Hacker News new | past | comments | ask | show | jobs | submit login
Giant Molecules Exist in Two Places at Once in Quantum Experiment (scientificamerican.com)
94 points by jonbaer 6 days ago | hide | past | web | favorite | 68 comments

Damn, it wasn't so easy to find the article, because TFA doesn't explicitly provide author names, even. But the link in the image title led to Fein et al. (2019).[0]

So what I'm curious about is how far apart those "Two Places at Once" are. And if I'm understanding Fig. 2 correctly, it's large. That is ...

> Fig. 2 | interference data. a, Counts as a function of the transverse position of the third grating with a sine-fit (solid black line) yielding a visibility of 25 ± 3%. The optical grating power was 1.2 W for this single scan. Counts are dark-rate-corrected and normalized to the control measurements.

... with peaks at ~200 nm, ~430 nm, ~680 nm and ~900 nm.

But a 25 kDa molecule is only ~4 nm in diameter.[1]

That's amazing!

0) https://sci-hub.tw/http://dx.doi.org/10.1038/s41567-019-0663...

1) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3055910/

Thank you!

Rant: Not linking to the source article is a crime conmited by many outlets trying to report on science. I do not understand that practice. It is even worse when the researcher's institution does this in a public press release (MIT is consistently guilty of this). Are these people afraid that their watered down "explanations" are so wromg that even a cursory glance over the paper will show this?

Some news sites such as Ars Technica provide the links. They even have agreements with major publishers that allow them to bypass paywalls and provide their readers with links to the the published full text as well.

There's a dated document that leaked at the start of the decade called The AOL Way that sheds a lot of light on these tactics -


External links are used for SEO and generally reserved for partner-websites or their own properties to recirculate traffic. Here we have an article reposted from space.com to scientificamerican.com that only links to nature.com and livescience.com. Future US owns space.com + livescience.com, and Springer Nature owns scientificamerican.com + nature.com.

It doesn't need to be a link. A citation at the bottom of the article would suffice.

Hey, this is my field. It's not as easy as you've laid it out.

A lot of SEO marketers try to get links into articles. This is part of what they do.

Many of them are legit.

Enough are not legit.

This causes links to get pointed to shady websites. It also happens that legit websites get taken over and re-built as shady websites.

This has gotten to the point where many newsmedia organizations or publishers have set blanket policies that NO ONE is to be linked to, or at the least no one receive will receive do-follow link.

I was hoping that someone would review my interpretation of the result. Because I am not a physicist, so most of their discussion is over my head.

What I pointed to tells me that the spacing of interference fringes for a ~4 nm object was ~230 nm.

But does that mean that the object's wave function leads to probabilities spread over hundreds of nanometers?

Or does the fringe spacing merely result from small angular displacements over a long distance?

Dunno if it was a link when you looked, but "Nature Physics" in the third paragraph links directly to the paper and bypasses the Nature paywall with some sort of referer link.

[0]: https://www.nature.com/articles/s41567-019-0663-9


> Now, in a paper published Sept. 23 in the journal Nature Physics, an international team of researchers has caused molecule made up of up to 2,000 atoms to occupy two places at the same time.

That wasn't there when I read it.

The original paper, fortunately linked in the article, is quite readable:


I was expecting it to discuss the largest species previously shown to demonstrate an interference pattern, but unfortunately there was none.

Other points of note:

Regarding the choice of molecule, and specifically fluorination:

> An intense neutral beam of intact molecules is a prerequisite for our experiments, but soft neutral volatilization and post-ionization of complex molecules is an outstanding technical challenge. While matrix-assisted laser desorption and electrospray ionization are useful tools for molecular analysis, the charged beams they pro- duce are incompatible with the stringent dephasing requirements of interferometry. Continuous effusive thermal beams, on the other hand, suffer from thermal fragmentation for masses beyond a few kilodaltons. This can be overcome via fluoroalkyl-functionalization of the molecules, which adds mass, reduces the polarizability-to- mass ratio and increases volatility

The group sees another factor of 10 increase in the ability to measure interference:

> With advances in beam sources for biomolecules and metal clusters26,27, techniques to cool the particles below 80K (refs.28,29), and refined grating26 and imaging technologies30, our experiment is scalable and will push matter-wave interference and macroscopicity tests by another order of magnitude24

The Coriolis effect was corrected at least in part mechanically rather than purely computationally:

> Compensation of the Coriolis effect is critical to obtaining high-visibility interference fringes in LUMI. By tilting the gratings, we introduce a gravitational deflection that opposes the Coriolis shift ...

