This video discusses the concept of cosmic horizons in the context of the expanding universe. It begins by explaining that the observable universe is limited by the age of the universe and the finite speed of light. The video introduces various horizons, including the particle horizon, the Hubble horizon, and the cosmological event horizon.
- The particle horizon represents the farthest distance we can observe, and it's currently at the cosmic microwave background (CMB), which is about 46.5 billion light-years away.
- The Hubble horizon is the boundary where galaxies are receding from us at the speed of light due to the universe's expansion. Currently, it is about 14.5 billion light-years away, but it will eventually collapse back on us.
- The cosmological event horizon is the ultimate limit of our observational reach. It started out larger than the Hubble horizon but has been shrinking over time. In about 10 billion years, it will merge with the collapsing Hubble horizon, and we will no longer receive new signals from beyond this horizon.
Despite these limits, the video notes that we will continue to receive light from the most distant parts of the universe, providing us with a broad view of the cosmos. However, our final particle horizon will be about 63 billion light-years away, approximately half again the size of our current observable universe.
Here are the key facts extracted from the text:
1. The observable universe is near 100 billion light-years wide.
2. The observable universe is only a tiny fraction of the greater bigness of space.
3. The universe is expanding, which means the cosmological horizons will eventually collapse and cut off our view.
4. There is an absolute limit to our access to the universe beyond our own Galaxy.
5. Light doesn't travel instantaneously, which means that when we look into the distance, we're seeing objects as they were in the past.
6. The most distant light that we can see is the cosmic microwave background radiation, which has been traveling to us for almost the entire age of the universe (13.7 billion years).
7. The cosmic microwave background radiation is the limit of our vision and the limit of the observable universe.
8. The observable universe is 46.5 billion light years in radius.
9. The particle Horizon is the absolute limit of the observable universe.
10. The particle Horizon is expanding and changing over time.
11. There's a limit to the amount of universe we'll be able to see even if we wait infinite time.
12. The universe has been expanding so at earlier times those regions were smaller.
13. The light cone encompasses more and more stuff into the past at some point it starts to encompass less and less physical space.
14. The particle Horizon encompasses a finite amount of the universe.
15. The Hubble Horizon is a sphere that surrounds us where the recession velocity equals the speed of light.
16. The Hubble Horizon is currently 14.5 billion light years away.
17. The Hubble Horizon will eventually stop moving away and actually collapse back on us.
18. The cosmological Event Horizon is the boundary Beyond which no signal can ever be received.
19. The cosmological Event Horizon will merge with the collapsing Hubble Horizon in about 10 billion years.
20. At that point, we will never be able to see new events from beyond this Horizon.
21. The sky will finally be dark in about 10 million years when we first get close to our full Panorama of the universe.
22. After a few hundred billion years, even the most energetic photons will be stretched to the point that we need a radio antenna larger than our contracted Hubble Horizon to see them.