Why is space cold if there’s no matter in it?
In: Physics
I would say the chance of two specific things hitting anything is very very small. The chance of once audition thing hitting anything is small, and the chance of anything hitting something else is common. If you’re traveling through space, you are far more likely to die from starvation or dehydration than something colliding with you.
It doesn’t matter. There’s just not much heat in it either and that’s what ‘cold’ means.
Cold is not matter or energy. If you go out in space, the only ‘heat’ you’ll get is extremely weak – coming from faint light from stars mostly unless you get too close to one.
Space is basically a vaccuum. In space you can only lose energy to radiation. Since nothing heats you up (unless if you are close to and in direct sight of a star) you will continually lose your thermal energy (heat) until you have no energy left. This is all it takes for anything in space to reach extremely low temperatures around 2.7 degrees kelvin.
Space itself contains a few atoms per square meter that has undergone the same effect which is why space is said to be 2.7 kelvin. But these few atoms are not enough to cool you down when you are in space so don’t expect space to cool you down like cold air. You will slowly lose your energy to radiation. Practically no energy is lost because of being in contact with these few cold atoms.
Cold is just the lack of heat. They aren’t two opposing forces; heat is the force, cold is what you get when heat is missing.
Without anything to warm it up (the sun, hot molten planetary core, a radiator), everything gets cold. That’s the natural way of things. Areas completely devoid of any sources of heat whatsoever sit at absolute zero.
Heat travels through particles (picture warm particles “vibrating” with warmth, so much so that they make their close neighbours vibrate too, which makes *their* neighbours vibrate). This means you need a lot of particles at a reasonable density in order for things to be warmer.
Space has so few particles that the heat that exists in the universe has no way to travel. The few particles that do exist out in the void of space are very spread out, and unable to transmit warmth to their neighbours.
The vacuum of space itself isn’t really cold, it’s empty. The things *in* the vacuum tend to be cold, because they are usually in space for long enough that they have radiated all of their heat away and aren’t getting much new energy. You tend to gain or lose heat in two different ways – through direct contact or through radiation. In space, you can’t gain or lose heat through direct contact most of the time, so you’re well insulated in that regard, but you can gain and lose heat by radiation. Since you radiate energy away faster than you gain it (unless you’re close to the sun), you will eventually cool down, but it’s nowhere near as fast as portrayed in movies.
In direct sunlight you might actually never freeze, since you can gain energy a lot quicker than you would radiate it, but again that depends on your distance from it. If something is blocking the sunlight, you’ll freeze in around 12-24 hours from radiating your heat away.
Basically there isn’t much to heat up because it is empty and any heat will fly off into empty space.
Heat is how much atoms are vibrating. Fast vibrations are hot and slow vibrations are cold. No movement is absolute zero. Space doesn’t have many atoms because it is mostly empty and the ones that are about have very slow vibrations and aren’t moving about.
Because there isn’t much atoms about in space the heat from the sun doesn’t have much to heat up, so it stays cold.
The atoms that are about in space will get heated up by the sun but will quickly cool back down without much chance of passing that heat onto something else nearby (unlike on earth where there are lots of atoms for heat to “move” into).
In space the heat kind of flies off into empty space by radiation, which is a slow process where the vibrating energy kind of gets released with nothing to cling to.
In space hot bodies transfer their heat to colder bodies through heat radiation. If you were floating in space you’d be giving your energy away to everything you can see around you (mostly empty space).
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.
Most answers here are plain wrong. Space being cold is entirely unrelated to it being mostly empty. Temperature is, informally, the average speed the molecules move at; the amount of said molecules is irrelevant.
So, why is space cold? The main reason is that it is not; humans and the things around us are just pretty hot. The average temperature of the universe is much lower than Earth or the Sun might suggest. Those two are just exceptions, which we rely on to survive.
But lets also talk about what happens if you would be dropped into space without protection from temperature (while somehow still being able to breath and not in vacuum). First, this depends on where “space” is supposed to be here: if I drop you “near” the sun in astronomical terms, lets say around Earth’s orbit, then one side of you will actually heat up quite a bit due to the Sun. The other one will slowly cool down due to thermal radiation leaving your body (this also happens on the solar side of you, but is totally overwhelmed by the sun). In short, one side gets cooked, the other frozen, but slowly. If you are far away from the sun (say, Pluto), then both sides do not get much sunlight and cool the same.
If somehow you have no protection from vacuum on your skin (yet do not die from lack of breathing), then another effect kicks in and cools you down much more rapidly: water evaporating. Just like wet skin or clothes on a hot day, water cools you when evaporating. However, in vacuum, water starts boiling already at 0°C! Thus your surface is more like a hot plate rather than just a bit warm, relatively speaking. Evaporation is extremely rapid under those conditions, untill the water gets down to 0°C (it actually starts freezing when left in vacuum, even in a chamber on earth that normally has room temperature). If you had a drop of water (or e.g. blood or any other liquid that mostly consists of it) on your skin, it would even look like water on your oven. But note that your skin substitutes for some pressure, i.e. holding blood and sweat in, thus making your insides not boil, only liquids that leave your body.
Any matter in space will radiate away it’s heat energy until it reaches a temperature a bit above absolute zero. So space isn’t cold, it’s just that the things in space tend to become cold over time.
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