All right. Heres a little something:
There's a particuarly nasty theme that runs through Alien that has to do with a fear of biology - concepts of family, of what biology actually is (and its merger with technology), and of loss of control.
Scott communicates it in a number of ways. Take the family thing - we see the crew waking, semi-naked, in the hypersleep chamber. Birth (and foreshdaowed by the ship's first 'breath' we see disturbing the dressing gowns as the hyeprsleep chamber activates). The design of the hypersleep chamber, with its capsules clustered around a single column, subliminally nudges us towards the crew being siblings. The dialogue around the breakfast table - possibly the most potent symbol of 20th century family - resembles sibling rivalry. They call their ship 'Mother'. And this is a basic set up for the crew, the family, being betrayed by their mother, for they have a cuckoo in their midst.
So we get shown the betrayal - Ash is a droid, but Scott shows full of milk, 'mother's milk'. What with SO937, it's nicely subliminal that Ash is Mother's favourite son. The set design of the lower levels of the Nostromo was informed by the design of the Allien, so that as the film progresses we see the ducts and tubing through the strobes and smoke and think we see the Alien (and this is reinforced by the Alien's appearance onboard the Nostromo) - we're being shown that Mother is more of a home to the Alien than the crew ever were. Except for Ash, whose innards are also more organic than what you'd expect for a droid, all that messy biology in synthetic form. Much like Kubrick's 2001 we're being shown that humans are distinctly unsuited for space travel, except Alien's starchild is a thing to be feared rather than wondered at.
We're also given a nice paralell to Mother with the Derelict. Everything here is imbued with the theme of procreation. The spacesuited figures entering the Derelict resemble sperm travelling through the fallopian tubes, Kane penetrates the hymen-like membrane of blue light, Kane meets an Egg and finds that he is the one who is fertilised.
There's a lot of subtext going on in Alien through set and costume design, disregarding the Alien itself. Giger's work gave Scott the needed subtext of the film, Scot took that and he built the whole film around it. This is what a good director should do - direct all the resources into a unified experience.
Hope that helps
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