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Thought experiment: Lets say we have two (or more) exactly same brains, in same state, doing exactly same neural activity (hardly possible in reality with biological brains, but eventually possible with artificial brains).

Paradox is that these brains necessarily have one single shared consciousness! If we assume otherwise, then we run into logical problems: multiple consciousnesses would mean that swapping individual atoms, molecules or neurons among equal brains would at some "magical" moment with no clear way to explain such divine moment, swap consciousnesses among brains. It is obvious, at least for me, that identity of consciousness is bound only to abstract computation going inside brain, not to specific parts of physical world (atoms, neurons).

But this also means that these exactly same brains share one consciousness not only across space, but also across time. One of these brains can be millions of years apart from another, yet they share same consciousness. This also proves that "present" moment is only illusion of given brain, all experienced moments of time are therefore equally "present".

This is not question, just observation. I would like to know any counter argument, this sounds too weird even for me, who came with this.

EDIT: With brains in the "exactly same state", I mean computationally same state: brains have same configuration of neurons doing same "firings". One can even be made of artificial neurons, while other is biological, I don’t think this makes any difference. Also, firings in one brain can be at a rate 100x higher, than in other brain, from computational perspective this doesn't change anything. Consciousnesses of "fast" and "slow" brain are still the same (same as having one identity), because brain computation itself have no external time reference, except its changing inner states.

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    What does it mean "exactly" ? They share all properties ? also space-time coordinates ? If so, they are the same brain. If not, they are not "exactly same". – Mauro ALLEGRANZA Oct 1 at 13:49
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    Identical brains do not share consciousness just like identical apples do not share redness, each is red on its own. Even if the shade is the same. – Conifold Oct 1 at 13:50
  • The particular set of circumstances that is the environment of a consciousness plays an integral part in the content of that consciousness. (you feel different standing on a beach than sitting in traffic) Therefore your question becomes whether the exact same environment can also be created. This would be highly doubtful since somewhere along the line the one would be to the left of the other... – christo183 Oct 1 at 14:35
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    What exactly do you mean by "sharing one consciousness"? Ok, assume that at moment T1 the brain B1 has the same state as brain B2 at T2. But at the very next moment Ti+dt brains B1 and B2 see something different, and their states diverge. What does your idea of "shared consciousness" add to a simpler point of view that two brains just happened to have similar thoughts? Also, if we forget about brains and imagine two absolutely, atom-to-atom identical cubes of sugar, what do they share? One sweetness? – IMil Oct 2 at 3:42
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The first problem with your thought experiment is the idea of "exactly the same." According to Leibniz's famous principle of the "identity of indiscernibles" no two distinct entities can logically be the same.

This would obviously be a fact in the case of brain states with billions of complex moving parts. And if they are not in the same place or "miles apart" within spacetime and the gravitational field they are not at all identical. They are distinct in the most fundamental way.

Another difficulty is your automatic equation of brain states with consciousness, which is not accepted even in theory by many philosophers outside of the most hardcore materialists. Your own scenario, on the contrary, suggests a fairly radical Idealism.

However, from your default Idealist position, yes, we might say the two brain states of your thought experiment do share one consciousness, the one doing the thought experiment. And, yes, for that consciousness "all experienced moments of time are equally present," since that is a fair definition of "present."

So, perhaps one of our logicians on the site can formalize the internal contradictions in your idea. Beyond that, it opens up many issues concerning identity and the definition of "consciousness" and its relation to "brain states," a much disputed topic in a pretty vast literature. Perhaps others on the site can suggest some relevant readings.

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Your thought experiment isolates a key tension in some modern views of consciousness. There is some underlying conflict between two views you are assuming in your question:

A) Consciousness is something "real", with discrete identity
B) Consciousness is wholly and deterministically generated by the physical state of a brain.

Both are views that are live and current in today's discourse, but they are difficult to resolve with each other. Dropping either one solves the problem, but keeping both leads to paradoxes of the kind that you outline.

The older, idealist view of consciousness is that it is something in of itself, that is in some way attached or allied to a brain, but not equivalent to it. This has the weakness that it does not have a good explanation for why or how the mind is attached to the brain, or why degradation of the brain leads to degradation of the mind.

