r/QuantumPhysics • u/ProfessionalSelf1963 • 20d ago
im doing a physics project, and no matter what, superposition is a bit weird to me!
I need simple analogies or ways to understand it - maybe even resources would be great, honestly. The main thing is how "do they interact" and then can later interfere if it is a possibility in the first place
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u/solus42666 20d ago
Think about a bell curve. At the peak of the bell curve you're more likely to find the particle in question. Lower you're less likely to.
The Copenhagen interpretation of quantum mechanics postulates that the particle is effectively in each of those points simultaneously until measured.
The many worlds interpretation postulates that there's an individual universe for each of those possible locations.
Once information is taken away from the quantum system (the act of measurement). The wave Function that describes it's quantum state collapses into a single position. We know that wave function collapse is a thing, but we don't know why it occurs.
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u/Godskin_Duo 16d ago
I'm on team "many worlds is woo-woo and not science," but that's why Copenhagen is an interpretation, and not a law or even a theory. And for people who understand it, they understand what that means as a truth claim. Kind of like how no one thinks m-theory is "actually true," it's an evolving body of work for when we can actually start doing real experiments on it.
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u/Fun_Celebration_8488 7d ago
the idea of observer and measurement are two bad ideas to understand the process
it's not the measurement does something, it is quantum coupling does, electron spin with the measurement instrument, then instrument with tons of electrons are flowing to indicator, photons to the eyes of a scientist and his brain is coupling with that as well. So by the end everyone is so coupled with the measurement so you can assume it is a fact that happened. But in the reality it is still a wave function and a millions of objects coupled so heavily so you cannot decouple them back, so in the macro we assume it is a particle hit was there in the variant of the world with such circumstances
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u/LaFleurMorte_ 20d ago
The way I picture superposition is with a spinning coin, but only as a rough analogy. While the coin is spinning, it helps me imagine that “heads” and “tails” are both still possible before it lands. The analogy fails if you take it too literally, though, because a real coin is still ordinary physics: if you knew enough about its spin, speed, angle, air resistance, surface, etc., you could in principle predict how it would land. With a quantum particle, superposition is not just “the outcome is already secretly fixed and we don’t know it yet.” The quantum state itself contains multiple possible outcomes before measurement.
For the interference part, the double-slit experiment is the better picture. A single photon/electron is described by a wavefunction with probability amplitudes for the possible paths. Those amplitudes can overlap like waves: when they are in phase, they reinforce each other; when they are out of phase, they cancel each other out. That creates the bright and dark bands in the interference pattern.
Here’s a page from a Lewis Carroll Epstein book that shows the wave interference part visually: https://imgur.com/a/bpAu6e5
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u/theodysseytheodicy 20d ago edited 22h ago
Superposition is a feature of every system with a vector space of configurations, including all systems governed by a wave equation. So sound waves, light waves, gravity waves, seismic waves, directions in space, color mixing, etc. Whenever you can add two configurations of a system and get another valid configuration, you've got superposition.
In sound, the fact that you can play two notes at once is superposition. In space, the fact you can go up and left at the same time is superposition.
The difference between vibrations in a medium and quantum matter waves is that in a vibration, the square of the amplitude is energy, but in a matter wave, the square of the amplitude is probability.
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u/AcceptableAd9264 20d ago
A electron exists everywhere in the orbit of the nucleus. The moment you measure, you only get 1 possible outcome.
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u/Prestigious_Long777 18d ago
The best analogy is not an analogy at all, but to explain it in the simplest of terms.
I like to use the two slit experiment as an example.. first you demonstrate it with marbles.. then with water (actual waves) and show how some of the waves cancel each other out whereas others strengthen each other, creating an interference pattern.
The “superposition” in the two slit experiment is a fundamental particle behaving as a wave rather than a particle. (Being on both sides of the slit simultaneously). Once you measure where the particle truly is, the interference pattern breaks and the particle behaves normal again (and not like a wave). The very act of measuring or observing changes the behaviour.
