That is in addition to left, right, back, forth and up, down, Kaluza proposed that there might be additional dimensions of space that for some reason we don't yet see.
除了我们熟悉的左和右，前与后，上跟下外， “卡鲁扎”认为空间里可能包含有额外的维度 只是因为某些特殊原因，我们还无法认知。