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Universe Sandbox is a paid space-physics simulator by Giant Army, sold on Steam for Windows, Mac and Linux (and in VR). There is no official free version, no browser version and no official Android or iOS app, so a search for "Universe Sandbox free" or "Universe Sandbox online" cannot be answered with the real game. What you can play on this page, free and without a download, is a browser space sandbox with the same core idea: build a cosmic body from almost nothing, grow it, and watch gravity do the rest. This page explains what the real Universe Sandbox is, what the free alternative here does and does not do, and which one fits what you are looking for.
What is playable on this page
The game in the frame above is myDream Universe, a free browser game (its own page with a full guide goes live on this site on 9 September in the simulation games category). You start as an asteroid, absorb rocks, moons and planets that are smaller than you, avoid anything larger, and climb through the stages: moon, planet, gas giant, star, neutron star and finally a black hole. It runs in Chrome, Safari, Firefox and Edge on desktop and on phones, and it needs nothing installed. It is a sandbox in the sense that there is no timer and no score to chase; it is not a physics simulation of the real solar system. Press Play, wait a few seconds for it to load, and steer with the mouse or your finger.
What Universe Sandbox actually is
Universe Sandbox (the current version was released as Universe Sandbox 2 and later renamed) simulates gravity, collisions, climate and stellar evolution with real physics. You can drop a second moon into Earth's orbit and watch the tides change, fire a planet into the Sun, raise a star's temperature and see oceans boil, or fast-forward billions of years. It is built by Giant Army in Seattle, updated regularly, and it is a desktop application: you buy it on Steam and install it. There is no legitimate way to play it in a browser, and sites that promise "Universe Sandbox online free" are either serving a different game, as this page did before it was rewritten, or something you should not download.
Universe Sandbox versus the free alternative
Physics. Universe Sandbox: real n-body gravity, climate, collisions and time scales. myDream Universe: simple absorb-or-be-absorbed rules with a light gravity pull from larger bodies. Freedom. Universe Sandbox: place anything anywhere, change mass, temperature and speed, run any scenario. myDream Universe: one body, one goal, grow. Price and platform. Universe Sandbox: paid, PC/Mac/Linux and VR. myDream Universe: free, any browser, mobile included. Time. Universe Sandbox rewards hours; the browser game is a ten-to-twenty-minute run. If you want to learn what a Roche limit is, buy Universe Sandbox. If you want the feeling of growing a planet on a phone in a break, play the game above.
Free alternatives that are closer in spirit
On this site: Solar Smash (planet destruction with 34 weapons, the closest thing to Universe Sandbox's collision scenarios), Spaceflight Simulator (build rockets and reach orbit with real orbital mechanics), mySolar (build a solar system and defend it) and Drop Planets (merge planets into a sun), all being added to the site this week. All free, all in the browser. See the simulation games category for more.
How to play the browser game on this page
Click Play. Move the mouse or drag on a phone; your body drifts in that direction. Touch anything smaller to absorb it and gain mass; touch anything larger and you are absorbed and restart. Start with the smallest debris near you, sweep through clusters rather than chasing single pieces, and give large bodies a wide margin because their pull is stronger than it looks. Once you pass moon size the growth accelerates, and the late stages (star, black hole) are relaxed and mostly about seeing how far the scale goes. A full myDream Universe guide, with the stages and the mistakes that end runs early, is published on 9 September.
Universe Sandbox FAQ
Is Universe Sandbox free?
No. It is a paid game on Steam. Prices change with sales; check the Steam page for the current one. There is no free edition.
Can I play Universe Sandbox online without downloading?
No. It is a desktop application. The free browser game on this page is an alternative, not Universe Sandbox.
Is Universe Sandbox on mobile?
There is no official Android or iOS version. Apps using the name on mobile stores are not from Giant Army.
Is there a Universe Sandbox 2 and a Universe Sandbox 3?
Universe Sandbox 2 was the name of the current version at launch; it has since been renamed Universe Sandbox and keeps receiving updates. There is no Universe Sandbox 3.
Does it work on Chromebook?
Universe Sandbox does not (no Chrome OS build). The browser alternative on this page does.
What are the system requirements?
Giant Army lists them on the Steam page; a 64-bit system with a dedicated GPU is recommended for the larger simulations. The browser game here runs on any recent device.
This page was rewritten on 8 September 2026 to describe accurately which game is embedded. Solar-Smash.io is an independent site and is not affiliated with Giant Army or Universe Sandbox.