital#/media/File:Hydrogen_Density_Plots.png https://en.wikipedia.org/wiki/Atomic_orbital#/media/File:Hyd... While you can argue they are still flawed, they do clearly show that the electrons have fairly large probabilities of being observed pretty much anywhere inside the "radius" of the atom.

RightMillennial 8y ago
Those are simply the electron orbitals which describe the probability of finding the respective election at a given point. That doesn't imply "smearing" any more than a picture with a long exposure does. Atoms are still mostly empty space.
- tzahola 8y ago
  Define “empty”.
- krastanov 8y ago
  I am really confused by what you are saying. It sounds like you think that electrons are point particles with charge that have some position somewhere. This is frequently a convenient model, but the last 100 years have showed pretty convincingly that the "reality" is that electrons are wavefunctions (or if you want to be pedantic, excitations of a particular quantum field). At this point, arguing about "are atoms mostly empty space" becomes a futile semantic argument. The model you picked in order to defend this statement is indeed useful in some limits, but it has been proven wrong. Imagining electrons as clouds has proven to be much closer to reality.
  - contoraria 8y ago
    It's hard to abandon the old idea, when the new idea, I mean, it's there, everywhere and nowhere at the same time, if you don't look, isn't particularly convincing, and the retort that it doesn't need to be convincing if you (read: I) just aren't smart enough, because it's counterintuitive, then I have a counterintuitive disregard for your cleverness. I have to concede, though, that "empty" is not a particularly meaningful physical concept, quite the opposite. Disregarding the Aether theory, only to replace it with fields of potentials, that is kind of running in circles. A model is fundamentally wrong. That's what it means to have a model. At that "clouds" is no more helpful then "empty". The fact of the matter is that no one has ever seen these things, no nucleus, no electrons, as far as I know. Yet, you haven't pointed out what was actually wrong with "Those are simply the electron orbitals which describe the probability of finding the respective election at a given point". Edit: Perhaps you intended to imply that this description is overly idealized (not to say simple).
metaobject 8y ago
Regarding the "smearing" concept, how does that square with the formation of neutron stars and white dwarfs? Those objects are incredibly dense because they're composed mostly (?) of nuceei or neutrons, respectively.
- krastanov 8y ago
  The plots I linked to are for a single atom. If you have many other atoms around it, the smearing becomes different. For instance, in metals some of the electrons are completely smeared over the whole macroscopic piece of metal (this is a bit handwavy, but not incorrect phrasing). Chemical bonds also happen due to deforming and sharing of those "smeared" clouds between neighboring atoms. If you have too much external pressure (gravity), those smeared electron clouds come too close to the nucleus, react with it, and the only thing left is neutrons.

credit_guy 8y ago

>gravitational lensing studies don’t support it As a non-astrophysicist, just scanning the wikipedia entry [1] it appears to me that gravitational microlensing studies must be fiendishly difficult, you probably need massive amounts of data and of compute power to get to highly confident conclusions. Is my impression accurate? If that is so, than the MACHO theory should not be discredited that quickly. It is after all the only theory that does not require any new physics in order to explain the missing mass. [1] https://en.m.wikipedia.org/wiki/Gravitational_microlensing https://en.m.wikipedia.org/wiki/Gravitational_microlensing

Semirhage 8y ago
It isn’t totally discredited, but the constraints on it make it exceedingly unlikely. Against it: No gamma ray signals as hoped/expected from evaporating PBH’s. LIGO is not seeing PBH mergers at a rate that would support the numbers required. Micro lensing studies don’t support it. Is it’s possible, but it’s much less likely than other theories which allow for less fine tuning of parameters. There’s a very good graphic that shows what I’m talking about. https://astrobites.org/wp-content/uploads/2017/08/constraintsPBH.png https://astrobites.org/wp-content/uploads/2017/08/constraint... From: https://astrobites.org/2017/08/31/could-dark-matter-be-black-holes/ https://astrobites.org/2017/08/31/could-dark-matter-be-black...
- perl4ever 8y ago
  The articles I read about LIGO detecting collisions between black holes said they were medium sized, meaning several solar masses. I kind of assumed that they wouldn't be able to detect anything orders of magnitude less than solar mass. Is that not correct?

