Lifting an analogy of a pond to question signals at natural or artificial boundaries in space-time I conjured up an idea to lift an analogy into the language of QFT and GR. I thought up the universe as a pond with a liquid. If we imagine a liquid poured into some pond (sort of bang and inflation with fluid still flowing to fill the pond, what have you), and imagine that most of what we know and see is from inside the liquid. We are trapped in this liquid. We imagine that space is really that liquid, a mixture of sorts. Possible fields of sorts , and we can play with this mixture using standard machinery with phase transitions, and such. May be we can even imagine that the Higgs mechanism is just viscosity(this might be totally naive as my knowledge is limited) and such. My question is the following ::QUESTION:: Following this analogy, there would be the boundary of the fluid and the outside, in this case there is such a thing as refraction, and total internal reflection. In what we currently know how is this boundary defined, and what happens to a signal sent at a critical angle to the boundary. Is it possible that we can lift this analogy into a QFT description of what happens at such a boundary?  I suppose I am really asking for help to model this boundary in the language of QFT. We might want degrees of freedom for if something shakes the pond and the boundary changes shape or oscillate too.  In fact if we take this a long way. We can think of a black hole as a situation where the boundary takes a certain shape as to modify the critical angle.  Do these analogies mean much, but most importantly, how can they be brought alive in the language of QFT or even Quantum mechanics? It is probably best if we pick the easiest process described from the list to model first.
 A: In a certain sense, I think it does not matter. We can't see outside of 4-D spacetime except by inference, whatever dimension or topology the higher dimensions might have, unless you start allowing parallel universes or the like. So even if you imagine spacetime as being like a fluid we swim in, what is outside of this fluid - what 'contains it', if you will, we will likely never see, at least if you believe in Cartesian-like objectivism and externalizing of experience (I do not, but a lot of people do), except through inference and this seems to me to beg more questions than it answers. 
That aside, the language of General Relativity - manifolds, differential geometry, spinors for spin 1/2 particles in curved spacetime - could be adapted to this purpose, I believe, fairly easily (after all, what are manifolds for if not for talking about flows), but again, you'd run into the problem of embedding coordinates. The question is the same - what are you floating in? I know this isn't a problem in string theory (hey, if you run out of dimensions or can't explain something, just invent another! I do not like this reasoning, and never have, in case you cannot tell). 
QFT? Not so easy. Might need some description of granular flow to make it work. But I don't think you'd gain much insight. 
I don't mean to sound harsh. I fully support dreaming and analogizing. What do I know anyway? I'm not even a professor.
