At very low temperatures, many interesting and new physical effects are found. Physicists find surprises at very low temperatures. But how low is low? To get a feeling for how cold things can be, we put some balloons in liquid nitrogen, which has a temperature of 321 Fahrenheit (or 77 Kelvin). The gas inside the balloon cools down, making the balloon shrink. In fact, we can fit many balloons inside a container suitable only for one balloon at room temperature. This gives you some idea that atoms can behave in strange and wonderful ways when very cold.