Physics
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Any discussion of cosmology requires a careful consideration of what we can see and when we can see it. A good way to keep track of these concepts is the space-time diagram . A space-time diagram is nothing more than a graph showing the position of objects as a function of time. The usual convention is that time runs up the diagram, so the bottom is the past, or early times, and the top is the future, or late times. A point on this graph describes both a position (the horizontal or x coordinate) and a time (the vertical or t coordinate).
Space-Time Diagrams
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The University of Utah operates a cosmic ray detector called the Fly's Eye II , situated at the Dugway Proving Ground about an hour's drive from Salt Lake City. The Fly's Eye consists of an array of telescopes which stare into the night sky and record the blue flashes which result when very high energy cosmic rays slam into the atmosphere. From the height and intensity of the flash, one can calculate the nature of the particle and its energy.
The Oh-My-God Particle
The layer of the Earth we live on is broken into a dozen or so rigid slabs (called tectonic plates by geologists) that are moving relative to one another.