Uncertainity principle?

Question

According to Heisenberg's uncertainity principle it is impossible to measure, simultaneously, both the position and velocity (or momentum) of a microscopic particle with absoulute accuracy or certainity. Why can't we detect them simultaneously?

Answer 1

Its not just for a microscopic particle. Its for any particle. The effect is only large for very small particles though.

Think of it this way.

If you want to know precisely where a particle is you will have to use a very short wavelength of light to measure its position - you cannot be more accurate than the wavelength of the light. But very short wavelength light carries a lot of momentum. Each photon has momentum h/wavelength (h is Planks constant) - the shorter the wavelength the greater the momentum.

But if you hit the particle with a photon with a lot of momentum, it will accelerate it. As a result you will not be able to get an accurate measurement for its momentum. To measure its momentum accurately you would have to use a very long wavelength photon.

These are competing requirements.

The Hesienberg relationship quantifies these competing requirements by saying that the error in position multiplied by the error in momentum cannot be lower than hbar (Planks constant over 2 pi).

Planks constant is very tiny - around 6.62 e-34 Js. So it only matter for tiny particles.

Answer 2

It's all about particles and waves. What Heisenberg did was choose two properties position and momentum. Position is a particle property and momentum is actually a wave property in this case. So as something cannot be a wave and a particle at the same time you cannot measure position and momentum accurately at the same time. Really the naughty thing was to choose momentum as a wave property which causes a lot of confusion.

Answer 3

Let us assume that we wish to determine the coordinate of a microscopic particle at some point x with an accuracy of dx.

To “see” a microscopic particle we use a microscope using a light of very short wavelength. Shorter the wavelength greater is the resolving power.

In principle dx may be made as small as desired. For this it is enough dx ~ the wavelength of the light.

However if the wavelength is short, the momentum of the photon is great, because p= h/wavelength.

This momentum will be transmitted to the particle under observation. When the particle is ‘flicked’ its momentum changes by dp the order of magnitude of which is h/wavelength.

Thus as we decrease dx we increase dp.

But dx ~ wavelength. and dp = h/ wavelength. Or the product of dx and dp is h.

Answer 4

I had a professor explain it to me this way:
when electrons have a wave particle duality, so you can treat it like a particle and find its position, or you can treat it as a wave and find its speed. But you can't do both simultaneously.
But a highschool teacher said it was like photographing a train, you can either use a fast shutter speed and see the train clearly, as well as what's in the background, but you won't be able to judge speed, or you can use a slow shutter speed and find the speed by dividing the blur by the time. But you won't be able to see it clearly.
I've always kinda thought it was more along the lines of, quantum mechanics does NOT follow the laws of Newtonian physics, it's all a matter of probability and statistics. So we have to accept that there is no hard data, and Heisenberg just quanitified the extent to which we can know it.
I've seen the mathematical proof for this, and it did make a strange kind of sense, but it was years ago. Take physical chemistry or quantum mechanics in physics. They'll explain it to you.

Answer 5

No joke... but the answer is "because it is not possible"

It is just the way that the world it (it is also why atoms are able to exist) And if the world was not that way then we would not exist to answer the question.

The heisenberg uncertainty principle is a direct restult of quantum mechanicts (meaning that quantum mechanics does not assume that it is true, but rather it proves that it is true)

And basicly it is because particles are not little balls , they are waves (it is only occationaly that they act like little balls)

Answer 6

Because if you measure velocity you have an affect on position and visa versa. It is kinda like trying to see if the light in the refrigerator goes off by opening the door.

Answer 7

The actuality is inaccurate. The uncertainty concept holds for macroscopic international also. yet those uncertainties are so small that we gained't take exhilaration in it in spite of the dazzling obtainable instruments that we've.

Answer 8

i think that when you study something you interfere with it even in a miniscule way. Thus it is not 'as it was'