Why don't we see quantum weirdness in everyday world?

[tarekatpf]

Since, we and everything else in our real world are made up of electrons, protons, and electrons, protons, and atoms show quantum weirdness, why don't we ever see such things to happen in real world? Such as, why don't we see part of an apple suddenly disappearing into thin air? Why do classical mechanics never fail to predict motion of things bigger than atoms?

 

[phinds]

Quantum weirdness happens at the quantum level. An apple is lots bigger than a quantum object. If all the quantum objects on one side of an apple ALL had quantum weirdness at the same time, you would see quantum weirdness in the apple. Theory says that if you wait until about the time when all the black holes in the universe have evaporated, you might actually see this happen.

 

[scoobmx]

http://en.wikipedia.org/wiki/Quantum_decoherence

 

[tarekatpf]

Quantum weirdness happens at the quantum level. An apple is lots bigger than a quantum object. If all the quantum objects on one side of an apple ALL had quantum weirdness at the same time, you would see quantum weirdness in the apple. Theory says that if you wait until about the time when all the black holes in the universe have evaporated, you might actually see this happen.

Thank you very much for answering.

I was thinking, say, I have a bag full of helium atoms. Say, the mass of the bag is 1 kg. Now, if I keep monitoring the weight of the bag, wouldn't there be significant chance of reduction of the mass of the bad suddenly by, say, 1%, in an hour, even if for a short instance? Wouldn't the mass be fluctuating?

 

[tarekatpf]

http://en.wikipedia.org/wiki/Quantum_decoherence

Thank you very much.

 

[vanhees71]

There is no quantum weirdness ;-)). The very fact that we live in an environment where we observe stable matter is a quantum effect that is everything else than weird but a basic constraint for us to exist.

Perhaps, what you mean by "quantum weirdness" are interference effects of particles at double slits, entanglement (a la Aspect, Zeilinger, et al "teleportation"), etc. That we observe such things never without carefully setting up simple (few-body) quantum systems that are isolated from disturbances from the "environment" is due to what's called decoherence.

A many-body system like everyday matter, as a quasi continuous energy spectrum on the microscopic level, and thus the slightest interaction which something in its neighborhood mixes a lot of microstates up that for our everyday observations of the macroscopic state make no difference. In other words our everyday experience is based on coarse grained (averaged) observables over a large set of microstates that are mixed up by tiny disturbances with the environment.

A nice website about these issues can be found here:

http://motls.blogspot.de/2009/09/Schrödinger-virus-and-decoherence.html

 

[ZapperZ]

From C.A. Mead, PNAS v.94, p.6013 (1997):

Although superconductivity was discovered in 1911, the recognition that superconductors manifest quantum phenomena on a macroscopic scale came too late to play a role in the formulation of quantum mechanics. Through modern experimental methods, however, superconducting structures give us direct access to the quantum nature of matter. The superconducting state is a coherent state formed by the collective interaction of a large fraction of the free electrons in a material. Its properties are dominated by known and controllable interactions within the collective ensemble. The dominant interaction is collective because the properties of each electron depend on the state of the entire ensemble, and it is electromagnetic because it couples to the charges of the electrons. Nowhere in natural phenomena do the basic laws of physics manifest themselves with more crystalline clarity.

There are other examples of such things nowadays where macroscopic phenomena are actually manifestation of quantum mechanical properties (solid state diodes and transistors, anyone?). Many people just don't realize it.

Zz.

 

[vanhees71]

Well, the very profane observation that matter around us is pretty stable, already is a quantum effect, as is the fact that we can't simply walk through walls although it's "pretty empty" as are the atoms making it up (Pauli principle).

 

[Vanadium 50]

Such as, why don't we see part of an apple suddenly disappearing into thin air?

Why would we? We don't see electrons disappearing into thin air.

Why do classical mechanics never fail to predict motion of things bigger than atoms?

Because classical mechanics is quantum mechanics, in the large n limit - i.e. the limit of everyday-sized objects.

