Layman Explanation Of The Most Realistic FTL Technology?

I don't think in any of your examples people had scientific reasons to believe those things were impossible. That's the main sticking point with FTL - it appears to break the universe, rather than just be very difficult to do. It is the 20th century version of reanimating the dead.

The "flying machine" for us is a reactionless drive - something that could propel a sublight starship without a need for more fuel than it could possible carry. We don't know how to do that, but it is at least a possibility.

 

@Fallow
I get you but see...like, if you want to go back far enough, like I said if I brought an Uzi to ancient Rome they wouldn't know what to make of it since the very notion of gunpowder to say nothing of full automatic sub-machine guns is literally implausible for them. To them, it "breaks" the universe, because in their universe such concepts were unheard of. That's kind of my point is that we don't know jack about the universe so what does and doesn't "break" it. We can ASSUME based on what we think we know now that time travel is impossible...and a millennium from now someone will find this site on the Internet Wayback Machine and think it's hilarious pre-posthuman species didn't have pocket time portals to tweet their past and future selves installed on their phones.

I guess, the most succinct way to put it is that we don't know dick about the universe, we know about this planet (kinda...) and maybe this star system, so (literally) God only knows what else is out there.

 

I think you misjudge the Romans. Their world was not turned on its ear by the invention of the arch or the stirrup, they understood a great deal of basic chemistry and had at least seen examples of Chinese quench hardened steel by then. An Uzi, devastating as it might be, is still just a simple mechanical device using physical principles that a natural philosopher of the time would recognize, even if they were unable to reliably duplicate it. Much like the Babbage Engine, the principles would have been clear enough even if the engineering kept the device out of production.

A laser or TV monitor would have been more mind blowing since the Romans had no real concept of electronics, but it still wouldn't have violated any physical laws that they knew of. In other words, the Romans wouldn't have seen a paradox of the scale that FTL represents.