This is the universe we are living is said to be existed for millions of years. And scientist have developed a lot of theory and equations to predict correct history of universe. They are searching a new theory so called "grand unified theory" which will correctly give the history of universe from big bang. But shall it give correct picture of universe?This is also a big question that arises while talking about this kind of problem. Let us see an example. We develope a machine according to few law. We look for the result that is right from mathmatical view. But there always error in the observed result then theoritical result. This is called error in the machine. This error increases with time. If the universe is compared with the machine then there should be error with that laws Which were valid in the begining of the universe. The error cannot be measured by us because life of man is too short to observe this error like a simple machine. Then we cannot be near to that equation.