The weak nuclear force's short range is due to its force-carrying particles, the W and Z bosons, having large masses. Unlike the massless photon of electromagnetism which leads to an infinite-range force, the hefty W and Z bosons require significant energy to produce, a consequence of Einstein's E=mc². This large energy requirement severely limits the bosons' range, confining the weak force to subatomic distances. The Heisenberg uncertainty principle allows these massive particles to briefly exist as "virtual particles," but their high mass restricts their lifespan and therefore the distance they can travel before disappearing, making the weak force effectively short-range.
The blog post by Professor Matt Strassler, titled "Why the Weak Nuclear Force is Short Range," delves into the fundamental reasons behind the extremely limited reach of the weak nuclear force, a force responsible for radioactive decay and crucial for processes like nuclear fusion in the sun. Unlike electromagnetism, whose influence extends infinitely outwards, the weak force is confined to subatomic distances, acting only within the nucleus of an atom. This distinction arises from the nature of the force-carrying particles involved.
Electromagnetism is mediated by photons, particles with zero mass. This massless nature allows photons to travel unimpeded across vast distances, resulting in the long-range nature of electromagnetic interactions. The weak force, however, is mediated by particles called W and Z bosons. These bosons, unlike photons, are extremely massive, approximately 80 to 90 times heavier than a proton. This substantial mass has profound implications for the range of the weak force.
According to the Heisenberg uncertainty principle, there's an inherent uncertainty in both the energy and lifespan of a particle. For particles like the W and Z bosons, their immense mass translates into a correspondingly large energy uncertainty. This large energy fluctuation permits their existence for only incredibly brief periods, even when seemingly at rest. Because their lifespan is so fleeting, these bosons can only travel extremely short distances before decaying back into other particles. This inherent limitation on their lifespan and travel distance directly translates to the short-range nature of the weak force.
The post further elucidates this concept by using an analogy. Imagine trying to throw a heavy medicine ball versus a light tennis ball. The heavy medicine ball, analogous to the massive W and Z bosons, requires significant energy to throw and travels a much shorter distance before falling to the ground. Conversely, the light tennis ball, representing the massless photon, can be thrown with less energy and travels a much greater distance.
Furthermore, the post emphasizes that the mass of the W and Z bosons isn't just an arbitrary property. It's a consequence of the Higgs mechanism, a fundamental aspect of the Standard Model of particle physics. The Higgs field, pervading all of space, interacts with the W and Z bosons, effectively "slowing them down" and imparting them with mass. This interaction with the Higgs field is what ultimately dictates the mass of these particles and, consequently, the short-range character of the weak nuclear force. In essence, the weak force is short-ranged because the particles that carry it are heavy, and their heaviness is a direct result of their interaction with the omnipresent Higgs field.
Summary of Comments ( 60 )
https://news.ycombinator.com/item?id=42669906
HN users discuss various aspects of the weak force's short range. Some highlight the explanatory power of the W and Z bosons having mass, contrasting it with the massless photon and long-range electromagnetic force. Others delve into the nuances of virtual particles and their role in mediating forces, clarifying that range isn't solely determined by particle mass but also by the interaction strength. The uncertainty principle and its relation to virtual particle lifetimes are also mentioned, along with the idea that "range" is a simplification for complex quantum interactions. A few commenters note the challenges in visualizing or intuitively grasping these concepts, and the importance of distinguishing between force-carrying particles and the fields themselves. Some users suggest alternative resources, including Feynman's lectures and a visualization of the weak force, for further exploration.
The Hacker News post titled "Why the weak nuclear force is short range" linking to an article by Professor Matt Strassler has generated several comments discussing various aspects of particle physics and the weak force.
A recurring theme is the explanation of the weak force's short range due to the large masses of the W and Z bosons, which mediate the interaction. Commenters delve into the details of this mechanism, emphasizing the role of the Heisenberg uncertainty principle in allowing for the temporary existence of these massive virtual particles and how their limited lifespan translates to the short range of the force. Some comments highlight the difference between this and the electromagnetic force, mediated by massless photons, resulting in its infinite range.
Several commenters praise the clarity and accessibility of Professor Strassler's explanations. They appreciate his ability to break down complex concepts into understandable terms, making the topic approachable even for those without a deep physics background. One commenter specifically points out the helpfulness of the analogies used in the article.
The discussion also touches upon related concepts, such as virtual particles, quantum field theory, and the electroweak unification. Commenters offer additional insights and explanations of these ideas, expanding upon the information presented in the article. One commenter mentions the importance of considering the weak force not as a force but as an interaction, reflecting the modern understanding within the framework of quantum field theory. Another commenter corrects a common misconception about virtual particles, emphasizing that they are not simply mathematical tools but are an integral part of the current understanding of quantum fields.
There's a brief exchange regarding the nature of force carriers and their role in mediating interactions. One commenter asks for clarification on the relationship between the weak force, W and Z bosons, and radioactivity, prompting another commenter to provide a concise explanation.
Finally, there are comments discussing resources for further learning about particle physics, including recommendations for books and websites. One commenter suggests a specific book known for its clear explanations of the Standard Model. Another highlights the value of Professor Strassler's website as a resource for understanding particle physics.