Throwing a tennis ball through a wall

[playmesumch00ns]

I was having an argument with my sister last night about the limits of scientific knowledge (her beliefs encompass a more "spiritual" world view than mine) and she brought up quantum mechanics as an example of how weird things are possible (as peddlers of hocus-pocus love doing).

Leaving aside the point that just because QM looks weird to us, doesn't mean the whole world is inherently "weird", and certainly shouldn't be used to try and pass off any mumbo-jumbo idea as worthy of credence...

The example she brought up was that of, "if you threw a tennis ball at a wall for long enough, eventually it would pass straight through the wall". This is something I remember being said from my school days, I think to illustrate the principle of quantum tunnelling.

Now I know it's dangerous to extrapolate quantum weirdness to the macroscopic world, and my scientific spidey sense is telling me that this is one of those times when a metaphor used to explain quantum weirdness to a layman is taken literally.

So, what's the score? Assuming that I threw a tennis ball against a brick wall from now until infinity, and assuming neither ball nor wall were damaged nor deteriorated over time, would it just so happen that one time the ball would pass through the wall?

Is it physically possible (and just very, very unlikely), or is it completely physically impossible?

 

[GOD__AM]

.

Now I know it's dangerous to extrapolate quantum weirdness to the macroscopic world, and my scientific spidey sense is telling me that this is one of those times when a metaphor used to explain quantum weirdness to a layman is taken literally.

I think what you said here is probably closest to the truth. Imagine a book sitting on a table, since it is in contact with the table it has more of a chance to (tunnel?) through the table than a ball that only contacts a wall briefly. I don't think there has ever been a book fall through a table yet, or anything even remotly like that.

It would be far easier, and more likely, that part of the book would pass through part of the table. Then we would be able to observe that part of the book is stuck in the table, but there again I don't think there is any evidence of that ever happening.

Considering all the things that touch each other, just here on earth, there seems to be a great potential for things to tunnel into one another, but as I said I don't see any evidence of it happening.

 

[ZapperZ]

So, what's the score? Assuming that I threw a tennis ball against a brick wall from now until infinity, and assuming neither ball nor wall were damaged nor deteriorated over time, would it just so happen that one time the ball would pass through the wall?

Is it physically possible (and just very, very unlikely), or is it completely physically impossible?

There are several issues that need to be considered here:

1. A "ball" is not a quantum particle.

2. An object that can exhibit such a behavior has every part of it in coherence with each other. A ball doesn't. the atom in one part of the ball cannot be described via a coherent wavefunction with another part of it, especially at ordinary room temperature. So different parts of the ball have different probability of tunneling through a potential barrier. But you also can't have parts of the ball going through while another part bouncing back, because you have to overcome the ball's cohesive forces also.

3. You have no ability to throw a ball exactly in the identical manner each time, so you are not repeating the identical situation. So the statistics doesn't quite work here.

4. We have never, ever observed a ball tunneling through a wall. This is where experiments (or lack of it) trump all claims that this can happen. In physics, a claim must be backed by empirical evidence, or else it isn't physics, but String Theory. <ZapperZ runs and hides>

Zz.

 

[PRodQuanta]

In physics, a claim must be backed by empirical evidence, or else it isn't physics, but String Theory. <ZapperZ runs and hides>

Zz.

ZING!

It would be far easier, and more likely, that part of the book would pass through part of the table. Then we would be able to observe that part of the book is stuck in the table, but there again I don't think there is any evidence of that ever happening.

I would guess that there have been millions of particles from a book that have tunnelled through a table. Just because one of the particles did doesn't mean that the whole book has to. Maybe I am wrong with this assumption. Correct me if I am.

Paden Roder

 

[Hurkyl]

I got the impression that QM says it really is possible for the ball to pass through the wall, or the book to fall through the table... it's just that that would be such a statistically rare event that it quite likely that a similar event has never happened in the history of the universe.

But, the point is that it's an analogy for what "can" happen in the microscopic world, where the statistics are actually favorable, as opposed to being so tremendously lopsided against.

 

[playmesumch00ns]

So the consensus is that it is possible (i.e. is allowed by the laws of physics as we know them), just astronomically impossible.

Bugger, I was hoping for a definitive no!

For the entire ball to tunnel through the wall, would a particular amount of energy be required? I understand that in quantum tunnelling, particles "borrow" energy from the vacuum to "jump" infinitesimal barriers. How much energy would all the particles in a tennis ball need to borrow to jump a six inch wall?

 

[vanesch]

So the consensus is that it is possible (i.e. is allowed by the laws of physics as we know them), just astronomically impossible.

Bugger, I was hoping for a definitive no!

For the entire ball to tunnel through the wall, would a particular amount of energy be required? I understand that in quantum tunnelling, particles "borrow" energy from the vacuum to "jump" infinitesimal barriers. How much energy would all the particles in a tennis ball need to borrow to jump a six inch wall?

The answer to your question is in fact, a matter of opinion. Quantum theory SAYS that there is an (indeed astronomically small) probability for the ball to tunnel through the wall. For that to be true, however, quantum theory must be a VALID theory on the macroscopic level (in other words, macroscopic objects must be describable by quantum theory). This is perfectly possible. It leads (again!) to a view on quantum theory which is a "many worlds" interpretation.
However, there's another view on quantum theory, which says that it DOES NOT describe macroscopic objects - which are strictly classical, but only microscopic objects, and that there is a kind of mysterious transition between them, called a "measurement process". This is the Copenhagen interpretation (the historical view on the matter). Personally, I don't like it, but it exists.

Now, the difficulty (and the reason why it is just a matter of opinion) is that the predictions of both viewpoints are essentially identical.
If you calculate that you have a chance of 10^(-23451234) to 1 to have your ball tunnel through the wall (quantum prediction), and you say that you've never seen it happening (and you've tried maybe, 10^(12345) times only), then there is PERFECT AGREEMENT between prediction and experiment so far. So the pure quantum prediction is verified.
If you take on the Copenhagen view and you say that, given that the ball is a macroscopic, and hence, classical object, it CANNOT tunnel through the wall, and you've tested that 10^(12345) times, then you ALSO conclude, that this is experimentally verified.

However, an argument in favor of the quantum case is that each time that there COULD have been a difference in prediction between the quantum and the classical case, the quantum case won. Albeit for much "smaller" systems than tennis balls. Still, it is a huge extrapolation, and it remains, as for now, still a matter of opinion to decide whether quantum theory is, or is not, valid for macroscopic objects. I like to think that it is, just for the economy of concept. But others are entitled to other opinions.

 

[ZapperZ]

And since vanesch has tried to introduce his pet point of view into this, there's no reason why I can't do the same. :)

The big question here is why isn't a tennis ball, or any of our familiar object, a "quantum object". While the consituents of the tennis balls (i.e. the atoms) are governed by quantum mechanics, the ball itself isn't. You can measure very accurately the position of the ball and its momentum simultaneously, and follow the trajectory of the ball every single step of the way. These are physical behavior that you cannot do with a quantum object.

So already we can clearly see that the ball obeys one set of rules, while the constituents of the ball obey a different set of rules. But what is causing such a difference, and do they actually converge into one another at some scale? Strangely enough, you get all kinds of answer when you ask that, mainly because (i) it is still an active research area i.e. the area of mesoscopic physics and (ii) we have no means of computing a gazillion interactions.

In putting together a gazillion atoms to make a tennis ball, you have produced an "emergent" object. This is where you do not have the ability to predict large, macroscopic phenomena simply by looking at the interactions at the microscopic scale. The atoms have no ability to mimick the behavior of the tennis balls, even as you try to include more and more interactions to account for the tennis balls, the same way one cannot derive superconductivity simply by writing down all the interactions of each individual electrons.

So for condensed matter physicists, there is a "discontinuity" in our knowledge in going from one scale to the next. To the atoms in the ball, the ball itself is an emergent object. All the interactions, plus the decoherence, plus the interactions with large degree of freedom with the surrounding, etc.. all produced the tennis ball. And according to Bob Laughlin, this emergent properties are what produced Newton's physics and Newton's objects.

Zz.

 

[WARGREYMONKKTL]

The answer to your question is in fact, a matter of opinion. Quantum theory SAYS that there is an (indeed astronomically small) probability for the ball to tunnel through the wall. For that to be true, however, quantum theory must be a VALID theory on the macroscopic level (in other words, macroscopic objects must be describable by quantum theory). This is perfectly possible. It leads (again!) to a view on quantum theory which is a "many worlds" interpretation.
However, there's another view on quantum theory, which says that it DOES NOT describe macroscopic objects - which are strictly classical, but only microscopic objects, and that there is a kind of mysterious transition between them, called a "measurement process". This is the Copenhagen interpretation (the historical view on the matter). Personally, I don't like it, but it exists.

as you say that the quantum theory does not describe the macroscopic object tive. but a macroscopic object are compose of the "quantum" particles.there must be a relationship between them. there must be a possibility that it will tunnel through the wall is we can give the ball a motion so that all particles of the ball will become a "wave-particle" with that energy(if i wrong please correct me).
i have a question here. is it possible that if a particle (electron) were accelerated to near the speed of light. it can become a wave?

