In usual English tunnels are things that you form when you dig a hole to connect two valleys
In
order to tunnel effectively you generally need to know what valley you
want to reach and you then pick a spot to start shoveling that minimizes
the energy you must expend digging
Why dig?
Because it takes less energy walking through a tunnel rather than hiking
over the mountain every time you want to visit the next valley, so over
time the effort is worth it.
This is the analogy with quantum tunneling with an odd twist.
If
an electron wants to get somewhere that is a valley separated by a
mountain blocking its path (not a valley in gravity but a valley in
electric potential) it must expend energy to “hike” up the electric
potential (voltage) mountain to then slide down to the next valley.
Without assistance from outside stimulae the electron will never have that energy to do so so it is stuck in the valley.
But
wait! The Lords of quantum have bequeathed the lowly electron with an
awesome power, like the knight on a chessboard it can move around
obstacles in its path! How? To explore this imagine the electron
debating with the Lord of Quantum:
Electron:
“Lord Heisenburg, thou sayest my position is uncertain and my
uncertainty in position times my uncertainty in momentum is never less
than a fixed value given by the equation bearing your name. I wish to
vanish from this valley and reappear in the next.”
Lord
Heisenburg: “Impossible, you lack the energy I require to climb the
voltage wall; the beautiful voltage wall that I have set in place to
imprison you.”
Electron: “Lord Heisenburg, I hereby beseech you to measure my momentum to great precision. Do you grant my request?”
Lord Heisenburg: “Whilest I choose to imprison you in this valley I am nonetheless a benevolent Lord. I grant your request.”
Electron:
“Lord Heisenburg you are a great Lord. Your laws are upheld throughout
the land. Your uncertainty law is as constant and immutable as your
energy law which mandates I climb the hill yes?”
Lord H: “Yes electron you speaketh the truth.”
Electron:
“Therefore since you have now measured my momentum precisely my
position is largely unknown lest the product violate your glorious law.
Correct?”
Lord H: “Yes electron you speaketh the truth.”
Electron: “And even the great Lord H must obey his own laws?”
Lord H: “Yes electron you speaketh the truth.”
Electron: “But I must remain in this valley by virtue of the law of electric potential?”
Lord H: “Yes electron you speaketh the truth.”
Electron:
“Then I must be in a state of superposition of being in both valleys at
the same time. And if you try to measure my position you may find I am
actually in the other valley.”
Lord H: “Arrrggggghhhhh my wall my beautiful wall (sobbing sounds) is undone. My prison destroyed at my own decries! Woe is me!”
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