Over 1.5 billion people use the internet every day, and they search for pretty much anything.

Like “Why are barns red?” and “What’s up with gluten?”    We here at SciShow are all about fostering curiosity. That’s why we’ve worked with Google and YouTube to answer ten of the most popular questions searched on the internet.   This is The World’s Most Asked Questions.   Today’s question: What is love?   It’s the kind of thing that keeps poets and philosophers up at night, but science actually has a pretty good explanation for it, too.   Actually, several explanations.   And the answer might change depending on what kind of scientist you ask.

A biologist would say it’s all about reproduction, and the evolution and survival of a species. A psychologist may go on about our need for togetherness and acceptance.   But possibly the best way to understand love is through chemistry. Brain chemistry.    Although the heart is our symbol of love for some reason, when it comes down to it, love is all about the brain.    We know this because we can actually see love in action in brain scans.    And you know what?

It looks a awful like a brain on cocaine.    As a person first falls in love, at least a dozen different brain parts light up to release powerful chemicals -- hormones and neurotransmitters -- that trigger feelings of excitement, euphoria, bonding, and butterflies.    Research also shows that the kind of unconditional love between a mother and child activates slightly different regions of the brain.   Early romantic love and attraction, what you might call passion, is all about flooding the brain’s reward systems in a tsunami of feel-good chemicals like adrenaline, norepinephrine, and dopamine.    This is why a brain on intense new love looks a whole lot like a brain on coke -- adrenaline and norepinephrine amp up your heart rate and get you all restless, while those dopamine drips leave you feeling euphoric.    These chemicals light up your brain’s pleasure centers, lowering your pleasure thresholds, and making it easier to feel good about... everything.   Interestingly, this kind of passionate new love is also marked by lowered serotonin levels, similar to those found in people with obsessive-compulsive disorders -- which may help explain those 30 texts your infatuated new lover sent while you were in the shower.   Eventually, most of these more intense, obsessive components of new love settle down into a deeper, calmer form of love associated with attachment and bonding. Here your brain chemistry starts changing again, and hormones -- like oxytocin and vasopressin -- take over.    Their mission, like Al Green’s, is to get you to stay together.    You may have heard of oxytocin, the so-called the “cuddle hormone.” It gets released during orgasms, and for women during childbirth, and it helps cement bonds between people.    And you can think of vasopressin as the monogamy hormone. And you know who’s taught us more about how it works than anything else?   Prairie voles, one of the very few mammals that mate for life.    After mating, a male vole’s brain gets flooded with vasopressin, and essentially gets hooked on his mate forever.

The two then have lots of sex, and all that tiny boot-knocking keeps the vasopressin flowing.    When researchers gave voles a compound that suppressed the effects of vasopressin, the pairs quickly fell apart, losing their devotion to each other.   So, while in the poetic sense, love may always be something of a mystery, from the scientific view, it is within the realm of comprehension.    But what about you? How are the love lives of the SciShow viewers? Well, of our survey takers, people within the ages of 51 and 60 are the most likely to have been in love.

People who got their energy most from exercise were also more likely to have been in love. On the other hand, people who said they got their energy from food were less likely to have been in love.   Of all the fascinating questions in the world, what question do you want answered most? Let us know on Facebook or Twitter or in the comments down below, and we will answer the best questions in a new video at the end of the month.

And don’t forget to use the hashtag #WMAQ and stay tuned for other videos this week.