Time field

"Those cracks on the wall, do you know where they came from? You don't, do you?"

- Prisoner Zero

The Cracks were a series of splinters in he "skin of the world". According to Prisoner Zero, the cracks were in the skin of the universe. The pattern of the Cracks is always the same, and the cause remains unknown.

When discussing the cracks with Prisoner Zero, the Doctor stated that somebody must have opened the cracks. When he was asked if he knew what the cause was, the Doctor remained silent; whether he didn't know or wouldn't say is uncertain. Prisoner Zero said the Pandorical will open and silence will fall in relation to their origin.

List of Cracks

 * The first was seen on Amy Pond's bedroom wall, which soon opened up to another area in the universe - an Atraxi prison.
 * The second was seen on the TARDIS monitor, which the Doctor looked at briefly and worringly before switching it off.
 * Another was present within the hull of the Starship UK, a space ship inhabited by the residents of the United Kingdom.