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/schrodinger-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/schrodinger-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.

 

[tarekatpf]

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.

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?

And about that helium balloon and coffee mug examples. Thank you very much for explaining those things. I didn't know that the probability decreases with distance. However, I wonder if even that kind of small randomness could produce significant effects. Such as, inside our neurons. Since neuronal communication is significantly dependent on transportation of ions, wouldn't randomness produce random effects as well? I am not sure if such random transportation of ions occur inside our brain ( from what I know, it's strictly dependent on voltage difference, but could voltage difference result from random movement of ions? ), and certainly from our everyday experiences, our behaviour is not quantum-random ( such as, I know I will get scared if I saw a snake on my bed right now, and if you do an experiment with me, you will get the same result. And I will feel angry if I read news on killing of blue whales. There's no randomness in that. ). So most probably my lack of understanding of quantum mechanics ( or behaviour of atoms and subatomic particles altogether ) is causing me problems.

 

[Simon Bridge]

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

I think our posts crossed each other - see post #30.

I wonder if even that kind of small randomness could produce significant effects. Such as, inside our neurons. Since neuronal communication is significantly dependent on transportation of ions, wouldn't randomness produce random effects as well?

... yes, and it does.
Neurons are too big, but there are electronic components that are small enough for these effects to matter.
Usually we exploit them to make the components work better.

Lots of random stuff happens to our neurons that are nothing to do with quantum mechanics all the time.
We have evolved to deal with that stuff so we learn what to ignore and what to pay attention to.

And I will feel angry if I read news on killing of blue whales. There's no randomness in that

You seem to have the wrong idea about randomness - you may always get angry at news of a whales death - but not everyone gets angry about it. How a particular human feels at any time is pretty random yes?
If you don't think so, then produce the formula that predicts it.

But human emotions are not purely random - we can predict broadly what people will feel about some things without getting very exact about it. i.e. I can predict that mothers generally love their kids - but not how much.

Quantum effects do not produce pure randomness - but a predictable randomness. We can tell in what way the situation will be uncertain. I'll explain: it's like rolling a dice - the number it rolls is not totally uncertain ... you cannot roll a 5.5 for instance. For a regular casino die, you can only roll integers from 1 to 6 ... so you won't get a 7 or higher on just one die.This is all very qualitative and descriptive - so you won't get the whole picture.
If you study probability math, you'll get a better picture of how these things work.
It's not that hard and doesn't take long - but you do need to get used to how regular probabilities work before you tackle quantum mechanics.

When you've done that, you won't have to take our word for it :)

 

[tarekatpf]

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!).

Thank you very much. I needed that. I don't like things that are absolutely unpredictable. I mean who wants to live in a world in which everything happens by a 50/50 chance?

So, I want to know how much can you predict about something? I read somewhere it's possible to predict accurately around 90% of times the motion of an electron. Is that true? How much can you predict about something as small as maybe an atom or subatomic particle? Is it different for larger things? What does predictability depend on?

I still don't understand some stuff, though. Actually lots of stuff. Please ignore the rest of the post if it violates the forum rules ( though I think my questions are still related to the original question. ) But if my questions do violate, I beg pardon in advance.

Say, you have a tennis ball. Now, if you hit it with a fixed amount of force, classical ( or Newtonian? ) mechanics says, the acceleration would always be exactly same, no matter how many times you experiment with it. But quantum mechanics should make it difficult. Because even if a hundred protons and electrons is "displaced" from its "home planet" that is the tennis ball at one moment, its mass has reduced, no matter how small. And at another moment, if even just 1 less proton has displaced, there should be a change, again, no matter how much. So it's not supposed to obey the laws of classical mechanics. So does the universe strictly follow the laws of classical mechanics?

