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Where is the center of the universe?


Narrator: Welcome to Space Place Musings, where an expert answers questions from our Space Place partners across the nation. I'm Diane Fisher of the New Millennium Program, and our expert is Dr. Marc Rayman, a scientist at the Jet Propulsion Laboratory.

Marc, today our question—a BIG one—comes from the CATO Rocketry Club in Gales Ferry, Connecticut. Here goes: Is it possible to point to a direction in the sky and say "that way is the center of the universe, where the Big Bang started?"

Rayman: Wow. Well . . . no. The "center of the universe" has always been a very intriguing idea for humans. Until the 16th century, even learned people thought Earth—and people—were at the center of the cosmos.

Then the Polish astronomer Nicolaus Copernicus had a better idea—although still wrong—for explaining the motion of the planets through the night sky. He thought that the Sun was actually the center of the universe, with Earth and the other planets circling the Sun.

Narrator: So Copernicus was the first to push humans off to the sidelines.

Rayman: Yes, and his theory was widely condemned and ridiculed at first. Now we know that not only are we humans not at the center of the universe, but there is no center of the universe!

Narrator: Now that is really hard to imagine.

Rayman: It is. But a center just doesn't fit with what scientists have learned through decades of modern astronomy. The Big Bang is the name scientists give to the events that started the universe. Although the Big Bang is often described as a huge explosion, an explosion has a central point, such as a bomb or a spark. The Big Bang wasn't like that.

Narrator: Why not?

Rayman: The Big Bang happened everywhere at once. It's an expansion of space itself, not the expansion of things in space. That means everywhere in space is moving apart from everywhere else. This has been going on in the entire universe for almost 14 billion years.

Narrator: But aren't we located somewhere with respect to the rest of the universe?

Rayman: We certainly are. We're right here, and we know where "here" is relative to other objects in the universe! But here is not special, like a center would be, and, for that matter, nowhere is special. That is like asking—if we had a powerful telescope that could see all the way to the end of the universe, would we find more of the universe on one side of Earth than on the other? No. We would find that it looks the same in all directions.

Narrator: So doesn't that mean we are still at the center of the universe?

Rayman: Well, no, it doesn't. Observers everywhere in the universe would find the same result. Imagine that you are on one of many dots on a spherical balloon. No matter which way you look along the surface of the balloon, the end of your world seems to be the same distance from you. But that doesn't mean you are at the center of this little world! The fact is that your two-dimensional world has no center.

Narrator: But what about the continuing expansion of the universe? Doesn't it have to expand from a center point somewhere?

Rayman: Well, suppose your balloon world is being inflated with air. All the other dots will be getting farther and farther away from you as the balloon gets bigger. In fact, all dots get farther from each other, so no matter where you are, it looks as if you are at the center of the expansion. The expansion of three-dimensional space is similar. Like the surface of the balloon, there is no center in the universe.

Narrator: How do we even know the universe started with a Big Bang?

Rayman: One of the ways is that scientists have been able to see the faint radiation left over from shortly after this cosmic birth. Some scientists predicted what this radiation would look like, and others found it using a radio telescope. As more measurements have been made from Earth and from space, the Big Bang has continued to provide an excellent description of how the universe has evolved.

Narrator: Is there any other way to learn about the Big Bang besides observing its leftover radiation?

Rayman: Well, yes there are several. And scientists would like to be able to study gravitational waves left by the Big Bang. Gravitational waves will be very hard to detect but should tell us a lot about the universe that electromagnetic radiation and matter cannot. Detecting gravitational waves will require some very advanced technologies but could lead to thrilling new insights into the workings of the universe.

The New Millennium Program's Space Technology 7 project is developing and testing a new micro-thruster technology that may be part of a future mission to detect gravitational waves.

Narrator: That's right. The Space Place web site has an interactive game, called Vec-touring, that explains the technology and helps kids learn about vectors in a fun way. Our listeners can visit and click on "Games" to find it.

Our time's up for now. Marc, thank you for another fascinating discussion. So long to our listeners for now, and we'll look forward to our next session of Space Place Musings.