Conceptual computer artwork of multiple universes: Some physicists believe that there are an infinite number of parallel universes, created for each possible quantum mechanical outcome. The collective name for these universes is the multiverse.

Credit: Mehau Kulyk/SPL

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Since Kardashev's original ranking of civilisations, scientific developments have refined and extended our perceptive analysis, including recent advances in the fields of nanotechnology, biotechnology and quantum physics.

For example, nanotechnology may facilitate the development of von Neumann probes. As American physicist Richard Feynman observed in his seminal essay, 'There's Plenty of Room at the Bottom', there is nothing in the laws of physics to proscribe building armies of molecular-sized machines. At present, scientists have already built atomic-sized, entertaining curiosities, ranging from an atomic abacus with buckyballs to an atomic guitar with strings, measuring about 100 atoms across.

Paul Davies speculates on the idea that a spacefaring civilisation could make good use of nanotechnology to construct miniature probes to explore the galaxy, perhaps no bigger than the palm of your hand. "The tiny probes I'm talking about will be so inconspicuous that it's no surprise that we haven't come across one," he says. "It's not the sort of thing that you're going to trip over in your backyard. So if that is the way technology develops – namely, smaller, faster, cheaper – and if other civilisations have gone this route, then we could be surrounded by surveillance devices."

The development of biotechnology has also opened the possibility that such probes may act as lifeforms, reproducing their genetic information, mutating and evolving at each stage of reproduction to enhance their capabilities, and may have artificial intelligence to accelerate their search.

Information theory has modified the original Kardashev analysis. Current SETI (search for extra-terrestrial intelligence) projects only scan a few frequencies of radio and TV emissions sent by Type 0 civilisations, but perhaps not an advanced civilisation. Because of the enormous static found in deep space, broadcasting on a single frequency presents a serious source of error. Instead of putting all your eggs in one basket, a more efficient system is to break up the message and smear it out over all frequencies and then reassemble the signal only at the other end. In this way, even if certain frequencies are disrupted by static, enough of the message will survive to reassemble the message accurately via error-correction routines. However, any Type 0 civilisation listening to the message on a single-frequency band would only hear nonsense. In other words, our galaxy could now be teeming with messages from a number of Type II and III civilisations, but through our Type 0 radiotelescopes, we would only hear gibberish.

Lastly, there is also the possibility that a Type II or Type III civilisation might be able to reach the fabled Planck energy with their machines – that is, a staggering 1,019 billion electron volts, which is a quadrillion times larger than our most powerful atom smasher.

The Planck energy only occurs at the centre of black holes and the instant of the Big Bang. But with recent advances in quantum gravity and superstring theory, there is renewed interest among physicists about energies so vast that quantum effects rip apart the fabric of space and time. Although it is uncertain that quantum physics allows for stable wormholes, this raises the remote possibility that sufficiently advanced civilisations may be able to move across inconceiveably vast distances of space in the blink of an eye, by using a wormhole as a 'back door' around the speed of light – almost like Alice's looking glass.

And if these civilisations can navigate through stable wormholes, attaining a specific impulse of a million seconds is no longer a problem. They merely take a short-cut through the galaxy. This would greatly cut down the transition time needed to progress from a Type II to a Type III civilisation.

Such an ability to tear holes in space and time may come in handy. Astronomers, analysing light from distant supernovae, have concluded recently that the universe may have been accelerating, rather than slowing down, since the Big Bang – and this is still occurring. If this is true, there may be an antigravity force – perhaps even the Cosmological Constant proposed by Albert Einstein and later retracted – which is counteracting the gravitational attraction of distant galaxies.

But this also means that the universe may expand forever, the stars burn out of fuel and the universe will eventually darken – ending in a Big Freeze, with temperatures approaching near absolute zero. Several papers have recently laid out what such a dismal universe may look like. It'll be a pitiful sight: any civilisation that survives will be desperately huddled next to the dying embers of fading neutron stars and black holes. All intelligent life must die when the universe dies.

Contemplating the death of the Sun, the British philosopher and mathematician Bertrand Russell wrote: "All the labours of the ages, all the devotion, all the inspiration, all the noonday brightness of human genius, are destined to extinction in the vast death of the solar system, and the whole temple of Man's achievement must inevitably be buried beneath the debris of a universe in ruins".

Today, we realise that sufficiently powerful propulsion systems may one day spare us from the death of our Sun in some five billion years when the Earth's oceans boils and the mountains melt. But how do we escape the death of the universe itself?

There could be a way out, according to John Barrows, a theoretical physicist at the University of Cambridge: "Suppose that we extend the classification [of advanced civilisations] upwards. Members of these hypothetical civilisations of Type IV, V, VI … and so on, would be able to manipulate the structures in the universe on larger and larger scales, encompassing groups of galaxies, clusters, and superclusters of galaxies." Civilisations beyond Type III may have enough energy to escape our dying universe via holes in space.

Lastly, physicist Alan Guth of the Massachusetts Institute of Technology, who helped create the inflationary universe theory, has even computed the energy necessary to create a new 'baby universe' in the laboratory: it requires a temperature of 1,000 trillion degrees Celsius, which is within the range of these hypothetical civilisations.

Of course, until someone actually makes contact with an advanced civilisation, all of this amounts to speculation – albeit tempered with the laws of physics – that is no more than a useful guide in our search for extraterrestrial intelligence.

But one day, many of us could gaze at the encyclopaedia that contains the coordinates of perhaps hundreds of Earth-like planets in our sector of the galaxy. Then we will ponder with wonder, as Sagan did, what an intelligent civilisation a millions years ahead of ours will look like.

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