We see them as they were 13 billion years ago. The most distant objects visible are galaxies photographed by the Hubble Telescope. Most scientists now think the shape of the Universe is flat.īecause light takes time to travel, when we look into space we are looking back in time. The mass of the Universe could bend this rubber sheet in one of three ways, depending on how densely packed with matter the Universe is. This is hard to visualize, so scientists use the metaphor of a two-dimensional rubber sheet to explain the idea. The three dimensions of space are bent by the force of gravity from matter in the Universe into a fourth dimension that we can’t see. The whole Universe may be vastly bigger than this, perhaps infinitely so. Only a fraction of it-the observable Universe-is visible to us. The Universe probably has no center or outer edge. People used to think of the Universe as a giant sphere, but we now know that things are not so simple. In recent years, planets have been seen around hundreds of other stars, showing that our Solar System may be one of billions in our galaxy. Our Solar System includes a star (the Sun) and a large family of planets and moons that formed from the same cloud of gas that gave birth to the Sun. They range from grains of dust to planets, stars, and galaxies. Floating in this vast, dark void are all sorts of different objects, which astronomers call celestial bodies. The Universe is at least 99.999999999999 percent empty space.

The Universe is so vast that it seems unimaginable, but we do know that it has been steadily expanding following its beginning 13.8 billion years ago in an explosive event called the Big Bang. The Universe is the whole of existence-all of space, matter, energy, and time.

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