June 9, 2026
Big gravity, bigger comment drama
Show HN: Gravity – interactive solar-system simulator, from Newton to Einstein
A gorgeous space toy wins hearts, sparks nitpicks, and gets roasted over giant North America
TLDR: Gravity is a slick interactive demo that explains how the Sun and Earth pull on each other and builds up to bigger ideas about space. People loved how fun and kid-friendly it feels, but the comments quickly turned into a mix of mobile complaints, science nitpicks, and jokes about a cartoonishly expanding North America.
A new Show HN project called Gravity set out to do something delightfully ambitious: turn the story of gravity into an interactive, swipeable solar-system experience that walks people from Newton’s simple “things pull on each other” idea to Einstein’s bigger-picture view of space. But in classic internet fashion, the real fireworks weren’t just in the simulator — they were in the replies.
The loudest vibe was “this is cool, but…” One commenter said it was so fun they wanted to show it to their kids, which is basically the gold medal for a science demo. Another praised the look of it right away. But the compliments came with instant side-eye: on mobile, one user complained a pop-up blocks a quarter of the screen, including the Sun itself, which is a hilariously bad place for a space app to hide. Then came the accuracy police. One commenter zeroed in on the Einstein mention and immediately asked how the creator handles the messy real-world effects that happen when gravity gets more complicated. Another called one section misleading, arguing the animation shows a super-slow change that takes about 26,000 years, not a single day.
And yes, the thread delivered jokes. The funniest dunk was about the app showing Earth being built by gravity, except North America apparently keeps getting bigger and bigger as the planet forms. So the verdict? The community seems charmed, picky, amused, and extremely ready to fact-check the cosmos.
Key Points
- •The article introduces Gravity as an interactive solar-system simulator with a guided tour.
- •Its first lesson defines gravity as attraction between any two masses using the formula F = G · m₁·m₂ / r².
- •A two-body example shows gravitational forces as equal and opposite, in line with Newton’s 3rd law.
- •The example states the force involved is about 3.5 × 10²² newtons.
- •The article explains that because the Sun is about 333,000 times more massive than Earth, the same force barely moves the Sun but strongly affects Earth’s motion.