What are the physics that prevents macroscopic tunneling?

[DanteKennedy]

Are there other general reasons macroscopic tunneling never happens, besides the exponentially smaller probability as mass increases?

 

[Demystifier]

Yes, decoherence. Macroscopic objects have many degrees of freedom, which interact with many degrees of freedom from the environment, so there is a fast and strong decoherence which makes macroscopic objects essentially classical.

In fact, decoherence can prevent or slow down tunneling even of microscopic objects. One version of this effect is known as the quantum Zeno effect, where frequent measurements slow down the decay.

 

[DanteKennedy]

Yes, decoherence. Macroscopic objects have many degrees of freedom, which interact with many degrees of freedom from the environment

Interesting. Are degrees of freedom a dimensionality for quantum object? Like the x y z of a 3d plane (or roughly like that)?

 

[Demystifier]

Interesting. Are degrees of freedom a dimensionality for quantum object? Like the x y z of a 3d plane (or roughly like that)?

No, the number of degrees of freedom is not directly related to the size of the system. It is more directly related to the number of particles. See also https://en.wikipedia.org/wiki/Degrees_of_freedom_(mechanics)

 

[DanteKennedy]

Yes, decoherence.

But how exactly is the process of collapsing superposition leads to the effective prevention of tunneling for large objects?

 

[Demystifier]

But how exactly is the process of collapsing superposition leads to the effective prevention of tunneling for large objects?

That's because tunneling is a consequence of superposition. For example, suppose that at time $t$ the particle can tunnel from the left to the right, through a barrier in the middle. This means that the wave function at $t$ is nonzero both at the left and at the right, i.e. the wave function is a superposition of a wave function on the left and a wave function on the right. But if the wave function at $t$ collapses to the left part only, then at $t$ it cannot longer tunnel to the right, because the wave function is vanishing on the right so the probability of being on the right vanishes.

 

[DanteKennedy]

But if the wave function at $t$ collapses to the left part only, then at $t$ it cannot longer tunnel to the right, because the wave function is vanishing on the right so the probability of being on the right vanishes.

So for large objects, their wave function is so localized and are constantly being measured by their surroundings, effectively pinning their position? Am I right?

 

[PeroK]

So for large objects, their wave function is so localized and are constantly being measured by their surroundings, effectively pinning their position? Am I right?

A human being (and other life) grows by cell division. Your question would be what stops an entire human being spontaneously cloning itself into two? If a cell can divide, why not an entire large animal?

The biology of a human being is not the same as the biology of a single cell.

A building is not just a large brick. A forest is not just a large tree. A book is not just a big word. And, a sofa is not just a large elementary particle.

You need to find a way to reconcile these differences of scale and how they affect the physics and biology of large things and their constituent parts.

 

[DanteKennedy]

You need to find a way to reconcile these differences of scale and how they affect the physics and biology of large things and their constituent parts.

I wonder if large object can be treated as many independent particles in quantum framework. If a single particle has higher tunneling probability than a whole object, why the object doesn't experience constant "partial tunneling"? Or did it already happen in biology?

I'm changing the subject from the original question but I think this is interesting

 

[PeroK]

I wonder if large object can be treated as many independent particles in quantum framework. If a single particle has higher tunneling probability than a whole object, why the object doesn't experience constant "partial tunneling"? Or did it already happen in biology?

I'm changing the subject from the original question but I think this is interesting

Quantum tunnelling is on a microscopic scale. Not just tunnelling (which you seem to be obsessed by), but QM phenomena are taking place inside a macroscopic object all the time. That does not equate to a macroscopic object itself coherently obeying the laws of molecular physics. A sofa is not just a big molecule.

And, even if all the molecules in a sofa "tunnelled" at the same time by a micron, how would you even notice? You're not going to come into your living room and say "my sofa has spontaneously transported itself $10^{-6} m$ to the left.

This is not interesting. This site had an interview a few years ago with David Griffiths, who wrote one of the most popular undergraduate text books on QM. He said one of things he dislikes is people who only want to talk about objects tunnelling through walls, as this has nothing to do with QM.

If you want to learn QM, learn QM. And, if you want to talk about sofas tunnelling through walls, then you are learning precisely nothing about QM.

 

[DanteKennedy]

Quantum tunnelling is on a microscopic scale. Not just tunnelling (which you seem to be obsessed by)

I admit that it could get annoying, hehe. But thank you for answering some of my questions, even the QM guide