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.