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calculate the transmission coefficient (mander.xyz)

submitted 4 months ago by BB84@mander.xyz to c/science_memes@mander.xyz

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[-] haerrii@feddit.org 19 points 4 months ago

What does the graph say? what's on the x and y axis?

[-] BB84@mander.xyz 55 points 4 months ago* (last edited 4 months ago)

The x axis is position. The y axis is energy. The blue box is a potential energy barrier. The red curve shows the wavefunction of a particle at a certain energy level coming in and tunneling through the wall. (the wavefunction actually live on a different y-scale from this plot and is only superimposed here for illustrative purpose, so don’t use the energy y-scale to read into the amplitude of the oscillatory part).

more info: https://en.m.wikipedia.org/wiki/Quantum_tunnelling

[-] arality@programming.dev 31 points 4 months ago

Sometimes I hate this community because, It makes me feel so dumb lol

Can you eli5 this for the dumb people in the room?

[-] model_tar_gz@lemmy.world 42 points 4 months ago

If anyone ever tells you that they understand quantum physics, punch them in the mouth and tell them they just got quantum pummeled.

[-] tdawg@lemmy.world 25 points 4 months ago

Sorry, the wave function of my fist must have existed inside your head for a moment

[-] BB84@mander.xyz 17 points 4 months ago* (last edited 4 months ago)

Imagine you release a ball from the top of a hill and it rolls down. The taller the hill, the faster the ball will get, the more energy it will have. If the hill is X unit high, the ball get X units of energy.

From conservation of energy, a ball with X units of energy can roll up a hill of height X before coming to a stop. If such ball is rolling on the ground and there is a hill (a “barrier”) of height greater than X in front of it, the ball will climb up X units, stop, and roll back down the same side. But if the hill is less than X tall, then the ball will roll over to the other side of the hill.

What I describe above is classical physics. It’s very intuitive and describe everyday life very well: you can try rolling balls at home too.

You can think of the wall the girl built in the meme as a kind of hill too. If you throw an electron at the wall, it gets repelled by the electrons of the atoms of the wall (in the same way the ball gets “repelled” away from the hilltop by gravity along with the slope of the hill). In classical physics, you can calculate how much energy an electron should need to surmount this repellent force and pass through the wall. This would be the height of the girl’s hill.

But it turns out that even electrons with lower energy can still sometimes pass through the wall. This is the phenomenon of Quantum Tunneling (because the particle cross through the hill without going over the hilltop: it used a tunnel). I can tell you it is a feature of the wavelike behavior of particles as quantum mechanics describe, but if you ask “why do particles have wavelike behavior” then you’ll have to see @model_tar_gz@lemmy.world ‘s answer.

The joke in the meme is that the girl thinks she is safe because she has a wall. But considering quantum effects, there can still be particles (knives) that tunnel through and hit her.

[-] Gormadt@lemmy.blahaj.zone 8 points 4 months ago

Basically it's a graph that shows where a particle is with the red (?) line showing where it is.

It shows how wacky particles can be.

Even putting up a wall that particle is gonna slip into your DMs.

[-] PM_ME_VINTAGE_30S@lemmy.sdf.org 15 points 4 months ago* (last edited 4 months ago)

I think this is quantum mechanics. Ψ(x) is the wave function of some quantum object (like an electron) as a function of (1 dimensional) space, U(x) is the potential as a function of space. Ψ(x) is a generalization of the state of a particle (a vector in a real space) for quantum mechanics (to a complex function). The squared magnitude of Ψ(x) can be interpreted (with suitable normalization) as a probability that the object will be measured to be located at x. The plot here actually shows the real component of the wave function; in general, it is complex, and it is complex in this situation.

Classically, if something is on the left side of the barrier created by U(x), it shouldn't be able to cross to the other side at all without being supplied external energy. Intuitively, imagine that I roll a literal ball to the right. You would expect it to bounce back at you. However, in quantum mechanics, it totally can appear on the other side of the barrier. Why? Based on the graph, the wave function has some nonzero magnitude on the right side of the barrier.

So this meme implies that some of the swords are going to appear on the other side of the wall.