Simplicity and Complexity Conference


Thoughts by Johns Hopkins Philosophers and Physicists

Saturday, September 17th, 2022 at the Glass Pavilion, Levering Hall, Homewood Campus; 9am-5:30pm

Sponsored by: The Johns Hopkins Center for History and Philosophy of Science, The William H. Miller III Department of Philosophy, and the William H. Miller III Department of Physics and Astronomy

“Simplicity is the ultimate sophistication” 

– Leonardo da Vinci

This conference is for all those who accept, reject, or don’t know what to make of Leonardo’s claim. With talks from five faculty members of the Johns Hopkins Philosophy and Physics and Astronomy departments, including our new faculty members Sean Carroll and Jenann Ismael, a variety of questions and perspectives on simplicity and complexity will be explored.


Each session is scheduled for up to an hour, with 30-40 minutes for the talk and the remainder for discussion.

There will be a 15 minute break following each session.

9:  Welcoming remarks

9.15:  Peter Achinstein, Philosophy.  “Does Simplicity Track Truth?  Isaac Newton and Gravity.”

10.30:  Jenann Ismael, Philosophy, “Why is the world simple from the outside but complex from the inside?.”

11.45-1: Lunch

1.15: Robert Rynasiewicz, Philosophy.  “Einstein, Simplicity, and the Light Postulate.”

2.30: Brice Menard, Physics.  “Observations, Patterns, Principles.”

3.45: Sean Carroll, Physics and Philosophy.  “Connecting the Microworld to the Macroworld.”

4.45: Panel Discussion with speakers and audience


Peter Achinstein, Philosophy.  “Does Simplicity Track Truth?  Isaac Newton and Gravity.”

In his proof of the law of gravity Isaac Newton makes explicit use of four methodological “Rules for the Study of Natural Philosophy.” The first two pertain to inferring unobservable causes from observed effects, the second two pertain to making inductive generalizations from regularities observed in some bodies to the claim that these regularities hold for all bodies. Newton justifies Rules 1 and 2 by claiming that “nature is simple and does not indulge in the luxury of superfluous causes.” He justifies his inductive rules by claiming that “nature is always simple and ever consonant with itself.” And he explicitly claims that because of this, simplicity tracks truth. Lots of scientists and philosophers seem to agree with these claims. Should they? Why?

Jenann Ismael, Philosophy.  “Why is the world simple from the outside but complex from the inside?.”

If the world is fundamentally simple, where does its manifest complexity come from?  One neglected source of complexity, I will suggest, comes self-reference.  I’ll illustrate by showing how taking self-reference seriously can provide a solution to outstanding problems reconciling relativity with time as we experience it.  

More specifically, I’ll argue that seeing how self-reference plays out against the background of a thermodynamic gradient gives us an interpretation of what Roger Penrose called “The arrow most difficult to comprehend … namely the feeling of relentless forward temporal progression, according to which potentialities seem to be transformed into actualities.” 

 Robert Rynasiewicz, Philosophy.  “Einstein, Simplicity, and the Light Postulate.”

In developing special relativity, Einstein had direct evidence for the principle of relativity but no direct evidence for the light postulate, viz., that the speed of light is independent of the motion of its source.  In fact, for a year or more prior to 1905, he tried to fashion an emission theory of electrodynamics, satisfying the principle of relativity but rejecting the light postulate.  Beginning with Ritz in 1908, a number of physicists later chose this route in order to avoid the counterintuitive kinematics of special relativity.  Direct evidence for the light postulate started to appear only in 1912 with DeSitter’s observations on a binary star system.  Further experiments ruled out special assumptions made by various emission theorists.

What convinced Einstein to give up the search for an emission theory and to adopt the light postulate?  In later testimony, he explained that, on an emission theory, one must make too many arbitrary choices in explaining basic optical phenomena—reflection, refraction, and diffraction—when the source is in motion.  In contrast, the light postulate yields simple answers, as attested to by the Maxwell-Lorentz ether theory.  And the latter can be made to comply with the principle of relativity under the Lorentz and field transformation equations.

 Brice Menard, Physics.  “Observations, Patterns, Principles.”

Physicists observe Nature, identify patterns and infer principles. I will discuss how the limits imposed by complexity have shaped the domain to which this sequence has been applied over time. I will then comment on the recent developments in Machine Learning and their impact on how physicists interact with complexity and simplicity.

 Sean Carroll, Physics and Philosophy.  “Connecting the Microworld to the Macroworld.”

Science successfully describes the world using multiple theories, each appropriate to some particular “layer of reality.” One of the tasks of philosophy (and science) is to describe how those layers fit together and are consistent with each other. I will describe two examples that I am currently thinking about. One is the emergence of the classical world from quantum mechanics, which I argue depends on the particular form of the quantum theory, and helps explain the distinction between position space and momentum space. The other is the emergence of temporally asymmetric cause-and-effect relations from underlying time-symmetric laws.