 

[atyy]

Decoherence is not enough to explain why we don't see quantum weirdness. It has to be coupled with some additional assumptions, called "interpretations of quantum mechanics". Some interpretations are:

(1) textbook (eg. Landau & Lifshitz, Peres): quantum mechanics as a theory always requires the division of the universe into classical and quantum. We only see classical results, which by definition are irreversible, definite marks. In this view quantum mechanics may be incomplete.

(2) Bohmian mechanics (eg. http://arxiv.org/abs/quant-ph/0308039) is an example of a theory or interpretation that completes non-relativistic quantum mechanics by postulating hidden variables. In this interpretation, there are truly particles with definite positions, but there is a randomness in their positions called quantum equilibrium, analogous to the randomness of particles in thermodynamic equilibrium.

(3) Many-worlds in which all definite outcomes occur, and the universe splits into distinct realities. If this interpretation works, then it is a logical possibility that quantum mechanics is complete. It is not yet clear if this definitely works, but an account that seems very convincing is in Wallace's http://users.ox.ac.uk/~mert0130/books-emergent.shtml.

 

[Vanadium 50]

It's not decoherence, and it's certainly not interpretations (which is something people do). If you ask what quantum mechanics predicts for a block down an inclined plane problem, the answer is "exactly what Newtonian mechanics predicts". (Only with a lot more work - one can get from Minneapolis to St. Paul via Shanghai, but it's more work than is necessary)

Quantum mechanics governs the behavior of everything, and classical mechanics is just a very, very good approximation (~30 decimal places for typical classical systems). This is not only true, but is a more useful way of looking at things than the ever-popular "the world is classical, but at some small scale, quantum weirdness is pasted on".

 

[tarekatpf]

There is no quantum weirdness ;-)). The very fact that we live in an environment where we observe stable matter is a quantum effect that is everything else than weird but a basic constraint for us to exist.

Perhaps, what you mean by "quantum weirdness" are interference effects of particles at double slits, entanglement (a la Aspect, Zeilinger, et al "teleportation"), etc. That we observe such things never without carefully setting up simple (few-body) quantum systems that are isolated from disturbances from the "environment" is due to what's called decoherence.

A many-body system like everyday matter, as a quasi continuous energy spectrum on the microscopic level, and thus the slightest interaction which something in its neighborhood mixes a lot of microstates up that for our everyday observations of the macroscopic state make no difference. In other words our everyday experience is based on coarse grained (averaged) observables over a large set of microstates that are mixed up by tiny disturbances with the environment.

A nice website about these issues can be found here:

http://motls.blogspot.de/2009/09/Schrödinger-virus-and-decoherence.html

Thank you very much.

I was doing a thought-experiment. I was thinking, say, I have a bag full of helium atoms. Say, the mass of the bag is 1 kg. Now, for the sake of argument, say, there are a billion atoms in the bag. Now, each helium atom contains 2 protons. Now, a proton can either be at the centre of the atom, or NOT, but elsewhere ( or can it? Would the neutrons hold them too strongly? If neutrons do indeed, you might replace the experiment with just protons instead of Helium atoms. ) If the proton is outside the bag at any given moment, the bag will lose the mass of that proton.

Now, would it be too much to think that at a given moment, maybe 1% of the 2 trillions of protons are outside the bag? And we'll find that mass of that bag decreased by 1%?

Or is it too much to hope for indeed? May it be that even if the protons are about to disappear from the centre of the Helium, chances are more that the protons will remain nearby, and chances are almost zero that they'll ever be outside the bag?

What would happen if I do another experiment? I have a bag large enough to pack just 1 kilogram of protons ( say, N number of protons weigh 1 kilogram, and I have a bag of which the volume is N times the volume of a proton ) and nothing else. Now, suppose the time a proton takes to disappear from its place, and my unit of time is T. Now, at any point of time, a proton can either be at its place or outside the bag. They wouldn't be able to remain inside the bag, because it was full of protons the moment I found them to weigh 1 kg. Now the chances are that only half of them can stay inside the bag at any given point of time. Wouldn't we expect to almost always see the mass to be that of half a kilo protons?

