zaroth 44 days ago [-]
Truly mind blowing being able to actually see the atoms align in an instant and the crystal structure just pop into existence.

Hard to believe it’s not a computer model. I mean, I guess underneath there must be a hell of a lot of signal processing going on to render that video, but atomic-scale video is wild.

Funny that it looks kinda like MPEGS online circa 1990s.

noneeeed 44 days ago [-]
I find a lot of the science being done at the moment truly astonishing, the precision and scale of many of the measurements being made are mind-blowing.

The sensitivity of instruments like LIGO is hard to get your head around.

mywittyname 44 days ago [-]
I also love how you can see the probabilistic nature of electron orbitals in action. The crystal fades in and out of existence during the early stages of nucleation. And even after the structure is established, the boundaries continue to be "fuzzy."

Even the movement of the crystal looks like a wave, but I don't know if that's because matter moves as a wave at the atomic level or if that's just an artifact from the camera.

Osmium 44 days ago [-]
> I don't know if that's because matter moves as a wave at the atomic level or if that's just an artifact from the camera.

Artifact of the imaging, note the time scale of the movie, it's much longer than any quantum oscillation. Each individual image of the movie is taken eons apart from the perspective of the crystal.

magicalhippo 44 days ago [-]
> Each individual image of the movie is taken eons apart from the perspective of the crystal.

Given the timescales of atomic reactions, which IIRC is typically measured in nano- or picoseconds, this video is more like watching galaxies form I suppose.

jng 44 days ago [-]
I would think that the coming in and out of view at the beginning is more related to the crystal moving around and falling "in and out of focus" (whatever that means for this type of camera). I'd love to watch quantum probability wave fluctuations, but I think we're still pretty far from probing that.
jtaillon 44 days ago [-]
In this case, "in and out of focus" is actually variations in the amplitude of the probability function for the electron density projected onto a single plane (to a first approximation). Sometimes the wave functions of all the electrons interfere constructively, so you see a bright spot, and sometimes deconstructively, so you see dark. Depending on the orientation of things, this results in the images of "atoms" that you see in the picture. As the crystal changes shape and size, the interference patterns change, which partially explains why it disappears and reappears a few times. There's a bit more going on than that, but the physics of what's happening in a TEM image is really neat.
gus_massa 44 days ago [-]
Most of the electrons in a NaCl crystal are quite localized (all the core electrons od Na+ and Cl-, and it's not a good conductor, so the valence band is full). So I don't expect too much interesting interference patterns. It looks like a problem with vibrations that make it go out of focus.
jng 44 days ago [-]
Wow, mind blown. Thanks for correcting me. Amazing to learn that the wave function is so directly sampled by TEM that the image we get shows Moiré patterns caused by its phase :)
Ericson2314 44 days ago [-]
Per the other comments, I think time scale is far to large for that to be the case in any not-also-explained-classically sense.
WClayFerguson 44 days ago [-]
It's almost like a "standing wave" (of the square pattern) emerged spontaneously out of a chaotic stew of probability waves, and I guess that's a better way to describe quantum mechanics at this level than to say "The Na and Cl atoms snapped together". Nothing snapped to together. This video shows a pattern emerging from pure chaos, all based on probabilities and the fact that each individual atom probability wave can only oscillate in certain patterns.

I'm pretty sure in Quantum Mechanics systems like this the entire unit behaves as one and there's no real distinction possible regarding "which is which" if you were to try to identify individual atoms. It would be like looking at a standing wave pattern in water (or any other medium) and labeling one peak "Wave A" and some peak "Wave B". You can't really do it. Because for the standing wave pattern to exist at all it has to be the entire system interaction to cause it to emerge.

I'm not saying atoms are "Standing Waves" but I'm merely making an analogy. However even from some perspective you could even say any oscillating system of wave probabilities when taken as a "system" comprises a standing wave.

l33tman 44 days ago [-]
There is really nothing quantum in this, you can simulate this completely classically, although it takes forever as it's a slow process, as you seen when you compare the timescale of the video in the seconds to the timescale the atoms move about, in the femtoseconds.

I'm not a salt nucleation expert by any means, but I'd imagine the process has a similar statistics as protein folding. Individual folding events (and nucleation events) are superfast but takes forever to trigger (a lot of stars have to align so to speak). This is why, from just looking at frames 1/25s apart, it looks like suddenly things appeared out of nothing, but really there were eons of time in between the frames in the video.

WClayFerguson 44 days ago [-]
> There is really nothing quantum in this

Even if you consider a Hydrogen atom floating in free space a billion miles from any planets, everything about it is 100% "quantum".

There are no actual electrons going around the nucleus, because it's purely just a quantum probability wave. If you then introduce Oxygen atoms near it, then the probability wave of the two begin to behave as a single system and will oscillate in a different pattern but STILL a single quantum mechanical system, and one big "wave function" that represents the entire system.

In this multi-atom system you also cannot even say that one specific electron is going around one atom, and another electron is going around a different electron (the incorrect classical view). The electron probability wave for the entire system is one big probability wave oscillator function, and both electrons contribute to magnitudes of observables in an identical way to each other. So the two electrons loose their individual identity. They're both part of a 'cloud' but you can't say where any of them are. Not because it's hard to measure, but because actually reality itself doesn't even know.

None of this is inconsistent with the fact that the classical view also holds true under ordinary observational conditions, and can be estimated (albeit incorrectly) as pre-existing atoms "snapping together" by the laws of chemistry, but that is the less 'complete' view. Just like Newton is a less complete view than Relativity, but still 'works'.

gus_massa 43 days ago [-]
[Replying here as you suggested in the other comment.]

The balls in a pool table are 100% quantum, but they are approximated very accurately by Classic Mechanics.

At this level, the position of the nuclei can be approximated to move classically, and the electrons quantically. Moreover, the standard trick is to approximate that the nuclei doesn't move, and then calculate the distributions of the electron with quantum mechanics. https://en.wikipedia.org/wiki/Born%E2%80%93Oppenheimer_appro...

Once you calculate the distribution of the electrons assuming the nuclei are at different positions, you can approximate an effective force between the nuclei and calculate how they move almost like classic objects.

The calculation is too difficult, and the other nearby atoms affect them, so there are a lot of approximations. For big system, you need to use something like https://en.wikipedia.org/wiki/Born%E2%80%93Oppenheimer_appro... that approximate the force between the atoms, with some formulas that hide all the quantumness and then move as if they were classic objects.

