What is Tensor: Definition and 1000 Discussions

In mathematics, a tensor is an algebraic object that describes a (multilinear) relationship between sets of algebraic objects related to a vector space. Objects that tensors may map between include vectors and scalars, and even other tensors. There are many types of tensors, including scalars and vectors (which are the simplest tensors), dual vectors, multilinear maps between vector spaces, and even some operations such as the dot product. Tensors are defined independent of any basis, although they are often referred to by their components in a basis related to a particular coordinate system.
Tensors have become important in physics because they provide a concise mathematical framework for formulating and solving physics problems in areas such as mechanics (stress, elasticity, fluid mechanics, moment of inertia, ...), electrodynamics (electromagnetic tensor, Maxwell tensor, permittivity, magnetic susceptibility, ...), or general relativity (stress–energy tensor, curvature tensor, ...) and others. In applications, it is common to study situations in which a different tensor can occur at each point of an object; for example the stress within an object may vary from one location to another. This leads to the concept of a tensor field. In some areas, tensor fields are so ubiquitous that they are often simply called "tensors".
Tullio Levi-Civita and Gregorio Ricci-Curbastro popularised tensors in 1900 - continuing the earlier work of Bernhard Riemann and Elwin Bruno Christoffel and others - as part of the absolute differential calculus. The concept enabled an alternative formulation of the intrinsic differential geometry of a manifold in the form of the Riemann curvature tensor.

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  1. J

    A Is the Dual Vector in Wald's Abstract Tensor Notation a Contraction?

    In Wald's "General Relativity", in his section on abstract tensor notation, he let's g_{ab} denote the metric tensor. When applied to a vector v^a, we get a dual vector, because g_{ab}(v^a, \cdot) is just a dual vector. Okay cool. But then he says that this dual vector is actually g_{ab}v^b...
  2. T

    A Question about properites of tensor product

    They are being 2 by 2 matrices and I being the identity. Physically they are Pauli matrices. 1. Is $$((A\otimes I\otimes I) + (I\otimes A\otimes I) + (I\otimes I\otimes A))\otimes B$$ = $$(A\otimes I\otimes I)\otimes B + (I\otimes A\otimes I)\otimes B + (I\otimes I\otimes A)\otimes B$$? I...
  3. J

    I Taking the Tensor Product of Vectors

    What is meant by taking the tensor product of vectors? Taking the tensor product of two tensors is straightforward, but I am currently reading a book where the author is talking about tensor product on tensors then in the next paragraph declares that tensors can then be constructed by taking...
  4. Isaac0427

    I Riemann/Metric Tensor Calculator

    Hi all! I'm really interested in the physical interpretation of the Riemann and metric tensors. Is there any program that let's you type in a Riemann or metric tensor (or even better, an Einstein tensor) and then gives you an image of how the space would look (i.e. the curved grid lines)? Thanks!
  5. S

    Maxwell equations from tensor notation to component notation

    Homework Statement Verify that ##\partial_{\mu}F_{\nu\lambda}+\partial_{\nu}F_{\lambda\mu}+\partial_{\lambda}F_{\mu\nu}## is equivalent to ##\partial_{[\mu}F_{\nu\lambda]}=0##, and that they are both equivalent to ##\tilde{\epsilon}^{ijk}\partial_{j}E_{k}+\partial_{0}B^{i}=0## and...
  6. Math Amateur

    I Tensor Algebras and Graded Algebras - Cooperstein

    I am reading Bruce N. Coopersteins book: Advanced Linear Algebra (Second Edition) ... ... I am focused on Section 10.3 The Tensor Algebra ... ... I need help in order to get an understanding of an aspect of Example 10.11 and Definition 10.7 in Section 10.3 ... The relevant text in...
  7. Math Amateur

    MHB Tensor Algebras and Graded Algebras - Cooperstein - Theorem 10.11 and Defn 10.7

    I am reading Bruce N. Coopersteins book: Advanced Linear Algebra (Second Edition) ... ... I am focused on Section 10.3 The Tensor Algebra ... ... I need help in order to get an understanding of an aspect of Example 10.11 and Definition 10.7 in Section 10.3 ... The relevant text in...
  8. S

