Time is part of the universe and so it didn’t exist. It's not that the universe was a dark, empty space and an explosion happened in it from which all matter sprang forth. Or really the entire universe (not just the matter in it) was one spot.ĭon't spend too much time considering a mission to visit the spot where the universe was born, though, as a person cannot visit the place where the Big Bang happened. A bit farther back in time, everything was in the same spot. But the past doesn’t go on forever.īy measuring the speed of galaxies and their distances from us, scientists have found that if we could go back far enough, before galaxies formed or stars began fusing hydrogen into helium, things were so close together and hot that atoms couldn’t form and photons had nowhere to go. The same can be said about any time in the past - last year, a million years ago, a billion years ago. Put another way, the matter, energy and everything in the universe (including space itself) was more compact last Saturday than it is today. In the distant future, the galaxies will be so far away that their light will not be visible from Earth. One might expect gravity to slow the galaxies’ motion from one another, but instead they’re speeding up and scientists don’t know why. The farther the galaxies are, the faster they’re traveling away. They also measured the expansion by observing the Doppler shift in light from galaxies, almost all of which are traveling away from us and from each other. Scientists arrived at that number by measuring the ages of the oldest stars and the rate at which the universe expands. The universe, on the other hand, appears to be about 13.8 billion years old. By studying the radioactive decay of isotopes on Earth and in asteroids, scientists have learned that our planet and the solar system formed around 4.6 billion years ago. While the distant future is difficult to accurately predict, the distant past is slightly less so. After all, humans have only just begun deciphering the cosmos. It might even expand large enough to swallow Earth itself. Several billion years from now, the Sun will expand, swallowing Mercury and Venus, and filling Earth’s sky. Nor will it last forever in its current state. For nearly two-thirds of the time since the universe began, Earth did not even exist. It may feel permanent, but the entire planet is a fleeting thing in the lifespan of the universe. Our planet, Earth, is an oasis not only in space, but in time. Image created by Reto Stöckli, Nazmi El Saleous, and Marit Jentoft-Nilsen, NASA GSFC The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument aboard NASA’s Terra satellite collected the land surface data over 16 days, while NOAA’s Geostationary Operational Environmental Satellite (GOES) produced a snapshot of the Earth’s clouds and the Moon. The image is a combination of data from two satellites. This true-color image shows North and South America as they would appear from space 22,000 miles (35,000 km) above the Earth. For humans and the other things living on our planet, practically the entire cosmos is a hostile and merciless environment. Earth is a tiny, fragile exception in the cosmos. It just so happens that things live here and the environment near the surface of this particular planet is hospitable for life as we know it. But Earth is a planet, and it’s in space and part of the universe just like the other planets. Humans say “out in space” as if it’s there and we’re here, as if Earth is separate from the rest of the universe. In fact, you’re technically in space right now. About 8,000 miles (12,800 kilometers) below your feet - on the opposite side of Earth - lurks the unforgiving vacuum and radiation of outer space.
Day or night, whether you’re indoors or outdoors, asleep, eating lunch or dozing off in class, outer space is just a few dozen miles above your head.
Wherever you are right now, outer space is only 62 miles (100 kilometers) away. Though the universe may seem a strange place, it is not a distant one. On the nebula's younger left side, many stars are just beginning to clear away the gas and dust. The dust and gas in the region are swept around even more when those stars die and explode as supernovas. The cavernous red region on the right side of W51 is older, evident in the way it has already been carved out by winds from generations of massive stars (those at least 10 times the mass of our Sun). "Star factories" like this one can operate for millions of years. The star-forming nebula W51 is one of the largest "star factories" in the Milky Way galaxy.
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