Why are the windows of airplane (aircraft) oval?

When traveling abroad and taking an airplane (aircraft), I often feel puzzled. Why are the cabin windows all small and oval in shape?

In fact, the aircraft cabin windows in the early years did not limit the shape, but with the advancement of science, scientists found that with the improvement of flight ability, rectangular windows can no longer afford high-performance flight mode, and the pressure will be concentrated on the four corners of the rectangular windows. As long as the pressure accumulates to a certain value, it may break the aircraft and even cause an accident of disintegration in the air.

The elliptical window has also been confirmed by scientists that this shape can best evenly share the internal and external pressure difference stress. Therefore, aircraft manufacturers in the industrial age will naturally develop aircraft designs that best meet the definition of safety to make flying safer. The cabin windows of modern aircraft are basically oval-shaped (unless a local tyrant spends a lot of money to use a fighter-grade glass structure, which is an exception to the situation where it is to be rectangular).