Quantum mechanics flummoxes physicists again

Nature ^ | 7/22/10 | Jon Cartwright

[LibWhacker]

A fresh take on a classic experiment makes no progress in unifying quantum mechanics and relativity.

If you ever want to get your head around the riddle that is quantum mechanics, look no further than the double-slit experiment. This shows, with perfect simplicity, how just watching a wave or a particle can change its behaviour. The idea is so unpalatable to physicists that they have spent decades trying to find new ways to test it. The latest such attempt, by physicists in Europe and Canada, used a three-slit version — but quantum mechanics won out again.

In the standard double-slit experiment, a wide screen is shielded from an electron gun by a wall containing two separated slits. If the electron gun is fired with one slit closed, a mound of electrons forms on the screen beyond the open slit, trailing off to the left and right — the sort of behaviour expected for particles. If the gun is fired when both slits are open, however, electrons stack along the screen in comb-like divisions. This illustrates the electrons interfering with each other — the hallmark of wave behaviour.

[Jack Hydrazine]

Double slit experiment.
http://www.youtube.com/watch?v=DfPeprQ7oGc

[Jack Hydrazine]

It’s as if the electrons know when they’re being watched and decide to behave as particles again. According to Nobel laureate Richard Feynman, the phenomenon “has in it the heart of quantum mechanics. In reality, it contains the only mystery”.

[kbennkc]

Acting differently when under observation shows flawed character. I am disappointed.

[JPG]

In this case, truth is stranger than fiction.

[HerrBlucher]

Well it makes sense, electrons are very negative in private.

[datura]

During my college years the more physics I learned (solid state physics was my major), the more obvious it became that God will never allow humans to understand it all.

[kbennkc]

the more obvious it became that God will never allow humans to understand it all.

Talk about God's sense of humor, I am convinced he just made this stuff up.

[Erasmus]

This illustrates the electrons interfering with each other — the hallmark of wave behaviour.

It's a little stranger than that. Even if you reduce the electron flux to the point that there is never more than one electron on the path from the source to the target at a time, you still get wave formation at the target in the case of multiple slits.

[Mere Survival]

It’s neither a wave nor a particle. It’s a wavarticle.

Problem solved.

[fhayek]

Yeah, this is weird. So is “spooky action at a distance”. Amoebas are closer to humans than we are to God.

[USMCPOP]

I leave electrons alone and let them run around the wiring. Last time I poked in an outlet with a screwdriver to see if they were there, they got really angry.

[SirJohnBarleycorn]

God will never allow humans to understand it all

And isn't it interesting that the first word of God was "let there be light."

Light being the most obvious manifestation to us humans of created energy in the form of a wave/particle duality.

[Cboldt]

-- the more physics I learned (solid state physics was my major), the more obvious it became that God will never allow humans to understand it all. --

I teach my kids some of the more basic stuff - no quantum yet, their math isn't ready, but I do tell them the scale (proton the size of a marble, electron is two miles away. What we think is solid, isn't. Not by a long shot. And then, to the grownups, "the closer we look, the more it disappears." Yet, here we are, quite real!

[wendy1946]

In the standard double-slit experiment, a wide screen is shielded from an electron gun by a wall containing two separated slits. If the electron gun is fired with one slit closed, a mound of electrons forms on the screen beyond the open slit, trailing off to the left and right — the sort of behaviour expected for particles. If the gun is fired when both slits are open, however, electrons stack along the screen in comb-like divisions. This illustrates the electrons interfering with each other — the hallmark of wave behaviour.

When you see evidence of both waves and particles, the simplest explanation there could be is that both waves and particles are present. Similarly if you're on safari on the Serengeti and you see lion dung and elephant dung on the ground, you assume both lions and elephants have been around; you do NOT assume that some magical creature with properties of goth elephants and lions has been around.

[AustinBill]

It’s only a mystery to those who stubbornly cling to a 19th century view that mind must somehow be an emergent property of matter. What quantum mechanics has been telling us, in excruciating detail, for over a century is that what we call physical reality is an emergent property of consciousness.

[Skepolitic]

Well it makes sense, electrons are very negative in private.

But the most recent experiment used protons, not electrons.

[VRW Conspirator]

Talk about God's sense of humor, I am convinced he just made this stuff up.

Ah Ha! Let us not forget about the flux capacitor.

[InMemoriam]

But the most recent experiment used protons, not electrons.

Are you positive?

[James C. Bennett]

The key to understanding the puzzle is in understanding to what level the “observer” is neutral.

That is, with sub-atomic particles, “watching” them is not the equivalent of a person watching a football game on a television, live. The observer in the latter case has practically no effect on the outcome of the game. However, in the former case, “observation” implies interference because there is no way of observing a sub-atomic particle without affecting the particle, directly. In other words, if you were to imagine the electron as a ball, in darkness, the very act of shining a hypothetical “light” to detect its reflection off of the “electron” has an effect on the electron itself. That is the scale we’re talking about here.