William James, Alfred North Whitehead, Hannah Arendt, Neils Bohr
Final cause: the sake for which something happens or is done. Principle of Sufficient Reason: “Nothing is without a ground or reason why it is.”
What do we do for the multiverse? Exactly this.
Gifford Lecture One: Cosmos, Time, Memory
California Institute of Technology
Science and philosophy have changed
our image of the world
Our everyday, common-sense way of thinking about
the world (the “manifest image”) has not caught up.
Manifest image Scientific image
Time flows from past Time is a label within
to future an eternal universe
For every event there is Parts of the
a reason; for every are related by patterns:
effect there is a cause the laws of nature
Life and mind are Life and mind are
distinct from matter physical and emergent
Purpose, morality, and Purpose, morality and
meaning are objective meaning are
the study of being,
• There is only one world, the natural world.
• We learn about it empirically, through science.
• But there are many ways of talking about the world.
• 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.
[Allesandro Bianchi, Reuters]
Cause and effect, motion and movers,
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)
evidence given theory
“Credence” = “degree of belief.”
1) Assign priors.
2) Calculate likelihoods.
3) Gather evidence.
4) Update credences.
Conservation of momentum:
the world moves by itself
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: Wikimedia Commons
Conservation of information:
each moment determines
its past and future
Laws are differential equations in time.
(Footnote: quantum indeterminism?)
Time doesn’t “flow,”
or bring the future
into existence; it’s
just a label.
Laws of nature are
“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
Cause & EffectFree Will
Major disconnect between fundamental physics
and everyday life: the arrow of time.
Nowhere to be found in the underlying, microscopic laws.
A single phenomenon underlies all
manifestations of time’s arrow: increasing entropy.
Entropy is a measure of disorderliness,
Second Law of Thermodynamics:
entropy increases with time
(in closed systems).
Ludwig Boltzmann, 1870’s:
Entropy counts the number
of ways we can re-arrange
a system without changing
its basic appearance.
all mixed up
grouped by macroscopic
simply because there
are more ways to
All makes sense,
if the entropy was
low to begin with.
The Past Hypothesis:
our universe started in a low-entropy state.
13.8 billion years ago, at the Big Bang.
1 sec 105
Our observable universe
“Memories” and “causes” are emergent features of
an underlying time-symmetric universe that has a
macroscopic arrow of time.
Memory: feature of now
that lets us infer something
about the past.
Cause: feature of now
that lets us infer something
about the future.
Low-entropy past gives
features of the present
leverage over other times.
what we know
about the present
different levels of description involve
completely different concepts/vocabularies
Microscopic fundamental physics
• arrow of time
• cause and effect
• “reasons why”
• laws of nature
• differential equations
• conservation of
1. Cosmos, Time, Memory
images of the world; causality; the arrow of time
2. The Stuff of which We Are Made
quantum theory; the laws underlying everyday life
3. Layers of Reality
effective theories; emergence; multiple vocabularies
4. Simplicity, Complexity, Thought
entropy vs. complexity; life; consciousness
5. Our Place in the Universe
ought vs. is; meaning, caring, constructing morals