The pressure difference in passenger planes is easily understandable if you take a soft and empty plastic bottle, close it at the highest position of your flight (in the upper part of the image) and watch again while landing. You will see that the pressure makes the bottle shrink (in the lower part of the image). The pressure at sea level is about 1.013 bar representing the weight of air/atmosphere between earth and space. In airplanes it is reduced to a level equivalent to a height of more than 2000m, means appr. 0.6 bar. This pressure difference lets the bottle shrink. This is the reason why divers should not scuba dive one day before flight since the pressure difference already caused decompression accidents in planes.