 

[vanesch]

Here we go again

The big question here is why isn't a tennis ball, or any of our familiar object, a "quantum object". While the consituents of the tennis balls (i.e. the atoms) are governed by quantum mechanics, the ball itself isn't. You can measure very accurately the position of the ball and its momentum simultaneously, and follow the trajectory of the ball every single step of the way. These are physical behavior that you cannot do with a quantum object.

Well, a quantum ball could be put in a quantum state of which the errors in position and momentum are well within what is experimentally possible with a classical ball. I think that there is no clash here. The "no trajectory" is only clearly valid for microscopic objects. The larger the object, the more a "trajectory" is quantum-mechanically possible (within certain errors which are tiny as compared to what can actually be measured).

So already we can clearly see that the ball obeys one set of rules, while the constituents of the ball obey a different set of rules.

My point was that it does not HAVE to follow different rules. Of course, its behaviour is compatible with different rules, but - what I called the economy of concepts - if we can do it all with the SAME set of rules, isn't that nicer ?

In putting together a gazillion atoms to make a tennis ball, you have produced an "emergent" object. This is where you do not have the ability to predict large, macroscopic phenomena simply by looking at the interactions at the microscopic scale. The atoms have no ability to mimick the behavior of the tennis balls, even as you try to include more and more interactions to account for the tennis balls, the same way one cannot derive superconductivity simply by writing down all the interactions of each individual electrons.

That's an unproven assertion! Although you are right that *up to now* nobody has been able to do all of the math to show it, nobody has been able to derive a contradiction either, in that he could prove that, when taking into account all the interactions, one cannot derive superconductivity. This is like, before Wiles, claiming that Fermat's last theorem was FALSE because nobody had succeeded in finding a proof.

So the honest statement, as of now, is that there are emergent properties that nobody has ever been able to derive from ab initio principles of an underlying theory - as there are emergent properties that people HAVE been able to derive in such a way. As far as I know, however, there is no proof that any of these emergent properties are UNDERIVABLE from the ab initio principles. As such, IT IS AN OPEN QUESTION of whether they are, or are not, an emergent property that is NOT accounted for by the underlying theory. On open questions, one has the right to have opinions, but they are not more than that.

Reductionists, like me, like to cherish the opinion that all emergent properties are accounted for by underlying principles (although it is sometimes such a hard mathematical problem that nobody has ever succeed yet in doing so explicitly). Holists like to think that this is not the case. But, again, it is a matter of opinion, and the reductionist viewpoint has not yet been *proved to be false* as far as I know.

 

[Locrian]

Quantum theory SAYS that there is an (indeed astronomically small) probability for the ball to tunnel through the wall.

Prove it!

Whether you prefer reductionism or emergence; whether quantum mechanics is valid on the macroscopic level (which it seems to me it obviously is) - regardless of any of these things, the fact stands that no one has ever used quantum mechanics and quantum particles to produce a working model of a tennis ball - or anything remotely like it.

So how do you know what quantum theory says about the way a tennis ball behaves? Are we really to assume that there exists anywhere near the same behaviour on a macroscopic scale, even within the framework of quantum mechanics?

 

[ZapperZ]

Here we go again

I blame you for starting it. :)

Well, a quantum ball could be put in a quantum state of which the errors in position and momentum are well within what is experimentally possible with a classical ball. I think that there is no clash here. The "no trajectory" is only clearly valid for microscopic objects. The larger the object, the more a "trajectory" is quantum-mechanically possible (within certain errors which are tiny as compared to what can actually be measured).

That isn't true. I could have a "macroscopic" object yet it still behaves quantum mechanically. The supercurrent in the SQUID experiments consists of 10^11 electrons. These are HUGE when compare to the typical quantum objects. Yet, they behave quantum mechanically.

And note, while emergent properties can produce Newton objects, they can also produce quantum mechanical objects. The issue here isn't just particle-particle interactions within the constituents of the object, but the coupling to the environment, what most people consider as decoherence. So the emergent phenomena is due to many different forms and causes. If you produce a lot of interactions, but still isolate it from external decoherence, you get a macroscopic object that is also a quantum object.

My point was that it does not HAVE to follow different rules.

And my point is that you do not HAVE to follow many-worlds rules to get the same thing.

Zz.

 

[vanesch]

I blame you for starting it. :)

And I really tried to be moderate so as not to trigger a reaction

That isn't true. I could have a "macroscopic" object yet it still behaves quantum mechanically. The supercurrent in the SQUID experiments consists of 10^11 electrons. These are HUGE when compare to the typical quantum objects. Yet, they behave quantum mechanically.

Yes, but that should have been MY argument! That's to me one more reason to claim that quantum theory is universal (even if we can't prove it rigorously for things such as a tennis ball).

And note, while emergent properties can produce Newton objects, they can also produce quantum mechanical objects. The issue here isn't just particle-particle interactions within the constituents of the object, but the coupling to the environment, what most people consider as decoherence. So the emergent phenomena is due to many different forms and causes. If you produce a lot of interactions, but still isolate it from external decoherence, you get a macroscopic object that is also a quantum object.

I couldn't agree more...

And my point is that you do not HAVE to follow many-worlds rules to get the same thing.

Well, if you claim that quantum theory is *universally valid* (which is, to me - although for sure unproven - the most *economical* hypothesis), you end up giving a hilbert space of states to everything, including yourself. I do not see how you get out of that without some flavor of MWI...

The only issue out of it (and I thought you took it) was to claim that quantum theory is NOT universally valid. Then the burden is to show where it FAILS to be valid, and how this fits into a more encompassing view. As far as I know, it has never been SHOWN to fail. This is the point I tried to make.

That said, it is entirely possible to be of the opinion that quantum theory is somehow not universally valid - such a viewpoint is ALSO compatible with experimental observation as of now. I just find that a less economic viewpoint, and there is no strict NEED for that. So - again - it is all matter of taste and opinion.

 

[vanesch]

Whether you prefer reductionism or emergence; whether quantum mechanics is valid on the macroscopic level (which it seems to me it obviously is) - regardless of any of these things, the fact stands that no one has ever used quantum mechanics and quantum particles to produce a working model of a tennis ball - or anything remotely like it.

Nor has anyone ever produced a working classical model of ALL ASPECTS of a tennis ball. So if we are allowed to MAKE APPROXIMATIONS to build a more or less realistic PHENOMENOLOGICAL MODEL of a tennis ball, I CAN give you some quantum model of it. The simplest one is a point particle with mass = mass of the tennis ball + degrees of freedom of rotation (and if you want to, vibration), some hamiltonian describing the elastic interactions of the tennis ball (which will give you its spatial extention and the correct "bouncing" of the ball off walls). A wall can be phenomenologically represented by some or other potential barrier, and here we go!

If you find this too crude, and you want me to descend down to nucleae, electrons and all that, then I go back to my previous remark: no such CLASSICAL model for a tennis ball exists either !

 

[GOD__AM]

ZING!

I would guess that there have been millions of particles from a book that have tunnelled through a table. Just because one of the particles did doesn't mean that the whole book has to. Maybe I am wrong with this assumption. Correct me if I am.

Paden Roder

Are you suggesting that some particles broke from their bonds in the book and travled through the table? Where are those particles now? They are no longer part of a book at this point. Electrons may be exchanged between the table and the book, and some may actually tunnel to their position, but I don't think a complete molecule (or group of molecules) would.

My point was that it is more likely that a massive object would begin to tunnel through another massive object, under the right conditions, but very quickly those conditions would change, and any further tunneling would be halted by the fact that it's such a small probability in the first place. This would leave the two massive objects entangled to some degree (in a classical sense). I just don't see any evidence that massive objects become entangled in this way.

 

[jackle]

If the tennis ball were radioactive, wouldn't bits of it be more likely to tunnel through the wall?

 

[-Job-]

Just a thought, regarding scale. If you look at a graph of the function pi(x) (the one producing the number of primes less than, or equal to x) close up, it doesn't look like it is following a pattern. But as you zoom out enough it almost becomes a smooth line. I saw this in this page:
http://primes.utm.edu/howmany.shtml
At the quantum mechanical level, there may not be much certainty regarding a particles position and momentum, but as you zoom out, if the particles belong to a whole, as a tennis ball, then the differences between the position and momentum of each constituent particle become too small relatively to the current scale, and so variables such as position and momentum might emerge as being the "average" of the constituent particles. Small deviations from the average by a few constituent particles are not enough to change the average, so we might see the tennis ball as having a definite position and momentum. Not that this "average" doesn't change, but that it doesn't change enough to be noticeable at this scale.
So i think, the Copenhagen view that i just heard Zapperz mention does seem reasonable, in my opinion.
If the 3D world we live in were just a graph of various functions, then we might notice similar behavior as the graph of the function pi(x).