So it's a quantum system, like everything in this word. But the apparent atoms that appear and disappear are not explained by weird quantum effects. They can be explained with the simplified classic model when the camera takes too few frames, the objects are moving too much, and the background is too noisy.

WClayFerguson 43 days ago [-]
I'm glad we agree that classical mechanics accurately predicts macro objects.

However, atoms, molecules, and even molecular lattices containing a small number of atoms (or large number actually), behave as quantum wave systems. Even the link you gave states that 'benzene' despite having 42 electrons, has a single wave function that determines probabilities for where an electron can be observed (but not WHICH electron. There is no WHICH ELECTRON in the function). In that wave function it means there's no longer 42 actual electrons that even exist. There is nothing but a probability of where you'd find one if you collapse the entire wave simultaneously by taking a measurement of any part of it.

When atoms join into a crystal formation that becomes even a 'higher level' new emergent pattern of vibrating probabilities, that's more complex and structured than what the individual particles exhibited before the new pattern emerged.

You think I'm wrong to say atoms pop into existence?, but we know for a fact all particles are merely probabilities until observed. All observation is synonymous with wave-collapse, and only upon wave-collapse do you have actual particles with actual positions in spacetime. Every 'frame' of every video you could ever create is a snapshot of "a series of collapses", because that collapse is what created the particles that make up the 'image' itself.

tsimionescu 43 days ago [-]
You are taking a mathematical formalism and giving it a physical meaning, in a way that doesn't make any sense.

The wave function is a way to describe the physical properties of an entire system - position, velocity, spin etc, for every component that you chose to model (e.g. electrons and nuclei, or electrons and protons and neutrons, or electrons and quarks etc). To get an accurate prediction, you need to input all of the relevant parts of the system. For example, when solving the Schrodinger equation for a hydrogen atom, people input the properties of the electron and proton. If you want to compute the properties of a benzene molecule, you input information about all of the 6 nuclei and 42 electrons. If you want to compute the wave function of a mole of benzene, you would have to input the properties of all ~10^23 atoms composing it. This has no physical meaning per se - this is just the nature of the formalism.

Depending on the exact system, you may or may not have separate components of the wave function which correspond to the different components of the system which you are modelling - such as a component indicating the position of the electron and a component for the position of the nucleus/proton for the Hydrogen atom.

Also, if you were to model an electron launched towards a benzene molecule, the wave function of the system would show different values for the 1 electron that was launched vs the 42 electrons which were part of the original system.

The 42 electrons are not distinguishable simply because we don't normally choose to input any way of differentiating them, because we don't think it's useful. You could in principle describe the system such that you get a particular prediction for each of the 42 different electrons - though we don't know any property that electrons have that we could use to actually measure and confirm.

> In that wave function it means there's no longer 42 actual electrons that even exist.

The 42 electrons absolutely exist as part of the wave function - otherwise, the charge of the system would be wrong. The wave function in fact predicts positions and velocities and spins for 42 electrons, and you could in principle do a measurement where you would identify the positions for all 42 of them, with probabilities that you can compare to the wave function predictions.

gus_massa 43 days ago [-]
> The 42 electrons are not distinguishable simply because we don't normally choose to input any way of differentiating them, because we don't think it's useful.

No, the electrons are truly undistinguishable, more specifically, they are fermions https://en.wikipedia.org/wiki/Fermion

(If you want to be super technical, the best model we have for electrons assume they are indistinguishable. This model has very accurate predictions for the experimental results. And all the models that we have tried that assume that electrons are distinguishable make some predictions that are wrong, so we have to send them to the trash can.)

(And there are some extensions that are useful for high energy experiments, but in these extensions the electrons are even more indistinguishable.)

The main discussion here is that in spite the nuclei of Sodium and Chloride are also undistinguishable quantum objects, I say that in these conditions the can be perfectly approximated as distinguishable and with a classic movement.

This is a good approximation, except in some specific weird experiments that measure the diffraction pattern when a crystal is used as a mirror for a beam of neutrons or helium or even bigger atoms.

WClayFerguson 43 days ago [-]
Well said. And furthermore: Any quantum mechanical system (i.e. all systems) is ultimately just a vibrational pattern, so trying to assign persistent identities to "things" is impossible because it's like trying to label the peaks and troughs in some standing wave oscillating on some medium. The wave is a pattern only, and the peaks/troughs are merely emergent phenomena with no actual identities, that have a history or a future, other than at the exact time of some observation.

My favorite philosophical thought experiment to ask people is: "Do football stadium waves actually exist or is it merely people in two states (standing/sitting)?" The answer to that question is a superposition of both Yes and No. lol. It sounds like a silly question, but it actually gets to the heart of the deepest philosophical questions Physics.

WClayFerguson 43 days ago [-]
Seems like you're mixing a lot of classical mechanics concepts into your 'understanding' of QM. Even in a single water molecule the electrons loose their "identities" and even if you could look close enough at infinitesimally small time intervals at the molecule you'd never be able to say "There's one electron here, and there's the other over there". And I'm not saying it's just too hard to have a microscope that good, I'm saying not even "Mother Nature Herself Knows them apart"

Imagine if you setup a standing wave on a water surface, and there are exactly two peaks in the wave system. You cannot label one "Wave A" and the other "Wave B" and then turn off the energy source and then turn it back on and create the pattern again and say "Ok now which is A and which is B". The question itself is nonsensical. The same thing is going on in physics probability waves. Particles don't have identities just because "when you look for one you find one".

People think QM is describing "where particles go". It isn't. It describes where they can be found, and there's a huge leap of knowledge in understanding to comprehend the difference.

tsimionescu 43 days ago [-]
Particles have a position and a momentum (even though they can't both be measured per the uncertainty principle, so you could say they don't both exist at the same time). The wave function gives you both a position and a momentum (and other properties).

I believe what you're referring to when you say that it's wrong to talk about 'where particles go' is that it gives the wrong image of the particle moving continuously through space, occupying each point between its current location and its final one. You're right that this model is wrong. But the wave function still has a position which evolves with time, which is what I would describe as movement (even though it's not continuous).

