So, as someone who has little to no practical technical knowledge of physics and stuff and more of a broad conceptual understanding, I find testable data to be the hard part to this discussion. However, I'll do my best:
So, for instance, on Lockheed Martin's website they have a page devoted to compact fusion. To quote a fragment on their site it is "our engineers are looking to the biggest natural fusion reactor for inspiration – the sun. By containing the power of the sun in a small magnetic bottle,". This falls in line with what I think. You would have to recreate a atomic reaction to produce the same forces that would be necessary for a propulsions system. We see fusion in the stars, so we have to take that as a foundation, and not some attempt at a 'shortcut'. To put it in simpler terms, it takes astronomical amounts of efficiency to get the energy, components within range of something we can produce. To scale it out is to say even if we are to produce a minute percentage of the suns power in a fusion reaction, we would have to have a corresponding percentage of reactants, or energy, or what have you to initiate the reaction. This is also to say that anything manmade trying to imitate this atomic process would have to follow the same rules of thumb, ie. how we detail the process and circumstances needed for the reaction as we see it in the universe happening.. Once again, an example here is stars and their fusion processes.
So, if you take all of that-The fundamentals of that and 'hypothetically' apply it to other reactions you have a logical conclusion: We simply do not logically have the money to buy the things we would need to become a space-faring species, unless a global undertaking was put in place to collect them. But, I digress, this could be applied to thing like darkmatter and antimatter, but I'm not sure how. If you want to talk about warp drives, well, you would first have to find something in the universe that has a warping effect..ie. a wormhole or an anomaly, and then reproduce that effect. The only thing I could post the most erm, data on is fusion. And that's merely saying what we know, a lot of the knowledge if any is probably recent..