I say rumour, cos that's all it is. Someone on another board posted thusly:
"The main rumours about Muse have come from a comment by Emily Eavis that they have someone 'huge' who would pose a 'health and safety risk' at the Park stage if they announced them. In addition Kerrang Magazine then said something along the lines of that one of the biggest bands in the world beginning with 'M' would be playing a secret slot at Glastonbury."
Also, check Eavis' twitter: http://twitter.com/michaeleavis
something about black holes.
This is all bullshit prob.