They are, but it's intriguing to think about in what way exactly Newton's three laws have been replaced or generalised in relativity.
- There are two ways to think about the first law -- the first is "inertial reference frames exist". This is unchanged in special relativity, but general relativity generalises the notion with that of geodesics. The law as it is typically stated -- "stuff moves in straight lines on spacetime unless forced" is generalised to the geodesic equation, d2xμds2=−Γμαβdxαdsdxβds.
- F=dp/dt is generalised to F=dp/dτ in special relativity, and is replaced by a covariant derivative in general relativity. F=ma has some weirder changes.
- The third law is the conservation of momentum. This is replaced in General Relativity by the statement ∇μTμν=0 (∇ instead of ∂).
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