Now, related again to identity - let's take a real experiment: we fire an electron cannkn at some benzene gas. We configure our cannon such that it fires a single electron per minute. We then want to compute what happens when this electron interacts with an atom in the gas. If we could solve the Schrodinger equation for the system, it would give us some wave functions which would probably show 42 electrons whose positions is always very close to the 6 nuclei, and 1 electron whose position can be far away, then close, then far away again. Now, whether this is even 'the same electron' between any two moments of time or not is more or less a philosophical question. But if it were a neutron instead of an electron, would you say it is not distinct from the 42 electrons? And if you wouldn't, then why say that when it is an electron?

I do understand that moving towards QFT, where we see the electron as an excitation of the field, it does make a lot of sense to say that even in a system with a single electron it's not 'the same' electron across different moments of time.

But on the other hand, we reach again the measurement problem at some point: we know that classical objects have identity. We also know that classical objects, like balls, are ultimately composed of electrons and quarks. If the electrons and quarks don't have identity, how can a ball?

gus_massa 43 days ago [-]
> Particles have a position and a momentum (even though they can't both be measured per the uncertainty principle, so you could say they don't both exist at the same time). The wave function gives you both a position and a momentum (and other properties).

It's much better to imagine that electrons don't have a property that is position and other that is momentum. Classic object have both. Electrons have neither. You can measure one of them, or the other, or some mix, but until you measure them, these properties don't exist.

> we know that classical objects have identity.

It's only an approximation. They can swap electrons using quantum mechanics or swap them using the thermal energy. It's easier to see with two glasses of water a few foots away. There is a tiiiiiiiiiiiiiiiiiiiny probability that a molecule of water decides to go from a glass to the other using quantum mechanics, but also it could just evaporate and after some time reach the other glass and dissolve. Anyway, the fact that both glasses are exchanging molecules classically does not prevent us to assign them an identity as an approximation.

About the canon with an electron and the benzene: When the electron is far away, you can assign it an identity as an approximation and all the calculation would be fine. When it is very close to the benzene of going thru the molecule, you must use the quantum mechanic version of the equation that assume all the electrons are identical. After a while, when the electron is far away, you can assign again an identity to the electron. The problem is: How are you sure that the electron that exits the molecule is the same electron that entered the molecule?

The answer is that you can't! Because they are all identical. In similar experiments you must do both calculations, when the electron that enters the molecule is the same that the electron that exits the molecule, and when it is a different electron, and the result is a combination of both.

When you use a neutron you can almost assign an identity and don't worry about weird things. (There are possible weird thing, but the probability is just too small.)

It is more interesting if you replace the neutron with a neutrino. When the neutrino is very close to an electron it can emit a W+ particle and get transformed into en electron. The election of the molecule that absorbs the W+ particle now gets transformed into a neutrino. So if you see that the neutrino went thru the molecule, you are not sure that it is the same neutrino or that it exchanged it's place with an electron in the molecule, so you must calculate both cases and combine them.

WClayFerguson 43 days ago [-]
well said. That neutrino W+ stuff went over my head, because I'm not actually doing Physics by profession. And unless you just now googled all that, it seems like you're my superior, and I bow down to your excellency. :)
WClayFerguson 43 days ago [-]
> wave function still has a position

The wave function specifies how the probability of "finding" a particle evolves over all of space and time for any point in space you yourself choose to solve it for. You can't really say the WF is predicting positions...if it's up to you to provide the positions.

> If the electrons and quarks don't have identity, how can a ball?

Macro objects can be separated, to where macro measurements make them appear separate (but they never really are), however at the atomic level this video helps (as a mental visualization) explain why actual electrons have no identity:

https://www.youtube.com/watch?v=-gr7KmTOrx0

In the video, ask yourself, do any of the "humps" in the string have identity? You can count them, see their position, measure velocity, etc., but they're purely an emergent phenomena, and have no true identity.

Nothing about any quantum mechanical wave system has any identities either. So when you "measure" something (i.e. "find" a particle) by collapsing the WF, you have actually not 'found' but 'created' something that seems to have a location in space and time, but it's not because it "moved there". It's because you "created it there".

soulofmischief 43 days ago [-]
Quantum Field Theory has a lot of strong evidence, as does the Copenhagen interpretation of QM, but it might be more suitable not to speak of these things as if they are 100% fact. It's theory, and it's likely that the eventual bridge between QM and classical physics will usher in an entirely new model unlike either individual model.
WClayFerguson 43 days ago [-]
I always refer to QFT + Standard Model as 'fact' even though myself and all other Physicists agree there may be deeper understandings than what is currently known by science.

At some point is becomes philosophy when you call into question something that has zero evidence against it and the evidence in favor of it has been measured out to 43 decimal places already.

tsimionescu 44 days ago [-]
While the electrons do form a cloud and aren't entirely well positioned in space as far as we know, it's important to remember that there still are a fixed number of electrons which can be detected one by one, even though they may interact with themselves or each other at multiple positions at the same time before our detection.

Furthermore, it is not yet proven that reality behaves the same in classical settings as it does in quantum interactions. For all we know, wave function collapse may be a physical phenomenon that happens at specific conditions, yielding purely classical behavior. Your explanation is one popular view of QM, but it is not the only possibility that would be consistent with observations.

WClayFerguson 43 days ago [-]
> Your explanation is one popular view of QM

If you want to call the "Standard Model" merely one among many "popular views" then you can, but that's not what I'd call accurate. No one really disagrees with it. They just have different "interpretations" of why it holds true.

Regarding your claim that electrons "interact with themselves", that's actually kind of misleading too. When electrons are "in the cloud" (pre-wave-collapse) they're pure probability and so none of them have an actual location in spacetime even if you had some infinitely fast camera to look. They simply don't exist at specific locations. They are genuinely everywhere at once, or stated even more correctly: they don't exist. Only the energy exists.

The "Bohr Model" of the atom is correct insofar as a way to track energies in a classically relevant way, but in no way at all is it actually "real". There's no electrons flying around. Only electrons that have already stopped. They don't exist until measured.

tsimionescu 43 days ago [-]
> If you want to call the "Standard Model" merely one among many "popular views" then you can, but that's not what I'd call accurate. No one really disagrees with it. They just have different "interpretations" of why it holds true.

