History of Topics in Special Relativity/Stress-energy tensor (matter)

From Wikiversity
Jump to navigation Jump to search
History of Topics in Special Relativity: Tensors (edit)

Electromagnetic field tensor

Electromagnetic stress-energy tensor

Material stress-energy tensor

Overview[edit | edit source]

The w:Stress–energy_tensor is defined as

where w is the energy density, S the energy flux density vector, and G the stress tensor. While it was historically introduced in electrodynamics, it was quickly adapted to mechanics in general. A well known example is the perfect fluid stress energy tensor:

where is the mass–energy density, is the hydrostatic pressure, is the fluid's w:four velocity, and is the reciprocal of the metric tensor. In the case of vanishing pressure it becomes the w:dust solution:

Its divergence represents the four-force density in that fluid, providing an alternative way to formulate equations of motion.

Tensor (a) was applied to mechanics by #Minkowski (1907), #Abraham (1909-12), #Laue (1911-20). Case (c) was implicitly given by #Minkowski (1907), and explicitly by #Nordström (1910–13), #Abraham (1912), #Lewis/Wilson (1912), #Kottler (1914), and in generally covariant form by #Einstein (1913-16). Case (b) was given by #Herglotz (1911) and in generally covariant form by #Einstein (1914).

Historical notation[edit | edit source]

Minkowski (1907)[edit | edit source]

In an appendix to his lecture from December 1907 (published 1908), w:Hermann Minkowski extended the postulate of relativity to mechanics, defining the space-time vector of second kind:[R 1]

which represents the general scheme of mechanical stress energy tensor (a). Subsequently he derived the following relation using four-velocity w and rest mass density defined as constant:[R 2]

Even though Minkowski didn't explicitly mention it, it includes the dust tensor equivalent to (c), from which he derived the mechanical equations of motion.

Abraham (1909-12)[edit | edit source]

In 1909, w:Max Abraham pointed out that the relativity principle requires that the mechanical forces must transform like the electromagnetic ones, so there must be a four-dimensional tensor for mechanics (i.e. mechanical stress energy tensor) in analogy to the electromagnetic one, and that the relation can alternatively be interpreted as relation between mechanical momentum and energy density first indicated by Max Planck (1907):[R 3]

equivalent to (a).

In 1912, Abraham introduced the expression “world tensor of motion” while formulating his first theory of gravitation. It has ten components representing kinetic stresses, energy flux and momentum of matter in terms of rest mass density :[R 4]

equivalent to (c). Then he combined with the world tensor (representing the electromagnetic-, gravitational-, and stress field) in order to formulate the momentum and energy conservation theorems.

Nordström (1910–13)[edit | edit source]

w:Gunnar Nordström (1910) explicitly formulated a “four-dimensional tensor” consisting of rest mass density and four-velocity [R 5]

equivalent to (c). Nordström used this tensor to formulate the four-force density based on the assumption of variable rest mass density:[R 6] and alternatively based on the assumption of constant rest mass density[R 7] equivalent to (c).

In 1913, he wrote the above tensor in the form

equivalent to (c) and called it “material tensor”, then he combined it with the “elastic stress tensor” p in order to reformulated Laue's symmetrical four dimensional tensor T representing spatial stresses and mechanical momentum and energy density:[R 8]

which can be used to add an elastic component to the four-force-density to give equation of motion. He went on to employ this notion in his theory of gravitation.

Laue (1911-20)[edit | edit source]

In the first textbook on relativity (1911), w:Max von Laue recognized that the “world tensor” T (i.e. stress-energy tensor) not only applies to electrodynamics but to mechanics as well, and that any form of ponderomotive force F must be based on such a world tensor, implying the complete reduction of mechanical inertia to energy and stresses. It includes the relation between momentum density and energy flux (“inertia of energy” according to Planck), and the Lorentz transformation of the tensor components into rest frame :[R 9]

equivalent to (a). From that he derived the total static system in which the total pressure vanishes[R 10]

In the second edition (1912, published 1913) he slightly rewrote the above mechanical world tensor and its Lorentz transformation in terms of momentum density as[R 11]

equivalent to (a).

In the fourth edition of his book (1921), he defined the following tensor in relation to the dynamics of mass points in terms of rest energy density , rest energy , rest volume :[R 12]

equivalent to the dust tensor (c).

Herglotz (1911)[edit | edit source]

w:Gustav Herglotz gave a complete theory of elasticity in special relativity which he defined using coordinates after deformation, and before deformation, from which he derived the deformation quantities and , together with the kinetic potential . He defined the Euler equations of motion using stress-energy tensor , whose components can be related to momentum density , energy density , velocity u,v,w, as well as “relative” stresses :[R 13]

and showed how to modify the above components using mass density m and pressure p, so as to become the hydrodynamic stress-energy tensor:[R 14]

which corresponds to (b) or in case of vanishing pressure to (c). He consequently derived the equations of motion and four-force density (X,Y,Z,T)[R 15] equivalent to (d).

Lewis/Wilson (1912)[edit | edit source]

w:Edwin Bidwell Wilson and w:Gilbert Newton Lewis (1912) devised an alternative 4D vector calculus based on w:Dyadics which, however, never gained widespread support. They defined the dyadic using four-velocity and rest mass density in order to formulate the fundamental equation of hydrodynamics:[R 16]

equivalent to (b,c).

Einstein (1913-16)[edit | edit source]

In 1913, in the context of his Entwurf theory (a precursor of general relativity), w:Albert Einstein discussed the motion of continuously distributed incoherent masses in gravitational fields, by using the contravariant “stress energy tensor of the material flow”[R 17]

equivalent to (c) in the case of being the Minkowski tensor. In a remark to that paper, they used the tensor[R 18]

which Einstein in 1914 denoted as “energy tensor of the ponderable mass flow”:[R 19]

and by including pressure p, the tensor of an ideal fluid becomes in case of adiabatic motion[R 20]

which Einstein in 1916 wrote as[R 21]

(with in special relativity).

equivalent to (b) in the case of being the Minkowski tensor.

Kottler (1914)[edit | edit source]

w:Friedrich Kottler credits #Nordström (1910) for introducing the “Nordström tensor” terms of rest mass density :[R 22]

equivalent to (c), for which he also derived the equations of motion. He commented that this tensor is realized when Laue's (1911) total static system is averaged over the total volume.

References[edit | edit source]

  1. Minkowski (1907/15), p. 105
  2. Minkowski (1907/15), p. 102-107
  3. Abraham (1909b), p. 737-739
  4. Abraham (1912), p. 312
  5. Nordström (1910), p. 441
  6. Nordström (1910), eq. 4'
  7. Nordström (1910), eq. 4"
  8. Nordström (1913), eq. 3
  9. Laue (1911), p. 136f., 149f., 184f
  10. Laue (1911), p. 169
  11. Laue (1913), p. 182ff
  12. Laue (1921), p. 207-209, 237
  13. Herglotz (1911), p. 508, 510
  14. Herglotz (1911), p. 514
  15. Herglotz (1911), p. 514, 502
  16. Lewis/Wilson (1911), p. 494ff.
  17. Einstein/Grossmann (1912), p. 232
  18. Einstein/Grossmann (1912), p. 261
  19. Einstein (1914), p. 1059
  20. Einstein (1914), p. 1062
  21. Einstein (1916), p. 811
  22. Kottler (1914), p. 716f