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17 The Twin Paradox
However, what about the dynamic consequences? Here, the numerical value of the
sound velocity (or the equivalent critical velocity c o ) figures in the energy equation
as a square factor; see Chap. 23. The sound velocity in ice for example is around
3 · 10
5 m/s, and is therefore smaller than that of light by the factor 10
5 . For the
corresponding energy, a factor of 10
10 arises. Whilst the destruction of dislocations
is normally an energetically harmless procedure (at the most an ice crystal would
melt), including the factor 10
10 would lead to a far more infernic reaction.