General Questions

What is Universe Sandbox ²?

Universe Sandbox ² is a complete rewrite of the original and has been in development since fall 2011.

It is no longer a one-person project; the new team has added a dedicated physics programmer, astrophysicist, climate scientist, graphics programmer, code architect, and technical artist to bring all of the pieces together.

Learn more about Universe Sandbox ².

When will it be available?

Universe Sandbox ² is now available for PC, Mac, and Linux:

Buy Universe Sandbox ² on Steam or
Buy Universe Sandbox ² on our website

Universe Sandbox ² is in Early Access development.

What does "Early Access" mean?

Universe Sandbox ² is Early Access software. We have many fixes and improvements planned. You, the Early Access user, will help us uncover bugs and highlight areas for improvement. Buying-in early means you won't have to wait to explore the many new and exciting features that are already in place. Just know that all of the final polish isn't quite there yet.


Learn more on our Steam page.

What platforms does Universe Sandbox ² run on?

Windows, Mac OS X, and Linux/Steam OS.

Where can I buy the soundtrack?

The original soundtrack is composed by Ryan Macoubrie. It is still a work in progress.


We plan to offer the soundtrack for sale separately from Universe Sandbox ², but we can't yet say when it'll be available.

Wasn't the new version going to be called Universe Sandbox 3?

For a time we called it Universe Sandbox 3, but we've decided it will be less confusing for most users to call it Universe Sandbox ².


Thanks for being dedicated fans who are paying enough attention to realize the inconsistency here. Hopefully everything is now clear.

System Requirements

Minimum requirements for running Universe Sandbox ²:


  • Graphics:
    • DirectX9.0c (Windows) or OpenGL (Mac, Linux)
    • 512MB Video Memory
    • Shader Model 3.0
  • System:
    • 1.6GHz dual core
    • 1GB RAM
    • 1GB free disk space
    • Windows XP+, Mac OS X 10.7+, Ubuntu 12.04+, SteamOS+


Recommended: 1GB Video Memory, 2.6 GHZ quad-core, 4GB RAM

What's New &

What's Planned

What new features are in Universe Sandbox ²?

Some of the new features include:

  • Climate simulation
  • Advanced collision simulation
  • Dynamic soundtrack and sound effects
  • Stellar evolution and supernovae
  • Terraforming
  • Material & composition simulation
  • Animated star surfaces and solar flares
  • Light-warping black holes
  • Dark matter
  • Procedural surfaces and planets

Learn more about what's new in Universe Sandbox ².

Will there be a mobile version?

Maybe. We'd love to make a mobile version, but if it happened, development wouldn't begin until after the final release for PC, Mac, and Linux.

Will there be a free version?

We're discussing the possibility of a feature-limited version, but not until after the initial release.

Will it support other languages beyond English?

We are currently working on language localization. Learn more on our blog.

Will you be able to simulate evolution/life on planets?

We plan to incorporate very basic support for "life." Essentially, given the right conditions — temperature, atmosphere, water, etc. — life may grow on planets. Greater complexity may be developed in the future, but it's a long way off.

Will there be support for Steam Workshop?

We plan to add support for Steam Workshop that will, in the least, allow for sharing user-created simulations.

How about modding?

Making it easy for the community to create mods is a great idea. "Light" modding will hopefully be available by final release, with more extensive modding possibilities made possible later on.

Universe Sandbox ²

Questions about use of Universe Sandbox ² coming soon.


For technical issues, please see our Support page.

Simulation Questions

How realistic are the physics in Universe Sandbox ²?

Unlike many other games and simulators, Universe Sandbox ² actually simulates gravity, temperature, and climate for various bodies. Many aspects are kept relatively 'simple' in order for it to run in real time on a modern desktop, but we strive to keep the results as realistic as possible.


The physics in Universe Sandbox ² is completely custom. Thomas, our physics programmer, discusses at length various aspects of the physics implementation on his YouTube channel.


What is "time step" in Universe Sandbox ²?

As a realistic physics simulator, Universe Sandbox ² performs calculations in order to advance each frame. It looks at how each object moves in relation to every other object, then calculates where they will be after a certain amount of elapsed time.


This amount of time is the time step.


