@lqiangecnu,
There is a general belief among physicists in a kind of basic Trinity -- space, time and motion. It is usually held that none of these can exist independently of each other. Time cannot exist without motion because motion is what time measures. And, of course, there can be no motion unless there is space to move in. QED, right?
But I wonder. . . Can space exist independently of the other two? Postulate empty space with no substances -- neither matter nor energy -- capable of motion therein.
Is it, then, still ‘space’ as we understand the word? Or has it become that which we call ‘nothing’? (If it has become ‘nothing’, then it no longer exists. )
The concept of ‘nothing’ is incredibly difficult for the human mind to grasp. We cannot visualize it, partly because ‘nothing’ would contain neither light nor even total darkness. Darkness would be ‘something’; it would imply the potential for light. (And light, of course, is very definitely ’something.’ It moves at a constant ,measurable speed. Ergo, if light, then motion; if motion, then space.) We can render the concept of ’nothing’ or ’nothingness’ mathematically, of course, but we can have no visual or otherwise sensory perception of it. There can be no statement about ’nothing is…’ because, quite simply, ’nothing isn’t.’