What is Tensors: Definition and 382 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. D

    Other Textbooks for tensors and group theory

    Hello, I am an undergraduate who has taken basic linear algebra and ODE. As for physics, I have taken an online edX quantum mechanics course. I am looking at studying some of the necessary math and physics needed for QFT and particle physics. It looks like I need tensors and group theory...
  2. P

    I Confusion about index notation and operations of GR

    Hello, I am an undergrad currently trying to understand General Relativity. I am reading Sean Carroll's Spacetime and Geometry and I understand the physics (to a certain degree) but I am having trouble understanding the notation used as well as the ideas for tensors, dual vectors and the...
  3. Math Amateur

    I Tensors & the Alternation Operator .... Browder, Propn 12.25

    I am reading Andrew Browder's book: "Mathematical Analysis: An Introduction" ... ... I am currently reading Chapter 12: Multilinear Algebra ... ... I need some help in order to fully understand the proof of Proposition 12.2 on pages 277 - 278 ... ...Proposition 12.2 and its proof read as...
  4. Math Amateur

    I Space of Alternating Tensors of Rank r.... (Browder, 12.22)

    I am reading Andrew Browder's book: "Mathematical Analysis: An Introduction" ... ... I am currently reading Chapter 12: Multilinear Algebra ... ... I need some help in order to fully understand the proof of Theorem 12.22 on page 276 ... ...The relevant text reads as follows: In the above...
  5. Math Amateur

    MHB Rank One Tensors .... Fortney Appendix A, Section A2 ....

    I am reading Jon Pierre Fortney's book: A Visual Introduction to Differential Forms and Calculus on Manifolds ... and am currently focused on Appendix A : Introduction to Tensors ...I need help to understand some statements/equations by Fortney concerning rank one tensors ... Those remarks...
  6. N

    Clebsch-Gordan Decomposition for 6 x 3

    Homework Statement [/B] I am trying to get the C-G Decomposition for 6 ⊗ 3. 2. Homework Equations Neglecting coefficients a tensor can be decomposed into a symmetric part and an antisymmetric part. For the 6 ⊗ 3 = (2,0) ⊗ (1,0) this is: Tij ⊗ Tk = Qijk = (Q{ij}k + Q{ji}k) + (Q[ij]k +...
  7. VuIcan

    I Interpreting The Definition of Tensors

    Hello, I've just been slightly unsure of something and would like to get secondary confirmation as I've just begun a book on tensor analysis. I would also preface this by saying my linear algebra is somewhat rusty. Suppose you have the inertia tensor in some unprimed coordinate system such that...
  8. T

    Is this derivative in terms of tensors correct?

    Homework Statement Solve this, $$\frac{\partial}{\partial x^{\nu}}\frac{3}{(q.x)^3}$$ where q is a constant vector. Homework EquationsThe Attempt at a Solution $$\frac{\partial}{\partial x^{\nu}}\frac{3}{(q.x)^3}=3\frac{\partial(q.x)^{-3}}{\partial (q.x)}*\frac{\partial (q.x)}{\partial x^{\nu}}...
  9. Digital_lassitude

    Is it possible to express friction force as a tensor?

    Homework Statement Consider the equation for the friction force Ff = m FN. is it possible to express the friction force as a tensor? If so, what rank tensor is it, and what are the ranks of the tensor m and the normal force FN? Homework Equations Ff = mFNThe Attempt at a Solution [/B] So I...
  10. N

    I Why vector lengths may not be preserved?

    Given some metric, what is an example where the length of a vector is not preserved?
  11. Ibix

    I Coordinates for diagonal metric tensors

    In the recent thread about the gravitational field of an infinite flat wall PeterDonis posted (indirectly) a link to a mathpages analysis of the scenario. That page (http://www.mathpages.com/home/kmath530/kmath530.htm) produces an ansatz for the metric as follows (I had to re-type the LaTeX -...
  12. E

    I Summation convention with expressions containing parentheses

    Is (Tii)2 equivalent to (∑i = 1nTii)2? That is, when you encounter parentheses with Einstein summation, you perform the summation first and then apply any mathematical operations indicated by the parentheses? The solutions manual gives a solution to a problem I've been working out seems to...
  13. Pencilvester

    I Comparing tensors at different points

    Hello PF, I have a question about comparing tensors at different points. Carroll says, “there is no natural way to uniquely move a vector from one tangent space to another; we can always parallel-transport it, but the result depends on the path, and there is no natural choice of which path to...
  14. K

    I Tensors: Bar Symbol Over Functions or Indices?

