Why is space cold if there’s no matter in it?
In: Physics
Because you can expand the definition of “cold” and “hot” to include heat radiation.
If you put something in space, it will radiate away its heat after a while, until it has a certain temperature that’s very cold.
You can do this at home easily: hold the back of your hand close to a hot cup of tea without touching it: you will feal the warmth. This warmth is not transmitted through the air, but through infrared radiation.
Now take a chilled drink and hold the back of your hand close to it. You will feel the coldness of it. This is also not the air, but the “absence” of infrared radation coming from the drink, as well as the infrared radiation from your hand that takes away the heat.
Since there’s nothing in space to radiate heat onto you, you will radiate your heat away and become very very cold.
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