2 places at once...outdated?

[Mitch Bass]

just now having watched a "physics documentary" called "the Universe" final episode of final season (on Netflix currently) called the microscopic universe. The widely reknown "double slit" experiment was discussed or as they called it "double hole" experiment. This documentary was made in 2007. Let me ask first...does the notion of the consquequnces of the experiment still produce the idea that a particle could exist in two places at once due to the "strange" "against common sense" "spooky" world of "quantum physics". Let me ask second...has all the technical understanding of why the experiment results are dependent upon whether or not the experiment was being observed?

[pavelcherepan]

I don't think double slit experiment has ever been done using single separate particles, although the theoretical idea is that the particle/wave is supposed to interfere with itself. Maybe I'm wrong, though.

[StringJunky]

I don't think double slit experiment has ever been done using single separate particles, although the theoretical idea is that the particle/wave is supposed to interfere with itself. Maybe I'm wrong, though.

It's been done with electrons.

 

http://physicsworld.com/cws/article/news/2013/mar/14/feynmans-double-slit-experiment-gets-a-makeover

[pavelcherepan]

Cool, haven't seen this one! Thanks StringJunky!

[imatfaal]

It has been done with C-60 Buckyballs - ie macromolecules

 

http://www.qudev.ethz.ch/phys4/studentspresentations/waveparticle/arndt_c60molecules.pdf

[StringJunky]

Cool, haven't seen this one! Thanks StringJunky!

Click on the image of the waves to see all the slit combinations.

[Enthalpy]

Yes, the photon passes through both slits, and it has been checked with individual photons too. But what shall be weird in that, apart from the fuss made around it? We don't need a particle to be contiguous. In fact, we need little from a particle: for instance the ability to concentrate its properties without splitting them, and not to repel itself.

 

"Observe" does not mean "by a human". A following interaction with an other particle qualifies as "observation".

 

I suggest to begin learning QM with recent scientific books, not with papers in the general Press nor with historic misconceptions. And observe and meditate some pictures by an atomic force microscope, because the double slit alone brings you easily to misunderstandings.

[studiot]

Yes thank you for an interesting viewpoint, enthalpy, particularly the non contiguous bit.

Even the maths of that situation is still nascent.

 

I further agree with your comments that multiple slit experiments are over emphasised.

 

+1

[Strange]

Yes, the photon passes through both slits, and it has been checked with individual photons too. But what shall be weird in that, apart from the fuss made around it? We don't need a particle to be contiguous. In fact, we need little from a particle: for instance the ability to concentrate its properties without splitting them, and not to repel itself.

 

The challenge with that interpretation is that, in all other contexts, photons (and electrons and C60 molecules) are indivisible so it is hard to understand what "through both slits" really means.

just now having watched a "physics documentary" called "the Universe" final episode of final season (on Netflix currently) called the microscopic universe. The widely reknown "double slit" experiment was discussed or as they called it "double hole" experiment. This documentary was made in 2007. Let me ask first...does the notion of the consquequnces of the experiment still produce the idea that a particle could exist in two places at once due to the "strange" "against common sense" "spooky" world of "quantum physics". Let me ask second...has all the technical understanding of why the experiment results are dependent upon whether or not the experiment was being observed?

 

To answer the original question: nothing has changed in the last 8 years in our understanding of quantum theory. In fact, as far as I know, nothing significant has changed since modern quantum theory was formulated about 90 years ago.

[Delta1212]

 

The challenge with that interpretation is that, in all other contexts, photons (and electrons and C60 molecules) are indivisible so it is hard to understand what "through both slits" really means.

 

 

To answer the original question: nothing has changed in the last 8 years in our understanding of quantum theory. In fact, as far as I know, nothing significant has changed since modern quantum theory was formulated about 90 years ago.

I think that depends on how you define significant. There have been a lot of developments, it's just that most of them seem to fall into the category of finding ways to show that the latest "This can't possibly be what is happening" argument is, in fact, wrong, and that that is exactly what is happening. Edited May 20, 2015 by Delta1212

[Strange]

I think that depends on how you define significant. There have been a lot of developments, it's just that most of them seem to fall into the category of finding ways to show that the latest "This can't possibly be what is happening" argument is, in fact, wrong, and that that is exactly what is happening.

 

Yep, I would say refinements in our understanding of what the theory says will happen, and the development of some seriously impressive experimental techniques to test them.

[swansont]

I think that depends on how you define significant. There have been a lot of developments, it's just that most of them seem to fall into the category of finding ways to show that the latest "This can't possibly be what is happening" argument is, in fact, wrong, and that that is exactly what is happening.

