Some will know from their childhood; some were not born yet.

If you were one of those who "were not born yet," then you probably don't have the Konami cheat code memorized ( ↑ ↑ ↓ ↓ ← → ← → B A ). Use the arrow keys and the actual B and A keyboard letters and enter the code anytime you're inside Universe Sandbox. A Wikipedia article about the Konami code will pop up in the side menu, as will the "achievement unlocked" box the first time you enter the code. I've noticed other games with cheat-code related achievements also use the Konami code, so it's worth memorizing for the sake of unlocking future Steam achievements.

Result of millions of years of computation.

It's a reference to the canon of a famous satirical sci-fi novel called The Hitchhiker's Guide to the Galaxy by Douglas Adams. Long story short, mankind constructs a sophisticated AI to solve the Ultimate Question: "What is the answer to life, the universe, and everything?" Centuries and millenia pass while the AI pours its entire processing power into researching the answer. Finally, almost at the end of time itself, the AI discovers the answer: 42.

Simply press the keys "4" and "2" anytime you have the Universe Sandbox window selected. A list of Wikipedia articles related to Hitchhiker canon will appear in the side menu and the "achievement unlocked" box will pop up the first time you try this.

These cheats may seem incredibly obvious to a lot of you (either before or after you read this guide), but according to Google results for these cheats, people on other forums tend to guess all over the place especially on the Answer achievement (such as exactly how the game expected you to use the number 42). I figured it'd be nice to have the verified solutions concisely recorded in one spot. Not every gamer is familiar with either the Konami code or Hitchhiker's Guide, nor are they expected to be, and that's why this guide exists. Enjoy achievement-hunting in Universe Sandbox!