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It has been proved by the Red Shift that universe is expanding. But if the universe is actually expanding, it needs energy to do so. I also do not know that with expansion in universe if mass increases.

My question is from where do the universe get the energy to expand? How does it not violate the law of conservation of energy?

Qmechanic
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Sarban Bhattacharya
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1 Answers1

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How does it not violate the law of conservation of energy?

It does violate the law of conservation of energy.

More precisely, the spacetime that describes our universe at cosmological scales is the FLRW spacetime (see also LCDM). It does not have time translation symmetry, there are no timelike Killing vectors. As a result there is no conserved energy at cosmological scales.

It is also difficult to even define a non-conserved energy for the whole universe. The issues are that due to curvature there is no unique way to add spatially separated vectors and that simultaneity is a matter of convention and will differ in different frames.

Dale
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  • No global timelike Killing vectors; there are certainly timelike Killing vectors. But absence of global timelike Killing vectors is also true in black hole solutions, and we usually don't say that they fail to conserve energy! I'd argue that Killing vectors aren't exactly the right thing to think about, here, because they only say whether the energy of test particles is conserved. – Sten Jul 25 '23 at 19:47