A fun thought experiment to counter this idea. Let's presume that the universe is full of Dyson Spheres, and the gravity they produce is what we call "Dark Mat

A fun thought experiment to counter this idea. Let's presume that the universe is full of Dyson Spheres, and the gravity they produce is what we call "Dark Matter". Well, Dyson Spheres must be built, right? So earlier in time, there would be fewer of them, and later in time there would be more of them. When we look into the sky, we look back in time. So if this were the case, when we look backwards in time we should see more brightness and less dark matter effects, while closer in time we should see less brightness and more dark matter effects. We do not see those patterns. Dark matter is consistent over time, as far as we can tell, and brightness from stars remains what we would expect.