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. L

    Information content of the metric, Riemannian and Ricci tensors

    I'm getting myself up to speed on GR to try to understand a book by John Moffat called "Reinventing Gravity...". So far I've been using Sean Carroll's sort of classic course notes and a fair bit of Wikipediea (sp?). It may be a naive question, but the point I wouldn't mind comments on is the...
  2. W

    Understanding Index Notation: Multiplying Vectors & Tensors

    I have a general question about index notation. For an arbitrary quantity, a, "a" denotes a scalar quantity. "a_i" denotes a vector. "a_ij" denotes a 2nd-order tensor. So, if I have something like "a_i*e_ij*b_j" Would this be like multiplying an nx1 vector, an mxm matrix, and an Lx1 vector...
  3. K

    Transformation matrix on tensors

    Hello. I wasn't sure whether to post this here on in some of the physics sections. I have a rank 2 tensor in one coordinate reference system [x1, x2, x3], the one where only the principal elements are non zero: R=[ a11 0 0; 0 a22 0; 0 0 a33 ]. I want the tensor R in some other...
  4. Hepth

    QFT : Why do tensors in lagrangian densities contract?

    What is the general rule behind why for any given lagrangian (QED/QCD show this) that any vectors or tensors contract indices? I know it must be something simple, but I just can't think of it offhand. QED : F_{\mu\nu}F^{\mu\nu} Proca (massive vector): A_\mu A^\mu QCD : G^{\alpha}_{\mu\nu}...
  5. P

    Understanding Tensors: A Guide to Transformations and Components

    Not really a homework problem. Need some help understanding tensors. Ok, so the chapter in the book I am using, Vector Calculus by Paul C. Matthews introduces first the coordinate transformation and proceeds to say that a vector is anything which transforms according to the rule...
  6. mnb96

    Tensors in Gemotric Algebra

    Hello, can anyone explain simply what is a tensor, using the language of Geometric Algebra? Thanks!
  7. B

    Deriving Field Equations for Real Vector Fields using Euler-Lagrange (Tensors)

    Homework Statement Show that the Lagrangian density: L=- 1/2 [\partial_\alpha \phi_\beta ][\partial^\alpha \phi^\beta ]+1/2 [\partial_\alpha \phi^\alpha ][\partial_\beta \phi^\beta ]+1/2 \mu^2 \phi_\alpha \phi^\alpha for the real vector field \phi^\alpha (x) leads to the field equations...
  8. D

    Tensors: Exploring Indices, Equations, & Transformations

    1. (a) Remembering the distinction between summation indices and free indices, look at the following equations and state whether they conform to tensor notation, and if not why not: (i) Tmn=Am^nB (ii) Uij^i=Ai^kDk (iii) Vjk^ii=Ajk (iv) Ai^j=Xi^iC^j+Yi^j (b) (i) Write out in...
  9. R

    Tensors versus differential forms

    What is the benefit of expressing Maxwell's equation in the language of differential forms? Differential forms seem to be inferior to the language of tensors. Sure you can do fancy things with the exterior derivative and hodge star, but with tensors you can derive those same identities with...
  10. L

    Is the Quotient Theorem Applicable to 4th Rank Tensors?

    Prove that b_{ijkl}=\int_{r<a} dV x_i x_j \frac{\partial^2}{\partial_k \partial_l} (\frac{1}{r}) where r=|x| is a 4th rank tensor. i've had a couple of bashes and got nowhere other than to establish that its quotient theorem. can i just pick a tensor of rank 3 to multiply it with or...
  11. mnb96

    Co/contra/in-variance of tensors in abstract algebra

    Hello, The concept of contravariance, covariance and invariance are commonly used in the domain of Tensor Calculus. However I have heard that such concepts are more abstractly defined (perhaps) in cathegory theory. Could someone explain shortly the connection between the abstract definitions...
  12. daniel_i_l

    Adding Inertia Tensors to 3D Shapes: Parallel Axis Theorem Explained

    Lets say that I know the inertia tensors for a few different 3D shapes and I want to connect them together into one big composite shape. From what I understand, I first have to find the new center of mass, then using the parallel axis theorem find the new inertia tensors for each body along an...
  13. L

    What is the span of (1,1)^T?

    Show that a tensor T can be written as T_{ij}=\lambda \delta_{ij} + F_{ij} +\epsilon_{ijk} v_{k} for the tensor \[ \left( \begin{array}{ccc} 1 & 2 & 3 \\ 4 & 5 & 6 \\ 7 & 8 & 9 \end{array} \right)\] find \lambda, F_{ij}, v_k i can't get anywhere whatsoever with this question?
  14. K

    Are Christoffel Symbols Considered Tensors?

    I'm sort of confused about Christofel symbols being called tensors. I thought that to be considered a tensor, the tensor had to obey the standard component transformation law. For example...
  15. D

    Mathematica How do I use tensors in Mathematica 7?

