simple principles of relativity and the whole theory unfolded. In particular, he
showed that the energy of a particle E is determined by the equation
E = ×mc^2. For the energy of a body at rest (when v = 0 and so = 1), this
leads to the iconic equation showing that mass and energy are equivalent:
E = mc^2
Lorentz and Einstein were both proposed for the Nobel Prize in 1912. Lorentz
had already been given it in 1902, but Einstein had to wait until 1921 when he
was finally awarded the prize for work on the photoelectric effect (which he had
also published in 1905). That was quite a year for the Swiss patent clerk.
Einstein vs Newton
For observations on slow moving railway trains there is only a very small
difference between Einstein’s relativity theory and the classical Newtonian theory.
In these situations the relative speed v is so small compared with the speed of
light that the value of the Lorentz factor α is almost 1. In this case the Lorentz
equations are virtually the same as the classical Galilean transformations. So for
slow speeds Einstein and Newton would agree with each other. Speeds and
distances have to be very large for the differences between the two theories to be
apparent. Even the record breaking French TGV train has not reached these
speeds yet and it will be a long time in the development of rail travel before we
would have to discard the Newtonian theory in favour of Einstein’s. Space travel
will force us to go with Einstein.
The general theory of relativityEinstein published his general theory in
- This theory applies to motion when frames of reference are allowed to
accelerate in relation to each other and links the effects of acceleration with those
of gravity.
Using the general theory Einstein was able to predict such physical
phenomena as the deflection of light beams by the gravitational fields of large
objects such as the Sun. His theory also explained the motion of the axis of
Mercury’s rotation. This precession could not be fully explained by Newton’s
theory of gravitation and the force exerted on Mercury by the other planets. It
was a problem that had bothered astronomers since the 1840s.
The appropriate frame of reference for the general theory is that of the four-
dimensional space–time. Euclidean space is flat (it has zero curvature) but