double the pressure

Two things I cannot visualise:

In one second, light travels 3e8 m, which is 30,000 km. Okay.
So a light year is several billion kilometres. Alright.
How is our NEAREST galaxy, Andromeda, 2.25million light years away?! That kind of distance is just impossible to grasp.

Next thing I can't visualise is a pressure of 2 atmospheres. I have nothing to compare with. I have one atmosphere on me right now, but I would have no idea what double that would feel like. Like when I'm at the bottom of the pool, I have no idea if that's 2 atm or 20atm. Or only 1.01atm.


While we're at it, I suck totally at guessing weights below 500g. I cannot tell the goddamn difference between 200g and 400g from memory.