I want to understand how the universe has come to such a state. We know it's just a product of the big bang. Now, in the earliest moments, the universe had no matter. Then came matter and antimatter, but matter slightly more. I suppose all the matter particles were still behaving weirdly then: here and there at the same time. Then how did the universe get a stable form? If things keep switching between places, how come something as big as a planet or star can form? Or is that the "final problem" for scientists? Like how gravity could arise from quantum world? ( I read that formulation of "theory of everything" is most probably the "ultimate goal" of physicists, which is an attempt to marry quantum mechanics with general relativity which explains gravity. )


Does the expansion of the universe have something to do with the behaviour of particles? Because at one moment in the early universe, there was less space for matter particles to switch places. Now they have more space. Does their switchability varies with the age of the universe? Is the universe becoming more of less predictable? Does gravity alter predictability of particles?

 

[phinds]

You would likely find it very informative to read "The First Three Minutes" by Weinberg.

 

[tarekatpf]

You would likely find it very information to read "The First Three Minutes" by Weinberg.

Thank you very much. Can you suggest any book for general readers that explains how random particles could together form objects that apparently follow Newtonian-mechanics? I can't visualize particles jumbling around coming together to make something that's as stable ( motion-wise ) as a planet.

 

[tarekatpf]

PS: Or any documentary?

 

[phinds]

Thank you very much. Can you suggest any book for general readers that explains how random particles could together form objects that apparently follow Newtonian-mechanics? I can't visualize particles jumbling around coming together to make something that's as stable ( motion-wise ) as a planet.

Hm ... not clear why you are puzzled by this. Newtonian Gravity is quite enough to cause planets and suns to form and to keep them in stable orbits. NASA has long been sending spacecraft to the moon and Mars without even thinking about GR. I'm not sure if the missions to the outer planets have to use GR or not, but if they do I would expect the corrects from Newtonian gravity to be small.

 

[analogdesign]

Thank you very much. Can you suggest any book for general readers that explains how random particles could together form objects that apparently follow Newtonian-mechanics? I can't visualize particles jumbling around coming together to make something that's as stable ( motion-wise ) as a planet.

You don't need quantum physics to understand this principle. For example think of a river. Even in classical terms a river is a vast collection of water molecules. The water molecules have thermal energy so they are vibrating and can travel every which way. However, because of the closeness of other molecules the overall flow of trillions of water molecules is regular and predictable.

Also, consider the air in the room where you are sitting. Each molecule in the air has thermal energy and different molecules are flying in all different directions. Why doesn't sometimes all the air go into the corner of the room so you can't breathe? There is nothing fundamental why this couldn't happen. It is just that, after you work out the probabilities, the odds of it happening are extremely, extremely low. It would take many times the age of the universe for such a thing to happen. It is very close to impossible. So it is with your tennis ball. The mass *is* changing slightly (in theory) but the changes are so small they could not be detected by any means we have today. So in practice, the mass is constant.

Also, consider this. Imagine that one of the electrons in the tennis ball is able to appear a measurable, macro distance from the tennis ball. Because the wavefunction decreases exponentially, this would be an almost unbelievably low probability of occurring but it could happen. But, for you to notice anything strange about the tennis ball, a large number of these unbelievably low probabilities would be multiplied. The odds of that are so small they are in practice zero.

So it's all probability. The odds of the kind of macro behavior of a tennis ball actually happening are so small it would almost require observing an infinite time. That's why people don't see them.

Does it make sense now why a planet can be stable? All the quantum weirdness tends to average out and the overall system is stable.

A great book written a low time ago about this type of thing is "one, two, three, infinity" by the great physicist George Gammow. It is a very popular book and you could get it at a library most likely. I loved the book and you may like it too.

 

[Simon Bridge]

Thank you very much. I needed that. I don't like things that are absolutely unpredictable. I mean who wants to live in a world in which everything happens by a 50/50 chance?

Since there are usually more than two ways that something could go, the odds of a particular thing happening would actually be a lot less than 50:50 were everything totally random.

Here - "totally random" would mean a "flat" probability distribution.
It would be like having to roll a million-sided dice each morning to see what the day may bring.
You've noticed that the world does not work like that - so you are puzzled when scientists keep going on about randomness.

I think this is core to your question.
You need to get a feel for probabilities before continuing.

So, I want to know how much can you predict about something?