The Standard Model doesn't contain an explanation for the measurement problem, which is essentially what your explanation is touching on, with the claim that everything is quantum and that the electron really doesn't have a definite position in space, rather than us being unable to know its position. Basically you stated a version of the Copenhagen Interpretation, which is very popular, but not the only way of making sense of the wave function.

> When electrons are "in the cloud" (pre-wave-collapse) they're pure probability and so none of them have an actual location in spacetime even if you had some infinitely fast camera to look. They simply don't exist at specific locations. They are genuinely everywhere at once, or stated even more correctly: they don't exist. Only the energy exists.

I think you're mixing things up a bit here. Before a measurement takes place, the movement of electrons is predicted by a deterministic equation, there is no probability. The electron is indeed (described by?) a wave function that has some amplitude at any point in space. My point about "interacting with themselves" was that the Schrodinger equation predicts the possibility of self-interference of a single electron's wave function, which is an observed effect.

I think you're also over-selling the wave part of the duality and disregarding the particle part. The electron doesn't behave entirely like a wave, it also has particle-like properties, such as a fixed mass and a fixed charge.

> There's no electrons flying around. Only electrons that have already stopped. They don't exist until measured.

This is exactly the part that people love claiming as if it is settled, when it is anything but. The reality is that we don't yet know what quantum particles are. If they don't exist until you measure and then they start existing, then you need to explain what a measurement is, which we have no idea how to.

In fact, even the Copenhagen interpretation doesn't exactly say what you are claiming. It is instead claiming that the wave function + the Born rule are a mathematical tool that predicts the behavior of quantum systems with excellent accuracy, and that the probabilities in the Born rule are fundamental. If we accept this fundamental impossibility of predicting deterministically the properties of a quantum system, it follows that it is unscientific to claim that the particles "have" properties that we fundamentally can't measure. This un-existence is then a philosophical argument, not a physical one: it's stating that something that can't in principle be measured can't be said to exist.

Other popular explanations that are perfectly compatible with the Standard Model are:

- the particles are real, and they exist at all positions in space as predicted by the Schrodinger equation, but these results happen in different universes; for some unexplained reason, "classical objects" can only observe one world at a time

- particles are real, and their movement is affected by a real carrier wave; the particle has a definite but unmeasurable location in space and speed, affected by the carrier wave; the carrier wave is the wave described by the Schrodinger equation

- Measurement is a physical process that causes particles to switch from being somewhat indefinite objects described by the wave function to being definite objects described by classical (rather, relativistic) mechanics

Of course, some of these interpretations have their own unintuitive aspects (non-locality), because of the Bell inequalities. There is also super-determinism, that could in principle allow QM to be both deterministic and local, at the cost of statistical independence.

And finally, the Standard Model itself doesn't yet account for gravity, and the current theories we have for gravity do not work with masses that have indefinite positions in space, so there is still room for discoveries that could contradict somewhat the fundamental properties of "particles" as known today (though, to be fair, it is more likely that our theories about gravity are the ones that will need adjustment).

WClayFerguson 43 days ago [-]
I can tell you're deep into Physics as I am. To be honest I was presenting the "Standard Model" the way a professor would explain it to a student, who is trying to explain QFT using the conventional beliefs held by most of the Physics community.

I agree with everything you said, actually, except for this one sentence which you stated which I know is some kind of typo, because I doubt you think it's true: "Before a measurement takes place, the movement of electrons is predicted by a deterministic equation, there is no probability." That sentence goes against conventional wisdom so I doubt you meant it litterally.

Anyway, if you want my own personal unproven belief (theory) here it is: (or a few aspects of it)

I think our universe is a 3D (excluding time) manifold that is an event horizon in a larger higher dimensional space and what we call "Wave Collapse" is actually the point where an actual existing real particle does travel across our manifold. That is, anything that we can assign a position to in spacetime coordinates is also "on" this manifold. You can also call this manifold our "universe".

So when something exists in what we call "Probability Wave" state that just means we haven't yet done something to pinpoint a particle "on" this (our) event horizon. Unless someone is a very good geometry mathematician they cannot really comprehend how our entire universe can be a "surface" in some a higher-dimensional space, and since it's unproven I generally don't bring it up on HN. I also believe all N-Dimensional spaces contain (N-1)-Dimensional constructs inside them. The example in our unsivers is 'black holes'. We see 2D (i.e (3-1)D) constructs where our physics fails and even have proven their informational content is proportional to surface area (Hawking+Susskind). Most people think black holes are 3D spheres, but they're really 2D surfaces to their "inhabitants". Similarly the higher dimensional universe in which our 3D space is embedded would see our universe similarly as some kind of construct where their own physics breaks down, and they are unable to "look" inside possibly, just like we can't see inside black holes.

Also if we are an event horizon it disproves the big bang theory. The inhabitants of a black hole would notice their "universe" is expanding, and therefore conclude they came "from" some center point, but in reality BHs form from outside in, not inside out. So our universe came from outside itself not inside itself. It doesn't solve the 'first mover' problem, it just inverts it, but it does simplify it.

All that to say, I appreciated your response and you're right I was putting the "professor hat" on when I described most of what I said on this thread, but the paragraph above should prove I'm capable of as much quackery as the next guy. lol.

tsimionescu 43 days ago [-]
Replying separately to this:

> We see 2D (i.e (3-1)D) constructs where our physics fails and even have proven their informational content is proportional to surface area (Hawking+Susskind). Most people think black holes are 3D spheres, but they're really 2D surfaces to their "inhabitants".

I think that is more complicated. From what Susskind explains, the current understanding is that black holes have a dual nature, similarly to the idea of wave/particle duality. Specifically, you can perform experiments that would see the event horizon of the black hole as a 2D surface which emits Hawking radiation; and you can perform experiments which will show the event horizon of the black hole is a completely unremarkable region of space. Importantly though, there is no way for an observer to notice both results, so there is no contradiction. The black hole is 1 thing to some observers, and 1 different thing to other observers, and the two can't even communicate.

Even more specifically, to an observer that will never cross the event horizon, the event horizon is a surface emitting Hawking radiation. For an observer approaching and passing the event horizon, the event horizon emits no radiation and is a completely unremarkable region of space-time. The two observers of course can't communicate, as the observer crossing the event horizon will never be able to send a signal outside again, and conversely, a signal sent from outside after they crossed the horizon will never reach them.

