Absolute zero

From Slackerpedia Galactica

Zero Kelvin. Negative 273 Celsius. Negative 459 Fahrenheit.

However you quantify, it is cold but thankfully, a theoretical cold. Even the coldest parts of the interstellar medium are about 20 Kelvin, which is still incredibly cold by Earth standards.

What makes Absolute zero impossible is that it requires the presence of zero energy, hence its name. This shouldn't happen until that whole heat death of the universe thing comes around which should hopefully be still a few trillion years away.