Like everything in life it depends.
The field of study that answers that question is applied math: probability and statistics.
It is a big field, you need to find books about that to suit your education level.
A good primer, though, is John Allen Paulos' Innumeracy - which I believe you can still get on Amazon.
Don't be put of the title.

I read somewhere it's possible to predict accurately around 90% of times the motion of an electron. Is that true?

I'm afraid the statement to far too vague to comment on.
Chances are the person you heard it from was just making numbers up.

Richard Feyman regularly stated that the methods of quantum electrodynamics could predict behavior of certain kinds for electrons and photons to something like 10 decimal places of accuracy ... that is a LOT more accurate that 90%.

How much can you predict about something as small as maybe an atom or subatomic particle? Is it different for larger things? What does predictability depend on?

It depends on how much of something you have, and what you need to know.
The position of a baseball only needs to be known well enough to catch it ... it is easy to predict it's position to within the size of a catchers mitt so catchers rarely miss.

You can use your experience of cards and dice to get other examples.
The main take-away lesson here is that probabilties are not all equal.

So does the universe strictly follow the laws of classical mechanics?

The "laws" of classical mechanics are only followed on average.
The question should really be "how strictly does the universe strictly follow the laws of classical mechanics?"
The short answer is "very".
Slightly longer: it depends.

We would describe how strictly something sticks close to an average course by telling you the distribution about that course ... but to understand that, you need to learn about probabilities.

I want to understand how the universe has come to such a state.

Lots of us do ... it's a popular obsession.
Nobody does yet though there are a lot of very shrewed ideas of how such a state, may have come about given certain assumptions.
Meantime, the quest for understanding is fascinating.

We know it's just a product of the big bang. Now, in the earliest moments, the universe had no matter. Then came matter and antimatter, but matter slightly more. I suppose all the matter particles were still behaving weirdly then: here and there at the same time. Then how did the universe get a stable form?

You are right - this is a new topic ... start a new thread.
However - I doubt the answers will do you a lot of good while you are still new to how probabilities behave.

If things keep switching between places, how come something as big as a planet or star can form?

Because the places they keep switching between are almost all inside the planet or star ... usually inside an atom.

Is the universe becoming more of less predictable? Does gravity alter predictability of particles?

The answers need you to know something of probability math so you can explain what you mean by "predictable" ... i.e. the entropy law says that the amount of chaos in a closed system increases (or stays the same). If we associate more chaos with less predictability, then, very loosely, this would mean that the Universe cannot get more predictable and is likely getting less. OTOH: that is a prediction that gets more certain over time... is that an increase or a decrease in predictability?

That's a rhetorical question btw.
What I want you to notice is how much of your confusion comes from being imprecise in your language. A lot of learning about science involves learning to be careful with language.


Summary:
1. not all probabilities are equal - you need to read up on probabilities.
2. much confusion is avoided by careful language

 

[tarekatpf]

Hm ... not clear why you are puzzled by this. Newtonian Gravity is quite enough to cause planets and suns to form and to keep them in stable orbits. NASA has long been sending spacecraft to the moon and Mars without even thinking about GR. I'm not sure if the missions to the outer planets have to use GR or not, but if they do I would expect the corrects from Newtonian gravity to be small.

No, no, no, I have no doubts about Newtonian mechanics, because they're not counter-intuitive. Unlike quantum mechanics, it has, at least apparently, cause-effect relationship between events. But quantum mechanics -- how order originates from disorder -- keeps bugging me.

 

[ZapperZ]

No, no, no, I have no doubts about Newtonian mechanics, because they're not counter-intuitive. Unlike quantum mechanics, it has, at least apparently, cause-effect relationship between events. But quantum mechanics -- how order originates from disorder -- keeps bugging me.

Please make sure we continue to discuss physics and NOT personal tastes. If this discussion degenerates into simply a matter of personal preferences, then it is no longer physics and this thread is done.

Zz.

 

[tarekatpf]

You don't need quantum physics to understand this principle. For example think of a river. Even in classical terms a river is a vast collection of water molecules. The water molecules have thermal energy so they are vibrating and can travel every which way. However, because of the closeness of other molecules the overall flow of trillions of water molecules is regular and predictable.

