The observable universe stretches about 46 billion light-years in every direction from Earth, giving it a diameter of roughly 93 billion light-years. That’s the theoretical maximum of what we can see. But most of what exists within that enormous sphere is invisible to us, and the full universe almost certainly extends far beyond it.
Why the Observable Universe Is Bigger Than Its Age
The universe is about 13.8 billion years old, so you might expect we could see no farther than 13.8 billion light-years in any direction. The actual boundary is more than three times that distance, and the reason is cosmic expansion. Space itself has been stretching since the Big Bang, carrying galaxies apart from one another. Light that left a distant galaxy billions of years ago has been traveling through space that kept expanding behind it. By the time that light reaches your telescope, the galaxy that emitted it has been carried much farther away.
This means the most distant objects we detect are no longer where they appear to be. A galaxy whose light took 13.1 billion years to reach us, as captured by the James Webb Space Telescope, is now far more than 13.1 billion light-years away. The true, present-day distance to the edge of the observable universe is about 46 billion light-years, or roughly 14 gigaparsecs. The full sphere has a diameter of about 93 billion light-years.
The Oldest Light We Can Detect
There’s a hard wall to how far back we can look. For the first 375,000 years after the Big Bang, the universe was so hot and dense that light couldn’t travel freely. Photons scattered constantly off charged particles, making the early universe opaque, like trying to see through fog. When the universe cooled enough for atoms to form, light was finally released. That first flash of freed light is still detectable today as the cosmic microwave background, a faint glow of radiation coming from every direction in the sky.
The cosmic microwave background is the oldest light in the universe and marks the farthest back in time we can ever see using any form of light. Everything before that moment is hidden from electromagnetic observation entirely. The matter that emitted that radiation was roughly 42 million light-years away at the time, but expansion has since carried it to the outer edge of the observable universe, about 46 billion light-years from us.
How Many Galaxies Are Inside It
The observable universe contains an almost incomprehensible number of galaxies. Earlier estimates based on Hubble Space Telescope observations put the count at around 200 billion. A more recent analysis, using deeper imaging data and mathematical models to account for galaxies too faint or distant to detect directly, revised that figure sharply upward. The updated estimate suggests at least 2 trillion galaxies exist within the observable universe, ten times the previous count.
Roughly 90 percent of those galaxies are too faint and too far away to be seen with current telescopes. We know they’re there because the total mass and light output of the observable universe wouldn’t add up otherwise. So even within the volume of space we can theoretically see, the vast majority of galaxies remain invisible to us in practice.
Most of the Universe Is Invisible Matter and Energy
Even setting aside distant, faint galaxies, what we can observe with light represents a tiny fraction of what’s actually there. Only about 5 percent of the universe’s total mass and energy is ordinary atomic matter: stars, planets, gas, dust, and everything made of atoms. Of that 5 percent, only about 4 percent is the kind of matter we can detect with telescopes. The remaining 1 percent or so is ordinary matter that’s difficult to observe, like thin gas between galaxies.
The other 95 percent is split between dark matter (about 27 percent) and dark energy (about 68 percent). Dark matter exerts gravitational pull on galaxies and bends light passing near it, but it doesn’t emit, absorb, or reflect any light. Dark energy is even more mysterious. It’s the force driving the accelerating expansion of the universe, and it has no direct observable signature at all beyond its effect on cosmic expansion. So in terms of the total contents of the universe, what we can actually see with any telescope amounts to roughly 4 to 5 percent of everything that exists.
What Lies Beyond the Observable Universe
The observable universe is not the entire universe. It’s simply the region from which light has had time to reach us since the Big Bang. Beyond that boundary, more universe almost certainly exists. There could be galaxies, stars, and planets in every direction past the edge of our observable sphere, and most cosmological models suggest the full universe is vastly larger. Some estimates place it at least 250 times the diameter of the observable universe, though the true size could be infinite.
We will never see those regions. In fact, the portion of the universe available to us is shrinking in a meaningful sense. Because expansion is accelerating, there’s a second boundary called the cosmic event horizon, currently about 16 billion light-years away. Any light emitted right now from beyond that distance will never reach us, no matter how long we wait. Space between us and those sources will expand faster than the light can cross it. Galaxies that are currently visible will eventually cross this horizon, their light stretching to longer and longer wavelengths until it becomes undetectable, effectively vanishing from our sky.
What Current Telescopes Actually Reach
The theoretical limit of the observable universe is 46 billion light-years in any direction, but our actual instruments fall well short of that. The James Webb Space Telescope has captured light from galaxies that existed within the first billion years after the Big Bang, detecting light that traveled for over 13 billion years. That represents the practical edge of current technology. Between that frontier and the cosmic microwave background at 375,000 years after the Big Bang, there is a gap filled with very few detectable sources, sometimes called the cosmic dark ages, when stars and galaxies had not yet formed.
So the full picture breaks down like this: the observable universe spans 93 billion light-years across, but around 90 percent of the galaxies within it are too faint to see with existing instruments. The matter we can see makes up roughly 5 percent of the universe’s total mass and energy. And the observable universe itself may represent a small fraction of the full cosmos. By almost any measure, what we can actually see is a sliver of what’s out there.