The origin and extent of the universe

 The origin and extent of the universe are among the most profound questions in science, drawing from cosmology, physics, and astronomy. Let me search for the most current scientific understanding on these topics.

Based on current scientific understanding, here's what we know about the origin and extent of the universe:

How and When the Universe Began

The prevailing scientific consensus is the Big Bang theory, which posits that the universe originated approximately 13.8 billion years ago from an extremely hot, dense state . This wasn't an explosion in space, but rather an expansion of space itself—creating time, space, and matter as we know them .

Key evidence supporting this model:

- Cosmic Microwave Background (CMB): Discovered in 1964 by Penzias and Wilson, this is the cooled remnant "afterglow" from when the universe became transparent about 380,000 years after the Big Bang . It represents the oldest light detectable, now cooled to just 2.7 Kelvin .

- Universal Expansion: Edwin Hubble's 1929 discovery that distant galaxies are receding from us revealed that the universe is expanding—meaning if wound backward, everything converges at a single point in the past .

- Inflation: In the first fraction of a second, the universe underwent exponential expansion (cosmic inflation), growing by factors of trillions. This explains why the universe appears flat and uniform on large scales .

Emerging challenges and alternative theories:

Recent research has introduced provocative alternatives. A 2025 "Black Hole Universe" model proposes our universe emerged from a gravitational collapse and "bounce" inside a massive black hole in a parent universe, avoiding the problematic singularity of traditional Big Bang theory . Another 2025 theory suggests gravitational waves alone—without hypothetical inflation fields—could have seeded cosmic structure from quantum fluctuations in spacetime .

Additionally, some cosmologists are questioning foundational assumptions like the "cosmological principle" (that the universe is uniform everywhere), with evidence suggesting potential anisotropies in the CMB .

The Extent of the Universe

The universe's size has two distinct interpretations:

Observable Universe:

- Diameter: Approximately 93 billion light-years 

- Radius: About 46.5 billion light-years from Earth in every direction 

- This is the region from which light has had time to reach us since the beginning. Due to cosmic expansion, objects that emitted light 13.8 billion years ago are now much farther away—about 46 billion light-years .

The Entire Universe:

The full extent remains unknown and possibly unknowable. Current possibilities include:

- Infinite: If the universe has "flat" geometry (which observations strongly suggest), it may extend forever without boundaries 

- Finite but unbounded: Like Earth's surface—finite area but no edge

- At least 250 times larger: Statistical analyses suggest the universe is minimally 7 trillion light-years across, potentially much larger 

- Vastly larger: If inflation theory holds, the universe could be 10²³ times bigger than what we observe 

Critical distinction: The "observable universe" is merely a bubble with Earth at its center—every point in space has its own observable bubble . What lies beyond our cosmic horizon remains inaccessible because light from those regions hasn't reached us, and due to accelerating expansion driven by dark energy, some regions will never become visible .

The universe contains roughly 5% ordinary matter, 27% dark matter, and 68% dark energy , with a total mass of ordinary matter estimated at 1.5 × 10⁵³ kg .

In summary: The universe began approximately 13.8 billion years ago in a hot, dense state that expanded dramatically, and while we can observe a sphere roughly 93 billion light-years across, the complete cosmos likely extends far beyond—possibly infinitely.