Παρασκευή, 13 Δεκεμβρίου 2013

On the Computing Spacetime

Fotini Markopoulou has published a paper entitled The Computing Spacetime. The first sentence of this paper is: That the Universe can be thought of as a giant computation is a straightforward corollary of the existence of a universal Turing machine. This is a very bold statement, to say the least. We have absolutely no idea what are the (ultimate) laws of the universe and yet we can immediately prove that it is a gigantic computer! Now let's see the proof:
The laws of physics allow for a machine, the universal Turing machine, such that its possible motions correspond to all possible motions of all possible physical objects. That is, a universal quantum computer can simulate every physical entity and its behavior. This means that physics, the study of all possible physical systems, is isomorphic to the study of all programs that could run on a universal quantum computer. We can think of our universe as software running on a universal computer.
First let me remark that Markopoulou confuses universal Turing machines with universal quantum computers, which means, I suppose, that she assumes that the Church-Turing thesis is valid. Second, it is known that the Turing machine operates in a Newtonian universe and naturally does not take under consideration any quantum phenomena. Third, to say that physics is essentially equivalent to the study of quantum programming is a fallacy because we have no idea what are the ultimate laws of universe. Unless, of course, we assume that fairytale physics is real physics. In this case, it is crystal clear that we are talking nonsense.

As with fairytale physics, the problem with the the-Universe-is-a-computer paradigm is that there is no experimental evidence that actually the universe computes something. In fact, I am pretty sure that this is something like an Illuminati conspiracy theory rather than a real scientific theory. Naturally, please bear on mind that the problem of quantifying gravity has not been solved yet.

PS Today (20/02/2014) I discovered a preprint entitled  The Universe is not a Computer. In this paper the author puts forth an interesting argument against the validity of the idea that the universe is a computer.

Τρίτη, 10 Δεκεμβρίου 2013

Fairytale Physics

Jim Baggot in his recent book that is entitled Farewell to Reality: How Fairytale Physics Betrays the Search for Scientific Truth  advocates the idea that modern physics is going in the wrong direction. In particular, he critically examines superstring theory and concludes that this theory cannot explain the existence of many things we know they exist! Similar ideas have been presented in Peter Woit's Not Even Wrong: The Failure of String Theory and the Continuing Challenge to Unify the Laws of Physics. Recently, the British newspaper The Guardian has published as debate between Baggot and string theorist Mike Duff. The later replied to Baggot's remark that "the positron was discovered in cosmic ray experiments just a couple of years after Dirac had agreed that this was what his theory predicted" as follows:
Dirac did not assume the positron; he discovered it to be a consequence of an equation that described the well-established electron. Similarly, string theorists did not assume supersymmetry, extra dimensions, the dualities of M-theory or the myriad possible universes; they discovered them to be consequences of a theory that subsumes empirically well-established features such as general relativity, gauge field theory and chiral quarks and leptons. Current research is devoted to finding out what else M-theory requires.
 The problem with Duff's argument is that none of the things superstring theory has been speculating about have been discovered! In fact, there are not even indirect evidence that might one lead to the conclusion that these bizarre things exist. (They do exist in Fringe's universe…)

One may wonder what all these have to do with computation. The answer, of course, is quite simple: when one proposes a bizarre model of computation she must make sure that the physics involved is valid beyond any doubt!

PS On the 20th episode of season 7 of The Big Bang Theory, Sheldon wonders: "Am I wasting my life on a theory that can never be proven?"  and decides to stop his work on string theory... (I read about this in the Not Even Wrong blog).

A "Solution" to Riemann Hypothesis

Riemann hypothesi s is "is a conjecture that the Riemann zeta function has its zeros only at the negative even integers and complex n...