 

[Sherlock]

Well, if you claim that quantum theory is *universally valid* (which is, to me - although for sure unproven - the most *economical* hypothesis), you end up giving a hilbert space of states to everything, including yourself. I do not see how you get out of that without some flavor of MWI...

The only issue out of it (and I thought you took it) was to claim that quantum theory is NOT universally valid. Then the burden is to show where it FAILS to be valid, and how this fits into a more encompassing view. As far as I know, it has never been SHOWN to fail. This is the point I tried to make.

That said, it is entirely possible to be of the opinion that quantum theory is somehow not universally valid - such a viewpoint is ALSO compatible with experimental observation as of now. I just find that a less economic viewpoint, and there is no strict NEED for that. So - again - it is all matter of taste and opinion.

It seems to me that the issue isn't whether quantum theory is universally valid as a predictor of experimental probabilities. There's every reason to believe that it is.

But to adopt MWI requires that one take quantum theory as a complete description of an underlying reality --- and there's no particular reason to believe that it is.

The viewpoint that quantum theory doesn't completely define an underlying reality is why there is a measurement problem in the first place. So, while solving the measurement problem by assuming that quantum theory is a complete description might seem economical, it isn't necessarily the most reasonable approach to take.

Thus, Bohmian Mechanics for example is a more reasonable approach to the measurement problem because it is a hidden variable theory of underlying processes, which MWI (as well as quantum theory according to the standard interpretation) isn't.

In saying that it's all, at least for now, a matter of taste and opinion, you've hit upon the most economical viewpoint which is that all of the alternative formulations-interpretations of quantum theory are models, ie. fictions, and there really is no physical basis for choosing one over the other --- which brings you right back to conventional quantum theory (at least until there is some compelling reason to adopt a different formulation).

Then there's Bell's (vis ttn) two-part argument for nonlocality. If this argument is indeed sound, then relativity's prohibition on superluminal causation is just wrong and the ONLY approach that then makes sense is something along the lines of Bohmian Mechanics.

But under no formulation is there any physical meaning to the notion that a tennis ball can tunnel through, say, a brick wall.

 

[selfAdjoint]

I want to propose a question here.

On the Beyond the Standard Model forum, several well-trained physicists have posted the opinion that "Planck scale physics" can have nothing to do (some say "cannot" others "is extremely unlikely to") with phenomena like the scattering of W particle on each other. This is the reverse hierarchy problem.

If this is true, then the success of quantum theory in accounting for such scattering, and by extension its successes in all current and past experiments, can have nothing to do with supporting such a statement as "Quantum uncertainty is a deep principle of the universe", and ditto for superpositon, entanglement and the rest.

How say ye all to this?

 

[Sherlock]

I want to propose a question here.

On the Beyond the Standard Model forum, several well-trained physicists have posted the opinion that "Planck scale physics" can have nothing to do (some say "cannot" others "is extremely unlikely to") with phenomena like the scattering of W particle on each other. This is the reverse hierarchy problem.

If this is true, then the success of quantum theory in accounting for such scattering, and by extension its successes in all current and past experiments, can have nothing to do with supporting such a statement as "Quantum uncertainty is a deep principle of the universe", and ditto for superpositon, entanglement and the rest.

How say ye all to this?

Quantum theory is valid at the level of instrumental phenomena. Since this is as deep as knowledge of the universe goes, then, in that sense, the principles of quantum theory are deep.

However, whether these principles describe a level of reality beyond or underlying instrumental phenomena is an open question.

As a student of quantum theory, I get sort of mixed signals from the theory itself regarding how it might be related to an underlying quantum world.

As to your specific question, I agree with what the well-trained physicists say --- at least until I become one myself, which at my current pace will require that I live well beyond the normal human life span.

Consider this post a boink to see what some of the well-trained physicists who frequent this forum have to say about it.

 

[vanesch]

But to adopt MWI requires that one take quantum theory as a complete description of an underlying reality --- and there's no particular reason to believe that it is.

The viewpoint that quantum theory doesn't completely define an underlying reality is why there is a measurement problem in the first place. So, while solving the measurement problem by assuming that quantum theory is a complete description might seem economical, it isn't necessarily the most reasonable approach to take.

Yes, but that's about the only argument. It doesn't seem "reasonable" ; it is "just too crazy". As I repeated zillions of times, quantum theory is no better than any other scientific theory, and can, as such, be falsified. When that happens, all what goes with it as "picture of the world" can of course go down the drain, and it is up to the new queen in town to say what's now the new picture. This ephemere nature of things is inherent in any scientific endeveour. So if you ask me if quantum theory "really" describes the world, as with all scientific knowledge, I put this caveat. However, quantum theory is NO LESS a scientific theory than any other. Given its empirical success, I don't see why it should be a LESSER theory than any other scientific theory. I don't see why quantum theory should receive that dubious stature of "complete description of outcome of experiment" together with "it is of course NOT a DESCRIPTION of an underlying reality". Why not ? What's so terrible about quantum theory as a scientific theory, that others don't have ? Why should we take the 4-dim space-time manifold of GR somehow as a "description of underlying physical reality" but the wavefunction of quantum theory not - apart from the usual caveat about scientific theories, namely that one day, they can be falsified ? Isn't this similar to accepting natural evolution for animals, and even as an empirically complete theory for humans, except of course that it is "not reasonable" to say that our far ancestors were apes ?

Thus, Bohmian Mechanics for example is a more reasonable approach to the measurement problem because it is a hidden variable theory of underlying processes, which MWI (as well as quantum theory according to the standard interpretation) isn't.

There are serious conceptual problems with Bohmian mechanics too, because of the mixture between epistemological and ontological concepts. In essence the "quantum equilibrium condition" - the requirement that our INITIAL KNOWLEDGE of the state of the system, as a probability distribution, corresponds to |psi|^2 of the ONTOLOGICAL state (the wavefunction, with all its parallel worlds, is as much part of the ontology of Bohmian mechanics as it is in MWI - the only thing we have extra is a "token" (the particle positions) which indicate which branch we're supposed to collectively experience). So if you say that, in Bohmian mechanics, the subjective experience is only derived from the particle positions, and not from the wavefunction (both are part of the "state of the world"), then there's no way of requiring that our knowledge of the particle positions of our body should not be more precise than what's allowed by the HUP and the wavefunction (and if you do that, Bohmian mechanics breaks down). It is only in the particular case when our subjective knowledge of our own bodystate corresponds to particle positions with a probability distribution given by the wavefunction, that Bohmian mechanics can save the HUP. But this means that the particle positions, by themselves are NOT the thing that determines (as in classical physics), our subjective perception: the wavefunction is just as much part of it. And in Bohmian mechanics, the wavefunction is exactly the same one as in MWI (no collapse) - with all its parallel branches and all that.
So the relationship between subjective experience, knowledge, particle positions and wavefunctions is just as involved in Bohmian mechanics as it is in MWI. On top of that, Bohmian mechanics is not compatible with the minkowski spacetime view of SR. So I'd say that Bohmian mechanics has its own interpretational issues, and is not as clear as Newtonian mechanics in any case.

In saying that it's all, at least for now, a matter of taste and opinion, you've hit upon the most economical viewpoint which is that all of the alternative formulations-interpretations of quantum theory are models, ie. fictions, and there really is no physical basis for choosing one over the other --- which brings you right back to conventional quantum theory (at least until there is some compelling reason to adopt a different formulation).

This is not entirely true. Ether theory also works for special relativity. Does that mean that special relativity has no ontology ?

Then there's Bell's (vis ttn) two-part argument for nonlocality. If this argument is indeed sound, then relativity's prohibition on superluminal causation is just wrong and the ONLY approach that then makes sense is something along the lines of Bohmian Mechanics.

I would like to point out that ttn agrees that the *other* way out is MWI - but considers it "just too crazy".

But under no formulation is there any physical meaning to the notion that a tennis ball can tunnel through, say, a brick wall.

I think it is of the same order as the physical meaning of all life on Earth dying, because all air molecules suddenly end up in a big lump on top of Antarctica.

My impression of the entire interpretational debate of quantum theory is that we've been inventing all of this "empirically complete but ontologically meaningless" positivist babble because we simply refuse to make the mental step which the quantum formalism cries out, and that is: the wavefunction describes reality - with the usual scientific caveat of the possibility of being falsified one day. Just as one could refuse the mental step that his great great great old dad was something close to a chimp, or that the sun doesn't turn around the earth, or that the Earth isn't flat, or that organic chemistry is like any chemistry... I agree that the mental shock is greater. The entire speculation, and the "matter of opinion" resides in fact in speculation of how quantum theory will be falsified.
For instance, according to Bohr, quantum theory does NOT describe macroscopic objects, but classical physics does. This means that certain quantum interference experiments, with large enough objects, will *falsify* quantum theory.
But this is an odd way of thinking! Never before, in the interpretation of a new theory, we started by speculating on how it was going to FAIL ! Newton didn't say that his theory of matter points in Euclidean space was probably just an approximation to a field theory ! Einstein never said that the 4-dim spacetime manifold was probably an erroneous concept which gave good empirical results, but which was probably going to be shown to be wrong ! So this is what I don't understand: people thinking about quantum theory seem to START with the assumption that it must be somehow fundamentally flawed, and base their view of things on that. Strange...

