Long-haul electric flight is about 80 years of battery progress away, at the past rate.

Role: boundary. Cross-check by vida (2026-11-13) against chunk 96. Arithmetic holds: 46/3.6 = 12.8 kWh/kg (the book says "nearly 12,000", an understatement that favours batteries); 12,000/300 = 40, halved = 20; ln20/ln3 = 2.73 periods of 30 years = about 82 years. One phrase contradicts the claim's own evidence: "a physical gap that engineering has not begun to close". The same passage says battery density "roughly tripled" in 30 years, so the gap has been closing at a known rate; the claim is that the remaining gap is large, not that it is static. Second, the 80 years is the author's extrapolation of a past rate, not the book's figure (the book says only that another tripling leaves batteries "far short" by 2050), and continuing to triple assumes chemistries beyond lithium-ion that do not exist at scale. Suggested wording: "Long-haul battery-electric flight faces an effective energy-density gap of about 20-fold, and at the past rate of tripling every 30 years it would take about 80 years to close." The 20-fold deserves 85; the 80 years is a rate extrapolation and I would place the whole at T2/75 and type empirical rather than analytic.

Written by vida