"Don't worry, be happy."

Oh, if only it were so easy. We try in so many ways to find the happiness that often eludes us — from money to cars, social work to religion. Is it stuff or is it experiences? What is happiness, anyway? Everyone from Greek philosophers to modern-day scientists has tried to figure that out.

Here's a look at what we know — and what we don't — with a bit of history to put things in perspective.

Greek philosophers didn't agree on happiness

In the time of the great philosophers, there were competing views of what brought great happiness. Aristippus of Cyrene, the founder of hedonism, believed that pleasure was the key to enjoyment. If you had pleasure — whether from food, possessions or sensual experiences — then you were happy. The Cyrenaics believed that humans were exclusively wired to seek pleasure, that pleasure was paramount and virtue had no intrinsic value.

However, there was the idea known as the paradox of hedonism (or the pleasure paradox). The belief refers to the practical problem of trying to find pleasure if you're purposefully looking for it. Happiness, it turns out, is elusive if you set out to find it.

But then Aristotle turned happiness upside down. He said forget hedonism, pushing the concept that "happiness depends upon ourselves." By that, the revered Greek thinker meant that happiness was associated with a sense of purpose and well-being. His theory of happiness was referred to as a belief called eudaimonia, which was living in a way that fulfilled an end game.

"Aristotle was saying, ‘Stop hoping for happiness tomorrow. Happiness is being engaged in the process,’” Helen Morales, a classicist at the University of California, Santa Barbara, told the New Yorker.

Modern researchers weigh in

people volunteering, planting trees Some people derive more happiness when there's a sense of purpose in their actions. (Photo: Syda Productions/Shutterstock)

Aristotle's theory may have been confirmed many, many years later by researchers at UCLA and the University of North Carolina who found that different types of happiness have surprisingly different effects on the human genome.

The study found that people who had high levels of eudaimonic well-being (happiness that comes from having a deep sense of purpose) had low levels of inflammation and high antiviral response. However, people with relatively high levels of hedonic well-being (happiness that comes from pleasure) had the opposite response. They had high levels of inflammation and low antiviral response.

The study was published in the journal Proceedings of the National Academy of Sciences.

Interestingly, people with high levels of hedonic well-being didn't say they felt any worse than those with higher levels of eudaimonic well-being, researchers reported. But sometimes things are not what they seem.

"What this study tells us is that doing good and feeling good have very different effects on the human genome, even though they generate similar levels of positive emotion," said Steven Cole, a UCLA professor of medicine and one of the study's authors. "Apparently, the human genome is much more sensitive to different ways of achieving happiness than are conscious minds."

So what brings you happiness?

We're all multitaskers. With our families, jobs and hobbies, we have all sorts of things that we're involved in, and some of these things have the potential to make us happy.

Cambridge University psychologist Brian R. Little is intrigued by what he calls personal projects. He told the New Yorker's Will Storr that he and his colleagues have “looked at literally tens of thousands of personal projects in thousands of participants.”

Little's work suggests that most people have about 15 projects going on at any one time, ranging from the mundane to the serious. Little says that in order for a project to bring us happiness, it must have two distinct traits: It must be meaningful in some way, and we must have efficacy over it.

For example, as Storr points out, "There’s little use trying to be the fastest human in the world if you’re an overweight, agoraphobic retiree."

But if you're an apartment-dwelling pet lover, it would make sense to volunteer at an animal shelter where your goal would be to gets dogs and cats adopted each week instead of lamenting that you can't bring them all home yourself.

The stuff vs. experiences argument

woman standing on mountain Experiences may lead to more intense happiness, but material things can give longer-lasting pleasure. (Photo: Dudarev Mikhail/Shutterstock)

In today's world, talk often turns to the appeal of minimalism and simplicity. Interestingly, that leads to the question about what brings happiness: actual, concrete physical items or experiences? If we're trying to simplify our lives, then it only makes sense that we should have adventures instead of adding to our collection of material goods. Forget the electronics and go on a trip. Forego the fancy shoes and splurge on concert tickets.

Or not.

The Atlantic points out that although accumulating stuff gets a bad rap, maybe the idea of buying experiences over things is actually what's overrated. A new study says material possessions may give you longer-lasting happiness than experiential adventures.

Called The Unsung Benefits of Material Things, the study was published in the journal Social Psychological & Personality Science.

It found that there are three stages of happiness: anticipatory, momentary and afterglow. Experiences give us more anticipatory and afterglow happiness. You buy concert tickets and you're psyched before the event and well after it happened. But here's the interesting part. Stuff gives you more momentary happiness. You splurge on a cool new phone or a new backpack and because you use it a lot longer than the experience lasted (even with the anticipation and afterglow), the overall happiness adds up and lasts longer.

“Material purchases have an unsung advantage in that they provide more frequent bouts of momentary happiness in the weeks after they are acquired,” researchers Aaron Weidman and Elizabeth Dunn from the University of British Columbia write.

One other interesting caveat: While the happiness felt from things was longer-lasting, the happiness due to experiences can often be more intense, albeit shorter-lived.

So, what's the solution? Should you spring for an amazing tech toy or a once-in-a-lifetime travel adventure?

It depends on whether you are “seeking an intense but fleeting form of happiness that is accompanied by a rosy afterglow,” Weidman and Dunn write, “or a more subtle, frequent form of happiness that will endure for weeks or months.”

What flavor will you choose?

Mary Jo DiLonardo Mary Jo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.