Finally, Sheldon Cooper's lifelong obsession of meeting Mr. Spock is coming true albeit in a dream sequence only (and I read we'll only be hearing Mr. Nimoy's voice so not really a physical meeting haha).
Image nicked from hollywoodreporter
Long time fans and Big Bang Theory followers were undoubtedly ecstatic when the news broke out of the two appearing on separate episodes of the popular TV series. I myself am super excited because it has been Sheldon's dream to meet the original Spock himself (again, technically he's not really gonna meet him, as Mr. Nimoy's non-screen appearance agreement still stands). But still, it's something.
As for nabbing the celebrated theoretical physicist Stephen Hawking to do an appearance, even the show's executive producer Bill Prady can't really explain how everything happened. He described it as a "mystery that only Stephen Hawking himself would understand." For them, Stephen Hawking has always been the dream guest but somehow the idea gets brushed aside, so how it happened is surely something that the whole team won't forget for a long time.
Screenshot from executive producer Bill Prady's twitter account