I would also note that our current theories do not permit any kind of structure to exist "inside" a black hole, which is a 0-volume point. If you mean "inside the radius of the event horizon of a black hole", I believe matter would be observed falling quickly towards the center. A theory of quantum gravity may give us some idea of the structure of a black hole, but I personally doubt that it could be allowed to contain another universe.

WClayFerguson 43 days ago [-]
I agree with pretty much all of what you said. It's an amazing brain teaser how the person falling across an event horizon would feel nothing (as far as science knows) and yet some observer far away watching it happen would see that it takes 'forever' to happen (time stops). Like QM itself, General Relativity has some 'contradictions' built in, related to observability.

Despite the contradictions, I agree with Susskind that the 'surface' of BHs might be where the interesting stuff happens, and that the singularity itself might not even 'exist' except as some endpoint boundary condition of oscillations like an end of a guitar string, that's interacting with everything yet contains nothing.

tsimionescu 43 days ago [-]
Glad we mostly agree :)

> I doubt you think it's true: "Before a measurement takes place, the movement of electrons is predicted by a deterministic equation, there is no probability." That sentence goes against conventional wisdom so I doubt you meant it litterally.

I meant that very literally, and it is very important to understand. Quantum mechanics contains two fundamental postulates:

1. The Schrodinger equation: any quantum system can be described by the Schrodinger equation, which is a linear partial differential equation - i.e. it is completely deterministic. The solution of the Schrodinger equation is one or more wave functions - complex-valued functions which have some value for every point in space.

2. The Born rule: when a measurement is made of the state of a quantum system, the probability that a particular result will be observed is equal to the square of the amplitude of the wave function. To predict the state of the system after the measurement, the wave function must be updated to have the exact value of the measurement and no others.

Without the Born rule, QM is completely deterministic, and predicts that particles have multiple positions. This prediction is actually correct until you measure anything. For an example, let's say you have a particle P0 whose wave function has some non-0 amplitude at far away locations A and B. Say you also have two other particles, Pa and Pb; Pa has amplitude almost 1 at point A and 0 elsewhere, while Pb has amplitude almost 1 at point B and 0 elsewhere. The positions of both Pa and Pb will be affected by the properties of P0. So, P0 was essentially in both places at once.

However, if you add detectors for P0 at positions A and B, what you will notice two things:

1. If detector A detected P0, detector B will never see it, and vice-versa. The probability for each of them will correspond perfectly to the square of the amplitude that P0 had at that point.

2. If detector A detected P0, the position of Pb will no longer depend on any property of P0, and vice versa.

So, the measurement changes the wave function of the P0, Pa and Pb system. The equation before the measurement is deterministic, and the equation after the measurement is also deterministic, but the switch from the first one to the second is probabilistic.

By the way, an excellent resource on this topic is Sabine Hossenfelder's blog, for example this post:

http://backreaction.blogspot.com/2019/10/what-is-quantum-mea...

WClayFerguson 43 days ago [-]
We may be getting into semantics but QFT doesn't say electrons are even moving. It says there are no particles at all anywhere period full stop UNTIL the precise moment of measurement. This is the "Measurement Problem". The measurement CREATES the particle.

The famous Bell experiment proved that the view of quantum mechanics as describing how particles "move" is incorrect, because the probability wave is not actually describing any movements of any actual particles.

If you think of a single Hydrogen atom floating in space, no there is not an electron moving around it. There is no electron that exists at all "until" something interacts (according to Standard Model) with the wave function and causes the wave to collapse and "choose" a place in spacetime to materialize an "electron" in and only then is there an electron.

tsimionescu 43 days ago [-]
The hydrogen atom has a wave function which shows properties for a negative charge and mass with some amplitudes at different positions in space and time, and a positive charge and mass at certain other positions.

Now, before you perform a measurement, you can't say that the electron is anywhere particularly in space, and netither can you say that about the proton. In fact, the atom itself isn't really somewhere definite.

On the other hand, just because they don't exist somewhere specific that doesn't mean that they don't exist. That charge and mass can't just disappear, so if we ever observed the atom, we know that it still exists in some sense. Even with QFT, you may dispute whether the particle exists or not, but its conserved properties certainly do, regardless of how non-localized they may be.

And again, this is just an interpretation of QM that were discussing. Adherents of MWI would say that the particles are perfectly real, perfectly localized (in a particular world) and move essentially like classical particles, but they happen to interact with all different versions of themselves in all the different worlds, as long as they keep the same phase.

I personally don't like MWI, but it is still consistent with all observations.

WClayFerguson 43 days ago [-]
well said.
gus_massa 44 days ago [-]
> I'm pretty sure in Quantum Mechanics systems like this the entire unit behaves as one and there's no real distinction possible regarding "which is which" if you were to try to identify individual atoms.

The grow experiment was at room temperature 298K. At this temperature the nuclei of the atoms behave almost classically. There are some important quantum effects between the electrons, but their mass is like 10000 smaller. The effects are small in the electrons in the lower levels that are close to the nuclei, but in the valence band they can be very important. Specially in conductors where the electrons are very delocalized, but this is not a conductor.

thaumasiotes 44 days ago [-]
> At this temperature the nuclei of the atoms behave almost classically.

The video seems to show a crystal made of fairly large spheres... which appear from nothing. I don't see a bunch of chaotic spheres which arrange themselves into a grid; I see a grid of spheres appearing where there was nothing before.

I have a hard time thinking this corresponds to classical mechanics. :/

tsimionescu 44 days ago [-]
The timescale is relevant. You're seeing 2 frames milliseconds apart of a process that took probably a few nanoseconds.
thaumasiotes 44 days ago [-]
Why are there any frames in which the sodium and chlorine atoms appear not to exist?

Suppose there was just the chlorine (no sodium), and we observed it the same way. Would we see mostly chaotic arrangements of big spheres, or mostly a smooth background with no spheres?

gus_massa 44 days ago [-]
Near the bottom is a figure with some cherry picked frames of the video and a handmade drawing showing the crystal and the incoming pairs of atoms.

The Brownian motion depends on the mass of the object, so the average movement of the individual atoms is higher than the average movement of the small crystal. So the isolated atoms are blurred in the image.

