adj.不存在的，不真实的

The unicorn is a mythical creature that doesn't exist in reality.
独角兽是一种现实中不存在的神话生物。
The concept of a perpetual motion machine is non-existent in the laws of physics.
永动机的概念在物理学定律中是不存在的。
In the desert, water sources can be non-existent for miles around.
在沙漠中，方圆几英里内可能找不到水源。
The idea that humans can live without sleep is purely non-existent.
人类可以不睡觉生活的想法纯粹是不存在的。
Aliens have not been proven to exist, so they are considered non-existent by many scientists.
外星人尚未被证实存在，因此许多科学家认为它们不存在。
The ancient city described in the legend has never been found, it's non-existent in the modern world.
传说中的古城从未被发现，它在现代社会中不存在。
A square circle is a mathematical entity that is non-existent.
正方形的圆是一个不存在的数学实体。
The notion of time travel to the past is still in the realm of science fiction, hence, non-existent in reality.
回到过去的时间旅行在现实中是不存在的，目前仍属于科幻范畴。
The memory of my childhood friend has become non-existent after so many years.
经过这么多年，我童年朋友的记忆已经消失了。
The concept of zero gravity on Earth's surface is non-existent; there's always some gravitational force acting on objects.
地球表面的零重力概念是不存在的；总是有一些重力作用在物体上。