There are obvious things which feel possible and would revolutionise so many things, like room temperature semiconductors, which we don't have yet. Also things we've better understood since 2012 like detecting gravity waves.
I don't understand how anyone could think we've "discovered all the physics which could matter to us", when we know full well there are massive gaps in our understanding.
Carroll says strange things sometimes. Epistemology doesn't appear to be his strong suit.
I doubt if dark matter can be used to make things lighter, possibly dark energy could be used for that (which is even more elusive than dark matter). It could only make thing heavier if there is a method to confine it. But because it seems that dark matter does not interact with normal matter (at least not often), I do not see how it can be confined to ordinary matter. Take notices that neutrinos also cannot used for this purpose, because the simply zap through us by the millions everyday, without us noticing anything. We have not found methods that to confine neutrinos yet. They seem to fly at speeds close to the light speed.
This seems to be a case of "not knowing what we don't know", as Donald Rumsfeld would say.
His claim implies that we know what we don't know. The reality is that we most likely don't...
That brought down Rumsfeld, not that he ever suffered for it. Millions of other people did, instead.
A adopted a very fringe, unified physics model. From this perspective we are looking at none of the possible signals that would make sense for long distance communication.