Reporter: Tara Brown
Producer: Stephen Taylor, Julia Timms
We all crave it. And when we find it, it's the best feeling in the world.
We are talking, of course, about love, that wonderful, knee-weakening, tummy-churning state that affects most of us at some stage in our lives.
Until now, love has been a beautiful mystery, more the realm of poets than academics.
But there are scientists in America who are cracking the love code, tracking the chemicals that go pop in our brain when we fall in love.
And some can even predict with near certainty those couples whose love will last and those who will crash and burn.
TARA BROWN: Instead of enjoying the glamorous streets of New York, I'm in a cold corridor of the city's university looking particularly unglamourous and missing my 18-month-old son, Jack. It's not how I'd like you to see me - no make-up and jet-lagged - but I'm exposing myself in this way for the sake of science. Anthropologist Dr Helen Fisher is analysing my love for Jack. She wants to see how my mind reads what my heart feels. And, to do so, I have to have an MRI brain scan.
TARA BROWN: What do your brain studies show about love?
DR HELEN FISHER: People live for love, they pine for love, they kill for love, they die for love. It's a very powerful part of the brain.
TARA BROWN: Dr Fisher and her research assistant, Dr Lucy Brown, have done hundreds of scans on loved-up couples, but this is the first time they've measured maternal devotion. These enthusiastic love doctors can't wait to see what my brain does when I'm shown photos of Jack. The result is amazing. When I'm shown a photo of a child I don't know - nothing. But when I see my son's face, the 'love centre' of my brain lights up. What's so incredible about this science is we can now see in the brain where our emotions start and, for Helen Fisher, that means unlocking the secrets of romantic love.
TARA BROWN: So what is driving that emotion?
DR HELEN FISHER: Everything that we do is chemical. Everything we think, everything we want, everything we feel is chemical. As a matter of fact, the same brain region that becomes active when you look at a photograph of your sweetheart becomes active when you feel a rush of cocaine.
TARA BROWN: Whoever said "love is a drug" knew something. When you're attracted to someone, the body goes into overdrive, producing feel-good chemicals like dopamine and adrenaline. Your pupils dilate, your heart beats faster and blood rushes from your tummy, leaving a sense of excitement and butterflies in its place. The blood goes to where it's needed most - lips and naughty bits. And pheromones are released in your sweat, so you even smell attractive. But science isn't just telling us that love exists. It's also able to predict whether love will go the distance. So tonight we'll test the compatibility of two brave couples. Is theirs true love, or simply lust? A fling, or will it last a lifetime? GILLI: Every step of the way has been just so 'ahhh', like, so easy.
TARA BROWN: LA performers Gilli and Jay have certainly been hit by the love bug. They've been together for four years, and blissfully married for one. GILLI: I didn't know if that he was going to be the guy when I met him, but it just happened, like, it just - it just happened.
JAY: I think I just had an innate knowing that the right chemistry, the right person was going to come.
TARA BROWN: So, Gilli ticks all the boxes?
JAY: And more, and more boxes than I thought I could have ticked. GILLI: Yeah.
TARA BROWN: Our second couple, Mark and Jodi, also say they're in love, but their relationship is suffering because they're not together enough. Jodi calls New York home. Mark, LA. But the biggest distance between them, after two years - she wants commitment and he's still not sure.
MARK: I'm a runner, more than anything else. If something gets difficult, I walk away, which is probably why, at 45, I'm still, you know, haven't lived with anybody.
TARA BROWN: To test their love, our two couples have come here, to Seattle. This unassuming building is the 'love lab' and it's where psychologist Dr John Gottman assesses couples' chances of staying together.
DR JOHN GOTTMAN: Beyond that first encounter, once they really get together and they're talking to each other, that's when my science comes in, 'cause that's when I can tell you whether it's going to work, right? And it really has to do entirely with emotion.
TARA BROWN: To measure the emotions of our couples, Dr Gottman's researchers scrutinise their relationships like never before. Everything is recorded - A sideways glance, or a happy laugh, signs of tension, and an almost imperceptible twinge of a facial muscle. Even the heart rates and sweat of our subjects is monitored.
DR JOHN GOTTMAN: We look at the videotapes and we look at what's going on physiologically inside couples, and and we can measure them very precisely, very reliably, and then we get a profile of what's wrong with the couple.
TARA BROWN: Dr Gottman's bold claim is he can predict the success or failure of any relationship, and he can do it with an accuracy of 90%. So, simply, this couple will love each other for the rest of their lives. And this couple, well, they should hire a divorce lawyer now. There's no guesswork, no star signs, no tarot cards. He uses a mathematical formula - a 'love equation' to measure the nice and nasty bits of a couple's relationship.
DR JOHN GOTTMAN: The ratio needs to be around 5:1 - five times as many positive as negative during conflict.
TARA BROWN: So, 5:1 and greater and you're happy for the rest of your life?
DR JOHN GOTTMAN: Yes.
TARA BROWN: Less than 5:1 and the marriage is doomed?
DR JOHN GOTTMAN: Pretty much, without therapy. Without couples therapy.
TARA BROWN: Both couples are asked to focus on their differences. For Mark and Jodi, that's easy.
MARK: And I think I've got to help more with your business, and I've got to help more with your apartment. JODI: But it isn't that you have to. It's more that you want to.
MARK: Yeah, exactly.