Please correct me where I am wrong, I have only studied quantum physics as a hobby.

I dislike this description of things existing in two places at once, this is because I believe that objects exist in one place, then they move to the next place.

The interference pattern only highlights the probability of where the particle will be when it's next observed, or "where it moved to". The object does not interfere with itself, it's the probability wave that is interfering with itself, and the wave is something separate from the object but is related to it.

The particle does not exist anywhere between its current position and the next. It does not travel in a "linear" or other way, if at time t it was at position 0 and at time tNext it was at position 1, at time tNext*0.5 you cannot assume it was at position 0.5, or both "position 0.5, slightly higher up" and "position 0.5, slightly lower down" at the same time.

In another way, in my mind, the object exists here, then it exists there, but it did not exist at the time between here and there, unless you happened to have observed it. Then of course "there" would be where you have made the observation because you have given it something to interact with.

I guess my issue is, at what moment does the article say that it exists in two places at once? Are they inferring this from the fact that there is an interference pattern?

To quote: "[1] Every particle or group of particles in the universe is also a wave—even large particles, even bacteria, even human beings, even planets and stars. [2] And waves occupy multiple places in space at once. [3] So any chunk of matter can also occupy two places at once."

I guess my problem is with [1] "is also a wave". I think that "there is a wave related to the object" but not "the object IS a wave". Then [3] does not follow.

>I dislike this description of things existing in two places at once, this is because I believe that objects exist in one place, then they move to the next place. The interference pattern only highlights the probability of where the particle will be when it's next observed, or "where it moved to".

No, that would just be regular motion -- and QM would be no really different from throwing a cannonball (for example) and running the ballistic equations.

Remember the classic quote as a guide: "If you think you understand QM, then you don't understand QM".

Even more so if what you think it all is, is a classic quaint motion description. That wouldn't be any mystery, wouldn't explain the two slits experiment results, and wouldn't perplex scientists and have different interpretations for a century.

>In another way, in my mind, the object exists here, then it exists there, but it did not exist at the time between here and there, unless you happened to have observed it. Then of course "there" would be where you have made the observation because you have given it something to interact with.

That would still not cause interference, of explain the experimental results.

It's just like regular solid body motion but with added intermittent existence of the object.

> No, that would just be regular motion -- and QM would be no really different from throwing a cannonball (for example) and running the ballistic equations.

This is not true. Under the DeBroglie-Bohm interpretation of QM an object exists at a single place at a time, what is fuzzy is our knowledge of where it is. And this interpretation holds up to all of the double slit and interference behaviors we expect from QM.

>This is not true. Under the DeBroglie-Bohm interpretation of QM an object exists at a single place at a time, what is fuzzy is our knowledge of where it is. And this interpretation holds up to all of the double slit and interference behaviors we expect from QM.

Under the DeBroglie-Bohm, yes. But the above description (which is also what I criticized in the prior comment):

(a) an object exists at a single place at a time,

(b) what is fuzzy is our knowledge of where it is

Are not enough to get to DeBroglie-Bohm interpretation though -- it misses it's critical element: the pilot wave / guide.

The problem you are having (I think) is this damned phraseology we have grown accustomed to "in two places at once". That's not the proper way to think about it. Anything and everything can be in a superposition of location and state where the location or state is not determined until forced to by some measurement/interaction. The universe if you will is not determined. It's in a superposition of states and positions to be later determined when acted upon.

