In today’s blog we chat with Dr. Cosimo Bambi, PhD from the University of Ferrara, and professor of physics at Fudan University in Shanghai China.
David: There’s something unique about how people interact in Italy that is likely rooted in hundreds of years of culture that I have not found in the USA. Like me, you are also from Italy but have lived in many different places including the USA, Europe, and China. What are some major cultural differences among the places you have experienced and how do they compare to Italy? Cosimo: I grew up and I studied in Italy. Then I lived one year in the US, three years in Japan, and one year in Germany. I have already spent eight years in China. There are clearly differences among different countries, but even within the same country among different regions. However, there are also a number of similarities. If we talk about culture, Italy and China share many common things that are not present in the other three countries. I am thinking about people interactions, concept of family, importance of traditions like regional cuisines. Italy and China are two millennial cultures, which is not the case for Germany, Japan, and US. David: Much of your recent work has been on testing general relativity theory. How did your interest in this develop and what can you conclude so far? Cosimo: If I think back to ten years ago, there were no tests on the strong gravitational field around astrophysical black holes. We had a number of evidence for the existence of massive and compact objects, so we called them black holes, but we had no evidence that the properties of these objects were those predicted by general relativity. So I found it quite a new and exciting line of research. Today the situation is different. In the past five years, there has been tremendous progress in the field and we can now study the intrinsic nature of black holes with gravitational waves, X-ray observations, and mm VLBI data. All observations are consistent with the predictions of general relativity. The precision of these tests will be improved in the future, but the current results already constrain possible new physics, which was not the case up to some years ago. David: You have studied the recent EHT image of the black hole horizon in M87 and concluded that a high spinning Kerr black hole is ruled out. Does this produce tension with general relativistic MHD simulations which tend to require high spins? Cosimo: My study with Kate Freese, Sunny Vagnozzi and Luca Visinelli constrains the dimensionless spin parameter of M87* to a* < 6.5. This constraint is obtained assuming the Kerr metric but without imposing the Kerr bound a* < 1 for the existence of the horizon. So there is no tension with GRMHD simulations that require high spins, as for those studies high spin means close to 1. David: Can you estimate the odds that GR, dark matter, and dark energy will all together survive the 21st century mostly intact?
Cosimo: It is difficult to make predictions, because often you also need to be lucky to have progress in physics. And as a physicist, I like to find new physics, so I hope we can find deviations from the predictions of GR and we can understand the nature of DM and DE before I retire.
David: Thank you professor!