Twitter is also very useful. I've made contact with many people who share my fascination with the subject I'm researching for my next book - the history and future of cities. I've listed nearly a hundred of these people here. I recommend them - they're well worth following.

It looks like some people have found my tweets useful too: the other day the cultural news website Flavorwire included me on a list of the "10 Book Types You Should Follow on Twitter". Quite an honour when you think it includes people like Sarah Weinman (@sarahw), Ron Charles(@roncharles), the Washington Post’s fiction editor, as well as book website The Millions (@The_Millions).

Oh, and by the way - I have my own list of book people to follow on Twitter here. So what are you waiting for?

It's based on research I'm doing for my next book which explores the past, present and future of cities. Here's a taster:

"For the first time in history, more than half the world's population live in cities: by 2030, three out of five people will be city dwellers. But the British are bucking this trend. The 2001 census revealed an "exodus from the cities". Since 1981, Greater London and the six former metropolitan counties of Greater Manchester, Merseyside, South Yorkshire, Tyne and Wear, West Midlands and West Yorkshire have lost some 2.25 million people in net migration exchanges with the rest of the UK; in recent years this trend has accelerated. This is not sustainable. British people need to be cured of the insidious fantasy of leaving the city and owning a house in the country: their romantic dream will become a nightmare for people elsewhere on the planet."

There's also a great piece by science fiction author Paul McAuley on the technological changes that could make cities carbon neutral:

"From the air, the ideal green city should resemble Mayan ruins poking out of a lush forest. Under the canopy, there'll be densely populated but diverse and vibrant streets humming with every kind of human life. Utopian? You bet."

Read my article here and Paul's here.

Sections of our city centres are being sold off to private developers to create shopping monocultures such as Westfield London or "malls without walls" like Stratford City, which is being built for the 2012 Olympics and is one of the largest retail-led developments in Europe. It is, says Minton, "a private city within a city" and represents a return to the early 19th century when aristocrats owned great swathes of London, fortifying their estates of up-market housing with gates and private security forces.

Now, “land and property which has been in public hands for 150 years or more is moving back into private hands”. Minton argues that today’s privatised city centres and gated communities are fostering "a new culture of authoritarianism and control". Private security guards watch and record our every move with CCTV: the UK now has more surveillance cameras than the rest of Europe combined. The small city of Coventry will soon have 700. At Stratford City they intend to use unmanned aerial drones to watch the streets. In these privatized zones, security guards routinely move on beggars and the homeless, and they can even ban groups of young people and prevent the taking of photographs.

Our modern houses and streets may be "secured by design" (to quote the jargon), but Minton’s compelling argument is that "we are making the city a far more fearful place". The obsession with security and the privatisation of public space is also “a challenge to a type of public life, public culture and democracy in British cities” that has existed since at least the nineteenth century. Instead of local councils "owning" the city for us, now our streets and buildings (for example, Manchester’s Free Trade Hall) are being bought by investors. According to Minton, “today the ‘public good’ is what makes the most money”. It is government policy to sell off local authority assets worth £30 billion by 2010. The manager of one “Business Improvement District” controlling a city centre tells her: “Bugger democracy. Customer focus is not democratic.”

Clearly, it is important that cities should have vibrant economies. But in Britain the pursuit of profit threatens to undermine the quality of urban life. Minton’s book is a powerful indictment of urban planning in the UK under both Conservative and New Labour governments. It is essential reading for anyone concerned about how our cities will feel and function in the future.

One of the great new contacts I've made on Twitter is Dr Tim Jones (@physicus) who is currently on a career break studying for an MSc in Science Communication at Imperial College. He co-presents a show called Mission Impossible on Imperial College Radio and he invited me on to talk about Doomsday Men. You can stream the program here. (The interview is about 40 minutes into the show.)

As I say, there are lots of fascinating people to meet on Twitter - one of my favourite authors William Gibson is there, disguised as @GreatDismal, as well as many other great writers, like Clare Dudman, Fiona Mackenzie, and Thomas Levenson, author of Einstein in Berlin, bloggers like John Self, publishers and agents, such as my own, Peter Tallack.

To quote one of my other favourite authors, Nick Harkaway, Twitter is like a "giant pub". So order a drink and join the big conversation...

