system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why do certain machines need helium? Can't there be an alternative?
gpt
Helium is particularly good for cooling things to very low temperatures. There are occasions where (until we come up with higher temperature alternatives) very low temperatures are unavoidable. Mostly these are connected with making very strong magnetic fields, which require very large currents in electromagnets.

To make this manageable the magnets are made from superconductors - special materials which, at a low temperature - have no electrical resistance. This means they don't get hot and can be made manageably small. 

Helium is, in many cases, the only safe way to do this.

As a lifting gas, helium is also the only safe way to do the job. There are other gases which are lighter than air but they're either dangerous, or not sufficiently lighter to be worth using.