Astrophysical journal of the 20th century was agog with Einsteins’ general theory of Relativity and this century is astir with Black holes. In our known universe the idea that no particle can pass faster than light was sacrosanct. Every theory had to fit in order to pass approval. In 2011 was a debate going on about faster-than-light neutrinos. Imagine the notion of the universe having internal boundaries! Only that we have not had any convincing proof to support this quirky idea. It has now been ditched.
What makes a black hole special is its event horizon. If you pass through you are lost forever, in the most complete way, from the universe you left behind. It’s a boundary to the knowable universe. Extraordinary claims require extraordinary evidence. The claim that the universe has internal boundaries is extraordinary. So what’s the evidence for event horizons? One may point to observations of hot matter around the postulated event horizon and say that matter is at least as far from the horizon as the size of the black hole itself. Einstein’s theory of gravity, describes these hot matter observations well, and if it continues to do so all the way down to the event horizon then black holes exist. But we’ve yet to see evidence for that.
Our theoretical explanations may require the existence of things for which there is no direct evidence. It happens all the time in physics. If you accept the Standard Model of Particle Physics then you probably believe in the Higgs boson even though it took a while in order to prove its existence. Similarly, if you believe general relativity then you probably believe in event horizons.
At best we may conclude the best theoretical model of the observational data implies a black hole. But that model includes general relativity, which we expect does not completely describe black holes, as it predicts a singularity – a point of infinite density and infinitesimal volume, at which space and time become infinitely distorted. Things can become quite weird is it not?
So when you come across the term “infinite” in physics it is more like the white spaces in old maps with a notation, ‘terra incognita’, meaning we have reached the limits of our understanding.
Thanks to Stephen Hawking who jiggered with black hole predicts small event horizons eventually explode due to’Hawking radiation.’
So it’s possible event horizons are where quantum mechanics first requires significant modifications to general relativity. Speculating further, it’s also possible that such modifications would prevent event horizons from forming. That might save us from living in a universe with parts that are unknowable.
‘Black holes are a bit like free will. Irrespective of the evidence, most of us live as if free will exists. And most astrophysicists live as if black holes exist’.
(The Conversation/ Black holes might exist, but let’s stay skeptical-Prof.craig savage, Theoretical Physics- Au.NU/ Nov.29, 2011)
(To be concluded)