The trigger for a nuclear explosion essentially involves one particle splitting. A negative-charged electron separates from an unstable core, strikes into others, and precipitates a chain reaction that releases tremendous destructive energy.
While nuclear physics and intimate relationships may seem far removed from each other, the results can be similar. When the two people in a couple go nuclear and break up, friends can be caught in the fallout with the resulting social contamination lasting for years.
Comedian Mike King has seen interpersonal mushroom clouds and has lived through social nuclear winter. Gatherings where two estranged parties are present can cause no end of anguish for mutual friends. "Parties and weddings can be especially awkward. You don't want to chat with one when the other's around, because they might take it the wrong way," he says. "It's worse when one side has a glam new replacement, while the other is left alone and gathering dust in the garage."
Some couples even try to divvy up and allocate their friends, along with the house and car and DVD collection and childcare.
So, as a friend, do you try to stay close to both - sit on the fence - or do you take sides? Do you invite one, or both, to coffee dates and dinners, or do you alternate invitations from one week to the next? Do you welcome their new partners to the fold? Or do you cross everyone off the Christmas card list and be done with it?
King has seen his good friend and OneNews anchor Simon Dallow recently split from fellow broadcaster Alison Mau. "We were professional colleagues, but now me and Si hang. He's a really cool guy who gave me advice when I was in a bad place."
The comedian and celebrity poker-player has decided to throw his chips behind his now-single friend. "I know Simon's going to be fine. He's strong and his main concern is for a smooth transition for the kids."
Going further, King draws gender-defined battle lines in the post-relationship wasteland. It's important for men to stick together, he says. "Over time, when a man is in a relationship, a wife axes all his friends - one by one by one by one - until he wakes up one day and all his friends are his wife's friends' husbands."
King may be half-joking but deciding whether to remain neutral or to go to war on behalf of one party is a dilemma that generates considerable popular chatter. Among psychologists, therapists, relationship "experts" and divorce lawyers, opinion is just as divided.
But outside the Family Court, the beauty salon discussions of Richie McCaw and Hayley Holt's reported split, the pub debates about Tony Veitch and Zoe Halford's break-up, or the pages of Cosmopolitan, the subject has generated precious little research.
"I was trying to find studies looking at what happens to friends of couples that split up - and there's actually very little research on that topic," says Patrick Markey, associate professor of psychology.
Markey directs the Interpersonal Research Lab at Villanova University in Pennsylvania and, while his studies have focused on what factors influence or predict breakups, he's willing to extrapolate some conclusions as to what happens to bystanders. Which person friends go with depends on the amount of time a couple have been together, he says. "If a relationship's at an early stage, people probably keep the friends they brought in - they take out what they came to the table with."
But, for long-term couples, an ecology of pairs builds up and the two social networks begin to become identical. "If you're married, most of your friends also tend to be married. Here's the good news: the more overlap couples have in their relationships, the less likely they are to break up."
This is partly due to a dynamic that Markey says resembles Mutually Assured Destruction: "People in this situation don't want their friends to break up, and so friends have a reason to keep everybody close together."
And here's the bad news: When long-term couples break up, their closely integrated social networks quickly take on a resemblance to scorched earth. "For the most part, everybody throws away their friends and starts again from scratch," says Markey.
"We find that if people get divorced, they tend to have more divorced and single friends. You end up completely changing your social networks."
But, at least in the short term, perceptions of blame as to why a relationship ended can help one party. "It's usually the rejector who tends to be vilified amongst their friends, and the rejectee gets a lot of sympathy."
Things don't always work out this way. Aucklander Julie (not her real name) says her long-term relationship with a colleague ended in self-imposed isolation. "He had an affair, and everyone at work knew he was having an affair before I did. As a consequence I left the job and cut all ties with anyone associated with anything I left behind. To this day I have not had any contact with any of them."
This was 10 years ago: how long did the fallout last? "The funny thing is, he later emailed me saying he was getting married and felt really bad about the way he treated me. I thought, well, good for you' - but I would still rip his eyes out if I saw him."
Julie has also seen friends' relationships melt down, and she says you can't stand aside. "It's like going to war. You definitely have to choose sides and wear a T-shirt."
A split between two well-known artistic figures led to her volunteering in one army, and she only resumed contact with the "enemy" after the couple mended fences. She is a staunch supporter of a splitting couple formally dividing their friends.
