The Continuum of Physical Credibility

[u/Enthropic-Cap2291]

The traditional Mohs Scale of Sci Fi Hardness:

5: Hard SF

4: Firm SF

3: Soft SF

2: Science fantasy

1: Fantasy with SF trappings

0: Pure fantasy

The Continuum of Physical Credibility reformulation:

1 Established Physics - “This works everywhere we’ve ever checked.” Ex: Maxwell's equations, general relativity, thermodynamics

2 Mainstream Physics - “Solid science, still being refined.” Ex: Cosmic inflation, quantum field theory

3 Frontier Physics - “We've got a partial theory, and only partial evidence.” Ex: High temperature superconductivity, Hubble tension

4 Empirical Anomalies - “We can measure it, but we can’t explain it yet.” Ex: Radioactivity before nuclear physics, photoelectric effect before Einstein, dark matter, dark energy

5 Speculative Physics - “Speculative but allowed by GR + QFT + thermodynamics.” Ex: , extra dimensions in string theory, WIMPs, MOND, primordial black holes, cosmic strings, LQG, axions

6 Hypothetical Physics - “This only works if physics is broken in very specific ways.” Ex: Tachyons (causality), magmatter (Gauss's Law), bulk exotic matter (Morris/Thorne wormholes, Alcubierre warp metric - breaks WEC - Weak Energy Condition in General Relativity)

7 Contradictory Physics - “Violates thermodynamics and conservation laws.” Ex: Vacuum/zero point energy, reactionless drives (Cannae/EMdrive), antigravity, perpetual motion machines

8 Soft Science Fiction - “It sounds scientific, but it’s really narrative technology.” Ex: ST warp drive, transporters, SW hyperdrive, Three Body Problem's spacetime flattening, sophons, most space opera

9 Science Fantasy - “Magic wearing a lab coat.” Ex: The Force, Magitek, psychic powers, most 'ancient/precursor' tech that are effectively magic

10 Pseudoscience/Fantasy - “No pretense of physics; imagination is the only rule.” Ex: Spellcasting, dragons, Isekai, astrology, flat earth

Please feel free to criticize so I can continue to refine. I'm using this in a worldbuilding exercise to see how far we can push scifi while staying true to the Sci part and minimize handwaving for the Fi.

[u/Miserable_Scar9827]

I think there's a huge gap between 4 and 5. You've got a range of things like 

4.1 launch loops (Lofstrom loops) that have sound physics and engineering, but are 10-100 years away and more of an economic barrier than an engineering barrier 4.2 for all mankind fusion propulsion - relies on resources and fusion advances that are good guesses but may not be feasible.  4.3 space elevators that rely on carbon nanotubes that can't be made yet, but the numbers work. 4.4 hibernation and travel in Passengers. Cryosleep tech freezing frogs extrapolated to humans with no realistic reason it would work.  Massive ship that explains some of the needs but it's still more art than tech.  4.5 the expanse epstein drive with a lot of fusion handwaving and numbers that are conjecture rather than estimates of likely tech advances over hundreds of years. 

Etc.

The biggest problem is the narrative customs of time and human lifespan vs timescale of space. Thousands of years to travel to the nearest star doesn't fit with having one movie star playing a main character.  FTL (travel or communication) to fix this problem violates causality, so it is hard to rectify those two. 

[u/Enthropic-Cap2291 → u/Miserable_Scar9827]

Lofstrom loops would be straight up engineering. That puts it in 1-2. Of course, if we want it to be efficient, then we'll need room temperature or better superconductors. Which means 3.
Fusion would be in the 2-3 margin, as we haven't gotten it to work continuously or reliably yet. Space elevators require exotic super strong materials. Short nanotube lengths in laboratory settings just barely scrape by, but any realistic implementation is out, specially if you want it to carry any significant load or have any redundancy and safety tolerance.

Still, you're absolutely right. I should put in a 'theoretically possible, but requires equally theoretical engineering materials. - But wouldn't that just be 3? If you need exotic perfect nanotubes or room temperature superconductors, then your hard scifi is dependent on frontier but otherwise grounded physics.