    Hi there! I'm tring to check some calculations of the propagator of a gauge field using the R_\xi gauge fixing. Since the propagator has a matricial structure, \Delta_{\mu\nu}=\frac{1}{(p^0)^2+E_p^2}\left[\delta_{\mu\nu}-\frac{1-\xi}{(p^0)^2+E_p^2}p_\mu p_\nu\right], I'd like to check it...
  16. D

    What are Tensors and how do they relate to General Relativity?

    Hello Everyone, I didn't know whether to post this here or in the Physics area. Basically I'm trying to get a good understanding of Tensors so that I can apply them to General Relativity. I'm a freshman in college and kind of been teaching myself this advanced physics since i was 14, and...
  17. S

    What is the dot product of tensors?

    Hello, I was trying to follow a proof that uses the dot product of two rank 2 tensors, as in A dot B. How is this dot product calculated? A is 3x3, Aij, and B is 3x3, Bij, each a rank 2 tensor. Any help is greatly appreciated. Thanks! sugarmolecule
  18. LarryS

    Need Book on Tensors: Recommendations for BS Math Holder

    Can anybody recommend a good introductory book on tensors? I have a B.S. in math. Thanks in advance.
  19. L

    Show Isotropic Tensor: \epsilon _{{{\it ijm}}}\epsilon _{{{\it mkl}}}

    I've been asked to show that \epsilon _{{{\it ijm}}}\epsilon _{{{\it mkl}}} is an isotropic tensor using \epsilon _{{{\it ijk}}}\det \left( M \right) =\epsilon _{{\alpha \beta \gamma }}m_{{i\alpha }}m_{{j\beta }}m_{{k\gamma }} . Then to take the most general form for a fourth rank tensor...
  20. M

    Help Finding Cartesian Tensor Books

    I am not able to find good books on this topic on net so if any 1 can help me i will be grateful .
  21. P

    Parallel Axis Theorem and interia tensors

    Is the parallel axis theorem always valid for inertia tensors? We have only seen examples with flat (2d) objects and was wondering if it would also be valid for 3d objects, like a h emisphere, for example. Thanks.
  22. P

    Tensors of Relativity: Inner vs Outer Indices

    I am a bit confused with tensors here. now i know that \Lambda, the transformation matrix has a different meaning when I write \Lambda^\mu\ _{\nu} and when I write \Lambda_{\nu}\ ^\mu One is the mu-nu th element of \Lambda and the other is the mu-nu th element of \Lambda^{-1}. Is it...
  23. G

    Book on diff. geometry, tensors, wedge product forms etc.

    Hi all, I am taking this math methods course in grad school, and in the lectures we stormed through differential geometry. My geometry is already horrible, I find it hard to understand all these forms, fields, tensors, wedge products etc... I would be glad if you could suggest some books...
  24. Q

    Tensors and differential geometry

    Hi, I've decided to learn GR myself recently since it's like the "sexy" side of physics. But I'm getting stuck with the tensors notations already. Maybe my math background is just not sufficient enough to do GR. In general, how do I know that an object is tensorial; for example, objects like...
  25. I

    Tensors: raising and lowering indices

    From Carroll's textbook: 1. The problem statement Imagine we have a tensor X^{\mu \nu} with components X^{\mu \nu} = \begin{pmatrix} 2 & 0 & 1 & -1\\ -1 & 0 & 3 & 2\\ -1 & 1 & 0 & 0\\ -2 & 1 & 1 & -2 \end{pmatrix} Find the components of: (a) {X^\mu}_\nu; (b) {X_\mu}^\nu.2. The attempt at a...
  26. W

    Maple Maple: Tensors and arbitrary dimensions

    Hello there, I'm currently trying to get my head around General Relativity for a term paper; the twist is that I'm dealing with an arbitrary amount of dimensions, that is 4+d, where d is unspecified. Now the maple tensor package does calculation with some fixed amount of dimensions just...
  27. R

    Matrix Representation of Tensors?

    How would you represent tensors as matrices? I've searched all over, and my book on GR (Wald) only has one example where he makes a matrice from a tensor, and I still don't understand the process.
  28. V

    What are basis vectors, one forms, and basis one forms?

    I'm not sure this is the correct forum section for this question, if not, please move me. Essentially, I'm looking for help understanding what basis vectors, one forms, and basis one forms are. I'm fairly sure I get basis vectors, I would describe them as a description of a co-ordinate system...
  29. E

    Divergence of mixed II-order tensors

    Dear friends, How is the divergence in curvilinear coordinates of a second order mixed tensor defined? I mean, shall I contract the covariant or the contravariant index?? And for both cases which is the physical meaning? \nabla_i N^i_j or \nabla_j N^i_j ? Thanks a lot, Enzo
  30. Phrak

    Understanding Bras and Kets as Vectors and Tensors

    Is there a way bras and kets can be understood in terms of vectors and tensors and coordinate bases? I'm fairly sure that if a ket is thought of as a vector with an upper index, then it's bra is a vector with a lower index, but getting the rest of it all to look like tensors is rather...
  31. malawi_glenn

    Tensors for Relativity: A Guide Without Tears

    Tensors for relativity: http://www.teorfys.uu.se/people/minahan/Courses/SR/tensors.pdf
  32. snoopies622

    Gaining Intuitive Understanding of Parallel Transporting Tensors

    A vector is drawn as an arrow, a covector (one-form) as a series of parallel lines. Is there a way to pictorially represent a tensor of rank greater than one? I want to have an intuitive/geometric sense of what it means to parallel transport such an object, and without a picture I don’t have one.
  33. A

    Understanding General Relativity without Tensors

    Is there any free online tutorial which completely explains General Relativity without concept of Tensors?
  34. J

    Why are tensors important in general relativity?

