Abstract:

The logo for world year of physics 2005 is a sandglass. It is also the illustration of light cone, a fundamental concept in the Einstein¡¯s special relativity which provides us a revolutionary view of space-time. But what is time? Is it real or imaginary, indefinite or cyclic, a parameter or a variable, one dimensional or half-dimensional, translational or having a starting point? All these to-be-or-not-to-be¡¯s indicate the absence of a universal role for time in physics.
 
 
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