[quantum tunneling] Debate with a friend, am I right?

In summary, the conversation discussed the concept of quantum tunneling and the possibility of a penny passing through a solid slab of steel through tunneling. While technically possible in theory, it would take an infinite amount of time and ideal conditions for it to actually happen. Additionally, the discussion touched on the role of coherence and decoherence in quantum behavior and the limitations of using macroscopic objects as examples for quantum phenomena.
  • #1
uperkurk
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It involves quantum tunneling, both of us know very little about physics but I watched a video on youtube about a guy explaining quantum tunneling, from what I underdstand a particle can, with enough energy pass right through other solid surfaces?

So I said that if you had a penny, and shot it against a solid slab of steel an infinite number of times, eventually the entire penny would pass right through leaving both the penny and the sheet of metal completely undamaged.
 
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  • #2


uperkurk said:
It involves quantum tunneling, both of us know very little about physics but I watched a video on youtube about a guy explaining quantum tunneling, from what I underdstand a particle can, with enough energy pass right through other solid surfaces?

So I said that if you had a penny, and shot it against a solid slab of steel an infinite number of times, eventually the entire penny would pass right through leaving both the penny and the sheet of metal completely undamaged.

The penny and/or the slab of steel would disintegrate long before it happened. Even if you weren't busy flinging the penny at the wall, the universe would be pretty much at maximum entropy before it would have any chance.

But, I suppose if you have some kind of perfect universe with an indestructible penny and steel wall, and literally an infinite amount of time, I suppose it would. It would just take much much longer than the age of the universe to happen, even if you had a universe full of pennies and steel walls.
 
  • #3


I don't think we really know if that's the case. A large ensemble of quantum particles are decohered, giving it classical properties. Can a decohered ensemble tunnel? I think lots of questions about decohered quantum behavior are unanswered.
 
  • #4
Technical arguments aside, in principle it's true. In fact, you don't really need anything as aggressive as a shotgun - just dropping a penny on the table will do.

Given enough tries, it will eventually pass through. How many is enough? That's beyond imagining.

PS. We just need to keep trying until the ensemble IS coherent.
 
  • #5
As was said earlier, a coin is too big of an object and has very different properties and behavior than particles and atoms so it's unlikely it could tunnel in any amount of time. For some reason, 'particles' and the objects they comprise behave very differently.
 
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  • #6
AJ Bentley said:
Technical arguments aside, in principle it's true. In fact, you don't really need anything as aggressive as a shotgun - just dropping a penny on the table will do.

Given enough tries, it will eventually pass through. How many is enough? That's beyond imagining.

PS. We just need to keep trying until the ensemble IS coherent.

I'm thinking there's no reason to believe it should ever be coherent. You can do a bunch of a priori probability calculations from a reductionist standpoint, but are they really valid? I think we will have to wait for some of the pressing questions in quantum chaos to be answered.
 
  • #7
Pythagorean said:
I'm thinking there's no reason to believe it should ever be coherent. You can do a bunch of a priori probability calculations from a reductionist standpoint, but are they really valid? I think we will have to wait for some of the pressing questions in quantum chaos to be answered.
I think the reasoning is that everything is in constant superposition and some particles can eventually decohere/collapse at a macroscopically forbidden place. Hence the conclusion, but i still don't believe it, it seems to interpret qm too literally and to an extent that might be inapplicable. I don't think the universe is smeared out and decoherence/collapse causes what we observe(i could be naive though).
 
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  • #8
As an illustration, maybe it's ok to use the penny example to get an idea across. I am not familiar with all aspects of quantum tunneling, but the tunnel diode is an example I happened to study many years ago...and not much seems to have changed in our understanding:A qucik synopsis from Wikipedia:

The heavy doping results in a broken bandgap, where conduction band electron states on the n-side are more or less aligned with valence band hole states on the p-side...Under normal forward bias operation, as voltage begins to increase, electrons at first tunnel through the very narrow p–n junction barrier because filled electron states in the conduction band on the n-side become aligned with empty valence band hole states on the p-side of the p-n junction.

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

Good luck trying to find a penny size alignment in a solid steel barrier.
[Maybe a better illustration would be to drill a penny sized hole or two in the barrier and consider those conditions.]

As implied in some of the posts already but not overtly stated, these conditions can be considered the result of standing wave patterns...which closely relates to coherence and decoherence as mentioned above.

As least as far as I understand this mechanism, I'd sure hate to be the poor slob waiting for the penny to be absorbed! In other words, a macroscopic object is just not going to make it through such a barrier.

I think the WBK method of approximation is still an approach to solving actual problems...maybe someone who knows about such modeling can offer some practical insights from solutions.

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

1. What is quantum tunneling?

Quantum tunneling is a phenomenon in which a particle can pass through a barrier that would normally be impossible to cross, due to its energy being lower than the potential energy barrier.

2. How does quantum tunneling work?

Quantum tunneling occurs due to the probabilistic nature of particles at the quantum level. The particle exists in a state of superposition, meaning it can exist in multiple places at once, and has a chance of passing through the barrier based on its energy level and the thickness of the barrier.

3. Is quantum tunneling a real phenomenon or just a theoretical concept?

Quantum tunneling is a real phenomenon that has been observed and studied in various experiments. It is a well-established concept in quantum mechanics and has many practical applications in technology, such as in transistors and scanning tunneling microscopes.

4. Is quantum tunneling faster than the speed of light?

No, quantum tunneling does not violate the speed of light limit. The particle is not actually "moving" through the barrier, but rather has a probability of appearing on the other side. The speed of the particle itself is still limited by the speed of light.

5. Are there any controversies or debates surrounding quantum tunneling?

There is ongoing debate and research concerning the exact mechanisms and interpretations of quantum tunneling. Some scientists argue that it is a purely probabilistic process, while others propose more complex explanations involving entanglement and multiple universes. Overall, quantum tunneling remains a fascinating and active area of study in the field of quantum mechanics.

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