system
Given the following post, respond as if you're commenting on Reddit:
human
We know that there's a superior speed limit in the universe, the speed of light. Is there an inferior speed limit?

 An obvious answer would be "staying in place". If you don't move, then obviously, you're at the slowest speed possible. But the small things of which you're made still move between them, and the smaller things like atoms are moving. Also, you're moving through space.

 So, how slow, or how close can you get to being *completely* still. Can molecules ever really be at a rest? If molecules aren't moving, what about atoms. Can the electrons ever stop "spinning*. What about quarks? Is this what absolute zero means?

 Also, could we ever have a point in space which doesn't move at all. But since movement is relative to an observer, would that mean that if something is truly not moving in any aspect, then nothing in the universe is moving either? Is this what will happen because of entropy?

 **Bonus question #1:** Can matter still exist without energy?
 
 **Bonus question #2:** Is the universe currently accelerating/decelerating/constant in its expansion?
 
 **Bonus question #3:** If the universe were decelerating in its expansion, would it at some point reach stillness (stop expanding). Once this happened, wouldn't it be logical that the universe would start to shrink because of gravity?
gpt
Motion is relative. You can always construct a perfectly consistent picture of the Universe (called a reference frame) in which you're at rest, or a particular given atom is at rest, and so on. In other words, complete rest is whatever you define it to be; there's no way to distinguish motion with a constant velocity from pure rest.

BQ1: Remember that matter is stuff, and energy is a quantity that any bit of stuff has. Energy isn't, as sci-fi movies and new age self-help books like to claim, some form of stuff as well. It's a *property* of matter. Can you have matter with zero energy? Not really. You have energy by moving, as well as an innate "rest energy" even when you're not moving (that's mc^(2)).

BQ2: The expansion is accelerating.

BQ3: If the Universe were decelerating (and until 1998 we thought it was, since gravity should pull everything together), then a big crunch collapse would be a possibility. But it wouldn't *have* to happen. The Universe could also decelerate, but at a slower and slower rate, so that the expansion rate slows down and slows down but never quite hits zero and turns around to contraction. This is a lot like launching a rocket at escape velocity (and turning the boosters off). It would always slow down due to the Earth's gravitational pull, but it would never slow down so much that it turned around and fell back down; it would just asymptotically approach zero speed.