    When dealing with any tensor quantity, when making a coordinate transformation, we should put a bar (or whatever symbol) over the functions or over the indices? For exemple, should the metric coefficients ##g_{\mu \nu}## be written in another coord sys as ##\bar g_{\mu \nu}## or as ##g_{\bar \mu...
  15. Remixex

    Stress and Strain tensors in cylindrical coordinates

    Homework Statement I am following a textbook "Seismic Wave Propagation in Stratified Media" by Kennet, I was greeted by the fact that he decided to use cylindrical coordinates to compute the Stress and Strain tensor, so given these two relations, that I believed to be constitutive given an...
  16. G

    B Tensors & Lorentz Transform: Is There a Connection?

    Are these two subjects closely related? It seems a tensor can be invariant when viewed from any **co ordinate system and The Lorentz Transformation seems to allow 2 moving co ordinate frames to agree on a space time intervals. Is there some deep connection going on? **=moving frames of...
  17. L

    A Tensor symmetries and the symmetric groups

    In one General Relativity paper, the author states the following (we can assume tensor in question are tensors in a vector space ##V##, i.e., they are elements of some tensor power of ##V##) To discuss general properties of tensor symmetries, we shall use the representation theory of the...
  18. Sorcerer

    I What are the differences between matrices and tensors?

    I have not really finished studying linear algebra, I have to admit. The furthest I have gotten to is manipulating matrices a little bit (although I have used this in differential equations to calculate a Wronskian to see if two equations are linear independent, but again, a determinant is...
  19. R

    Difference/convert between covariant/contravariant tensors

    Homework Statement 1. Explain the difference between a covariant tensor and a contravariant tensor, using the metric tensor as an example. 2. Explain how the components of a general covariant tensor may be converted into those of the equivalent contravariant tensor, and vice versa. Homework...
  20. vibhuav

    I Exploring Tensors in Physics: Understanding Rank and When to Use Matrices

    I am quite new to tensors, with my knowledge based on Daniel Fleisch’s “Student’s guide to vectors and tensors” and Neuenschwander’s “Tensor calculus for physics”. I had the following questions: 1. What are the higher rank tensors with physical meaning attached to them? I know tensors up to...
  21. W

    Contracting dummy indices tensors

    Homework Statement We've been told there's this operation called 'contraction' where if you have a superscript and a subscript that are the same they cancel. I don't understand how that works, partly in the sense that we haven't got round to what the superscripts and subscripts actually mean...
  22. W

    Contracting dummy indices tensors

    Homework Statement Write out this covariant derivative in terms of partial derivatives and Christoffel symbols: ##\nabla_{\mu} S^{\nu}_{\nu \rho}## Homework EquationsThe Attempt at a Solution I think you can contract that so it reads ##\nabla_{\mu} S_{\rho}##, in which case the solution...
  23. e2m2a

    Wire tension that might involve tensors

    I need help with this problem. This is not a homework assignment, so please don’t send it over to the homework forum. It involves mechanical engineering dynamics that probably are more subtle and advanced then first year mechanical engineering dynamics. It might involve tensor analysis...
  24. J

    A Evaluate Covariant Derivative on Tensors

    Hello there, Recently I encountered a type of covariant derivative problem that I never before encountered: $$ \nabla_\mu (k^\sigma \partial_\sigma l_\nu) $$ My goal: to evaluate this term According to Carroll, the covariant derivative statisfies ##\nabla_\mu ({T^\lambda}_{\lambda \rho}) =...
  25. W

    Calculus Vector Analysis and Cartesian Tensors by Bourne and Kendall

    I have to do a teaching assistant job on a multivariable calculus class, I have to survey books that can be useful as resources. Has anyone used this book by Bourne and Kendall? I noticed that the treatment of vector analysis seems good and the chapter on Cartesian tensors seem to be a good...
  26. S