 

[ZapperZ]

Thank you very much.

I was doing a thought-experiment. I was thinking, say, I have a bag full of helium atoms. Say, the mass of the bag is 1 kg. Now, for the sake of argument, say, there are a billion atoms in the bag. Now, each helium atom contains 2 protons. Now, a proton can either be at the centre of the atom, or NOT, but elsewhere ( or can it? Would the neutrons hold them too strongly? If neutrons do indeed, you might replace the experiment with just protons instead of Helium atoms. ) If the proton is outside the bag at any given moment, the bag will lose the mass of that proton.

Now, would it be too much to think that at a given moment, maybe 1% of the 2 trillions of protons are outside the bag? And we'll find that mass of that bag decreased by 1%?

Or is it too much to hope for indeed? May it be that even if the protons are about to disappear from the centre of the Helium, chances are more that the protons will remain nearby, and chances are almost zero that they'll ever be outside the bag?

What would happen if I do another experiment? I have a bag large enough to pack just 1 kilogram of protons ( say, N number of protons weigh 1 kilogram, and I have a bag of which the volume is N times the volume of a proton ) and nothing else. Now, suppose the time a proton takes to disappear from its place, and my unit of time is T. Now, at any point of time, a proton can either be at its place or outside the bag. They wouldn't be able to remain inside the bag, because it was full of protons the moment I found them to weigh 1 kg. Now the chances are that only half of them can stay inside the bag at any given point of time. Wouldn't we expect to almost always see the mass to be that of half a kilo protons?

Can you explain what this has anything to do with the original question you asked in this thread?

Is the question on whether one can't observe quantum effect at the macroscopic scale is still up there? After all the examples you were given, is this still something that you want to know? Or has that question been answered already and you are now turning this thread into a completely different topic?

Zz.

 

[phinds]

...

Now, would it be too much to think that at a given moment, maybe 1% of the 2 trillions of protons are outside the bag? And we'll find that mass of that bag decreased by 1%?

Yes, it would be WAYYYYY too much to expect. VERY unlikely that in one hour even a single proton would leave.

 

[atyy]

It's not decoherence, and it's certainly not interpretations (which is something people do). If you ask what quantum mechanics predicts for a block down an inclined plane problem, the answer is "exactly what Newtonian mechanics predicts". (Only with a lot more work - one can get from Minneapolis to St. Paul via Shanghai, but it's more work than is necessary)

Quantum mechanics governs the behavior of everything, and classical mechanics is just a very, very good approximation (~30 decimal places for typical classical systems). This is not only true, but is a more useful way of looking at things than the ever-popular "the world is classical, but at some small scale, quantum weirdness is pasted on".

It is true that classical mechanics is a limit of quantum mechanics. However, there must still be a mechanism or postulate for definite results from the wave function. As Landau and Lifshitz say, quantum mechanics requires classical mechanics for its formulation, and classical mechanics is also a limit of quantum mechanics. If one omits the postulate that classical mechanics is required in the formulation of quantum mechanics, and postulates that quantum mechanics applies to everything, then one needs an interpretation such as many-worlds to obtain definite results. So yes, an interpretation is required, whether it be textbook or many-worlds.

 

[tarekatpf]

Can you explain what this has anything to do with the original question you asked in this thread?

Is the question on whether one can't observe quantum effect at the macroscopic scale is still up there? After all the examples you were given, is this still something that you want to know? Or has that question been answered already and you are now turning this thread into a completely different topic?

Zz.

Sorry, I did not explain. I read somewhere ( a long time ago, maybe in Hawking's The grand design ) an electron in my coffee mug can at any point of time disappear and pop up in, say, a distant planet. I thought if that's reality, that subatomic particles keep disappearing, it's very much likely that at least a significant percentage of all the electrons and protons that make up the visual centre of my brain or eyes will not be in my body, and I will go see darkness occasionally. I didn't know that even though the protons can pop up elsewhere in the universe once in a while, it's not very likely. And I said so before phinds said it's way unlikely indeed.