    Finding tensor components via matrix manipulations

    Homework Statement Imagine we have a tensor ##X^{\mu\nu}## and a vector ##V^{\mu}##, with components ## X^{\mu\nu}=\left( \begin{array}{cccc} 2 & 0 & 1 & -1 \\ -1 & 0 & 3 & 2 \\ -1 & 1 & 0 & 0 \\ -2 & 1 & 1 & -2 \end{array} \right), \qquad V^{\mu} = (-1,2,0,-2). ## Find the components of...
  9. Math Amateur

    I Tensor Algebras - Dummit and Foote, Section 11.5

    I am reading Dummit and Foote: Abstract Algebra (Third Edition) ... and am focused on Section 11.5 Tensor Algebras. Symmetric and Exterior Algebras ... In particular I am trying to understand Theorem 31 but at present I am very unsure about how to interpret the theorem and need some help in...
  10. Math Amateur

    MHB Tensor Algebras - Dummit and Foote, Section 11.5

    I am reading Dummit and Foote: Abstract Algebra (Third Edition) ... and am focused on Section 11.5 Tensor Algebras. Symmetric and Exterior Algebras ... In particular I am trying to understand Theorem 31 but at present I am very unsure about how to interpret the theorem and need some help in...
  11. S

    Energy-Momentum Tensor for the electromagnetic field

    Homework Statement Maxwell's Lagrangian for the electromagnetic field is ##\mathcal{L}=-\frac{1}{4}F_{\mu\nu}F^{\mu\nu}## where ##F_{\mu\nu}=\partial_{\mu}A_{\nu}-\partial_{\nu}A_{\mu}## and ##A_{\mu}## is the ##4##-vector potential. Show that ##\mathcal{L}## is invariant under gauge...
  12. Math Amateur

    I The Tensor Algebra - Cooperstein, Example 10.1

    I am reading Bruce N. Coopersteins book: Advanced Linear Algebra (Second Edition) ... ... I am focused on Section 10.3 The Tensor Algebra ... ... I need help in order to get a basic understanding of Example 10.1 in Section 10.3 ...Example 10.1 plus some preliminary definitions reads as...
  13. F

    I What is the outer product of a tensor product of vectors?

    If one has two single-particle Hilbert spaces ##\mathcal{H}_{1}## and ##\mathcal{H}_{2}##, such that their tensor product ##\mathcal{H}_{1}\otimes\mathcal{H}_{2}## yields a two-particle Hilbert space in which the state vectors are defined as $$\lvert\psi ,\phi\rangle...
  14. Math Amateur

    MHB Tensor Algebras - Cooperstein Example 10.1

    I am reading Bruce N. Coopersteins book: Advanced Linear Algebra (Second Edition) ... ... I am focused on Section 10.3 The Tensor Algebra ... ... I need help in order to get a basic understanding of Example 10.1 in Section 10.3 ...Example 10.1 plus some preliminary definitions reads as...
  15. Math Amateur

    I The Tensor Algebra - Cooperstein, Defn 10.5

    I am reading Bruce N. Coopersteins book: Advanced Linear Algebra (Second Edition) ... ... I am focused on Section 10.3 The Tensor Algebra ... ... I need help in order to get a basic understanding of Definition 10.5 in Section 10.3 ...Definition 10.5 plus some preliminary definitions reads as...
  16. Math Amateur

    MHB Tensor Products and Associative Algebras

    I am reading Bruce N. Coopersteins book: Advanced Linear Algebra (Second Edition) ... ... I am focused on Section 10.3 The Tensor Algebra ... ... I need help in order to get a basic understanding of Definition 10.5 in Section 10.3 ...Definition 10.5 plus some preliminary definitions reads as...
  17. J

    Single shear element in stress tensor: Finding Von Mises

    When finding the Von Mises of given a stress tensor who's only element is a single shear component (τ): \begin{bmatrix} 0 & τ & 0\\ τ & 0 & 0\\ 0 & 0 & 0 \end{bmatrix} the result is simply √3×τ. Is the Von Mises criterion not valid when considering a single component as in this example? I...
  18. S