You are absolutely right. I personally have adopten the BSM-SG (developed by Dr. Stoyan Sarg) model which puts very strict limits on the superposition concept. No particle is ever at two places at once nor does it jump around. The model is however much much finer in it's structural organization. A neutrino for example is quite a large object from the BSM perspective. When a photon for example pumps the CL space volume occupied by a electron orbit, there is a limited time in which the CL is pumped in a way that the photon is existing as a complete structure anymore, but the electron is not yet pushed to a higher orbit. Chapter 7 in the book goes in very much detail of this.

This uncertainty is very limited for is existence in time and very limited which processes can implement such uncertainties. From the BSM perspective, looking at the experimental setup, I can not really see, how this will prove uncertainty.

> I believe that objects exist in one place, then they move to the next place.

Bohmian mechanics was made for people like you.


To go further, I have a colleague who says there are actually no particles, only waves interacting with other waves. I am trying to get him to make a proper thesis out of this but he is busy trying to earn money to support his family. If there are any theories about this, please link them in the thread! It sort of resonates with what Richard Feynman has been demonstrating in some of his lectures but I have not been able to find the right keywords to search the internet, or the best way to ask scientists.

Problems of hobby scientists...

That's indeed a layman explanation of the mainstream theory.

From what I understand of this theory (not a physicist), particle are not small atomic objects but they're not waves either. Nobody can describe what they are otherwise than by mathematic equations describing their interaction. Some of these equations describe some aspects of reality accurately if you think of particles as objects, some others describe some other aspects of reality well if you think of particles as wave. Doesn't mean that particles are either, they just behave like one or the other depending what you're studying

It is called Quantum Field Theory.


And it has been the mainstream quantum theory for decades. Nothing new. But physics doesn't concern itself with what "actually exists", only which models work the best. Whether fields or particles are ontologically more basic is a question as of now relegated to the realm of metaphysics. Some physicists have opinions in one way or another, others just subscribe to the "shut up and calculate" school of thought.

QFT, the new ether basically

> the wave is something separate from the object but is related to it.

This is a common idea in Bohmian epistemology, but, speaking as a professional physicist, I don't think most physicists would hold this position. The wave is the object, the object is the wave. "Particle/wave duality" or whatever is just bad language for "a quantum mechanical thing"

I think the point of saying it "exists at two places at once" is that if the molecule exhibited classical behavior then it either would have gone through slit 1 or slit 2, and you'd see two peaks of probability. Instead, you see an interference experiment, so the molecule went... well, here's where language difficulty comes in.

It 'went' through both slits 1 and 2?

'It' went through both slits 1 and 2?

Its wavefunction went through both slit 1 and slit 2?

Its wavefunction went through both slit 1 and slit 2 without becoming entangled with anything else?

However, whatever it did, quantum mechanics is clear about one thing: [something] [moved] THROUGH the screen! That is, because probability current [1] is conserved as a direct result of the Schrödinger equation, it definitely did not happen that the molecule vanished on one side in a puff of smoke and WHAM appeared on the other side.

So, the molecule "went through the screen", if what you mean is "at the beginning almost all of the probability was on one side of the screen and smoothly evolved to be mostly on the other". Or, rather, at the beginning you measured the position to be definitively on one side of the screen and it smoothly evolved so that later it hit the target, so that its probability was non-negligible on the other side of the screen.

Or, strictly speaking, it went forward through the screen one more time than it backtracked... You're right that the molecule didn't have to take some classically-expected "beautiful" trajectory (straight line, parabola, whatever). In fact it did all sorts of crazy things, coherently. Saying that it was coherent is a shortcut for saying that all those crazy ways' probability amplitudes sum (so that they might interfere), rather than their probabilities directly.

"occupy two places at once" is just bad language for what things do quantum mechanically. For example, "occupy" is laden with classical expectations---if a solid metal ball occupies a space, air does not. But that's not how quantum mechanics works. You can have a weird quantum mechanical state like

"ball at x and air at y"+"ball at y and air at x".

In neither addend of the sum are ball and air at the same place (just as you'd expect classically). But if you look at the sum and decide only to look at the description of the ball and forget about the air you'd decide that the ball "occupies two places at once".