TARA BROWN: Mark has asked Jodi to give up this, her fashion career and home in New York, for this, his West Coast life. Jodi would in a heartbeat but she fears Mark's not really committed to their relationship. JODI: I know you do want to but you just have to show it.
MARK: But I think, equally, it's been hard for me to show excitement.
DR JOHN GOTTMAN: He should be moving to New York if he really loves her and wants her, and he's not. He's kind of passively letting it die.
TARA BROWN: Second by second, Dr Gottman analyses Mark and Jodi's responses to each other...
DR JOHN GOTTMAN: They're not leaning in, there's not a relaxation in their body, there's not an openness.
TARA BROWN: ..what they say and what their body language says. And, so far, it's not good.
DR JOHN GOTTMAN: What we see here in her mouth is a contempt facial expression, and that contempt facial expression is really a very good prognosticator that the relationship is going to end, that she's going to pull out. She's going to say, "OK, I'm outta here."
TARA BROWN: On the other hand, it's all sweetness and light for Gilli and Jay, even when they're meant to be fighting.
DR JOHN GOTTMAN: She laughs, she moves toward him, she's relaxed, and it's an enormous strength in the relationship for them to be able to do this.
TARA BROWN: And, after only a few moments of analysis, Dr Gottman's seen enough.
DR JOHN GOTTMAN: All the indications are is that this is a marriage that's really going to work out.
TARA BROWN: This is one of the good times in the 'love lab'.
JAY: I feel like there's one thing that is the most important thing of all, and that is our relationship and our love.
TARA BROWN: But everyone, even Mark and Jodi, know their report card won't be as rosy. Dr Gottman takes them through the highs...
DR JOHN GOTTMAN: And you guys are very strong on fondness and admiration.
TARA BROWN: ..and lows.
DR JOHN GOTTMAN: You said, you "I'm a woman with backbone."know, But then later on in the conversation, you look like a woman with no backbone.
TARA BROWN: And, after crunching the numbers, he finds the ratio of good to bad signals they send each other is no where near the 5:1 it needs to be for this relationship to succeed.
TARA BROWN: Because currently, going by your formula, this relationship would fail?
DR JOHN GOTTMAN: Yeah, I think - I think it really needs to improve.
TARA BROWN: To hear that, right now, you guys are unlikely to make it, what's it like to hear that?
MARK: We have known there's been an issue and, clearly, we have to do some training to make the relationship work.
TARA BROWN: What are the killers of love? What kills a relationship?
DR JOHN GOTTMAN: There's really one thing that is essentially sulphuric acid for love - you pour it on love and it's going to die - and that is contempt. Not only does it destroy love, but it also destroys the immune system of the person who receives this contempt.
TARA BROWN: So the person can become sick from it in a relationship like that?
DR JOHN GOTTMAN: Yes, so we can predict how many infectious illnesses that person receiving the contempt will have in the next four years. People in those kinds of relationships really live significantly less, you know, they die earlier.
TARA BROWN: So bad love is bad for you?
DR JOHN GOTTMAN: Bad love is bad for you.
TARA BROWN: Despite the bad prognosis, Jodi and Mark believe their love is essentially good. After meeting Dr Gottman, the commitment-phobic Mark decides it's time to make more effort.
TARA BROWN: Are you going to run away this time?
MARK: No, I don't think so. I think the relationship's got to a stage where it would, ah, it would be a waste to not work on it a little bit harder. Um, and in a funny way, it's now got an interesting little competitive challenge associated with it.
TARA BROWN: So you're going to stay in the relationship to prove John Gottman wrong?
MARK: No, not exactly.
TARA BROWN: Back in New York, I'm in the MRI scanner where Dr Helen Fisher has been looking deep inside my brain to see what happens when I see pictures of my son, Jack. But then she tries to mess with my mind by throwing in a photo of Brad Pitt.
DR HELEN FISHER: And we'll find out what Brad Pitt does to Tara's head.
TARA BROWN: He's the heart-throb of millions, and undeniably attractive.
DR HELEN FISHER: But what we want to find out is whether she finds him aesthetically pleasing or whether she gets that rush of romantic love for him.
TARA BROWN: After almost an hour in the MRI machine, it's good to be free.
TARA BROWN: But you found a brain, right?
DR HELEN FISHER: Yeah, we found a brain! You've got a beautiful brain, with nothing bad in it.
TARA BROWN: Now, the moment of truth.
DR LUCY BROWN: What happened with Brad wasn't that interesting.
TARA BROWN: Turns out there was little activity in the part of my brain associated with love when I saw his face.
DR HELEN FISHER: You're not in love with Brad.
TARA BROWN: This is what a brain in love looks like.
DR LUCY BROWN: And just look at the difference here in the amount of activity, too. There's just so much more when you're looking at Jack.
DR HELEN FISHER: As well there ought to be!
TARA BROWN: Absolutely.
DR HELEN FISHER: This is the future of your DNA, Jack, and Brad Pitt came and left.
TARA BROWN: Despite the research, Dr Helen Fisher remains an old-fashioned romantic at heart, but she says far from killing romance, a better understanding of the science of love will help it.
DR HELEN FISHER: If there's any time, I think, in human evolution when we can make happy marriages, that time is now, 'cause we really are collecting the science to understand how to do it and what happens during it, how to get around the bumps, and make your dreams come true.
TARA BROWN: You'll have couples queuing up for miles!
DR HELEN FISHER: There will always be magic to love but I think science can enable us to kiss fewer frogs.