Since I thought both quantum mechanics and my understanding of it can't be right, I made up a thought experiment to see if there are any flaws in my way of thinking about quantum mechanics. Since quantum mechanics has always been proved right, I thought I might tell you what/ how I think about quantum mechanics, and you would help me by pointing out the errors in my reasoning/ understanding/ conception about quantum mechanics.

However, you already helped me a lot. Thank you very much for that.

 

[tarekatpf]

Yes, it would be WAYYYYY too much to expect. VERY unlikely that in one hour even a single proton would leave.

Thank you very much, again. I didn't know that.

 

[tarekatpf]

Well, the very profane observation that matter around us is pretty stable, already is a quantum effect, as is the fact that we can't simply walk through walls although it's "pretty empty" as are the atoms making it up (Pauli principle).

Thank you very much.

 

[StevieTNZ]

Since, we and everything else in our real world are made up of electrons, protons, and electrons, protons, and atoms show quantum weirdness, why don't we ever see such things to happen in real world? Such as, why don't we see part of an apple suddenly disappearing into thin air? Why do classical mechanics never fail to predict motion of things bigger than atoms?

It's clear that a definite outcome occurs from a superposition upon observation. A superposition of a quantum object is not that its in position A and position B at the same time (as it exists in those two places at the same time) - rather its in a potentiality so doesn't exist in either position until observation. So why we don't see nothing rather than something is because observation (by whatever cause [its unclear what causes a definite outcome]) has taken place.

If you're talking about why we don't see quantum tunneling of macroscopic objects, or the sudden disappearance and reappearance of objects at another point in space at the same time, I guess its because such a possibility has a low probability. That doesn't mean it can't happen - it may happen in the future.

 

[tarekatpf]

Why would we? We don't see electrons disappearing into thin air.



Because classical mechanics is quantum mechanics, in the large n limit - i.e. the limit of everyday-sized objects.

Thank you very much.

About that apple argument. I thought if protons/ electrons disappeared, they wouldn't be the same atoms any more, and hence the atoms that make up apple won't be there, and there wouldn't be a complete apple any more as well.

And thanks a lot for letting me know that quantum mechanics is actually classical mechanics. I was wrong to think that the reason scientists can't unite quantum theory and general relativity is because quantum theory works for small objects, and general relativity works for larger objects; and the only difference between those subatomic particles and larger matter I could think of is quantum weirdness vs classical ( = predictable ) observation.

 

[tarekatpf]

Decoherence is not enough to explain why we don't see quantum weirdness. It has to be coupled with some additional assumptions, called "interpretations of quantum mechanics". Some interpretations are:

(1) textbook (eg. Landau & Lifshitz, Peres): quantum mechanics as a theory always requires the division of the universe into classical and quantum. We only see classical results, which by definition are irreversible, definite marks. In this view quantum mechanics may be incomplete.

(2) Bohmian mechanics (eg. http://arxiv.org/abs/quant-ph/0308039) is an example of a theory or interpretation that completes non-relativistic quantum mechanics by postulating hidden variables. In this interpretation, there are truly particles with definite positions, but there is a randomness in their positions called quantum equilibrium, analogous to the randomness of particles in thermodynamic equilibrium.

(3) Many-worlds in which all definite outcomes occur, and the universe splits into distinct realities. If this interpretation works, then it is a logical possibility that quantum mechanics is complete. It is not yet clear if this definitely works, but an account that seems very convincing is in Wallace's http://users.ox.ac.uk/~mert0130/books-emergent.shtml.

Thank you very much for your elaborate answers. I was certainly anticipating somebody who would tell me about those things.

 

[tarekatpf]

It's not decoherence, and it's certainly not interpretations (which is something people do). If you ask what quantum mechanics predicts for a block down an inclined plane problem, the answer is "exactly what Newtonian mechanics predicts". (Only with a lot more work - one can get from Minneapolis to St. Paul via Shanghai, but it's more work than is necessary)

Quantum mechanics governs the behavior of everything, and classical mechanics is just a very, very good approximation (~30 decimal places for typical classical systems). This is not only true, but is a more useful way of looking at things than the ever-popular "the world is classical, but at some small scale, quantum weirdness is pasted on".

