Accelerated Turing machines are Turing machines that perform tasks commonly regarded as impossible, such as computing the halting function. The existence of these notional machines has obvious implications concerning the theoretical limits of computability. 2 1. Introduction Neither Turing nor Post, in their descriptions of the devices we now call Turing machines, made much mention of time (Turing 1936, Post 1936). 1 They listed the primitive operations that their devices perform - read a square of the tape, write a single symbol on a square of the tape (first deleting any symbol already present), move one square to the right, and so forth - but they made no mention of the duration of each primitive operation. The crucial concept is that of whether or not the machine halts after a finite number of operations. Temporal considerations are not relevant to the functioning of the devices as described, nor - so we are clearly supposed to believe - to the soundness of the proofs that Turi...

This paper surveys a wide range of proposed hypermachines, examining the resources that they require and the capabilities that they possess.

Are there `biologically computing agents' capable to compute Turing uncomputable functions? It is perhaps tempting to dismiss this question with a negative answer. Quite the opposite, for the first time in the literature on molecular computing we contend that the answer is not theoretically negative. Our results will be formulated in the language of membrane computing (P systems). Some mathematical results presented here are interesting in themselves. In contrast with most speed-up methods which are based on non-determinism, our results rest upon some universality results proved for deterministic P systems. These results will be used for building "accelerated P systems". In contrast with the case of Turing machines, acceleration is a part of the hardware (not a quality of the environment) and it is realised either by decreasing the size of "reactors" or by speeding-up the communication channels.

This is the text added to the Russian edition of our book Computing with Cells and Atoms (Taylor & Francis Publishers, London, 2001) to be published by Pushchino Publishing House. The translation was done by Professor Victor Vladimirovich Ivanov and Professor Robert Polozov.

Abstract not found

Accelerating Turing machines are abstract devices that have the same computational structure as Turing machines, but can perform super-tasks. I argue that performing super-tasks alone does not buy more computational power, and that accelerating Turing machines do not solve the halting problem. To show this, I analyze the reasoning that leads to Thomson's paradox, point out that the paradox rests on a conflation of different perspectives of accelerating processes, and conclude that the same conflation underlies the claim that accelerating Turing machines can solve the halting problem.