What is the definition of a momentum *measurement*?

In summary, the conversation discusses the process of measuring the momentum of a quantum system and the conditions that need to be met for the result to be considered a proper measurement. The speaker also mentions their lack of complete understanding and asks for recommended texts on the topic.
  • #1
pellman
684
5
Let's say I have made a measurement of some sort of a quantum system. That is, I have some macro/classical devices whose states have numbers associated with them, and their resulting states depend (in some way) on a quantum system. So I arrange the lab-plus-quantum system as desired and note down the numbers representing the states of the lab devices.

How do I then infer that I have measured the momentum of something?

I pose the question in terms of momentum rather than position because I suspect the position question may have a more straightforward answer. But I don't really know.

As far as the theory is concerned, I can speak of the momentum operator, and write the down what should be the state of the system (given the initial conditions to be arranged in the lab) in terms of momentum eigenstates, etc. But how do I connect this with a particular actual measurement?

I've read a few things over the years about quantum measurement theory but I have never seen a discussion of "Given an observable O, what conditions does the measuring apparatus have to satisfy for the result to be called a 'measurement of O'?"

Anyone know any texts which cover this?
 
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  • #2
I don't have a complete answer, but you may find this thread interesting.
 
  • #3
Thanks.

Fredrik said:
Some time ago, someone in this forum asked how you measure momentum. One of the answers said that if it's a charged particle, ...

I bet that someone was me. :biggrin:
 

FAQ: What is the definition of a momentum *measurement*?

What is momentum measurement?

Momentum measurement is the quantification of an object's motion. It is a measure of the amount of motion an object has, taking into account both its mass and velocity.

How is momentum measured?

Momentum is measured by multiplying an object's mass by its velocity. The units for momentum are kilogram meters per second (kg*m/s).

What is the importance of momentum measurement in physics?

Momentum measurement is important in physics because it allows us to understand and predict the behavior of moving objects. It is a fundamental concept in Newton's laws of motion and is crucial in studying the interactions between objects.

Is momentum measurement affected by the direction of motion?

Yes, momentum is a vector quantity, meaning it has both magnitude and direction. Therefore, the direction of motion does affect the momentum measurement.

Can momentum be negative?

Yes, momentum can be negative if an object is moving in the opposite direction of its defined positive direction. This simply indicates that the object has a negative velocity and is moving in the opposite direction.

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