# Quantum mechanics basics

#### Waveparticle

From what i understand quantum mechanics has large part to do with probabilities. So is it valid to say that if i walked head on into the wall in my room for an infinite period of time that eventually i could be able to walk straight through it? Also is there a way to calculate a simpler version of the above problem that would say take only 20 years to happen but is normally very unlikely to happen without repeated trying?(hope this makes sense)

#### Nervous

Proooobably not, I'm guessing...

#### lj19

It is unlikely because it depends on the mass differences, although it could be considered possible. You can't physically walk through a wall, unless the wall itself broke. Could you explain the question a bit?

#### Waveparticle

It is unlikely because it depends on the mass differences, although it could be considered possible. You can't physically walk through a wall, unless the wall itself broke. Could you explain the question a bit?
I remember hearing someone say that due to the probability factors of quantum mechanics that if you walked into a wall for an infinite number of times that one of those times both the molecules in the wall and in your body would be arranged in a way that you would theoretically be able to pass through the wall.

#### giant_bog

This sounds like a pop-science explanation of quantum tunneling.

Classically, a charged particle will not be able to 'walk through a wall' (penetrate a barrier of electrical charge) if its kinetic energy is less than the potential energy of the barrier.

In quantum mechanics, there's a small probability that it can, based on the energies involved and the width of the barrier.

Scaling that up to a human size, we're dealing with on the order 10^28 charged particles. And I suppose you can see a brick wall as a barrier of charge.

So you could probably accomplish the tunneling in an infinite amount of time.

There's got to be a better way to explain tunneling though.

#### unusualname

That wiki answer isn't very accurate, the main reason your head doesn't go through the wall is due to the Pauli exclusion principle rather than electromagnetic repulsion (or even nuclear force repulsion).

And banging your head on the wall will likely have little effect on the quantum tunnelling probabilities compared to say, just walking towards the wall, in fact it might reduce the tunnelling probabilities by heating the wall up or compressing the surface molecules closer together.

According to QM you always have a probability of being anywhere in the entire universe, never mind the other side of a wall, but due to decoherence these probabilities are so microscopically tiny as to be ignorable (scientifically)

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