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Matter, dark matter and dark energy "make up" 5%, 27% and 68% of the Universe. I can understand that matter and dark matter are comparable, but what does it mean that there is more than twice as much dark energy as dark matter? Don't they need to have the same units to do a comparison? It sounds like I would say that my body is 40% mass and 60% length.

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This comes from Einstein's mass-energy equivalence:

$$E=mc^2$$

Mass–energy equivalence states that all objects having mass, called massive objects, also have corresponding intrinsic energy, even when they are stationary.

where $E$ is the energy of a particle and $m$ is it's rest mass. This is one of the fundamental result of special relativity.

note that this only holds for object who are at rest. the full relation, called the Energy-Momentum relation, states:

$$E^2=m^2c^4+p^2c^2$$

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  • $\begingroup$ Thank you Tomka. Clear. $\endgroup$
    – ADBF
    Feb 17 at 7:45

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