I have had the priviledge of being called a 'World Expert' several times in my life.
Once the World Bank called me 'The Worlds Expert on utility billing systems', another time I was called by Sybase 'one of the top 24 experts in the world' and there have been a couple other times that I have reached similar acolades, such as when I was called the second expert for a particular database (the #1 guy was way ahead of me, my #2 position was a very distant location).
Now, let me first say - just because someone or some company says you are a world expert doesn't mean you are! Conversely, just because you aren't 'the' world expert on a topic, doesn't mean that people won't think you are. So, as they say - "don't read your own press release."
But in any event, I have had people through the years ask me how to become a world expert. I have some tips, some serious, some jokes, but even the jokes are mostly serious. So, here they are in no particular order:
Write a book on the subject. (And ignore all the nasty coments from people who are jealous that you are called an expert and they aren't just because you wrote a book and they didn't)
Write a series of articles on the subject and get them published in multiple magazines.
Write a blog/series of eArticles and find a way to have lots of people see them. This is even better if some of them are published in a so called 'real' magazine - in print.
Now, how do you decide what to be an expert on? One way to look at it is that there are two broad subject areas to become an expert, one is in a field that is fairly static, the other is in a dynamic field. I have done both so I can offer comments on both.
First, it is a lot easier to become an expert in a dynamic field, a field where the subject matter changes quickly. If you are a quick study and willing to devote all your spare time to it, in many cases, as little as 1000 hours of study and practise is a reasonable amount of time to become a very high level expert, a little longer to be a world expert. This assumes that you have the basic 'non-expert' level of knowledge before you started the 1000 hours, if you are coming with no knowledge, you will need to first get the basic level of knowledge and experience before you try to become an expert. Now, with a dynamic field expert, the big problem is: staying an expert. When I became a expert in these types of subject matters, I would say 'what is the difference between an expert and a has-been? ... 3 weeks'. You see, in a dynamic field, if you rest very long, you are no longer an expert. It can be extremely tiring to stay an expert in this type of field, so you had better pick a field that you love to study, where you consider the time staying an expert to be your 'personal fun' time, not 'work' time.
Becoming an expert in a static field definitely takes far longer, but has the huge advantage that staying an expert is easier. In the utility billing field, I stopped working in that field years ago - and yet, with just a few hours of refresher, I am fairly confident that I could reach the level I was at previously, and certainly, if you were to ask me questions, while I couldn't immediately talk at a level that would make people think I am 'the' world expert, I could certainly immediately start talking at a level that would make many people, including some of those in the field, think that I am 'a' world expert. But where the dynamic fields each took about 1000 hours of prep time, the utility billing field took me years of working 6 days of week 16 hour days. I may have been able to reach the level slower by not working that many hours a week - and indeed, if I wanted to become an expert in another static field (and I am in the process of doing so as 'this' page was being written) I would probably cut back to something like 6 days a week, 12 hours a day, partly because I have experience and can be more efficient.
In whatever area you pick, I would strongly suggest you pick something that you really enjoy. The more you enjoy it, the more fun it will be becoming an expert, the quicker you are likely to become the level of expert you want to become.
You also need what I call 'intentionality', meaning, you have be be intentional in what you do. You have to be willing to make mistakes if that is what it takes to learn. You need to study, you need to listen to what others can offer while not necessarily deciding they are correct. You need to actively look for learning opportunities as you go along. You need to read and study much material directly related as well as, especially for static field expertise, indirectly and obliquely related.
Also, think about the responsibility of the field you are picking. Do you want that responsibility? Being an expert in utility billing systems had a level of responsibility I was willing to live with, but when I considered the field of 'aviation parts control management' back in 1987, after talking with a lawyer, I decided that to go from the level I was at to the level of expert wasn't worth the legal risk. Similarly, I would like to write some books on Christianity/God, but I see the responsibility of that being so high that I have not yet done so. Maybe sometime I will feel I have the expertise and knowledge necessary to feel comfortable and confident to write it - but I am not there yet.
btw ... Since I have become (by other people's reconing) a world expert in several fields, I think I can safely declare myself an expert in one field: An expert at becoming an expert. And indeed, I honestly think that is why I have enjoyed success in several companies and fields.
Pick an area that you have the ability to be an expert. What I mean by that is, some people are good with logic, other with math, others in art, others with their hands, others with music, others at learning laguages, others at sports and so on. It would be foolish of me to try to be an expert in most of those areas, because quite simply, I'm incompetent in them. Rather it makes sense for each of us to pick areas that we have a natural ability in.
Now, I hate to say this - but I need to. Not everyone is cut out to become an expert. It would be nice if everyone had that capability, but I know that is not the case. There are many many people who are a lot smarter than I am, and they can easily become a world expert in a topic of their interest faster than I can. At the other end, I have some relatives that are known technically, medically, as 'retarded', and clearly, they will never have the capability of choosing to and becoming an expert in any subject. Obviously there are people in the whole range between these 2 extremes. I'm in the middle somewhere, probably on the high side, and chances are, if you are reading this, you are in the middle somewhere. It may be that becoming a world expert is in your capability, or it may not be. It also may be easily within your capability or it may be in the range of very difficult for you. You probably know where you are in that continum, and if you are in the 'can' side of the equation, you will have to decide whether you want to do what is necessary to reach that goal. If you are in the 'can't' - then don't worry about it - pick a different objective, one that you will be much happier striving for. On the other hand, if you aren't sure, and there is a field you'd like to give it a try, and you might enjoy the process even if you don't succeed to the ultimate level you want - if it were me, I'd say 'go for it' and enjoy the ride!
I knew a man once that tried 3 times to pass the mensa exams. He failed each time and he seemed to rank his personal value based on these failures. I have two general comments: First, Mensa only tests intelligence in 3 areas - and there are a lot more than that, and second, who said God made everyone to be at the upper end of intelligence. If you try and fail - don't worry about it, find something you can do and enjoy and do it. For me I look at this way: I will never be a star basketball player, I never had a chance, I didn't get enough of that skill set. But I enjoy hiking, skiing, snowshoeing even though I'll never be a top sports athlete. You probably don't think any less of me because I am in the bottom half of that skill set - so why should you think lowly of yourself even if you are in the bottom half of the intellectual level? I know, I know, people see raw intelligence as different from raw physical prowess - but why? So, think 'soberly' about what your skills are and then pick something that is reasonable for the 'gifts' God gave you to work with.