22 November 2010

Experimental Confirmation – 'Information = Energy'

Illustration: Peter
Macdonald, Edmonds UK
In a letter published in the journal Nature Physics on 14 November 2010, Japanese scientists have reported the first experimental confirmation of a thought experiment, dubbed 'Maxwell's Demon', that was first proposed around 150 years ago by James Clerk Maxwell .

The significance of the experiment is that it verifies the equivalence of information and energy, ie that information can be converted to energy (and vice versa), just as energy and mass are equivalent (ie according to E=mc2).  Thus, it can truly be said that mass, energy and information are all convertible, from which it follows that none is any more or less 'physical' than the others.

Under the current Australian law relating to patentable subject matter (ie 'manner of manufacture'), a necessary prerequisite for patentability is a 'physical effect in the sense of a concrete effect or phenomenon or manifestation or transformation' (Grant v Commissioner of Patents [2006] FCAFC 120, at [32]).  This experiment proves that the manipulation of information is sufficient to satisfy this requirement.


Maxwell's original thought experiment was designed to demonstrate that the Second Law of Thermodynamics has only a statistical certainty, rather than being more fundamental in nature.  (The Second Law states that the entropy of an isolated system can never decrease, or in other words that systems become more 'disordered' over time.)

Maxwell stated his thought experiment as follows:

... if we conceive of a being ['Maxwell's Demon'] whose faculties are so sharpened that he can follow every molecule in its course, such a being, whose attributes are as essentially finite as our own, would be able to do what is impossible to us.  For we have seen that molecules in a vessel full of air at uniform temperature are moving with velocities by no means uniform, though the mean velocity of any great number of them, arbitrarily selected, is almost exactly uniform.  Now let us suppose that such a vessel is divided into two portions, A and B, by a division in which there is a small hole, and that a being, who can see the individual molecules, opens and closes this hole, so as to allow only the swifter molecules to pass from A to B, and only the slower molecules to pass from B to A.  He will thus, without expenditure of work, raise the temperature of B and lower that of A, in contradiction to the second law of thermodynamics....

Even accounting for the fact that, in practice, some work must be done in opening and closing the trapdoor, this may be made almost arbitrarily small, by reducing the size and mass of the door.  This work is not sufficient to account for the decrease in entropy associated with ordering the molecules into 'hot' and 'cold' partitions.


If, as many scientists believe, the Second Law is more fundamental than a mere product of statistical behaviours, there must be a problem with Maxwell's thought experiment.

Hungarian physicist Leó Szilárd suggested that a real-life Maxwell's demon would need to have some means of measuring molecular speed, and that the act of acquiring information would require an expenditure of energy.  This should be sufficient to prevent a decrease in entropy of the isolated system comprising both the gas molecules and the demon.

Szilárd's argument was challenged by IBM physicist Rolf Landauer, who suggested that some measuring processes need not increase thermodynamic entropy as long as they were thermodynamically reversible.  By using reversible measurements to sort the molecules, the Second Law might be violated.

However, Landauer's work also proposed that information has entropy and that, consequently, the disposal of information from a physical system (such as an electronic circuit) must result in an increase of entropy and a corresponding dissipation of heat.  So each time the demon acquires information about the state of a molecule, it must either discard it or store it.  To avoid an increase in entropy the demon must store the information indefinitely.  However, the computer scientist Charles Bennett (also with IBM) showed that  eventually the demon must run out of information storage space and begin to erase the information it has previously gathered (or discard all new information).

Over the long term, therefore, there can be no net decrease in the entropy of the gas/demon system.

The debate continues, however, because the status of the Second Law of Thermodynamics as a fundamental and inviolable universal law has not been conclusively established, even though it has never been observed to be violated.


In the experiment conducted by researchers from Chuo University and the University of Tokyo, a miniature version of a spiral staircase was set up, and a molecule caused to climb the staircase using information.  The 'staircase' was created using electric fields, while the movement of the molecule was solely due to its thermal energy (ie Brownian motion).

A high-speed camera was employed to photograph the molecule.  When it moved up the staircase it was allowed to move freely, but when it attempted to move down an electric field was applied to block its passage.  By moving up the staircase, the molecule gained potential energy.  Yet the researchers never had to 'push' the molecule (ie do any work directly on the particle).  Instead, they simply used the information about which direction it happened to be moving in at any given time to guide the climb.

The researchers were able to precisely measure how much energy was converted from information, experimentally confirming the postulated equivalence between the two.


We are pleased to report that the current state of the law in Australia is broadly consistent with this result.

While the court in the Grant case found that there was no relevant 'physical effect' produced by the manipulation of legal and financial 'information' recited in the patent claims, recent Patent Office decisions have (in our view correctly) pointed out that while a 'physical effect' may be a necessary condition for patentability, it will not always be sufficient.  As Deputy Commissioner Phil Spann stated in the recent Iowa Lottery decision (which we reported here), '[i]nformation even if represented in a physical way has never been considered sufficient for patentability save for some material advantage or mechanical effect in the arrangement of the information.'

While there may be no such thing as 'abstract' information (ie any information must inevitably be 'represented in a physical way', whether or not expressly recited as such), this is not going to open the floodgates to allow anything to be patented!


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