The newer, reductionist view is that consciousness is an epiphenomenon, it doesn't have any independent reality other than as a kind of summary of a particular physical state. This is very unsatisfying to many people, and seems to miss some valid and important features of consciousness. Essentially, it solves the problem by denying the meaningful existence of the problematic thing.

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Suppose two distinctly located cognitive systems that nonetheless are fed exactly the same information, all the time. Presuming these two systems are as a result exactly in the same state, we can nonetheless observe that their locations remain different. Now, suppose consciousness is (somehow) analogous to space. QED.

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Newton and Laplace might have allowed what seems to be the basic premise, that similar input should give similar output… is that a reasonable simplification?

However, don’t both Brown and Heisenberg leap to point out the conditions couldn’t be measured, and Schrodinger that if they could, it would never be with accuracy guaranteed?

Last things first, doesn’t trying to compare “Consciousnesses of "fast" and "slow" brain” at all, let alone concluding that they’re “still the same (same as having one identity), because brain computation itself have no external time reference, except its changing inner states” suggest the Query came from someone paying far too much attention to an unfamiliar altered state of consciousness?

The statement and exposition seem too full of assumption and contradiction to float, let alone fly. Right off, an artificial brain having any consciousness, let alone sharing one with a wet-ware sibling is speculation, however optimistic.

If this was about the price of eggs such doubts might not matter but here, how is it clear whether “Identity of consciousness, illusion of present time” is one thing, or two or three or four? Who but the author could guarantee to re-phrase that statement accurately?

Newton and Laplace might have allowed what seems to be the basic premise, that similar input should give similar output… is that a reasonable simplification?

Don’t both Brown and Heisenberg leap to say the conditions couldn’t be measured and Schrodinger that if they could, it would never be with accuracy guaranteed?

That switching individual atoms, molecules or neurons might “swap consciousnesses” is no more clear than that “magic” might be the only explanation.

How could the idea that identity or consciousness was bound only to “abstract computation” find itself promoted into an axiom, taken as read with no proof needed, merely by being obvious to some? What would “abstract computation going on inside the brain” be, without relying on “specific parts of the physical world (atoms, neurons)”?

In terms of the Question, how could more than one brain ever get identical input, or attempt identical neural activity while separated by millions of… well, anything, really?

Whether you want to crawl through quantum tunnels or down wormholes or ride flying carpets or what to cross squillions of distance and time are you thinking of jumping either without the other, or both together? If space or time separately or space-time as one can be ignored, how were your brains ever “separate”?

Where you would hit a paradox is in suggesting any of this made it likely or possible, let alone “necessary” for the brains to share one consciousness. Rather, sharing one consciousness would mean knowledge of each other forced them to have different perspectives, preventing them from sharing one consciousness as stipulated… and doesn’t that go round and round until the pin-dance ends?

The whole thing might be akin to asking whether the "present" moment is only illusion of given brain, and all experienced moments of time are equally "present" but how does it “prove” anything?

How you got round to time travel isn’t obvious and either way, how would that support the idea “that these exactly same brains share one consciousness not only across space, but also across time. One of these brains can be millions of years apart from another, yet they share same consciousness”? Not until you explain it, they don't.

Other than by assertion, how could any of this “prove” that "present" moment is only illusion of given brain or quite separately that all experienced moments of time are equally "present". Even then, does “all experienced moments of time” include your, my and everyone else’s experience, or only a single individual’s? There you are, right back at the potential identity of different consciousnesses in different brains.

Did you notice, “this sounds too weird even for me, who came with this…” might well mean simply “This is too weird”?

EDIT: When brains are in the "exactly same state", what other choices would there be than “computationally same state: brains have same configuration of neurons doing same "firings””?

When you don’t think it makes any difference whether one is made of artificial neurons while other is biological, how would you like to explain that?

Doubly, when firings in one brain can be at a rate 100x higher than in other, how could that not change everything from computational perspective?

Brain 1 working even a tiny fraction faster, let alone 100x, breaks your initial conditions of similarity. Getting the answer 100x faster means one of two things…

Is Brain 1 twiddling its neural fingers for 100 cycles? That would break your conditions.

Is Brain 1 moving on to do anything else you care to mention? That would break your conditions.

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