Is 4D less or more dense than 3D?

[Raukura Waihaha]

I would've thought that for us to embody more light, the body would be more dense to handle more intense vibration?
I think of it like spirits passing through walls.
If they were less dense than the wall, it would be like blowing smoke at it. They're more dense so the wall is easy for them to move through.

Maybe I'm missing something...I'm not a physics major.