The History, Physics, and Philosophy of Time
0312603517
Dan Falk
Notes
What is emerging in Rome at the time of Caesar seems to be a uniquely Western sense of time, an image of time as something like tick-marks on a meter stick – very much like the mental picture most of us have today when we look at our watch or jot down an appointment in a calendar.
“In view of all you have to do, when you waste an hour, it seems to me a thousand…For I deem naught so precious to you, both for body and soul, as time, and methinks you value it too little.”
Letter to Francesco di Marco Datini from his wife.
Newton reasoned, there must be a true “universal” clock: a perfect cosmic chronometer whose precise movements real clocks can only approximate.
In the relational view, time is not independent of the material objects and their motions are what define the passage of time. One might argue that this more closely matches our experience of the world: We do not “see” time, just as we do not see space. What we perceive are events in time, and objects in space…If time is motion, what happens when all motion ceases? Would time stop? A relationalist would have to say yes: no motion, no time. In Newton’s scheme, time would march on, somehow, in a metaphysical background.
…starting from some particular low-entropy state, the statistical argument that we’ve been using tells us that entropy increases not only in the future, but into the past as well. This is a subtle but profoundly important point: the same analysis that we used to predict that a low-entropy system will evolve into a high-entropy system in the future could be used to “predict” that a low-entropy system was probably preceded by a high-entropy system.
This is the final answer to Einstein’s thought experiment about catching up to the speed of light: it can’t be done. Light can neither be given a boost nor slowed down; and no matter how fast you move, the beam of light will still appear to be traveling at its usual speed. (This also has the effect of making the speed of light the ultimate “speed limit” in the universe.)…in order for the speed of light to be constant, time and space must be relative.
Since speed is equal to distance divided by time, and since the distance is larger, the time between each “tick” must increase. Therefore an observer on the ground sees the clock on board the moving train as running slow.
It turns out that, according to general relativity, time slows down in a gravitational field. The stronger the field, the greater the effect (known as gravitational time dilation).
Rutherford immediately recognized the importance of his discovery: the earth’s interior isn’t simply getting cooler over time, as Buffon had assumed two hundred years earlier; instead, it is being continuously heated from within, by the decay of radioactive elements in the planet’s molten core.
We now know, for example, that the universe is “flat”, meaning that it can be described by the simple geometry of Euclid parallel lines remain parallel, and the three angles of a triangle add up to 180 degrees. We also know that “ordinary matter” – stars and planets, for example – accounts for just 4% of the contents of the universe. (Of the remainder, mysterious “dark matter” makes up about 23% , and even more mysterious “dark energy” accounts for 73%.)
Using the gravity formula, we can solve for “s” as measured on earth, of a system in different gravity…What if the second measure is different for an observer in each system? – Moon-Earth thought experiment.
Need to factor a coefficient of friction.
Does salad dressing settling resemble reverse-entropy?