Employment in academia for doctorates w/o same field undergrad I'm an undergraduate in Mechanical Engineering interested in a career in academia, especially Physics. A middle aged person in India (from where I am) I recently met told me he couldn't find employment in academia in India or abroad after completing his doctorate in a Physics field, because he did an undergrad in Mechanical Engineering. Is this situation where there is difficulty finding employment when doctorate and previous education do not match generally true in academia, Physics or otherwise, or probably a very specific problem?
Don't base life decisions on anecdotes. I'm sure such cases exist, and, other cases in almost any combination. But your future as an academic, or even in industry, will depend far more on your later work and far more than that on the potential for success that you can demonstrate to anyone in a position to hire you. 

But it would be a mistake to stay in Mechanical Engineering for life just for such a reason. It might be a reason to switch earlier, rather than later, but only so that your path into a physics doctoral program might be eased a bit. 

But, a single case is always a poor indicator as there are always, potentially, other, unstated, reasons for the outcome. 

Create your own life. But work hard at it.