One of the most surprising discoveries in modern cosmology is that the expansion of the universe is not slowing down due to gravity, as once expected, but is actually accelerating. This means galaxies are moving away from each other faster and faster over time.
How It Was Discovered:
- In the late 1990s, astronomers studying distant Type Ia supernovae (which act as standard candles for measuring cosmic distances) found that these explosions appeared dimmer than expected.
- This dimness indicated that they were farther away than predicted, implying that the universe’s expansion has sped up over time.
What Drives the Acceleration?
- Scientists propose the existence of a mysterious form of energy called dark energy, which is believed to make up about 70% of the universe.
- Dark energy works in opposition to gravity, pushing space itself apart.
- Its exact nature remains unknown, but it is thought to have a constant energy density even as the universe grows.
Why It Matters:
- The discovery of the accelerating universe revolutionized cosmology and led to the 2011 Nobel Prize in Physics.
- It suggests that the ultimate fate of the universe might be a continual, eternal expansion—possibly leading to a “Big Freeze” where galaxies grow increasingly distant and isolated.
- It also points to major gaps in our understanding of fundamental physics, especially the role of vacuum energy and quantum fields.