system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:why do we assume that " aliens" consist of the same building blocks as life on earth and that they need the same energy sources?

Isn't it possible that they do not need sunlight and live of energy that is considered poisionous or dangerous for life on earth?
gpt
Yes, it is possible, and we've explored a few possible types of life that don't exist here on Earth (silicon-based instead of carbon-based is probably the best known). But if we're going to look for aliens, we have to look for *something*, and we may as well look for the one set of conditions we know work.