Commutator with gradient operator (nabla)

In summary, the commutator with gradient operator (nabla) is a mathematical operation used in vector calculus to calculate the change in a vector field with respect to its position. To calculate it, you take the gradient of the first vector and then take the dot product of that with the second vector, then subtract the dot product of the second vector with the gradient of the first vector. This operation has physical significance in many areas of physics, including electromagnetism and fluid dynamics, and can be used in three-dimensional space. It also has many real-world applications in fields such as physics, engineering, and other scientific fields.
  • #1
Replusz
142
14
TL;DR Summary
I don't understand what is happening from line 1 to 2.
It looks like he is taking out the derivative operator from the commutator.
Which I presume is not allowed?

Or he could be using product rule on commutator and then neglecting the 2nd part (maybe because it is trivially 0? I don't see why it is 0 tho: it is [nabla, Pi]Phi )
1586598000065.png
 
Physics news on Phys.org
  • #2
I think you can take the gradient outside because ##\pi(t,\vec{x})## doesn't depend on ##\vec{x}'##
 
  • Like
Likes vanhees71 and Replusz
  • #3
Gaussian97 said:
I think you can take the gradient outside because ##\pi(t,\vec{x})## doesn't depend on ##\vec{x}'##

And the Nabla acts on x' right?
Then it makes sense.
 
  • #4
Yes, normally one makes the distinction and calls it ##\nabla'## or ##\nabla_{\vec{x}'}##, but in this case, you simply must deduce it from the context. Look that they change
$$\nabla_i = \frac{\partial}{\partial x' ^i}$$
 
  • Like
  • Informative
Likes vanhees71 and Replusz
  • #5
Nice!
Thanks so much and all the best! :)
 

1. What is a commutator with gradient operator (nabla)?

A commutator with gradient operator (nabla) is a mathematical operation that calculates the difference between two quantities, where one of the quantities is a gradient operator (nabla). It is commonly used in vector calculus and is denoted as [∇, A], where A is the quantity being operated on.

2. How is a commutator with gradient operator (nabla) calculated?

To calculate a commutator with gradient operator (nabla), the gradient operator (nabla) is applied to the first quantity, and then the second quantity is subtracted from the result. This can also be written as ∇A - A∇. The resulting quantity is known as the commutator.

3. What is the significance of the commutator with gradient operator (nabla)?

The commutator with gradient operator (nabla) is significant because it allows us to calculate the difference between two quantities in vector calculus. It is also used in quantum mechanics to determine the uncertainty between two observables.

4. Can the commutator with gradient operator (nabla) be applied to any type of quantity?

Yes, the commutator with gradient operator (nabla) can be applied to any type of quantity, as long as it is a differentiable function. This means that it can be used with scalars, vectors, and tensors.

5. What are some real-world applications of the commutator with gradient operator (nabla)?

The commutator with gradient operator (nabla) has many applications in physics, engineering, and mathematics. It is used in fluid dynamics to calculate the rate of change of a fluid's properties, in electromagnetism to calculate the electric and magnetic fields, and in quantum mechanics to calculate the commutation relations between observables.

Similar threads

  • Quantum Physics
Replies
7
Views
531
  • Quantum Physics
Replies
2
Views
810
  • Quantum Physics
2
Replies
56
Views
3K
Replies
1
Views
946
  • Quantum Physics
Replies
17
Views
1K
  • Quantum Physics
Replies
5
Views
736
  • Quantum Physics
Replies
2
Views
627
Replies
17
Views
765
Replies
9
Views
498
Replies
7
Views
3K
Back
Top