Can someone explain these properties of light particles?

Question

(Refering to the two-slit experiment) How is it possible that a single photon can pass through both slits and interfere with itself? If it is because it is a wave of possibilities, how does it not ultimately choose one of those possibilites? How can a single thing be in more than one place at one time, an idea that seemingly contradicts logic itself?

Also, when an attempt is made to observe how this happens, the single photon does not behave in this manner, going through only one slit at a time. How is the photon's behavior changed by the mere act of observation? Does this experiment imply that light is somehow intelligent?

Answer 1

In physics, you get the hang of saying, "as if", instead of "is". Light behaves "as if" it were a wave, or "as if" it were a particle, or "as if" its existence is really spread throughout space, etc. Forget the "is" part, because nobody really understands how light could be all these things. In the double slit experiment, the light behaves "as if" it left a single atom as an emission, then behaves "as if" it travelled like a wave through the double slit with typical wave self-interference, and then behaves "as if" it it struck the detector at a single place of atomic size. Imagine that a magician has performed this trick, and he has successfully created the illusion of these things happening. Now, the question is, how did he do it? Physicists don't know yet, but they sure got excellent equations predicting what would happen.

It's an entire field of study, called, "Quantum Interpretations", that's devoted to trying to answer your kind of questions about this. Even Einstein himself brought himself to bear on this subject as well, and he didn't fare well, and yet he couldn't deny the results. Check below for links to this subject. I personally believe that we cannot use a simple concept of space of "nothing", and some photons wafting through. At a minimum, we have to look at things from a quantum field model where the vacuum is anything but "nothing", and that the ordinary 3D space we're comfortable may only be an approximation of what may be relativistic Hilbert infinite-dimensional space, where quantum time may even run backwards. We fail to understand it because we persist in thinking that it MUST make sense in an overly-simple concept of space and "particles" in it.

Oh, by the way, forget ordinary logic, it doesn't apply in the quantum world. That's why quantum logic has been devised. On a side note, most computers today are based on ordinary logic, but work is already underway on developing quantum computers which do NOT use ordinary logic, but quantum logic. And it's very real. Link on this given too below.

Answer 2

Read this whole thing and you ll understand:
According to quantum mechanics each single free photon is associated with a wave function(its like a mathematical model of the photon).This wave function, as it encounters the slit, travels through every possible route i.e.,any number of slits present and then interfere on the other side to give the characteristic pattern of reflections. This is the essence of the "sum over histories" concept(here "history" refers to a particular path of wave function through a slit).
Let me tell you another consequence of this: According to "sum over histories" approach as a light is incident on a plane surface (as set of wave functions for each photon), the wave functions get scattered in all the directions possible even along those paths that contradict laws of reflection but only that there is a constructive interference only along the path predicted by laws of reflection. And there is nothing like "choose a path" property for light or any matter or energy.(water flow is guided by "least action principle and light path by "least optical path rule",the latter being equivalent to laws of reflection and refraction.)
You cannot prove the existence of a single thing at two places at the same time unless you observe that thing or particle:thats what quantum physics says-the existence is just the result of you observing it -its like you cannot predict the result when a coin is tossed.The coin is said to be in a "mixture state" of head and tail though it does not mean that head and tail are existing at the same time. The outcome becomes meaningfully head or tail only when you stop the tossing coin and see it and mind that the sole action of stopping it affects the outcome-or your observation affecting the result OR in your case the photon behavior, the head or tail being analogous to a path through a single slit out of the two.

Answer 3

You can't perform the experiment with a single photon. A single photon cannot interfere with itself, just as a single electromagnetic wave cannot interfere with itself. Observation doesn't change the behavior of a photon... quantum mechanics dictates uncertainty, which means you CANNOT truly observe all of its properties accurately.

Answer 4

You have just reminded me of my past. It was 10 years before when I had the same questions in my mind. I had just finished reading the book "In search of Schrodinger's cat" by J.Gribbin, a book about Quantum theory's philosophical implications.
In these 10 years, I have lost my interest in physics since I have not yet got any satisfactory answers so far. Noone seems to really know the nature of light. There is too much speculation and so far, no one has been able to physically explain the nature of subatomic world.
As for why I have not tried to find myself, well, Iam not that clever!