 

[Milind_shyani]

hi,
it is possible for the the ball to tunnel through the wall or the brick.but the probability of that to happen is 1 out of 10^34 times.
so please don't try this at home.otherwise you will have to do this almost up to infinity. but these probability is only true if take the points into consideration given by zapperZ

 

[susmit]

see theoritically it is possible. the chances of transmission of a particle (or group) is expressed as the transmission coefficient T

T= 16E/U [1-E/U] exp -2kx where k is
k=2PI(2m(U-E)^1/2 / h

so, T increases with particle mass and with barrier energy (ball width). so there are chances but really REALLY small, probably that's why you don't fall through the floor to the other side of the earth.

 

[masudr]

But wait, the tennis ball is not a single particle. Instead it is about ~10^23 particles all interacting with each other.

 

[Chaos' lil bro Order]

Zz

There are several issues that need to be considered here:

1. A "ball" is not a quantum particle.

2. An object that can exhibit such a behavior has every part of it in coherence with each other. A ball doesn't. the atom in one part of the ball cannot be described via a coherent wavefunction with another part of it, especially at ordinary room temperature. So different parts of the ball have different probability of tunneling through a potential barrier. But you also can't have parts of the ball going through while another part bouncing back, because you have to overcome the ball's cohesive forces also.

3. You have no ability to throw a ball exactly in the identical manner each time, so you are not repeating the identical situation. So the statistics doesn't quite work here.


Zz.

1. You try to disprove this statement in a later post, in a sense when you say, 'That isn't true. I could have a "macroscopic" object yet it still behaves quantum mechanically. The supercurrent in the SQUID experiments consists of 10^11 electrons. These are HUGE when compare to the typical quantum objects. Yet, they behave quantum mechanically.' CAn you give a link to this experiment, I'd be curious to learn about it, ty.

2. Irrespective of the fact that different parts of the tennis ball have different wave functions and therefore different probabilities of tunnelling through the wall, it is still possible for every one of these parts to tunnel through the wall simultaneously. So you are wrong there (at least in the 'theory' of tunnelling), but experimentally we just don't know.

3. This is just nitpicking to the nth degree, forshame.



In a later post you said, 'The big question here is why isn't a tennis ball, or any of our familiar object, a "quantum object". While the consituents of the tennis balls (i.e. the atoms) are governed by quantum mechanics, the ball itself isn't. You can measure very accurately the position of the ball and its momentum simultaneously, and follow the trajectory of the ball every single step of the way. These are physical behavior that you cannot do with a quantum object.'

This is just a silly argument. 'Quantum objects' are limited to the Uncertainty Principle because of the limitations of Rayleigh's Criterion and the particle(s) needed to 'probe' them. Inelastic scattering and the interference patterns observed from particle collision experiments are limited by the wavelengths of the particles used (the higher their energies the lower their wavelengths) and not some deeply rooted property of the Universe that gives us the Uncertainty Principle.

The reason you can easily measure a tennis ball's momentum and position simultaneosly is because you measure it with visible light (~500 nm wavelength) which under Rayleigh's Criterion, can EASILY resolve the position of the tennis ball (a ~100,000,000 nm diameter object!). AND this visible light imparts such a NEGLIBIBLE amount of energy onto the ball that its momentum is virtually unchanged.
So using the Uncertainty Principle to question why a tennis ball isn't a 'quantum object' while its particle constituents are, makes entirely no sense.Zzz

 

[ZapperZ]

1. You try to disprove this statement in a later post, in a sense when you say, 'That isn't true. I could have a "macroscopic" object yet it still behaves quantum mechanically. The supercurrent in the SQUID experiments consists of 10^11 electrons. These are HUGE when compare to the typical quantum objects. Yet, they behave quantum mechanically.' CAn you give a link to this experiment, I'd be curious to learn about it, ty.

2. Irrespective of the fact that different parts of the tennis ball have different wave functions and therefore different probabilities of tunnelling through the wall, it is still possible for every one of these parts to tunnel through the wall simultaneously. So you are wrong there (at least in the 'theory' of tunnelling), but experimentally we just don't know.

I suppose you know better. After all, I ONLY did my Ph.D thesis on tunneling spectroscopy of high Tc superconductor.

I based my "knowledge" not simply on things I read, but things that I do, and things that have been shown experimentally. For example, when do we get something as LARGE as buckyballs to behave like a "quantum particle"? We have to (i) cool it down to extremely low temperatures and (ii) we eliminate as much as we can all possible collisions to reduce decoherence on different parts of the buckyball. Do this at room temperture under normal conditions and you'll never obtain any quantum effects at all!

We have never seen "partial tunneling" of an "object". Do you know of any description, even in theory, that describes the partial tunneling of an object? What the simultaneous tunneling of an object (i) with a gazillion particles AND (ii) when parts of it are in utter decoherence with each other. I would love to see if you can show me theoretical papers on this process to back up your claim.

3. This is just nitpicking to the nth degree, forshame.

Really? Let's examine this, shall we?

What does it mean when I say the probability of something is 1/5? It means that (i) if I make an observation of that single event, there is 1 in 5 chance that the desired event will occur, OR (ii) that if I have 5 identical events, one of them is likely to be the desired event.

But look at what is IMPLIED here! Implicit in the asumption here is that all the events are identically done. I need to repeat the event 5 identical times for the statistics to give me the 1 event that I want! It is why, in the OP, the person is asking for repeated throwing of the ball. It is why, in high energy physics, we make a gazillion collisions, all so we can generate identical events to produce the desired events.

But "throwing a ball", when we are dealing with (i)such weak occurence and (ii) the huge variability in human repeatition mean that you do NOT have identical repeatition of these events. The first throw isn't the same as the 2nd throw. Even if you just have ONE particle (you're throwing a proton), the probability for the 1st going through isn't the same as the probability of the 2nd going through. These are separate SETS of events.

In a later post you said, 'The big question here is why isn't a tennis ball, or any of our familiar object, a "quantum object". While the consituents of the tennis balls (i.e. the atoms) are governed by quantum mechanics, the ball itself isn't. You can measure very accurately the position of the ball and its momentum simultaneously, and follow the trajectory of the ball every single step of the way. These are physical behavior that you cannot do with a quantum object.'

This is just a silly argument. 'Quantum objects' are limited to the Uncertainty Principle because of the limitations of Rayleigh's Criterion and the particle(s) needed to 'probe' them. Inelastic scattering and the interference patterns observed from particle collision experiments are limited by the wavelengths of the particles used (the higher their energies the lower their wavelengths) and not some deeply rooted property of the Universe that gives us the Uncertainty Principle.

The reason you can easily measure a tennis ball's momentum and position simultaneosly is because you measure it with visible light (~500 nm wavelength) which under Rayleigh's Criterion, can EASILY resolve the position of the tennis ball (a ~100,000,000 nm diameter object!). AND this visible light imparts such a NEGLIBIBLE amount of energy onto the ball that its momentum is virtually unchanged.
So using the Uncertainty Principle to question why a tennis ball isn't a 'quantum object' while its particle constituents are, makes entirely no sense.Zzz

I didn't apply the HUP for this argument. You missed the whole point entirely. I applied the EMERGENCE property. If I apply the HUP, I would have brought up the ONE particle case, and then make it decohere with other particles. That I didn't do. I did, however, brought up the gazillion particles making the gazillion interactions and with a gazillion degrees of freedom.

And note, your "application" of the HUP is based on the "measurement" ability when you said that visible light imparts a negligible amount of energy to the ball. This is what I had address many times before when I point out the misconception of the HUP. The HUP has NOTHING to do with such effects and uncertainty. It isn't a measurement issue!

Zz.

 

[Chaos' lil bro Order]

Sorry, I didn't know you had your Ph.D, guess I'll just assume you know everything. I'm really not trying to attack you personally, I just see inconsistencies in your argument. Point out mine and I'll be happy to retract them.
As for the nitpickiness, come on now, if we averaged out a billion throws would the slight changes in trajectory and velocity really make that much of a difference to such an already loosely worded theoretical problem? It seems like excessive badgering to me.

And note, your "application" of the HUP is based on the "measurement" ability when you said that visible light imparts a negligible amount of energy to the ball. This is what I had address many times before when I point out the misconception of the HUP. The HUP has NOTHING to do with such effects and uncertainty. It isn't a measurement issue!

Zz.

