Eli5: Why is the universe/ space so cold if there is nearly no matter?

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I always thought that the term „temperature“ describes the amount of movement in matter on a microscope scale. The movement of atoms. So how can there be a temperature in space if there is a vacuum?

In: Planetary Science

5 Answers

Anonymous 0 Comments

there is essentially no temperature in space as there is nearly no matter, but given how we define temperature that also means almost no matter = almost no movement which would mean the temperature is low.

why space is “cold” is mostly because if you put something into space it would simply radiate its energy outwards over time and cool down more and more.

interestingly we do have the exact opposite problem with the electronics we send into space, they produce waste heat while running and since theres no matter to interact with you can only rely on radiating that heat away.

thats why the ISS has large folding panels that kinda look like white solar panels, these are used to radiate the heat away from the station.

Anonymous 0 Comments

Yeah, your intuition is quite correct. Space itself is neither really hot or cold, rather, it’s empty. Spacecraft and people on spacewalks and stuff experience extreme temperatures, but that’s mostly because of either being in the sun or not being in the sun, not from exposure to space. Actually, for spacecraft, losing heat is a much bigger issue than keeping warm, despite space being “cold in the shade” – there’s hardly anything to carry away heat so you have to rely on radiating your heat away, which is slow and depends on surface area and other factors. Stuff and people released into deep space will freeze eventually, but slowly – without any way to warm up (if they’re far from the sun) they’ll slowly but inevitably radiate all their heat away. Movies showing people and things freezing instantly are wrong

Anonymous 0 Comments

The notion of temperature breaks down in vacuum.

On the one hand, parts of space are millions of degrees, because the two protons that occupy it move really fast.

On the other hand, you’d freeze to death as all your heat radiates away. That’s kind of cold.

On the third hand (it’s all the radiation, get some shielding) it’s really easy to overheat in space, if you don’t radiate enough. Say, if the sun is shining on you. That’s not very cold at all.

Anonymous 0 Comments

The other comments are correct.  There is no temperature in space, and objects in space can run hot or cold depending on how far from the sun they are and how much radiating surface they have.

If you want a notion for what it’s like in space, think of wrapping yourself in a *lot* of blankets and then going outside on a cold night and sitting in front of a campfire.  In this analogy, the campfire is the sun, the cold weather is deep space, and the blankets are the insulating vacuum of space.  Despite the cold night, you will likely overheat because your body is producing heat which you can’t shed effectively with all those blankets around you.

Replace the person with an object that’s warm but not producing heat (say a hot sandwich), and it’ll probably stay at a reasonable temperature because the fire will keep it warm.  Get rid of the fire though and *eventually* it’ll freeze, but that will take a long time with all that insulation.

Similarly, an object in deep space (not near a star) will eventually freeze, but that will take a long time.  An object near the sun, say in Earth orbit, will generally stay pretty near 0C because the sun will keep things relatively warm, just like it does for the Earth itself.  The main concern for satellites is often trying to keep them cool, because in addition to heat from the sun, they’re also burning a lot of power in their internal electronics which they have to try to shed.

Anonymous 0 Comments

Who told you it’s cold or hot? Some matter told you that. Same way matter = planets gets hot or cold. The vast majority of emptiness in the Universe is generally temperature less unless some matter is there to reflect. It is cold relative to human perspective, but it maybe just x = normal for universe’s perspective.