    I Getting to Grips with Rank-2 Tensors

    Hello! I am reading about tensors and I am a bit confused about rank-2 tensors. From what I understand they can be represented by a matrix. However I am not sure I understand the difference between (2,0), (0,2) and (1,1) tensors. I understand that they act on different objects (vectors or one...
  27. Wrichik Basu

    Classical Good Books on Tensors: Recommendations for Undergraduates

    I need a good book on tensors, so that I can understand and get good hold of the topic. Can anyone recommend me a good book, like one used in undergraduate level?
  28. P

    I Differential forms as a basis for covariant antisym. tensors

    In a text I am reading (that I unfortunately can't find online) it says: "[...] differential forms should be thought of as the basis of the vector space of totally antisymmetric covariant tensors. Changing the usual basis dx^{\mu_1} \otimes ... \otimes dx^{\mu_n} with dx^{\mu_1} \wedge ...
  29. S

    I Understand Tensors: Difference from Matrices

    Hello! I am not really sure I understand the idea of tensors and the difference between them and normal matrices, for example (for rank 2 tensors). Can someone explain this to me, or give me a good resource for this? I don't want a complete introduction to GR math, I just want to understand the...
  30. T

    Proof of trace theorems for gamma matrices

    Hi, I'm currently going through Griffith's Particle Physics gamma matrices proofs. There's one that puzzles me, it's very simple but I'm obviously missing something (I'm fairly new to tensor algebra). 1. Homework Statement Prove that ##\text{Tr}(\gamma^\mu \gamma^\nu) = 4g^{\mu\nu}##...
  31. T

    I Metric tensor : raising/lowering indices

    Hi everyone, I'm currently studying Griffith's Intro to Elementary Particles and in chapter 7 about QED, there's one part of an operation on tensors I don't follow in applying Feynman's rules to electron-muon scattering : ## \gamma^\mu g_{\mu\nu} \gamma^\nu = \gamma^\mu \gamma_\mu## My...
  32. C

    How to prove that something transforms like a tensor?

    Homework Statement I have several problems that ask me to prove that some quantity "transforms like a tensor" For example: "Suppose that for each choice of contravariant vector (a vector) A^nu(x), the quantities B_mu(x) are defined at teach point through a linear relationship of the form...
  33. sa1988

    I What does this notation mean? (suffix/prefix on tensors?)

    Looking at relativistic transformations and suddenly we have this transformation matrix with an upper and lower index. See below: A bit of googling tells me the upper index means a co-ordinate. However I'm not sure what the lower index is. Overall I have no idea what makes it so special, or...
  34. ParabolaDog

    Struggling immensely with tensors in multivariable calculus

    Homework Statement If f(x) is a scalar-valued function, show that ∂ƒ²/∂xi∂xj are the components of a Cartesian tensor of rank 2. Homework Equations N/A The Attempt at a Solution I don't even know where to begin. We began learning tensors in multivariable calculus (though I don't think this is...
  35. arpon

    I Two metric tensors describing same geometry

    Consider two coordinate systems on a sphere. The metric tensors of the two coordinate systems are given. Now how can I check that both coordinate systems describe the same geometry (in this case spherical geometry)? (I used spherical geometry as an example. I would like to know the process in...
  36. E

    I Order of Operations for Tensors

    Hey so probably a really simple question, but I'm stumped. How do you simplify: ν∇⋅(ρν), where ν is a vector ∇ is the "del operator" ⋅ indicates a dot product ρ is a constant. I want to say to do the dyadic product of v and ∇, but then you would get (v_x)*(d/dx) + ... which would be...
  37. S

    Recommended Books for Studying Relativistic Electrodynamics

    Hey guys, Can you please refer some good books to refer to in studying relativistic Electrodynamics (introductory parts), covering the Maxwell's equations in tensor form the L-W potentials and other aspects. FYI am just a beginner in relativistic Electrodynamics. Thanks for the help.
  38. K

    I Can a Tensor be Represented by a 3-Dimensional Matrix?