Thank you very much. I did not know about that. Thanks, again.

 

[tarekatpf]

Yes, it would be WAYYYYY too much to expect. VERY unlikely that in one hour even a single proton would leave.

Thank you very much. So, that was one thing, among many, I was wrong about.

 

[tarekatpf]

It's clear that a definite outcome occurs from a superposition upon observation. A superposition of a quantum object is not that its in position A and position B at the same time (as it exists in those two places at the same time) - rather its in a potentiality so doesn't exist in either position until observation. So why we don't see nothing rather than something is because observation (by whatever cause [its unclear what causes a definite outcome]) has taken place.

If you're talking about why we don't see quantum tunneling of macroscopic objects, or the sudden disappearance and reappearance of objects at another point in space at the same time, I guess its because such a possibility has a low probability. That doesn't mean it can't happen - it may happen in the future.

Thank you very much. That's what I was talking about indeed. Yes, it has low probability, of course.

 

[DrChinese]

Since, we and everything else in our real world are made up of electrons, protons, and electrons, protons, and atoms show quantum weirdness, why don't we ever see such things to happen in real world?

Actually, pretty much everything you see illuminated by the sun is a direct result of such a quantum process. One of the steps in the fusion of hydrogen into helium requires tunneling through an energy barrier that is not possible in the classical picture.

"The fusing of two protons which is the first step of the proton-proton cycle created great problems for early theorists because they recognized that the interior temperature of the sun (some 14 million Kelvins) would not provide nearly enough energy to overcome the coulomb barrier of electric repulsion between two protons.

"With the development of quantum mechanics, it was realized that on this scale the protons must be considered to have wave properties and that there was the possibility of tunneling through the coulomb barrier."

http://hyperphysics.phy-astr.gsu.edu/hbase/astro/procyc.html

 

[analogdesign]

There is one kind of "quantum weirdness" that is used all the time in electronics. Quantum tunneling is the probability that an electron will "appear" on the other side of an energy barrier that the electron does not have enough energy to cross. This happens sometimes because the barrier is thin enough that the electron's wave function continues through the barrier.

This effect is a very serious problem in electronics, but has been harnessed as a "feature" in Flash memory. In Flash memory the data is stored inside a thin oxide and removed from the oxide by way of tunneling currents. By varying the barrier we can write a bit of data and then reduce the probability the charge will tunnel back out. This is why Flash memory is non-volatile and can last for years. Eventually the charge will tunnel out, though.

http://en.wikipedia.org/wiki/Field_electron_emission#Fowler.E2.80.93Nordheim_tunneling

http://en.wikipedia.org/wiki/Floating-gate_MOSFET

Flash memory is most certainly a quantum weirdness because not only is it not explainable by classical physics, it is also intuitively amazing. (all reality is a "quantum effect" in practice, but I think you were looking for macro quantum effects that differ from everyday effects)

 

[Simon Bridge]

To summarize:

1. we do see quantum effects on an everyday scale - we just don't think it's weird ... this is because, well, it happens on an everyday scale. We don't see the stuff pop-science shows like to dramatize because their startling aspects are too small to notice.

Basically all the small random effects average out on the large scale - it's like when you feel the wind on your skin you do not feel the impact of each individual air molecule and bit of dust. Instead you get a kind of steady force.

In fact, apparently still air has components moving around 500m/s but you never notice.
You needn't invoke quantum mechanics to get unexpected behavior.

2. although there is arguably a probability that a particle ostensibly "part of your coffee cup" could be detected in orbit about a distant star (I mean - how would anyone know it came from your coffee cup? But I know what you mean) this is not a very big probability ... in order for us to be able to consider it part of your coffee cup, it must have a very high probability of being found in the vicinity of the cup. That probability decreases exponentially the further from the cup the detector is.

Besides, there is also a similar probability that some particle from the distant star will get detected inside the coffee cup.

