The question has theological implications. In the Christian view, human beings are persons, having free will and the ability to reason abstractly, precisely because God has gifted each of us with an immortal soul. A person has sentience, also called consciousness, because of the soul. If a being has the ability to reason abstractly, then that being has free will and, in the case of bodily creatures, an immortal soul.
This view implies that a computer can never become conscious or sentient. No matter how complex or fast the computer system may be, it can’t substitute for an immortal soul, nor can it constitute or express a will that is truly free. Modern computer science tends to assume that, with sufficient complexity or some type of design cleverness, a computer could become conscious. However, there is no scientific proof of that assumption, which a theological understanding of reason and free will contradicts.
There is also some evidence from computer science and mathematics (“maths”) to support this theological conclusion.
An article at NewScientist.com reports on the theories of Dr. Phil Maguire, Researcher in Computer Science at National University of Ireland, Maynooth.
Maguire and his team have shown mathematically that computers can’t handle any process that integrates information completely. If you accept that consciousness is based on total integration, then computers can’t be conscious. “It means that you would not be able to achieve the same results [as the human brain] in finite time, using finite memory, using a physical machine,” says Maguire. (Sentient robots? Not possible if you do the maths)
In other words, a human brain — not any brain, but one with the abilities of reason and free will — deals with “information” in a way that is impossible for a computer. I suggest that the difference is partly due to free will. Consciousness includes abstract reasoning, but abstract reasoning is largely a result of free will — choosing how to relate various pieces of information to one another, so as to arrive at understanding and not merely an output of information. No matter how much memory or speed a computer has, it does not amount to free will, so it cannot result in abstract reasoning or consciousness.
A Halting Problem
Consciousness is a halting problem. Famed computer researcher Alan Turing proposed a type of hypothetical computer, called a Turing machine, with an unlimited amount of memory and an unlimited amount of time. In this thought-experiment, the Turing computer can accomplish anything that any future computer might accomplish: speed and memory are no longer the issue. What is at issue is the types of problems that computers can ever solve.
A halting problem is a type of problem that a Turing machine, that is to say, any future computer, can never solve. The specific form of the halting problem that Turing proposed has to do with a computer analyzing its own software, to determine if it loops infinitely or not. But subsequent researchers often use the term “halting problem” more generally, for the entire category of problems computers can’t ever solve or for abilities that computers can’t ever possess.
I consider that self-awareness is one example of a halting problem. Turing’s discussion of a computer analyzing its own software is essentially a type of rudimentary self-awareness. And his conclusion, that the problem is not solvable by any computer, implies that self-awareness is not possible for computers. Sentience is a halting problem.
From a theological point of view, computers lack free will, so they can’t reason abstractly. They can never become self-aware and express themselves in a selfless love of God and neighbor. Science fiction stories to the contrary are examples of impossible fiction: you can formulate the concept, but it can’t ever occur.
The theory of evolution is largely true. But it errs whenever it plays god or substitutes for God. The claim that sentient human beings evolved from non-sentient lower animals, without any intervention from God, is one such error.
I accept that evolution, guided by the Providence of God, produced ever more complex life forms, starting with the single cell prokaryote and progressing all the way up to the most advanced mere-animal life form: anatomically modern humans (AMHs). These creatures began about 200,000 years ago (200 ka) and had bodies very much like humans today. However, all human beings in existence today are behaviorally modern humans (BMHs), not merely AMHs. This distinction is the majority view among anthropologists; it is not my own proposal. They say that BMHs have the ability to reason abstractly, while the prior AMH species or subspecies could not.
I conclude that the ability to reason abstractly implies free will, which implies an immortal soul. So modern humans (BMHs) are human persons, whereas the AMHs of the distant past are merely animals. And I believe as a matter of faith that Adam and Eve were the first two behaviorally-modern humans (BMHs), and the first parents of all human persons on earth today. God miraculously created Adam and Eve, but He did so based on the pattern of the body found in the highest form of mere-animal life: AMHs.
With the formation of AMHs, evolution hit a glass ceiling. It is impossible for evolution to produce an immortal soul, and therefore impossible for evolution to produce a being with free will or the ability to reason abstractly. God intervened because His creation was not capable of advancing, by the God-given natural principles inherent to created things, to obtain reason and free will. Evolution cannot create a being capable of solving the halting problem of self-awareness, i.e. consciousness.
When did BMHs begin? According to anthropologists, only about 70 to 50 thousand years ago. So human persons have not been on this earth for longer than that period of time. The AMHs were not sentient; they did not have self-awareness or consciousness. They could not understand concepts such as an eternal all-powerful God or the eternal moral law or the love of God and neighbor. But we behaviorally-modern humans can understand. For we have reason, free will, and immortal souls. And therefore we are obligated to act accordingly.