    Question 1 - I know a tensor is not a matrix. But the values of each component of a tensor of the form Aμ1μ2 can be arranged in exactly the same way as in a usual 2-dimensional matrix. I was wondering if it would be possible to represent a Aμ1μ2μ3 tensor by a 3-dimensional matrix, and likewise...
  39. W

    Geometry Tensors and Manifolds by Wasserman

    I would like to know at what level is the book Tensors and Manifolds by Wasserman is pitched and what are the prerequisites of this book? Given the prerequisites, at what level should it be (please give examples of books)? If anyone has used this book can you please kindly give your comments and...
  40. Victor Alencar

    A Geometrical interpretation of Ricci and Riemann tensors?

    I do not get the conceptual difference between Riemann and Ricci tensors. It's obvious for me that Riemann have more information that Ricci, but what information? The Riemann tensor contains all the informations about your space. Riemann tensor appears when you compare the change of the sabe...
  41. J

    Relativity Opinions on Zee's "Einstein Gravity in a Nutshell"

    Hello again, I would like to know what your opinions about this book. As I have figured out, there are a lot of great GR books out there, but this very rarely gets any mention in forums like this. Why is this? Its got pretty good reviews at amazon and goodreads. Thanks in advance!
  42. C

    I Can "extremal" strain tensors be in the interior of the body

    I am new to elastic theory. I have a question about elasticity. We assume we have a body with no internal forces. Surface forces are applied on the border. Can we leave the elastic domain (reach the yield surface) in an interior point without leaving the elastic domain on the boundary? If no...
  43. P

    A How Do SU(3) Tensors Decompose into Irreducible Components?

    Suppose that in the tensor component ##T^a_b ## the upper index is the ## \bf{3}## component and the lower index is the ##\bf{\bar{3}} ## component. To be concrete, consider the decomposition u^iv_j= \left( u^iv_j-\frac{1}{3}\delta^i_j u^kv_k \right) +\frac{1}{3}\delta^i_j u^kv_k which...
  44. F

    Prove Lorentz invariance for momentum 4-vector

    Homework Statement I am meant to show that the following equation is manifestly Lorentz invariant: $$\frac{dp^{\mu}}{d\tau}=\frac{q}{mc}F^{\mu\nu}p_{\nu}$$ Homework Equations I am given that ##F^{\mu\nu}## is a tensor of rank two. The Attempt at a Solution I was thinking about doing a Lorents...
  45. W

    I The Order and Valence of Tensors

    I'm having a bit of trouble understanding the nature of tensors (which is pretty central to the gen rel course I'm currently taking). I understand that the order (or rank) of a tensor is the dimensionality of the array required to describe it's components, i.e. a 0 rank tensor is a scalar, a 1...
  46. F

    I Proving Orthogonality of Vector w/ Schnutz Special Relativity Tensors

    There's a question in Schnutz - A first course in special relativity Consider a Velocity Four Vector U , and the tensor P whose components are given by Pμν = ημν + UμUν . (a) Show that P is a projection operator that projects an arbitrary vector V into one orthogonal to U . That is, show that...
  47. 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...
  48. Math Amateur

    I Tensors - Winitzki - Lemma 3

    I am reading Segei Winitzki's book: Linear Algebra via Exterior Products ... I am currently focused on Section 1.7.3 Dimension of a Tensor Product is the Product of the Dimensions ... ... I need help in order to get a clear understanding of an aspect of the proof of Lemma 3 in Section 1.7.3...
  49. Math Amateur

    MHB Tensors - Winitzki - Lemma 3

    I am reading Segei Winitzki's book: Linear Algebra via Exterior Products ... I am currently focused on Section 1.7.3 Dimension of a Tensor Product is the Product of the Dimensions ... ... I need help in order to get a clear understanding of an aspect of the proof of Lemma 3 in Section 1.7.3...
  50. G

    I Learn About Tensors: Simple Explanations & Examples

    Dear Friends! I am learning Tensors so my question may look simple to you. "All observers in all reference frames agree not on the basis vectors not on the components but on the combination of components and basis vectors" Q Why this happens? Please guide me where I can study it in brief and in...
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