What is the purpose of the Mirror, it shows you as you are. Like that there is another Mirror which shows you the Past, it shows you how was the culture, what types of vehicle they used in the past and what was the source of communcation.
That Mirror is called the Films. Films are those Mirror which shows us how people used to live in the Past. Like when you take one movie which was taken in the past and same movie in the present. Then you will know the difference.
Take for example, Chori Chori (1956)and Dil Hai Ke Manta Nahin (1991) , you can see that Raj Kapoore what kind of Phones they used and what kind of Phone Aamir. Even the transportation was different at that time.
When you see any old movie, don't just see the movie, try to find what they are using in olden days. Then you will accept that Films are Mirror to the Past !!!