The news of Stephen Hawking’s death may have come as a source of sadness for many of us. His family have reported that he was at peace as he passed away on the morning of the 14th of March 2018.
However, it may certainly be hard to imagine a world without his regular new contributions to popular culture, not to mention his specific academic and scientific arenas.
Professor Hawking leaves us with an unprecedented depth of theoretical background on the most compelling and exciting areas of cosmological physics. He has also provided physical scientists with some interesting phenomena to test with real-world models.
A lasting legacy
Professor Hawking used his mathematical and theoretical expertise to make incisive new claims about the nature of black holes. These are bodies that were originally thought to pull all surrounding matter into them.They were termed ‘black holes’ as they appeared to exude nothing, including energy of any kind, in return. However, Professor Hawking was able to demonstrate that it could be possible for certain particles to escape from black holes. Those particles were termed Hawking radiation in his honour.
The presence of Hawking radiation can be confirmed or denied in various models of black holes known to physics today. An example of these is a form of rubidium atoms reduced to nearly absolute zero in temperature. The atoms assume a quantum state as a result, which can evince the effect of one particle existing as two at the same time. This is known as a Boseian/Einsteinain condensate (BEC), and leads to one of the resulting, high-energy quasi-particles escaping the black hole through the propulsion provided by the energy of the other. This is what makes up Hawking radiation.
Therefore, Hawking and his colleagues argued that black holes do not negate everything in their horizons, as once thought. However, he disagreed with other physicists as to what happens to information that goes into a black hole.
Hawking initially asserted that such data is lost to the universe forever should it get too near one of these objects. This is based on findings that information that goes into black holes cannot be detected again; thus leading to reasonable conclusions that it vanishes forever. However, some researchers argue that certain black hole types spare some information because their models leave an informational ‘credit’.
An example of such research is the recent paper by Matt Visser of the School of Mathematics and Statistics at the Victoria University of Wellington and Ana Alonso-Serrano of the Institute of Theoretical Physics at Charles University in Prague. They have recently published a paper in the journal Physics Letters B in which they argue that general-relativity black holes can support an informational imbalance between what goes in and what comes out.
The researchers based this argument on previous findings that blackbodies (theoretical objects in which the absorption and emission of electromagnetic radiation is perfectly optimal) are associated with a specific entropy measured in bits per photon. This figure, which roughly equates to 3.9b/photon, is associated with blackbody radiation. However, this only represents informational ‘credit’ if this emission is present as one unified entity, or is unitary. Furthermore, the same theory only applied to Hawkingseque black holes under the same conditions.
Blackbodies are simulated using an apparatus quite like a furnace, in which the physics involved in burning processes within it are used to model EM radiation and absorption. Alonso-Serrano and Visser have claimed not to be able to observe the phenomenon of ‘informational loss’ when assessing the quantum physics of burning using such a furnace. Data is thought to be lost in the process of Hawking evaporation that is associated with normal black hole function. Therefore, the researchers applied the same search for entropy to Hawking radiation in BEC-emitting experimental black holes.
These black holes provide the only empirical evidence of Hawking radiation. However, the two researchers found that they needed to use their informational entropy-related figure when calculating the quantum entropy associated with their experimental black hole. However, it was not required to balance the normal (i.e. thermodynamic) entropy with Bekensteinian entropy (a concept developed to compensate for the lack of normal thermodynamic behaviour in a black hole) of the same.
Therefore, the researchers’ new model presumes that a black hole in the cosmos, together with its attendant Hawking radiation, behaves as classically expected with respect to its environs, including any information that may have become part of the black hole/radiation system. In addition, atypical effects on information would require the actual observation of an event horizon in an experimental black hole, which no physicist – Visser and Alonso-Serrano included – has ever reported. Hawking also acknowledged this requirement in a 1970s publication.
In his lifetime, Professor Stephen Hawking had achieved the difficult feat of making physics at the highest levels compelling, challenging and more interesting to the general public.
He has left a considerable body of work that includes ground-breaking theories to be tested by his successors. They concern black holes and what happens inside them. The wonder implied by his reasoning inspires practical science that, ironically, will make black holes much more commonplace items in the human consciousness.
Top image: Stephen Hawking at Gonville & Caius College, Cambridge. (CC BY 2.0)
Alonso-Serrano A, Visser M. Entropy/information flux in Hawking radiation. Physics Letters B. 2018;776:10-6.
Alonso-Serrano A, Visser M. On burning a lump of coal. Physics Letters B. 2016;757:383-6.
Crew B. A Lab-Made Black Hole Just Gave Us The Strongest Evidence Yet For Hawking Radiation. Science Alert. 2016. Available at: https://www.sciencealert.com/a-lab-made-black-hole-might-have-finally-proved-stephen-hawking-right
Resnick B. Stephen Hawking’s most mind-blowing discovery: black holes can shrink. Vox. 2018. Available at: https://www.vox.com/science-and-health/2018/3/14/17119320/stephen-hawking-hawking-radiation-explained