Often, that’s because other electrons are in those lower-energy states if they’re all occupied, then that electron is in its lowest-energy configuration. Electrons within atoms, for example, often find themselves in an excited state: where they’re in a higher energy level other than the ground state.Some common examples of quantum systems that exhibit tunneling involve atoms and their constituent particles. While most of the wavefunction, and hence the probability of the field/particle that it’s a proxy for, reflects and remains on the original side, there is a finite, non-zero probability of tunneling through to the other side of the barrier. This generic illustration of quantum tunneling assumes there is a high, thin, but finite barrier separating a quantum wavefunction on one side of the x-axis from the other. Only in the true ground state is it impossible to transition down to an even lower-energy state. If you can overcome the next energy barrier, you have the opportunity to wind up in an even more stable state: a state that takes you down closer to, and possible even all the way to, the ground state. to “kick” that system out of the false minimum. If you’re a classical system, the only solution is Sisyphean: you have to input enough energy into your system - irrespective of whether that’s kinetic energy, chemical energy, electrical energy, etc. What can you do when you’re stuck in a false minimum? Even though it would be more energetically stable in the ground state, or in its true minimum, it can’t necessarily get there on its own. This state can happen naturally for a great variety of physical systems, and we generally think about it as though the system is “hung up” in some sort of false minimum. Rather, it can roll into a valley that’s still lower than where it started, but that doesn’t represent the true ground state of the system. Only, that last example has a catch to it: sometimes, if your conditions aren’t precisely right, your ball won’t end up in the lowest-energy state possible. Whenever we encounter a finely-tuned physical situation, there are good reasons to seek a physically-motivated explanation for it when we have hills with false minima on them, it’s possible to get caught up in one and not arrive at the “true” minimum. A much more stable position is for the ball to be down somewhere at the bottom of the valley. When we see something like a ball balanced precariously atop a hill, this appears to be what we call a finely-tuned state, or a state of unstable equilibrium. Here’s what we know, today, about how precarious our continued existence is. And in one of the most terrifying realizations of all, we’ve learned that the fabric of our Universe itself may inherently be one of those unstable things as well. Unstable states all have one thing in common: they decay. Some of the conditions that arose spontaneously under those high-energy conditions could no longer persist at lower energies, rendering them unstable. But earlier on, the Universe underwent transitions: from higher-energy states to lower-energy ones. Wherever and whenever we can measure or infer the fundamental physical properties of the Universe, it appears that they do not change over time or space: they are the same for everybody. The fact that the Universe appears to be consistent with these presumptions - at least, to the limits of our observations - seems to support this view, placing great constraints on how much it’s possible these various aspects of reality have evolved. The fundamental constants that relate various physical properties of our Universe are assumed to truly possess the same, constant value at every time and place. The laws of physics, we presume, are the same at other locations in space and other moments in time as they are in the here-and-now. There are certain properties about the Universe that for better or worse we take for granted.
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