Researchers at the University of Surrey have theoretically demonstrated that two opposing arrows of time can emerge within specific quantum systems. By examining the evolution of entanglement within these systems, they found that while one subsystem experiences time flowing forward as entropy increases, another subsystem can simultaneously experience time flowing backward, with entropy decreasing. This doesn't violate the second law of thermodynamics, as the overall combined system still sees entropy increase. This discovery offers new insights into the foundations of quantum mechanics and its relationship with thermodynamics, particularly in understanding the flow of time at the quantum level.
Hans Bethe, renowned for calculating stellar energy production, surprisingly found success by applying simplifying assumptions to complex quantum problems. He tackled seemingly intractable calculations, like the splitting of energy levels in magnetic fields (Zeeman effect) and the behavior of crystals, by focusing on the most dominant interactions and ignoring smaller effects. This approach, though approximate, often yielded surprisingly accurate and insightful results, showcasing Bethe's knack for identifying the essential physics at play. His ability to "see through" complicated equations made him a pivotal figure in 20th-century physics, influencing generations of scientists.
Hacker News users discussed Bethe's pragmatic approach to physics, contrasting it with more mathematically driven physicists. Some highlighted his focus on getting usable results and his ability to simplify complex problems, exemplified by his work on the Lamb shift and stellar nucleosynthesis. Others commented on the article's portrayal of Bethe's personality, describing him as humble and approachable, even when dealing with complex subjects. Several commenters shared anecdotes about Bethe, emphasizing his teaching ability and the impact he had on their understanding of physics. The importance of approximation and "back-of-the-envelope" calculations in theoretical physics was also a recurring theme, with Bethe presented as a master of these techniques.
A 1923 paper by John Slater, a young American physicist, introduced the idea of a virtual radiation field to explain light-matter interactions, suggesting a wave-like nature for electrons. While initially embraced by Bohr, Kramers, and Slater as a potential challenge to Einstein's light quanta, subsequent experiments by Bothe and Geiger, and Compton and Simon, disproved the theory's central tenet: the lack of energy-momentum conservation in individual atomic processes. Although ultimately wrong, the BKS theory, as it became known, stimulated crucial discussions and further research, including important contributions from Born, Heisenberg, and Jordan that advanced the development of matrix mechanics, a key component of modern quantum theory. The BKS theory's failure also solidified the concept of light quanta and underscored the importance of energy-momentum conservation, paving the way for a more complete understanding of quantum mechanics.
HN commenters discuss the historical context of the article, pointing out that "getting it wrong" is a normal part of scientific progress and shouldn't diminish Bohr's contributions. Some highlight the importance of Slater's virtual oscillators in the development of quantum electrodynamics (QED), while others debate the extent to which Kramers' work was truly overlooked. A few commenters express interest in the "little-known paper" itself and its implications for the history of quantum theory. Several commenters also mention the accessibility of the original article and suggest related resources for further reading. One commenter questions the article's claim that Bohr's model didn't predict spectral lines, asserting that it did predict hydrogen's spectral lines.
Summary of Comments ( 81 )
https://news.ycombinator.com/item?id=43072483
HN users express skepticism about the press release's interpretation of the research, questioning whether the "two arrows of time" are a genuine phenomenon or simply an artifact of the chosen model. Some suggest the description is sensationalized and oversimplifies complex quantum behavior. Several commenters call for access to the actual paper rather than relying on the university's press release, emphasizing the need to examine the methodology and mathematical framework to understand the true implications of the findings. A few commenters delve into the specifics of microscopic reversibility and entropy, highlighting the challenges in reconciling these concepts with the claims made in the article. There's a general consensus that the headline is attention-grabbing but potentially misleading without deeper analysis of the underlying research.
The Hacker News post titled "Opposing arrows of time can theoretically emerge from certain quantum systems" linking to a Surrey University news article about a physics paper, has generated a moderate discussion with a mix of skepticism, attempts at understanding, and tangential explorations.
Several commenters express skepticism about the practical implications or the interpretability of the research. One commenter points out the frequent use of "could" and "may" in the article, suggesting a lack of strong conclusions. Another questions the meaningfulness of the findings, asking whether they represent anything more than mathematical curiosities. A further commenter highlights the distinction between theoretical possibilities and experimental verification, implying the reported work is still far from practical relevance.
Some commenters attempt to grasp the core concepts of the research. One asks for clarification on the relationship between the described quantum system and a closed system, a crucial element in discussions of entropy and the arrow of time. Another commenter asks for a simplified explanation, acknowledging the complexity of the topic. This demonstrates a desire within the community to understand the science despite its inherent difficulty.
A few comments drift towards related topics, showcasing the diverse interests sparked by the original post. One commenter notes the prevalence of "two-time physics" in science fiction, touching upon the cultural fascination with temporal manipulation. Another thread discusses the concept of retrocausality, a distinct but related idea that explores the possibility of future events influencing the past. This tangent reveals the broader philosophical implications of time's directionality and our understanding of causality.
Finally, some comments express a general appreciation for theoretical physics, even without fully grasping the specifics of the research. These commenters acknowledge the importance of exploring fundamental questions about the universe, recognizing the value of such investigations even in the absence of immediate practical applications.
Overall, the comments section reflects a mixed reaction to the reported research. While some express excitement and curiosity, others remain skeptical. The discussion highlights the challenges of communicating complex scientific concepts to a broad audience while simultaneously demonstrating the public's enduring fascination with the mysteries of time and the quantum realm.