This is the first paragraph:

"At 7.30 on the evening of April 24, 1913, President Woodrow Wilson pushed a button on his desk in Washington, DC, sending a telegraphic signal to New York where it set off an alarm bell in the engine room of a skyscraper and set in motion four mighty Corliss-type engines and dynamos. In an instant, some 80,000 incandescent bulbs flashed on, illuminating for the first time the world’s tallest skyscraper – the Woolworth Building. Thousands of spectators had gathered in City Hall Park and along lower Broadway to witness the dazzling electrical spectacle that marked the opening of this fifty-five-storey addition to New York’s skyline. On the New Jersey shore, people caught their breath as the tower appeared, shimmering against the night sky, a gleaming beacon of modernity visible from ships a hundred miles away. As the 792-foot tall skyscraper was bathed in electric light, the news was being transmitted from its pinnacle by Marconi wireless to a receiver on the Eiffel Tower. From there it was beamed around the world. This modern media event was, as one commentator said, 'the premier publicity stunt of this or any other day'. It was a fitting opening for what would become the most famous office building in the world."

Read the rest here.

For a time, in the summer of 1933, the scientist who invented the first weapon of mass destruction – poison gas – was staying in the same genteel Georgian square in London’s Bloomsbury as the man who would play a key role in the creation of the atomic bomb.

Fritz Haber was a broken man. He was suffering from chronic angina and had been forced out of the research institute to which he had devoted his entire life. For a proud man, it was a deeply humiliating experience. To friends, the 64-year-old German chemist admitted feeling profoundly bitter. Einstein, who had just renounced his German citizenship, wrote him a pointed letter saying he was pleased to hear that “your former love for the blond beast has cooled off a bit”. Haber had only months to live. Exiled by the country he had tried to save during World War I with his chemical superweapon, he spent his last days wandering through Europe.

In July 1933 he visited London, staying at a hotel on Russell Square in Bloomsbury while he explored the possibility of working in England. He met Frederick G. Donnan, a tall and rather dashing professor of chemistry at nearby University College London, who sported a black eyepatch. During World War I, Donnan had worked on the production of mustard gas. Now he was attempting to arrange a fellowship for Germany’s leading chemical warfare expert.

That summer, another scientist who had fled Hitler’s Germany was also living in Russell Square. Leo Szilard, a Hungarian physicist who had been working in Berlin for the past decade, had brought his two suitcases to the Imperial Hotel in April. It was less costly than Haber’s hotel, the Russell, but for the scientist who had once declared that “there is no place as good to think as a bathtub”, what made the hotel irresistible were its famous Turkish baths.

Both hotels overlooked the elegant gardens of Russell Square, designed in the previous century by Britain’s foremost landscape designer, Humphry Repton. The British Museum and Library, University College London, and the London School of Economics were all within a fifteen-minute walk. T. S. Eliot (the “Pope of Russell Square”) worked in his garret office at number 24 for the publisher Faber & Faber, and in nearby Gordon Square was the fine Georgian townhouse where Virginia Woolf had once lived.

Szilard was essentially running the Academic Assistance Council (later the Society for the Protection of Science and Learning), an organisation he had helped found which dedicated itself to helping academics fleeing from the Nazis. His work for the AAC was unpaid. Szilard was living off earnings from patents which he held jointly with his close friend Albert Einstein. At the end of the 1920s, two of the greatest minds on the planet had applied their combined brain power to the problem of designing a safe refrigerator. Unfortunately, no one ever kept their groceries cool in an Einstein-Szilard fridge. But their invention of a liquid metal refrigeration system was later used to cool nuclear reactors.

Politically, the nationalist Haber and the socialist Szilard had little in common. However, unlike scientific purists such as Ernest Rutherford, for whom knowledge was its own reward, both men were enthralled by the idea of science as power. Neither Szilard nor Haber had set out in their careers intending to create new weapons. But both scientists played key roles in developing a new generation of scientific superweapons. Haber thought that chemical weapons would make him the saviour of his country. Szilard, an internationalist fired by an idealistic vision of how science should transform human life and society for the better, wanted to save the world with atomic energy and create Utopia.

What might these two refugee scientists have said to each other if they had met while walking through the neatly manicured gardens of Russell Square, just outside their hotels? Fritz Haber was at the end of his career, disowned by his country and thrown out of the institute he had founded by the Nazis. He was at the end of his life. Haber was a shadow of the dynamic man he had once been. Every few steps, he had to pause and catch his breath. By contrast, Leo Szilard, the budding nuclear physicist, was 35 years old, his figure still slim and youthful. He would have been striding past through the square, perhaps on his way to see his and Haber’s mutual friend, Professor Donnan at UCL.