Can you explain to how HUP is not based on measurement. I didn't know this. Please explain it to me in less than 200 words if possible. Thanks

 

[ZapperZ]

Sorry, I didn't know you had your Ph.D, guess I'll just assume you know everything. I'm really not trying to attack you personally, I just see inconsistencies in your argument. Point out mine and I'll be happy to retract them.

I did already! That last post was a rebuttal! Did you think the buckyball example was simply for decorations?!

As for the nitpickiness, come on now, if we averaged out a billion throws would the slight changes in trajectory and velocity really make that much of a difference to such an already loosely worded theoretical problem? It seems like excessive badgering to me.

Badgering? Hello?

The whole point of repeating the EXACT experiment under the identical situation IS the whole point of what makes QM so weird - you don't get the identical result, unlike classical mechanics! So yes, it DOES matter!

Can you explain to how HUP is not based on measurement. I didn't know this. Please explain it to me in less than 200 words if possible. Thanks

200 words or less... right. I forget that physics is done nowadays to statisfy cute bylines and attention-grabbing headlines. I'd point to you the essay I wrote on this a long time ago in my journal, but I won't, because it is WAY more than 200 words.

Zz.

 

[my_wan]

In physics, a claim must be backed by empirical evidence, or else it isn't physics, but String Theory. <ZapperZ runs and hides>

I like it

1. You try to disprove this statement in a later post, in a sense when you say, 'That isn't true. I could have a "macroscopic" object yet it still behaves quantum mechanically. The supercurrent in the SQUID experiments consists of 10^11 electrons. These are HUGE when compare to the typical quantum objects. Yet, they behave quantum mechanically.' CAn you give a link to this experiment, I'd be curious to learn about it, ty.

Here is a link
http://www.amherst.edu/~jrfriedman/Scientific%20American/scientific-american%20edited.html

Quantum mechanics also predicts that you can get the same interference pattern with BBs as you can with photons. The caveat being that they must move so slow that it would take longer the the age of the universe to reach their target. Sure I would prefer a theoretical framework that pinned down the ontology a bit more. Creating theoretical fromameworks for this purpose only is not science though and shouldn't be. I do think we must take QM seriously and classical mechanics as a prejiduce. The wavefunction does describe reality. However it is entirely logical that the 'predictions' of QM are 100% true yet not completely describe the entire system even in it's domain. We like to pretend that we can know who hit who in an automobile accident, yet the laws of physics alone can't make such a distinction. This is why empirical data is paramount. The insistance that science must include your pet ontology is a waste of everybodies time, even your own.

Chronos uses the signature;

A fish cannot comprehend the existence of water. He is too deeply immersed in it. - Sir Oliver Lodge

How much more difficult for Dr fish if he's not only in the water but defined by the water?

 

[vanesch]

But wait, the tennis ball is not a single particle. Instead it is about ~10^23 particles all interacting with each other.

This is true, but this might even be true for a proton! We don't know it's ultimate internal degrees of freedom.

However, your argument stands, for the following reason: the energy levels of these 10^23 degrees of freedom are not way higher than the potentials that will intervene in the tunneling (the binding forces in the ball are of comparable magnitude than those in the wall). So yes, this is the reason why, if ever a tennis ball might tunnel through the wall, it will have a reasonable probability to appear as a sock on the other side

 

[my_wan]

This is true, but this might even be true for a proton! We don't know it's ultimate internal degrees of freedom.

Couldn't it be argued in a sense that since we can perform calculations (quantum computer) that require an arbitrarily large number of classical switches to perform it's internal degrees of freedom are arbitrarily large. One might say these are probabilistic and not true degrees of freedom but that would also belie the experimental reality of them, not to mention that the calculations are real calcultuions. Even if we argued these degrees of freedom weren't internal but rather arose from myriad interactions with the environment we must still contend with the theoretical reality that even a modest number of quantum cubits can perform more calculations than there are particles in the universe. This begs the question, could a purely classical wave via interference in any way mimic this exponential growth in computing power, not the power itself, even in principle. A system where all possible spatial coordinates become the 0 and 1s.

 

[Chaos' lil bro Order]

Badgering? Hello?

The whole point of repeating the EXACT experiment under the identical situation IS the whole point of what makes QM so weird - you don't get the identical result, unlike classical mechanics! So yes, it DOES matter!




Zz.

Averaging, averaging, AVERAGING.

1) Here's a question, I fire an electron with energy of 0.888MeV at a barrier of 20MeV, what are the odds it penetrates it?



2) Disprove that the tennis ball cannot pass through the wall.



3) Why do you think no experiment has seen an 'object' pass through a wall, who has the lifetime of the Universe to try such a dumb experiment, whether QM predicts it MAY be possible or not.

 

[Chaos' lil bro Order]

ZapperZ

I read your journal topic on HUP, what an excellent summary.

QUOTE'
Now THIS is the uncertainty principle at work. The slit width, and thus Delta(y) is getting smaller. This implies that Delta(p_y) is getting larger. Take note that the measurement uncertainty in a single is still the same as in the classical case. If I shoot the particle one at a time, I still see a distinct, accurate "dot" on the screen to tell me that this is where the particle hits the detector. However, unlike the classical case, my ability to predict where the NEXT one is going to hit becomes worse as I make the slit smaller. As the slit and Delta(y) becomes smaller and smaller, I know less and less where the particle is going to hit the screen. Thus, my knowledge of its y-component of the momentum correspondingly becomes more uncertain.'


So in essence, Classically, a small slit width means a small gausian distribution width in y-momentum; where as in QM, the smaller the slit width, the larger the gausian distribution width in y-momentum.
Question: Does the width of the slit walls THEMSELVES effect the outcome in the QM example? I mean, if the slit walls were books, for example, would the thickness of the book effect the outcome in the QM example, is so how? ty.

 

[ZapperZ]

Averaging, averaging, AVERAGING.

1) Here's a question, I fire an electron with energy of 0.888MeV at a barrier of 20MeV, what are the odds it penetrates it?

And the fact that you ask this means that you have COMPLETELY missed the whole point of my objection to this. You have somehow turned this around into arguing about the phoenomena of tunneling itself. This is riduculous.

Think about this. I did 4 years of research work on a phenomenon that I don't think exist! No Kidding!

2) Disprove that the tennis ball cannot pass through the wall.

Again, you didn't read. *I* asked you this way early in this thread. Show me theoretical formulation that a "tennis ball" can! Cite me peer-review journals that have accounted for the thermal fluctuation of such a macroscopic object, and the gazillion degree of freedom, and THEN showed that, DISPITE of that, it can still tunnel through as a WHOLE object. Not just one electron, not just one proton or neutron, but the whole thing at once!

I pointed out the difficulties we had in trying to make something the size of a buckyball to behave like a quantum particle. Somehow, you completely ignored this, or simply didn't get the significance of that description. As large as a buckyball is, it is puny when compared to a tennis ball, and with even less of a thermal decoherence.

So this works both ways. Show me that it can! As an experimentalist, I can easily point to the fact that there are ZERO experimental evidence for a tennis ball tunnelling through ANYTHING. Unless you think QM is String theory that do not require experimental observation to be religiously followed, I have presented my case.

3) Why do you think no experiment has seen an 'object' pass through a wall, who has the lifetime of the Universe to try such a dumb experiment, whether QM predicts it MAY be possible or not.

But yet you still want to argue for such "possibility"?

And I am being VERY consistent about my stand in this whole thing dispite what you think. I question the use or the acceptance of something when it isn't based on valid empirical evidence. I question people who bastardize the application of the phenomenon of tunneling to apply to things that are so complicated in its structure and claim that such-and-such should also occur. People who use physics principles in mystical and spiritual aspect are apt to apply such bastardization. The FACT that one hasn't observe a decoherent macroscopic object exhibiting ANY QM properties (much less undergo tunneling) is somehow dismissed.

But you have no problems in accepting something like that, the same way you had no qualms in accepting a gamma-gamma collision dispite the lack of valid experimental evidence. It is one thing to understand and verify the basic idea of the phenomenon. It is another when it extrapolated into other region beyond the current experimental reach. My object over BOTH arguments, if you pay attention, is CONSISTENT. I question the way such a comfortable acceptance to something that has not been empiricially verified. An electron tunneling is DIFFERENT than a tennis ball tunneling. It is no longer one single wavefunction penetrating a barrier. It is a gazillion wavefunction (I don't even know how one would write such a wavefunction, or even its Hamiltonian), somehow tunneling through with the SAME probability, without undergoing inelastic scattering, thermal fluctuation, higher-order interactions, etc. And remember, in electron tunneling, apply a potential gradient across the barrier. What "potential gradient" would you apply here? The tennis ball is "neutral". It can't be an electrostatic potential. Gravitational? Oh, but wait! We have ZERO experimental evidence of tunneling through gravitational potential of anything, be it simple particles such as electrons, protons, neutrons, etc. So now we want a tennis ball?

It is this LACK of concern about realistic experimental evidence is what bothers me. I suppose if you are training to be a String physicist, then you are well on your way. But if you intend to do physics, then I'd say your dismissal of experimental evidence, and your very low level of what you accept as valid, need to change drastically.

