When confronted with the question of the shape of the world, many people are quick to assert that they live on a globe because they believe that they have personally seen the curvature of the earth from their airplane window. Some people even believe when they visit the beach or climb a top a mountain that they are able to see the horizon curve downwards far in the distance. The reality is however that anyone thinking they can see curvature on the horizon from any altitude is suffering from a serious case of confirmation bias and cognitive dissonance. To begin with, the glass used in all commercial airplane passenger windows is actually round, layered and slightly curved, which distorts the edges, giving the impression that the horizon and other straight lines curve downwards. These rounded windows have the effect of evenly distributing pressure and reducing the likelihood of cracks or breaks because they have no corners for stress to concentrate, making them better at withstanding pressure. Unfortunately though, these windows also have the strange side effect of causing people to believe that the earth is a globe because they mistake the curvature of the glass for that of the horizon. If these passengers would instead take a visit to the cockpit window and view the horizon from the pilot's vantage point, they would see clearly that the horizon remains completely flat as far as the eye can see. In fact that is why the horizon is named as such because it is always perfectly horizontal. Likewise, the reason airplanes are named airplanes and not air globes is because they are flying over a level plane. Based on the curvature math for a globe of given proportions, a small amount of curve should already be visible to the naked eye even at sea level. After just one mile there would be 8 inches of curvature, increasing exponentially so that after 2 miles there would be 32 inches and after 3 miles there would be an entire 72 inches, 6 feet of earth's curvature necessarily visible on the horizon. The fact of the matter is however that this supposed exponential curvature drop is not visible or measurable from any altitude whatsoever. Whether at sea level, 5 miles high at top mount Everest, 7 miles high in a commercial airliner, 12 miles high in a U2 spy plane or over 20 miles high aboard an amateur high altitude balloon, there is never the slightest bit of curvature and the horizon rises to the level of the observer all the way up. If the horizon was actually the physical curvature of a globular earth, it would necessarily stay fixed and as an observer gained altitude they should have to look down to see it. This never happens though and no matter the altitude, the horizon always rises to eye level, remaining perfectly flat, 360 degrees around as is only possible over a level plane. Furthermore, if the earth were truly a spheroid, nearly 25,000 miles in circumference, airline pilots would have to constantly correct their altitudes downwards so as not to fly straight off into outer space. For example, a pilot wishing to simply maintain their altitude at a typical cruising speed of 500 miles per hour would have to consistently dip their nose downwards and descend 2,777 feet over half a mile every minute. Otherwise, without compensation in one hour's time, the pilot would find themselves 31.5 miles higher than expected. In reality, the only times pilots make such drastic altitude adjustments are just after takeoff and just before landing. Once cruising altitude is reached, commercial planes remain level for the entire duration of the flight with no such constant adjustments necessary. In fact, the only necessary adjustment truly needed in this matter is for globe earth apologists to simply humble themselves and admit as Mark Twain quiped that unfortunately it is easier to fool people than to convince them they have been fooled.