For someone interested in robotics but do not know the ABC of robotics or mechanical/electronic engineering .What's a good roadmap for becoming an amateur roboticist . I'm studying theoretical physics so that I have no problems on the physics/math . If the question is too broad and doesn't meet the criteria of posting on this site . Please inform me of any helpful advice/study material etc. before the question get closed . Thanks in advance.
Start with basic electronics, ditch the books, start empirically do stuff. Chances are you will be bored as hell and it will be over.
Buy some cheap breadboard, LEDs transistors, buttons and see if its fun. Next buy some cheap engines and play with them. Still reading? Buy some books like "Robot Building for Beginners-David Cook" or surf the web. Next buy Arduino Uno (the cheapest) and learn some C or Java to program it.
Then you will know enough to decide for yourself and you will spend no more than 100$ on the stuff until then.
That being said, I would suggest taking a programming course for a start. The Udacity CS373 class is the gentlest introduction to robotics I'm aware of. I also recommend the textbook that the prof co-authored (but it's not used in the class).
Then you can use the time as you're working through the class to educate yourself more on hardware options.