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Wait, there’s no conservation of energy?
by asimpletune 8y ago
Wait, there’s no conservation of energy?
- dschuetz 8y agoRight, according to this blogspot post, one could figure that what we've learned about entropy is completely wrong! But no! The net amount of energy inside an isolated system does not change. It dissipates evenly through the system, and the system as a whole reaches it's maximum entropy/equilibrium. That means, each part of the system which can exchange energy, has the same amount of energy.
- nabla9 8y agoThat's true. Conservation of energy is not a physical law. It's a consequence of mathematical theorem called Noether's theorem. All systems with certain differentiable symmetries have a corresponding conservation laws. In a system that is not time translation invariant, energy don't have to be conserved. Expansion of universe breaks the time symmetry.
- noobermin 8y agoI'll say that most systems are time invariant, so conserve energy. One should always know the system one works with. For example, first year undergrad problems near the surface of the earth for example since they ignore the earth do not conserve momentum.
- cygx 8y agoNote that Noether's second theorem still applies, so any timelike vector field will yield a conservation law due to diffeomorphism invariance. In that sense, energy conservation still holds even in the absence of Killing fields, though some people argue this doesn't count as a 'proper' law of energy conservation as it includes contributions by the gravitational field, for which an energy-momentum tensor cannot be defined...
- sunstone 8y ago"Noether's" theorem. Is that a joke or what?