This thread is going in circles, and I find that I have to repeat almost everything I have said. Therefore, stick a fork in me. I'm done with this one.

Zz.

 

[Chaos' lil bro Order]

1) I simply wanted to know the probability, I wasn't changing topics.

2) You cannot disprove it since it can be inductively inferred from QM tunneling, albeit not EXPERIMENTALLY TESTED and therefore not truly valid. Agreed.

3) String Theory is the best model we have so ripping on it shows narrow-sightedness and staunchness of belief on your part, not to mention it has nothing to do with this post other then serving as a 'poor' analogy for EXPERIMENTALLY UNPROVEN theories like those in this post.

A little vision wouldn't kill you would it? I guess the rigors of experiment can eat at your creativity after I'm guessing 20+ years. Perturbative theory and first principles are the cornerstone of physics from which the 'house of experiment' is built; no foundation, no house. Does your house sink into the ground? How do you see the sun with your windows at soil level?

If you want to know the truth, I agree with everything you've said, I just find it interesting that you cannot see the possibility that the tennis ball COULD pass through the wall regardless of the EXTREMELY REMOTE POSSIBILITY that it will.

P.S. You spelled 'despite' 'dispite' several times in your last post. I did my P.h.d thesis in English on common spelling mistakes.

;)

 

[ZapperZ]

1) I simply wanted to know the probability, I wasn't changing topics.

2) You cannot disprove it since it can be inductively inferred from QM tunneling, albeit not EXPERIMENTALLY TESTED and therefore not truly valid. Agreed.

Ah, but that is the WHOLE ISSUE of emergent properties. You CANNOT inductively, or use whatever means, to derive such a thing! If you think you can, then you have some explaining to do to physicists like Phil Anderson and Bob Laughlin. More is Different! More isn't just "more complicated and can be derived via induction!". Want an example? Go write down all the interactions of an electron and add more and more of them. When you have done that, show me where you could deduce superconductivity in your Hamiltonian. I bet you a Nobel Prize you can't.

There are no "induction" here. A macro object is DIFFERENT than a quantum object. You can't "deduce", because even if we eliminate any inherent differences between the two regimes, the very fact that we have zero ability to compute a gazillion interactions prevents you from proving your "deduction".

3) String Theory is the best model we have so ripping on it shows narrow-sightedness and staunchness of belief on your part, not to mention it has nothing to do with this post other then serving as a 'poor' analogy for EXPERIMENTALLY UNPROVEN theories like those in this post.

A little vision wouldn't kill you would it? I guess the rigors of experiment can eat at your creativity after I'm guessing 20+ years. Perturbative theory and first principles are the cornerstone of physics from which the 'house of experiment' is built; no foundation, no house. Does your house sink into the ground? How do you see the sun with your windows at soil level?

What does my objection to "string theory" have anything to do with "perturbative theory"? Did I just have a stroke and suddenly objected to perturbative theory? Last time I checked, I used perturbative theory in applying the Luttinger Liquid theorem to analyze my experiments!

And whose opinion is it that String theory is the "best" theory we have for ... ? Are you implying that it is the consensus of physicists everywhere? Where did you get such a conclusion from? On the other hand, I can point out several articles by respected physicists and mathematicians that argue that String theory could be the biggest cancer in physics. Want to race and see who can come up with the sources first?

If you want to know the truth, I agree with everything you've said, I just find it interesting that you cannot see the possibility that the tennis ball COULD pass through the wall regardless of the EXTREMELY REMOTE POSSIBILITY that it will.

Let's see. I, the person who spent a lot of time studying the theory (I published a paper on the tunneling matrix element effects in electron tunneling that is an extension of the work by Bardeen and Harrison) and also actually did experimental work on such phenomenon under different aspects and conditions (planar tunneling, point-contact tunneling, STM, break junctions, etc) somehow cannot or refuses to consider the "extremely remote possibility" of such a thing? Really? Why would I refuse to do that? Did you ever figure it out, or did you simply block out all the reasons I gave and think my objection is just irrationial? (Buckyball, emergent phenomena, etc). You never once addressed those arguments. I have specific example on when "large" objects such as buckyball could behave as a quantum particle. Did you see how difficult of a condition we had to apply to get that? Under what condition did we manage to make 10^11 electrons behave like a single quantum particle in those SQUID experiments? Did you ever figure that out?

So now, how do you expect me to buy an argument that (i) ignores completely emergent phenomena and (ii) ignores completely what we have already known in terms of trying to make large number of particles to behave as a single quantum object? I'm not being narrow sighted. In fact, I'm being quite wide in casting my net because I have SEEN quite a number of things that have to be done, and to realize that the devil is in the DETAIL rather than just a superficial "oh, that looks so nice and possible" kind of thing. It is YOU who are being quite narrow in your view into thinking that the simple, naive QM that we teach in schools are sufficient to handle the unbelievable level of complexities and realistic situations. Have you ever considered that?

Forget about experimental observations, which you obviously don't care about. When you can show me the theoretical Hamiltonian and wavefunction of all the various constituent of a tennis ball and then derive a transmission amplitude through a wall, then we'll talk.

P.S. You spelled 'despite' 'dispite' several times in your last post. I did my P.h.d thesis in English on common spelling mistakes.

;)

If this were a discussion on "English" and spelling mistakes, then I would care. And if you get your kicks by pointing out spelling errors in a physics forum, then you're more than welcome to amuse yourself with all my other posts, which I believe have a lot more hilarious spelling errors and typos than this.

Zz.

 

[Ratzinger]

I have a question here.

Why can't we make a big wave function of all the degrees of freedom of that system (tensor product of all the single gazzlions wave functions)? Wouldn't we then have a wave function of the tennis ball?

Something else: I remember reading of the possibility of one big wave function describing the whole universe. Does that make sense?

 

[vanesch]

Ah, but that is the WHOLE ISSUE of emergent properties. You CANNOT inductively, or use whatever means, to derive such a thing! If you think you can, then you have some explaining to do to physicists like Phil Anderson and Bob Laughlin.

On the other hand, you're in the company of people like Steven Weinberg.

I'd invite you to a read of the debate on the two visions:

http://pespmc1.vub.ac.be/AFOS/Debate.html

 

[vanesch]

I have a question here.

Why can't we make a big wave function of all the degrees of freedom of that system (tensor product of all single gazzlions wave functions)? Wouldn't we then have a wave function of the tennis ball?

Yes, that's also my POV, and in general, people who adhere to a reductionist view. Other people (like Zapper) say that there's an intrinsic upper limit to the utility of a number of degrees of freedom, and from a certain point onwards, the underlying theory is not applicable anymore to the overall system, and a new theory of the overall degrees of freedom has to be postulated. At least, that's what I _think_ they say

 

[ZapperZ]

I have a question here.

Why can't we make a big wave function of all the degrees of freedom of that system (tensor product of all the single gazzlions wave functions)? Wouldn't we then have a wave function of the tennis ball?

Something else: I remember reading of the possibility of one big wave function describing the whole universe. Does that make sense?

Remember, even in classical mechanics, we already have a problem with constructing the most general solution to the 3-body problem. Think of how you would solve a Hamitonian of a 4, 5, 6, 7, ... body interactions without doing any kind of approximation. Now, "extrapolate" that to a gazillion bodies.

This is why we have many-body physics.

Zz.

 

[vanesch]

Remember, even in classical mechanics, we already have a problem with constructing the most general solution to the 3-body problem. Think of how you would solve a Hamitonian of a 4, 5, 6, 7, ... body interactions without doing any kind of approximation. Now, "extrapolate" that to a gazillion bodies.

This is why we have many-body physics.

This looks to me like a similar discussion in mathematics between "constructivists" and "standard" mathematicians. Constructivists essentially claim that the only way of showing the existence of a mathematical object, is by constructing it explicitly ; while standard mathematicians accept non-constructive existence proofs.

A typical case, is for instance, that a harmonic function reaches its maximum on its boundary. You do not construct the maximum, you simply start assuming that, if the maximum occurs somewhere in the middle of the domain, then this leads to a contradiction ; hence it must be somewhere on the boundary.

It seems to me that you require an explicit procedure to write down a quantum theory (writing down explicitly the degrees of freedom and the hamiltonian) before considering that the theory "exists" ; while others (like me) can accept the abstract existence of this theory even if we have no clue of how it should be written down explicitly.

I have no difficulties considering, in an abstract way, the tensor product of 10^25 one-particle hilbert spaces. Of course I don't know how to write it down explicitly! In the same way, I have no problem in considering, in an abstract way, the hamiltonian that will give you the dynamics of this system ; although, again, I'd have troubles writing it down explicitly.
Once I accept the abstract existence of this hamiltonian, I can consider it to be exponentiated to give us a unitary operator U(t). That, I _certainly_ don't know how to do explicitly. Nevertheless, there are existence theorems that guarantee me that U(t) exists, as a mathematical object.
I don't see what's wrong with considering the abstract, Platonic existence of this structure.
In a typically non-constructivist way, if it is claimed that this hilbert space does NOT exist, or that a hamiltonian over this hilbert space, exponentiated, would NOT give rise to a unitary operator over it, I could use this claim to derive, through reductio at absurdum and the induction principle over integers (a typically non-constructivist approach) A LOT OF CONTRADICTIONS.

