So many of us, when we are little, dream of going to visit distant planets by simply hopping in our space ship, having a death ray or light saber reminiscent of that in Star Wars to fight away all the baddies, or travel backwards in time to visit the courts of our favourite English Kings and Queens (or, for the more scientific minded, the labs of our favourite scientists). Upon growing up, however, we realise that reality is often disappointing, and ‘impossible’ dreams like this are dashed. However, in ‘Physics of the Impossible’, Michio Kaku is in some respects still a little kid dreaming of achieving the impossible. Of course, he is also a highly esteemed theoretical physicist and leading theorist on string theory; his unlimited energy and optimism for the future, coupled with the strong scientific backing on the edge of knowledge, make you wish you could live for thousands of years to come to witness the rise of such fantastic technology.

‘Physics of the Impossible’ is divided into three main sections. Type I impossibilities, which involve everything from force fields to psychokinesis, are concepts which don’t violate the laws of physics and theoretically are possible, but are not a fully-fledged reality yet. These ‘impossibilities’ are in some cases present in the world today, but in a very embryonic form, such as the teleportation particles hundreds of meters under the Danube river using quantum entanglement or the ITER fusion reactor in the south of France, which, thanks to plasma physics, hopes to begin generating massive amounts of energy by 2035. I found these two technologies particularly fascinating as they involve cutting edge research in particle physics, but with two very different applications.

Secondly there are type II impossibilities, which don’t violate the laws of physics as we know them, but are on the furthest extent of our scientific understanding. Type II impossibilities include faster than light travel, time travel, and parallel universes. These technologies are largely theoretical, but Kaku does detail how a so-called type III civilisation – one with the power of their whole galaxy at their disposal – may have these technologies largely and widely available. I was excited but a little disappointed by the chapter on faster than light travel, as this entails travel by worm holes and black holes rather than actually exceeding the 3x10⁸ms^-1 speed limit of the universe. Although I know that Einstein’s famous equation E=mc² forbids speeds over this limit, I was still excited to find out whether there were any possible loopholes allowing faster speeds. Einstein’s rule stands ironclad, however, but this was still an intriguing section of the book.

Finally there are type III impossibilities, which are not allowed by the rules of physics as we know them. Surprisingly there are very few of these, with only perpetual motion machines and precognition discussed by Kaku. I particularly enjoyed the chapter on precognition, as it discussed the concept of time, which is a topic I find both fascinating and perplexing. In this chapter I was presented with a simple fact which, I don't know how has evaded me thus far. Did you know that an anti-electron is just a regular electron going backwards in time? This simple fact has changed my perspective on matter and antimatter forever, as its simplicity and significance is astounding. As Kaku points out, the entire universe may just be a single electron whizzing forwards and backwards in time to create everything we know. This is an amazing possibility, but as Kaku points out, I won't be able to see forwards into time to see if it is true, as precognition violates the known and accepted laws of Physics.

On top of the fascinating subject matter, ‘Physics of the Impossible’ is a very enjoyable read as it reaches out to the Sci-Fi nerd in each of us. Everything from ‘Star Trek’ to Asimov’s ‘Foundation’ series is referenced here, not only making the book more fun and not as heavy to read, but also providing a useful visual of the technologies described, as we have already seen them on the big screen or read about them in novels. It also made it especially exciting to hear that invisibility cloaks, like those used on the ‘Enterprise’ or in Harry Potter have already been created to some extent, invisible to radiation in the infrared section of the electromagnetic spectrum. Unfortunately though, these are still ‘clunky devices’ and will require a lot more development to become the invisibility cloaks as we know them on TV.

Overall, ‘Physics of the Impossible’ is an entertaining and engaging tale of the union of physics and engineering on the bleeding edge of knowledge. It is a tale of the future of the human race as we search for our place among the stars, and the technology which will help us get there. Creations such as LISA remind us how far we have come so far, and go to show the feats of engineering and science we are already capable of. This begs the question, what will we achieve in the future? Perhaps what would now seem ‘impossible’, what would now make pessimists scoff and announce that it will never happen, will be a reality for our descendants? Let us not forget, that the great scientist, Lord Kelvin, dismissed X-rays and radio waves as impossible, and the greatest scientist of the 20th century, Albert Einstein, vehemently protested against quantum mechanics, a pillar of modern physics, stating that ‘(God) does not play dice’. Through ‘Physics of the Impossible’ Michio Kaku shows us that the word ‘impossible’ is perhaps not one to throw around so lightly, as well as highlighting the weird and wonderful universe which we live in, which makes the leap from fantasy to reality not quite so big.