pvg 8y ago

it’s an artifact of the Bohr model of the atom which doesn’t take the wave-particle duality of the electron into account. It's the direct result of the Geiger–Marsden experiments.

turndown 8y ago
Isn't this misinterpreting the results of that experiment? The Geiger-Marsden experiments established that most of the mass in an atom is concentrated within the nucleus, where all positive charge is located. It does not try to establish whether or not the area outside the nucleus is empty or not.
- pvg 8y ago
  The (oversimplified) notion that the matter we typically deal with is mostly empty space is a direct consequence of that experiment, not an artifact of the Bohr model.

danbruc 8y ago

The wavefunction of the electron is “smeared” around the atom, which is not empty. The wave function may be smeared out over space, but that does not mean that there is an electron everywhere. Electrons are never at two places, never has anyone looked and found the same electron at two different places at the same time. What happens if nobody looks is up for debate, whether you think the electron has no position, whether you think it is guided along its path by a pilot wave, whether you think it split into zillions of copies in different universes, or whatever. But the electron or many electrons filling out its entire orbit is not compatible with any of that or any experimental evidence. At least as far as I know, I am not a physicist.

pvg 8y ago
never has anyone looked and found the same electron at two different places at the same time. https://en.wikipedia.org/wiki/Double-slit_experiment https://en.wikipedia.org/wiki/Double-slit_experiment
- danbruc 8y ago
  The photon - or electron or whatever - hits the screen in exactly one spot, not in several and not in any smeared out way.
  - pvg 8y ago
    I think the other comment addresses this somewhat and, of course, there is the endless verbiage online on all levels - you can't really explain the observed phenomena by treating the particle as little ball with a somewhat uncertain location.
krastanov 8y ago
> But the electron or many electrons filling out its entire orbit is not compatible with any of that or any experimental evidence. On the contrary, imagining the electron as a smeared cloud (a complex-valued wave function with a bunch of specific properties), is pretty much the only way to explain chemical bonds. The confusion stems from semantics. Sure, nobody claims that an electron has been detected at two spots simultaneously, not because it does not happen, rather because to say that you need the premise that the electron is a point particle with a position. Sure, it is useful to claim that the electron is a point particle - in plenty of circumstances it does look like one. But modern physics pretty conclusively has demonstrated that it is actually something described by a wave function, that is most certainly smeared over space. I am a physicist, so I will leave the discussion of whether "smeared" is a good word for it to the philosophers and linguists. It is a good enough word for me, when I try to derive properties of atoms.

perl4ever 8y ago

I've read this a lot about gravitational lensing, but I'm not clear on whether we would be seeing lensing if most black holes were sand-grain-sized or smaller.

yk 8y ago
It is actually when the primordial black holes are too large, that we can't find them with lensing, we know the mass density of dark matter and if the black holes are large on average, then we would not see them with lensing because lensing events would be too rare. If the black holes are smaller, then there are a lot of lensing events and we can detect them. At somewhat larger scales one expects to see black holes due to interactions with stars. That leaves a rather small window in between were black holes as dark matter works, but nobody has postulated a plausible mechanism to only generate black holes in a narrow mass range, so the idea can be made to work, but fell out of fashion because the wimp miracle looked theoretically more attractive.

oldandtired 8y ago

The wave function is a mathematical construct that doesn't actually have anything to say about the actually of a particle. It is, in essence, the probability of where you might find the entity if you make measurements. As such to say that the electron is "smeared" around the atom is not saying anything meaningful about the electron. All we can say is that we don't know where it is. To attribute a dispersal property to the electron (or any other particle for that matter) is not doing anything helpful to discover or understand what an electron is.