Thank you very much. But the flow of a river can be explained easily, at least how I understand it. I could be wrong, but isn't water pouring down from mountains and falls into a channel pushes all the water molecules in a river towards the sea? Maybe all individual molecules are moving in random directions, but the flow from the mountain is always downhill. And since the channel from the mountain up to the sea is packed with water molecules, any additional molecules will be pushing other molecules towards the sea. Isn't that how a river flows?

Also, consider the air in the room where you are sitting. Each molecule in the air has thermal energy and different molecules are flying in all different directions. Why doesn't sometimes all the air go into the corner of the room so you can't breathe?

That's true, and that's my point. Random movements of any number of molecules remain random. They never form something stable, like a ball of air molecules. How did such stable stuff like stars, galaxies and planets could originate from molecules/ atoms that are apparently hopping around? Maybe as Simon Bridge said, I need to understand the mathematics of probability first. I need some time, but I hope I can get back to it soon ( I have exams for next two months, so can't for now. )

Because the wavefunction decreases exponentially,

Thank you very much. That's something I didn't know.

Does it make sense now why a planet can be stable? All the quantum weirdness tends to average out and the overall system is stable.

No, sorry, despite your sincere efforts ( and that of other members who tried to help me in this post ) I couldn't get it. I can't visualize order arising from chaos. Maybe I need to think about it more.

Thank you very much about your recommendation on the Gammow book. I do have that book in my computer. ( Off the topic, I have thousands of ebooks on my computer. Almost on any subject. If anybody needs a catalogue, please let me know through a private message. )

 

[tarekatpf]

You need to get a feel for probabilities before continuing.

Yes, I think so too.

A good primer, though, is John Allen Paulos' Innumeracy - which I believe you can still get on Amazon.

Thank you very much. I will start reading it once my exams are over ( that is not before March. )

It depends on how much of something you have, and what you need to know.

Say, I have an electron and there is wall with 10000 holes each 1 cm apart. I am 10 mitre away from the wall and at a right angle on the middle point of the wall. I throw the electron straight towards the hole in front of me. Now, what are the chances that the electron will go through, say, the number 189 hole from the left in the wall?

We would describe how strictly something sticks close to an average course by telling you the distribution about that course ... but to understand that, you need to learn about probabilities.

Yes, thank you. I'll try.

Because the places they keep switching between are almost all inside the planet or star ... usually inside an atom.

Thanks. The idea that matters keep switching places usually between a long distance ( say a mm ) makes me kind of grow a disliking for the universe.

the entropy law says that the amount of chaos in a closed system increases (or stays the same).

But that's what troubles me to think. As the second law of thermodynamics says, the universe is going from relatively ordered state to a disordered state. How could order arise from a chaos which the early universe has been?

What I want you to notice is how much of your confusion comes from being imprecise in your language. A lot of learning about science involves learning to be careful with language.

Thank you for your suggestion. I don't have a proper understanding of this whole thing, so my thoughts are in a disordered state as well. I need to have clearer conception on this quantum thing first, maybe.

Thanks a lot again for helping so much.

 

[tarekatpf]

Please make sure we continue to discuss physics and NOT personal tastes. If this discussion degenerates into simply a matter of personal preferences, then it is no longer physics and this thread is done.

Zz.

Sorry, I couldn't articulate my thoughts properly. What I meant is I can't visualize, despite best efforts from several members of the Physics Forums in this thread, how quantum mechanics makes transition to Newtonian mechanics. Maybe I need to know more about both, and probability first.

 

[ZapperZ]

Sorry, I couldn't articulate my thoughts properly. What I meant is I can't visualize, despite best efforts from several members of the Physics Forums in this thread, how quantum mechanics makes transition to Newtonian mechanics. Maybe I need to know more about both, and probability first.

Actually, if you want my opinion, based on what I've read of your posts, you have a more general issue with understanding how something that can behave randomly at the single-particle level can actually have a well-defined collective behavior. In other words, you don't have a grasp of not quantum mechanics, but rather, statistical mechanics in general.