 

[Chaos' lil bro Order]

I feel sorry for you Zapper, you can't see the tree while in the forest. We've exhausted both sides of the argument and neither party agrees to the other's points, case closed.

 

[ZapperZ]

This looks to me like a similar discussion in mathematics between "constructivists" and "standard" mathematicians. Constructivists essentially claim that the only way of showing the existence of a mathematical object, is by constructing it explicitly ; while standard mathematicians accept non-constructive existence proofs.

A typical case, is for instance, that a harmonic function reaches its maximum on its boundary. You do not construct the maximum, you simply start assuming that, if the maximum occurs somewhere in the middle of the domain, then this leads to a contradiction ; hence it must be somewhere on the boundary.

It seems to me that you require an explicit procedure to write down a quantum theory (writing down explicitly the degrees of freedom and the hamiltonian) before considering that the theory "exists" ; while others (like me) can accept the abstract existence of this theory even if we have no clue of how it should be written down explicitly.

I have no difficulties considering, in an abstract way, the tensor product of 10^25 one-particle hilbert spaces. Of course I don't know how to write it down explicitly! In the same way, I have no problem in considering, in an abstract way, the hamiltonian that will give you the dynamics of this system ; although, again, I'd have troubles writing it down explicitly.
Once I accept the abstract existence of this hamiltonian, I can consider it to be exponentiated to give us a unitary operator U(t). That, I _certainly_ don't know how to do explicitly. Nevertheless, there are existence theorems that guarantee me that U(t) exists, as a mathematical object.
I don't see what's wrong with considering the abstract, Platonic existence of this structure.
In a typically non-constructivist way, if it is claimed that this hilbert space does NOT exist, or that a hamiltonian over this hilbert space, exponentiated, would NOT give rise to a unitary operator over it, I could use this claim to derive, through reductio at absurdum and the induction principle over integers (a typically non-constructivist approach) A LOT OF CONTRADICTIONS.

If this is true, then discovering BE condensates in atomic gas would be no big deal. Why? Because we already had it in liquid helium, and we already had it in superconductors years and years ago, and in principle, people predicted it theoretically for certain atomic gasses too. Yet, it WAS a big deal, and people won Nobel Prizes for it!

There are MANY theoretical predictions that went nowhere. Just browse through old issues of PRL if you don't believe me. Even Phil Anderson had to back down from his interlayer tunneling theory for High Tc superconductors after been proven wrong (he's still clinging to his RVB scenario). Especially for theoretical formulation that had to make some form of approximation when dealing with LARGE quantities of interactions, there is no way to know if such an approximation is valid. This means that in these cases there's a difference between "theoretical derivation" and "experimental verification", and the latter is CRUCIAL in verifying the validity of the former. We have seen enough where the theory went nowhere!

Therefore, I am VERY puzzle why people think that applying a principle that works under a very naive, single particle scenario should be an non-issue when applied to something as complicated and large as a tennis ball. The way Chaos has described it appears as if something like this should be TRIVIAL! Using the same logic, I could easily tell Eric Cornell that his Nobel Prize was for something "trivial". After all, it WAS predicted in principle, and the phenomenon was already discovered elsewhere. What's the freaking deal with seeing the same thing in atomic gasses?

Not realizing these things means that one has no understanding of the theoretical development of such ideas and that these things are NOT guaranteed just because there are theoretical predictions. These are all many-body phenomena. How you model the interactions and approximate the potential are not something that falls onto your lap when you are constructing the Hamiltonian. Thus, the theoretical predictions are NOT automatically true! It is only valid upon experimental verification, which then verifies the original Hamiltonian as being acceptable. This is why the discovery of BE condensation in atomic gasses is such a big deal, and not just in my book!

You have zero ability to solve the many-body problem that forms a tennis ball. Instead, what you do have a one-body CLASSICAL problem. This is THE approximation you have to make. So not only is there no experimental evidence for a tennis ball tunneling through a wall, there isn't even a THEORETICAL formulation to test! All you have are "haunches" that if it works for a single quantum particle, it must work for LARGE number of interconnected particles, dispite the huge decoherence effect on the whole object.

I just don't see how something THAT complicated is obvious.

Zz.

 

[Physics Monkey]

Hi ZapperZ,

I think it's fair to say that Ketterle, Cornell, and Wieman got Nobel Prizes for BEC because they performed beautiful experiments, overcame many challenging obstacles to condensation, and opened up a whole new world of possibilities for tests of many body quantum mechanics. It don't think it has anything to do with theoretical predictions. Indeed, condensation is one of those things that is "theoretically obvious" on quite general grounds as evidenced by the fact that it was predicted very early on.

 

[ZapperZ]

Hi ZapperZ,

I think it's fair to say that Ketterle, Cornell, and Wieman got Nobel Prizes for BEC because they performed beautiful experiments, overcame many challenging obstacles to condensation, and opened up a whole new world of possibilities for tests of many body quantum mechanics. It don't think it has anything to do with theoretical predictions. Indeed, condensation is one of those things that is "theoretically obvious" on quite general grounds as evidenced by the fact that it was predicted very early on.

You will notice that, per the Nobel charter, performing "beautiful experiments" is not a valid criteria for awarding Nobel prizes. Even theoretical ideas can have a rather shaky ground for being awarded Nobel Prizes due to the "discovery" criteria.

The BEC in atomic gasses is as significant as the condensation in the Fermionic gasses. No one was surprised by either one, but the ability to actually show that those things are REAL and not just impossible or unattainable theoretical constructs are highly significant. They contain new physics! People can now rely on such theory to build other theories because they can use it with confidence that this is not some unverified idea.

Again, the extrapolation of microscopic description cannot be accepted without experimental verification simply because it worked at the simplest scale. Even when we have a valid model to use at the many-body scale, there's nothing to say that it will work all the time. I can easily point to mean-field theory and show where it works, and where it fails miserably. How does one know the large scale approximation will be valid all the time when applied to a different situation? Band theory works very well in many material, but apply it to Mott insulator and it says it should be a metal!

So not only is your extrapolation dubious in the first place, but even when you could prove that your many-body approach is right in one instant, you cannot claim that it will be a valid approximation for other cases without performing an experimental verification.

It is a long way between "electron can tunnel through a potential barrier" and "a tennis ball can tunnel through a wall". I would not put it past nature to put a huge "gap" between those two.

Zz.

 

[vanesch]

Therefore, I am VERY puzzle why people think that applying a principle that works under a very naive, single particle scenario should be an non-issue when applied to something as complicated and large as a tennis ball. The way Chaos has described it appears as if something like this should be TRIVIAL! Using the same logic, I could easily tell Eric Cornell that his Nobel Prize was for something "trivial". After all, it WAS predicted in principle, and the phenomenon was already discovered elsewhere. What's the freaking deal with seeing the same thing in atomic gasses?

Two answers to this. You are of course correct to point out that the naive model of tunneling for a particle may very well not apply to a tennis ball in the same way. It might even be true that, if one had a brain the size of the orbit of Jupiter, and one COULD work out a better approximation, that it would turn out that, after all, the component in the wavefunction that corresponds to "tennis ball on the other side of the wall" vanishes exactly! I'd be surprised, but you are correct that there's no way of knowing that for sure. However, MOST of what we know of quantum systems does seem to point out, that what's not explicitly forbidden by a certain symmetry, is going to turn up in the final state. As there is no deep principle in quantum theory *forbidding*, a priori, the component "ball on the other side of the wall" it is reasonable to assume that it will appear with SOME amplitude. I am with you when you tell me that the prediction with the naive one-particle model might be, say, 500 orders of magnitude off. But that doesn't change the idea: I don't think that the OP cared whether the probability was 10^(-313245452) or 10^(-480723452345).

I'm even convinced you're right, because before the ball gets a chance of getting through the wall, it has probably already sublimated, turned into a black hole, or whatever, and these intermediate states may have a serious effect on the outcome in higher order perturbation theory. But it was my impression that the OP just wanted to know: is there, or isn't there, according to quantum theory, a non-zero probability for the ball to be on the other side ; I translate this into: is the quantum state of the tennis ball PERFECTLY ORTHOGONAL to any state with "ball on the other side", and I'd guess that, as this is not forbidden explicitly, that there is no reason to assume that the state remains *perfectly* orthogonal to this space of states - in other words, that there WILL be a tiny amplitude and hence a tiny probability.

Hey, even according to classical physics, there's a finite probability to have the ball on the other side: the atoms might sublimate from the ball, diffuse through the wall and condense on the other side, to form another tennis ball !