Throughout 1933, Szilard worked tirelessly and selflessly on behalf of his fellow refugee academics. His daily routine at the Imperial Hotel began with breakfast in the plush restaurant, followed by a leisurely and extended soak in a bath – the only luxury the decidedly non-materialistic Szilard permitted himself. It was not uncommon for him to spend three hours in a tub, awaiting Archimedean inspiration. However, it was not in the bath that Leo Szilard had his Eureka! moment in 1933, but on Southampton Row, one of the main roads running into Russell Square.

Late on the morning of September 12, 1933, Szilard was reading The Times in the foyer of the Imperial Hotel. An article reported Ernest Rutherford’s speech on how subatomic particles might be used to transmute atoms. Rutherford was quoted as saying “anyone who looked for a source of power in the transformation of the atom was talking moonshine”. Leo Szilard frowned as he read these words. Moonshine! If there was one thing in science that made Szilard really angry, it was experts who said that something was impossible.

Szilard always thought best on his feet. So he went for a walk. Many years later in America, Szilard would recall this moment, as he walked through Bloomsbury, pondering subatomic physics and Rutherford’s comments. “I remember,” said Szilard, “that I stopped for a red light at the intersection of Southampton Row.” The London traffic streamed by, but he scarcely noticed the vehicles. Instead, in his mind he saw streams of subatomic particles bombarding atoms.

As the traffic lights changed and the cars stopped, the physicist stepped out in front of the impatient traffic. A keen-eyed London cabby, watching Szilard cross, might have noticed him pause for a moment in the middle of the road. Szilard may even have briefly raised his hand to his forehead, as if to catch hold of the beautiful but terrible thought that had just crossed his mind. For at that moment Leo Szilard saw how to release the energy locked up in the heart of every atom, a self-sustaining chain reaction created by neutrons:

“As I was waiting for the light to change and as the light changed to green and I crossed the street, it suddenly occurred to me that if we could find an element which is split by neutrons and which would emit two neutrons when it absorbed one neutron, such an element, if assembled in sufficiently large mass, could sustain a nuclear chain reaction… In certain circumstances it might become possible to set up a nuclear chain reaction, liberate energy on an industrial scale, and construct atomic bombs. The thought that this might be in fact possible became a sort of obsession with me.”

I know Russell Square well. It’s one of my favourite parts of London. I often walked through it on my way to classes, first as a graduate student, then while lecturing at UCL. Two hundred years after its paths were first laid and its trees planted, the gardens have now been restored to their former glory. It is a leafy haven of peace amidst the noise of the metropolis.

While researching Doomsday Men, which tells the story of Szilard and Haber, I often worked at the University of London Library in the impressive art deco Senate House which overlooks Russell Square. Its foundation stone was laid in June 1933 and during the war George Orwell worked here in the Ministry of Information, an experience that provided the model for his fictional “Ministry of Truth” in 1984. On the way to the library each morning, I walked through the square and was often struck by the thought that Szilard and Haber had passed under these very trees seventy years earlier. Indeed, a stone’s throw from here Szilard realised how to release the energy of the atom. In a sense, the road to Hiroshima’s destruction begins here in this elegant Georgian square.

Strangely enough, a literary scientist also discovered the secret of releasing the atom’s energy while working in this part of London. In H. G. Wells’s The World Set Free (1914), the scientist Holsten succeeds in “tapping the internal energy of atoms” by setting up “atomic disintegration in a minute particle of bismuth”. This explosive reaction, in which the scientist is slightly injured, produces radioactive gas and gold as a by-product. The quest of the alchemists is over – gold can now be created on demand. But Holsten has also discovered something far more valuable than even gold: “from the moment when the invisible speck of bismuth flashed into riving and rending energy, Holsten knew that he had opened a way for mankind, however narrow and dark it might still be, to worlds of limitless power”. When Holsten realises the implications of what he has found, his mind is thrown into turmoil. Like Szilard, he goes for a walk to think things through.

What is astonishing is that Holsten makes his discovery in Bloomsbury in 1933, the very year in which Szilard walked down Southampton Row and had his Eureka moment. The significance of this coincidence in time and space was not lost on Leo Szilard. Indeed, the similarities between the two scientists are striking. Both the fictional and the real scientist were born at the beginning of the atomic age, Holsten in the year X-rays were discovered, 1895, and Szilard in the year radium was discovered, 1898. Szilard had read Wells’s novel in 1932. It is clear that he regarded it as prophetic, and frequently referred to it in relation to key moments in both his life and the discovery of atomic energy. He shared Holsten’s dreams and his nightmares.