Zz.

 

[tarekatpf]

Actually, if you want my opinion, based on what I've read of your posts, you have a more general issue with understanding how something that can behave randomly at the single-particle level can actually have a well-defined collective behavior. In other words, you don't have a grasp of not quantum mechanics, but rather, statistical mechanics in general.

Zz.

Your observation is correct. I didn't know what statistical mechanics is ( I googled it after I read your post ), but you are spot on the fact that I don't understand "how something that can behave randomly at the single-particle level can actually have a well-defined collective behavior".

 

[Simon Bridge]

Your observation is correct. I didn't know what statistical mechanics is ( I googled it after I read your post ), but you are spot on the fact that I don't understand "how something that can behave randomly at the single-particle level can actually have a well-defined collective behavior".

The word "random" is a common everyday term without a very tight definition ... when we need to make a distinction, we usually call the small-scale behavior of particles "statistical" rather than random.

You would be quite happy with the idea that adult human males are about a certain height where you live - despite the fact that the height of individuals varies randomly. Even though people's height is random, you don't get just any old height.

It seems there is a predictability in spite of the randomness.

In fact - the predictability is because of the randomness ...
... a graph showing number of people with a particular height against the height shows a rough bell-shape: it is humped up around the average height and trails off exponentially the further the height is from that.

In fact, if you graph the number of occurrences vs the thing occurring for anything that has a large number of random factors contributing to it, you get a similar shape to the graph.
i.e. a ral simple example: you roll 3 dice and add the values - do this a 100 times, and plot the number of times a particular total appears against the total, then you get a similar bell-shaped graph.

Do you have trouble understanding how this happens?

...which is where a study of probability and statistics will help you.
Like I said - the amount you need for the understanding you seek is not that hard, and does not take all that long to get.



From there, the usual path takes you through ideal-gas thermodynamics to classical statistical mechanics and quantum mechanics. But you need a grounding in probability and statistics.
Bon apetit.

 

[tarekatpf]

The word "random" is a common everyday term without a very tight definition ... when we need to make a distinction, we usually call the small-scale behavior of particles "statistical" rather than random.

You would be quite happy with the idea that adult human males are about a certain height where you live - despite the fact that the height of individuals varies randomly. Even though people's height is random, you don't get just any old height.

It seems there is a predictability in spite of the randomness.

In fact - the predictability is because of the randomness ...
... a graph showing number of people with a particular height against the height shows a rough bell-shape: it is humped up around the average height and trails off exponentially the further the height is from that.

In fact, if you graph the number of occurrences vs the thing occurring for anything that has a large number of random factors contributing to it, you get a similar shape to the graph.
i.e. a ral simple example: you roll 3 dice and add the values - do this a 100 times, and plot the number of times a particular total appears against the total, then you get a similar bell-shaped graph.

Do you have trouble understanding how this happens?

...which is where a study of probability and statistics will help you.
Like I said - the amount you need for the understanding you seek is not that hard, and does not take all that long to get.



From there, the usual path takes you through ideal-gas thermodynamics to classical statistical mechanics and quantum mechanics. But you need a grounding in probability and statistics.
Bon apetit.

Sorry about being late to reply. Am dead busy with exams.

Thanks a lot, again. Hopefully I'll get back with some understanding of these things once my exams are over.

 

[Simon Bridge]

Good luck - hopefully you won't need it :)

 

[MightyKaykoher]

I think ( but may be wrong ) quantum mechanics allows for practically anything to happen. As I said I could be wrong. The probability of something like an entire apple disapearing would be maybe 10^(-10^100) % per (year)??. I wouldn't count on it happening in your lifetime with you there to witness it either. I have pondered on this same topic. If you could calculate the probability of a single atom vanishing I could give a better statistic... (Wonder what the probability of the Earth dissapearing is)


But in this same sense (which I am completely unsure of ) if their in an infinite amount of time the apple will eventually dissapear. Because infinite time times 1/10^(10^100) is like... Infinite? Yeah in an infinite amount of time practically everything is possible??Is this true?