If a conspiracy really exists, then our understanding of basic laws of physics is flawed as the speed of light must not be a limiting factor to the speed at which travel can occur and some government somewhere would tip their hand at having been in on the conspiracy by funding a lot of research in this area of physics.
Given what I've read about UFOs, I'd bet money on the notion that we don't know so much about esoteric physics. By the way, I majored in physics.
Even Albert Einstein said, "Knowledge is the measure of the radius of the Sphere of Ignorance". He also said, "Imagination is more important than knowledge". Another interesting statement, "The only thing that interferes with my learning is my education".
If would be silly and arrogant to assume that we have mastered the Cosmos. We can't even get income tax correct.