Space Expanding
- [Space Expanding - NASA]
- Overview
Some evidence that the universe is expanding includes:
- Doppler red-shift:Light from distant stars and galaxies exhibits a Doppler red-shift, which means the universe is moving away from a central point.
- Redshift: The expansion of the universe stretches the wavelengths of light from supernovas, which astronomers call "redshift". Edwin Hubble discovered in 1929 that the redshift of galaxies is directly proportional to their distance from Earth. This means that galaxies farther away from Earth are moving away faster, which supports the theory of a growing universe.
- Analogies: Some analogies used to explain the expanding universe include a loaf of raisin bread dough and a balloon with dots drawn on its surface.
Hubble noted that light from faraway galaxies appeared to be stretched to longer wavelengths, or reddened, a phenomenon called redshift. By precisely determining the expansion rate, called the Hubble constant, the cosmic clock can be rewound and the age of the universe calculated.
- How Big is the Universe in Light Years?
The observable universe is 93 billion light-years across. However, the universe itself is likely infinite.
A light-year is the distance light travels in one Earth year. For most space objects, we use light-years to describe their distance.
One light-year is about 6 trillion miles (9 trillion km). That is a 6 with 12 zeros behind it! It's a convenient unit for measuring the size of the universe because nothing can travel faster than light.
The universe is 13.8 billion years old, but its diameter is 93 billion light-years. This may seem confusing because nothing can travel faster than light. However, the Theory of Relativity can help clear up this confusion.
- Doppler Red-Shift
The evidence that the universe is expanding comes with something called the Doppler red-shift of light. Light travels to Earth from other galaxies. As the light from that galaxy gets closer to Earth, the distance between Earth and the galaxy increases, which causes the wavelength of that light to get longer.
In 1929, Edwin Hubble discovered that the universe is expanding. He observed that the red shift of galaxies is directly proportional to the distance of the galaxy from Earth. This means that things farther away from Earth are moving away faster.
Astronomers call the amount of stretch "redshift," and they measure it with a device called a spectrograph.
The expansion of the universe stretches the wavelengths of light that reach us from supernovas. This causes the light from these galaxies to be shifted to longer (and this means redder) wavelengths.
Hubble's brilliant observation was that the red shift of galaxies was directly proportional to the distance of the galaxy from earth. That meant that things farther away from Earth were moving away faster. In other words, the universe must be expanding.
- (Photo: Princeton University, Office of Communications)
- The Big Bang Theory
In 1927, Georges Lemaitre derived equations that showed the universe's expansion. He then proposed that the receding galaxies suggest that the universe is really expanding.
The Big Bang Theory suggests that the universe has been expanding since it was formed 15 billion years ago. The expansion of the universe is the increase in distance between parts of the observable universe over time.
Georges Lemaitre also added that the universe should have been smaller in the past, concentrated in a single small and dense point he called "primeval atom." His theory was strengthened by Hubble's observations and the discovery of the cosmic microwave background radiation (CMB) by Penzias and Wilson.
The Big Bang model doesn't assume an explosion occurred at a single point in the center of the universe. Instead, the model suggests that the entire universe was once a single point, and has since expanded to its current size.
The expansion of the universe is supported by evidence from the Doppler red-shift of light from distant stars and galaxies. This red-shift indicates that the universe is expanding, or moving away from a central point.
The Big Bang model also suggests that the universe's temperature and density decrease as it expands.
The Big Bang Theory predicts that the universe has been increasing in size since the Big Bang. Some evidence that supports the Big Bang Theory includes:
- Doppler red-shift: The Doppler red-shift of light from distant stars and galaxies shows that the universe is expanding. This is because after the Big Bang, all matter moves away from the point of origin.
- Redshift of galaxies: The redshift of galaxies is a measure of how much the light from the galaxies has been stretched by the expansion of the universe.
- Cosmic background radiation: The discovery of cosmic background radiation that is left over from the initial heat of the Big Bang.
- Element abundance: The amount and types of elements in the universe are almost exactly the amounts predicted by the theory.
[More to come ...]
