hope this would help you understand..
in special theory of relativity and Lorenz transformations, you basically fix light speed at C. and as a result you get seemingly absurd results such as "time relative between observers", "length contraction" as you move faster and stuff..
it's not easy to explain.

Jon Snow ගැන දන්නවා ගෑනු හැමවෙලාවෙම ඌ ගැන කිය කිය වැළපෙන හින්ද