Throwing a tennis ball through a wall

[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.

 

[vanesch]

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's a difference: the last proposition is totally meaningless, even in principle, but I object to your "cannot be made simple".
After all, when you use a quantum description of, say, a Calcium atom, then you take it that the nucleus is a single point particle, with just an x, y, z continuous position degrees of freedom, and eventually some discrete spin degrees of freedom.
Now, any nuclear physicist will tell you that that is a rather naive view of a nucleus, and that you have a complicated system in there, with complicated interactions between neutrons, protons and pions. And if you turn to a particle physicist, he will tell you that a proton made up of 3 quarks is a rather naive model, and that you have miriads of degrees of freedom in there, with gluons, a sea of virtual quarks and all that.

Nevertheless, for the purposes of atomic physics, it is sufficient to put all these internal degrees of freedom under the carpet, and just stick to some overall kinetical degrees of freedom: the position of the center of mass, and eventually a spin degree of freedom.
So I don't see why I'm not entitled to do the same to the object "tennisball". I abstract away its internal degrees of freedom (the atoms, the electrons, whatever), and I just keep some overall kinetical degrees of freedom: the position of its center of mass, and eventually a spin degree of freedom (which can take here very high values, to start looking like a classically spinning object).

I know that there is a difference with the nucleus case: we could say that we don't need the nuclear degrees of freedom because essentially only the ground state matters in the energy range we're exploring in atomic physics, because nuclear exitations are on much higher energy levels
So we limit ourselves to the "neighbourhood" of the nuclear grond state in the Hilbert space that does describe the nuclear degrees of freedom.
You could correctly argue that this is NOT the case for the ball-wall interaction, which could eventually be considered to be of the same order of magnitude as the exitations of the internal degrees of freedom. Granted. I already alluded to this before. So we're making errors here: we're excluding degrees of freedom which may have their say. In other words, we're making a very rough approximation... But that was granted!

 

[ZapperZ]

There's a difference: the last proposition is totally meaningless, even in principle, but I object to your "cannot be made simple".
After all, when you use a quantum description of, say, a Calcium atom, then you take it that the nucleus is a single point particle, with just an x, y, z continuous position degrees of freedom, and eventually some discrete spin degrees of freedom.
Now, any nuclear physicist will tell you that that is a rather naive view of a nucleus, and that you have a complicated system in there, with complicated interactions between neutrons, protons and pions. And if you turn to a particle physicist, he will tell you that a proton made up of 3 quarks is a rather naive model, and that you have miriads of degrees of freedom in there, with gluons, a sea of virtual quarks and all that.

But there is a difference here and with a tennis ball. A "nucleus" and an "atom" ARE quantum particles already! I don't have to put any effort to detect such properties. A nucleus and an atom are not "tennis balls".

I can even go a step further, and you should have seen me mentioned it - 10^11 electrons! I can consider that many electrons as a "quantum particle" when they are in a superfluid. Again, it has nothing to do with quantity. However, I can do that because I have the evidence that all of these are quantum particles, and I have a theoretical description on why they should behave quantum mechanically.

I have no such thing for a tennis ball. You cannot make it quantum mechanically simple because there have been zero instances where you can theoretically cause it to be simple, and empirically show it. it is different!

Zz.

 

[selfAdjoint]

Excuse me zapper, but aren't you rather contradicting yourself here?

In post #47 you said

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.

But in #52 you're back to

But there is a difference here and with a tennis ball. A "nucleus" and an "atom" ARE quantum particles already! I don't have to put any effort to detect such properties. A nucleus and an atom are not "tennis balls".

There are big fairly complicated molecules (buckeyballs) that behave quantally and which we could get at least a sensible estimate of the probability of tunnelling through a given barrier. Is thiis or isn't it enough to show that the calculation problem for macroscopic objects, although technically beyond our present resources is not IN PRINCIPLE impossible?

 

[ZapperZ]

Excuse me zapper, but aren't you rather contradicting yourself here?

In post #47 you said

But in #52 you're back to
There are big fairly complicated molecules (buckeyballs) that behave quantally and which we could get at least a sensible estimate of the probability of tunnelling through a given barrier. Is thiis or isn't it enough to show that the calculation problem for macroscopic objects, although technically beyond our present resources is not IN PRINCIPLE impossible?

Ah, but that's the whole point I'm trying to get across here.

The ability of buckyballs to produce interference effect is under an extremely RARE condition that we have to put them in. We must have ALL parts of the buckyball in coherence with each other so that the whole buckyball is really ONE single quantum object! It is then a large object but with a coherent wavefunction.

This is very much like a supercurrent. You have the 10^11 electrons, but they are all in ONE single coherent state. One could easily consider the whole glob of electron as a single object, the same way one considers a pair of entangled particle as being a single "macro" particle.

A buckyball at room temperature without being put in that state would not produce interference patterns, no matter how much you coax it. And note, tunneling processes are more difficult to achieve than the 2-slit interference experiments. So there's an extra whammy there.

But at least I can see how one can make each part of the buckyball coherent with each other. I have no idea how one does that to a tennis ball.

Zz.

 

[baryon]

Is it correct to say that there is no chance that any of the particles from the book would ever tunnel through the table and vice versa because neither object is radioactive? Pardon me for mentioning the weak force, but isn't that the force that dissolves the strong atomic bonds in nuclei? Based on what is known about the weak force, is it truly probable that this force would actually interact on the book or the table?
I'm not asking if the book could ever be driiven through the table or vice versa because this may be possible in a lab.
Also, I'm aware of Everett's theory but I do not believe we need introduce this to the conversation.

 

[Locrian]

Why is this thread back? In a thread prior to this, conversing with reductionists, I was presented with rocketship shoes and a diamond chair. In this thread I was presented with a point-like tennisball, which of course would fail you in a situation as complicated as a bumpy corner. I was actually hoping such inanity could slide its way into history.

 

[WhyIsItSo]

...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...

But would it still be a tennis ball?

 

[jackle]

Inanity

Why is this thread back?...I was actually hoping such inanity could slide its way into history.

Asking questions (even meaningless ones) is how we learn. I don't see a problem with it.

 

[jackle]

This is probably irrelevant but I seem to remember all sorts of crazy things in my degree course. Massless springs come to mind.

 

[Farsight]

Vanesch, Zapper, anybody: how about a small "tennis ball" that was actually a Bose-Einstein condensate. Could that tunnel though a barrier?