Why?
- A scientific "theory" is a well-accepted model that represents the world in a consistently useful manner
- A model does not need to be correct, just useful
- We use flat-earth approximations all the time
Just like we use Newtonian "classical" physics despite knowing more accurate models, just like we use lower-precision constants, we can make use of approximations that we live on a flat earth.
Meaning, the following theories are also correct given they're generally useful in some scenarios:
- Point-mass Earth
- COBE sky cube Earth
- Torus Earth
- Massless Earth
- Motionless Earth
- Perfectly spherical Earth