New Delhi, Aug. 18 -- From Demolition Man-where Sylvester Stallone's cryogenically frozen whole body is revived to chase a futuristic villain played by Wesley Snipes-to movies like The 6th Day, Gemini Man, and Universal Soldier, Hollywood has long toyed with the idea of cheating death through scientific advancements such as cloning and cryonics.

That notion of resurrecting the dead is no longer confined to pulp fiction and sci-fi. From Berlin to Arizona, companies are freezing brains-and sometimes the entire bodies-of humans and pets, betting that future science will one day bring them back. For instance, Tomorrow Bio, Europe's only provider of whole-body cryoprotection, recently made headlines when it raised about $6 million.

However, ...