    Energy-Momentum Tensor for the Klein-Gordon Lagrangian

    Homework Statement The energy-momentum tensor ##T^{\mu\nu}## of the Klein-Gordon Lagrangian ##\mathcal{L}_{KG} = \frac{1}{2}\partial_{\mu}\phi\partial^{\mu}\phi-\frac{1}{2}m^{2}\phi^{2}## is given by $$T^{\mu\nu}~=~\partial^{\mu}\phi\partial^{\nu}\phi-\eta^{\mu\nu}\mathcal{L}_{KG}.$$ Show...
  19. Math Amateur

    I Tensor Algebras - Cooperstein Theorem 10.8

    I am reading Bruce N. Coopersteins book: Advanced Linear Algebra (Second Edition) ... ... I am focused on Section 10.3 The Tensor Algebra ... ... I need help in order to get a basic understanding of Theorem 10.8 which is a Theorem concerning the direct sum of a family of subspaces as a...
  20. Math Amateur

    MHB Tensor Algebras - Cooperstein Theorem 10.8

    I am reading Bruce N. Coopersteins book: Advanced Linear Algebra (Second Edition) ... ... I am focused on Section 10.3 The Tensor Algebra ... ... I need help in order to get a basic understanding of Theorem 10.8 which is a Theorem concerning the direct sum of a family of subspaces as a...
  21. Math Amateur

    I Tensor Products - Understanding Cooperstein, Theorem 10.2

    I am reading Bruce N. Coopersteins book: Advanced Linear Algebra (Second Edition) ... ... I am focused on Section 10.1 Introduction to Tensor Products ... ... I need help in order to get a basic understanding of Theorem 10.2 regarding the basis of a tensor product ... ... My apologies if my...
  22. Math Amateur

    MHB Tensor Products - Basic Understanding of Cooperstein, Theorem 10.2

    I am reading Bruce N. Coopersteins book: Advanced Linear Algebra (Second Edition) ... ... I am focused on Section 10.1 Introduction to Tensor Products ... ... I need help in order to get a basic understanding of Theorem 10.2 regarding the basis of a tensor product ... ... My apologies if my...
  23. pellman

    I Tensor Product in QM: 1D vs 3D Hilbert Spaces

    A particle in a 1-D Hilbert space would have position basis states ## |x \rangle ## where ## \langle x' | x \rangle = \delta(x'-x) ## A 3-D Hilbert space for one particle might have a basis ## | x,y,z \rangle ## where ##\langle x', y', z' | x,y,z \rangle = \delta(x'-x) \delta (y-y') \delta(z-z')...
  24. C

    Stress/strain tensor for anisotropic materials

    Hi, I understand stress, strain but when it moves on to 3 dimension anisotropic materials using tensors and stiffness matrices I get confused with einstein's notation. can someone please help me out in this regard to undrstand how stiffness and compliance matrices get reduced for monoclinic...
  25. H

    Inertial tensor remains diagonal during a shift along a principle axis

    In the middle of the below paragraph: "only if the shift vector ##R## is along one of the principal axes relative to the center of mass will the difference tensor be diagonal in that system." I suppose the difference tensor means new inertial tensor ##-## old inertial tensor. That means the new...
  26. F

    I Conservation of matter energy momentum tensor beyond GR

    Hello, Is the covariant conservation of the matter energy momentum tensor Tμν ; μ = 0 also valid in a theory of gravity having an action for the gravitational field different from the Einstein Hilbert action ? I'm asking because in GR the einstein field equations require Tμν= Gμν where Gμν;μ=0...
  27. Math Amateur

    MHB Extension of Scalars: Dummit & Foote's Section 10.4 Q&A

    I am reading Dummit and Foote's book: Abstract Algebra ... ... and am currently focused on Section 10.4 Tensor Products of Modules ... ... I have a basic question regarding the extension of the scalars ... Dummit and Foote's exposition regarding extension of the scalars reads as...
  28. Math Amateur

