Poetry of Physics and the Physics of Poetry

Prelude to Relativity 117

112 The Poetry of Physics and The Physics of Poetry

the Earth’s motion and hence, it would no longer be necessary to tilt the

telescope through the angle of aberration to capture the starlight.

Fig. 13.2

The Irish physicist, Fitzgerald, proposed that the negative result of the

Michelson-Morley experiment could be explained if one assumes that

matter in motion contracts in the direction of its motion through the

aether. He claimed that the contraction, which increases as the velocity

of the matter increases, was due to the pressure of the aether wind

encountered as the body moved through the static aether. If a body has a

length, Lo, at rest then, as a result of its motion, it would have the length

Lo

!

1 "v^2 /c^2. Unfortunately, this contraction could not be measured

since any meter stick employed to measure this contraction would also

contract. This reduces Fitzgerald's hypothesis to an ad hoc (after the fact)

status. His idea is not without merit, however. For one thing, Fitzgerald,

using his formula, correctly predicted that no material body could ever

travel faster than the speed of light, c, since at this speed the length of the

body, L= Lo

!

1 "v^2 /c^2 goes to zero. Secondly, the contraction, which he

attributed to an actual physical force reappeared later in Einstein's

Theory of Relativity with a more sophisticated interpretation. Finally,

Fitzgerald's idea stimulated the Dutch physicist, Lorentz.

Lorentz reasoned that the mass of a charged particle would increase

as its length decreased. Assuming that the mass of a particle was due to

the potential energy of its own charge, he argued that as the particle was

crowded into a smaller space, its potential energy would increase and

hence, its mass would increase. Since the potential energy is inversely

MICHELSON–MORLEY APPARATUS

Fig. 13.2

The Irish physicist, Fitzgerald, proposed that the negative result of the
Michelson–Morley experiment could be explained if one assumes that
matter in motion contracts in the direction of its motion through the
aether. He claimed that the contraction, which increases as the velocity
of the matter increases, was due to the pressure of the aether wind
encountered as the body moved through the static aether. If a body has a
length, Lo, at rest then, as a result of its motion, it would have the length
Lo 1 −v^2 /c^2. Unfortunately, this contraction could not be measured
since any meter stick employed to measure this contraction would also
contract. This reduces Fitzgerald’s hypothesis to an ad hoc (after the fact)
status. His idea is not without merit, however. For one thing, Fitzgerald,
using his formula, correctly predicted that no material body could ever
travel faster than the speed of light, c, since at this speed the length of the

body, L = Lo 1 −v^2 /c^2 goes to zero. Secondly, the contraction, which
he attributed to an actual physical force reappeared later in Einstein’s
Theory of Relativity with a more sophisticated interpretation. Finally,
Fitzgerald’s idea stimulated the Dutch physicist, Lorentz.
Lorentz reasoned that the mass of a charged particle would increase
as its length decreased. Assuming that the mass of a particle was due to
the potential energy of its own charge, he argued that as the particle was
crowded into a smaller space, its potential energy would increase and
hence, its mass would increase. Since the potential energy is inversely
proportional to the distance, he predicted the product of the mass and the
length of the particle would remain constant and hence, the mass would

increase according to the formulae m = mo/ 1 −v^2 /c^2 where mo is the

C^2 −V^2

C + V

C V−