Physics: Stranger Than Fiction

Nice video.

There was a slight problem with the animation of the interfering waves .. well, not with the animation but with the interference pattern on the screen (the bright lines didn’t all line up with the places that the waves were adding to each other). But … that’s just being picky.

It was a nice demonstration of real experients .. and done in such a way that people can understand what happens (not WHY, but what).

For those who are curious about how observing could possibly change the behavior of the electron (how could the electron KNOW that it is being observed?) … it isn’t that mysterious. An observation of an object REQUIRES interaction with an object (even if that interaction is as simple as bouncing a photon off of it to SEE it .. there are other means of observing, but ALL require interaction of some sort).

“For those who are curious about how observing could possibly change the behavior of the electron (how could the electron KNOW that it is being observed?) … it isn’t that mysterious. An observation of an object REQUIRES interaction with an object (even if that interaction is as simple as bouncing a photon off of it to SEE it .. there are other means of observing, but ALL require interaction of some sort).”

I don’t follow here.

Let’s say a room is lighted and an event takes place in it. In the room is a person who could see the event or not see it, depending on where they are looking.

So here’s the order: An event happens, the light from the room bounces off the event and spreads off into the room.

Now that this has taken place, and that light (which serves as documentation of the event) is now in the room, it shouldn’t matter whether or not someone looks at that light and “sees” the event or not. The event was recorded via the light anyway; it’s there for anyone to look at.

So the viewing takes place after the fact. The light that allows the viewing is constant, so that’s the only thing interacting with the event, not the human looking at the light that was scattered about the room.

What am I missing?

I’m with Daniel on this one. How does recording an event that happens anyway keep that event from happening? Is that why a watched pot never boils?

:) nice .. that “watched pot” comment got a chuckle from me.

OK, let me try to explain. And, let me be clear, what I intend to explain is ONLY that observation can be expected to change the outcome of an experiment. Not that observation changes it in the precise way that it does.

First of all, the act of observing the electrons pass through one slit or the other requires some specialized observation equipment. We want to know for each individual electron whether it is passing through the left slit or the right slit. It is not a simple matter of simply LOOKING vs NOT LOOKING. To “see” the electron, we need to direct a light source at it OR use some sort of detector that can detect moving charges (which create a magnetic field which can be detected). Here’s the thing. For light to be able to SEE something with light, the wavelength has to be roughly the size of the object being seen (or smaller). The smaller the wavelength of light, the more energetic it is. Electrons are tiny and to SEE them with light, we need to direct photons of fairly high energy at them. When the light reflects back to the observer (us), it imparts energy to the electron (the whole action-reaction thing). This changes the momentum (direction and speed) of the electron. You can see that this could change what happens. It doesn’t matter if we actually LOOK at the reflected light. That is, we don’t actually have to OBSERVE the light .. it is enough that we directed the energy beam at the electron. This is the thing that causes the disruption. We could instead simply try to detect the magnetic field generated by the electron. But putting a detector near a slit that the magnetic field pushes on (a simplification, but you get the idea) will result in (you guessed it) an equal and opposite push. This also changes the momentum of the electron. The double slit experiment works only when the electrons are free from interference of these sorts.

Here’s an interesting page if you really want to read more about this stuff:

http://www.ncsu.edu/felder-public/kenny/papers/quantum.html

OK, I’m not sure I’ve convinced anyone of anything, but (on an ALMOST entirely different subject — inspired only by my mention of the magnetic field detector above) let me mention a couple of interesting things you can do with a loop of wire and a battery.

(1) Create an electromagnet. (2) Create a metal detector. (The hand held things that people use to look for treasure on the beach are essentially loops of wire. So are the detectors at traffic lights.) (3) Create a transformer (requires a couple of loops of wire).

OK, I’m getting off subject … I’ll get back to my lecture writing. :)

This site is lame…

So, let me see if I can simplify what Carl is saying here. Let me know if I’m getting this right.

If I have a pile of sand and I want to look at just one grain, I have to disturb the pile (which changes the environment).

Furthermore, to make any worthwhile observations about that grain of sand, I have to move it or shine light on it.

Which means the grain of sand I’m observing is different from the grain of sand I wanted to observe, despite the fact that it’s the same grain of sand I was originally after.

Is this where we start talking about Heisenberg’s Uncertainty Principle?

Indeed, the uncertainty principle is key to much of this stuff. Your explanation is good .. just keep in mind that when objects are large, our observations don’t disturb them in any significant way. But when objects are tiny, the observations can disturb them in significant ways.

True. It’s hard to think of a life sized example that fits properly.

As my dad says, it’s like trying to give an example of Avagadro’s number using marbles.