Okay, as I've a little more time now, and for the record, I'm going to quote myself from my first post in this thread and elaborate a little:
I don't think we yet have an adequate explanation of what consciousness is. Certainly not a universally-accepted one. It's so lacking in definition that we also can't define what it means to lose consciousness, and so there is no scientific consensus even on how anaesthetics work.
It seems to me that that's a question that needs answering before we can determine whether or not rocks are conscious.
I think that definitions of consciousness tend towards the tautological. What is consciousness? It's the state of having qualia. What are qualia? They're units of experience. What does it mean to experience something? To be conscious of it.
To quote myself again from earlier in the thread:
That's really going to come down to how we defined "consciousness". If it's just as "an emergent property of data processing", and if we define "data processing" to include, say, particles appearing and disappearing within the quantum foam, then empty space would have consciousness by definition. It'll come down to what people are trying to communicate and what utility that idea has.
I mean let's say, for example, that we determine that empty space has a minute amount of consciousness. The question then is "so what?" What useful does that tell us about space? What useful does that tell us about consciousness? How will that affect our understanding of cosmic physics? How will that affect our understanding of neurophysics? How will that affect our understanding of anaesthesiology? How will that affect our understanding of psychology?
At the moment, it seems to me that the answers are "nothing" and "not at all". Perhaps that's because I don't yet have a deep enough understanding of the subject. Perhaps that's because the field is relatively new. Or perhaps it's because it does tell us nothing useful.
If it does tell us something useful, then it'll become mainstream. If it doesn't, then it'll go the way of aether.
But the point is that it will come to be defined in science to mean whatever is the most useful way for people within relevant fields to define it. The fuzzy edges will be worked around in the same way they are with other sciences.
Where do I think consciousness comes from? I don't know, but I think it's most likely a product of the brain. Whether that's as an emergent property of the brain's particular wiring, an emergent property of a neural net, an emergent property of data processing, something that the brain is specifically wired to produce due to self-awareness being a survival trait, or something else, I don't know. I see no reason to posit the existence of any new entities to explain it, though. We know, for example, that damage to certain parts of the brain can alter consciousness in predictable and replicable ways (for example, damage to the fusiform gyrus can cause prosopagnosia), and we know that ingesting certain chemicals can alter consciousness in predictable and replicable ways, which suggests that there is an intrinsic relationship between the two.
I see no reason to suppose it's any different to a running computer programme, albeit one that is unquestionably immeasurably more sophisticated and complex than anything created by humans. But I see no reason to suppose that there's a hard line between the computer programmes running in our biological computers and the computer programmes running in our technological computers.
Are things other than humans conscious? To again repeat what I've already said in this thread, there are most likely degrees of consciousness. There are animals that certainly display outward signs of consciousness, albeit a lesser consciousness than humans. How much and how true that is will depend again on how consciousness is defined. A scale with fuzzy edges seems to me to be the most reasonable explanation.
Are inanimate objects conscious? I see no reason to suppose they are, and have heard no cogent arguments for why they should be considered so. But, as I spent the first couple of pages of this thread discussing, it will all come down to how we define consciousness and how we define consciousness will come down to what utility that definition has. I can't see any utility to defining consciousness in a way that would include inanimate objects, but I'm open to hearing a good argument for it.