Dropping an egg on its side significantly increases its chances of surviving a fall, according to physics simulations. The curved shape of the egg distributes the impact force over a larger area than if it landed on one end, reducing pressure and the likelihood of cracking. Specifically, the side-landing allows the egg to rotate, further dissipating energy and lessening the shock. While cushioning materials are typically used in egg drop experiments, this research suggests the egg's shape itself can be exploited for protection.
Earth experiences two high-tide bulges, one directly facing the Moon and another on the opposite side. The bulge facing the Moon is caused by the Moon's gravitational pull being strongest on that side, pulling the water towards it. The opposite bulge is a result of inertia. The Moon's gravity also pulls on the Earth itself, and this pull is stronger on the side closer to the Moon. This difference in gravitational pull effectively stretches the Earth, causing the ocean on the far side to bulge outwards as if being flung away. So, while the near-side bulge is due to direct gravitational attraction, the far-side bulge is due to the residual effect of the Earth being pulled towards the Moon more strongly on the near side.
Hacker News users discuss the physics behind the double-bulge high tide phenomenon, generally agreeing with the Stack Exchange explanation. Some emphasize the importance of frames of reference, pointing out that the bulge opposite the moon is due to inertia in a rotating frame, effectively being "left behind" as the Earth and Moon orbit their barycenter. Several commenters use analogies, like swinging a bucket of water or a hula hoop, to visualize the forces at play. One clarifies the common misconception that the far-side bulge is solely due to the moon's gravity "pulling the Earth away from the water," explaining it's a combination of inertial effects and the gradient of the gravitational field. Some also discuss how the sun's gravity contributes to tides and the complexities of real-world tides beyond the simplified model.
John Baez's post explains that the common notion of black holes shrinking due to Hawking radiation is a simplification. While Hawking radiation exists, it's emitted by the hot "quantum atmosphere" surrounding the black hole, not the singularity itself. This atmosphere is formed from infalling matter interacting with intense spacetime curvature. The black hole's mass, contained within its event horizon, only decreases because this infalling matter effectively loses some energy as Hawking radiation before crossing the horizon. Therefore, it's more accurate to say the black hole's atmosphere radiates and shrinks as it loses energy, indirectly causing the enclosed black hole to shrink over vast timescales.
Hacker News users discuss the surprising assertion that dead stars don't radiate, focusing on the definition of "dead" in this context. Several point out that even black dwarfs, the theoretical endpoint of stellar evolution, would still emit some radiation due to Hawking radiation, though at an incredibly low temperature and over vast timescales. The discussion also touches on the complexities of heat death, the challenges of simulating such long-term processes, and the limitations of current scientific understanding regarding proton decay and other long-term phenomena. Some users highlight the immense timescales involved, emphasizing the difference between theoretical predictions and observable reality. Others express fascination with the concept and appreciate the thought-provoking nature of the article.
Ocean tides are primarily caused by the gravitational pull of the Moon and, to a lesser extent, the Sun. The Moon's gravity creates bulges of water on both the side of Earth facing the Moon and the opposite side. As Earth rotates, these bulges move around the planet, causing the cyclical rise and fall of sea levels we experience as tides. The Sun's gravity also influences tides, creating smaller bulges. When the Sun, Earth, and Moon align (during new and full moons), these bulges combine to produce larger spring tides. When the Sun and Moon are at right angles to each other (during first and third quarter moons), their gravitational forces partially cancel, resulting in smaller neap tides. The complex shapes of ocean basins and coastlines also affect the timing and height of tides at specific locations. Friction between the tides and the ocean floor gradually slows Earth's rotation, lengthening the day by a very small amount over time.
HN users discuss the complexities of tidal forces and their effects on Earth's rotation. Several highlight that the simplified explanation in the linked NASA article omits crucial details, such as the role of ocean basin resonances in amplifying tides and the delayed response of water to gravitational forces. One commenter points out the significant impact of the Moon's gravity on Earth's angular momentum, while another mentions the long-term slowing of Earth's rotation and the Moon's increasing orbital distance. The importance of considering tidal forces in satellite orbit calculations is also noted. Several commenters share additional resources for further exploration of the topic, including links to university lectures and scientific papers.
This blog post explores creating spirograph-like patterns by simulating gravitational orbits of multiple bodies. Instead of gears, the author uses Newton's law of universal gravitation and numerical integration to calculate the paths of planets orbiting one or more stars. The resulting intricate designs are visualized, and the post delves into the math and code behind the simulation, covering topics such as velocity Verlet integration and adaptive time steps to handle close encounters between bodies. Ultimately, the author demonstrates how varying the initial conditions of the system, like the number of stars, their masses, and the planets' starting velocities, leads to a diverse range of mesmerizing orbital patterns.
