Booming Indices-A signal of real growth or another alarm

The stock markets are booming again. Some say it is because of the increased activities of Foreign players, others predict that this the result of the faith of the Retail Investors in India, which has been restored.
Anyways, be it an activity of Foreign Players or a faith of the Retail Investors being restored, the stock markets are seeing a new high.
This certainly calls for some deliberation because the natural rule says that everything that has gone up has to see a low, and that's inevitable.
The markets will soon see some depression, The only thing that has to be observed is, EXACTLY WHEN and HOW MUCH?