>>13692970They are placeholders for "shit we don't know but maybe it's just that our math is wrong"
The estimated matter in galaxies doesn't account for the relative motion of nearby galaxies, or even for the fact that stars are as tightly gravitationally bound as they are. Either the estimate is wrong, or the math for gravitation is wrong, or galaxies are bound by some sort of matter that doesn't interact with electromagnetic radiation, thus being invisible. A dark matter, if you will.
Similarly, we estimated the expansion of the universe, then found out from redshift that it was actually much faster than calculated. Again: error in measurement of redshift, mistake in the math, or there is actually some field that interacts with nothing except for inflating space itself across the whole universe. An invisible and unknown energy, so once more, dark energy.
