It is a sunny winter's afternoon in Sydney and the District Court judge – affectionately dubbed Judge Judy by waggish elements of the profession – is holding forth on the merits, or otherwise, of social media.

Facebook, home to millions of pictures of lunch and other inanities, gets the judicial thumbs down. But Twitter, Gibson says, is an "enormously valuable research tool".

We are lunching at Chiswick, the ground-floor restaurant at the NSW Art Gallery overlooking Woolloomooloo, and the irony of her lunch quip is not lost on me as I make a furtive note of her order of pan-fried barramundi with pine mushrooms, artichokes and onion.

I opt for the same and we stick to mineral water.

As courts grapple with defamation on new media platforms, including Facebook and Twitter, Gibson is at the coalface in the District Court. She is one of the few judges who seem entirely au fait with technology.

"What interests me about social media is how profoundly it's changing the law; how it's changing social interactions generally," she says.

Gibson was enthralled by computers as a young solicitor at Allen Allen & Hemsley, now global firm Allens, and raised the eyebrows of some of the male partners by putting her hand up for training courses.

"One of the partners called me in," she recalls, "and said, 'young Judith, it's hard enough for women to be taken seriously without you sitting in the typing bay after hours typing letters.'

"So I said, 'One day you'll have one of these machines on your desk!' And he laughed."

Gibson is "not a big eater", as far as fine dining goes, but it is clear she has a voracious intellectual appetite. The defamation list judge is also a member of the Art Gallery society and tells me she loves to come in and wander around.

"When I first came here as a child I was entranced by art nouveau-style art," Gibson says.

At the age of eight or nine, she had decided to become a barrister after finding a copy of defamation text Hatred, Ridicule and Contempt in her local library.

"I still have that book – it's in my chambers," she says.

The first case Gibson read was Liberace's defamation battle with the UK Daily Mirror over an acerbic column implying he was gay (he was, but homosexuality was then illegal in Britain). The American entertainer was awarded £8000 in damages.

"It was a fantastic case to start with," she says. "After that, of course, I just had to be a barrister."

After a short stint at Phillips Fox, Gibson was called to the bar in 1987 and says she learned a "great deal" appearing before Supreme Court defamation list judges David Hunt and David Levine.

"When I was an anxious young barrister I always used to ask David Hunt if I could be the last case in the list, so that way I could sit through the others and see how he dealt with them," she says.

Gibson appeared in a range of high-profile matters including for a police officer in the 1995 inquiry into the conviction of Sydney hotelier Andrew Kalajzich for the contract murder of his wife.

But defamation cases formed the backbone of her practice and she acted for plaintiffs as well as media defendants, including the ABC and SBS.

She says Stuart Littlemore, QC, the former Media Watch host who occupied the chambers next door, "told me a story once – he went to the jail and somebody said, 'I asked all the other prisoners here about you and they'd never heard of you.'

"He said, 'well, that's because all my clients are acquitted.' So I'd like to say the reason that you don't see very many cases where I'm appearing for defendants is we managed to make them go away."

The Strathfield Girls High School and University of Sydney alumna describes herself as the "non-musical member" of a musical family. If she is less musically inclined, it is clear she has excelled at languages. In addition to her Arts/Law degree, she has a Master of Arts in Medieval French and is fluent in French, Italian and Chinese.

She started studying Chinese in the 1990s "solely because it is a beautiful language". In her "spare time" after court – Gibson was appointed to the bench in 2001 – she has sat in on Chinese law courses at the University of Sydney. And she says China has made "enormous progress" since she first saw a trial in 2004.

"Every year some of the courts such as the Beijing High People's Court publish volumes of the best cases," Gibson says.

"In fact, a friend of mine won a competition for publishing the best judgment."

We should have a prize here, I jest.

"I don't know," she deadpans. "What if the award was the subject of an appeal?"

