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All physical objects are made up of atoms. To a first approximation, this means everything is connected by springs, which means the assumption of zero elasticit
by archgoon 15y ago
All physical objects are made up of atoms. To a first approximation, this means everything is connected by springs, which means the assumption of zero elasticity is impossible. 'Inelastic' objects just have very large spring constants, they don't deform much, but they still deform. By the way, long before we talk about speed of light considerations we run into the speed of sound. This is material dependent, true, but that'll again be dictated by the physics of atoms.
Or alternatively (if you want to start imagining crazy ass materials made of dark matter), zero elasticity is defined by invariants of length. Length is not something which is preserved by the symmetries of special relativity (Lorentz Transformations), so a rigid object is not a compatible notion with the idea that the laws of physics are invariant under Lorentz Transformations.
- noonespecial 15y agoI think maybe you can have a perfectly inelastic object in a "spherical chicken of uniform density" type thought experiment. The catch is that space is deformable(1) so it makes the experiment not especially useful. And that might be the point. (1) Unless you assumed that your material did not deform with the space that contained it, which would make the experiment nonsense.
- archgoon 15y agoNo you can't have an inelastic object and at the same time say that "Special Relativity is Correct". They are incompatible definitions. It's like talking about all even primes greater than 2. Or green objects that aren't green.
- geon 15y agoExactly. To clarify: When you tug the string, you create a shockwave of tension traveling along it. Since this is a wave of actual moving matter, it is an acoustic wave, moving at the speed of sound (whatever it is for the string material).