HN users generally praised the Orbit Spirograph visualization and the clear explanations provided by Red Blob Games. Several commenters explored the mathematical underpinnings, discussing epitrochoids and hypotrochoids, and how the visualization relates to planetary motion. Some users shared related resources like a JavaScript implementation and a Geogebra applet for exploring similar patterns. The potential educational value of the interactive tool was also highlighted, with one commenter suggesting its use in explaining retrograde motion. A few commenters reminisced about physical spirograph toys, and one pointed out the connection to Lissajous curves.
This paper explores the implications of closed timelike curves (CTCs) for the existence of life. It argues against the common assumption that CTCs would prevent life, instead proposing that stable and complex life could exist within them. The authors demonstrate, using a simple model based on Conway's Game of Life, how self-consistent, non-trivial evolution can occur on a spacetime containing CTCs. They suggest that the apparent paradoxes associated with time travel, such as the grandfather paradox, are avoided not by preventing changes to the past, but by the universe's dynamics naturally converging to self-consistent states. This implies that observers on a CTC would not perceive anything unusual, and their experience of causality would remain intact, despite the closed timelike nature of their spacetime.
HN commenters discuss the implications and paradoxes of closed timelike curves (CTCs), referencing Deutsch's approach to resolving the grandfather paradox through quantum mechanics and many-worlds interpretations. Some express skepticism about the practicality of CTCs due to the immense energy requirements, while others debate the philosophical implications of free will and determinism in a universe with time travel. The connection between CTCs and computational complexity is also raised, with the possibility that CTCs could enable the efficient solution of NP-complete problems. Several commenters question the validity of the paper's approach, particularly its reliance on density matrices and the interpretation of results. A few more technically inclined comments delve into the specifics of the physics involved, mentioning the Cauchy problem and the nature of time itself. Finally, some commenters simply find the idea of time travel fascinating, regardless of the theoretical complexities.
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https://news.ycombinator.com/item?id=44104832
Hacker News users generally agreed with the article's premise that dropping an egg on its side distributes the force more evenly, increasing the chances of survival. Several commenters shared their own egg-drop experiment experiences, emphasizing the importance of proper padding and the sometimes unpredictable nature of such experiments. Some debated the merits of different padding materials, with mentions of Styrofoam peanuts, bubble wrap, and even Jell-O. A few users pointed out the real-world applications of these principles in packaging design and impact absorption. One commenter offered a counterintuitive approach, suggesting dropping the egg from a very short distance to minimize impact force, regardless of orientation. Others discussed the importance of considering the egg's center of gravity and the potential for cracks to propagate even with seemingly successful landings.
The Hacker News post titled "The key to a successful egg drop experiment? Drop it on its side" referencing an Ars Technica article on the same topic, has generated several comments. Many of the commenters discuss their own experiences with egg drop experiments, offering various strategies and reflecting on the physics involved.
A recurring theme is the importance of distributing the impact force. Several users echo the article's point about dropping the egg on its side, emphasizing that this maximizes the surface area absorbing the impact and reduces the pressure on any single point of the eggshell. One commenter draws a parallel to landing a spacecraft on its side, while another highlights the similar principle behind crumple zones in cars.
Another significant discussion thread revolves around different cushioning materials and designs. Commenters mention using straws, cotton balls, bubble wrap, and even pantyhose, discussing the advantages and disadvantages of each. Some describe elaborate constructions, while others advocate for simpler solutions. There's some debate about the optimal balance between minimizing weight and maximizing impact absorption.
Beyond the practical aspects of egg drop experiments, some commenters delve into the theoretical physics. They discuss concepts such as impulse, momentum, and the mechanics of brittle fracture. One commenter points out the role of the egg's internal structure in absorbing some of the shock. Another explains how the shape of the egg affects its resistance to cracking.
A few commenters share anecdotal stories of their successes and failures in egg drop competitions. One user recounts a winning strategy involving suspending the egg within a container using rubber bands. Another laments a loss despite meticulous planning. These anecdotes add a personal touch to the discussion and illustrate the challenges and rewards of the egg drop experiment.
Finally, some comments touch upon the educational value of such experiments, emphasizing their ability to engage students in STEM principles in a fun and practical way. One commenter suggests that the egg drop experiment is a classic example of engineering problem-solving.
Overall, the comments on the Hacker News post offer a diverse range of perspectives on the egg drop experiment, from practical tips and personal experiences to theoretical discussions and reflections on the educational value of the challenge.