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.
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.
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.
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.
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?
> 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.
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 ...
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: " 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.  And waves occupy multiple places in space at once.  So any chunk of matter can also occupy two places at once."
I guess my problem is with  "is also a wave". I think that "there is a wave related to the object" but not "the object IS a wave". Then  does not follow.
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.
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.
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.
Bohmian mechanics was made for people like you.
Problems of hobby scientists...
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
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  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.
That's true, but those that do hold it hew to it rather vigorously.
That is a truly splendid turn of phrase.
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.
Will this provide us with insight into how gravity and the quantum world relate?
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.
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.
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?
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.
However, given that I'm no expert on the topic, I wish someone in a better position could elaborate on this idea.
Wouldn't it be ironic if decades of misdirected science could have been avoided if Schrodinger put his hamster in the box.
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.
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.