As the question came up in this thread and I couldn't find a dedicated topic, I thought I'd start up a new one. I don't have terribly much to say, but maybe somebody else has a few observations as well, or this can be a place to discuss its origin as well.

LCL is described as some form of primordial soup of life by Maya when Shinji gets dissolved. There is an apparent contradiction here, because if Shinji is made from LCL, how can he alter LCL by dissolving into it? The answer, I think, is Shinji's need to breathe. He needs free oxygen for that (IIRC, LCL oxygenation is mentioned at some point in the series). But on primeval earth, all life was anaerobic. When Shinji dissolves, his molecules bind the oxygen in the LCL, leaving only primitive, short strands of aminoacids and other chemicals behind, which then corresponds to the primeval soup theorized to be the place where abiogenesis took place. His suit dissolving as well can account for elements normally not found in abundance in seawater right now, which might have been common in early oceans or puddles from which life originated (things like sulfur compounds).

So the LCL in the entry-plug wasn't crude LCL, but refined and oxygenated LCL (you have to filter out all the elements harmful to aerobic life). As shown in episode 16, it gets cloudy when left alone, so some form of purification must have taken place previously. As to WHY you'd want to use something like LCL as a carrier for free oxygen is beyond me, though. Oxygen is highly reactive, which is why we need this whole kerfuffle of "life" to pump it into the athmosphere constantly. Introducing it into some form of primeval soup, which by it's nature contains many different elements which can form bonds with oxygen seems foolhardy and needlessly complex to me, especially considering that its normal composition should damage the pilots' lungs.

There are some breathable liquids, mostly used for burn victims and toddlers with lung problems, so there's that; although none of them are remotely close to being primordial soup. If we go with the practical piloting aspect, I'd say that we could find something that it could reasonably be; for the blood of Lilith/source of all life aspect I think it's a lost cause

Well, it's fictional, so we'll probably never find a satisfactory realistic answer. I think that the closest substances we have IRL are the synthetic oxygen carrier liquids. They're typically used in liquid-breathing therapies and have been studied as artificial blood substitutes. Using the LCL characteristics we're presented on the show (clear liquid, organic, high oxygen solubility, blood-like smell), the ones that tick most boxes are the haemoglobin-based oxygen carriers. They're usually polymerized versions of the protein in our blood, and if my memory isn't broken, caused a bit of a buzz in the early-90's as a possible solution for the shortage in blood-banks (don't think that it went anywhere, though).

Here is a really old thread where the nature of LCL was thoroughly debated. Note that the thread's originator went on to largely abandon his theory, though I'm still fond of it.

https://forum.evageeks.org/thread/3778/Behavioral-logic-of-LCL/?hilit=lcl

I don't know but it looks fucking delicious

@thewayneiac: Thanks for posting the link! Having finally managed to read the whole thread, I think the idea is worth discussing a little more, so I'll post the basic proposal here to hopefully generate some interest.

In short: LCL can seemingly transition very quickly from a gas to a liquid (explaining things like Asuka bleeding "underwater"). The proposed mechanism for this is running electricity through it, which somehow causes a direct phase shift.

@Chee: Well it smells like blood. Which can, of course, be delicious.

I doubt we'll ever get a conclussive answer to what LCL really is out of all the bits and pieces of information that are scattered throughout the show, but we can always speculate and fill in the gaps.

In my headcanon, LCL is a form of exotic matter that can embed regular molecules (biomolecules, molecular oxygen, etc.) within itself and that can be 'molded' by souls to create physical bodies. It is channeled by Lilith from another universe, plane of existence or pocket dimension (whatever it is that the Chamber of Guf, the LCL Sea and the Dirac Sea are part of).
If we go by this interpretation, the pure LCL that flows out of Lilith is completely devoid of regular molecules, and therefore needs to come into contact with pre-biotic molecules to turn into "primordial soup" and give rise to lifeforms. Thus, the LCL in the entry plugs only contains molecular oxygen (to allow breathing) and carbon dioxyde (as a result of breathing), and its composition is altered when Shinji's body, which is biomolecule-rich, dissolves into it.

Derantor wrote:As to WHY you'd want to use something like LCL as a carrier for free oxygen is beyond me

The main function of LCL is not to provide oxygen, but to act as a medium for the mental link between Eva and its pilot.

Electreel wrote:The main function of LCL is not to provide oxygen, but to act as a medium for the mental link between Eva and its pilot.

Is it really the main purpose tho? Even for that, we get conflicting information.

Also before anyone brings it up - the name does explicitly not stand for "Link Connect Liquid"

Blockio wrote:the name does explicitly not stand for "Link Connect Liquid"

The storyboards for episode #1 have a note on the side saying

LCL = short for Link Connect Liquid

Hard to get more explicit than that.

(Now, that said, this is Anno we're talking about. He absolutely picked that acronym because of its potential to stand for more than one thing.)

Blockio wrote:Is it really the main purpose tho? Even for that, we get conflicting information.

There has to be a connection between LCL and synchronization. When Toji and Kensuke enter Unit-01's entry plug in episode 3 they interfere with the Eva-pilot mental link and they aren't wearing any of the pilot paraphernalia. Shinji also pilots Unit-01 wearing plain clothes on several occasions, which doesn't seem to affect his sync performance. So, either the pilots can synchronize with the Evas through some unknown mediation, or the LCL provides a link between the two. I think the latter makes more sense.
It's also worth mentioning, although probably unrelated, that when Rei is seen inside the tube-like thing in the Dummy Plug Plant, she's freely floating in LCL, which means that the substance is directly transmitting her thought patterns to the machine.

Reichu wrote:The storyboards for episode #1 have a note on the side saying

LCL = short for Link Connect Liquid

Hard to get more explicit than that.

(Now, that said, this is Anno we're talking about. He absolutely picked that acronym because of its potential to stand for more than one thing.)

Wait, really? I though Anno said in an interview that it was explicitly not that, but refused to say what it stands for; this changes things

Electreel wrote:There has to be a connection between LCL and synchronization. When Toji and Kensuke enter Unit-01's entry plug in episode 3 they interfere with the Eva-pilot mental link and they aren't wearing any of the pilot paraphernalia. Shinji also pilots Unit-01 in plain clothing on several occassions, which doesn't seem to affect his sync performance. So, either the pilots can synchronize with the Evas through some unknown mediation, or the LCL does provide a link between the two. I think the latter makes more sense.

Oh I don't doubt that LCL is a key part of the process; however I could very much imagine that that is merely a pleasant side effect and not the main reason that LCL is used. My kneejerk explanation would be that LCL is just there to dampen the impacts when the Eva makes large movements so the pilots don't get concussions from running

Blockio wrote:Oh I don't doubt that LCL is a key part of the process; however I could very much imagine that that is merely a pleasant side effect and not the main reason that LCL is used. My kneejerk explanation would be that LCL is just there to dampen the impacts when the Eva makes large movements so the pilots don't get concussions from running

How about 'all of the above' like the restraints/armour?

Probably, yeah.