1. Free will and quantum mechanics ↑
One misconception about the Everett, or many worlds, approach to quantum mechanics, is that new worlds are created every time we make a decision or toss a coin. This is not the case because these are macroscopic events, and we only branch when quantum interactions have macroscopic effects.
In 2006, physicist Harald Atmanspacher showed that there's little evidence that quantum events in the brain affect consciousness. This is because standard accounts show that the experiences of qualia are correlated with neuronal assemblies, formed from several thousands of coupled neurons. The superpositional qualities of objects this large are suppressed by decoherence, and so our mental representations are described classically.
This means that if there's a world where a parallel version of yourself is committing some kind of action that you find abhorrent, then you would probably have branched much earlier, and led a very different life.
If we focus on single components of neuronal assemblies then it is more likely that quantum behaviour can occur. In 1992, German physicist Friedrich Beck and Australian neurophysiologist John Eccles showed that the process of exocytosis can be described as a quantum mechanical event[2a].
Exocytosis refers to the process of sending neural information through a chemical synapse. The synapse is triggered by a nerve impulse that arrives in accordance with a small probability.
Beck and Eccles showed that this probability corresponds to quantum, rather than thermodynamic, statistics, and stated that these quantum events offer, "a natural explanation for voluntary movements caused by mental intentions without violating physical conservation laws"[2b]. It's our conscious will that increases the probability of the interaction.
2. Free will and classical mechanics ↑
At first glance, we appear not to have free will whether we accept that our choices are determined by quantum necessity or not. Classical mechanics shows that if we knew all of the natural laws, and the entire physical state of a person's brain, then we should be able to determine what they would do in any given situation. If we knew everything about the multiverse, then we should be able to predict the future of every conscious mind. American neurophysiologist Benjamin Libet explored this idea in a series of experiments conducted in 1985.
Libet found that the brain begins initiating a voluntary act "about 400 ms before the appearance of the conscious will to act"[4a], where a ms is a thousandth of a second. In 2008, Chun Siong Soon and colleagues showed that you can predict a person's free choice up to 10 seconds before they're aware of what they'll do.
This appears to show that we do not make conscious decisions freely, however Libet did not accept this because there is a 100 ms interval when we can choose to veto the action. This is after it has been initiated by the brain, but before it has actually been carried out.
This option is not available to people who appear to act against their will, such as addicts or people with physical compulsions, and so the appearance of this option provides a good definition of when someone is acting freely.
Libet concluded that because we never freely choose to initiate an act, moral systems that punish us for impure thoughts "create a physiologically insurmountable moral and psychological difficulty"[4b].
Libet's belief that we can freely choose to veto an action is based on the idea that this choice is not itself the product of unconscious activity. He stated that:
"the awareness of the decision to veto could be thought to require preceding unconscious processes, but the content of that awareness (the actual decision to veto) is a separate feature that need not have the same requirement"[4c].
Libet was reluctant to accept a material theory of the mind because he did not think it could explain the subjective nature of consciousness. He also believed that it contradicts our belief in free will.
Libet argued that we instinctively believe we have free will, and this belief forms "a fundamental basis for views of our human nature"[4d]. Free will is required in order to show that people are responsible for their actions, and our systems of justice and desert are based upon this fact.
Libet's first concern may be resolved by adopting a many minds approach to quantum mechanics and, by 1954, British philosopher Alfred Jules Ayer had shown that determinism is not incompatible with free will because the two are not mutually exclusive[6a].
In order to be held morally responsible for our actions, Ayer argued that we must be acting consistently with our character and this implies that our behaviour is, to an extent, predictable. He stated that:
"from the fact that my action is causally determined it does not necessarily follow that I am constrained to do it: and this is equivalent to saying that it does not necessarily, follow that I am not free"[6b].
Since it is inconsistent to contrast free will with causality, Ayer stated that it should instead be contrasted with constraint.
This can be illustrated with a simple analogy: imagine that an electronic device is implanted in your brain without your knowledge. The device makes it so that the only fruit you can pick up when you go to the supermarket are apples. When you get there you may freely choose to pick up apples, and so the electronic device would not be activated to coerce you. It is fully determined that you will pick apples, because had you not chosen to, then the device would have forced you. Yet despite this determinism, your choice was made freely.
According to Ayer, our free choices will always coincide with the determined result and so there is no need for an actual device to force us into action. Ayer stated that:
"the fact that my action may nevertheless have a cause is…irrelevant. For it is not when my action has any cause at all, but only when it has a special sort of cause, that it is reckoned not to be free"[6c].
Ayer suggested that people make the mistake of contrasting free will with causality because they falsely believe that causality means "one event is somehow in the power of another"[6d].
In 1990, neurophysiologists K. Ammon and Simon Gandevia showed that it's possible to influence someone's free choices by stimulating frontal regions of their brain. Joaquim Pereira Brasil-Neto and colleagues found similar results in 1992.
In 2002, American psychologist Daniel Wegner suggested that free will can be understood an illusion generated by the brain. Like English philosopher Thomas Hobbes, Wegner argued that this is due to our inability to obtain a complete knowledge of our own mind.
This idea leads to the question of whether we would be able to choose to act differently if we were made aware of what our future actions will be. This question invokes a paradox because if we could choose to act differently, then we would not have accurately predicted our behaviour in the first place.