If one thinks of 'atoms' as ultimate constituents of matter, indistinguishable apart from their spatial and temporal position, then it is hard to see how changing them for identical duplicates at the same location could make a difference. (I'm interpreting the experiment as replacing every atom with an identical duplicate: same atomic weight, same charge, etc.) After the experiment, one would have replaced every atom with a partner with exactly same causal powers at the same location, and it is hard to see how this could effect an overall difference in her consciousness. The only difference between Sarah before and after the operation is an historical one: the atoms in Sarah after the operation would have a different history to those in Sarah before the operation. But it is difficult to see how this difference could make a difference to Sarah's consciousness. (Going through a freezing process might make a difference to her consciousness though!)

There is another question that might be worrying you: Why does the language of physics turn out to be mathematical? Why does mathematics turn out to be our best way of describing the physical world? I don't think that anyone has a good answer to this question. There may be no good answer, since it might just be a brute contingent feature of our world. One could imagine a world in which events were so disorganised that there would be no useful regularities that could be captured in a perspicious mathematical formalism. Interestingly, Putnam and Quine have used the claim that mathematical language is central to our physics as a roundabout argument for the existence of mathematical objects. One of the best reasons we have to believe in the existence of an object is if our best physical theories make ineliminable reference to them (e.g. electrons). If, as appears to be true, our best physical theories make ineliminable reference to mathematics, then by parity of reasoning, we should believe that those...

The theory of evolution by natural selection is sometimes claimed to be an unfalsifiable theory, since it appears that no matter what fossil evidence we uncover, a 'just so' evolutionary story could be told to fit it. However, this simple-minded position seems to wrong. There does appear to be plenty of that evidence could tell against the theory if that evidence were discovered. For example, if the age of the earth were discovered to be much shorter than is required for evolution by natural selection to operate (say, a few thousand years), then that would be good reason to reject the theory. Fortunately, we have every reason to think that the earth is old enough for evolution by natural selection to have operated, and so no reason to reject the theory.

Hi Martin. I'm not sure about your justification for not studying philosophy (the intention of which is to encourage thinking things through for yourself!), but you'll be glad to know that there are plenty of philosophers who think along similar lines to those that you mention. There are too many to list, but two prominent philosophers concerned about the kind of big picture that you mention are Daniel Dennett ( Consciousness Explained , Darwin's Dangerous Idea ) and Fred Dretske ( Naturalising the Mind ).

You bring up several interesting points: (1) Sometimes philosophical arguments are hard to understand. This is to some extent par for the course: problems in philosophy are hard, and the arguments often sophisticated. Mental effort is required in order to grasp what is going on. Doing philosophy, like acquiring many forms of knowledge, is often hard. (2) Sometimes philosophers write in an unclear way. This is undoubtedly true and also a bad thing. Sometimes philosophers write in an obtuse style, sometimes philosophers do not take enough time to revise the presentation of their ideas to make them clear, sometimes philosophers only have inchoate ideas which require effort on the reader's part to develop. (3) It is possible for there to be no argument at all, only gibberish. This, although possible, goes against the entire point of doing philosophy (just as 'proving' a result in mathematics by writing down gibberish goes against the whole point of proving results in mathematics). The point of...

Thomas Kuhn in Chapter 10 of The Structure of Scientific Revolutions gives a wonderfully vivid description of the contrast between the Aristotelian world-view and that which developed from Galileo. Kuhn describes how an Aristotelian and Galileo would see (apparently the same) phenomenon: a pendulum. The Aristotelian would see a pendulum as an example of constrained motion. For an Aristotelian, a heavy body always seeks to move from a higher position to a lower one; the pendulum was simply achieving this downward trajectory with tortuous difficulty. Galileo would see the pendulum, not primarily as a body falling, but an oscillator repeating the same motion over and over again ad infinitum. If the pendulum were ideal (if we discount friction), it would continue oscillating forever. Galileo's view of the pendulum as an oscillator is the seed of one of the most productive mathematical frameworks in physics: the notion of an harmonic oscillator. This framework has been successfully applied in...

If you mean 'Can a computer have human feelings?', then the answer seems to be probably not. One of the main characteristics of a computer is that you can build it out of any physical stuff you like: clockwork, silicon, carbon, some might say, even Swiss cheese. What a computer is made out of is (to a first approximation) unimportant, all that matters is that its material is organised in the right way. Now consider the the following project (thought up by Ned Block): give each of the 1.3 billion people in China a 2-way radio and ask him/her to simulate the computational behaviour of a single neuron. Then arrange the network of radio connections between individual Chinese people to exactly mirror the arrangement of neurons in your brain. The Chinese nation now appears to be able to perform any computation that your brain performs. Yet it seems bizarre to say that the Chinese nation---as a group, not as individual people---would experience pain, happiness, itchiness, and so on. It seems implausible...

Searle's argument is that merely running a program cannot be enough for understanding, provided one understands 'running a program' in terms of symbol shuffling, rather than shuffling any particular physical stuff around. The response that you suggest involves shuffling particular physical stuff: proteins and nucleotides. There are two senses of 'running a program' at issue. What Searle has in mind is the sense in which electronic computers run their programs. In this case, it doesn't matter what physical stuff the symbols are made out of: they could be electronic pulses, clockwork springs, or anything. Your sense of running a program is more specific: it is the sense in which our genetic material 'program' for our developed physiology. In this case, physical stuff matters a great deal: only proteins and nucleotides do the job; 'running a program' is shorthand for a very specific biological process. Searle might interpret your response as therefore agreeing him that there is more to understanding...

I agree with Peter's response, and I'd like to pick up on the possibility that the machines in question are not computers. Although it is not clear what computation is, it seems plausible that not all machines are computers. A claim that such non-computational machines can have knowledge would escape Turing's or Searle's arguments. One might argue that human beings are such machines: we work in mechanical ways, we have knowledge, but we are more than mere computers. John Searle has a mechanistic, non-computational, view along these lines. A potential challenge that such a view faces is to explain what this broader sense of 'mechanical' means. It must mean something different from 'performs a computation', but one might be reluctant to broaden the notion so far that it applies it to all possible systems: that would render it trivially true that machines can understand. Finding an intermediate ground is not obvious.

I think that the question that you ask is still an open one: it is not known to what extent our mental life is underwritten by logical reasoning. The question may eventually be resolved by cognitive science. However, one worry that might face someone in answering your question is how broadly 'intelligence' should be understood. If you mean our general ability to cope with difficult situations that confront us in day-to-day life, then it is highly unlikely that logic is ultimately responsible for our degree of success. If you mean our ability to solve problems in IQ tests, then logic is highly likely to be responsible. I'm personally rather sceptical of any approach that divides up human cognitive life into different general 'intelligences'. To my mind, a more interesting approach would be to pick a particular cognitive process---say, language learning---and try to determine, for that particular cognitive process, the extent to which logical inference plays a role.