Proving the Cross Product Rules with the Levi-Civita Symbol

# Proving the Cross Product Rules with the Levi-Civita Symbol - The Levi-Civita Symbol is a Compact Formula for the Cross Product The analysis shows that the complicated, three-component formula for the cross product can be expressed concisely using the Levi-Civita symbol ( $\varepsilon_{i j k}$ ). By explicitly expanding the sum in the tensor notation $\left(v \times w=e_i \varepsilon_{i j k} v^j w^k\right)$ for each basis vector, you arrive at the familiar Cartesian components of the cross product: $\left(v^2 w^3-v^3 w^2\right),\left(v^3 w^1-v^1 w^3\right)$, and $\left(v^1 w^2-v^2 w^1\right)$. This proves that the tensor notation is not just an alternative representation, but a powerful, single equation that generates the entire standard formula. - Tensor Notation Unifies the Rules for Basis Vectors The Levi-Civita notation is also the fundamental source for the basic rules of the cross product, such as the right-hand rule. The analysis demonstrates this by setting the general vectors $v$ and $w$ to be the basis vectors themselves (e.g., $e_1$ and $e_2$ ). When you use the substitution $e_j \times e_k=$ $e_i e_{i j k}$, the values of the Levi-Civita symbol automatically yield the correct results: - For $e_1 \times e_2$, only the term with $i=3$ is non-zero, correctly giving $e_3$. - For $e_i \times e_i$, the properties of the symbol immediately show that the result is zero. This proves that the standard rules for cross products (e.g., $e_1 \times e_2=e_3$ and $e_i \times e_i=0$ ) are not just arbitrary definitions but are a direct, logical consequence of the Levi-Civita tensor notation. ## :clapper: Demonstration #### The Cross Product and the Right-Hand Rule <iframe width="1172" height="659" src="https://www.youtube.com/embed/U1S70T3Uumg" title="The Cross Product and the Right Hand Rule" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe> ## Latest update <iframe src="https://viadean.notion.site/ebd/2491ae7b9a3280a8aed7ff53ab3e54dd" width="100%" height="600" frameborder="0" allowfullscreen />