WClayFerguson 44 days ago [-]
I answered all this in my reply to l33tman, above so I won't repeat that here, but check it out.
tsimionescu 43 days ago [-]
Because you are seeing frames once every few milliseconds of atoms moving back and forth at speeds a fraction of the speed of light. It's only when they happen to be in very fixed positions that you have any hope to notice a definite image of the NaCl molecule.

In general, the very fact that you can see something should be a clear indication that you are not observing quantum behavior: particles whose properties (such as position) are measured DO NOT behave according to classical physics, they no longer display quantum effects. And while we have yet to understand what exactly counts as a measurement, something which allows you to have a picture of the atoms certainly counts.

WClayFerguson 44 days ago [-]
It's not that the individual atoms didn't exist before they joined, but it's that they start oscillating in unison with each other in a pattern that emerges purely from wave interactions.

Nature settles into the most stable patterns of oscillation it can find, even without anything "causing that". To fully understand this kind of emergence you need to realize even the following video is in the same category of phenomenology called "emergence":

https://www.youtube.com/watch?v=5v5eBf2KwF8

Atoms themselves "emerge" from probability waves, not the other way around.

On a wild tangent: I believe all emergent patterns represent "negative entropy" so I claim this disproves the Second Law of Thermodynamics, because it fails to take into account (i.e. quantify) "pattern-ness" or "order" in systems. Total entropy of the universe maybe doesn't increase but remains at zero, where the order perfectly counterbalances the randomness. Since there's no way to "measure" order in a system, the Second Law remains somewhat philosophical despite it being consistent with 'gross averages' measurements like temperatures, pressures, volumes, etc., in classical systems for which essentially only one side of the equation can be quantified.

thaumasiotes 43 days ago [-]
However accurate this description may be, it definitely cannot support the claim that "at this timescale the nuclei of the atoms behave almost classically".
WClayFerguson 44 days ago [-]
Not that I'm trying to blow anyone's mind but here's a couple of other 'emergent patterns' in reality which can also be called standing waves, which proves some very low level patterns like DNA can cause identical patterns to emerge billions of layers higher in the causal chain of reality, and way higher than just the physical structure of the body and brain but also into the surrounding world.

https://www.reddit.com/r/BeAmazed/comments/l2mtfx/separated_...

anthk 44 days ago [-]
Also, static from no TV signals on the TV.
m463 44 days ago [-]
self-organizing static
jagraff 44 days ago [-]
This is incredibly cool:

> Two novel techniques, atomic-resolution real-time video and conical carbon nanotube confinement, allow researchers to view never-before-seen details about crystal formation. The observations confirm theoretical predictions about how salt crystals form and could inform general theories about the way in which crystal formation produces different ordered structures from an otherwise disordered chemical mixture.

> To hold samples in place, we use atom-thick carbon nanohorns, one of our previous inventions. With the stunning videos Sakakibara captured, we immediately noticed the opportunity to study the structural and statistical aspects of crystal nucleation in unprecedented detail.

Creating shaped nucleation sites using carbon nanotubes (nanohorns?) sounds like a fascinating technology. I don't have access to the paper unfortunately - I'm curious what other types of crystals could theoretically be grown with this technology. The authors mention graphite - what about silicon? Could it be used to grow more regular crystals for use in electronics? With fewer defects, I'd imagine we could reduce the failure rate in manufacturing.

grishka 44 days ago [-]
> I don't have access to the paper unfortunately

The website you're looking for starts with sci and ends with hub.

sebmellen 44 days ago [-]
Not up there yet. Probably needs a few weeks, unless a HN reader is so kind as to add it: https://sci-hub.se/10.1021/jacs.0c12100.
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MizelMiser 44 days ago [-]
Ericson2314 44 days ago [-]
Are you angling for some scintillating chub?
dragontamer 44 days ago [-]
> “Salt is just our first model substance to probe the fundamentals of nucleation events,” said University Professor Eiichi Nakamura. “Salt only crystallizes one way. But other molecules, such as carbon, can crystallize in multiple ways, leading to graphite or diamond. This is called polymorphism and no one has seen the early stages of the nucleation that leads to it. I hope our study provides the first step in understanding the mechanism of polymorphism.”

I'm amused that Chemists / Physicists also have the word "Polymorphism" and that it means something completely different from the programming term.

MereInterest 44 days ago [-]
In some ways, they are sort of related. In chemistry, you have different representations (diamond/graphite) of the same underlying thing (carbon). In programming, you have different representations (PointXY/PointRTheta) of the the same underlying concept (Point2D).
jxramos 44 days ago [-]
right, the roots of the word make it applicable to lots of stuff, poly or many, morph or structure/form.
adrianmonk 44 days ago [-]
Arguably it's the strategy pattern. Graphite and Diamond are subclasses of CrystalizationStrategy.
iainmerrick 44 days ago [-]
Things could get messy real fast if you need to inherit from both Graphite and Diamond...
chrisweekly 44 days ago [-]
Favor composition over inheritance!
frumiousirc 44 days ago [-]
Yes, the diamond inheritance pattern is a classic OO problem. :D
LightMachine 44 days ago [-]
That isn't what polymorphism means, polymorphism would be more like Point<Float> and Point<Double> using the same Point definition.
flobosg 44 days ago [-]
It’s also a term used in biology: https://en.wikipedia.org/wiki/Polymorphism#Biology
skulk 44 days ago [-]
My second confrontation with the term "polymorph" was a Java tutorial, the first was Larn (https://larn.fandom.com/wiki/Spells)
louthy 44 days ago [-]
> I'm amused that Chemists / Physicists also have the word "Polymorphism" and that it means something completely different from the programming term.

Seems like a good reason to stop using it [in programming], and the technique behind it.

thepace 44 days ago [-]
Every time I see these kinds of video, whether that is of protein translation, kinesin walking on microtubule, or birth and death of a galaxy, I get this feeling that Panpsychism is closer to truth that it gets credit for. Any constraints we put in the defining consciousness and life seems to be just some arbitrary constraint put there for our own convenience.
TeMPOraL 44 days ago [-]
Isn't panpsychism a kind of reverse materialism? Both seem to correctly recognize that terms we create are just lines we draw on our map through the terrain of reality, which we rank by their usefulness, by how close they seem to be "carving nature at its joints". Based on my brief skimming, panpsychism seems to say the terrain is all mysterious and wonderful, whereas materialism says it's all just mundane.

