system
Given the following post, respond as if you're commenting on Reddit:
human
[General] Why is there gravity inside spaceships?

Why is there always gravity (or what appears to be gravity) inside spaceships. This is prevalent in Star Wars, Star Trek, pretty much every Sci-fi media, and it's always bugged me. 


We never see any sign of artificial gravity while inside spaceships, and it seems the instant the characters step outside for a spacewalk they are in zero gravity. What gives?
gpt
Most kinds of "artificial gravity" rely on a conceit like Mass Effect fields or "gravity plating". 

Newer sci-fi (the Martian, Red Mars, and Halo, for instance) have ships with rotating toruses intended to simulate gravity via centripetal force. 

When you move between toruses you experience different levels of gravity. In Halo they use special "gravity gyms" to get buff, while in Red Mars they use it to adjust to what it will be on Mars (.3G). On military vessels these toruses would be hidden behind layers of armor; the UNSC Halcyon is a pretty good example. 

Magnetism can also produce gravity fields, however, you need extreme cold to keep the magnets superconductive (which drains power). This was actually the underlying conflict in 2009's Avatar; the humans wanted "Unobtanium" (stupid name) because it was a room temperature super-conductor. Just recently a device was made to levitate a small mouse using magnetism, thereby producing a 1G field to cancel out the Earth's gravity, so it is possible.

String theory posits that gravity and electromagnetism unify in hidden dimensions, however, no one knows how to manipulate this.