Practice question · Multiple choice
Newtonian mechanics was superseded by relativity and quantum mechanics, and engineers still use it to build bridges and launch spacecraft. Why is a superseded theory still the right tool?
Hints
- Compute the relativistic correction for a spacecraft at 10 km/s. How large is it?
- Ask what the newer theories predict in the low-speed, large-object limit.
Show the answer
C. Because it is an excellent approximation within a definite domain.
Why
The newer theories contain the old one as a limit, relativity's corrections scale like v²/c², about one part in a billion at 10 km/s, far below any bridge's tolerances. What supersession actually provided was knowledge of the boundary: before relativity nobody could say where Newton would fail, and now the failure conditions are quantitative.
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