Don’t wait around trying to find something that you are innately passionate about. Find something reasonable and then BECOME passionate about it. Obsess over it. Become boring to talk to at parties because of your single minded focus. You’ll be making metaphors and similes about aspects in peoples’ personal lives and aspects of the sociopolitical, framing them based on your area of research, just like those crazy fans who turn everything into a sports metaphor. These might even be funny and suitable for framing as a meme. Everyone likes a good joke about how the electron band gap structure of different materials relates to phases of dating difficulties.
The choice of obsession is somewhat arbitrary and linked to availability; that’s why you are more likely to be rabid soccer fan if born in Brazil, a rabid hockey fan if born in Canada, or a basketball fan in the US. However, becoming the rabid fan is the key step. The particularly domain/sport is somewhat arbitrary, be it American football (e.g. doing cancer research) or curling (e.g. doing work the genomics of coral reef nitrogen metabolism).
An important point is that when you become a crazy, obsessed fan about something, people actually cut you a lot of slack and let you get away with a decent amount of selfishness around your area of obsession, like a sports fan monopolizing a TV. Once you have been identified as an obsessed fan, people also tend to support you in your efforts, and this helps amplify your focus. They bring things to your attention or just plain give you things related to your obsession, they allow you to skip other life dutie and obligations because of your obligations to your fandom. You’re also allowed by others and yourself to take things in your area of fandom way too seriously (dressing up like your favorite Harry Potter character, or thinking that the enzymatic reaction you study is the one the universe was created to just permit to happen); however, you can give yourself the space to know that you are indeed taking yourself and your obsession too seriously, but it’s okay.
By being a obsessed fan, you are living a wonderful aspect of the teenage years, when you had the option to fall easily into a different subcultural group based on your shared obsession with a teen idol singer, being a goth, skateboarding, playing WoW, or whatever. That gave you the support of your fellow co-fans, and your own community with its own incomprehenible jargon and inside jokes. It also meant that you could keep in mind that you were just going through a phase, and that you could, eventually exit, that phase as a mostly normally functioning adult, and leave that period behind you, if you so choose. Either to be a boring person without a crazy obsession (or a research topic), depending on your choice.
As you grow in your obsession mania of fanning. You become a somewhat of an authority, so people ask your advice; a lot of times you won’t know what they expect you to know, but then you’ll be embarassed and quickly learn it, continuing to increase your obsession and your expertise. Once you are an acknowledged authority and expert fan, you are also excused all kinds of other failings and lacks of knowledge, slipping through other requirements. Once you love something so much that you need to learn everything there is to know about it, want to travel around talking to other obsessed fans (you don’t have to stay in an RV as there are few academic tailgate opportunities, you can just stay in the conference hotel) and then start to discover new things about it everyone gets sick of your obsession. They soon make you a doctor of your area of obsession in the hopes that you’ll go talk about your bizarre academic passion somewhere else or at least shut yourself away to write some books. That is how you succeed in a PhD program. Face paint is optional.