I guess my confusion lies in propulsion. Not fantasy, real propulsion. If space cannot be compressed then what do the expanding gases push against to gain propulsion( forward motion). All systems currently in use as propulsion in space rely on the expansion of gases that are directed in one direction to gain momentum in the opposite direction. If space cannot be compressed then what is the expanding gas pushing against? I understand that there is a negative pressure in space but you must be able to increase that pressure in order to gain any momentum. I am not a physicist. My background is very mechanical. I have ideas for propulsion in space but I need a better understanding of the compressibility of space.