I agree. There has been a slew of "it is, in fact, that strange" experiments, and nothing on the side of "it's really just classical in quantum clothing"

 

In terms of 2 places at once, Kasevich's 10m tower experiments achieve cm separation of the wave packets

http://web.stanford.edu/group/kasevich/cgi-bin/wordpress/?page_id=11

[Strange]

In terms of 2 places at once, Kasevich's 10m tower experiments achieve cm separation of the wave packets

http://web.stanford.edu/group/kasevich/cgi-bin/wordpress/?page_id=11

 

That is a pretty impressive experiment.

[Mitch Bass]

I know to the senior mentor who wrote about misunderstanding conclusions to double slit eXPERMENT. But this knowledge comes from only personal obsrvarions leading to what seems so insanely relative theories to Ll universal motion rheories

[MigL]

Once you let go of the classic, deterministic interpretation of waves and particles ( contiguous or not ) at the quantum level, and accept that quantum particles ( definitely different from classical particles ) are governed by probability, as specified by the equations and theory, you realize that their behavior isn't 'strange' at all.

It is our trying to re-interpret these quantum effects in terms of classical rules that is strange.

 

But of course TV programming has to appeal to a wide audience, and so past and even current programs on the subject always stress this 'wow' factor, as it would be a fairly dry program otherwise, and only appeal to a few viewers ( just us nerds ).

[Enthalpy]

[...] nothing significant has changed since modern quantum theory was formulated about 90 years ago.

 

I feel many thrilling experiments and interpretations have come recently, which have sorted out diverging understandings of QM, and made QM much more concrete and simpler to understand.

 

Take Aspect's experiment, it has brought the debate about indetermination and hidden variables much further.

 

Or the atomic force microscope, which make the wavefunction observable and observed. The ancestors could still say "no physical existence, just an artefact to compute a probability" but now this position isn't defendable any more.

 

Or some experiments in Munich that show the probability of an excited electronic state increase as cos(time). All these make QM very much concrete now.

The challenge with that interpretation [Enthalpy's "through both slits"] is that, in all other contexts, photons (and electrons and C60 molecules) are indivisible so it is hard to understand what "through both slits" really means.

 

We do need particles as a way to count some properties as integer numbers, for instance the charge - yes, "indivisible". But we don't need these particles to be at one place. Misregarding that is what makes QM apparently weird.

 

Though, I still have to understand why a particle doesn't interact with itself. Between two particles, we compute an interaction over all possible pairs of positions, but for one particle, never: it doesn't repel itself.

Edited May 21, 2015 by Enthalpy

[imatfaal]

 

I feel many thrilling experiments and interpretations have come recently, which have sorted out diverging understandings of QM, and made QM much more concrete and simpler to understand.

 

Take Aspect's experiment, it has brought the debate about indetermination and hidden variables much further.

 

Not really - Aspect and the other experimental tests of Bell's theorem/inequality confirmed (or went a long way towards confirming) the "spukhafte Fernwirkung" of Quantum mechanics and showed that even the great Einstein could not explain away QM's weirdness. The fundamental non-classical and non-quotidian nature of QM remains - the fact that there are handfuls of competing interpretations vying for recognition and that these remain mere interpretations rather than testable hypotheses demonstrates that this is NOT concrete and simple.

 

All these make QM very much concrete now.

 

Really No. We have the maths that works and the predictions are as well tested as any theory so far in science. But there are gaping holes in our knowledge, which most scientists rightly ignore much of the time for the sake of expediency, the proposed solutions to which are wide-reaching, incredibly exciting, and mutually contradictory. This is not settled concrete science - this is the cutting edge where sometimes the imagination is let loose and all is still to play for.

 

 

We do need particles as a way to count some properties as integer numbers, for instance the charge - yes, "indivisible". But we don't need these particles to be at one place. Misregarding that is what makes QM apparently weird.

 

Though, I still have to understand why a particle doesn't interact with itself. Between two particles, we compute an interaction over all possible pairs of positions, but for one particle, never: it doesn't repel itself.

 

"But we don't need these particles to be at one place" Thinking that this is normal and not a massive departure from classical physics is why you do not appreciate the game-changing nature of quantum mechanics. That a photon can behave as a particle or a wave is an argument that extends back many years - some might say that Huygens and Newtons were both right and yet others would argue that they were both wrong; but that a marcromolecule of significant size has wave like properties is not readily acceptable to the classical mind. It works; we understand the protocols, the maths, and the predictions as well as any part of science; we deal with quantum mechanical particles and understand their interactions and can calculate their likelihood -- but it is still weird.

[StringJunky]

Couldn't the duality be explained by: matter travels as a wave but that wave can only be absorbed/measured in discrete units? It's the discreteness that implies a particle. Wavy-particles.

[Mitch Bass]

my educated guess is that the seeming duality can be explained by undestanding the objective reality of what light is