Or am I completely mis-skimming the Wikipedia entry on panpsychism?

lewispollard 44 days ago [-]
I think you'd enjoy the work of Bernardo Kastrup, who is a proponent of idealism, while also arguing against panpsychism, for basically the reasons you just stated - ie, there is a reality made of parts, and those parts are x, where x is 'matter', 'mind', 'consciousness', 'electromagnetism' and so on. But the trouble then is that you can only describe the constituent parts in terms of those parts. For example, subatomic particles have properties like spin and charge, but that's the only way you can describe them - in relation to one another - without having to go a level 'deeper' if it were possible to describe them in further parts (which would only be describable in terms of those parts, and so on).
perfmode 44 days ago [-]
my question to you: do you consider yourself to be mysterious or just mundane? what is your experience of your own Being-ness?
gus_massa 44 days ago [-]
> Do you consider yourself to be mysterious or just mundane?

Mundane, that is even more amazing.

> What is your experience of your own Being-ness?

My electrons and nuclei are arranged in a weird pattern. If you ask them if I'm conscious, they can move another electrons and nuclei to type "yes". If you ask them if I'm lying, they can move another electrons and nuclei to type "no". It's just a strange pattern that simulates a delusion, don't trust them.

perfmode 44 days ago [-]
> Mundane, that is even more amazing.

What's amazing about the mundane?

TeMPOraL 44 days ago [-]
A good question, something I'll have to think about.

The immediate if indirect answer I can give you: I stopped feeling this sense of wonder, mystery, greater purpose of reality, somewhen during my university years. I only ever experience these feelings when consuming works of fiction.

mensetmanusman 44 days ago [-]
C.S. Lewis described something similar with fiction ‘baptizing the imagination in longing’

https://andrewmarrosb.blog/articles/baptizing-the-imaginatio...

csomar 44 days ago [-]
> Any constraints we put in the defining consciousness and life seems to be just some arbitrary constraint put there for our own convenience.

The definition of consciousness is very much tied to how humans (or some scientists) perceive consciousness. I'm pretty sure my dog is conscious of itself and its surrounding. It just happens to have a less sophisticated consciousness than the one I have. Some animals might have a pretty high consciousness but they fail to communicate it to the humans.

jes 44 days ago [-]
I am an Alan Watts fan. I think he would agree with you.
jng 44 days ago [-]
I love Alan Watts too. In any case, I need to insert the necessary reference to recently passed John Conway's Free Will Theorem. I recommend every one to watch his 6-lecture long presentation on this, available on YouTube and underappreciated given the number of views, where he captivatingly describes his proof that, if we have free will, so do elementary particles. This is a purely mathematics- and physics-based proof which I understand is fully accepted by the scientific community, and while it, of course, does not provide an explanation of the underlying cause, it provides the best possible description obtained by scientific methodology so far.

I like to think that, somehow, Alan Watts and John Conway were digging the same tunnel, just starting from the two endpoints, and bound to meet at some point in the future. We just need a few more diggers of that stature (tall order, I know).

jes 44 days ago [-]
Thank you for this reference. I’m a free will skeptic. Now looking forward to watching Conway’s series.

I have a paper by Anthony Cashmore that I will cite here later.

jes 44 days ago [-]
Paper from Anthony Cashmore that I mentioned previously:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2842067/

djedr 44 days ago [-]
He would definitely dig that. Curiously, I was drawn to this thread because I was just listening to him today, talking about crystals and the nature of reality. He would go thru so many topics in such detail and clarity, it's incredible.
jes 44 days ago [-]
Same. I often notice the precision with which he used language. Such a joy to listen to.

I especially like the chill-step YouTube videos some people assemble and publish. I download them with youtube-dl and listen to them on my phone at night while drifting off to sleep.

At 61 years of age, the philosophy he describes (Advaita Vedanta / Zen Buddhism / Taoism) brings me great comfort.

djedr 44 days ago [-]
> I often notice the precision with which he used language.

Indeed. Hard to find an inaccuracy, even when he's talking about some details of technical subjects. He had an exceptional ability to translate between the spiritual and the technical in a way which seems to make complete sense.

> Such a joy to listen to.

A true spiritual entertainer. Never boring. I imagine he could be a stand-up comedian today.

> I especially like the chill-step YouTube videos some people assemble and publish. I download them with youtube-dl and listen to them on my phone at night while drifting off to sleep.

Similar, I went thru a lot of the material on youtube. High-quality material with transcripts can also be found here: https://www.organism.earth/library/author/alan-watts A lot of it I listened to many times over and I keep getting new insights out of it, it's so densely packed.

> At 61 years of age, the philosophy he describes (Advaita Vedanta / Zen Buddhism / Taoism) brings me great comfort.

Definitely helps to know these philosophical perspectives, especially if one gets tangled up in some harmful model of reality.

Somehow the basic (non-religious, just philosophical) Taoism seems to most align with me at the moment. I credit the Dao for solving a very tough naming problem for me. ;)

thepace 44 days ago [-]
Out of the many people I have heard talk about vedanta, Alan Watts is one of the most original ones.
kharak 44 days ago [-]
I can't see this connection at all. Could someone who thinks or feels this way elaborate?

Does this feeling arise because those atoms move? Or is it the self-assembling behavior? Is this the same feeling some people have when they see a door suddenly close due to the wind, as if some spirit is responsible? I remember feeling like this as a kid. But getting older, I realized that this feeling of agency behind everything is unfounded. And the feeling faded away.

wahern 44 days ago [-]
Panpsychism, pantheism, etc, are enticing because humans are predisposed to see patterns, structure, reason, and intelligence; to anthropomorphize nature. Characterizing as "arbitrary" our admittedly feeble and flawed attempts at distinguishing the human mind is an easy way to placate that underlying, intrinsic desire.

Of course, maybe it is true! (That felt good to say :)

mncharity 42 days ago [-]
> Every time I see these kinds of video, whether that is of protein translation, kinesin walking on microtubule, [...] I get this feeling that Panpsychism is closer to truth

Those two are... sadly quite different than the TFA video. Those are cartoons, steeped in artistic license, accommodation of animation software limitations, and artists regrettably but intentionally prioritizing "pretty" over a misconception-spawning lack of resemblance to reality. Think of a video of Saint Trump's day, with frames selected to show him floating along, limbs unmoving, through a deserted White House. Problematic when learning biology. Not a good source of ground truth.

kvakkefly 44 days ago [-]
You may also like my paper “ Direct Atomic Simulations of Facet Formation and Equilibrium Shapes of SiC Nanoparticles”

Not as cool as experiment of course

https://pubs.acs.org/doi/full/10.1021/acs.cgd.9b00612

blix 44 days ago [-]
This is a neat paper. Cool to see kinetic phenomena make it's way into MD. How many GPU-hours did you need to get those 500ns simulations?