On the other hand, many Nobel prizes went to people discovering what was already predicted theoretically ; two instances come to mind immediately: Carlo Rubbia for the discovery of the Z0 at CERN (in the beginning of the 80ies, while it was predicted since end of the 60ies by Weinberg and Co), and the guys (forgot their names) who observed the spinning down of a pulsar in agreement with the emission of gravitational radiation and its loss of energy, something that was predicted for about 40 years. Hey, Charpak even got a prize for inventing something (the wire chamber) that was OBVIOUSLY going to work, because a similar version existed already (the proportional counter)!

 

[ZapperZ]

Two answers to this. You are of course correct to point out that the naive model of tunneling for a particle may very well not apply to a tennis ball in the same way. It might even be true that, if one had a brain the size of the orbit of Jupiter, and one COULD work out a better approximation, that it would turn out that, after all, the component in the wavefunction that corresponds to "tennis ball on the other side of the wall" vanishes exactly! I'd be surprised, but you are correct that there's no way of knowing that for sure. However, MOST of what we know of quantum systems does seem to point out, that what's not explicitly forbidden by a certain symmetry, is going to turn up in the final state. As there is no deep principle in quantum theory *forbidding*, a priori, the component "ball on the other side of the wall" it is reasonable to assume that it will appear with SOME amplitude. I am with you when you tell me that the prediction with the naive one-particle model might be, say, 500 orders of magnitude off. But that doesn't change the idea: I don't think that the OP cared whether the probability was 10^(-313245452) or 10^(-480723452345).

Then this is what I've been asking for. I've asked for the theoretical formulation for the transmission amplitude of a tennis ball through a wall. I would love to see such a thing if anyone is willing to come up with such numbers. Why? I'd like to see how someone handle a "decoherent" particle tunneling through a barrier. I have never seen such a thing. This would be new physics. I've seen particles as large as alpha particles tunneling through, but wait! that is just a simple nucleus with NO electrons! Can the electrons confined to a potential might have some unusual behavior that would make it different?

And we have an added complication. An "electron" in a solid or material is NOT the same electron that you get freely tunneling through a material. Remember, you want the WHOLE GLOB to tunnel through COHERENTLY, not just various parts separetely. Thus, you have to deal with a "quasiparticle" that is called an electron, with a finite lifetime and thus, very prone to scattering not just within the solid itself, but also via indergoing inelastic scattering with the potential barrier (which, by the way, has not been defined for a neutral ball).

But don't answer yet, there's still more!

If we ever get to THAT kind of precision and significant figures, then don't forget higher order scattering with vacuum fluctuations that can easily destroy your coherence. In fact, once you have formulated your tunneling theory (assuming you can), then such effects at that scale will be dominant.

Forget about tennis balls. I would be happy just to see a buckyball tunnels through something. We already can see that it CAN behave as a quantum particle under a certain condition. Yet, why hasn't anyone done tunneling studies on it? Hum? What would be a "potential barrier" for such an object that would be consistent for ALL parts of the buckyball (a barrier for a proton is not the same as a barrier for an electron).

I have tried to describe, some time in painful detail, all the circumstances that can and do make "single electron tunneling" significantly different than "tennis ball tunneling". I have listed as much as I can why they are differnt and can't be described by the same thing. However, I still get the "but QM says it can at individual particle, so it has to have a non-zero probability". Really? QM can say we can spontaneously disintergrate. Yet, do we base our physical reality on such a thing? If the probability is so small that it will take longer than the age of the universe, at what point do we get to say "it doesn't occur"?

If we go by this route, we might as well close up shop and say that everything and anything is "possible" and let the mystics take over.

Zz.

 

[vanesch]

Then this is what I've been asking for. I've asked for the theoretical formulation for the transmission amplitude of a tennis ball through a wall.

Ok, see further down...

And we have an added complication. An "electron" in a solid or material is NOT the same electron that you get freely tunneling through a material. Remember, you want the WHOLE GLOB to tunnel through COHERENTLY, not just various parts separetely. Thus, you have to deal with a "quasiparticle" that is called an electron, with a finite lifetime and thus, very prone to scattering not just within the solid itself, but also via indergoing inelastic scattering with the potential barrier (which, by the way, has not been defined for a neutral ball).

But don't answer yet, there's still more!

If we ever get to THAT kind of precision and significant figures, then don't forget higher order scattering with vacuum fluctuations that can easily destroy your coherence. In fact, once you have formulated your tunneling theory (assuming you can), then such effects at that scale will be dominant.

Forget about tennis balls. I would be happy just to see a buckyball tunnels through something. We already can see that it CAN behave as a quantum particle under a certain condition. Yet, why hasn't anyone done tunneling studies on it? Hum? What would be a "potential barrier" for such an object that would be consistent for ALL parts of the buckyball (a barrier for a proton is not the same as a barrier for an electron).

I have tried to describe, some time in painful detail, all the circumstances that can and do make "single electron tunneling" significantly different than "tennis ball tunneling". I have listed as much as I can why they are differnt and can't be described by the same thing.

You are entirely correct. To calculate, even up to a few hundreds of orders of magnitude, the probability for tunneling would be a mindbogglingly difficult problem...

However, I still get the "but QM says it can at individual particle, so it has to have a non-zero probability". Really? QM can say we can spontaneously disintergrate. Yet, do we base our physical reality on such a thing? If the probability is so small that it will take longer than the age of the universe, at what point do we get to say "it doesn't occur"?

I think we all agreed upon the fact, in the beginning of this thread, that this was just a "mind game" and that for all practical purposes, a tennisball doesn't tunnel through a wall. And you make a valid point as to when is a probability of 10^(-235134523) to be considered different from 0. Mathematically of course (and I thought this was the discussion), it is clear that no matter how small, if it is different from 0, it is not 0. But you touch upon a very reasonable requirement: should we consider an event with a probability that is so low that it is highly improbable that it is ever observed during the entire lifetime of the universe, still as a possibility ?

Let's take it your way, and say that if the probability is ridiculously low then this is the same statement as saying that it will NOT happen. Well, then our over-simple model of a single particle with mass equal to the mass of the tennis ball, and the height of the potential barrier equal to the entire binding energy of the atoms of the tennis ball, gives us the correct answer! All your objections withstanding (and you are right that they are physically meaningful), this super-simple model already predicts ridiculously low probabilities, and using the criterion for when "ridiculously low probability" becomes "will not happen", the simple quantum model tells us that a tennis ball will not tunnel through a wall. So this simple model is making an experimentally valid prediction ! So there is a valid, and simple, quantum description of the tennis ball after all (concerning wall tunneling).

Nevertheless, as a "mind game" I think it is still instructive to make a difference between "ridiculously small probability" and "it will not happen" ; when the last one is predicted with exactly 0 probability ; because that's then due to a law of nature (a symmetry, for instance).
It was in *that* spirit that I was arguing for the non-zero probability of the said (non-) phenomenon. There's nothing that *explicitly forbids* the ball from going to the other side in quantum theory, while in a (model of) a classical ball, there IS such a principle (namely that the kinetic energy of a ball can never be negative). And as I pointed out, if you push the classical theory far enough (make a detailled enough model of the ball, so that sublimation of atoms, diffusion of atoms through the wall and condensation is modelised), even there the ball CAN get to the other side at ridiculously small probability.

 

[LnGrrrR]

Zapperz,

Good questions on the buckyball and tunnelling...and I think that will most likely be an interesting and lively subject of research for quite awhile, with physicists trying to make bigger and bigger objects 'tunnel', as there's a chance it can have fantastical outcomes (assuming we can ever get past decoherence).

 

[ZapperZ]

Let's take it your way, and say that if the probability is ridiculously low then this is the same statement as saying that it will NOT happen. Well, then our over-simple model of a single particle with mass equal to the mass of the tennis ball, and the height of the potential barrier equal to the entire binding energy of the atoms of the tennis ball, gives us the correct answer! All your objections withstanding (and you are right that they are physically meaningful), this super-simple model already predicts ridiculously low probabilities, and using the criterion for when "ridiculously low probability" becomes "will not happen", the simple quantum model tells us that a tennis ball will not tunnel through a wall. So this simple model is making an experimentally valid prediction ! So there is a valid, and simple, quantum description of the tennis ball after all (concerning wall tunneling).

Ah, but this is where we differ.

To me, the "super-simple" model of a tennis ball is a classical object! If you want to apply a QM description of a particle the size of a tennis ball, then you have used an invalid assumption that has no merit. It is not realistic by any measure. A QM description of a tennis ball is not and cannot be made "simple". You are just applying a set of rules to where it was never meant to be applied. You might as well say "OK, I am now moving greater than c at a time 20 million years BEFORE the Big Bang. What do I see?" That is a mind game too, but it doesn't mean it has any reasonable answer.

There are no reasonable QM description of a tennis ball. It isn't a single quantum object, and it never was. It can, however, be described as a "single" classical object.

Zz.