Proving invariance of scalar product

In summary, the conversation discusses proving the invariance of the scalar product of two four-vectors under a Lorentz transformation. The speaker also mentions using a similar approach to prove the invariance of the scalar product of two vectors in the plane under rotation. They eventually figure out the correct transformation formulas and thank the other person for their help.
  • #1
Gabor
3
0
Hi everyone,

How would I go about proving that the scalar product of two four-vectors (A,B) is invariant under a Lorentz transformation?
 
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  • #2
As a warmup, you might try to prove that the scalar product of two vectors in the plane is invariant under a rotation.
 
  • #3
Okay... I could do that for 2 vectors (x1, x2) and (y1, y2) in a plane.

As for the four-vector proof, I'm not even sure I'm doing it right... My understanding is that I have to take the scalar product of the two vectors A and B. Then I have to apply Lorentz transform to both vectors and calculate the scalar product of A' and B'. For invariance, these two scalar products should be equal?
 
  • #4
yes.

How did you do the problem for the dot product of vectors in the plane?
 
  • #5
I figured out the proof for the four-vectors. Now I see the similarity between that and the rotation proof. Turns out I was using the wrong transformation formulas for my vectors and that's why things didn't add up. Thanks for your help!
 

1. What is the definition of invariance of scalar product?

Invariance of scalar product refers to the property of a scalar product, or dot product, remaining unchanged under certain transformations, such as rotations or translations.

2. Why is proving invariance of scalar product important?

Proving invariance of scalar product is important because it allows us to use the dot product as a tool for solving problems in various fields of science, such as physics, engineering, and mathematics. It also provides a deeper understanding of the geometric properties of vectors.

3. What are the common methods used to prove invariance of scalar product?

The most common methods used to prove invariance of scalar product are mathematical induction, direct proof, and proof by contradiction. These methods involve using algebraic manipulations and geometric reasoning to show that the scalar product remains unchanged under specific transformations.

4. Can invariance of scalar product be proven for all types of vector spaces?

Yes, invariance of scalar product can be proven for all types of vector spaces, including Euclidean spaces, inner product spaces, and abstract vector spaces. However, the specific methods and techniques used may vary depending on the properties of the vector space.

5. Are there any real-world applications of proving invariance of scalar product?

Yes, there are many real-world applications of proving invariance of scalar product. For example, it is used in the fields of computer graphics, robotics, and physics to calculate distances, angles, and projections. It is also fundamental in understanding the laws of motion and conservation of energy in physics.

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