system
Given the following post, respond as if you're commenting on Reddit:
human
[The Mist] Tell me about this "mist".

How far did it spread? Was this a door to another dimension? What is it made of? Why were some people unharmed when walking through it? My Physics class is attempting to recreate the even on a smaller scale. Any information you have would be appreciated.
gpt
The Mist, itself, wasn't special. Some sort of portal opened allowing the creatures through to our world, and the Mist is simply atmosphere from wherever they are from. We have no idea where this portal goes; is it another dimension? Another part of our galaxy? Another universe entirely? We don't know, but they clearly follow many of the same physical rules that we do. People are unharmed walking through the Mist because it is simply some form of fog, most likely made of plain-old water vapor. Is there other stuff mixed in with it? Probably. We don't know. It's not like the government is sharing what it discovered after the event. 

As for how far it spread, we can assume it wasn't more than a few square miles, because reports from the few survivors that existed mentioned leaving the fog as they left the city.

Everything is very "hush-hush" from the government. They aren't sharing their findings, and even the people that were there and saw it with their own eyes are given bullshit explanations.