"If I split from my current partner, I wouldn't want him to hang out with certain people."
Why? "It's probably a jealousy thing."
One high-flier is even known to spy on her former husband through the internet, then take to task any "friend" who has dared to maintain contact with her ex.
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Auckland divorce lawyer Deborah Hollings QC says her office sees around 100 couples each year, and says the law can't help in divvying up friends - divorce agreements can only bind the couple involved. But, fortunately, there's often a natural division of social networks: "Quite often with particular friends and particular social groups and clubs, they tend to be more associated with one partner than the other. He's the golfer, she's the yachtie. But you can end up in embarrassing positions where they own season tickets to the opera and both want to keep them."
Or, perhaps, season tickets to the rugby. Sitting side by side, cheering for the same team, could be awkward.
While Hollings acknowledges she deals with the more acrimonious end of the spectrum, she says most splits she sees have friends falling into two warring camps. And while there may be some rare mutual friends who maintain cordial relations with both sides of a fractured couple, often friendships don't last. "We have a concept of a clean break, financially, socially and emotionally, and that's often for the best."
Sometimes, family ties can draw a couple back together - with awkward results. "Weddings, first communions, school graduations, 21sts - these can be tense for divorced couples."
Organisers of such events may fret over who to invite, but sending invitations to both is a Clayton's compromise, says Hollings. "There's usually one person in that couple who doesn't want contact with the other, and they'll pull out."
While this may sound awfully cruel, Hollings says good intentions often don't survive contact with real-world break-ups: "We're human beings, with human emotions, and we behave accordingly - not always rationally."
This "warring camps" approach horrifies Jann Blackstone-Ford. The Californian divorce mediator is the author of Ex-Etiquette for Parents: Good Behavior After Divorce or Separation, and she says friends and family should avoid taking sides at all costs. "It's human nature to identify with a friend - but there are long-term repercussions when you start taking sides."
Blackstone-Ford says she recently counselled a woman who lost contact with a good friend from secondary school after divorcing three decades ago. "Her husband was also best friends with that woman - and she hasn't talked to her best friend for 30 years."
The costs can be multiplied when children are involved, says Blackstone-Ford. Blacklisting the "other side" can inadvertently cause children of a splitting couple to have their own social networks cut off. Auckland divorcee Pieter (again, not her real name) says their shared child is the main reason she's maintained civility with her ex-husband - and she says she never chooses sides in other people's separations: "If I had done that, I would have lost contact with a lot of people I'm still friends with."
While legal agreements can't dictate the allocations of friends; club and society membership can come with its own social groups; who gets what determines who stays friends with whom, says Blackstone-Ford.
"I had a counselling session with a woman who thinks her social life is over because her husband got the membership to the country club."
And for those tricky invites where both members of a warring couple are potential guests? Blackstone-Ford says to invite both. "And tell them they're both invited. You expect them to act like adults, and if they opt not to go at least they had the option."
But, on the other coast of the US, and in stark contrast to Blackstone-Ford's Californian message of peace and neutral understanding, Cheryl Fishbein preaches a different message. She's a clinical psychologist and attorney who practises in Manhattan. "It's the centre of shrinkhood!" she says in her nasally Noo York accent. She says Splitsville should have clearly defined social territory.
"Sometimes there's a clear billing - a lovely sweet wife and a husband who's a cad who cheats on her. She finds out and it's horrible. Even his friends think he's lousy. In this case it's the wife who inherits the friends."
But, in less clear-cut separations, and in contrast to Mike King's thesis that men suffer most, Fishbein reckons it's the fairer sex that gets the raw deal: "What often happens with friends who are couples is that they get exceedingly uncomfortable, and the single woman becomes a threat to other women's spouses - very often they shun her and don't allow their husbands to interact with her or stay friends with her. A single woman is pushed out because she's now a femme fatale."
She's had couples who draw up lists of who gets which friends. "The friends have to be willing to go along with that. It's been known to happen that one will call up his friends and say You are not permitted to talk to her. If you invite her to your next party I will not be there. You have to make a choice.'"
Fishbein says that while her clients may be more blunt than New Zealanders, the same emotions will still lie beneath the surface:
"People tend to say what they're thinking rather than being polite. Even though people in New Zealand might try to be friends with everybody, that doesn't take away from the fact that they are embarrassed and don't like having two people in the room glaring at each other."