How Much Of The Universe Can Humanity Ever Witness?
Summary
This PBS Space Time episode explores the absolute limits of what we can ever see in the expanding universe. It explains how the accelerating expansion of space, driven by dark energy, causes the Hubble horizon to collapse, creating a cosmological event horizon that eventually cuts off our view of distant galaxies. The discussion details that while we will see more of the universe for billions of years, the light from the most distant objects will eventually become too redshifted to detect, leaving the sky permanently dark.
Topics discussed
Introduction: The limits of our view of the universe
Light travel time and the cosmic microwave background
Calculating the distance to the CMB and observable universe
The particle horizon and potential future signals
Visualizing the past light cone in spacetime diagrams
Expansion history: Matter dominance vs. dark energy
Introducing co-moving coordinates for expansion
The effect of dark energy on the ultimate view
Defining the Hubble horizon and recession velocity
How photons cross the Hubble horizon to reach us
The collapse of the Hubble horizon due to acceleration
The cosmological event horizon and its shrinking radius
The final size of the particle horizon in 10 billion years
Redshifting and the eventual darkness of the sky
Conclusion and preview of future exploration limits
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