3. these probabilities are so small that for the helium balloon to lose noticeable mass by quantum mechanical effects would take many lifetimes of the Universe. By comparison, the normal diffusion of the helium through small openings in the foil is much faster.

The more frequent "tunnelling" effects in electronics take place over distances thousands of times smaller than the thickness of the skin of a helium balloon.

But as already noted, there are many quantum effects that show up on an everyday scale.
I'd put forward the wave-behavior of light... though the particle behavior is also quantum mechanical, the wave behavior was historically the more startling.

 

[tarekatpf]

Actually, pretty much everything you see illuminated by the sun is a direct result of such a quantum process. One of the steps in the fusion of hydrogen into helium requires tunneling through an energy barrier that is not possible in the classical picture.

"The fusing of two protons which is the first step of the proton-proton cycle created great problems for early theorists because they recognized that the interior temperature of the sun (some 14 million Kelvins) would not provide nearly enough energy to overcome the coulomb barrier of electric repulsion between two protons.

"With the development of quantum mechanics, it was realized that on this scale the protons must be considered to have wave properties and that there was the possibility of tunneling through the coulomb barrier."

http://hyperphysics.phy-astr.gsu.edu/hbase/astro/procyc.html

Thank you very much for answering. Maybe I couldn't give words to my question properly. Actually I don't understand how unpredictable small things together make up a bigger thing that behaves predictably? For example, say, there's a tennis ball. Isn't that tennis ball a combination of lots of electrons and protons and neutrons? If all of them behave in one way at a particular moment, and in another way in another instance, how come at both instances, the tennis ball behave precisely in the same manner?

 

[tarekatpf]

There is one kind of "quantum weirdness" that is used all the time in electronics. Quantum tunneling is the probability that an electron will "appear" on the other side of an energy barrier that the electron does not have enough energy to cross. This happens sometimes because the barrier is thin enough that the electron's wave function continues through the barrier.

This effect is a very serious problem in electronics, but has been harnessed as a "feature" in Flash memory. In Flash memory the data is stored inside a thin oxide and removed from the oxide by way of tunneling currents. By varying the barrier we can write a bit of data and then reduce the probability the charge will tunnel back out. This is why Flash memory is non-volatile and can last for years. Eventually the charge will tunnel out, though.

http://en.wikipedia.org/wiki/Field_electron_emission#Fowler.E2.80.93Nordheim_tunneling

http://en.wikipedia.org/wiki/Floating-gate_MOSFET

Flash memory is most certainly a quantum weirdness because not only is it not explainable by classical physics, it is also intuitively amazing. (all reality is a "quantum effect" in practice, but I think you were looking for macro quantum effects that differ from everyday effects)

Thank you very much for answering. Maybe I couldn't give words to my question properly. Actually I don't understand how unpredictable small things together make up a bigger thing that behaves predictably? For example, say, there's a tennis ball. Isn't that tennis ball a combination of lots of electrons and protons and neutrons? If all of them behave in one way at a particular moment, and in another way in another instance, how come at both instances, the tennis ball behave precisely in the same manner?

 

[Simon Bridge]

I don't understand how unpredictable small things together make up a bigger thing that behaves predictably?

But surely you have rolled dice or played darts? Cards? Then you have experienced how random events can lead to predictability. (Casinos make money from random events dragging in a predictable income.)

Things are only predictable, or unpredictable, to a degree. These are not absolutes ... I may not know where the dart I throw will end up but I'm pretty sure it will hit the board (I may be bad at darts but I'm not that bad!)

If you roll two die and add them up, the number to bet on is a seven yes?
That's with only two unpredictable things... already you have a degree of predictability.

Similarly - the air around you is bombarding you from all sides - each molecule of the air averages around 500m/s - and yet you get a completely 101.1kPa air pressure as a result. But the same air, bombarding a grain of pollen, is much more uneven and much less predictable.

With the tennis ball - if you look closely - it does not go exactly precisely the same way every time.
"Precise", like "predictable", is not an absolute concept - things can be more or less precise than others.
You think the tennis ball hit the same way does the same thing because you are not looking closely enough.