Stephen Hawking turned 76 last Monday. Or did he? A conspiracy theory claims that the renowned physicist was replaced with a lookalike around 30 years ago, who has been impersonating the professor ever since.

Proponents of the theory claim that the professor is so trusted as a voice of science that when he "died" in 1985, scientists at NASA (it's always NASA) decided that he was too useful a figurehead to give up. So instead of announcing his death, they swapped him for a lookalike. Much like how the Beatles did when Paul died.

Unlike the Paul conspiracy, proponents of "fake Hawking" say that he hasn't been replaced with someone of comparable abilities, but an ordinary man who is being fed complex astrophysics by NASA.

Stephen Hawking speaks by controlling his speech synthesizer using a muscle in his cheek. A cursor on Hawking's computer screen scans across his keyboard, row by row. By moving his cheek he stops the cursor on the row he needs, and then the letter. The computer also uses predictive text, meaning he can select a whole word after typing only a few letters. The cheek movement is detected by a sensor in his glasses.

Rather than believe this, conspiracy theorists think he's most likely having his words typed by a team of astrophysicists. These astrophysicists, who for some reason don't want credit for their own work, also type out Hawking's theories and attribute them to him.

According to this excellently named Reddit thread, theorists think that this happened before the publication of his most famous work, A Brief History of Time. They genuinely propose that rather than take credit for the work, the unknown authors attributed it to Stephen Hawking to make it appear to have more authority. They believe that Hawking was replaced so that NASA (and other scientists) could use the trust the public places in him for their own advantage. 

So what are their reasons for believing this, other than lunacy? They can't get over the fact that he's lived for so long with ALS.

Most people diagnosed with ALS (amyotrophic lateral sclerosis) die within five years of diagnosis. Stephen Hawking has lived 55 years so far since his diagnosis at the age of 21. 

The (admittedly brilliantly named) Daily Sheeple outline that him surviving these many years more than anyone else proves the Hawking we know and love is more than likely an imposter.

"That is a more than 100% difference between first and second place," Miles Mathis writes on the website. "It would be like Justin Gatlin running the 100 meters in 9.8 seconds, and Usain Bolt beating him with a time of 4.5 seconds. In other words, statistically, it doesn’t happen."

This is willfully misunderstanding how the estimates of life expectancy are made. They are based on how long others with the same condition have lived; however, there will be a percentage of people with that condition (outliers) that live a lot longer or shorter than this range suggests. As more people live longer (with better care) these estimates get adjusted.

Leo McCluskey, medical director of the ALS Center at the University of Pennsylvania, told Scientific American that Hawking's case has highlighted how variable the disorder is.

"On average people live two to three years after diagnosis. But that means that half the people live longer, and there are people who live for a long, long time," McCluskey said. He went on to explain that with ALS, the most common cause of death is either respiratory failure, as motor neurons run the diaphragm, or malnutrition and dehydration, as swallowing muscles deteriorate. 

"If you don't have these two things, you could potentially live for a long time – even though you're getting worse," he said. "What's happened to him is just astounding. He's certainly an outlier."

Mathis also suggests that photos of Stephen Hawking on the Internet are "conveniently not dated" and Hawking appears to have gotten more youthful as time has gone on. On the other hand, he bafflingly compares photos taken decades ago of the professor with more recent ones, pointing out that he had dark brown hair when he was younger and "now he is gray", proving conclusively they are different people. Astonishing stuff.

Other "evidence" points to photos from Hawking's wedding to Elaine Mason in 1995. Mathis shows two pictures in which her dress looks slightly different (most likely due to lighting) and claims that it's evidence that the photos have been re-staged using the imposter Hawking, to erase visual evidence of the first Hawking ever having existed.

Weirder still, conspiracy theorists appear to think that the replacement Hawking does not have ALS by suggesting the "new" Hawking does not have hands that have been curled by the condition. They believe he is a man who has for the last 30 years pretended to be paralyzed in an attempt to cover up Stephen Hawking's death, rather than, you know, Stephen Hawking.

Which is all, of course, nonsense.