A simulation running in "real time" would have a time step of one simulated second per one real time second.


An appropriate time step depends on what you are trying to see and what simulation is running. Because of the large scale of the universe, many simulations are better seen at higher time steps. For example, in order to watch the seasons change on Earth, you may want to run your simulation at a time step of one simulated month per one real time second. This means that a simulated year will pass every 12 seconds, making it much easier to observe long-term change.


Why can't I increase the time step as high as I want to?

Short answer: In Universe Sandbox ², the time step automatically slows down in order to maintain accuracy. You can adjust this accuracy in Sim Settings.


The less accurate it is, the faster it can run, but the likelier it is that errors will add up and orbits will fall apart.


Long answer: Let's say the time step calls for advancing the simulation one year every frame. Depending on a few factors, this may not be something the simulation can do in a single calculation, while still maintaining accuracy.


But maybe it can maintain enough accuracy if, instead, it takes smaller steps of one month per frame. It then has to make 12 such calculation-heavy steps to advance the whole year. This effectively lowers the time step.


When you increase the time step, you're actually increasing the target time step. This is how fast you are asking the simulation to run. The actual time step, which is shown in the toolbar, will likely not be able to reach this target sooner or later. Its limit is affected by the number of objects being simulated, whether or not there are collisions, and also your hardware.


If you'd prefer speed over accuracy, you can lower the accuracy of the simulation in Sim Settings.

Legal Questions

Can I create content with Universe Sandbox ² for use in other products?

Yes, you may use screenshots and video from Universe Sandbox ² for use in other works/products.


Please see Usage for full details.

Other Applications

Are there other programs like Universe Sandbox ²?

TestTubeGames' Gravity Simulator

  • Fling Planets or redefine the formula for gravity in this easy-to-use 2D simulator.

Pixel Gravity

  • Gravity simulator with both a free trial and full version for Windows PCs.
  • Extremely impressive feature list and comprehensive simulator.

Gravity Simulator

  • An n-body simulator similar in concept to Universe Sandbox and capable of scale simulations of our Solar System.
  • Using the rotating frame feature, you can easily study the complex orbital relationship between the various moons of Saturn, or the relationship between Earth's orbit and the horseshoe orbit of 3753 Cruithne, an asteroid often referred to as "Earth's 2nd moon".
  • It also includes some advanced features for recording data that can be graphed in a spreadsheet app.
  • Gravity Simulator is for Windows PCs.


  • A gravity simulator available for both Mac and Windows as a 15 day trial.
  • Uses Newton's Law of Gravitation to run scale simulations of our Solar System.

Milky Way

  • An astrophysical sandbox game in early development.
  • "Incorporates real observational data and accurate theoretical models to predict various phenomena such as planetary impact, spaghettification and gravitational redshift around a black hole."
  • Free demo available for Windows PCs.




  • Free, realistic space flight and gravity simulation program for Windows PCs.
  • Explore the solar system in realistic and fictional spacecraft.

Kerbal Space Program

  • Build your own rockets, launch them, crash them, land on the moon.
  • Not a full gravity simulator as only one planet or moon acts on the spacecraft at a time, but still really great.


Are there other physics sandboxes?


  • Physics based 2D sandbox (for things here on Earth).
  • Commercial software for Windows and Mac OS X.

Garry's Mod

  • Physics based 3D sandbox (for human sized objects).
  • It's a game Windows and Mac.


  • A simple gravity simulator that's more aesthetic than representative of reality.
  • Runs under Linux, Windows and Mac OS X.


What are some astronomy apps that don't simulate gravity?


  • A space simulator that lets you explore our universe in three dimensions (but it's not interactive and doesn't simulate gravity).
  • All movement in Celestia is seamless and you can zoom from the Earth to the edge of our Galaxy.
  • Celestia runs on Windows, Linux, and Mac.


  • From the creator of Celestia, an easy to use and beautiful solar system visualization tool for Mac OS and iOS.

Eyes on the Solar System

  • Our solar system and NASA mission data.
  • Runs in a browser.
  • Created by JPL & NASA.

Digital Universe

  • A free program from Hayden Planetarium for Windows, Mac, Linux, and IRIX.
  • Includes data on thousands of stars and galaxies.
  • This is not a gravity simulator, only a viewer.

