Knocking on Heaven's Door - Lisa Randall [165]
The Large Hadron Collider is now testing such ideas. Whatever the LHC discovers will guide and constrain model building in the future. With its higher-energy experimental results, we’ll be able to piece together observations to determine what is right. Even if observations don’t conform to any one particular proposal, the lessons we learned from constructing those models will help narrow down the possibilities for which theory is ultimately correct.
Model building helps us recognize the possibilities, suggest experimental searches, and interpret data once they are available. We might be lucky and get it right. But model building also gives us insights into what to look for. Even if no particular model’s predictions turn out to be completely correct, they will help us deduce the implications of any new experimental result. The results will distinguish among the many ideas and determine which—if any—of the specific implementations correctly describes reality. If no current proposal works, data will nonetheless help determine what the right model might be.
High-energy experiments are not merely searching for new particles. They are searching for the structure of underlying physical laws with even greater explanatory power. Until experiments help determine the answers, we are all just making guesses. For now we’ll apply aesthetic criteria (or prejudice) to favor certain models. But when experiments reach the energies or distances and statistics necessary to distinguish among models, we will know much more. Experimental results, such as those we hope that the LHC will provide, will determine which of our conjectures are correct and help us establish the underlying nature of reality.
Part V:
SCALING THE UNIVERSE
CHAPTER NINETEEN
INSIDE OUT
Back when I was in elementary school, I woke up one morning to read the bewildering news that the universe (at least in our understanding) had suddenly aged by a factor of two. I was astonished by this revision. How could something as important as the universe’s age be at liberty to change so radically without destroying everything else about it that we knew?
Today my surprise works in the opposite direction. I am stunned by how much we can precisely measure now about the universe and its history. Not only do we know the universe’s age much more accurately than ever before, but we know how the universe grew with time, how nuclei were formed, and how galaxies and clusters of galaxies began their evolution. Before, we had a qualitative picture of what had happened. Now we have an accurate scientific picture.
Cosmology has recently entered a remarkable era in which revolutionary advances, both experimental and theoretical, have precipitated a more extensive and detailed description than anyone would have believed possible even 20 years ago. By combining improved experimental methods with calculations rooted in general relativity and particle physics, physicists have established a detailed picture of what the universe looked like in its earlier stages and how it evolved into its form today.
So far, this book has focused primarily on smaller scales at which we examine the inner nature of matter. Having reached the current limit of our inward journey, let’s now complete the tour over distance scales we began in Chapter 5 and turn our attention outward to consider the sizes of objects in the outer universe.
We need to be wary of one big difference in this journey to cosmic scales since we can’t neatly characterize all aspects of the universe according to size alone. Observations don’t just record the universe today. Because of the finite speed of light, they also look back in time. Structures we observe today can be early universe occupants whose light reached our telescopes only billions of years after being emitted. The size of the current greatly expanded universe we now see encompasses many times the size of the universe