    I Extension of scalars .... D&F, Section 10.4: Tensor Products

    I am reading Dummit and Foote's book: Abstract Algebra ... ... and am currently focused on Section 10.4 Tensor Products of Modules ... ... I have a basic question regarding the extension of the scalars ... Dummit and Foote's (D&Fs) exposition regarding extension of the scalars reads as...
  29. Markus Hanke

    I Geometric Interpretation of Einstein Tensor

    Is there a simple geometric interpretation of the Einstein tensor ? I know about its algebraic definitions ( i.e. via contraction of Riemann's double dual, as a combination of Ricci tensor and Ricci scalar etc etc ), but I am finding it hard to actually understand it geometrically...
  30. F

    Is Qij=AiBj a Tensor of Rank 2?

    Homework Statement Suppose A and B are vectors. Show that the object Q with nine components Qij=AiBj is a tensor of rank 2. Homework Equations A tensor transforms under rotations (R) as a vector: Tij'=RinRjmTnm The Attempt at a Solution I wanted to just create the matrix, but I don't know how...
  31. D

    Covariant derivative of Killing vector and Riemann Tensor

    I need to prove that $$D_\mu D_\nu \xi^\alpha = - R^\alpha_{\mu\nu\beta} \xi^\beta$$ where D is covariant derivative and R is Riemann tensor. ##\xi## is a Killing vector. I have proved that $$D_\mu D_\nu \xi_\alpha = R_{\alpha\nu\mu\beta} \xi^\beta$$ I can't figure out a way to get the required...
  32. Math Amateur

    I Tensor Products - Issue with Cooperstein, Theorem 10.3

    I am reading Bruce N. Coopersteins book: Advanced Linear Algebra (Second Edition) ... ... I am focused on Section 10.2 Properties of Tensor Products ... ... I need help with an aspect of the proof of Theorem 10.3 ... ... basically I do not know what is going on in the second part of the proof...
  33. Math Amateur

    MHB Tensor Products - Issue with Cooperstein, Theorem 10.3

    I am reading Bruce N. Coopersteins book: Advanced Linear Algebra (Second Edition) ... ... I am focused on Section 10.2 Properties of Tensor Products ... ... I need help with an aspect of the proof of Theorem 10.3 ... ... basically I do not know what is going on in the second part of the...
  34. F

    I Transformation of Tensor Components

    In the transformation of tensor components when changing the co-ordinate system, can someone explain the following: Firstly, what is the point in re-writing the indicial form (on the left) as aikTklajl? Since we're representing the components in a matrix, and the transformation matrix is also...
  35. P

    I Mathematics of tensor products in the Bell states

    I'm having trouble with the mathematics of tensor products as applied to Bell states. Say I have the state \begin{align*} \left|\psi\right> &= \frac{1}{\sqrt{2}} \left(\left|0\right>_A \otimes \left|0\right>_B + \left|1\right>_A \otimes \left|1\right>_B\right) \end{align*} How would the...
  36. S

    A Is the Riemann Curvature Tensor a Mathematical Tool or Physically Significant?

    Can someone explain mathematically why do we say Riemann Curvature Tensor has all the information about curvature of Space Thank You
  37. S

    A Weyl Tensor Gravity propagation

    I read Weyl tensor helps on propagating gravitational effects. Ricci is local depending on mass energy at that point and would vanish at other points. Weyl propogates the gravity effects (for example gravity at any point between Earth Moon is due to Weyl Tensor). I didn't quite get it...
  38. Math Amateur

    I Properties of Tensor Products - Cooperstein, Theorem 10.3

    I am reading Bruce N. Coopersteins book: Advanced Linear Algebra (Second Edition) ... ... I am focused on Section 10.2 Properties of Tensor Products ... ... I need help with an aspect of the proof of Theorem 10.3 regarding a property of tensor products ... ...The relevant part of Theorem 10.3...
  39. Math Amateur

    MHB Properties of Tensor Products - Cooperstein, Theorem 10.3

    I am reading Bruce N. Coopersteins book: Advanced Linear Algebra (Second Edition) ... ... I am focused on Section 10.2 Properties of Tensor Products ... ... I need help with an aspect of the proof of Theorem 10.3 regarding a property of tensor products ... ... The relevant part of Theorem...
  40. Math Amateur

