Yesterday I attended the public talk by theoretical physicist and string theorist Brian Greene at Lehigh, which was held as part of the celebrations for the university's 150th anniversary. The auditorium at Zoellner Arts Center was packed with students, professors and members of the general community. The central theme of Greene's talk (as I understood it) was that at any point in time, innovations and discoveries are made by people who have been able to keep a child-like ability to look at the world anew, and their predecessors, who made their own innovations and discoveries, might be their fiercest opponents in not recognizing the validity of their younger colleagues' claims. Greene motivated his talk through the example of Albert Einstein, who pioneered general relativity (Greene pointed out that November 25, 2015 will mark the 100th anniversary of general relativity, by the way) but then didn't believe Karl Schwarzschild when the latter first wrote that Einstein's theory led to black holes. In a way, Einstein had lost the ability to see how far his own theory went.
Greene then translated this issue to present times when he argued in favor of the holographic principle, which suggests that we are 3D projections of a 2D universe. (You can read more about his theory in this 2012 Wired article.) This principle arose from the resilience of information in black hole that apparently follows from Einstein's principle. When an object enters a black hole, its information is smeared over the boundary of the black hole and thus the object can be reconstituted.
Greene had three main stories related to Einstein, prefaced by one about the sense of wonder of a second grader. Somewhere along the way he touched upon the issue of universe vs multiverse, and argued (I think, if I understood him correctly) that in many years, if the universe keeps expanding, we would have very dark skies that would look empty but wouldn't be, and we could try to warn our future descendants but if given the choice between listening to ancestors of an era long past or believing their state-of-the-art observations, they would believe their observations, and be wrong.
He talked for one hour without notes, was an exceptionally engaging speaker who told some jokes and never stayed behind the lectern for long, except when he showed many short, excellent videos to explain the physics he was talking about. During the Q&A, he answered every single question with ease, including the more technical ones. He also made it clear that, although the holographic principle does seem outlandish (my words, not his), he has no interest in wasting his time on theories that can't possibly be true.
I enjoyed reading Greene's books The Elegant Universe and The Fabric of the Cosmos some years ago, and it turns out Greene is as good a speaker as he is a writer. Unsurprisingly, he gave a TED Talk back in 2012, which you can watch below (from the TED channel).