Most of the matter in the universe has never been observed directly, and the existence of “dark matter” is essentially a placeholder name for the gap between what we can see and what the math requires — a placeholder we’ve been using confidently for about ninety years

Most of the matter in the universe has never been observed directly, and the existence of “dark matter” is essentially a placeholder name for the gap between what we can see and what the math requires — a placeholder we’ve been using confidently for about ninety years – Space