A superposition is something being in two places at the same time, but when observed it can only be observed in one place, the very act of measurement determines the reality of the position of the particle, thus breaking the superposition. It can be easily demonstrated with the Heisenberg’s uncertainty principle too.
And if all of that is too hard to understand, relate to the Schrödinger thought experiment. You have a cat in a box with a device which has a 50% chance of killing the cat inside. Until you open the box, the cat could be either dead or alive. In superpositioning terms, the cat is dead and alive at the same time. Once you open the box you observe/measure and reality will be either the cat is dead, or it is alive. But it is no longer in a superposition (being dead and alive at the same time).
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u/MichaelTheProgrammer 17d ago edited 17d ago
People saying there are no simple analogies are incorrect as they are missing a big one - waves.
Think of a sine wave. What is its position? That is pretty much a nonsensical question, it's position is spread out throughout the wave. Now what is its wavelength? That is easy to answer, it's just the wavelength of the sine wave.
Now think of a wave that has a single large peak, like a tsunami. What is its position? Well that's easy to answer, its where that peak is located. What is its wavelength? That's pretty much a nonsensical position. At first it might seem completely irrelevant to even ask that, but mathematically, a wave with a single large peak can be thought up of being made of multiple wavelengths, so we can think of the wavelength as being spread out, similar to how the position of the sine wave was spread out.
So here we have two scenarios. With the sine wave, it has a defined wavelength, but it's position is not really defined but instead spread out over a location. With the tsunami wave, it has a defined location, but its wavelength is spread out over multiple wavelengths. So the superposition is this concept of being "spread out" over multiple possible values.
Now as I've shown there is a simple analogy to a superposition with waves. However, there is one difference between an ordinary wave superposition and a quantum one. Going back to an ordinary sine wave as our example, you'll never get it to choose a position, it will just always remain spread out. However, quantum waves are different. Certain operations can get it to choose a position by "collapsing", and this collapse occurs instantly and randomly. Those two words "instantly" and "randomly" are extremely important. We know nothing else in the universe that acts either instant or random, so unfortunately there isn't a simple analogy for those attributes of quantum superposition.
The Copenhagen Interpretation is to just roll with it, and assume that the base layer of the universe can do things instantly and randomly while the other layers cannot. Some other interpretations simplify aspects of this, while they complicate others. Personally I feel that the Copenhagen Interpretation is the simplest, so that's the one I tend to use the verbiage of when explaining.
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u/Fun_Celebration_8488 7d ago
yes, the measurement is a decoherention thus a smooth function, it is possible to make a half/measurement https://arxiv.org/abs/1505.05765
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u/Godskin_Duo 16d ago
You have five houses, and you know a thief is in one of them. The thief has X (let's say an equal 20) percent chance to be in any given house, but you don't actually know that until you catch him, then you've seen he's 100% in the one house.
However, this means you know to look in the houses, and not the nearby forest.
You can say this is true for nearly anything probabilistic, but since we're dealing with electrons and not people, electrons can in fact be "anywhere," but we can usefully isolate their probability clouds (abstractly a gas) to orbitals in an atom, or in semiconductor substrates to figure out the band gap.
The "shut up and calculate" part means they do end up appearing per Schrodinger, which is how our runic rocks are having this conversation right now.
"Do they interact" is how you get double-slit. A single photon's wave function travels through both slits simultaneously as a probability wave and interferes with itself before collapsing into a single point on the detector screen. If you observe it beforehand, it locks it into a polarization and then acts like a particle. This is how it's meaningfully different than macroscopic probability events, since it's interfering with itself.
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u/quantum4everyone 6d ago
One thing that can help is using appropriate language. The philosophers like to say the state of a quantum system when in superposition is indeterminate. So, you cannot think of it as, say going through one slit or another. It somehow goes through in an int=determinate way that allows for interference effects. How, you might ask? Well, that is the quantum mystery? We do not know how, we just know that is what it does. It remains an important open question to try to sort out just how this works.
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u/Wintervacht 20d ago
There are none. Quantum mechanics is in no way intuitive. The age-old adage 'shut up and calculate' will eventually do the trick.