Architecture of the Universe

An Elegant Universe

Within our observable Universe--the portion of the Universe we can examine--we see remarkable organization: countless stars grouped together as galaxies; countless galaxies clumped into clusters; clusters arranged in vast filaments, sheets, and bubbles. Astronomers think all of this began in a colossal explosion billions of years ago and evolved into the wondrous place we know and marvel at today: beautiful, elegant, violent, bizarre-and always surprising.

What is the Universe Like?

How old is the Universe? How big? Does it have a center or an edge? Is space simply emptiness between stars and galaxies or does it have properties of its own? What do we mean when we say the Universe is expanding? Expanding into what? Some of the answers may surprise you. Theories about what the Universe is like are still being refined as new ideas surface and new evidence comes to light. So some of the answers presented here may change as astronomers continue to explore the Universe.

How Old is the Universe?

It depends upon who you ask. Astronomers have come up with different estimates, but the most widely accepted age is around 15 billion years, or about three times older than the Earth. Astronomers continue to refine their estimates as new observations produce new data.

Astronomers measure the age of the Universe indirectly, by studying the motions of galaxies. By measuring how far away the most distant galaxies are and how fast they appear to be moving, astronomers can calculate the expansion rate of the Universe. The expansion rate tells them how long the galaxies have been traveling since the big bang, and thus provides a rough age for the Universe.

How Big is the Universe

The farthest we can see into Universe in all directions is about 15 billion light-years--the distance light can travel in 15 billion years, the most widely accepted age for the Universe. The Universe is probably bigger than that. It may even be infinite, but at present we have no way of knowing.

Does the Universe Have an Edge or a Center?

We don't really know--it only looks like it does. On Earth we appear to be at the center of a circle called the horizon, whose edge is only tens of kilometers away. Within the Universe we appear to be at the center of sphere, whose edge--our "cosmic horizon"--is about 15 billion light-years away, the distance light has traveled since the big bang. What lies beyond that cosmic horizon? No one knows.

Space: It Warps! It Expands! It Stretches Light!

Space is not merely emptiness; it has certain properties, some of which are pretty strange and hard to picture. Matter causes space to bend--we call this bending "gravity"--and this warping of space in turn affects the way matter and light move. According to the big bang theory, space is expanding, stretching light waves as they move through the Universe and carrying distant galaxies away from one another.