Of course rather than "air" you can put "nothing" or "vacuum" or whatever. But it still isn't the case that the ball is taking up twice its volume---it's taking up its full volume, but in two alternative ways? Again, language isn't great here.

[1] https://en.wikipedia.org/wiki/Probability_current

> I don't think most physicists would hold this position

That's true, but those that do hold it hew to it rather vigorously.

The issue then becomes the difficulty of enjoying a Bohmian lifestyle when trying to formulate a relativistic, many-body, QFT.

> enjoying a Bohmian lifestyle

That is a truly splendid turn of phrase.

I've been trying to get it to catch on, to little avail! Maybe I need to render it as Boh[e]mian? I feel like that gives it away!

Thank you for your detailed explanation, this helps a lot in my understanding!

> Because physicists already knew that electrons had mass and were definitely particles ...

I think that evidence for existance of particles is pretty old and should be reconsidered. I think we 8should more carefully treat the data that convinced physicists that matter is particles, before they knew matter is a wave. Maybe it's counter productive to percieve matter as made of particles with particle qualities (what are those? pointlike, with specific (even if unmeasurable) momentum, position energy).

Maybe momentum, position and energy is not something 'particles' have all the time. Maybe it's just something they manifest only while interacting.

> That’s big enough that the researchers had to account for factors like gravity and the rotation of the Earth in designing the beam emitter

Will this provide us with insight into how gravity and the quantum world relate?

I have not read the paper, am not an expert, and can't judge with 100% reliability - but my understanding is no, I don't think an experiment of this type will necessarily provide the insight into a quantum nature of gravity.

The effects described here are purely Newtonian - in particular, the earth's rotation and gravity are the same "kind" of impact, just an F=ma force which deflects the beam of molecules in the same manner that gravity deflects a stream of water out of a garden hose or the earth's rotation deflects a Foucault pendulum. In general I think I quantum gravitation experiments would require very low-mass particles in a very high-mass gravitational well: high-mass particles on Earth will be dominated by Newtonian gravity and quantum effects will be extremely difficult to detect.

The relation this does give insight on is between Newtonian and quantum physics - the fuzzy boundary between determism and randomness - which is itself interesting, but also better understood. Perhaps a more precise measurement may reveal that the gravitational deflection is significantly more/less than expected from classical gravitation in a way that can only be explained with a new quantum theory, but that is quite speculative and almost certainly not supported by the evidence in this particular experiment.

Soon, things that are today considered fantasy and disregarded as mysticism will become science facts, just as electricity and magnetism were alien things a century ago. In the end we will realize that every myth comes from a true source. Everything can be made to be, once you put enough energy to make it manifested; I have absolutely no doubt in my mind about this, since I've seen and read things that are well beyond from what is common knowledge;

Listen to this episode where Sean Carroll talks about Superposition of larger objects https://podcasts.apple.com/us/podcast/52-many-quantum-worlds...

The scientist who find the point where super position stops will get the Nobel price for sure, I could give you a hint, it is less than my cat, I'm sure it never been in two places at once (Schrödinger is right about his cat too)

Superposition is not stopping as far as we know it.

Cat typically weighs 3,6 – 4,5 kg. De Broglie Wavelength of 4 kg cat moving 1×10^-10 m/s is 1.7×10^14 m.

You cat is in many places at once, those places are just very close to each other.

Something I don't quite understand about quantum mechanics and the MWI... At the point the atom passes through the diffraction grating, it has a quantum superposition. According to MWI, reality has "branched", right?

Then the two realities interfere with each other to form the probabilistic pattern at the detector. So, according to MWI, reality has "merged" again?

If we accept the mulitiverse idea of MWI, doesn't that mean at some point particles aren't able to marge with their branched-reality versions?

The "at some point" doesn't have to do with time. It has to do with the rest of the wavefunction of the universe. If the atom becomes entangled with everything else (in fact, a single quantum-mechanical spin suffices) the two branches become orthogonal and the interference terms from 'merging' vanish. We say the wavefunction 'decohered' when it becomes too complicated to see how to reverse this effect---as more and more particles get involved it becomes hopeless.

