Quantum Mechanics

[Drotar]

A virtual particle , if I may, is a particle (Jet Black is it a sub-atomic?) that is said to spontaneously appear anddisappear without cause. From my limited knowledge, I can say that it comes from energy that is "borrowed". I don't know too much about this, but it's a result of the Heisenberg's Uncertainty Principle.

In classical mechanics, you are able to calulate the speed, direction, momentum, mass, everything of an object. I n QM, you can only measure one aspect PRECISELY, and not the other. Or you can measure both, and apply probabilities to both. The more certain you become of something's speed and direction, the less certain you become of its position, and vice versa.

I still don't know how, but for some reason, partly by means of this principle, virtual particles "pop" into existence, and then cease being VERY quickly.


We can be certain of their existence because of the Casmir Effect, for one. The attraction of two plates in a vacuum, if I'm not mistaken, is caused by virtual particles.

And, as Lucaspa added, in a particle accelator, you can sustain their short life cycle and longevity by providing energy therein.

That was probably full of errors and so I'll just wait for Jet Black or Lucaspa to correct me. TTYL Jesus lvoes you!

 

[vajradhara]

hey Drotar,

here's a website that has a good catalog of stuff that you can buy that's related to QM.

http://members.aol.com/jimb3d/quantum.html

 

[Jet Black]

A virtual particle , if I may, is a particle (Jet Black is it a sub-atomic?) that is said to spontaneously appear anddisappear without cause. From my limited knowledge, I can say that it comes from energy that is "borrowed". I don't know too much about this, but it's a result of the Heisenberg's Uncertainty Principle.

indeed they are subatomic. a good example of virtual particles is the electron positron pair, since when they pop up, they still obey all the rules like lepton number and charge conservation etc.

In classical mechanics, you are able to calulate the speed, direction, momentum, mass, everything of an object. I n QM, you can only measure one aspect PRECISELY, and not the other. Or you can measure both, and apply probabilities to both. The more certain you become of something's speed and direction, the less certain you become of its position, and vice versa.

there are basically pairs of measurements which cannot be measuerd simultaneously, for example (momentum,position), (energy,time)

I still don't know how, but for some reason, partly by means of this principle, virtual particles "pop" into existence, and then cease being VERY quickly.

well this is just the simple rule that "allows" it. A more thorough explanation comes from quantum electrodynamics and field theories.

We can be certain of their existence because of the Casmir Effect, for one. The attraction of two plates in a vacuum, if I'm not mistaken, is caused by virtual particles.

And, as Lucaspa added, in a particle accelator, you can sustain their short life cycle and longevity by providing energy therein.

That was probably full of errors and so I'll just wait for Jet Black or Lucaspa to correct me. TTYL Jesus lvoes you!

looks good

 

[bagfullofsnakes]

I remember reading where Feynman had said something to the effect of, "There's no sense in asking why QM is that way, it just is that way."

I've probably butchered it, but that was the gist.

 

[bagfullofsnakes]

Interesting article in Nature...

http://www.nature.com/nsu/030901/030901-8.html

Physicists have watched biological molecules become waves in a dramatic demonstration of the effects of quantum mechanics.

...physicist Roger Penrose of the University of Oxford, UK, and psychologist Stuart Hameroff of the University of Arizona in Tucson have proposed that consciousness might arise from wave-like quantum-mechanical effects involving protein filaments called microtubules in nerve cells.

 

[BInC]

If I may, I'd like to hop in and give a kind of explanation why you can't know position and momentum of electrons (basically the reason for the uncertainty principle). In school I had to do a reports on the Heisenberg Uncertainty Principle. Here is how I demonstrated it:

I blindfolded a volunteer, gave him a ruler, and put a ball on the floor in front of him. I had him use the ruler to try to find the ball's position and momentum. Of course, he couldn't do it because ever time he hit the ball with the ruler, it would roll to a different place.

The way that we observe things is by bouncing photons (or electrons, with an electron microscope) off of them and observing the reaction. That is how we make all observations: we look at the reaction. This is just fine when trying to find the position and momentum of a large object, like a car. However, when you hit a subatomic particle with another, you will cahnge the position and momentum of the particle you are trying to observe. Therefore, you can't tell both it's position and it's momentum.

This was a 7th grade project, so I am open to correction if I missinterpreted part of it. However, it seems to me that this theory relies on the fact that we can only observe reactions. That is what disturbs me. Here is why: God knows everything about everything. That is a fact. So, wouldn't He then know the position and momentum of a sub-atomic particle? Quantum mechanics relies on different possibilities. If God knows the answer, then really there is only one answer. This goes agaisnt all I understand of quantum mechanics.

If I am interpreting the situation right, it seems to me that scientists have gotten lazy. We have run into a problem we cannot solve, so we just tell everyone that there is no possible way to solve it. From my understanding, the particles do have a definite position and momentum, and don't exist in two places at the same time (somthing I read in another article, I think at hyperphysics.com). I think just because we don't know it, doesn't mean it can't be known. Kind of like how we can't see God, so some people just assume He can't exist.

