Possibilism is the idea that there are real possibilities available in an open future.

It stands in contrast to actualism, the idea that the events that do happen are the only possible events that could possibly have happened.

Actualism denies the existence of alternative possibilities. Actualists are determinists and eliminative materialists. Philosophers from Diodorus Cronus to Daniel Dennett argue that actualism is true, that there is only one possible actual future. How could anything have been otherwise, Dennett asks.

Actualism is closely connected to the mistaken belief, held by some prominent theoretical physicists, that information is a conserved quantity, just like matter and energy. Information philosophy has shown that the total information content has been increasing since the origin of the universe. We have explained the cosmic creation process that allows pockets of negative entropy to appear in what we call "information structures," like the galaxies, stars, and planets, even as the total entropy is increasing, in conformity with the second law of thermodynamics.

Possibilism should not be confused with the idea of possible worlds, the analytic language philosopher David Lewis's methodology in modal philosophy for investigating the logic of "nearby possible worlds" that differ only slightly from our world, designed as a tool for examining concepts like truth and falsity, necessity and contingency, possibility and impossibility.

Nor should it be confused with the extravagant idea of "parallel universes" - Hugh Everett's "many worlds" interpretation of quantum mechanics which postulates the world "splitting" into two or more complete universes whenever a quantum experiment requires a "collapse of the wave function."

The idea of many possible worlds was first proposed by Gottfried Leibniz, who famously argued that the actual world is "the best of all possible worlds."

The analytic language philosopher David Lewis developed the philosophical methodology known as modal realism based on his claim that for every non-contradictory statement there is a possible world in which that statement is true.

Hugh Everett III's many-worlds interpretation of quantum mechanics is an attempt to deny the random "collapse" of the wave function and preserve determinism in quantum mechanics. Everett claimed that where the projection postulate of standard quantum mechanics says that one of the possible eigenstates of a quantum system is randomly realized, his many worlds interpretation says that the world "splits" into multiple universes so as to realize all the possible eigenstates, one in each new world.

David Layzer argues that since the universe is infinite there are places in the universe where any possible situation is being realized. This is a cosmologist's version of philosopher David Lewis's "possible worlds."

Possibilism finds support in the fact that quantum physics is a statistical or probabilistic theory. When a quantum measurement is made, the theory accurately predicts (to many significant figures) the probabilities that the measurement apparatus will end up in one of its possible energy values (eigenvalues).

At the microscopic quantum level, the future is distinctly open to many possibilities.

According to the information interpretation of quantum mechanics, quantum systems evolve in two ways: the first is the wave function deterministically exploring all the possibilities for interaction; the second is the particle randomly choosing one of those possibilities to become actual.

The complex probability amplitude wave function, whose square gives the probabilty (between 0 and 1) of finding the particle somewhere, should perhaps be called the "possibilities function,"because it explores all space and tells us where particles will possibly be found.

Diodorus Cronus, Harry Frankfurt, Daniel Dennett, J. J. C. Smart, and many other determinist philosophers deny the existence of possibilities.

Aristotle asked whether the statement "There will be a sea battle next week," was already true or false. Actualists like Didorus had argued that its truth necessitates its happening in the future.

A few hundred years later, Porphyry asked what is called his "Fateful Question." Do the Platonic categories exist? Information philosophy answers yes. They exist in the realm of immaterial, but physical, information. It is the realm of thought, the very stuff of philosophy.

In quantum mechanics, especially in the information interpretation, possibilities have calculable probabilities. Their existence is shown by the fact that they interfere with one another, determining the actual outcomes of physical experiments.

In the most plausible solution to the problem of free will, the generation of alternative possibilities is the first stage. The second stage is the evaluation of those possibilities and the selection of one that is consistent with and statistically determined by the agent's motives, reasons, feelings, etc., as compatibilists have always insisted.

But what becomes of the many possibilities that are not actualized? Jean-Paul Sartre said they become "nothingness." Would Hugh Everett give each one of them its own universe?

Claude Shannon's information theory requires multiple possible messages or no new information can be communicated. Unless there can be "surprises," no new information is possible. But it goes deeper than that. Without possibilities, no new information can even be created.

Chance in quantum physics is the basis for the many possible thoughts that can pop into our heads when we are evaluating alternative possibilities and making a decision. But we must deny that our decisions and actions are the direct result of a random quantum event.

Two-stage models of free will claim that noise quantum noise in the brain generates alternative possibilities (new "thoughts") for action. But they do not determine the action, because our actions are the result of the statistically determined evaluation of those possibilities, subsequent deliberation, and finally an ultimate choice governed by our character (beliefs, desires, motives) so that we are responsible for our actions.

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