Overwhelming scientific consensus and empirical validation drive the 99.3% market-implied odds against a flat Earth, as traders assess centuries of astronomical observations, satellite imagery, and gravitational physics that have long settled the debate in academic and cultural spheres. This near-certain trader consensus reflects the absence of credible challenges, with flat Earth ideas remaining a fringe pop culture conspiracy without mainstream traction or new evidence. Realistic upset scenarios would demand unprecedented reversals in observable global phenomena or fundamental physics, developments the market views as virtually impossible given the strength of existing data.