Well, I’m off to get six hours of sleep before the big announcement tomorrow! The Event Horizon Telescope teams are talking about an announcement of “groundbreaking” results tomorrow at 13:00 CEST. Given that they set out to “image” the event horizon of a black hole, this suggests (suggests) that they are going to announce some landmark on that stated mission. We shall have to see what they say. See here.

I’ve been asked a lot by press people for my thoughts over the last couple of days. I’ve no inside knowledge, and do not want to over-promise on what the results could be, so I’ve not said much. I just sent off some remarks to one outlet, and since they are lengthy and late I expect they won’t be used. So I’ll record them here. Also, it’ll be amusing to see them alongside whatever it is I think once the results are announced! So here goes:

I was asked why the project is important. My response:

While we confirmed the existence of black holes and studied their properties in so many ways, nothing beats a direct observation. The Event Horizon project aims to effectively image the horizon of a black hole on the background of the glowing matter that surrounds it! It’s rather like seeing the shots fired as well as the smoking gun.

What would we learn from an image of a black hole’s horizon?

The shape of the horizon itself is important to determine. We know what it should be like if our best theory of gravity -Einstein’s General Relativity- is true. Deviations from that would be a stunning result. But before even worrying about that, it is important to check whether the sharp region corresponding to the edge of the horizon is even there. Establishing that something less than sharp is there could also spark a revolution in our understanding of what lies in those strong gravity regions we believe to be black holes. Could there be some alternative that acts like a black hole, being massive and compact, but deep down is quite different – no sharp horizon? This will help rule that possibility in or out.

What would it mean for the field? For my own research?

The answer to those questions depends upon what is announced! Either way there’ll be genuine and justified excitement. We’ll either have confirmation of the core property of a black hole -the existence of and nature of its horizon- confirming General Relativity (GR) or we’ll have a result that suggests something new and surprising about the massive compact centers of the galaxies being studied (our Milky Way and our neighbor M87) – maybe telling us that black holes behave differently from what we know from GR. Either way it will be a huge result.

A lot of my research time is spent thinking about black holes and understanding their properties in various situations in theoretical physics. They are central to a lot of core ideas. More confirmation that they are real objects with the expected properties is great to have. On the other hand, I also hope that black holes can one day provide a window into how the physics of space and time works beyond where Einstein’s GR can go. Work such as string theory (one of the things I work on) tries to go beyond Einstein in seeking how to combine quantum physics and gravity. Such a combination will ultimately produce deviations from what Einstein’s theory tells us. But the issue is that we do not know robustly where such deviations would show up. The theory is not predictive enough in that regard. Deviations from GR beginning to show up near a supermassive black hole (although I’d expect it to be a long shot that this is the announcement!) would be a huge boost for that thread of investigation, and may provide much needed clues for how to tackle the whole “beyond Einstein” program.


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