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Cosmology. Cosmology seeks to explain how the universe began, how it evolves, and its fate. The Universe - is all of the matter, energy, and spacetime that will ever be detectable from Earth or that will ever affect us.
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Cosmology seeks to explain how the universe began, how it evolves, and its fate.The Universe - is all of the matter, energy, and spacetime that will ever be detectable from Earth or that will ever affect us.
Cosmic microwave background (CMB)Radio waves were found to be coming from all directions in the sky by early radio astronomers.These are now believed to be the remnants of blackbody radiation from the early universe, red-shifted to long wavelengths by the expansion of space itself.Einstein's theory of general relativity predicts that the entire universe could be expanding (or contracting).
Redshift of light can occur if the space in which it travels is being stretched like a rubber membrane. It is not necessary to have a moving source of light.
The cosmic microwave background was first seen by a radio receiver designed and built by Arno Penzias (on the right in the picture) and Robert Wilson of Bell Laboratories (both later won the 1978 Nobel Prize).
The Cosmic Background Explorer satellite (COBE) operated from 1989-1994 and earned a Nobel prize for John Mather and George Smoot (2006).
Data from the Cosmic Background Explorer satellite confirmed that the microwaves seen coming from deep space have the shape of a spectrum from a blackbody source, as though the entire universe is the source.
ESA’s Planck spacecraft • A European satellite has been mapping the CMB in greater detail, and has now obtained a full-sky picture of the temperature distribution of the CMB. • Some data is shown in the next slides. George Smoot in front of two parts of the Planck spacecraft. (See full size graphic on next slide.)
We also have to subtract microwaves coming from nearby sources in the Milky Way in order to see the CMB (see bottom and top regions for the patchy-looking CMB coming from outside the galaxy, next slide).
This top region, cropped from the previous slide, shows patchy-looking CMB coming from outside the galaxy. This is from the Planck satellite (European Space Agency), from data released in July 2010.
If we look at the large-scale distribution of hydrogen gas in distant regions of the visible universe, we see a fairly uniform (but patchy) distribution of gas in all directions. (from SDSS results - link)
The large-scale distribution of matter (visible galaxies and invisible dark matter) indicates that the universe is Homogeneous (the same density as seen from different locations). (Recall the use of homogenized to describe milk; the cream is uniformly distributed and not on top.) The uniformity of the CMB in different directions indicates that the universe is Isotropic (the same as seen when looking in different directions).
The brief history of everything: The best theory that we have for the evolution of the universe is called the Big Bang theory of the Universe. The origin of the Universe occurred about 13.8 billion years ago, in an event called the Big Bang. Into what is the universe expanding? Nothing. The Big Bang “created” space and time (spacetime), as well as all matter and energy in the universe. Spacetime is expanding to accommodate the expansion of the universe.
The Universe began as an exceedingly dense cosmic singularity (like a point) that expanded explosively in an event (the Big Bang). The Hubble law describes the ongoing expansion of the universe and the rate at which superclusters of galaxies move apart. v = H x d (Hubble’s constant H = 22 km/s / 106ly) Calculating backwards from the current rate of expansion, we estimate that all the matter was clumped together in a small volume about 13.8 billion years ago. The observable universe extends about 13.8 billion light-years in every direction from Earth to what is called the cosmic light horizon. We cannot see any objects that may exist beyond the cosmic light horizon because light from these objects has not had enough time to reach us and be seen by observers on Earth, even if it started traveling toward us at the beginning of the Universe.
As the universe expanded and cooled, different effects dominated the behavior and evolution of the universe.
A period of time, called the inflationary period, caused the size of the early universe to increase by a large amount (1050 or more) in a very short interval of time (10-32 seconds), hence causing a homogeneous and isotropic region around the part that we now see. This would cancel out any early fluctuations by stretching and smoothing out the early universe.
The expansion of the universe thus had a peculiar period of “inflation.”
The result of the inflationary epoch is that we are able to see only a small fraction of the universe, and don’t know how big it really is.
Radiation dominated the early universe, and matter and radiation were at the same temperature because of constant interchange on energy between the two.
The early universe was mostly radiation and not particulate matter. But the expansion reduced the density of radiation faster than it reduced the density of matter.
Before the universe was about 378,000 years old, the matter was not in the form of atoms, but was ionized. Then hydrogen atoms formed, and the universe became “transparent” and we call the following epoch the “dark ages” because stars had not yet formed. This event is the source of the Cosmic Microwave Background. The radiation then “cooled” by expansion of the whole universe.
After removing the effects of the motion of Earth, small fluctuations remain in the CMB (seen by WMAP).
Huge clouds of primordial gas started forming massive stars. This is an artist’s painting, representing star-forming regions.
We see evidence of early galaxy formation in the Hubble “Deep Field.”
Chandra X-ray telescope pictures show hot gas around a huge cluster of galaxies forming 11.2 billion light-years from us.
Ellipticals have already gone through star formation, while spiral galaxies continue to form stars out of recycled interstellar matter.
Slow star formation may leave enough gas to cause the formation of a disk and the result is a spiral galaxy. Rapid star formation may result in an elliptical galaxy. The stars will not collide with each other like gas clouds do, hence no disk forms.
The fate of the universe. What will happen in the distant future? Will the expansion end? Will the universe start to contract and end in a big crunch?
Dark matter is one factor that will influence the future of the universe. We are just beginning to understand dark matter.
The overall shape of spacetime may be similar to a spherical shape, which implies an “closed universe.” Or it may be “flat”. Or, the overall shape of spacetime may be similar to a saddle shape, which implies an “open universe.”
Distant supernovae appear to be dimmer than they should be. This implies that the universe is expanding at a greater and greater rate. The expansion is accelerating.
The cause of the acceleration is called “dark energy.” This dark energy has apparently dominated the universe for several billion years.
Keep our perspective • The Universe is filled with complex behavior, but none of it compares to what we see in a thin shell on a small planet, the biosphere of Earth. • We return to the most important place in the Universe.
