All digital cameras are imperfect - there is always a bit of noise, but usually it doesn't come through since your scene is bright enough to make small amounts of noise imperceptible. In a completely dark room the camera still tries to get data from the photo sensor, but the noise (created by temperature fluctuations, imperfections in the chip itself and so on) is all you get. You may theoretically be able to predict the noise on short time scales, but it's a chaotic system.