How Will the Universe End? | Space Time

TL;DR

The universe will eventually reach a state of eternal darkness.

Transcript

MATT O'DOWD: Thank you to Wix for supporting PBS Digital Studios. We live in an unusual age, the age when the stars still shine. We should count ourselves lucky. Nearly all of future history will be dark. But events will still unfold in that long-cooling blackness, and civilizations may endure. So how will the universe and its far-future denizens s... Read More

Key Insights

• In 100 trillion years, the last star will become a white dwarf and fade to black, marking the end of the Era of Stars.
• The universe will spend most of its time in darkness, moving towards maximum entropy and heat death.
• Future civilizations might harness energy from mechanisms like Hawking radiation to survive in the dark ages.
• All galaxies will eventually dissolve, with stars and planets scattered into the void or falling into black holes.
• Protons may decay, leading to a universe filled only with photons, electrons, and black holes.
• Black holes will eventually evaporate via Hawking radiation, leaving behind a void of elementary particles.
• If protons don't decay, matter could persist longer, but quantum tunneling will ultimately lead to iron stars.
• The universe may end as an expanding void, or dramatic events like the Big Rip or vacuum decay could occur.

Questions & Answers

Q: What will happen to the last star in the universe?

In 100 trillion years, the last star will exhaust its hydrogen fuel and become a dim white dwarf. Over time, it will radiate away its remaining heat and fade to black, marking the end of the Era of Stars.

Q: How will galaxies dissolve over time?

Galaxies will dissolve as stellar remnants and planets are scattered into the void due to gravitational interactions. Heavier objects like neutron stars and black holes will sink towards the galactic center, while lighter stars are flung out, leading to the galaxy's eventual dissolution.

Q: What role does proton decay play in the universe's future?

Proton decay, if it occurs, will lead to the breakdown of all matter in the universe over time. This process would leave the universe filled with only photons, electrons, and black holes, ultimately contributing to the universe's transition to the Black Hole Era and eventual heat death.

Q: How do black holes contribute to the universe's energy dynamics?

Black holes can serve as energy sources through mechanisms like Hawking radiation, which allows them to emit particles and slowly lose mass. Advanced civilizations might harness this energy to survive during the universe's dark ages, extending their existence through the Black Hole Era.

Q: What happens to matter if protons do not decay?

If protons do not decay, matter could persist for a very long time. Quantum tunneling would eventually cause lighter elements to fuse and heavier elements to decay, leading to the formation of iron stars. Over unimaginably long timescales, these iron stars could evolve into neutron stars.

Q: What is the ultimate fate of black holes?

Black holes will eventually evaporate through Hawking radiation, a process in which they emit particles and lose mass over time. This evaporation will lead to occasional flashes of gamma rays, and once all black holes have evaporated, the universe will be left with a void of elementary particles.

Q: Could dramatic events alter the universe's end?

Yes, dramatic events like the Big Rip, where dark energy tears space apart, or vacuum decay, which could alter the universe's energy state and laws of physics, might occur. These events could lead to more dramatic endings for the universe than the gradual heat death scenario.

Q: How might civilizations survive in the universe's dark future?

Future civilizations might survive by harnessing energy from cosmic mechanisms such as Hawking radiation from black holes. They could develop advanced technologies to exploit these energy sources, allowing them to persist through the universe's dark ages and even the Black Hole Era.

Summary & Key Takeaways

• In 100 trillion years, the last star will fade, ending the Era of Stars. The universe will spend most of its time in darkness, moving towards maximum entropy and heat death, but future civilizations might survive by harnessing energy from cosmic mechanisms.

• Galaxies will dissolve over time, scattering stars and planets into the void. Protons may decay, leaving only photons, electrons, and black holes. Black holes will eventually evaporate, resulting in a void filled with elementary particles.

• If protons do not decay, matter could persist longer, but quantum tunneling will eventually lead to the formation of iron stars. The universe may end as an expanding void, or dramatic events like the Big Rip or vacuum decay could occur.