Quantum theory can be very bizarre if one tries to understand with classic thought. Based on Quantum theory, particle can exist in many different places at the same time. Strictly speaking, the location of the particle is not fixed and is not yet determined until someone actually observes by the means of measurement tool or human eyes. In other words, until it is observed, the location of the particle exists as a possibility function varying across the space so called "Wave function". Therefore, if the wave function looks like sine wave, the possibility of the particle being observed at certain location varies smoothly up and down as you move to different location. However, at the moment of observation event occurred, the wave function collapses into delta function which has a peak at certain position which means the possibility of the particle being in that location is almost certain and the possibility of the particle being in other location is almost zero.
This same phenomenon can be observed in the Double Slit experiment video below. In the video, the pattern of the particles arrived on target becomes different when the particle is observed from when no observation is done. This is because the wave function which determines the probability of an particle being in certain location changes at the moment when the measurement is done. If no measurement is done to the particle, the wave function will not be touched, resulting in different result.
One very interesting topic to think about is what does it really mean by "observation". We know that if one person sees an object, that object is observed. However, if we use some machine to record event without a human looking at the recording video, is it considered to be observation, and it will change the wave function even before human actually watches the video? Or is it that, even in the video, the location of object just exist as many different possibilities until a human actually starts watching the recorded video. If the latter is true (which I think it is), it means our perception actually changes physical world by merely looking at it. At the moment when we perceived the location of the object, we actually changes the wave function of the universe.
Affecting the physical word by mere perception sounds very surprising, but if we come to think of it, we are actually doing the similar thing all the time. Our body can be changed depending on how we think. As a very simple example, when we get nervous, our body temperature goes up, and our heart starts beating quicker. Merely thinking differently actually affects the physical world.
It sounds to me that somehow quantum theory might be related to understanding how our perception work with our body. This is very interesting discussion topic. Please share your thought if you are also interested in this topic.
Enjoy the video.
Double Slit Experiment part of "What the bleep do we know"
Full movie of "What the bleep do we know"