Reply to post: Re: DE not DM

Captain, dark energy sensor readings show dwarf galaxies orbiting the Milky Way

Anonymous Coward
Anonymous Coward

Re: DE not DM

It is true that more "normal" (baryonic) matter has been found as technology has improved, people have thought of more things to look for, etc. But there is a limit to how much more there can be without it being visible in some way (either radiating or blocking electromagnetic radiation).

Note that dark energy and dark matter are hypothesized to explain very different phenomena. The only thing they have in common is the word "dark". In the case of dark matter, it is dark because it doesn't interact with light. In the case of dark energy, it is dark because no one knows what it is.

Dark matter is required to explain the unexpected orbital velocities of stars, gas and dust around galaxies (and galaxies in clusters, and gravitational lensing, and ...). The best explanation so far is simply that there is more mass in galaxies than we can see. It is *possible* that this is actually due to something like gravity not working quite as we think. But the more evidence that is gathered, the more likely it seems that it is some form of matter that doesn't interact electromagnetically (like neutrinos; but not neutrinos - for various reasons).

Dark energy is really a placeholder for whatever is behind the apparent (and unexpected) accelerating expansion of the universe. The simplest way of representing this is to plug an extra energy term into the Einstein Field equations (did I say "simple"?); hence the name. But no one really has any idea if it is some form of energy or something else completely. New physics: yay!

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