Void

The Void is the term given to the empty space beyond the generated boundaries of each map. It can be seen through gaps in the lowest layer of Bedrock on maps generated prior to the Halloween Update, but also simply by looking up from ground level, as the sky and the void are one and the same. For this reason, the void is a light source, and its brightness depends on the time. As per a recent update when lava generates on layer 2 the bedrock on layer 1 below it is replaced by smooth stone meaning it is possible to enter the void again through much larger entrances than ever before without hacking.

It is potentially endless, although falling excessively far would cause the game to crash due to memory limitations and obscenely large numbers whose digits extend beyond those capable of being processed. However, falling into the Void causes the player's health to be depleted by about 4 hearts per second, leading to the player's death in 2.5 seconds or less, should he or she drop.

In The Nether, the Void is red. It can be entered if one uses a map editor to make a hole in the top bedrock layer of the Nether.

Entities (blocks, mobs and items, excluding the player) entering the Void will be deleted in the following tick (as soon as possible). This may be due to the Void not being part of a Chunk, although it is most likely a deliberate optimization/crash prevention method implemented by Notch. For this reason, Blocks cannot be built on the underside of the Bedrock layer, and although Water and Lava appear to flow into it, they will not actually spread and form beneath the lowest layer. This prevents players from descending into the Void safely via swimming.

There is currently a bug in SMP that will remove chunks client-side, so while the data is still there, the client cannot see it and will glitch if they step on it. This can be fixed by reconnecting, placing a torch next to the missing chunk or changing the fog distance by pressing F. If you ride a Minecart into this missing chunk, and then you step out of the Minecart, you will fall to the void and die, regardless if you disconnect and reconnect.

Light cannot travel through into The Void.

Media
Click here for A video of The Void when fallen into.

Click here for A video of The Nether's Void.