What if you opened a door in a spaceship without a spacesuit? In movies/cartoons you see astronauts and people in spaceships opening doors and closing them again with no suits on. Is it possible in "real life" or would you die immediately? Because consider this:


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*If we built some giant space colony/living facility (like in Star Trek), isn't there always the danger of someone opening a way outside from which you could die instantly if no one is in a spacesuit (if true?)?

*What about the fear of being in closed, confined spaces too long? Some people may panic and even kill themselves/others or become destructive in chaos from being trapped in an enclosed space colony.
Obviously an alternative to the long-winded process of terraforming other planets is to create safe ships to fly around in and live in. And future technology could prove this to be better than terraforming since a spaceship is magnitudes more versatile and easier to self-sustain and maintain than a gigantic planet.
 A: 
people in spaceships opening doors and closing them again with no suits on. Is it possible in "real life"

No, it is not.
Any sane engineer will build doors that open inward, or have latches that over-center when closed so it is simply impossible to open an airlock in a pressurized vessel. An aircraft, for example, has about 6-8 tons of pressure holding the door against the frame. Superman himself won't open the door against that much force, simply because the handle will break off.
In sci-fi shirtsleeve airlocks the air is held in by a forcefield, the door can then be opened and closed with impunity.
If you really want to know what happens to humans in explosive decompression situations (it's not pretty) search for the Byford Dolphin decompression accident.
A: The biggest, immediate problem with "openning the door" of a spacecraft is not that you would die immediately from exposure to the vacuum of space: you don't - you have of the order of minutes to do something about it.
The problem is the violent outrush of air. User rob offers this answer to the Physics SE question Do airlocks in space decompress violently as they do in movies?. With its containing vessel suddenly open, air, from its thermal motion, suddenly becomes a rush outwards that's really going to whack you big time: rob does a calculation that shows that being shoved by this outrush is to suffer the same order of impulse as you would being hit by a car.
If you are uninjured by the blow, once in space you could be quite OK if someone could get you a lifeline in a few minutes. Given the size of the blow above, it's likely going to need to be a long lifeline, but, as explained by Phonon's answer to the physics SE question What exactly happens to an exposed human body in space? if you get back inside in a minute or two, you'll likely be OK. You may need some hyperbaric oxygen treatment to lower any risk of "The Bends" - although your blood wouldn't boil violently, your blood may have micro-clots that divers for example have after an emergency free ascent in it. You may be also be really unlucky and be pierced to death by a micrometeorite, but this is not likely.
A: Bad Things Happen
The air, as it has no pressure or enough gravity to keep it in the ship, will attempt to expand. Air, in fact, attempts to expand to fill the container it is placed in. If there is no walls to the container, like on a planet, it will only be stopped by gravity.
When the airlock is unsafely open or a hole is made in a spaceship, the air inside attempts to fill the void of space. Space is really big, as truly pointed out in many scifi movies, despite their other many other false claims about it. This means the the air pressure practically drops to zero, as practically all the air moves out of the spaceship in a terribly feeble attempt to fill the void.
Depending on how quickly the air moves out, and how large the hole is, you may have a few seconds or less to realize your fate. Scishow does an accurate and entertaining video on being exposed to the vacuum of space. You actually go unconscious really quickly, as your bodily fluids boil off your exposed surfaces (including your lungs). The oxygen pressure in your blood drops, and you black out. After that, you do an interesting freeze/burn combo as the sun cooks you on one side and you freeze on the other. It does not sound pretty.
Fighting Claustrophobia
Windows. This may be the number one reason to have windows on your ship. Being able to see out, a feeling of a very open space, will help those with claustrophobia fight their fears, or at least give them refuge from them.
If you're the type of sci-fi reader who believes in holodecks or other VR, they can help with that, too. Ultimately, this isn't a physics question, but a better one for the cognitive sciences stack exchange.
