Quantum Physcics,...Heisenberg Uncertainty Principle

[deltro300111]

I recently had a discussion with a friend about quantum physics, he sorta ticked me off (I didn't show it) with his seemingly infinite knowledge of the subject, I later decided to do some reasearch of my own and forund this website...

http://www.jracademy.com/~jtucek/science/what.html

It helped quite a bit, but can someone explain to me the Heisenberg Uncertainty Principle there is a short explaniation up on the page but that didn't help all that much...

can someone please explain?

- so like, you can't really prove that you have the correct location, velocity, unless you can see it in it's normal state, which you can't?

[Dronak]

I think the description on the terms page is basically right. There are certain pairs of properites, position and velocity is the most common one, where the more accurately and precisely you measure one of them, the less accurately and precisely you know the other one. You can know something about the second parameter, but the error on the measured value gets larger the smaller you make the error on the first parameter. It's kind of like if you have a well known velocity, say because you start a particle moving with that velocity, you can't tell its position because it sort of fuzzes out and could theoretically be in a very large space. Similarly, if you confine a particle to lie within a certain space, it will be moving around pretty randomly in it and you won't be able to tell what its velocity is. It's one of the strange things about the quantum world because obviously it doesn't work like in the normal, everyday world.

BTW, reading this reminded me about some books I have, basically updates on one original one, the Mr. Tompkins books by George Gamow. The newest one, The New World of Mr. Tompkins, is by George Gamow and Russel Stannard, the latter adding a few chapters on subjects Gamow didn't originally cover and updating the text a bit. It's a fun read if you're interested in this stuff because basically the main character has dreams about worlds where the physical constants are different. There are some equations, but I don't remember them being very complicated. For example, it starts with special relativity and the speed of light and demonstrates things like length contraction and time dilation by making the speed of light very small, small enough that you can easily approach it riding on a bicycle. It does cover some quantum stuff, too, I saw some of the uncertainty principle covered with billiards/snooker examples. It should help you understand things like this.

[GuidoHunter]

Well, in order to observe something's position, you'd have to bounce a piece of radiation off of it and let that radiation come back to a detector. It's like how you see a baseball: A photon of radiation in the form of light strikes the ball and reflects to the detector (your eye). The only problem is that radiation which can actually strike a subatomic particle has to be very high energy so that its wavelength isn't long enough to just pass right over it. Since the electron is so small, being struck by such a high-energy piece of radiation will actually move the electron, giving it velocity. I'm pretty sure you could calculate its velocity, but now that it's moving, it won't be in the same position when the radiation hits the detector to show where it was when it struck the electron (poor pronoun/antecedent use?).

Being able to measure position well, but not velocity, is a bit more complicated, and I'd have to study up a bit more on it.

Heisenberg's uncertainty principle is a fundamental law of quantum physics, and is EXTREMELY useful and important, even in discussion of the collapse of stars.

Haha, George Gamow... A fellow named Alpher and he wrote a paper, but they asked another guy by the name of Bethe to get in on it just so they could call it the Alpher-Bethe-Gamow paper (a pun on the first three letters of the Greek alphabet, alpha, beta, and gamma).

--Guido

http://andy.mikee385.com

[talisman]

Probably the most important conclusion of the Heisenber Uncertainty Principle is that the observer is an essential part of every experiment, and that by observing an experiment, the experiement changes.

[GuidoHunter]

Okay, position is definitely a quality of particles. Momentum is a quality of waves, whereas position is not. Electrons and other fundamental entities are both particles and waves. Particle detectors measure particle properties, and wave detectors detect wave properties, so it's impossible to precisely measure both at the same time.

Probably the most important conclusion of the Heisenber Uncertainty Principle is that the observer is an essential part of every experiment, and that by observing an experiment, the experiement changes.

The uncertainty principle supports that theory, but it was more Born who came up with the idea, before Heisenberg's time.

--Guido

http://andy.mikee385.com

[talisman]

Very true, guido. What we need a thread about is the mindblowingness of the double-slit experiment. Talk about the uncertainty principle.

[Xaimus]

Momentum is dependent on mass. It can not be a property of a wave.

The uncertainty principle states that one can not precisely measure both the position and momentum of a particle.

The result of the observation of momentum becomes more precise when the observation of position is less precise; one could not take a still image of a car and magically spout out the momentum of the car at the time the image was taken.

Similarly, one can not precisely measure the position of a particle if its momentum is well defined; it would be similar to try to determine the exact location of a speeding car when looking at a poorly made video recording of the incident.

[/beatingdeadhorse]

[zajac]

i'm polish.... i know nothing of the matter.... lol

[GuidoHunter]

No, momentum for a wave can be determined. It's not necessarily measured by the usual mass times velocity equation, but it is a quality of waves.

AUGH, the double-slit experiment! How confounding it is, moreso than what drives the heart of man!

But seriously, if you send particles through individually, you get the same pattern as if you sent a bunch through at a time?! How in the hell?

--Guido

http://andy.mikee385.com

[talisman]

Exactly.

Correct me if I'm wrong, but isn't this the mathematical expression of the Uncertainty Principle?

pq-qp=h/(2*pi*i)

where p and q are the matrix representation of momentum and position and h is planck's constant. That's all from memory though. I'd have to dig up In Search of Schroedinger's Cat to check.

[deltro300111]

thank all of you for the very useful information, hopefully I can comeback with another topic, and we can cure cancer XD XD XD

btw- posting from an internet cafe in new oreleans

[GuidoHunter]

Wait, you read In Search of Schrodinger's Cat? Because that's where most of my knowledge came from, too. It's such a great book.

--Guido

http://andy.mikee385.com

[talisman]

Yeah, most of my quantum physics info comes from there as well.

[Xaimus]

No, momentum for a wave can be determined. It's not necessarily measured by the usual mass times velocity equation, but it is a quality of waves.

Mm, okay. I learned something new today.

[deltro300111]

t3h welcome corr Xaimus