Only when you observe the moon does it come into being in one place. All other possibilities become zero. So in this part of quantum mechanics, human observation really does change things!OK... what happens when TWO or more people see it at the same time? then what???
I was waiting for that question, and I knew you would ask it! It is night. You are inside and cannot see the moon. So the moon "exists" everywhere it possibly could be, including in the sun.
I am outside. I am observing the moon. It is where I see it, and nowhere else.
So where is the moon? Some physicists say it's where I, the actual observer, see it. Others say that your interpretation is equally valid, and so the question can have no definite answer.
With large objects it does not matter. For you, the moon is everywhere, but it is most probably in its normal orbit, where I see it. For you, the chances of it being anywhere else are real, but very low. So you wouldn't complain too much about my observation.
But as objects become smaller, the chances of a far-away observation increases. If the moon were the size of an electron, there would be a decent chance that it would be observed in the sun, then an instant later past Mars, then an instant later in its normal orbit.
Weird stuff. As I mentioned earlier, Einstein could not accept it. And that's one reason he made almost no useful contributions to science in the last 25 years of his life.
“In science, the term observer effect refers to changes that the act of observation will make on a phenomenon being observed. This is often the result of instruments that, by necessity, alter the state of what they measure in some manner. A commonplace example is checking the pressure in an automobile tire; this is difficult to do without letting out some of the air, thus changing the pressure. This effect can be observed in many domains of physics.
The observer effect on a physical process can often be reduced to insignificance by using better instruments or observation techniques.
Historically, the observer effect has been confused with the uncertainty principle.[1][2]”
http://en.wikipedia.org/wiki/Observer_effect_%28physics%29
Once we have measured the system, we know its current state and this stops it from being in one of its other states.[3] This means that the type of measurement that we do on the system affects the end state of the system. An experimentally studied situation related to this is the quantum Zeno effect, in which a quantum state would decay if left alone but does not decay because of its continuous observation. The dynamics of a quantum system under continuous observation is described by a quantum stochastic master equation known as the Belavkin equation.[4][5][6]
An important aspect of the concept of measurement has been clarified in some QM experiments where a small, complex, and non-sentient sensor proved sufficient as an "observer"—there is no need for a conscious "observer".[7]
A consequence of Bell's theorem is that measurement on one of two entangled particles can appear to have a nonlocal effect on the opposite particle. Additional problems related to decoherence arise when the observer too is modeled as a quantum system.
The uncertainty principle has been frequently confused with the observer effect, evidently even by its originator, Werner Heisenberg.[1] The uncertainty principle in its standard form actually describes how precisely we may measure the position and momentum of a particle at the same time — if we increase the precision in measuring one quantity, we are forced to lose precision in measuring the other.[8] An alternative version of the uncertainty principle,[9] more in the spirit of an observer effect,[10] fully accounts for the disturbance the observer has on a system and the error incurred, although this is not how the term "uncertainty principle" is most commonly used in practice."