Renowned physicist, author, and co-founder of 'String Field Theory', Dr Michio Kaku believes that alien civilisations may have learnt to harness the energy of galaxies and travel through the universe using wormholes. Dr Kaku has described what we might expect of alien cultures in an article on his website, titled "The Physics of Extra-Terrestrial Civilisations".

In the short essay, Dr Kaku discusses the ideas of Russian astrophysicist Nicolai Kardashev who theorized in 1964 that advanced civilizations might be grouped according to three types: Type I, II, and III -- which have respectively mastered planetary, stellar and galactic forms of energy. He points out that we on Earth are a Type 0 civilization well on our way to becoming Type I.

He raises the issue of inter-galactic probes, positing that space exploration would best be achieved through the use of "Von Neumann probes" - self-replicating robots which are designed to reach distant star systems and then create factories which will reproduce copies themselves by the thousands, which continue the process.

Dr Kaku also points out that extremely advanced civilizations may have the ability to create stable wormholes through which they could travel, and perhaps even have the ability to create their own universes.

Dr Kaku is an internationally recognized authority in theoretical physics and the environment. His most popular and best selling books include HYPERSPACE: a Scientific Odyssey Through Parallel Universes, Time Warps and the Tenth Dimension (Amazon US and UK ) and VISIONS: How Science Will Revolutionize the 21st Century (Amazon US and UK ).