You should throw up some videos of these somewhere, if you have the time.

vhold 44 days ago [-]
fantod 44 days ago [-]
This is super cool but who's idea was it to feature the video as a pretty small gif on the side of the page?
codezero 44 days ago [-]
literally every grad student in science fields - they don't care about video compression or download quality - and gifs are fast and easy to make and simple to grok and come out with straightforward and predictable fidelity.
anthk 44 days ago [-]
webm's are smaller and ffmpeg can convert any gif in a breeze.
codezero 44 days ago [-]
They don’t care, and their PI will find a way to complain about it not playing on Word ‘97.
at_a_remove 44 days ago [-]
Still cannot look at an embedded .webm on my iPad in Firefox.
jerzyt 44 days ago [-]
What is absolutely mind blowing to me is that when I was in college, in my crystallography class, we were inferring the crystal structure through the X-ray diffraction. Now we can observe it directly. I took the crystallography class in late 70s. I doubt that anyone had expected so much progress.
6nf 44 days ago [-]
In the same vein, I'm blown away what we can do with xray crystallography these days! Structures of proteins with hundreds of atoms can somehow be deduced from some tiny light spots in a kaleidoscope picture? Magical.
jasondclinton 44 days ago [-]
Non-physicist question: why does the block of the forming crystal move as a whole back and forth? Is this Brownian motion in action?
magicalhippo 44 days ago [-]
The containing structure (the carbon nanohorn as they call it), is vibrating. So I'm guessing it's getting kicked around when it touches the walls, so to speak.
hindsightbias 44 days ago [-]
Guessing the crystals are probably connected in some lattice so won't move independently. The expansion horizontally is gated by the walls so it gets bounced around until it moves to a wider section. There seems to be some ratio of horizontal vs vertical growth.
adrianmonk 44 days ago [-]
Amazing achievement! Not only the world's first video of this type, but I imagine also the world's smallest salt shaker.
dylan604 44 days ago [-]
A salt shaker that makes its own salt to boot! Never run out of salt again with our new patented shaker! Just $19.99 if you buy within the next 15 minutes. Order now, and we'll also throw in the matching pepper shaker (not self re-filling) for free! (just pay S&H for both)
jcims 44 days ago [-]
I’m curious how they managed to make it happen so slowly. If that crystal had grown to 100 molecules in 10 seconds it would take roughly the age of the universe to form a grain of table salt.
jacquesm 44 days ago [-]
The growth rate is proportional to the surface area.
goalieca 44 days ago [-]
They confined the reaction to a tiny horn.
mvanga 44 days ago [-]
Can anyone more knowledgeable comment on the details and significance of the comment regarding the frequency of formation being a normal distribution?

> Straight away, they noticed a statistical pattern in the frequency at which the crystals emerged; it followed what’s known as a normal distribution, which has long been theorized but only now experimentally verified.

blt 44 days ago [-]
I am also wondering about this. Normal distributions have support on all real numbers, which would imply that negative frequencies have nonzero probability. That is strange. Perhaps the underlying mechanism is more faithfully modeled by another distribution with nonnegative support, but due to the central limit theorem it is well-approximated by a normal distribution.
bearerofgarbage 44 days ago [-]
Could one be able to upscale the video with a GAN like the following example?

https://www.geoffreylitt.com/images/article_images/enhance/g...

Bjartr 44 days ago [-]
I'm pretty sure such upscaling systems train against ground truth higher res video and purposefully downres'd versions of that video. So, at the very least, we'd need to first get higher res video of the same phenomena once. Though maybe you could style transfer from frames that have been improved by hand.
dannyw 44 days ago [-]
One could, but it wouldn’t be real.
bearerofgarbage 44 days ago [-]
All models are wrong, some are useful
overdrivetg 44 days ago [-]
This was a cool AlphaPhoenix video doing a large-scale crystal growth simulation that looks amazingly similar:

https://youtu.be/06TscuHNvGQ?t=305

soheil 44 days ago [-]
This looks like how microscopic proteins and bacteria move in the body. I wonder how much of their motion is caused by the atomic level forces that form a lattice structure similar to that of salt crystals.
rightbyte 44 days ago [-]
The "tube"/horn is vibrating. I would make that connection from the gif. The scale difference is quite big.
frongpik 44 days ago [-]
Another interesting experiment is the effect of strong magnetic fields on crystals: when the field is turned off, is there something left in the crystal, e.g. a certain motion pattern of crystal nodes?
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edumucelli 44 days ago [-]
Amazing! Also kudos to the master student that, although starting his career in science, already actively participated in this incredible work!
convery 44 days ago [-]
It's shit like this that makes me re-consider the simulation argument, like how statistics is just an optimization to save compute power.
bearerofgarbage 44 days ago [-]
enchiridion 44 days ago [-]
In which direction?
acvny 44 days ago [-]
I can't see the video. Incredible that the actual appearance of the crystal happens in phase transition - almost instantly.
tomsmeding 44 days ago [-]
Direct link to a higher-framerate video than the gif on the linked page: https://pubs.acs.org/doi/suppl/10.1021/jacs.0c12100/suppl_fi...
biggio 44 days ago [-]
Hope this will help finding a way to dissolve calcium oxalate stones formed in kidney
amelius 44 days ago [-]
Why are the atoms not visible when they are still in dissolved state?
peter_d_sherman 44 days ago [-]
Star Trek's Replicator -- version 0.000001... <g>
anthk 44 days ago [-]
Is there a way to watch the video without JS?
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zer0n1ght 44 days ago [-]
Just like a bunch of sphere magnets.
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codercotton 44 days ago [-]
Super cool, where's my replicator?
krylon 44 days ago [-]
The trivial task of building a working replicator is left as an exercise to the reader. ;-)
curtainsforus 44 days ago [-]
Just build your own
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