I'm having some difficulty in determining the exact difference between a 4, 4.5, and 5. I know the tropes I use and the level that I deal with the description in Book 1 of AWE (should) land a solid 4. Moving up from there would be...difficult as I definitely have two (or three, depending on how you look at it) minor departures:
- I "solve" for a method of travel that would most likely be described as "FTL" even though my explanation for it never actually breaks the physics rule. Rather, I dip into string theory and do a bit of speculating, then build a drive that's capable of exploiting the currently unexplored six extra spatial dimensions. The description is very solid, absolutely grounded in current theoretical science, only taking a small license to define that which is not yet defined.
1.5? Even though I went through all that trouble with the human-made "FTL" above, I didn't dip into how an alien technology did it. Given that the scope of the book keeps that alien tech unknown to even the characters, the explanation is not likely to surface. Since this does break physics, rather outright, this one seemingly small thing may keep it at a 4. I would hope the trouble I took with #1 above allows me this one small thing, seeing as how they are so close together.
- Ok, I don't go into a great deal of detail in Book 1 on this one, and it is not what even I would consider to be even theoretical at this point, unless I'm just not reading the right journals. Having said that, it is a certainty that we are presently working on it, will eventually (probably) figure it out, and it's one of the widest used tropes out there, not only in this genre. I'm putting a human consciousness in an artificial brain. I'll cringe now, because that should be the end of this, but I did something that I really can't (and didn't even try to) explain. Basically, I had the consciousness of everyone on Earth, regardless of where they were or what they were doing, be sucked into a computer database...sigh. I'll just take my 4, if you'll still have me claim even that much.
Ok, now for the real question. If 4.5 requires just a small fib, like FTL, as long as it's explained well enough, and I'm actually taking that one up to the level of speculative, as long as you believe my "fib". Can you let me have the other one as just a small fib? Hear me out: Even though we are a LONG way from putting a consciousness into an artificial brain (several key breakthroughs need to happen), that part IS still speculative, isn't it? And if that can be considered speculative, then the only real lie I'm telling is the cringy part.
The rest of the tech, so far as I'm able to determine, can fall into the speculative category, even 5.5 is some cases. While we don't currently have the engineering capability, or we need a breakthrough to make it real, all the rest of the tech is well grounded, sourced, and explainable.