[HN Gopher] The Failure of the Thermodynamics of Computation (2010)
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The Failure of the Thermodynamics of Computation (2010)
Author : nill0
Score : 45 points
Date : 2026-03-27 02:47 UTC (2 days ago)
(HTM) web link (sites.pitt.edu)
(TXT) w3m dump (sites.pitt.edu)
| svantana wrote:
| It's an interesting article but I fail to see the point they are
| trying to make. I always thought of reversible computing as a
| sort of platonic ideal that cannot truly exist in real life, but
| the principle can still be used to reduce waste heat and energy
| use. For example, it will be interesting to see if the chips from
| Vaire ever become practically useful:
|
| https://vaire.co/
|
| https://spectrum.ieee.org/reversible-computing
| smitty1e wrote:
| From the abstract, the idea is that we can continue to shrink:
| "...in a manner in which no thermodynamic entropy is created or
| passed to the surroundings."
|
| The objection seems to be the "free lunch" assumptions being
| made about shrinkability.
|
| "What Is TANSTAAFL?"
| https://youtu.be/ZrZUe7R44eA?si=oK2H1L9ha1zQhDOh
| cwillu wrote:
| > I always thought of reversible computing as a sort of
| platonic ideal that cannot truly exist in real life
|
| It's been experimentally demonstrated. Practical or not, the
| effect is real.
| debatem1 wrote:
| The author should write a followup article about how theory of
| computation has failed because nobody makes a Turing machine with
| enough tape.
| oh_my_goodness wrote:
| Very clear intro to this notoriously slippery area.
| ogogmad wrote:
| I think I arrived at the same suspicion independently -- it was
| when I was trying to understand thermodynamic entropy as an
| instance of Shannon entropy - where the latter is defined
| abstractly as a property of probability distributions - which
| left me wondering about where the thermodynamic probabilities
| came from. I was wondering whether they were supposed to be
| subjective probabilities, or derived from ensembles. Then I
| recalled that entropy was originally defined _non_
| -probabilistically as dS = (1/T)dQ. Then I started reading about
| Boltzmann distributions as a bridge between Shannon's entropy and
| entropy in the earlier sense (Clausius entropy). I then concluded
| that instead of thinking about bits and bytes, it was much easier
| to think about gases and machines doing work, like a 19th century
| engin-eer building, er, engines.
|
| I am pretty ignorant of this field.
| cwillu wrote:
| The effect has since been experimentally demonstrated.
| svnt wrote:
| This was published right before people started experimentally
| validating the Landauer limit. I am not sure why it hasn't been
| taken down at some point as the evidence has accumulated:
|
| 2012 -- Berut et al. (Nature) -- They used a single colloidal
| silica bead (2 mm) trapped in a double-well potential created by
| a focused laser. By modulating the potential to erase the bit,
| they showed that mean dissipated heat saturates at the Landauer
| bound (k_B T ln 2) in the limit of long erasure cycles.
|
| https://www.physics.rutgers.edu/~morozov/677_f2017/Physics_6...
|
| 2014 -- Jun et al. (PRL) -- A higher-precision follow-up using
| 200 nm fluorescent particles in an electrokinetic feedback trap.
| Same basic physics, tighter error bars.
|
| https://pmc.ncbi.nlm.nih.gov/articles/PMC4795654/
|
| 2016 -- Hong et al. (Science Advances) -- First test on actual
| digital memory hardware. Used arrays of sub-100 nm single-domain
| Permalloy nanomagnets and measured energy dissipation during
| adiabatic bit erasure using magneto-optic Kerr effect
| magnetometry. The measured dissipation was consistent with the
| Landauer limit within 2 standard deviations using the actual the
| basis of magnetic storage.
|
| https://www.science.org/doi/10.1126/sciadv.1501492
|
| 2018 -- Guadenzi et al. (Nature Physics) -- Opens with:
|
| The erasure of a bit of information is an irreversible operation
| whose minimal entropy production of kB ln 2 is set by the
| Landauer limit1. This limit has been verified in a variety of
| classical systems, including particles in traps2,3 and
| nanomagnets4. Here, we extend it to the quantum realm by using a
| crystal of molecular nanomagnets as a quantum spin memory and
| showing that its erasure is still governed by the Landauer
| principle.
|
| https://www.nature.com/articles/s41567-018-0070-7
|
| The Landauer limit is not conjecture.
| ogogmad wrote:
| I'm not sure, but isn't 2 standard deviations a bit low?
| Especially so for something that can be done in a lab. It seems
| that 2 SD is the minimum threshold for getting published. Can
| we be sure that these are properly reviewed?
| spocchio wrote:
| Could it be possible that you confused the number of standard
| deviations one needs to falsify something? For instance, if
| two things are different we may want to be as many SD as we
| can apart. Here, on the other hand, the data agree _within_
| 2S D.
| svnt wrote:
| That was the limit of just one experimental approach that was
| peer reviewed and published in a major journal. As you can
| see there are many experiments validating the limit and none
| invalidating it.
|
| The reality is that the Landauer limit is vanishingly small.
| I would encourage you to review the experiment methodology
| and see if you can come up with better, fundable methods.
| griffzhowl wrote:
| Is the focus on the erasure of a bit, rather than writing a
| bit, just conventional or is there a significant difference
| between the processes?
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