That exponent for the wavelength is wrong. It should be more like 1.6x10^-33m. At least it should be negative.

Yes. it should be 1.7×10^-14 m.

Our cat is often in many places at once. He's able to remain in superposition between the garden, the sofa and our bed until I open the fridge, whereupon his wave-function collapses and he's instantly in the kitchen without moving through the intervening space.

Or maybe the odds of your cat being in two places at once is miniscule and is less and less likely the more lasagna he or she eats.

Or your cat is always in all places but your experience only one. At least that one of you.

In any case, the cat is the boss in all instances. My cat is very disappointed in me right now that I can't stop the onset of winter and demonstrates it very effectively!

There is probably some space-time position where he is completely content but I think that's rarer than seeing him in two places at once.

I'm off shooting cats through two slits I made in my living room wall now, to prove or disprove you. For Science!

The result of which is more Jackson Pollock than interference pattern...

Always wondered about the backstory for Bill the Cat.

I always wondered about Fritz the Cat...


Superposition doesn't stop, or that at least is what I understand. The uncertainty principle can be expressed in terms of increments of energy and increments of time: the farer I could be from where I am supposed to be, so to say (that is the energy increment) is inversely proportional to the time that can be measured (that is the time increment).

However, given that I'm no expert on the topic, I wish someone in a better position could elaborate on this idea.

> it is less than my cat...

Wouldn't it be ironic if decades of misdirected science could have been avoided if Schrodinger put his hamster in the box.

My guess is that if the object can record for itself which slit it went through, the effect would stop.

could it be down to the speed of light and distance between both apparent positions of the particle?

It s a PROBABILITY of being at the same position and not a position per say.

Since the molecule of 2000 atoms exists in two places, it doubles the mass. Doesn’t this break the law of conservation of mass and energy. Can someone please explain how this is possible.

From a quantummechanic standpoint its wrong to say, that its at two places at once. I really dont like the Headline. Superposition means, that it didnt decide for one of the two possible states, and so these both exist in superposition.

Can you say it’s moving between two places with an infinite frequency?

My own understanding of QM at this point is that it's sort of wrong to think of anything being exactly anywhere, ever.

The way I intuit it, QM systems seem to be described by their wavefunctions sort of the same way a bunch of sine waves together makes music. You could have a QM system that is spatially (mostly) at X, represented by a wave function, or at Y, represented by another, but the third option, a superposition, is the combination of those two wave functions.

No not really, only when you observe the particle, the location is determined. ANd at this point it behaves like a localised single particle.

It’s probably more accurate to say that the wave function that describes the probability of it being in any location is spread between two places.

As long as we know how the universe works it's perfectly possible that the molecule is steady and all those places go to visit it at once. Recursively apply to its components. When we'll really know how it works we'll be able to do wonders.

Please see my other comment in this thread, especially the part about "occupying space"---the issue is exactly the same with mass.

i feel like my brain is too abstract to accept the idea of something can be at multiple places at once, feels like a chess game, in which every possible move is already known, you only chose one at a time, and thus you decrease the possibilities toward your goal, and there is no go back.

I have trouble with this especially since I’m not sure if the language they’re using is just creating a misunderstanding.

My example is quantum entanglement, which judging from a lot of sci-fi, people think means you literally have the same particle in two places, and changing it in one place changes it instantly in the other. Really it just breaks entanglement and you now have two different particles (so you can’t use it for FTL communication, hear that sci-fi authors?). It took me awhile to understand that, and I’m sure I have similar misunderstandings about this.

So could you have these two places be inside and outside a black holes event horizen?

No. That would allow objects to gain energy by quantum tunneling, which (as far as I know) quantum mechanics doesn't allow.

Finally they can get started on quantum superposition human teleporters. I want to see Neptune but I want to be home by dinner.

The process being discussed is not really compatible with being alive.

Guidelines | FAQ | Support | API | Security | Lists | Bookmarklet | Legal | Apply to YC | Contact