Do atoms always exist even when unobserved?

[Thenewdeal38]

The moon is still there right?

I understand how the act of measuring can cause subatoms to collapse into fixed positions but they do not have mass. And the moon is made of atoms not a flurry of electrons its made of atoms. My question is are atoms (which have mass) there even when they haven't been "observed". I mean atoms arnt in a wave like superposition like electrons an atom can't be in two places at the same time right? An atom is there even if youre not observing it right?

 

[xts]

Electrons have their mass too.
Atoms exhibit QM behaviour (may interfere, are subjects to uncertainity principle, etc).
Even large molecules exhibit measureable quantum behaviour.

The Moon is there because it is measured very frequently (even when Einstein does not look at it) and those measurements affect its further movement quite a little.

(Anyway - to be quite sure about Moon, you must ask Aussies. I can't tell you if it is still there right now...)

 

[HallsofIvy]

No, you don't understand. The "act of measuring" causes anything to "collapse into fixed position", not just things that "have no mass". What, exactly do you mean by "subatoms"? Electrons? Neutrons? Protons? They certainly do have mass!

Of course, for a "large" (larger than atomic size) object the possible variation in position is very small- it has such a very short wavelength, it can always be treated as an "object" rather than a wave.

 

[Thenewdeal38]

Scuese me isn't "measuring" just the physical interaction with other subatoms that irreversibly forces electrons and things into fixed positions. Dont wave functions collapse naturrally in the universe even when no physicist "observes" them, I mean were just recreating a process that happens in nature anyways. So atomic structures which are not isolated from the rest of the universe are constantly bombarded by subatoms forcing it into a static position. Correct?

"Atoms exhibit QM behaviour (may interfere, are subjects to uncertainity principle, etc).
Even large molecules exhibit measureable quantum behaviour." Examples please?

So atoms are waves I thought that only applied to electrons? Everything in the universe is a accumulation of wavefunctions that concentrate in certian "possible" positions where the bigger they become the smallr their superposition. I am sorry no way this has to be an oversimplification.

 

[DrChinese]

"Atoms exhibit QM behaviour (may interfere, are subjects to uncertainity principle, etc). Even large molecules exhibit measureable quantum behaviour." Examples please?

So atoms are waves I thought that only applied to electrons? Everything in the universe is a accumulation of wavefunctions that concentrate in certian "possible" positions where the bigger they become the smallr their superposition. I am sorry no way this has to be an oversimplification.

All quantum objects exhibit a mixture of wave and particle behavior, and this is often described by the Heisenberg Uncertainty Principle (HUP). There is no specific size at which this behavior is no longer evident, it simply tends to vanish quickly as the objects get larger (atoms are bigger than electrons, molecules are bigger than atoms, etc. up the chain). Below is a reference to quantum properties of a reasonably large molecule.

http://hexagon.physics.wisc.edu/teaching/2010s%20ph531%20quantum%20mechanics/interesting%20papers/zeilinger%20large%20molecule%20interference%20ajp%202003.pdf

 

[Thenewdeal38]

What about this part?

Scuese me isn't "measuring" just the physical interaction with other subatoms that irreversibly forces electrons and things into fixed positions. Dont wave functions collapse naturrally in the universe even when no physicist "observes" them, I mean were just recreating a process that happens in nature anyways. So atomic structures which are not isolated from the rest of the universe are constantly bombarded by subatoms forcing it into a static position. Correct?

 

[xts]

Thenewdeal: could you, finally, answer yourself (but also to me) what do you mean by 'collapse'?

Even large molecules exhibit measureable quantum behaviour." Examples please?

E.g. Anton Zeilinger's experiments with interference of fulerenes.
http://www.univie.ac.at/qfp/research/matterwave/c60/index.html - pop-science version (but I like it!)
http://arxiv.org/PS_cache/quant-ph/pdf/0110/0110012v1.pdf - serious publication

So atoms are waves?

You definitely should avoid the verb 'to be'. It carries too much metaphysical baggage. Hamlet was one of those who assigned to much meaning to that verb...
Say it rather: In some situations atoms may be successfully described in terms of wave mechanics and in those cases the "miniature snooker ball" model fails.

 

[DrChinese]

What about this part?

Scuese me isn't "measuring" just the physical interaction with other subatoms that irreversibly forces electrons and things into fixed positions. Dont wave functions collapse naturrally in the universe even when no physicist "observes" them, I mean were just recreating a process that happens in nature anyways. So atomic structures which are not isolated from the rest of the universe are constantly bombarded by subatoms forcing it into a static position. Correct?

As far as we know, physicists are not required for the moon to have a position. Nonetheless, unobserved particles can be anywhere - although they are more likely to be in some places than others.

 

[atyy]

The collapse of the wave function is an unsolved problem in quantum mechanics. It works, but doesn't make sense.

The best coherent alternatives are the many-worlds interpretation (which is aesthetically terrible to many, including Yakir Aharonov and Steven Weinberg), and Bohmian mechanics (which I am told doesn't work for relativistic situations - I expect Demystifier to say something here:)

 

[SidBala]

First of all: Electrons have mass. Atoms, molecules, both massless and massive particles, all exhibit quantum behaviour.

