Cosmology is the study of the origin, current state, and future of our Universe. With recent technological advances, we have been able to probe deeper and deeper into the large scale structure of the vast universe and the small scale structure of matter. Our basis of understanding and determining fundamental physical laws in assumed to be correct when measured locally in laboratory experiments. These laws are verified over and over again so that they can be extrapolated to a distant time and place where they can be investigated with modern astronomical methods. The universe is basically used as a massive laboratory. The universe as defined by Dr. Green, is "everything that can be measured ...view middle of the document...
By the time the light reaches us, the spectral wavelength will have been redshifted by exactly the same factor that the universe had been stretched in the time interval since the light left the source. In order to get the time interval, the speed of light (3*10^8 meters/second) must be multiplied by the object's distance from earth. The apparent brightness of the object must then me compared to a local "standard" of the same class of object. When the redshift and brightness of the distant object is recorded, we can see the expansion of the universe since the time the light was emitted (California Academy of Sciences online) In cosmology, Type 1a supernovae are the standard candle of choice because they have a very well determined maximum absolute magnitude as a function of the shape of their light curve. A light curve as defined by the Cyprus Astronomical Society is: "Brightness or intensity of light plotted against time on a graph. Astronomers discover dark stellar companions using the light curve of the star. As a dark orbiting object eclipses the star, the brightness falls, producing a dip on the light curve. Careful analysis of the light curve reveals the masses of the star and dark companion plus the distance to this eclipsing binary system" (Cyprus Astronomical Society online) Using very distant supernovae as standard candles, one can trace the history of cosmic expansion and try to find out what's currently speeding it up.In Edwin Hubble's discovery of cosmic expansion in the 1920's, he used entire galaxies as standard candles. But galaxies are hard to match against standard brightness since they come in many shapes and sizes. They can grow fainter with time or brighter if merged with other galaxies. In the 1970's it was suggested that the brightest member of a galaxy cluster could be used as a standard candle, but in the end it was realized that all of the proposed galactic candidates were too susceptible to evolutionary change (Perlmutter 53) A supernova with no hydrogen features in its spectra had always been classified as Type 1. If a silicon absorption feature was present, it determined if the supernova would be further subdivided into 1a or 1b. When the Type 1a supernovae were studied in greater detail, their light curves and spectra matched. Also, astronomers could tell that the same physical processes were occurring in all of the massive explosions. The type 1a supernovae were studied when they brightened and faded. (Burrows 727 EBSCOhost) With this breakthrough, there was an immediate interest in trying to use them to determine the Hubble constant, which measures the present expansion rate of the universe. This could be done by finding and measuring type 1a supernovae that occurred 100 million years ago just beyond the nearest cluster of galaxies. If a standard candle supernova could be found 10 times further away, we could sample the expansion of the universe several billion years ago and possibly see the expected slowing of the...