Space Engine

  • Free simulator with both real and procedural content allowing unlimited exploration of our galaxy.


  • 3D space simulation with lots of great visuals.


  • Free planetarium for your computer (not a gravity simulator).
  • Runs under Linux, Windows and Mac OS X.

Explore the Solar System

  • Solar system 3D exploration tool developed in the Unreal 3D engine.


  • Tools for creating sci-fi space maps.


  • An iOS app by Casey Donnellan for iPhone and iPad.
  • Teaches players about the "Goldlocks Zone."
  • Uses a real climate model to determine Earth's average temperature.


What about electrostatic simulations?

I know of nothing as full featured as Universe Sandbox, but a user sent me links to these:

Electrostatic Fields Applet

  • Free and easy to use.

Electrostatics 3D

  • Expensive and designed for education specifically.


Atom visualizations?

Atomic Dashboard

  • Chemistry resource and visualization tool.
  • Mac only.

Atom in a Box

  • Easy to use visualization tool for iOS (iPhone & iPad).


And life simulation?

Species: Artificial Life, Real Evolution

  • A realistic evolution simulator.
  • Free alpha versions.

Purchase & Installation

I purchased Universe Sandbox ² through the Steam Store and need help with my order.

Please contact Steam.

I bought Universe Sandbox ² from your website. Where is my code?

You should receive an email from Humble Bundle shortly after receiving payment confirmation. This email will link you to a key page with your Steam code.


If you did not receive an email, try using the Humble Bundle key resender:


Make sure it is not being sorted into your spam box.


If you still have not received an email, please contact us.

I clicked on the link in the Humble Bundle email. Now what?

Click the Steam button at the top of your Humble key page to generate your Steam code.


Open the Steam application and log in. Click the "+ ADD A GAME…" button in the bottom left-hand corner. Select "Activate a Product on Steam..." When it asks for a Product Code, enter the Steam code from your Humble key page.


For detailed step-by-step instructions, check out Humble Bundle's support page.

Do I need Steam in order to install and run Universe Sandbox ²?

Yes, you will need the free Steam app and account. You can download Steam and create an account on their site:


We have not yet decided whether or not we will release a DRM-free version along with the final Steam release. It's a strong possibility that we will, but as it stands, Steam provides the easiest and most efficient platform for distribution and updates.

What is Steam?

Steam is a digital distributor and publisher of video games and other software. For developers, it provides an efficient platform for all steps of distribution. It makes it easy to implement anti-piracy tools, connect with users, and release frequent updates.


For players, it makes it easy to access a large catalog of games and organize them in a single spot, as well as receive updates automatically. It is also host to a large and vibrant community of gamers. You can read more about Steam on their site:


How much does Universe Sandbox ² cost?

Individuals, Teachers, Schools, & Non-Profits

  • Instant access to the Early Access version of Universe Sandbox ² is $24.99 USD.
  • There are currently no educational discounts for Universe Sandbox ², and future plans for discounts have not yet been determined. Universe Sandbox Legacy is free for all schools.

Commercial & For-Profit

  • A special license is required for using images or video created with Universe Sandbox ². Please contact sales to inquire about a commercial license.

If I buy the Early Access version now do I have to buy Universe Sandbox ² again when the final version is released?

No, a single purchase gives you instant access to the Early Access version plus a pre-order for the final release. You will receive updates along the way as we continue development.

Will Universe Sandbox ² become more/less expensive as development continues?

It's possible the price will change in the future, but we have no plans to change it at this time.

If I bought Universe Sandbox Legacy will I receive Universe Sandbox ² for free?

No, Universe Sandbox ² is not just an upgrade, it's a completely new product. You can read more about why in this post.

Do I need a special license to use screenshots and video generated with Universe Sandbox ² for commercial purposes?

  • Yes. Please contact sales to inquire about a commercial license.
  • Using video or images for non-commercial or educational use is encouraged and doesn't require a license. Please credit Universe Sandbox ² and include a link back to

Universe Sandbox Legacy

When was Universe Sandbox Legacy first released?

Universe Sandbox Legacy was originally released in 2008 with a major update released in 2010.


Read the FAQ about the 2008 and 2010 versions.