Our Universe as a Laboratory for Understanding Physical Laws

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 now or at any time in the future." What if our current understanding of the universe is not as perfect as we believe it to be? Our just we being egocentric in assuming that the fundamental physical laws that we have determined locally can apply to the rest of the universe? I am going to discuss why our universe is the best laboratory for understanding and determining the fundamental physical laws and then I will make an argument against this premise using dark matter, dark energy, Standard Candles, and Type 1a supernovae as a basis for discussion.

A great reason why our universe is such a good laboratory is that everything is right in front of us; it is just a matter of us looking in the right direction at the right time using the right tools. A standard candle is a term used for an astronomical object, often a star, of well understood intrinsic brightness which enables us to determine cosmic distances (CAS online). If an object can be found whose luminosity you knew absolutely just from looking at it, then by comparing the apparent luminosity with the absolute luminosity, you could figure how far away it was. As the light from a distant object travels to Earth through an expanding universe, the cosmic expansion stretches the distances between galaxy clusters and the wavelengths of the photons emitted from the object. 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 expansion rate from gravity. We would be, in effect, weighing the universe because the deceleration rate would depend on the cosmic mean mass density. The changing expansion rate would also determine the curvature of space and determine if the universe is finite or infinite and if mass density is the primary energy force of the universe as was generally assumed a decade ago. (Perlmutter 53) After many measurements were made and compared of type 1a supernovae, it was evident that there were some major errors in our understanding of the universe. Dozens of distant supernovae appeared surprisingly faint leading to the conclusion that the universe is accelerating disproving the belief that "gravity always wins." We could only do this by making direct measurements on the universe itself.

If the universe is in fact accelerating, there has to be some mysterious force causing this. This force has been labeled dark energy by physicists and astronomers. Dark energy would be almost impossible to detect in a local laboratory because of its tiny density and its very weak interactions. The best way to try to understand dark energy would be to thousands of type 1a supernovae. This is exactly what the SuperNova/Acceleration Probe (SNAP) is going to do. SNAP is going to orbit a 3-mirror, 2-meter telescope circling the globe every 14 days. It will discover and accurately measure over 2,000 type 1a supernovae a year. This would be 20 times the amount that was found in a decade of ground-based research. It will have a very wide-field camera with a billion pixels that will collect images hundreds of times larger than its predecessors. Measuring spurts or slowdowns in the expansion history of supernovae will provide an excellent way in understanding dark energy (Preuss online).

While using the universe to measure such