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### Uncertainty in Position and Uncertainty in Momentum

Posted: Sat Nov 02, 2019 11:08 pm
I understand why uncertainty in momentum would lead to uncertainty in position (because we don't know which pathway electrons take after being perturbed by a photon). But why is it that the more precise we know about the position, the less we know about the momentum at that instant?

### Re: Uncertainty in Position and Uncertainty in Momentum

Posted: Sat Nov 02, 2019 11:18 pm
It is because these two characteristics are inversely proportional to each other. Since both are greater than or equal to the constant, h/4pi, if either the uncertainty in position or momentum increases, the other must decrease. This maintains the rule that the product of both these variables is greater than or equal to the constant, h/4pi.

### Re: Uncertainty in Position and Uncertainty in Momentum

Posted: Sun Nov 03, 2019 2:20 am
I have the same issue understanding this concept. I understand how it works mathematically using the Heisenberg indeterminacy equation, but I do not quite understand it conceptually. If there is more uncertainty regarding the position, shouldn't there be more uncertainty about the momentum as well?

### Re: Uncertainty in Position and Uncertainty in Momentum

Posted: Sun Nov 03, 2019 9:13 pm
Petrina Kan 3C wrote:I have the same issue understanding this concept. I understand how it works mathematically using the Heisenberg indeterminacy equation, but I do not quite understand it conceptually. If there is more uncertainty regarding the position, shouldn't there be more uncertainty about the momentum as well?

I'm having the same issue as you too. Mathematically, I definitely see the inverse relationship between the two. But I don't understand it like I did with the example Dr Lavelle gave about an electron going through two light detectors.

### Re: Uncertainty in Position and Uncertainty in Momentum

Posted: Tue Nov 05, 2019 10:06 pm
From what I understood in lecture, it's difficult to experimentally know/record both the momentum and position experimentally. It's possible to measure the position of an electron through the light detectors, but this would veer it off course because of the photons that hit it. From this position, you can calculate the momentum. However, if you try to measure the momentum experimentally, you cannot be sure whether the electron veered off course in the process. Since you can't experimentally record both at the same time, the other must be calculated making it an uncertain value. When one value is more precise, the other is less precise, which is why it's inversely proportionate.