For me it’s quantum computing - especially considering its impact on most current encryption methods
Fusion. I think it’s our only hope of making it through climate change without massive losses.
There’s a massive fusion reactor in the sky that we could easily use by turning the radiation from it into electricity or harnessing the winds that are caused by the temperature differences it creates.
Nuclear fusion still has a long way to go, but to slow climate change (already too late to stop it) we need to act now.