    I Basis of a Tensor Product - Theorem 10.2 - Another Question

    I am reading Bruce N. Coopersteins book: Advanced Linear Algebra (Second Edition) ... ... I am focused on Section 10.1 Introduction to Tensor Products ... ... I need help with another aspect of the proof of Theorem 10.2 regarding the basis of a tensor product ... ...Theorem 10.2 reads as...
  41. Math Amateur

    I Basis of a Tensor Product - Cooperstein - Theorem 10.2

    I am reading Bruce N. Coopersteins book: Advanced Linear Algebra (Second Edition) ... ... I am focused on Section 10.1 Introduction to Tensor Products ... ... I need help with an aspect of Theorem 10.2 regarding the basis of a tensor product ... ...Theorem 10.2 reads as follows: I do not...
  42. Math Amateur

    MHB Basis of a Tensor Product - Theorem 10.2 - Another Question .... ....

    I am reading Bruce N. Coopersteins book: Advanced Linear Algebra (Second Edition) ... ... I am focused on Section 10.1 Introduction to Tensor Products ... ... I need help with another aspect of the proof of Theorem 10.2 regarding the basis of a tensor product ... ... Theorem 10.2 reads as...
  43. Math Amateur

    MHB Basis of a Tensor Product - Cooperstein - Theorem 10.2

    I am reading Bruce N. Coopersteins book: Advanced Linear Algebra (Second Edition) ... ... I am focused on Section 10.1 Introduction to Tensor Products ... ... I need help with an aspect of Theorem 10.2 regarding the basis of a tensor product ... ... Theorem 10.2 reads as follows:I do not...
  44. T

    Bel-Robinson Tensor in empty spacetime

    Homework Statement This is Exercise 15.2 in MTW - See attachment Homework Equations See attachment The Attempt at a Solution [/B] My attempt at a solution is also in the attachment. Are my initial assumptions OK? If not can someone nudge me in the right direction. If my initial...
  45. Math Amateur

    I Proof of Existence of Tensor Product .... Further Question ...

    I am reading Bruce N. Coopersteins book: Advanced Linear Algebra (Second Edition) ... ... I am focused on Section 10.1 Introduction to Tensor Products ... ... I need help with another aspect of the proof of Theorem 10.1 regarding the existence of a tensor product ... ...The relevant part of...
  46. Math Amateur

    MHB Proof of Existence of Tensor Product: Cooperstein Theorem 10.1

    I am reading Bruce N. Coopersteins book: Advanced Linear Algebra (Second Edition) ... ... I am focused on Section 10.1 Introduction to Tensor Products ... ... I need help with another aspect of the proof of Theorem 10.1 regarding the existence of a tensor product ... ... The relevant part of...
  47. A

    Weyl Tensor invariant under conformal transformations

    Homework Statement As the title says, I need to show this. A conformal transformation is made by changing the metric: ##g_{\mu\nu}\mapsto\omega(x)^{2}g_{\mu\nu}=\tilde{g}_{\mu\nu}## Homework Equations The Weyl tensor is given in four dimensions as: ##...
  48. Math Amateur

    I Tensor Product - Knapp - Theorem 6.10 .... Further Question

    I am reading Anthony W. Knapp's book: Basic Algebra in order to understand tensor products ... ... I need some help with a further aspect of the proof of Theorem 6.10 in Section 6 of Chapter VI: Multilinear Algebra ... The text of Theorem 6.10 reads as follows: The above proof mentions Figure...
  49. Math Amateur

    MHB Theorem 6.10 in Knapp's Basic Algebra: Exploring Bilinearity & Descending Maps

    I am reading Anthony W. Knapp's book: Basic Algebra in order to understand tensor products ... ... I need some help with an aspect of Theorem 6.10 in Section 6 of Chapter VI: Multilinear Algebra ... The text of Theorem 6.10 reads as follows: The above proof mentions Figure 6.1 which is...
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