Understanding Black Holes

Matt Leo

On Tuesday, September 27, Professor Seth Major from the Physics Department at Hamilton College spoke in a lecture titled “Seeing and Quantizing Black Holes.” During the lecture, Major set out to explain the current state of research on black holes, as well as to inform the audience about how black holes are understood in regard to general relativity as well as quantum mechanics. 

To begin the lecture, Major discussed the warping of spacetime and black holes. He discussed different understandings of black holes, such as Newtonian black holes as well as Schwarzschild black holes. Major discussed different methods used to find the escape velocity of light and its radius. The key to this is the Schwarzschild radius, which is often referred to as the gravitational radius. This is the radius of the sphere such that, if all the mass of an object were to be compressed within that sphere, the escape velocity from the surface of that sphere would equal the speed of light, as is

apparent in a black hole. 

In order to paint a clearer picture of what constitutes a black hole, and what occurs to light when affected by the gravitational pull, Major provided examples of ripples on water that can focus light. He discussed how Einstein’s research that gravitational masses “bend” the path of light made headline news in the twentieth century in an article titled “Lights All Askew In the Heavens.” This was the first time that black holes had made headline news. 

Interestingly, Major discussed the concept of there being a horizon in black holes that is a causal membrane. This horizon acts as a boundary where light escapes into infinity and events outside of the horizon can affect events inside, but events inside cannot affect those outside. The discovery of this concept has hugely impacted how diagrams are drawn about black holes as our understanding of them has changed. Major described the horizons of black holes as “the smoking gun” of black hole research.

Physics concentrator junior Brendan Corrodi commented on the impact that this had upon his understanding of black holes. 

“The lecture opened my eyes to the possibility that something actually can escape the event horizon of a black hole,” Corrodi said. “I never knew that any kind of radiation could do that, let alone a type that we could possibly detect.” 

To conclude the lecture, Major discussed specific evidence of the black holes Sagittarius A* and GW150914+. The current implications of this evidence includes the fact that there are no known solutions to general relativity that are not black holes, and that the “smoking gun” of black holes has not quite been observed. 

The story of black holes is far from complete, and new advancements are constantly made. For instance, there are current suggestions within the field that thermodynamics may potentially play a future role in the research of black holes, as it tracks large scale flows of heat while working through systems. Through this relatively new branch of research, there have already been findings that black holes are extremely cold and that tiny black holes do in fact relay a thermal spectrum that can be used to conduct research. They are not in fact “black.” 

Ultimately, there is still a long way to go in regard to any direct detection of black holes, yet physics has come a long way in regard to its understanding of them. There is some evidence of their existence and of their effects, and there may soon be definitive proof.