I make a none-too-subtle bid to lower the tone by inquiring if Gibson is familiar with the Chinese television program If You Are the One, in which potential suitors are paraded before a bevy of ruthlessly honest beauties.

Gibson has already told me life is "too short to watch TV", apart from the news, the ABC's flagship current affairs program 7.30 and Mad Men, so my expectations are low.

"Oh, I know it well," Gibson exclaims, adding there are big television screens everywhere in China which make it "impossible not to watch".

"Another one I've seen is their version of Antiques Roadshow. In China, of course, their big problem is all the fakes, so people go on with the Ming vase and they want to know if it's Ming, Qing or just bling."

If the experts agree it's a fake, and the owner gives the nod, they smash it in front of the cameras – leading to an unfortunate incident once in which a real Ming vase was smashed to smithereens.

We order a coffee and a green tea, and Gibson tells me her colleagues in China "enjoy laughing about the high profile of defamation in Australia and particularly in NSW".

But she says she is "very concerned" at the number of cases involving publication to a small number of readers, including on social media, where costs can run into hundreds of thousands of dollars.

"The great tragedy of so many of these cases is the defendants don't have insurance and their lives are destroyed," Gibson says.

The courts, including Gibson and Supreme Court justice Lucy McCallum, have been developing principles of proportionality in an attempt to weed out cases where the costs outweigh the interests at stake.

Gibson expressed the principle in one judgment – involving, improbably, sparring cake decorators – as a question of "whether the game is worth the candle".

"That's an old gamesters' saying and it's a reminder that once upon a time candles were very expensive," she says.

At the other end of the spectrum are epic battles between well-resourced litigants, including Treasurer Joe Hockey's Federal Court case against Fairfax Media.

Hockey was awarded $200,000 in damages in July after the court found he was defamed by advertising posters and tweets by the Sydney Morning Herald and The Age featuring the headline "Treasurer for Sale."

But Justice Richard White found the stories being promoted by the posters and tweets were not defamatory.

The case was a salutary reminder that a headline stripped of explanatory context can be defamatory. But the tweet also contained a link to the full article online, and commentators have questioned whether the law needs to change to recognise the nature of online publications.

"I do think in relation to the poster there was a problem because that was probably a stand-alone [publication]," Gibson says.

"But I would have found for the defendant [Fairfax] on the tweets."

The Hockey case led to calls in some quarters for Australia to adopt a US-style public figure doctrine which restricts the ability of politicians to sue for defamation.

Gibson says the defence "would not work in Australia because we'd have to change the way defamation cases are run".

"We'd have to run them in the Federal Court here the way they run them in the Federal Court in the United States."

But she says other parts of the defamation law are ripe for reform, including qualified privilege – which provides publishers with a defence where a story was in the public interest and the defendant acted "reasonably".

Newspapers publishing stories under pressure are rarely judged to have met this standard, and Gibson says the defence is one of many that need to be overhauled.

As for the hypothetical "ordinary reasonable reader" against which a court assesses whether a story is defamatory, Gibson has a blunt assessment: "I've never met the ordinary reasonable reader and I've never met the reasonable man.

"You should be able to weigh these things up objectively without resorting to these fanciful tests."

Almost two hours have passed and Gibson is due back in court. As we wander back into the city together via the Domain I am reminded of a line in Gibson's swearing-in speech as a new judge.

Justice, she said at the time, is depicted in our legal system wearing a blindfold and on a pedestal. But Gibson once saw a painting in Paris showing Justice sitting at the back of the courtroom "watching the judge very closely indeed". That was how she liked to see her.

There are no pedestals with Judge Gibson. And I rather suspect Justice would enjoy sitting at the back of her court.

LIFE AND TIMES

1977 Graduates from University of Sydney with Arts/Law degree and Master of Arts in Medieval French

1978 Admitted to practice as a solicitor

1981 Starts as a solicitor at Allen Allen & Hemsley

1985 Moves to Phillips Fox

1987 Called to the bar

2001 Sworn in as District Court judge