I don't understand why this notion of subjective experience keeps being raised. Why is it important?

Once we know enough to create a synthetic brain, it really doesn't matter what its subjective experience is, we will judge it the same way we judge our fellow humans.

And this is fine since we have no way to truly know the subjective experience of say color for any other human either. Yet we don't question each others claim of consciousness.

It's enough that we can both say "blue" to name the ~ 490–450nm wavelength of light regardless of our personal subjective experience of it.

Because subjective experience is not a one way affair. It clearly plays at least some functional role. The proof of that is that we're having a conversation about it.

But the same conversation could be had with a synthetic brain. It's no more important than any other feature of brain functionality. What I don't understand is how this concern about subjectivity limits us in understanding consciousness and brain functionality.

It doesn't mean we can experience the subjective states of a synthetic brain or another human, but we can definitely replicate the physical aspects of the brain that produce them.

I think it's likely that the brain violates the Church-Turing thesis. It doesn't seem possible that a Turing machine can produce subjective/conscious experience. This strongly limits our ability to make a synthetic brain via solely computation.

Update:

I'm not sure I'd say supernatural. I think consciousness is different in kind from the rest of how we understand the universe to work. It seems likely that it's a fundamental property of the universe.

I see this all pretty much the same way that the philosopher David Chalmers does. He probably does a better job of explaining it than me. It's worth looking at his thinking on the matter.

So you believe that consciousness is supernatural and not the product of a physical brain. I don't see any reason to believe that, but it definitely makes it clear why we hold differing opinions.

Edit:

I think all that philosophy is going to have to be updated when we eventually start having conversations with synthetic brains that can tell us about their sense of consciousness ;-)

Edit 2:

If we had a device that could instantly make a carbon-copy (unintended pun) of a human (let's say me), identical down to the last atom, what you're saying is that copy would NOT be conscious. That it is not enough to capture the physical nature of someone to capture the state of consciousness.. that it is beyond physical. I just don't know how to come to terms with that idea. To me consciousness simply must be a product of our physical bodies and thus within the purview of rational study and comprehension.

That's not what I mean actually. If we could make a carbon copy of a person, it would be presumably be conscious too. But I do think that an attempt to model the brain mathematically and run a computer simulation of it would fail to create consciousness.

Ah, then we're much closer together than I thought.

However, there is no reason future computers will be limited to current (Turing) technology instead of being a collection of many co-processors with differing capabilities.

The main point though, is that since consciousness is housed in the physical brain, we can dissect, understand, and recreate fully-functional synthetic versions. While each person is in their own subjective world, the brain which is responsible for it is an objective object that is open to study.

>However, there is no reason future computers will be limited to current (Turing) technology instead of being a collection of many co-processors with differing capabilities.

That would violate the Church-Turing thesis, which is pretty widely accepted, unless the universe itself is a hypercomputer that we can leverage to perform computation.

You're essentially saying that our brains can't exist.

But they do, and we can copy them, what is the problem with making a synthetic brain? Why is the natural brain an allowed exception, but the one we make is not allowed?

Edit:

On the one hand you want to use Church-Turing to invalidate the possibility of us creating non-Turing based technology, and yet in a previous post you claimed the human brain likely violates Church-Turing. So which is it? Is reality allowed to violate Church-Turing or is it not?

If you honestly believe that the human brain violates Church-Turing, then you have to explain why you also believe that we can not copy the brain and achieve the same result ourselves.

If the universe is not computable, and if the non-computable aspects are relevant to the functioning of the human brain, then our ability to build a brain simulation is strongly limited. A functioning synthetic brain would have to leverage the same relevant natural phenomenon as a real brain; a mathematical simulation running on a standard computer would not suffice.

I do think that I actually agree with your earlier point that once we have a functioning synthetic brain, we can ignore subjective experience itself and just focus on its functional implications for the entire system.

> t doesn't seem possible that a Turing machine can produce subjective/conscious experience.

Why?

I think it's easier to see why if we use a non-conventional Turing Machine, like thousands of monks using abacuses and integrating their results by spoken word. Do remember that all Turing machines are equivalent. How in the world would the act of moving beads around create consciousness?