You have no doubt heard of the F-35 or F-22 and wondered why these aircraft are so damn expensive, and why they are so controversial. I can't seek to answer those questions for you, but I can help to explain the academics behind fifth generation aircraft and their low observable (or "stealth") technology.
Low observable technology is important for several reasons, not least of which is the simple fact that you cannot shoot what you do not know exists. Hollywood movies like to highlight the importance of "heat seeking missiles" (professionally known as "infrared (IR) missiles"), but most modern warfare is conducted now beyond visual range and relies heavily on radar guided missiles. These are an impressive jump in technology, but they do rely heavily on your ability to detect the target on your radar.
More likely than not, the existence of fifth generation aircraft is signaling the start of a new arms race in which the four major super powers (European Union, United States, Russia, and China) are modernizing their air forces to ensure their pilots are able to fly longer and strike further against any adversary they may encounter. This recent push to modernize is likely an attempt for those powers to retain their competitive edge in a global deterrent based strategy similar to that of the Cold War. However, unlike the Cold War, these weapons can be used and exported without fearing for their direct contribution to humanity's destruction