Why does the wave function collapse upon observation?

Question

Given that an observer is composed of matter, and therefore governed by the same quantum mechanical rules as the object he is observing, what property of the observer causes the wave function to collapse, and a certainty to replace it, once the event in question is observed?
ie, if I toss a coin, and prior to looking at it, it represents a probability function with an equal chance of being heads or tails, what compels it to be heads, or to be tails, when I observe it? For that matter, what mechanism makes the selection 'heads', or 'tails', between two equal probabilities?

Considering also that, given an appropriate arrangement of beam-splitters and unobserved alternative pathways, a single photon can be shown to interfere with itself, as a consequence of simultaneously travelling down all possible paths prior to observation, which fact suggests to me that it really can't make up its mind which route its has taken without the intervention of the observer.

Answer 1

I myself have wondered about the question you ask, and have bought and read many books about quantum physics in search of the answer. The best answer I have found concerns the concept of decoherence. To put it simply, it is a principle that relates to the changing of the behavior of a system from quantum mechanical physics to classical physics.
A book that was helpful to me was "Quantum" by Jim Al-Khalili.
If you are looking for a more metaphysical/spiritual hypothesis, check out "Self Aware Universe" by Amit Goswami. Although his view is dismissed by some as being hokey, I feel it is very interesting - good food for thought.
Truth is, it is a question that has not been conclusively answered yet. As much as we know, we do not yet know everything. There is still some mystery in our universe.

Answer 2

Collapse Of The Wave Function

Answer 3

Wave Function Collapse

Answer 4

I believe we misunderstand what "observation" truly means. If you go back to the fundamentals, it is not the act of OUR observing that causes the function to collapse. Rather, it is the act of the coin interacting with another object, say, the table, or your hand. Going back to Heisenberg's Uncertainty Principle, it is not our observation per se that causes the position and momentum of a particle to not be both simultaneously determinable; it is only the act of a photon colliding with that particle. We do not have to actually look at it; all it takes if for a photon (or any other particle) to strike the particle in question and that's enough for the Principle to be good. Or looking at Shroedinger's Cat, I think it is really absurd that the cat is neither dead nor alive, or both dead and alive. Does not common sense tell us that the cat surely knows whether it is alive or not. The box that holds the cat knows whether the cat is alive or not. The poison that killed or not killed the cat knows whether it killed the cat or not. So definitely the cat is either dead or alive. Once the poison is released or not released, the wave function collapses regardless of whether we open the box to see if the cat has been killed or not.
Really, the mathematics is awe-inspiring and suggests some other-worldly counter-intuitive stuff, but I believe the universe is really not so mysterious after all. Shroedinger's cat is either dead or alive whether we look or not. The coin is either showing heads or tails whether we look or not. The falling tree in the forest does, yes, does make a sound whether or not anyone is there to hear it.

But of course, I could be wrong.

Answer 5

To start with,the vedeos ive seen on the 2 slit begin with a particle that has to transform to a wave while passing through the 2 slits.Why did they chose particle form when wave form would explain it more sensibly. Then the observer turns on a detector to determine which slit the particle(photon) passed through, detects a photon half the time and is amazed to find the disappearance of the interference pattern. Why doesn't the observer not consider the effect that the electromagnetic waves produced by the detector might have on the incoming light wave changing it to a photon(decoherence) and then blames Just seems to easy to be true.it on his brain or 2 worlds. Could I assume that the collapse of a light wave leads to photon formation.

Answer 6

Alright! Schoroder's Cat! Love Schoroder's Cat! MEOW! Well, if the cat in Scroder's experiment collapses the wave function, then you would be watching the collapse made by the cat. Else, you would collapse it for the cat. So either way, you or the cat are collapsing the wave functions!

Answer 7

The wave function is all the possible results. Observing the event reduces-collapses the number of possible results to 1.
I and some others believe that the wave function that collapses is that of the observer since the coin or whatever "knows" its state - we are the ones who don't know until we look.

Answer 8

All your replies have shown a considerable understanding of the situation. However, they fail to explain some of the underlying problems with the question.

For example: the probability wave form that collapses, does so because once we view the outcome, only one end-state exists. It isn't that the object exists in two realities, it's just that until we do something that "observes" the outcome, it is "mathematically" possible that there are two outcomes. This is not really a paradox, it is only a paradox if we pretend it is. It is the same as saying "the light in my room is either on or off". Yes, that's true, and if you're not sure, it could be either condition. However, in "reality" it exists in one or the other state, and you won't know until you look. Your "looking" will not cause the light to come on half the time; it's either already on or it's off. But looking collapses the mathematically probability to one final state.

The real point is that schrodinger's cat was a mind experiment used to show that sometimes you need to interact with something to determine its state. You can know its velocity or its position, but knowing one will negate your knowledge of the other. In "observing" you remove your ability to know "everything" about it in favor of knowing "something" about.

Regarding photons, protons and crystal gates; it is only a paradox if your "observation" could be done without interaction. When you "look" by closing off one gate, or putting a measuring instrument on a gate to see if it went through or not, you have become part of the gate, and in doing so, have altered the event. If you are a wave theorist, you have no problem with "wave particle" duality because to you "everything" is a wave (string, etc.), it's just that some waves are non-linear and thus appear as something else when their linear motion is zero (e.g. "Matter"). What we do not know is whether or not our "looking" at "matter" is somehow affecting some dimension of the experiment that is unknown at this time. As far as what makes a coin go heads or tails, it has to do with chaos theory and probability. Your looking at the outcome merely collapses a mathematical probability, it doesn't necessarily "force" reality one way or the other (as far as we know today). The fact that you were close enough to the coin to see the outcome, or had a camera close enough, might in small degree alter the gravitational field in the area and change an outcome...but that is not the same as saying it "forced" a single outcome.

It's all a bit confusing at times, but as long as you remember that "collapsing" probabilty waves is actually collapsing mathematical probability waves and not collapsing "reality", you'll be on the right track. Observing an event "will" affect the outcome because your observation interacts with the experiement, even when you aren't sure exactly how or to what extent.

Understand those two principles and you'll miles ahead of your peers.

Answer 9

Wave function collapse is not an objective phenomenon, and is not part of the formalism of quantum mechanics. It has more to do with perspective. The observations of the various distinct possible outcomes are simply decorrelated from each other. That just means the observation of one possibility doesn't interfere with the observation of the other. Now, in such cases, some people prefer to interpret things to mean only one of the two observations are manifest in the real world. Once you use the word "real", however, you depart from physics and begin talking metaphysically. Metaphysics is a field where nothing can be settled. It's trees falling with no one to hear it type stuff.

Answer 10

Physics plays an essentially descriptive role with regards to nature. This means that we postulate theories and gather evidence to support them but there is no mechanism to then proclaim that the particular theory or model we are working with is in fact how nature works.

Quantum theory has developed in such a way that although we have a strong model and can make exceptional predictions, we are still left in a position of doubt about how the various aspects of the theory and methodology actually relate to 'reality'.

The idea of wavefunction collapse is part of a certain methodology which we can use in quantum theory. As you mentioned we consider the wavefunction of a system to contain many possible outcomes to measurement but when 'observed' only one of these is evident in the future system. We call this process of reduction, 'collapse'.

So, we have a mathematical system which is corroborated with lots of evidence but we have no idea 'why' any of it might be true. This isn't just a quantum phenomena, as I mentioned physics' role is descriptive (and predictive) and to ask 'why' a ball rolls down a hill is no more answered by me saying:

"Gravity acts on it"

than,

"It just does".