Secondly: The act of measuring a physical observable(like position) forces the wavefunction to an(or multiple) allowed state of that observable. This does mean that electrons are forced into a small volume when it's position is observed. However, when you observe it's energy it becomes less confined. There are a lot of physical observables like energy, position, spin etc. Measuring anyone of these will force the particle to take an allowed state of that observable. Measuring one observable hence will change the state of the electron with respect to another. Ie: if you measure position, its energy is no longer what it was when you measured it.

Thirdly: The electron/atom is really there regardless of whether you observe it or not. Your detector for position cannot be infinitely small. Even after you measure position, the electron still exists in many places at once. Except now, all the places where it exists are confined to a small region.

 

[Maui]

The collapse of the wave function is an unsolved problem in quantum mechanics. It works, but doesn't make sense.

...and this gives rise to a multitude of incredible suggestions about reality. That's all there is to the question "is the Moon there when nobody is observing?"

 

[Naty1]

The collapse of the wave function is an unsolved problem in quantum mechanics. It works, but doesn't make sense.

I basically agree, but would change "doesn't make ssense" to something like "is not completely understood"...but of course a lot of things in physics and QM are like that.

Dont wave functions collapse naturrally in the universe even when no physicist "observes" them, I mean were just recreating a process that happens in nature anyways.

I'd generally agree with that...when particles interact which they typically do, wavefunctions( if that is the description one is using" collapse...so where there is a lot of interaction, stuff
tends to be localized. For example, an electron bopund to an atom is expetced to be found within the electron cloud and exists in quantized (discrete energy states)...but when it is flying around freely in outer space it spreads everywhere...

"Measuring anyone of these will force the particle to take an allowed state of that observable." is one nice way to summarize that.

So atomic structures which are not isolated from the rest of the universe are constantly bombarded by subatoms forcing it into a static position. Correct?

confined to some localized area, yes, but not "a static position". An instantaneous position to an accuracy dictated by the Heisenberg uncertainty principle,yes, but another measurement in general will reflect a distribution of values. Even after all measurement corrections are made, HUP prevents you from achieving some perfect result...even 'instantaneously'.

 

[xts]

The collapse of the wave function is an unsolved problem in quantum mechanics. It works, but doesn't make sense.
I basically agree, but would change "doesn't make ssense" to something like "is not completely understood"...but of course a lot of things in physics and QM are like that.

I would rather say: it is a lexical problem rather than physical. There is nothing more to understand in 'collapse' except of lack of commonly accepted definition of that word. People use the term 'collapse' without defining it clearly. There are severeal different meanings commonly used. There is quite a little mystery in it if we agree to use only one of those meanings. In some contextes the meaning is obvious, but more often it is not clear and people tend to take a metaphysical baggage frokm one meaning and assign it to other uses of that word.

That is why I hate to speak about 'collapse'... Vast majority of minunderstandings and paradoxes may be avoided if we don't use such words and speak about well described experiments (or thought-experiments) in terms of their initial conditions and outcomes.

 

[bugatti79]

Folks,

May I input my understanding of 'the act of measuring'? When a particle has to be examined, some measuring device which emits a light beam is required. Since the particles we are measuring are so so small they are sensitive to any interaction from a light beam...ie the particle gets pushed around due to the interaction of the light beam, the particle is sensitive to the imposing elecromagnetic field.

Hence we can never know about the particles position because the very act of measuring disturbs it. I don't see anything mysterious about this...I don't see why we need to use the word 'collapse'...

 

[StevieTNZ]

Hence we can never know about the particles position because the very act of measuring disturbs it. I don't see anything mysterious about this...I don't see why we need to use the word 'collapse'...

What about interaction-free measurements?

It is also often stated that measurement creates the outcome, not reveals an existing definite property.

 

[bugatti79]

What about interaction-free measurements?

It is also often stated that measurement creates the outcome, not reveals an existing definite property.

Interaction free measurements...? hmmmmm...I have never heard of that before...:-)

All experiments I have heard of are not interaction free ie, double slit, stern...

 

[xts]

What about interaction-free measurements?

Yeah? What about them? Could you explain what do you mean by 'collapse' in context of interaction free measurement?

I have never heard of that before...

Seems like you never flew El Al - they invented interaction free bomb-tester to make your flight safe :
http://en.wikipedia.org/wiki/Elitzur–Vaidman_bomb_tester

 

[DrChinese]

Folks,

May I input my understanding of 'the act of measuring'? When a particle has to be examined, some measuring device which emits a light beam is required. Since the particles we are measuring are so so small they are sensitive to any interaction from a light beam...ie the particle gets pushed around due to the interaction of the light beam, the particle is sensitive to the imposing elecromagnetic field.

Hence we can never know about the particles position because the very act of measuring disturbs it. I don't see anything mysterious about this...I don't see why we need to use the word 'collapse'...

