Light and physics questions?

Question

1) Does einsteins explanation of the photoelectric effect invalidate Young's explanation of the double-slit experiment? Explain.
2) Consider one of the many electrons on the tip of your nose. If someone looks at it, will its motion be altered? How about if it is looked at with one eye closed? With two eyes crossed? Does Heisenbergs uncertainty principle apply here?
3) If the behavior of a system for some period of time is measured exactly and is understood, does it follow that in the future behavior of that system can be exactly predicted? (Is there a distinction between measurable and predictable qualities?)

Answer 1

1) At the time, it sure seemed to be a contradiction. You can't be BOTH a particle AND a wave right? right? It took almost 30 years for people to accept that yes, you could have discrete particles that obeyed a differential equation that looked a lot like a wave equation. Not only were photons (previously thought to be waves) dual natured, but so were electrons and other particles, previously thought to be particles. It's hard to appreciate today just how confusing this must have been for early 20th century physics. Even Einstein himself never got his head wrapped around some of the philosophical implications of quantum mechanics. Most of the old physicists alive at the time never really "got it". They had to die and be replaced by younger guys for physics to advance.

2) No, it doesn't care if someone looks at it per se. But to be looked at, it has to get bombarded by photons which will alter its wave function. So it can't be looked at without such alteration (which in a lit room is happening irrespective of whether anyone is lookin).

3) Yes, that's the gist of how Newton viewed the universe. God's perfect clockwork creation. Too bad Heisenberg had to go and ruin in with that quantum uncertainty stuff that spoils the premise of your statement.

Answer 2

1) Photons of high energy like X-rays, behave as partical n photons of low energy like photons of visible region n IR behave as wave, so the expriment of Young is correct n Einstein's explanation is also correct.
2) The Heisenbergs uncertanity principle is effective on particals with v.small masses, such as electron, photons, protons, etc, so there is some uncertanity in massive bodies, but it is too small that nearly unmeasurable.
3) Yes, there is difference in b/w measurable n predictable quantities.

Answer 3

I like your textbook if that's where these questions came from. Or your prof if that's where they originated. These are really insightful. They make you look at the physics rather than memorize a bunch of equations without understanding the physics.