IT’S ABOUT TIME
Exploring Time from the Physical
to the Metaphysical to the Practical
Merideth Frey
Physics Faculty
Sarah Lawrence College
Time is nature’s way of keeping everything from happening at once.
- John Archibald Wheeler
Time is Money
All time is all time. It does not Change. It Does not lend itself to warnings or explanations.
It simply is.
-Slaughterhouse-Five,
Kurt Vonnegut
A BRIEF HISTORY OF TIME
(When you steal, steal from the best)
Looking to nature...
Quantifying time...
Aristotle: Time is nothing other than the measurement of change.
Newton: There is a time that passes even when nothing happens.
Wrote his laws of mechanics using equations containing the letter t that explain how objects move in time
Time is “absolute, true, mathematical” and assumed to run independently of things that change or things that move.
The crumbling of absolute time...
Newton’s interpretation of time held firm for centuries, until…
Albert Einstein showed in the early 20th Century...
When is now?
"...henceforth, space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union between the two will preserve an independent reality."
The further degradation of absolute time...
Then quantum mechanics comes along and time is...
No clear direction of time at the microscopic level...
“The distinction between the fixedness of the past and the malleability of the future is nowhere to be found in the known laws of physics. The deep-down microscopic rules of nature run equally well forward or backward in time from any given situation. If you know the exact state of the universe, and all of the laws of physics, the future as well as the past is rigidly determined.”
"There is no need in any of this to choose a privileged variable and call it ‘time.’ What we need, if we want to do science, is a theory that tells us how the variables change with respect to each other. That is to say, how one changes when others change."
WHAT, THEN, IS LEFT OF TIME?
Time as a measure of change
"The entire evolution of science would suggest that the best grammar for thinking about the world is that of change, not of permanence. Not of being, but of becoming."
The world is not a collection of things, it is a sequence of events.
Time has a direction
The arrow of time
Entropy ~ disorder ~ energy dissipated as heat
Time flows in the direction of increased entropy.
"The difference between past and future does not lie in the elementary laws of motion; it does not reside in the deep grammar of nature. It is the natural disordering that leads to gradually less particular, less special situations."
Psychological Arrow of Time
Psychological arrow points in the same direction as the thermodynamic arrow (direction of increased entropy)
Treat our memory like computational memory (which we understand)
“Disorder increases with time because we measure time in the direction in which disorder increases.”
- A Brief History of Time, Stephen Hawking
Broken symmetry in the laws of nature...
The arrow of time is not a feature of the underlying laws of physics, rather a result of emergent behavior on a macroscopic scale and breaks the symmetry.
Past Hypothesis
“When it comes to the past, however, we have at our disposal both our knowledge of the current macroscopic state of the universe, plus the fact that the early universe began in a low-entropy state. That one extra bit of information, known simply as the ‘Past Hypothesis,’ gives us enormous leverage when it comes to reconstructing the past from the present.”
-pg. 43, From Eternity to Here, Sean Carroll
Why was entropy lower in the past?
Regardless, our experience of time is intertwined with our very existence, so we ought to appreciate it fully.
EXPERIENCING TIME
“Put your hand on a hot stove for a minute, and it seems like an hour. Sit with a pretty girl for an hour, and it seems like a minute. That's relativity.”
In conclusion...
“I had chosen to replace nothingness with something . . . From now on, there would be a future, a present, and a past. A past of nothingness, and then a future of something. In fact, I had just created time. But unintentionally. It was just that my resolution to act, to make things, to put an end to the unceasing absence of happenings, required time."