 

[BInC]

Just thought I'd clarify my earlier post. I am not trying to disprove quantum mechanics. I want to understand how this all works. I want someone to prove me wrong.

 

[David Gould]

Scientists have not 'gotten lazy'. They have conducted - and still are conducting - many experiments involving quantum mechancial behaviour.

At the moment, all the evidence points to the fact that it is literally impossible to know the position and momentum of a particle.

And it has nothing to do with our measuring tools. We can measure where a particle is to 100 per cent accuracy. But at the same time that means that its momentum has an infinite possible range. We can measure a particle's momentum with 100 per cent accuracy. But at the same time that means its position has an infinite possible range.

It really is that weird.

 

[Jet Black]

Just thought I'd clarify my earlier post. I am not trying to disprove quantum mechanics. I want to understand how this all works. I want someone to prove me wrong.

your experiment is a very basic one, but it is a classical experiment though. It does have some parallels with trying to find out the location of a particle and giving it a kick. However, it is also possible to carry out more careful structured quantum experiments that show indeterminacy without a doubt... and when one looks at the mathematics of the situation, it is "built into the universe" so to speak. Indeterminacy is not a simple experimental problem that can be overcome with expensive equipment.

 

[ThePhoenix]

If I may, I'd like to hop in and give a kind of explanation why you can't know position and momentum of electrons (basically the reason for the uncertainty principle). In school I had to do a reports on the Heisenberg Uncertainty Principle. Here is how I demonstrated it:

I blindfolded a volunteer, gave him a ruler, and put a ball on the floor in front of him. I had him use the ruler to try to find the ball's position and momentum. Of course, he couldn't do it because ever time he hit the ball with the ruler, it would roll to a different place.

The way that we observe things is by bouncing photons (or electrons, with an electron microscope) off of them and observing the reaction. That is how we make all observations: we look at the reaction. This is just fine when trying to find the position and momentum of a large object, like a car. However, when you hit a subatomic particle with another, you will cahnge the position and momentum of the particle you are trying to observe. Therefore, you can't tell both it's position and it's momentum.

This was a 7th grade project, so I am open to correction if I missinterpreted part of it. However, it seems to me that this theory relies on the fact that we can only observe reactions. That is what disturbs me. Here is why: God knows everything about everything. That is a fact. So, wouldn't He then know the position and momentum of a sub-atomic particle? Quantum mechanics relies on different possibilities. If God knows the answer, then really there is only one answer. This goes agaisnt all I understand of quantum mechanics.

If I am interpreting the situation right, it seems to me that scientists have gotten lazy. We have run into a problem we cannot solve, so we just tell everyone that there is no possible way to solve it. From my understanding, the particles do have a definite position and momentum, and don't exist in two places at the same time (somthing I read in another article, I think at hyperphysics.com). I think just because we don't know it, doesn't mean it can't be known. Kind of like how we can't see God, so some people just assume He can't exist.

So, basically, the hidden variables theorum? That's actually my favorite one, but it doesn't suggest that better equipment could overcome the problem.

 

[Jet Black]

So, basically, the hidden variables theorum? That's actually my favorite one, but it doesn't suggest that better equipment could overcome the problem.

It's not one I particularly like. My personal opinion is that our model is still missing something, and is still very incomplete (well it is!)... and I think that the unification of GR and QM will answer an awful lot of questions. I hope it happens in my lifetime, heck, I hope it is me that does it

 

[David Gould]

I was going to write a post about how I thought that the universe was simply weird but then I thought, 'Weird compared to what?'

The only thing that the universe ends up being weird in comparison to is our own limited conception of what the universe is like.

The example I was thinking of was objects gaining mass as they got faster. That seems pretty weird at first glance.

But it is only weird in comparison to our everyday experiences where we cannot possibly detect such mass changes at the comparatively low speeds that the things we deal with travel at.

Sorry - a bit off topic but I was caught in the middle of posting something that I then found I disagreed with ...

 

[Jet Black]

it is an important point that though... our "view" of the universe is very limited in its scope. the things we see are all classical objects in pretty much flat space, so when we look at QM or GR, then things look very odd and not at all intuitive to us. the only way to understand them properly is to look at the maths, which, regardless of how wierd things look, is always nice and logical.

 

[vajradhara]

Namaste JB,

Hawking was talking about that very thing, a GT of unification.. what did he call it... M Theory or something like that...

He, too, was hopeful that we could have an M Theory that unified GR and QM. IIRC, he though that if there was a unified theory that may have some implication on Free Will, since we could predict what anyone would do..

i'm sure i've not remembered that correctly...

in any event, my question to you is along those same lines... do you think that a unified M Theory would effect free will?