Timeshifting

The problem: Most computer users manually save versions of files with names like Presentation-2027-Jan-11, followed later by Presentation-2027-Jan-11-UPDATED and Presentation-2027-For-Sally-Only, perhaps with Presentation-panic-edits-before-event. This is manual versioning, and even people who stick strictly to a naming convention still get confused at times. Some applications append .bak or prefix ~ to create their own backups, and then occasionally an automatically-created TMP or $tmp$ file can really save the day, and so on. Then when it comes time to clean up and organise a filesystem, everyone hesitates. Am I really sure there is not useful work in each of those ten versions? Which ones do I need to keep? So, we usually keep them all. After all, storage is cheap. ...

Not Before Time is a public broadcast facility built on existing technology. Not Before Time gives three strong guarantees that information: will not be readable before a certain future time was not sealed before a certain past date and time was not electronically signed before a certain time These support human rights, democracy and business. The second guarantee is a lower bound on sealing, not a creation date. A released NBT private key cannot be inside a package sealed before its release, although it can be added to old material later. The claim cannot be checked until the package opens; a priority claim needs the ciphertext published or independently anchored at the relevant time. ...

This wee note is about physics results I noticed suggesting it may be possible to greatly reduce the power and water required by datacentres. This is in a field of physics I am not remotely able to verify but I’m keeping an eye on what seems to be happening. Large Language Models are subject to the laws of physics in a bad way, because they use so much electricity and make so much heat. Landauer’s principle ↗ identifies the thermodynamic cost of information erasure, and some later work builds on this to show that computation can avoid erasure through logical reversibility. ...

Reversible execution creates computers that seem to run backwards, applying time shifting techniques with simulation/virtualisation to address software unreliability and complexity. I stand by my excited comments from way back in 2005: Reversibility is the biggest advance in debugging since source code debugging — Me, on the GDB developers list ↗ in 2005 In 2026, reversibility still isn’t seen as an ubiquitous must-have for software development, but awareness is increasing. 💡 Confusingly similar names I also have an article on the totally different but similar-sounding topics of logical reversibility and thermodynamic reversibility . If you’re interested in the problems power-hungry AI datacentres present the world you might find it interesting. What is checkpoint-based reversible execution? Reversible execution is about giving the appearance of a program executing backwards in time. If you’ve not seen it before, it is just as strange and impressive as it sounds. ...