- Vacuum State Encoding: Information encoded in vacuum states of quantum fields (Greg Egan's "Schild's Ladder")
- Quantum Entanglement Patterns: Messages hidden in the patterns of entangled particles (Robert Charles Wilson's "Spin")
- Virtual Particle Fluctuations: Alien communications encoded in quantum fluctuations (Peter Watts' "Blindsight")
- Mathematical Constants: Information embedded within fundamental constants like π (Carl Sagan's "Contact")
- Multidimensional Particles: Sophons that unfold across dimensions carrying information (Liu Cixin's "Three-Body Problem")
- Orbital Patterns: Messages encoded in the orbital mechanics of celestial bodies (Alastair Reynolds' "Pushing Ice")
- Baby Universe Constants: Messages encoded in the fine-structure constants of artificially created universes
- Gravitational Wave Encoding: Information preserved in gravitational waves to survive cyclical big bangs
- DNA/Genetic Encoding: Information stored in the genetic code of species
- Linguistic Spacetime: Languages that encode perception of spacetime itself (Ted Chiang's "Story of Your Life"/"Arrival")
- Environmental Mutations: Information transmission through environmental changes (Jeff VanderMeer's "Annihilation")
- Genetic Cultural Archives: Human genetic code designed to preserve cultural information (Neal Stephenson's "Seveneves")
- Relativistic Time Capsules: Information preserved through relativistic time dilation (Poul Anderson's "Tau Zero")
- Tachyon Communications: Messages sent via faster-than-light particles (Gregory Benford's "Timescape")
- Memory Objects: Physical items that encode memories across time (Ken Liu's "The Paper Menagerie")
- Mathematical Boundary Encoding: Information stored at the boundaries between contradictory mathematical systems (Greg Egan's "Luminous")
- Trajectoid Messages: Objects whose physical trajectories trace out information when viewed properly
- Natural Unit Measurements: Objects whose dimensions, when measured in specific natural units, yield meaningful decimal expansions
- Resonant Frequency Objects: Three-dimensional "Chladni objects" with information encoded in their resonant frequency patterns
- Cache Weapons: Computational objects with deadly information (Alastair Reynolds' "Revelation Space")
- Temporally Shifting Structures: Objects that move through time, encoding information in their structure (Dan Simmons' "Hyperion")
- Resonant Frequency Objects:
- Conservative estimate: ~40,000 bits (5 kilobytes) using 1,000 independent resonant modes
- Enhanced potential: Megabytes to gigabytes with multiple materials, amplitude/phase encoding, and directional excitation
- Ideal material: Diamond with engineered defects for stability over billions of years
- Robust against degradation: Information recoverable even with partial damage
- Universal physical principles make decoding possible across different civilizations
- Robust against technological changes (unlike digital media formats)
- Potential for hierarchical information revealing itself at different technological levels
- Natural camouflage as ordinary objects until properly analyzed