That's not to say we can't measure or detect dark matter and dark energy, though. If you look at the map, you'll see a web of galaxies and places where dots clump. Dark matter still feels gravity's pull, so galaxies align themselves along the webs and clumps of dark matter. We can detect dark energy too. When we look into space, really distant things we'd expect to look white actually look red; they've been redshifted. That's because their light rays have stretched out, because the space itself the light travels through expands, like a stretched-out tattoo on someone who's gaining a lot of weight.