My knowledge of these historical moments has given this genteel London square a special resonance for me. I’ve often sat on the grass while taking time out from research and wondered what other meetings or Eureka moments have occurred in this green urban space. The square has gained a whole new dimension for me. It is not just a few trees and flower beds surrounded by some over-priced townhouses. It has a history, its own unique time-scape, one charged with global significance. A scene in a great scientific tragedy unfolded on this urban stage. And who knows how many minor domestic dramas have also been acted out in the shade of its trees. I became so fascinated by the secret histories of urban spaces like Russell Square that I even wrote a book proposal on the subject.

I was powerfully reminded of these themes recently when reading The Spaces of the Modern City: Imaginaries, Politics, and Everyday Life, edited by Gyan Prakash and Kevin Kruse (Princeton 2008). This is an excellent collection of essays by scholars who are united in the view that cities are not inert containers for social, political and economic processes, but historically produced spaces that shape, and are shaped by, power, economy, culture, and society. They want to replace Rem Koolhaas’s post-modern notion of a Generic City “free from history”, by investing urban spaces with a new sense of place and history, within a context of global change.

As Gyan Prakash rightly says, cities “are the principal landscapes of modernity”. Streets and sidewalks, parks and squares, tube trains and buses – these are the everyday settings for “dynamic encounters and experiences”. Despite globalization, our urban experiences still depend on “local lifeworlds”, rich with memories and imagination. The Spaces of the Modern City is a fascinating attempt to map the poetics of the urban everyday – from the liminal spaces of racially mixed neighbourhoods in London of the 1950s, the Situationists in West Berlin during the 60s, to Tokyo’s extraordinary Street Science Observation Society in the 1980s.

In 2008, Homo sapiens became an urban species. This year, for the first time in the history of the planet, more than half the population – 3.3 billion people – are city dwellers. Two hundred years ago only 3 per cent of the world’s population lived in cities, a figure that had remained fairly stable (give or take the occasional plague) for the last thousand years.

The experience of living in cities is universal. It crosses continents, cultures and even time. Urbanism is not a western phenomenon. The ideal of the global village was first glimpsed in cities seven thousand years ago, in today’s Iraq. As one historian has written: “A town is always a town, wherever it is located, in time as well as space.”

I believe cities are our greatest creation as a species. They embody our unique ability to imagine how the world might be, and to realise those dreams in brick, steel, concrete and glass. For our species has never been satisfied with what Nature gave us. We are the ape that builds, that shapes our environment. We are the city builders – Homo urbanus.

Undoubtedly, urban planners face some daunting challenges in the coming years. About a billion city dwellers are homeless or living in squatter towns without adequate access to clean water. That’s a sixth of the planet’s entire population. Indeed, until recently more people died in cities than were born in them. Thomas Malthus, in his Essay on the Principles of Population (1803), said that half of all children born in Manchester and Birmingham died before the age of three.

Problems remain, but cities are more popular than ever. By 2030, sixty percent of people will be urbanites. Across the world from Shanghai to São Paulo, people are flocking to the cities – to buy and sell, to find work, to meet lovers and like-minded people, to be where it’s all happening. For like magnets, cities have always attracted creative people from both the arts and the sciences.

So next time you’re strolling down the street and you notice some guy who is lost in thought, don’t forget – he could be the next Leo Szilard, chasing visions of scientific Utopia on a dusty urban sidewalk.

Central Park is one of my favourites. Perhaps because the contrast between the concrete canyons of the city and the leafy shade of the park is so great in New York. It's a wonderful place to walk.

But did you know that in 2002, naturalists discovered that Central Park is home to a species found nowhere else on the planet: Hoffman's dwarf centipede. And that as many as 275 bird species have been spotted there, including bufflehead ducks and hooded mergansers.

These facts are courtesy of Leslie Day's Field Guide to the Natural World of New York City, an amazing book that reveals a surprisingly green side to the Big Apple. The illustrations - such as this image of a peregrine falcon - are by Mark Klingler. I've written a review of it for today's Guardian Review, along with Abrahamson & Freedman's paean to disorder, A Perfect Mess.