Sellars and the Philosophy of Physics

In a letter to Chisholm, Wilfred Sellars wrote:

Thus, while I agree with you that
'. . .' means - - -
is not constructable in Rylean terms ('Behaviorese,' I have called it), I also insist that it is not to be analyzed in terms of
'. . .' expresses t, and t is about - - -.
My solution is that "'. . .' means - - -" is the core of a unique mode of discourse which is as distinct from the description and explanation of empirical fact, as is the language of prescription and justification.

Although Sellars was concerned with the philosophy of mind, there is something important here for philosophers of physics to learn as well. A major activity of physics is the collection of empirical facts. Another is the prediction and justification of these facts. But the activity of investigating meaning is a distinct activity altogether. This last activity includes much of what concerns the philosophy of physics, when it is done well.

Whether it be causation, equivalence, gauge, prediction, or simultaneity -- among many examples -- I think much of what distinguishes philosophy of physics from physics is a central concern with the (particularly philosophical) activity of explicating meaning.

Elegant Desktop ToDo List

A lot of people have been asking me about the Desktop ToDo list that appears in my last screencast. So, here's the scoop on this simple and elegant ToDo list system, which can be easily synchronized across multiple (Mac) computers.




Here's what you need to set this stuff up.

Mac OS X. I don't know of any good windows analogues for Quicksilver and Geektool. Let us know if you do!

Geektool. This beautiful little app is available for free from Tynsoe.org. For more on what it can do, try this tutorial. For our purposes, here's how to display a TXT file on your Desktop:

• Create a new Shell geeklet in the Geektool preference pane
• Enter the command: cat PathToYourList/YourList.txt
• To synchronize multiple computers, make sure the file is in a Dropbox folder.

Quicksilver. This is why I own a mac. It's free from Blacktree.com. If you're new to it, try this beginner's guide. To set up the 'Append' and 'Completed' functions seen in the screencast:

• On the Quicksilver > Plugins page, add the 'Text Manipulation Actions' plugin. Then make sure 'Append' box is checked on the Preferences > Actions page.
• Now you can append text to any .TXT file -- but only files with that extension.
• Download the Completed script.
• Open it with ScriptEditor and set the path to your Completed.txt file.
• Add the Completed.scpt script to the folder YourUsername/Library/Application Support/Quicksilver/Actions. Create this folder if it doesn't exist yet.

And that's it! As always, be sure to leave your thoughts, ideas or improvements in the comments below.

Related Posts:

• Get started handling academic citations like a pro
• Get started reading books and articles on the cheap
• Get started reading recent classics in the philosophy of physics

The three-way duel

The late great Martin Gardner once posed this puzzle.

Suppose you're involved in a duel with two other people. You (Person A) shoot first, followed Person B, followed by Person C, then it goes back to you, and so on. Moreover, you know the following about everyone's shooting skills.

• You (Person A) will hit your target with probability 1/3.
• Person B will hit her target with probability 2/3.
• Person C is a perfect marksman, will hit his target with probability 1.

You get to go first. Who would you shoot at, and why? Best solution gets a free sheep.

(Note: your options are Person B, or Person C, or neither.)

Update:  Jonathan of Unshielded Colliders has been awarded a free sheep for his solution. Here you go, Jonathan:

CPT: The 'Intuitive' Approach

Khriplovich and Lamoreaux (1997, §2) suggest a very interesting argument that CPT provides the correct notion of "complete reversal" in physics.

The background assumption is that "complete reversal" should have effect of reversing the sign of 4-vectors in spacetime. David Malament, for example, has suggested that time reversal in classical electrodynamics should have this effect on timelike vectors. The proposal here is that "complete" motion reversal to have this effect on all vectors (timelike, spacelike, and null).

Clearly, time reversal T on its own is not enough for this -- it doesn't reverse spacelike vectors. Parity reversal P isn't either -- it doesn't reverse timelike vectors.

What about PT? After all, flipping about two axes is equivalent to a rotation. Shouldn't that be enough to reverse all four vectors? As it turns out, it's not enough, at least when it comes to 4-current j^a. Since both P and T fix charge density and reverse current, we have:


PT j^a = PT (p, j) = P (p, -j) = (p, j).
To reverse current, we need an operator C that sends particles to antiparticles, and thus sending j^a to -j^a. Thus, to get "total" motion reversal in a world with current, we need the CPT operator.

What I like about this thinking is that it depends crucially on the kind of matter fields in play. It's only in the presence of 4-currents that PT is not enough to completely reverse motion. But similarly, the discovery of additional exotic matter fields might someday imply that CPT is not enough to reverse motion, either.

Update: Wolfgang reports news about evidence for CPT-violation in a recent Fermilab experiment.

Even more philosophy of physics conferences, Summer 2010

If you know about the usual summer conferences and are still looking for more:

Hannover: Philosophy of Physics in Germany - Current State and Perspectives (11-12 Jun 2010). If you happen to be in or around Hannover next week (which unfortunately I am not), stop by to check this out! Meinard Kuhlmann (of recent Pittsburgh-fellow fame) organized this formidable program.

Scheduled Speakers: Claus Beisbart, Arianna Borrelli, Matthias Egg, Michael Esfeld, Brigitte Falkenbur), Cord Frieb), Mathias Frisch, Ulrich Gähde, Reiner Hedrich, Carsten Held, Rafaela Hillerbrand, Paul Hoyningen-Huen), Andreas Hüttemann, Meinard Kuhlmann, Dennis Lehmkuhl, Christoph Lehner, Holger Lyre, Paul Näger, Thorben Petersen, Wolfgang Pietsch, Helmut Desks, Wolfgang Rhode, Gregor Schiemann, Francisco Soler -Gil, Manfred Stöckler, Michael Stöltzner.

London: Emergence in Physics (13-14 Jul, 2010). This looks like a great meeting to check out after the BJPS/FoP weekend. It's organized by the distinguished Prof. Eleanor Knox, the former Oxford student, recently-hired IP faculty, and deft climber of Swiss mountain-tops.

Currently scheduled speakers: Bob Batterman, Jeremy Butterfield, Roman Frigg, Stephan Hartmann, Eleanor Knox, David Wallace.

Vienna: What Exists in the Quantum World? (19-24 Jul, 2010). This is a great idea for a workshop, and includes a great mix of philosophers and physicists. Applications to join are due by Monday though, so do hurry if you'd like to go!

Senior participants: Markus Aspelmeyer, Gennaro Auletta, Tina Bilban, Časlav Brukner, Jeffrey Bub, Vladimir Chaloupka, Raymond Chiao, Daniel Greenberger, Alexei Grinbaum, Richard Healey, Michael Horne, Tarja Kallio-Tamminen, Henry Krips, Franck Laloë, Xiaosong Ma, Stefano Osnaghi, Sorin Paraoanu, Sven Ramelow, Stig Stenholm, Anton Zeilinger.