The PRINCE and p (A quest for the nature of motion)

  • Robert Gilmore


“Once upon a time there was no Universe, “ began the Storyteller. He paused and thought for a moment.

“No, that is not quite right, “ he corrected himself, “I cannot say ‘once upon a time’ because Time and Space began and developed together with the matter that is in the Universe. They were born with no father and no mother-and as for the midwife, who can say?”

His audience, who had been listening quite attentively, looked at one another. “I don’t see how that can be so!” exclaimed Rachel. “There must have been time. There is always time (you could tell that she was quite young). How could anything happen if there is no time for it to happen in?”

“You have no reason to believe that anything was happening before the Universe first appeared with the dramatic entrance that we call the Big Bang. Everything that we know about, almost certainly everything that we can know about, has happened since the Big Bang. Subsequent events have most certainly required time in which to happen, but time had then become available. The Big Bang provided the stage-the space and the time-as well as the cast of particles that make up the matter around us. The way these particles moved qfter they were formed has brought us eventually to where we are today.

“Because such movement is so vital I shall begin by telling you a story to illustrate the nature of motion.”

“Why?” asked Adam. “Why don’t you just tell us about the Big Bang itself ?”

“That must come later, “ was the firm reply. “Since the Big Bang was the beginning of the whole Universe, it would make little sense to talk of it if you do not know what it is that was beginning. You would be hopelessly confused.”

“So you are going to tell us what the Universe is like now, “ said Elizabeth, just to be sure about things.

“Not exactly, “ replied the Storyteller. “I cannot tell you what it is like now because there is no sensible way in which you can even talk about now for the whole Universe. Look at the stars.” He looked intently at his audience as he said this, and such was his command of their imaginations, they seemed to see the clouds part and the black night of space revealed to them. Its remote depths were sprinkled with a multitude of stars, stars everywhere.

“There you see a small sample of the Universe around us, but you must not believe that you are seeing it ‘as it is now.’ The light from those stars has taken a long time to reach you, and you are seeing them as they were years ago, thousands, even millions of years in the past. As you look outward you are seeing samples in time from a changing cosmos, and that change involves the nature of time and space and motion.

“Before you can usefully talk about the Universe you need to know about space and time and how both are tied up with motion in surprising ways. You need to consider what motion is, what is moving and what is at rest, and whether that is a question you can actually ask. For that reason our first story will be about motion and change, about how things move and how you see them move. It is about velocity and it is about energy and momentum, and so it becomes also a story about time and space themselves. It is the story of ‘The Prince and p’.”

“What does a pea have to do with motion?” asked Jordan in some confusion.

“I didn’t say ‘a pea’,” replied the Storyteller rather irritably. “I said ‘p’ You must listen more carefully. The symbol ‘p’ is used almost universally to denote momentum and that is what I meant. Now sit down and hear the story.” He cleared his throat, adjusted to a more comfortable position on his seat and began his tale.

“A certain king had three sons and as was the custom in that kingdom, as each son came of age he called him into his presence and assigned him a quest. In due course he called his youngest son....


Angular Momentum Light Cone Gravitational Potential Energy Sonic Boom Past Light Cone 
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© Springer Science+Business Media New York 2003

Authors and Affiliations

  • Robert Gilmore

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