What will the hand feel in outer space? Will she be cold or hot? Even if it doesn't feel anything, how is it nothing? And will everything evaporate in it?
Engineers 'reasoning like "space is not cold - vacuum" is WRONG , despite the abundance of readers' approval. The exact answer is given only by physics.
A bare hand in open space will freeze in a few hours. Any body with a nonzero (in the Kelvin sense) temperature is a source of infrared (thermal) radiation. We feel comfortable when the radiation from our body is compensated by the heat radiation received from the environment. Out of curiosity, a bare hand stretched out into outer space does not receive any heat energy from space and only emits it. Therefore, hand will be very cold . And now the numbers.
The Stefan-Boltzmann law, with an average surface area of the hand of 0.15 m², gives the value of the thermal radiation power of the hand ~ 77 W . The role of the suit in space is to reflect this heat back, thereby returning most of this energy. A bare hand in space only irrevocably loses this energy. Is it a lot or a little?
A person at rest (on the couch) needs about 7 MJ of energy per day to maintain a normal metabolism in the body. This corresponds to a power consumption of about 81 W, which is absolutely not enough to support both metabolism and heat loss of an arm extended into space (77 W). Considering that the weight of the hand is about 5% of the body weight (from here), the hand will only get 81 × 0.05 ≈ 4 J of energy per second. As a result, in ~ 2 hours the temperature of the hand will drop from 36.6 ° C to zero, and after another ~ 5 hours the hand will completely freeze up. Sad of course, but this is how things are.
If, together with the hand, all the air does not stick out, then nothing like that. At least the hand will not burst or break. At first you will feel a chill because the moisture will rapidly evaporate, and if you are not under the sun's radiation, you will cease to feel the temperature, for the vacuum and perfect thermal insulation, and if under the sun it will heat up to hundreds of degrees.
After a few seconds, the hand will begin to swell, because the blood will rush due to the pressure difference. Then, apparently, it will swell completely, strongly, blood circulation will be disturbed, etc. But this will take a few minutes.
At least one should understand that the pressure difference in space and spacecraft is less than 1 atmosphere - 0.1 MPa, which, in fact, is not so much.
Technically, this is quite difficult, because this person will immediately begin to be sucked out of the ship with tremendous force, due to the pressure inside the ship. As for the "rupture" of the arm due to the difference in pressure, I cannot say for sure, but I think that most likely it will be so, as well as instant icing, because it is unimaginably cold in space.
I can offer an answer to a similar question. In general, it depends on how long. It will not be pleasant, but if not for long, there will be no irreversible consequences.
http://thequestion.ru/questions/43837/chto-budet-s-rukoj-esli-ee-vysunut-v-otkrytyj -kosmos-na-10-30-60-sekund # [already moved here]
Wiki in the article "outer space" talks a little about how it affects a person. In addition, more than once I found articles that once, in one emergency (emergency) situation, a Soviet cosmonaut was in a space vacuum for about a minute practically without a spacesuit. 15 seconds completely in a depressurized spacesuit in open space without oxygen, even in your consciousness.
In addition, there are known cases of "contact" of the skin (body surface) with "open space" (as if "covering the hole with your hand". I do not specifically remember how it happened in those cases). In general, as the unfairly minded Victor wrote, there will be no irreversible consequences within a minute, but it can be painful and unpleasant. Indeed, you will not become an ice in space, because you cannot give off heat through heat transfer and convection, only by radiation, and our body itself produces heat (while it is alive) in greater quantities than is radiated at body temperature, so it will soon become hot. The problem is that water boils at this pressure. But if we take into account that not only the atmosphere creates the necessary pressure inside our body, but also different surfaces / walls / membranes that usually hold water, moreover, if you stick out only your hand, and on the other hand, the pressure will be maintained at atmospheric (and the liquid transfers pressure in all directions), then instantly the water will not boil away from you and your hand will not swell. Moreover, NASA claims that death in outer space will come from a lack of oxygen (suffocation), and not from the rupture of internal organs by evaporated liquids. So, air bubbles will gradually form in the capillaries, which can make the vessels in the hand impassable for blood, but if the hand is returned in a minute, most likely, it will not have to be cut off, the damage caused will "heal" over time.
Almost nothing. The fact is that space is not "cold" in the usual sense, since there are practically no molecules in vacuum, the temperature of which depends on the speed, and the pressure is only one atmosphere less than on the surface of our planet, which is not fatal for humans (as is not a fatal dive to 10 meters, where the pressure is 2 atmospheres). Most likely, the hand will instantly dry up or freeze up as a result of the instant evaporation of moisture that is present on it.