Take the lift to the third floor and turn left, following the signs to the Science in the 18th Century gallery.

SCIENCE IN THE 18TH CENTURY

ARMILLARY SPHERE, 1731 - walk through the gallery - the sphere is in the second case along in the middle of the gallery

The Hitchhiker’s Guide to the Galaxy is a fine example of the way that science fiction turns upside down accepted wisdom about the way the world works. For thousands of years it seemed logical that the human race and the planet Earth were at the centre of things - we don't feel that we are moving, so people thought it must be the Sun, planets and stars that move.

In the early sixteenth century Nicolaus Copernicus put forward a model of the Solar System with the Earth and planets orbiting the Sun, and the Moon circling the Earth.

This armillary sphere, made by Jonathan Sissons, shows the Solar System as it was thought to be in 1731. Although closer to reality than previous models, it shows the planets moving around the Sun in a circle, instead of in the elliptical orbits they really have.

Exit the Science in the 18th Century gallery at the far end and turn right into Optics.

OPTICS GALLERY

THE FIRST LASERS - walk towards the exit of the gallery - the lasers are at the end of the gallery, on the right of the exit

Most science-fiction films feature a laser beam at some point or another. But strangely, lasers - or something very like them - featured in many films even before the real thing had been invented. The basic idea of 'stimulated emission of light' was predicted in 1916 by Albert Einstein, but we had to wait until 1960 before Theodore Maiman built the first working example at Hughes Research Laboratories in California.

Just to make things a little stranger still, the laser - light amplification by stimulated emission of radiation - was patented in the same year by Charles Townes and Arthur Schawlow, before Maiman had made his working example.

Lasers, like the examples on display, use the atomic structure of a crystal such as ruby to produce light that is all the same wavelength. The light is then bounced back and forth between mirrors to get the light waves in step - peak to peak, trough to trough. The result is a powerful beam of light that can repair eyes or cut through metal - just like in science fiction!

Go back through Science in the 18th Century and turn right. Go into Health Matters.

HEALTH MATTERS

THE GESELL DOME AND THE PECKHAM EXPERIMENT - follow the gallery round and you will see the Gesell Dome in front of you. The Peckham experiment is behind and to the right.

In The Hitchhiker's Guide to the Galaxy, planet Earth is a huge experiment, part of which involved humans being observed - by mice. The Gesell Dome and the Peckham Experiment of the 1930s allowed scientists to observe other humans.

The Gesell Dome was invented as an aid for the study of child development. While children played, solved puzzles or had their teddy bears taken from them, white-coated scientists watched, recorded and filmed their every move from behind a two-way mirror.

Built as a community health and leisure complex, the Peckham Health Centre allowed local people unheard-of luxury as they swam and played sports. But every movement was monitored by scientists eager to learn more about human health and behaviour.

Leave Health Matters via the door by the Peckham Experiment and take the lift to The Science and Art of Medicine on the fifth floor.

THE SCIENCE AND ART OF MEDICINE

POWERED ARM PROSTHESIS, 1960s - turn right when you enter the gallery and follow the cases round - the prosthesis is in its own case in front of you.

If lasers are one essential element in science fiction, then robots – like Marvin in The Hitchhiker’s Guide to the Galaxy – and robotics are another. This battery-powered arm was designed to be used by children born without limbs after their mothers took the painkiller thalidomide during pregnancy, before the drastic effects of the drug were realised. Moving in a robot-like way, it was controlled by movements of the shoulder. There have been huge advances since this primitive mechanical arm was made, and in the future it will be possible to use a feedback system that allows the wearer to 'feel' objects.

Go back to the lift and go to the ground floor. As you leave the lift, turn right and then right again, past the café and into the Space gallery.

SPACE GALLERY

BOOKS PREDICTING SPACE FLIGHT - turn left as you enter the gallery - the cases are on your left, past the Sputnik.

The Hitchhiker's Guide to the Galaxy is part of a long tradition of science-fiction writing. The three books in front of you, from the seventeenth, eighteenth and nineteenth centuries, predicted flights into outer space - some rather more believable than others.

In The Comical History of the States and Empires of the Worlds of the Moon and Sun, written by Cyrano de Bergerac in 1687, the hero lands on the Sun and survives.

In Voyage to Cacklogallinia, written by Samuel Brunt in 1727, the hero meets a colony of highly intelligent roosters. Pulled along by the birds, he visits the Moon, which turns out to be a utopia.

In 1865, Jules Verne wrote From the Earth to the Moon. Verne predicted many things that now seem familiar, including spacecraft with aluminium construction, a launch from the coast of Florida and a splashdown in the ocean.

