Sean Carroll
California Institute of Technology
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Astronomy-Cosmology-Physics view of the space, time, and galaxy.
Typology: Slides
2016/2017
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Sean Carroll California Institute of Technology
Science and philosophy have changed our image of the world
Our everyday, common-sense way of thinking abou the world (the “manifest image”) has not caught up
Ontology: the study of being, what exists
Reality
Monism
multiple one
Idealism
nature mind
Naturalism
Property dualism
Physicalism
extra- physical physical
Austere naturalism
Poetic naturalism
eliminative expansive
Poetic Naturalism
- (^) There is only one world, the natural world.
- (^) We learn about it empirically, through science.
- (^) But there are many ways of talking about the wor
- (^) If a way of talking accurately describes (part of)
the world, the concepts it refers to are real.
Our task: understand how the fundamental-physics way of talking about the world is compatible with the everyday-life way of talking about it.
Everything that happens has a cause/reason?
Aristotle: Eric Gaba.
Aristotle Spinoza Leibniz
We learn about the world by looking at it (not just by thinking about it)
Hume (^) Bayes
Conservation of momentum: the world moves by itself
Ibn Sina
Ibn Sina: Adam Jones; Voyager: NASA/JPL. Wikimedia commons
“An intellect which at a certain moment would know all forces and all positions of all items of which nature is composed… for such an intellect nothing would be uncertain and the future just like the past would be present before its eyes.”
- An Essay on Probabilities, 1814
Laplace’s Demon.
Laplace: Wikimedia Common
Conservation of information: each moment determines its past and future
Time doesn’t “flow,” or bring the future into existence; it’s just a label.
Laws of nature are patterns connecting different moments.
time
“Cause and effect” isn’t fundamental
“The law of causality, I believe, like much that passes muster among philosophers, is a relic of a bygone age, surviving, like the monarchy, only because it is erroneously supposed to do no harm.”
- Bertrand Russell
A single phenomenon underlies all manifestations of time’s arrow: increasing entropy.
Entropy is a measure of disorderliness, messiness, randomness.
Time
Entropy
Second Law of Thermodynamics: entropy increases with time (in closed systems).
possible arrangements of atoms/molecules, grouped by macroscopic indistinguishability
Entropy increases simply because there are more ways to be high-entropy than low-entropy.
All makes sense, if the entropy was low to begin with.
low entropy
high entropy
The Past Hypothesis: our universe started in a low-entropy state.
13.8 billion years ago, at the Big Bang.