First some basic considerations. The No! answer requires more than just having some physical aspect or process associated with every event. The No answer requires that the causal process be completely and entirely physical. If any part of the causal process involves something that is not physical, then the laws of physics do not furnish a complete explanation. And then we have a Yes answer.

Second, and more important, I have come to suspect that most of my peers in psychology do not properly understand physics. If you had at least two college courses on physics, I ask you to pull out your textbook and spend a few minutes looking at what's inside it. Ask yourself how those laws and processes can explain some social event like the effects of the federal bailout on the national debt, or Sarah Palin's resignation, or the NBA Finals outcome.

Physical laws are based on a tightly limited set of variables. An electron has mass, location, velocity, acceleration, electrical charge. Larger things also have chemical composition and molecular structure. There are a few other variables, but most of them are made out of these few. Force, for example, is mass times acceleration, and momentum is mass times velocity.

I believe that any honest scientist will admit that we cannot yet imagine how social events can be fully explained by physical processes. What I'm asking is only a small additional step: have the courage to entertain the possibility that what you cannot imagine is not there. Social events will not be able to be fully and completely reduced to physical processes. There is something else other than molecules that is needed in order to understand human behavior.

If you are open-minded, I invite you to try this exercise. Don't make a snap judgment on these ideas. Try them out for a couple months. That involves two things: Try seriously and in good faith to see them as correct, and try also seriously and in good faith to find them wrong. Switching back and forth is most effective, I think.

SYMBOLISM IS NOT A PHYSICAL RELATIONSHIP
In your college physics textbook you will find many symbols, but symbolism itself is not explained. Symbolism is not a physical relationship. What links the American flag to the American nation, or the dollar bill to a unit of value, or Arnold Schwarzenegger's name to his body, is not contained in the electrons and the physical forces that link things. That connection cannot be expressed in terms of the laws of physics.

Remember, if any part of a causal chain contains things that are not physical, then the laws of physics are not adequate to explain everything. If any physical action is caused partly by something symbolic, then not everything is reducible to physical processes, and we have our Yes answer.

SOCIAL REALITY AND MEANING
I am going to suggest that the non-physical aspects of reality consist of meaning. Meaning is not, in its essence, a physical reality.

Take the sentence "5x6=22." This is a mathematical expression. It is also a false one. Its falseness is not arbitrary. Every culture that has mastered multiplication knows that that expression is false. But what are the physical properties of its falseness? That falseness does not have mass, or velocity, or acceleration. It does not have chemical composition, molecular structure, or the rest. It is not something "in" your brain, as if destroying your brain or performing psychosurgery on your brain could make it true that 5x6=22.

Chess is a useful example. Molecules do get moved because of chess: pieces get moved around, trophies are manufactured and awarded, cash prizes enable the winner of the game to buy things he or she would not have bought otherwise. But is the game of chess a physical thing? It is not contained in the pieces of a particular chess set, because if you smash those pieces, the game still exists.

It is not equal to all the pieces in all the chess sets in the world. If you smash one set, you have altered the totality of all those pieces, but you have not changed the game. Likewise, manufacturing new sets does not necessarily change the game, even though it changes the totality of chess sets,

The game's existence is not in the neuron firings in the brains of the two players. The game would still exist if one of them had never learned to play, or if one of them dies, thereby ceasing that brain activity. The game exists independently of any particular brain. That makes it impossible to equate the game with brain events.

Money is another good example. You might be misled to think money is physical stuff, because there exist coins and bills, which are physical things made of molecules. But this is wrong, as can easily be shown. First, the equivalence of a dollar bill and ten dimes cannot be explained on the basis of the molecules in them. Second, consider what happened to those Dutch guilders in your pocket when the Netherlands switched to the Euro. The molecular structure of those coins remained the same, but one day you could use them to buy socks, and the next day you couldn't.

Third, economists note that all the dollar bills and coins in the world make up only a third of the total amount of dollars that officially exist. That is, most American money does not have any physical form whatsoever. It exists as only abstract ideas, represented as notional sums recorded in various computers (but hardly being the same as the electrical signals inside those computers; your bank account retains its value even if the bank turns off its computer).

Pi is another excellent example. The value of pi is a mathematical truth, based on abstract ratios of every circle's radius to circumference. If Arkansas had succeeded in passing that law declaring pi to equal 3.0 (in order to make life easier for schoolchildren), things could not have been built properly thereafter. Yet the value of pi is not a physical thing at all. It does not have mass, velocity, molecular structure, or the rest.

Before moving on, let's consider a few other things that are quite important to psychology, insofar as they influence behavior. The English language does not have mass, velocity, acceleration, chemical composition, molecular structure, or other properties of physical reality. The same can be said for democracy, justice, and culture. Laws - here I refer to legal and social entities, not the physical kind - have a huge influence on human behavior, but laws are not physical things, but rather symbolic constraints enacted by elected representatives and applied by police and judges to alter the disposition of individual bodies. The economic crisis and the national debt are having an effect on many of us, but although the national debt can be called "massive," it does not have mass that can be measured (e.g., weighed), the way your body or your desk has measurable mass. It is not a physical thing.

DO SOCIAL EVENTS BREAK THE LAWS OF PHYSICS?
In order to entertain these ideas, people stumble on the alarming thought that I am suggesting that the laws of physics are routinely broken. We have no way to countenance violating the laws of physics.

Relax! The laws are not broken. Nothing that happens has to violate the laws of physics.

All I am suggesting is that physical events are sometimes influenced by non-physical realities. Perhaps another way to put it is that some physical things are capable of allowing themselves to be influenced by non-physical things.