I haven't tried entering it yet, but would "The Universe is truly big" be a possible translation?
I think that yes, although wouldn't it be a bit different in the shade of meaning? Like 'really big' is kinda like 'very big', but 'truly big' is like 'big indeed'?
They're more or less interchangeable, but truly/indeed could sound weird and off in some contexts.
I checked, it is accepted.
it wouldn't take bardzo (wszechświat jest bardzo duży), I can't understand why.
Well, we usually accept "really" for "bardzo", so I guess it should be accepted the other way round. Added now.
'naprawde jest duzy' should work just as well?