I love medicine -- but maybe not for the reasons you think.

Most people go into the field desiring to help others, but not me -- at least not at first.

Many people go into medicine to make scientific discoveries. Not me.

And, alas, some people go into medicine to gratify their ego, pad their wallet, or satisfy parental expectations. Not me, thank goodness. I went into medicine because, well, I don't really know why. And that's the point.

One of my physician friends observed that medicine is the last universal field of study. He's right. Medicine is the biggest tent on the parade ground, and it's so big that it touches all the others -- and almost threatens to push them aside.

If you're interested in mathematics or computers, there's a place for you in medicine. If you're interested in nanotechnology, there's a gigantic place for you in medicine. If you're interested in medieval agrarian farming techniques, there's a place for you in medicine. If you're interested in people at all, medicine is the place to be. And if you are so misguided as to be interested in finance, yes, there is place in medicine for you too (but we don't have to like you). You name the field, and there's a medical aspect.

Conversely, if you want to learn about and maybe even affect the world in general, medicine will give you the best and broadest tool set to do that.

So the first reason I love medicine is that your choice to apply to medical school at the tender age of 21 (or whenever) doesn't close any doors. Anything is still possible. Without question, doctors will be among the first on Mars.

The second reason I love medicine is for the magic. I can look at the top of your ears and know that your back hurts. I can put my hand on your groin (not in public, of course0 and know that you need a heart operation. I can look at your fresh mosquito bite and know that you have cancer. And I can know how your mother died just by the way you shake my hand.

This is powerful magic -- not just for its obvious medical uses but also for its ability to motivate and inspire. It has certainly been a major factor in my own life.

The type of magic discussed so far is clinical magic, directly associated with taking care of patients. Painstakingly assembled by 95 successive generations of physicians following in the rationalist footsteps of Hippocrates, it is, of course, not magic at all. But it is genius.

Technology can appear magical too, and there are no better examples than technology used in medicine. Early in my career, for example, CT scanners appeared, and suddenly we could see into an intact human body in three dimensions. We could know so many previously unknowable things that it was simply breathtaking every day as we learned to use this incredible tool.

However, if I were to use the word "breathtaking" now, it would have to apply to the genetics revolution. No matter what you predict for the evolution of computers, the technology that will most fundamentally change the world in the next 100 years is DNA technology.

So far in clinical medicine, we have mostly been reading DNA sequences, and even then, not very often. The revolution will truly start when it becomes routine to write DNA sequences into our cells, and when we can predict the effects of that writing.

From an information-science point of view, DNA is a digital medium, and so there is a coming generation of app-writers who will use DNA as their programming language, not Python or Java. Thus, the incredible imaginative creativity that we now see on our smartphone screens will be redirected to produce and alter living things. Breathtaking.

In fact, it's more than breathtaking. The molecular workings of living systems are beautiful. Nature activates and deactivates segments of DNA depending on what's happening in your life. Fragments of RNA (DNA's close cousin) are now known to be part of our immune system. A significant fraction of your DNA comes from viruses that infected your ancestors. Only 1.2 percent of our DNA is different from a chimpanzee's. And changing just six atoms out of the hundreds of billions in your original DNA would have made you six inches taller and look like Abraham Lincoln.

Wow.

Someday all of this subtlety and richness will yield tools that improve human health. (Its terrible potential is another story.) Although Americans are living longer and better than ever before, there is enormous room for improvement, for us and for the rest of the world.

Most likely, the greatest improvements in human health worldwide will come not from almost-magical DNA technology but from simpler innovations, like extracting safe drinking water from the moisture in the air, as is currently being tested.

That's another great thing about medicine: Innovation on all technological levels can do incredible good. It's just one more bit of magic from medicine's big tent, and that's a key reason I'm trying to spread the word at the USA Science & Engineering Festival (usasciencefestival.org). Medicine needs the world's brightest and most motivated people -- no matter what their interests and strengths -- to join the team.

It will matter to all of us.