Cryonics: Both Freezing and Revival Remain Unsolved Problems
Cryonics faces two unsolved problems: freezing (vitrification works for small samples but cryoprotectants are toxic at scale) and revival (entirely unsolved — no method to rewarm or repair large tissue).
Both halves of the cryonics problem — freezing and revival — remain unsolved as of 2026. Freezing challenges: Ice crystal formation damages cells at the microscopic level during conventional freezing. Vitrification (using cryoprotectant chemicals to achieve a glass-like state without ice crystals) addresses this partially, but the cryoprotectant chemicals themselves are toxic to tissue, and the process has severe scaling challenges beyond small samples. Revival challenges: Entirely unsolved. No methods exist to reverse cryoprotectant toxicity in tissue, repair accumulated cellular damage, or safely rewarm large tissue masses without thermal cracking. Current success: Vitrification works for small biological samples (embryos, sperm, small tissue sections). However, preserving a human brain — with its 86 billion neurons and approximately 100 trillion synaptic connections — is orders of magnitude more complex than anything achievable with current technology.