Explaining the Uncertainty Principle

In summary, the Uncertainty Principle states that it is impossible to know both the velocity and position of a particle with complete certainty. This is due to the fact that to observe the particle, we must disturb it in some way, which affects the accuracy of our measurements. However, this principle applies even without any disturbance, and is more related to the fundamental nature of reality and the limitations of our knowledge. While some explanations suggest that the observation itself causes the disturbance, recent studies have shown that this is not always the case. Despite its limitations, the Uncertainty Principle is a useful tool for understanding the behavior of subatomic particles.
  • #1
vizzard
4
0
Could someone explain the Uncertianty Principle?
Please and Thank you!
 
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  • #2
Heisenberg's uncertainty principle states that we can never be completely certain of both the velocity and position of a particle, as to observe it, we must affect the particle (usually by shining photons onto it).
 
  • #3
vizzard said:
Could someone explain the Uncertianty Principle?
Please and Thank you!

It would probably make sense if you check out wikipedia and the PhysicsForums faqs on the subject:

Uncertainty Principle

After, you might find it beneficial to ask some specific questions.

Please note that the principle has nothing directly to do with the fact that to observe a particle, you must disturb it. (The principle applies even when there is no disturbance.) It has more to do with the nature of reality and/or limits to knowledge.
 
  • #4
If we can affect the particle by shining photons onto it, then can we affect it in a predictable/measurable way?
 
  • #5
Belzy said:
If we can affect the particle by shining photons onto it, then can we affect it in a predictable/measurable way?

Note that this has nothing to do with the HUP. The HUP isn't a "measurement technique" limitation.

Zz.
 
  • #6
I got my definition from 'A brief history of time', which I have just got out again to see if I remembered it correctly. It clearly states here, that it is only due to the fundamental uncertainty created from bouncing photons off the particle. Are you saying it's wrong, or that it is not giving the full picture?

I know that in quantum theory, we have to assume that an electron/other particle is in all states until it is observed (like schrodinger's cat), but I assumed that the uncertainty principle was only a restriction on the measuring of that particle.
 
  • #7
jamesb-uk said:
I got my definition from 'A brief history of time', which I have just got out again to see if I remembered it correctly. It clearly states here, that it is only due to the fundamental uncertainty created from bouncing photons off the particle. Are you saying it's wrong, or that it is not giving the full picture?

I know that in quantum theory, we have to assume that an electron/other particle is in all states until it is observed (like schrodinger's cat), but I assumed that the uncertainty principle was only a restriction on the measuring of that particle.

It is wrong, this is a leftover explanation (from the early days of QM) that is thrown around as a simple way to avoid further explanation. But still wrong. There are several ways to see this.

First, observing particle spin - for example - does not affect other commuting attributes (say momentum). So obviously the observation is not the issue, it is only whether the observables are non-commuting.

Second, and more recently studied in detail (last 20+ years): entangled particles obey the HUP. Even at distances of 10 km, non-commuting observations on a pair (say vertical polatization for Alice and diagonal polarization for Bob) obey the HUP. So again, the issue is not the observation itself disturbing the particle.

And keep in mind, there is no prohibition against measuring non-commuting attributes to any degree of accuracy. The issue is that the values you obtain are NOT indicative of the particle at any single point in time. It is best to simply say that the value you get is indicative of the particle at that time. If you make a second, identical measurement, you will get the same value. If you make a non-commuting measurement, and then go back to the first again, all bets are off.

-DrC
 
  • #8
Well it is wrong, but it's still a useful way of thinking about the HUP in practice. When you observe a particle, you collapse the state of that particle to an eigenstate of the observable which erases the information you have of non-compatible (commuting) observables. When you go to measure the momentum, after you measured where the particle is, you get a different value than before you measured where the particle is.

In practice this is sort of a "disturbance" to the particle. In reality it's a disturbance to the wavefunction, but since wavefunctions are very abstract, it's sometimes useful to think of it as a disturbance to the particle. I suppose this view may not work for entangled pairs but that doesn't diminish the usefulness of this way of thinking.
 
  • #9
I am sorry you have to forgive my limited understanding of Uncertianty Principle.

The way I understand it is that if someone watches a subatomic particle or a piece of light as it passes though slits ( The 2 Slit experiment ) the particle behaves like a bullet fired from gun going from one to the other. However if no one is watching it then can behave in all manner of ways, like a wave going through both slits at the same time.

Now is this only our perception of the particle as it passes though or does our perception of the particle make it this way.
 

FAQ: Explaining the Uncertainty Principle

What is the Uncertainty Principle?

The Uncertainty Principle, also known as Heisenberg's Uncertainty Principle, is a fundamental concept in quantum mechanics that states that the position and momentum of a particle cannot be simultaneously measured with perfect accuracy. This means that the more precisely one quantity is known, the less precisely the other can be known.

Who discovered the Uncertainty Principle?

The Uncertainty Principle was first proposed by German physicist Werner Heisenberg in 1927. Heisenberg's work on quantum mechanics revolutionized the field of physics and earned him a Nobel Prize in 1932.

How does the Uncertainty Principle affect our understanding of the physical world?

The Uncertainty Principle challenges our classical understanding of the physical world by showing that there is a fundamental limit to our ability to measure and predict the behavior of particles. It also highlights the probabilistic nature of quantum mechanics, where the behavior of particles is described by probabilities rather than definite values.

Can the Uncertainty Principle be observed in everyday life?

While the Uncertainty Principle is a fundamental concept in quantum mechanics, its effects are only observable at the microscopic level. In our everyday lives, the uncertainty is too small to be noticed. However, technologies such as scanning tunneling microscopes and electron microscopes have allowed us to directly observe the effects of the Uncertainty Principle.

How does the Uncertainty Principle relate to other principles in physics?

The Uncertainty Principle is closely related to other principles in physics, such as the principle of complementarity and the wave-particle duality. It also has applications in other fields, such as information theory and cryptography. Its implications have also been explored in philosophy and other areas of study.

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