what happens after death?

There are two ways to look at what happens after death: 1- your perception of the experience. 2- what actually happens.

1- Unfortunately, there is very little credible first-hand evidence of this, so speculation is rife. Some say there's a white light, some think there is nothing. Personally, I think our perception of the experience would be fundamentally different to mundane senses, such as Sight, Sound, etc, if our consciousness does indeed stretch beyond the veil.

2- What actually happens is well documented, including future predictions. Initially, decomposition takes place, reducing the cadaver and redistributing the nutrients back into the ecosystem via insects, plants, scavengers, bacteria, etc, until nothing is left. Eventually, our star will expand and consume the solar system before going supernova- at which point all of our corpses will be spread across the universe as stardust, until gravity asserts itself and the clouds of stellar dust coalesce into nebulae, asteroids and even more planets.

Realistically, the teachings of Buddha got it closest to correct, as far as rebirth is concerned. Eventually, there very well could be another life-form born from the stellar ashes of each of our corpses! One person's carbon, for example, could potentially end up as part of the carbon making up multiple different organisms or even stellar bodies!