About Building Alan

The chapters ask what physics allows. This part asks a different question: how close does today’s technology come, and what would close the gap? The answer changes every year, so these pages are living documents. Each one has a review date, and every number in it carries the date it refers to and its source.

Each living review looks at one technology or one bottleneck and measures it against the same yardsticks:

• The Landauer bound: the least heat that erasing one bit can release, \(k_B T \ln 2\) at the temperature the device runs at (Landauer 1961; Bérut et al. 2012).
• The Margolus-Levitin bound: the most operations per second that a given amount of energy allows (Margolus and Levitin 1998; Lloyd 2000).
• The Bekenstein bound: the most information that a given mass and size can hold (Bekenstein 1981).
• Energy at the wall plug: what the whole system draws from the grid, cooling and power delivery included. A device that runs near the Landauer bound at 4 K can still cost more, counted at the wall plug, than one at room temperature.

These pages are written for engineers and researchers who design processors, memory, AI hardware and data centers, and for any reader who wants to know where real machines stand. The numbers behind them are published as data (see the data folder), so they can be reused and checked.

The same method, applied beyond computing, is Escape Velocity: an open atlas of what each technology still needs to reach maturity, from fusion to medicine, and of which technologies wait on which. Its entries on quantum computers, data movement, heat removal and the energy of AI inference link back to these living reviews.

Living reviews

Living review	Status	Last reviewed	Review due	Curators
CMOS: The Baseline	proposed	never	not reviewed yet	none yet
The Cost of Moving Data	proposed	never	not reviewed yet	none yet
Getting the Heat Out	proposed	never	not reviewed yet	none yet
Adiabatic and Reversible Logic	proposed	never	not reviewed yet	none yet
Superconducting Logic	proposed	never	not reviewed yet	none yet
Quantum Hardware	proposed	never	not reviewed yet	none yet
Thermodynamic and Probabilistic Computing	proposed	never	not reviewed yet	none yet
Neuromorphic Computing	proposed	never	not reviewed yet	none yet
Optical Computing	proposed	never	not reviewed yet	none yet
The Energy of a Token	proposed	never	not reviewed yet	none yet

Bekenstein, Jacob D. 1981. “Universal Upper Bound on the Entropy-to-Energy Ratio for Bounded Systems.” Physical Review D 23 (2): 287–98. https://doi.org/10.1103/physrevd.23.287.

Bérut, Antoine, Artak Arakelyan, Artyom Petrosyan, Sergio Ciliberto, Raoul Dillenschneider, and Eric Lutz. 2012. “Experimental Verification of Landauer’s Principle Linking Information and Thermodynamics.” Nature 483 (7388): 187–89. https://doi.org/10.1038/nature10872.

Landauer, R. 1961. “Irreversibility and Heat Generation in the Computing Process.” IBM Journal of Research and Development 5 (3): 183–91. https://doi.org/10.1147/rd.53.0183.

Lloyd, Seth. 2000. “Ultimate Physical Limits to Computation.” Nature 406 (6799): 1047–54. https://doi.org/10.1038/35023282.

Margolus, Norman, and Lev B. Levitin. 1998. “The Maximum Speed of Dynamical Evolution.” Physica D: Nonlinear Phenomena 120 (1-2): 188–95. https://doi.org/10.1016/s0167-2789(98)00054-2.