One of the most exciting things about dark energy is that it seems to live at the very nexus of two of our most successful theories of physics: quantum mechanics, which explains the physics of the small, and Einstein's Theory of General Relativity, which explains the physics of the large, including gravity.
Your chemistry high school teacher lied to you when they told you that there was such a thing as a vacuum, that you could take space and move every particle out of it.