SPACE FOOD - cross the gallery, the case is behind the Lunar Landing Module

In The Hitchhiker's Guide to the Galaxy, Arthur Dent is appalled by something that is 'almost but not quite, completely unlike tea'. He would probably feel the same way about the food carried on Apollo space missions in the 1960s and 1970s.

In zero-gravity conditions and with cabin space at a premium, crumbs were out of the question and everything had to be as small as possible. Freeze-dried stew and soup were reconstituted with water produced in the spacecraft's fuel cells. Hydrogen suspended in the water could cause unpleasant and embarrassing gastric problems for the crew and drinks were squeezed into the mouth from concertina-like plastic containers. Astronauts accepted all this as a small price to pay during their relatively short missions.

For today's, long-duration missions, food has become much more palatable. Special nozzles even allow astronauts to sip their favourite fizzy drinks.

Now walk from the far end of the Space gallery into Making the Modern World.

MAKING THE MODERN WORLD

HAND LOOM WITH JACQUARD MACHINE - second large object on the right as you walk through the middle of the gallery

This may seem a long way from Deep Thought, but the punched cards that controlled this loom were the forerunners of the ones used in early computers. The Jacquard machine replaced a human being - the draw boy previously needed for complex weaving patterns. In 1890, Herman Hollerith developed a standard-size punched-card system that carried coded information for the United States census. Later, Hollerith's company became IBM and the same system proved ideal for early electronic computers.

GENETICALLY ENGINEERED MICE, 1988 - walk straight through the gallery - opposite the Apollo 10 capsule

Mice have long been one of the most widely used lab animals. In an amusing reversal of the real world, Douglas Adams cast mice as the most intelligent animals on the planet, using humans as the subject for their experiments.

The mice on display have had part of their DNA altered to make them more likely to develop cancer, so that scientists can study the disease and look for a cure. They were the first patented mammals, and their development was controversial - many people predicted a future of uncontrolled manipulation of animals. In 1987, after four years of intense debate, the US Patent Office declared that 'higher forms of life are patentable'.

APOLLO 10 COMMAND MODULE

In films like The Hitchhiker's Guide to the Galaxy, spacecraft are big - really big. With plenty of headroom, flights of stairs and individual bedrooms, they are, perhaps not surprisingly, about the size of a film studio sound stage. The reality is rather different. In 1969, Apollo 10 astronauts Tom Stafford, John Young and Gene Cernan shared a capsule about as big as a medium-sized motorcar during their eight-day lunar mission. They had to do everything in that one small space - even use the solid-waste collection bags - all without the help of gravity.

Despite the cramped, smelly conditions, the mission was a success. The command module in front of you, nicknamed 'Charlie Brown', orbited less than 60 miles above the Moon, while Stafford and Cernan in the lunar module, Snoopy, descended to within 9 miles of the surface. On re-entry, this spacecraft reached a speed of just under 25,000 mph, making its occupants the fastest people in history. Just two months later, the whole world watched as humans stepped onto the surface of the Moon for the first time.

Go back towards the Space gallery and take the lift or stairs down to the basement. Enter The Secret Life of the Home.

THE SECRET LIFE OF THE HOME

AUTOMATIC DOOR, 1933 AND CASH DISPENSER, 1970 - walk straight through - the objects are just past the computer games case

The automatic door was a novelty when it was installed in the Museum's Children's Gallery in the 1930s, and people still enjoy using this early piece of automation - millions have now passed through it.

The cash dispenser was cutting-edge technology of the early 1970s. By putting a punched card into the slot, the machine gave you a £5 note in an envelope and kept the card - which was posted back later.

Both these exhibits show just how quickly technology has changed over the years. One of Douglas Adams's inspirations for The Hitchhiker's Guide to the Galaxy was seeing the automatic doors of a lift as they opened and closed for non-existent customers.

As you leave The Secret Life of the Home, walk away from the lifts you used earlier and head towards Launch Pad. To the left, you will see another lift. Take this lift to the first floor of the Wellcome Wing. Go into Who Am I?

WHO AM I?

CRYOGENIC HEAD CONTAINER - walk down the middle of the gallery - the container is in the back of the third case on the right.

Zaphod Beeblebrox might have the luxury of an extra head, but could our own heads give us another shot at life? The people at the ALCOR Life Extension Foundation certainly think so.

Heads, removed from the body immediately after death, are stored in liquid nitrogen at minus 196 °C. As soon as the technology exists to repair and rebuild the heads - and to attach them to new bodies - life can begin again. The cost is a snip at $80,000 - or $150,000 if you fancy having the same body you started with.

The catch? No-one has so far been revived from cryogenic storage and the technology to repair the body does not yet exist. But ALCOR predict that all this could be possible - in a hundred years or so.