Page 22 - GALIET PHYSICS BLOSSOMS III

Fig. 322
(iii) Explain in what sense one can describe the General Theory of Relativity (GR) as a ”field theory” like EM theory. You should do this by comparing and contrasting in detail the 2 theories, and at the same time explaining the basics of GR. What are the key differences between the two field theories?
Compare/Contrast
Both GR and EM theories posit fields. GR’s field itself is “spacetime,” a four dimensional space in which the four directions of possible motion are length, width, depth and time. EM’s field itself is the “electromagnetic field.”
Both GR and EM fields have sources. GR’s field’s source is “mass-energy.” EM field’s source is “a charge.”
Both GR and EM fields are polarized. GR’s field is polarized by “mass-energy” generating spacetime curvature. EM’s field is polarized by “a charge” to generate the Electric Field “E” and the Magnetic Field “B”. Each field affects the other and vice versa.
Both GR and EM fields cause motion. GR’s field causes “mass-energy” to move. EM’s E-field and B-field cause “charge” to move.
22 Bennet, Donahue, Schneider, Voit. The Cosmic Perspective. 6th Edition. Figure S3.19. 441. •22•