You can't assume that they can build a Dyson sphere while their technology is as limited as us earthlings. If you can imagine some alien species building a meg

You can't assume that they can build a Dyson sphere while their technology is as limited as us earthlings. If you can imagine some alien species building a mega structure in such a short time, you should be able to imagine that they have a way to transfer and store that amount of energy. The laws of thermodynamics, as we know it, prevents 100% efficiency in doing that, but if they have a directional heat dissipation device, and their generator is highly efficient, we will hardly have any chance to detect that. I can imagine they could have some version of our power plant, only orders of magnitude more advanced. Instead of moving electrons, they could be generating and moving matter anti-matter stuffs.