This is somewhat misleading, because we know (from Bell) that it is not the measurement which causes collapse. Rather it is the gaining of knowledge. In other words, I can confine a particle to a certain position (volume) without directly disturbing or affecting it in any way - if I am able to similarly observe (confine) its entangled partner. So it is not the measurement apparatus, it is something more fundamental than that.

Keep in mind that partial collapse is possible as well! Which shouldn't be possible if the apparatus is disturbing our target.

 

[bugatti79]

Yeah? What about them? Could you explain what do you mean by 'collapse' in context of interaction free measurement?


Seems like you never flew El Al - they invented interaction free bomb-tester to make your flight safe :
http://en.wikipedia.org/wiki/Elitzur–Vaidman_bomb_tester

Is this equivalent to the delayed choice experiment in the context of 'interaction free'?

 

[bugatti79]

... I can confine a particle to a certain position (volume) without directly disturbing or affecting it in any way - if I am able to similarly observe (confine) its entangled partner. So it is not the measurement apparatus, it is something more fundamental than that.

but how else would you similarly observe its entangled partner without the aid of an apparatus?

 

[xts]

Is this equivalent to the delayed choice experiment in the context of 'interaction free'?

No. Why do you think so? It has absolutely nothing to delayed choice...

Other (also famous) interaction free measurement is a 'Three Men in a Boat Tea-pot' or 'quantum-Zeno' paradox. But beware: as you read about 'quantum-Zeno' - never forget they measure not a spontaneous, but stimulated emission. There is no such paradox for spontaneous one...

 

[DrChinese]

but how else would you similarly observe its entangled partner without the aid of an apparatus?

I observe Alice here. Now Bob is confined over there. Yet I never touched Bob. It really has nothing to do with disturbances imparted by apparati.

 

[StevieTNZ]

I observe Alice here. Now Bob is confined over there. Yet I never touched Bob. It really has nothing to do with disturbances imparted by apparati.

Also, to add on what DrChinese says, it might be a good idea to read into the implications of Bell's theorem. That might clear up what has happened despite no measuring device being used to probe 'Bob'.

 

[Fra]

For those who doubts the collapse is an information update, there an maybe easier to understand analogy to this in economy as well.

Consider what's called "bubbles", the IT bubble, real estate bubbles etc. Somehow the bubble concept is that the market value is way out of proportion to the "fundamental values", like what it is REALLY worth. The bubble bursts (collapses) when the market revises their valuations.

To the point is that in economy just as in physics, the notion of what the fundamental value IS, is ill defined. All there IS are expectations. If someone wants to pay x USD/stock for a certain company stock, then that's their market value, even if it's fake.

A somewhat imperfect but still illustrative correspondence is that when peoplel in physics ask what the state really IS when not measuresd, is just like when people in economy ask what is the fundamental value of something. The point is how to you MEASURE the fundamental value if not on the market?? And that market only works with expectations, that's how the game works.

So to perform measurements corresponds to buy and sell actions on the market and watch market reactions. For example "how will the market or a subset of the market" react (respond) if I suddnly offer to buy stocks way above expectations?

IMO economist that reference "hard fundamental values" are the ecnomist version of "realists in physics", while a hardcore empirist would reject the notion of fundamental values completelt.

I'm not economist, but I would not be surprised if this is debated also in economical spheres.

The point is now that ecnomical bubbles, does not actually physicall collapse company buildings or factors... all that collapses is the market expectations. If you understand THAT, you should understand also the same in QM as it's quite analogous.

/Fredrik

 

[ZealScience]

To my perspective, measurement doesn't simply mean looking at it. When photons strike electrons, measurement is made.

Like double slit, when you emit a photon to a slit to see whether there is electrons passing through, you don't need to use a apparatus or look at the photon to make the state collapse. When the photon strikes the electron, measurement has already been made.

Thus, even when nobody, no animal and even no chloroplast is looking at the moon, measurement has already been made.

 

[Thenewdeal38]

Quantum Interference with Buckyballs link

Wait a structure of 60 atoms shapled like a soccer ball forms an interference pattern with one slit how is this possible?

 

[DrChinese]

Quantum Interference with Buckyballs link

Wait a structure of 60 atoms shapled like a soccer ball forms an interference pattern with one slit how is this possible?

From the article:

"It is interesting to compare the de Broglie wavelength of the fullerene with its actual size: The buckyball has a diameter of about 1 nm, which is 350 times larger than its de Broglie wavelength. Our interference experiments clearly show that the concept of the de Broglie wavelength is not merely academic for objects with dimensions"

 

[StevieTNZ]

To my perspective, measurement doesn't simply mean looking at it. When photons strike electrons, measurement is made.

Like double slit, when you emit a photon to a slit to see whether there is electrons passing through, you don't need to use a apparatus or look at the photon to make the state collapse. When the photon strikes the electron, measurement has already been made.

Thus, even when nobody, no animal and even no chloroplast is looking at the moon, measurement has already been made.

A photon would also be governed by QM, hence be described by a wavefunction. Squires said any QM system governed by Scrodinger's equation cannot collapse another QM system.