# A simple question about uncertainty principle

1. Dec 22, 2008

### mskaroly

Why is uncertainty principle said to be a very strange thing?

"Heisenberg uncertainty principle states that locating a particle in a small region of space makes the momentum of the particle uncertain; and conversely, that measuring the momentum of a particle precisely makes the position uncertain."

Isnt it just a limitation of our measuring techniques?

I remember reading some scientist exclaiming that one who is not shocked by this principle has not understood it. But I am not at all shocked. Can anyone please help?

2. Dec 22, 2008

### ZapperZ

Staff Emeritus
Please do a search in this forum. There are already numerous explanation given (and examples) on why this has nothing to do with measurement/experimental accuracy out of a single measurement.

Zz.

3. Dec 22, 2008

### DrChinese

Welcome to PhysicsForums, mskaroly!

The answer to the question is NO. Our measurement techniques are easily capable of discerning this. A 100% certain measurement of an observable always leads to complete uncertainty for all non-commuting observables, but not for commuting observables. There is nothing classical about this.

The reason I replied is that ZapperZ is a Forum mentor (and administrator), and his answer (to search other similar threads) should be considered on good authority. Since this has been covered many times before, it makes sense to review what is already written and then follow-up if you still do not understand a particular point. I hope this helps!

4. Dec 22, 2008

### edguy99

Consider this problem: you have an electron point charge and a proton point charge with both fixed in an exact point in space at an exact time. Say you put them 100 picometers apart and try and figure out what will happen in the next 100 attoseconds using coulomb forces.

If you plot it every 1 attosecond it probably looks pretty good and the electron ends up on the other side of the proton. But if you want more accuracy, you decide to calculate the position every 1/10th of an atto second. Instead of getting more accurate regarding the electrons position after 100 attoseconds, it actually is worse. Since the electron landed very close to the proton in one of these 1/10th attosecond time slots, it actually is thrown farther away. This problem does not go away. The more accurate the time slots the more erratic the electron becomes as it passes the proton.

This is an example of the problem of trying to measure position and velocity of point charges that attract each other to a high degree of accuracy when they are very close.

I believe one of the consequences of the uncertainty principle for point charges is that an electron and proton can never be truly at rest with respect to each other.