Everyone has heard of Stephen Hawking. The British physicist was world famous for his work on space and time.

So how did a wheelchair-ridden man who could barely move his muscles get around to giving lectures and writing books?

Well, here's how...

Source: World Lifestyle

At 22, Hawking contracted amyotrophic lateral sclerosis (ALS) also referred to as motor neurosis. It is a degenerative disease that leads to the death of neutrons in a person's brain. It causes muscle twitching and a deterioration of muscles which leads to difficulty in swallowing, talking and eventually breathing.

Hawking was given 2 years to live, but he went to live on for more than half a century.

Source: ABC News

Hawking used a speech-generating device developed by Intel that helps with speech/writing for people who have trouble communicating.

To feed information into his computer, Hawking used an infrared switch mounted on his spectacles that caught the slightest of twitches in his cheek.

The software moved a cursor across rows and columns of letters and Hawking could select the desired letter by twitching his cheek. Individual letters could be selected this way which would then form words and sentences.

The software learnt from him to be able to predict and autofill the words he often used, thereby reducing the time and effort required for him to form sentences. It also learnt to analyse the content of a specific book or lecture he was working on to further simplify the process. A speech synthesizer helped him speak the sentence once it had been completed.

Source: EE Times

Along with talking and writing, the software also let him check his email, browse the internet, chat on Skype and make notes. Intel had a dedicated team of engineers who worked on making the communication process easier for him.

The software was updated frequently to help him cope with the gradual loss of control over his muscles.

Source: Chronicle Live

Hawking once wrote a post titled 'The Computer' about the software that helped him speak. You can read it here.

And here he is talking on Last Week Tonight With John Oliver: