A Brief History of Time

Principais ideias

• Espaço e tempo estão entrelaçados, e a massa os curva como um peso sobre um lençol
• O universo está em expansão, o que indica que começou em um estado quente e denso
• A relatividade rege o muito grande e a mecânica quântica, o muito pequeno
• Buracos negros não são totalmente negros; eles emitem radiação e podem evaporar aos poucos
• O tempo tem uma direção porque a desordem aumenta, e é por isso que lembramos do passado

Dentro deste bit

1. O universo em palavras simples

   A scientist gives a public lecture on astronomy and an elderly listener insists the world rests on the back of a giant turtle. Asked what the turtle stands on, she replies that it is turtles all the way down.

2. Space and time bend

   For centuries, people thought of time as a universal clock ticking the same everywhere. Einstein overturned that.

3. Tudo está se afastando

   In the 1920s, Edwin Hubble noticed that distant galaxies are moving away from us, and the farther away they are, the faster they recede. This is what an expanding universe looks like from the inside.

4. As regras estranhas do muito pequeno

   Relativity governs stars and galaxies, but a different set of rules runs the world of atoms. Quantum mechanics says that you cannot know both the exact position and exact speed of a particle at once; nature has a built-in fuzziness.

5. Black holes and the arrow of time

   A black hole forms when a massive star collapses so far that not even light can escape its gravity. For decades it was assumed nothing could ever come out.

6. Coloque em prática

   This week, step outside on a clear night and pick one star, remembering that the light entering your eye left it years or centuries ago, so you are looking at the past. Watch a short explainer on how GPS satellites correct for relativity, and you will see Einstein's ideas at work in your phone.