渺小 is almost same as 微小. (Tiny, little, few, small) However, we usually use 渺小 to describe something mentally feeling, such as hope; 微小 is used to describe sizes of things in reality, such as boxes, we would rather say 微小的箱子 (small boxes) or 微小的微生物 (tiny micro-organisms) than 渺小的箱子/微生物. In general, we would say 渺小的希望 (little hope), but never 微小的希望 (small/tiny hope).

渺小是相对于大而言的。Just like that human is really small compared with this huge would.微小强调细微，不易看见。Eg:This germ is really small.The 'small' here means 微小。

不好意思，写错了一个词，是”具体事物“，不是”具体事务“。

异： ”渺小“比较侧重于人的主观感觉。如： 你考上的希望渺小。 人在宇宙中显得很渺小。 ”微小“可以形容很小的具体事务，如：微小的颗粒/灰尘 同： 两个词在形容个人力量时可以换用，如：个人的力量是微小/渺小的。用微小强调力量本身小，用渺小强调人的感觉，感觉人的力量很小。

渺小 usually describe for a person,微小usually describe for things