fuckyeahphysics:

Hello all, your trusty friend ummwhat here. Trust me, this isn’t as scary as it looks.

Quantum tunnelling is a strange phenomenon of quantum mechanics that allows particles to pass through barriers that normally would be impassable. It all has to do with the Heisenberg uncertainty principle. This is a fundamental principle of our universe: we can never know exactly everything about a particle, we can only measure the probability that it has particular characteristics. For instance, take this model of a Helium atom (2 protons, 2 electrons).

The darker areas are the areas where it is more probable that the particle is. It’s still possible for it to be in the fuzzy areas, it’s just not as likely. This is an important thing to understand. We never know exactly where a particle is, has been or will be.

Got it? Good. Another important thing to know about the universe is the particle-wave duality. It’s exactly as it sounds. Particles have an annoying habit of acting like a particle and a wave at the same time. They can never decide. Just leave it at that, accept that, and get over it. The more complex physical properties at work here are not necessary to understand quantum tunnelling, or even to understand most concepts that feature the duality.

Before we talk about quantum tunnelling, let’s get it out of the way first that quantum tunnelling is not a theory, it’s an observable property of the universe. We’ve observed it in radioactive decay and nuclear fusion (the process that happens in the Sun), and we use the property in some electrical components. This observation is a anchor of the theory of quantum mechanics, as well as evidence for other concepts like the particle-wave duality.

Now we’re ready. Say you take one of these fuzzy probability blobs and you chuck it at a barrier. You’ve at this point assigned energy to it. This is called a wave packet, and it is an envelope of energy that travels with a particle. The uncertainty principle says also that we can never know exactly how much energy is in the wave packet at any given time. Now, because of the particle-wave duality and the uncertainty principle, there is a probability that a particle can sort of “borrow” energy from the wave packet, giving it more energy than it should have.

As the particle moves toward a barrier, the particle is moving fast and the barrier enters the probability cloud. Now, in the above picture, there is a probability, though small, that the particle is in the area on the other side of the barrier. As the particle gets smaller and the energy gets higher, the probability is greater. When chance so inclines it, the particle will have “tunnelled” through the “impassable” barrier:

On the left you see a wave packet containing a particle as it approaches a barrier. After it collides with the barrier, you see a particle come out on the other side. It has taken energy from the wave packet, so it moves at the same speed, but its wavelength is shorter, meaning that the particle is more difficult to detect and the probability it is in a particular spot is smaller, which is why it is depicted as very faint. The part that seems to “bouce” on the left side are the waves reflecting off of the surface of the barrier.

So that’s quantum tunnelling. The probability that it happens is very small, though much higher than the probability that, say, your basketball will tunnel through the Earth. Leave questions in the ask box!

I had a friend who learned some form of this concept at far too young of an age to fully understand it, so she would run into walls all of the time because there was “about one sixtrillionth” probability that all of her particles would pass through it. 

(via oh-delial)

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   I had a friend who learned some form of this concept at far too young of an age to fully understand it, so she would run...

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    I’LL TUNNEL THROUGH YOUR IMPASSABLE BARRIER.

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    this one explains everything awesomely. Quantum physics - get

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    Holy shit, my mind...blown right now.

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