Green's Function Homework: Infinite at Infinity?

In summary, the conversation discusses the behavior of the Green's function for the Laplace operator, which is known to be badly behaved at infinity. The speaker is trying to prove that the integral of the Green's function diverges for d=1,2,3 and is seeking help in understanding what happens for d>4. They mention that the 1D Green's function is given by -|x-y|/2 and that for d>2, it is proportional to |x-y|^{-(d-2)}. The speaker is stuck on how to show that the integral diverges for d>4.
  • #1
the_kid
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Homework Statement



I'm trying to show that the Green's function for the Laplace operator $-\nabla^2$ is badly behaved at infinity. I.e.

$$\int d^dx|G(x,y)|^2=\infty$$ for d=1,2,3. What happens when d>4?

I know the 1D Green's function is given by

$$G(x,y)=-\frac{|x-y|}{2}$$

Homework Equations


The Attempt at a Solution



$$G(x,y)\propto|x-y|^{-(d-2)}$$ for d>2

I need to be able to show that the above integral diverges...
 
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  • #2
$$\int d^dx|G(x,y)|^2=\int d^dx|x-y|^{-2(d-2)}$$This is where I'm stuck. I can't see how to show the integral diverges for d>4. Any help is appreciated.
 

1. What is the purpose of studying Green's Functions?

Green's Functions are mathematical tools used in physics and engineering to solve differential equations. They allow us to find solutions to complicated problems by breaking them down into simpler components.

2. What does it mean for a Green's Function to be "infinite at infinity"?

A Green's Function is said to be "infinite at infinity" if its value approaches infinity as the distance from the source point increases without bound. In other words, the function has an unbounded response at infinitely large distances.

3. How do you determine the Green's Function for a specific problem?

The Green's Function for a specific problem is determined by the differential equation that needs to be solved. It involves finding a function that satisfies the differential equation and certain boundary conditions. This can be done analytically or numerically.

4. What is the significance of "infinite at infinity" in Green's Function Homework?

The concept of "infinite at infinity" is important in Green's Function Homework because it allows us to find solutions to problems that have unbounded responses at infinitely large distances. This is common in many physical systems, such as electromagnetic fields and heat transfer.

5. Can Green's Functions be applied to real-world problems?

Yes, Green's Functions have many practical applications in physics and engineering. They are used to solve a wide range of problems, including heat transfer, electromagnetism, fluid dynamics, and quantum mechanics. They are also used in signal processing, image reconstruction, and many other fields.

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