No matter where in the world our friends are, or how long it's been since we've seen them, as long as they stay on social media, we never have to lose touch.

But is social media strengthening friendships or making them shallower?

According to anthropologist Robin Dunbar, the highest number of people you can maintain a meaningful relationship with at one time ranges from 100 to 200, depending on how social you are.

And many of us have a lot more social media connections than that.

Friendship researcher William Rawlins divides friendships into three categories: active, dormant, and commemorative.

A friendship is active if you're regularly in touch with this person, if you feel you can call on them for emotional support, and if you pretty much know what's going on with their lives.

A dormant friend is someone you have history with, but whom you haven't spoken to in a while.

But if you were in the same town as them, you'd definitely hit them up, and it wouldn't be weird.

And then, a commemorative friend is someone who was important to you at an earlier time in your life, but you don't really expect to see or hear from them, maybe ever again.

You remember them fondly, but they remain firmly in the past.

Or they would have before social media.

Facebook is like a trophy case for these commemorative friendships.

You can see what your childhood camp friend thinks about politics, you can get a "Happy Birthday" message from your old Little League teammate.

As you grow older, more and more of your active friendships will become dormant or commemorative.

That's because friendships naturally fade as people grow up.

According to the American Time Use Survey, young people aged 15 to 19 spend the most time socializing per day while older adults have less time to spend with their friends.

One study found that the more people moved, the more willing they were to get rid of objects, but the more willing they were to get rid of their objects, they also reported being more willing to cut social ties too.

Which suggests that people who move a lot may see their friendships as more disposable.

But a friendship isn't the same as that crumpled soccer team sweatshirt that you finally threw out after your third move.

Technology offers us a way to extend the lifespan of these friendships, even long-distance ones, with minimal effort.

But some of those friendships aren't really living.

It's more like they're on life support.

According to friendship researcher Emily Langan, any contact at all is the bare minimum of what it takes to keep a friendship alive.

So, if you write on someone's Facebook wall, or comment on their Instagram, you're doing a form of friendship maintenance.

Social media allows you to maintain more friendships, but more shallowly.

But if you just focus on your closest friends, it's also a tool that can help you deepen your relationships.

The more platforms friends use to communicate, in addition to seeing each other in person, the stronger their relationship.

Researchers call this media multiplexity theory.

So, social media can both strengthen the friendships you care about, and keep some relationships alive past their natural expiration date.

Friendships are a uniquely flexible kind of relationship because unlike with our family members or romantic partners, there are no clear expectations or obligations.

This makes it easy to drop them when things get busy, but it also means that a period of dormancy doesn't mean that the friendship is over.

In a series of interviews Rawlins did with middle-aged Americans, he found that many still considered themselves to be friends with people they hadn't been in touch with in a long time.

But they felt like they could pick right back up where they left off.

So, maybe that's the biggest gift the Internet gives us.

A place to find our friends when we're ready to pick up where we left off.

The effort has to come from you, and liking a status won't be enough, but when you're ready, your friends are there, in your pocket, waiting for you to reconnect.

This is "You Are Here," a new series about the science behind everyday life.

Let us know what topics you'd like us to explore in the comments.

I'm Julie Beck, thanks for watching.