Can anyone here using Dyn4j explain what physics scale can be used for between Dyn4j and JME? I’m having trouble understanding this element 
The scene graph doesn’t have a specific “real world” size, you can decide how you want it, e.g. 1 world unit = 1 meter or so.
Ah, so if I wanted 1 world unit to match 5 meters, I would scale by 5. Okay. Thanks.
No, what Normen means is that you can make a 3D-model of an atom that is 100 world units large. Or a model of the moon that is 100 world units large. It doesn’t matter to jME what you think 1 WU is equivalent to.
Edit: link to Dyn4J forum about scaling:
http://forum.dyn4j.org/viewtopic.php?f=1&t=296&p=1055&#p1055
So scaling is only needed if values (sizes and velocities) does not reside in the ranges for which Dyn4j is ‘tuned’ ? For instance if my space ships (Circles) are more than 10 world units wide… (at least that’s what i could read on the link you gave).
Scaling is used as a way of normalizing so that ranges fit with Dyn4j ?
No. Dyn4j most certainly has an inbuilt size relation, most probably 1m = 1 unit. You could of course change all gravity and forces accordingly and then “play as if” 1 unit = 1km or whatever though.
Anyway all of this doesn’t have ANYTHING to do with the numbers you use in the scene graph. You can make your dyn4j object 1x1x1 and the spatial 100x100x100 or 0.1x0.1x0.1, it will look the same, you just have to move the camera closer
Also what I was trying to say. But Dyn4j and Bullet apparently has ranges for which they are more accurate (at least that’s what I read), so if you did have 100x100x100 you would need to scale it when you integrated to Dyn4j.
Well no you wouldn’t have to scale the spatial, it can still be 100x100x100, you just have to make the dyn4j object 1x1x1.
Its like converting between imperial and metric… You don’t make the objects larger because 1m = 3feet, its just that “1” and “3” are the same in that case.
Also what I’m saying, but I seem to be failing miserably at communicating that we are in agreement 
Ah, alright, I guess the word “scaling” was what got me off track there