    I quite often hear that GR is formulated in terms of tensors because laws of physics expressed in terms of tensor equations are indepedent of choice coordinates because they `transform nicely'. I thought the motivation for tensors was that since spacetime is curved, we locally linearize it by...
  35. E

    Understanding Surface Tensors: Pauli's Theory of Relativity

    I'm reading through Pauli's "Theory of Relativity", which has a discussion of tensors in the mathematical tools section of the book. When introducing surface tensors, he states "Such tensors can be obtained by considering two vectors x, y which together span a two-dimensional parallelepiped...
  36. F

    Tensors links or ebooks ?

    somebody know some link or ebook about tensor with examples solved and execises
  37. P

    What is a Basic Introductory Book on Tensor Calculus?

    What is a good book that introduces tensor notion clearly?
  38. Q

    Non-Degenerate Tensors: What is the Meaning and Significance?

    in general, what exactly does it mean for a tensor to be non-degenerate? does it mean that the vector space underlying it all has a zero kernel? I'm still a bit hazy on the degeneracy of bilinear forms in general. They're not exactly like tensors, either, but I am guessing there's some...
  39. Q

    Symmetrizing and skew symmetrizing tensors

    I understand that all rank 2 tensors can be decomposed into a symmetric and a skew symmetric part, but I don't really understood how this is done. It has something to do with permutations of the indices, I guess, but I never learned anything about what a permutation is. Can anyone explain how...
  40. F

    Trying to understand tensors and tensor notation

    Hello folks, During my education I was not exposed to tensor notation much at all. Therefore I never developed an understanding for it. I spend some time on my own now, but often find it quite obtuse and lacking some of the detail I feel I need to reach that point of comfort. Does anyone...
  41. C

    Tensors: Lorentz vs Galilean invariance

    What is the physical significance of tensors? Occasionally, motivating statements are made roughly along the lines of "if an equation can be expressed purely in terms of tensors, then it is true for all observers". But that doesn't seem quite complete because different tensor-users would have...
  42. C

    Maple How can I store tensors in maple for multiple usages?

    sow I'm working on learning some of the maple commands for tensors, and I see a lot of the basic structure, however I don't know how to store a tensor in maple for multiple usages, can anybody help?
  43. H

    Cartesian Tensors and transformation matrix

    I was just reading chapter on Cartesian tensors and came across equation for transformation matrix as function of basic vectors. I just do not get it and cannot find a derivation. I am too old to learn Latex, I uploaded a word document with the equation. Thanks, Howard
  44. N

    Non Linear Optics (tensors)

    Homework Statement a) What does the tensor nature of susceptibility mean? Ie. the xxxx in: \overline{P}=\epsilon_0\chi_{xxxx}\overline{E} b) What does the 3 vertical dots mean in: \chi^{(2)}\vdots\overline{E} ?The Attempt at a Solution a) I understand that...
  45. N

    Tensors: Defining & Expressing Equations

    Homework Statement Let us define 4 vector by 4 co-ordinates:(x1,x2,x3,x4) where (x1,x2,x3) are space components (like x,y,z) and x4 is related to time as x4=ict.Express the following equations in tensor notation. (i)The continuity equation: div J+(del*rho/del t)=0 (ii)The wave...
  46. B

    Symmetric Tensors and Matrices

    Is the matrix of a second order symmetric tensor always symmetric (ie. expressed in any coordinate system, and in any basis of the coordinate system)? Please help! :blushing: ~Bee
  47. Q

    Linear algebra and tensors in GR

    Hi folks, I'm looking for some interesting questions/challenges regarding linear algebra and general relativity for fun. I'm particularly interested in tensors, but my background here is a bit weaker. Just wondering if anyone has any thoughts or ideas? :cool:
  48. J

    Interpreting Body Wave-Surface Wave Energy Transfer with Vectors & Tensors

    Homework Statement Hi, as part of my final year project I am investigating how rayleigh surface waves are generated by transverse body waves. I've seen how Kolsky derives these waves by slving the wave equation for this type of waveform. My supervisor wants me to describe the energy transfer...
  49. N

    Visualising Tensors: Physics Explanation & Examples

    Can anyone help me to unerstand what tensors are in physics, a few basic examples would probably do, and how they actually go about giving you the results. the only explanations I've been given of them are through maths which are useless to me since i still can't manage to visualise what a...
  50. T

    Covariant and Contravariant Rank-2 Tensors

    Dear Fellows, Do anyone have an idea of whether there must be a system tensor in order to be able to transform from the covariant form of a certain tensor to its contravariant one? This is a bit important to get rigid basics about tensors. Schwartz Vandslire...
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