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The Universe Forum's role as part of NASA's Education Support Network concluded in September, 2009. Please visit NASA at for current information about NASA's science, education, and public outreach activities.

exploring: big bang > where did the universe come from

The ultimate mystery is inspiring new ideas and new experiments.

No one knows how the first space, time, and matter arose. And scientists are grappling with even deeper questions. If there was nothing to begin with, then where did the laws of nature come from? How did the universe "know" how to proceed? And why do the laws of nature produce a universe that is so hospitable to life? As difficult as these questions are, scientists are attempting to address them with bold new ideas - and new experiments to test those ideas.

Understanding how the universe began requires developing a better theory of how space, time, and matter are related. In physics, a theory is not a guess or a hypothesis. It is a mathematical model that lets us make predictions about how the world behaves. Einstein's theory of gravity, for example, accurately describes how matter responds to gravity in the large-scale world around us. And our best theory of the tiny sub-atomic realm, called quantum theory, makes very accurate predictions about the behavior of matter at tiny scales of distance. But these two theories are not complete and are not able to make accurate predictions about the very earliest moments when the universe was both extremely dense and extremely small.

Some of the best minds in physics are working on a new theory of space, time, and matter, called "string theory," that may help us better understand where the universe came from. String theory is based on new ideas that have not yet been tested. The theory assumes, for example, that the basic particles in nature are not point particles, but are shaped like strings. And the theory requires - and predicts - that space has more than the three dimensions in which we move. According to one version of the theory, the particles and forces that make up our world are confined to three dimensions we see - except for gravity, which can "leak" out into the extra dimensions.

String theory has led to some bizarre new scenarios for the origin of the universe. In one scenario, the Big Bang could have been triggered when our own universe collided with a "parallel universe" made of these extra dimensions. Scenarios like these are very speculative, because the string theory is still in development and remains untested, but they stimulate astronomers to look for new forms of evidence.

A new window on the universe: waves of gravity.  
The most promising clue to our cosmic origins may be the tiny gravity waves set in motion during the Big Bang itself. These ripples of gravity have eluded detection so far, but NASA aims to look for them with the LISA mission, to be launched in the next decade. LISA technology will be so precise that it will measure the equivalent of the distance to the Moon to less than the width of a single atom. The mission will be complemented by the ground-based LIGO detector, already in operation.

Gravity waves are important because they are the only known form of information that can reach us, undistorted, from the instant of the Big Bang itself. The different scenarios for the early universe make different predictions for the size and pattern of these gravity waves. The hope is that gravity waves will help refute or support some of these theories of the early universe. The truth is, no one knows what we'll find. This is uncharted territory – a new window on the universe.

Is our universe unique?
Perhaps the most unsettling and far-reaching prediction of string theory - and also of the inflationary universe model - is that the universe we live in is probably not unique. The inflationary model predicts that Big Bangs are continually taking place in other regions of space - and string theory suggests that these other mini-verses may be so different from our own that even the laws of nature and the number of dimensions of space may be different.  

This notion - that the universe as whole may not look like the part we live in - may help explain a puzzling mystery about our own universe: Why are the constants and laws of nature just so, and not different? For example, why is the speed of light not faster than it is? Why are electrons so much lighter than the protons they orbit in atoms? What we do know is that if these fundamental laws and constants were even slightly different from what is observed, then life as we know it would not exist. (For example, atoms would be less stable, or stars and planets would not form.) Traditionally, physicists have sought some logical explanation for why the universe is as it is. But the likelihood of multiple universes raises the possibility that nature is merely playing dice: some universes have the right conditions for life, while others - the vast majority - do not.

Nature is full of surprises, and this dialogue with nature has far to go. With every generation, the universe we observe seems to be getting larger and more wonderful. Just a few hundred years ago, the stars we see in the night sky seemed to be the limits of our universe. Then Galileo's telescope opened up the panorama of stars that make up our Milky Way galaxy of stars. A mere century ago, humanity still had not discovered that there are billions of galaxies far beyond our own. Today, we can see as far as nature currently allows - back to the moment of the Big Bang itself. Our ideas and ingenuity are conjuring a universe even larger and more varied than we had ever imagined. Is it any wonder this is a great exploration?

























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