## Why can't you define the exact position of an electron again?

nopistons93 - 25-7-2009 at 12:42

I know in P-chem we learned why Schrodinger's equation can't define where an e- is exactly, but I have recently forgot the exact reason.

From what I remember, as you slow the velocity down to pinpoint where it is at, the region in which it could lie grows to infinity. I just can't completely remember!

Vogelzang - 25-7-2009 at 15:26

Heisenberg's principle of uncertainty. I was wondering Heisenberg's philosophy conflicts with the results of Compton's experiment.
ammonium isocyanate - 25-7-2009 at 15:47

Vogelzang is right. Heisenberg's uncertainty principal says that you can know either the motion or location of an electron, but never both at the same time. This is because any attempt to measure these properties will change one in an unpredictable way.
JustMe - 25-7-2009 at 17:25

While there are all kinds of quantum mechanical explanations (wave/particle duality stuff) - an intuitive (although technically inaccurate) way to visualize it is thus...

Imagine you locate an electron by bouncing an energetic photon off of it. Well, as soon as you do that you move the electron, i.e. you've changed its location, so your measurement is wrong.

I know, I know, this is crazy oversimplified and that billiard ball arguments are inaccurate for "wavicles" - still anything that helps is good.

As an aside, one of my favorite questions to demonstrate electron behavior is to draw a representation of a p-oribital and explain that this is a probability map of electron location in a p-orbital and point out that accordingly, the electron in said orbital is NEVER found BETWEEN each lobe. So, asks I, how does it get from one side to the other? I then go into explaining by drawing a sine wave and that the intensity of the wave is zero at the nodal point... same thing for the electron, the intensity (likelihood of location) is zero at the nodal plane. Ah... such "fun" trying to explain the intangible in tangible terms.

Just having fun with this.

bfesser - 25-7-2009 at 18:45

And that's about the point where 'normal' people would start to bleed out the ears.
JohnWW - 25-7-2009 at 20:18

That is correct basically. The Heisenberg Uncertainty Principle sets a minimum size limit on measurements of quantum-mechanical properties. It was derived from the DeBroglie hypothesis and wave-particle duality. For more info about it, see. in the first instance, http://en.wikipedia.org/wiki/Uncertainty_principle .
Other web references include:
http://www.aip.org/history/heisenberg/
http://scienceworld.wolfram.com/physics/UncertaintyPrinciple...

However, Einstein was never able to grasp quantum mechanics, as first formulated by Planck. Textbook references on quantum mechanics, including the Heisenberg Uncertainty Principle, are included for example in the "Great Science Textbooks DVD Series" available as torrent downloads (Google for the .torrent files), and in the scanned classic textbooks on the site http://lib.org.by .

[Edited on 26-7-09 by JohnWW]

JustMe - 26-7-2009 at 13:57

 Quote: Originally posted by bfesser And that's about the point where 'normal' people would start to bleed out the ears.

ROTFLMAO - and isn't it fun to watch!

> Why can't you define the exact position of an electron?

You can, you can. But you cannot say when it will be there.

Globey - 27-7-2009 at 10:38

 Quote: Originally posted by Paddywhacker > Why can't you define the exact position of an electron? You can, you can. But you cannot say when it will be there.

Are you
*certain*?!

Globey - 27-7-2009 at 10:41

 Quote: Originally posted by ammonium isocyanate Vogelzang is right. Heisenberg's uncertainty principal says that you can know either the motion or location of an electron, but never both at the same time. This is because any attempt to measure these properties will change one in an unpredictable way.

If I didn't believe in god before quantum, I most certainly do now. In the future, when quantum is every day/taken for granted, we may not have the luxury of deciding to have faith in god.