In case the following position on free will might look to some colleagues too strong and not sufficiently "politically correct," please see the two notes at the beginning of The world is four-dimensional - Hermann Minkowski's irrefutable proof.
That is why it is important to understand that any view which contradicts experiment has nothing to do with Nature. The view that we have free will scientifically undeniably contradicts all experiments (not just a single experiment) that confirmed the kinematic relativistic effects.
Of course, no one can impose on us a given (even scientific) view - we are all entitled to our own views. However, we should never forget that there is a small problem - Nature does not care at all about our personal opinions.
So the greatest challenge to free will comes not from neuroscience or philosophy, but from physics - from Hermann Minkowski (Einstein's mathematics professor) who in 1908 reformulated Einstein's special relativity and demonstrated that special relativity is a theory of an absolute four-dimensional world, which contains all moments of time given at once (since they form the fourth dimension). [Now it is clear to every physicist that Einstein gave a wrong name to his theory of relativity - relativity is not the essence of the theory since, as Minkowski showed, the relativity of three-dimensional quantities is only possible in an absolute four-dimensional world, which can be described in the ordinary three-dimensional language of our perceptions in terms of three-dimensional spaces in relative motion with respect to one another.] Unlike Poincare, Minkowski believed that the four-dimensional world (spacetime) is real, not just a convenient mathematical abstraction.What makes this challenge to free will the greatest ever is that it implies that the non-existence of free will is a scientific fact (which does not just disappear if denied or ignored): if Minkowski's four-dimensional world were indeed an abstract notion without a counterpart in the world, then all physical objects would not be four-dimensional worldtubes, containing the ordinary three-dimensional bodies at all moments of their histories, but will be the three-dimensional bodies of our perceptions and none of the experiments that confirmed the kinematic relativistic effects would be possible.
This is perhaps best demonstrated by length contraction explained by Minkowski himself. As in the Minkowski four-dimensional world the ordinary three-dimensional objects of our perceptions (including our bodies) are four-dimensional worldtubes which contain the entire histories in time of the ordinary three-dimensional objects, this means that our lives are utterly predetermined like a movie story is predetermined since it is entirely given on the film strip (in the case of old movies). This means that nothing happens in the higher reality of the four-dimensional world discovered by Minkowski - there is no birth, no death, no change at all; it only turned out that what exists and our lives are a much greater puzzle that we could even imagine.Like any other physical objects, our bodies also undergo relativistic length contraction. To see why the view that we have free will contradicts the relativistic experiments, assume that the four-dimensional worldtubes are nothing more than mathematical abstractions and our bodies are the familiar ordinary three-dimensional objects. See the six pages (taken from From Illusions to Reality: Time, Spacetime and the Nature of Reality) where Minkowski's explanation of length contraction of a meter stick (and a visualization of it) is given and it is shown that this effect would be impossible if the meter stick were not a four-dimensional worldtube.
Not only Minkowski, but also many scientists had to deal with the implications of the strange Minkowski world, notably Einstein himself:
"People like us, who believe in physics, know that the distinction between past, present and future is only a stubbornly persistent illusion"
and Hermann Weyl:
"The objective world merely exists, it does not happen; as a whole it has no history. Only before the eye of the consciousness climbing up in the world line of my body, a section of this world "comes to life" and moves past it as a spatial image engaged in temporal transformation."
Regarding Weyl's reconciliation of the higher reality of spacetime - the Minkowski four-dimensional world (in which there is no distinction between past, present and future) - and the everyday reality created by our perceptions (in which we perceive an apparent flow of time, involving a sharp distinction between past, present and future), I would like to stress the following as strongly as possible. The perceived reality of our everyday life has two possible explanations (most of those who blindly believe in free will do not seem to be aware of this fact):
It is obvious that it is the Ultimate Judge - the experimental evidence - that should decide which explanation is the correct one. As explained above, the Ultimate Judge has already and repeatedly ruled on this crucial issue - none of the experiments which confirmed the kinematic relativistic effects would be possible if the world were not four-dimensional.What indirectly supports the ruling of the Ultimate Judge is the fact that our perceptions have been constantly fooling us about what really exists and we have been constanly correcting our view of the world. Only two examples:
That is why, we all should face the fact that the ruling of the Ultimate Judge invites us to make the next (and huge) correction of our view of the world.
Note on the most frequent objection: - that the reality of spacetime has nothing to do with free will because it does not provide "an adequate approach to the emergence of complexity" (as a colleague put it). Such objections completely miss the point by failing to see the obvious - the reality of spacetime shows that physical macroscopic objects are forever given (four-dimensional) worldtubes and as our physical bodies are precisely such macroscopic objects the ruling of the Ultimate Judge applies with full force to humans regardless of whether or not we have any idea of what kind of "emergence of complexity" is involved in our brains and in the appearance of the feeling of free will. In short: the experimental evidence that confirmed the reality of spacetime demonstrated that the entire history of our physical bodies is forever given (that is why, it does not matter at all what goes on in our brains).
Although I would rather say that insisting that free will exists is not science at all, I agree with her arguments. However, the fact that the view (based on the assumption that our bodies are three-dimensional objects) that we have free will contradicts the experimental evidence confirming the relativistic effects (as shown by the example above) is much stronger proof. It does not even require to mention the probabilistic behaviour of quantum phenomena since our bodies are macroscopic objects.
Earlier this month (January 10, 2016) Sabine Hossenfelder added a post "Free will is dead, let's bury it" on her blog Backreaction which started with "I wish people would stop insisting they have free will. It's terribly annoying. Insisting that free will exists is bad science."
1. I fully understand the colleagues who would prefer that the issue of free will should not be discussed at all. Personally, (like most people, I guess) I detest the block Universe view. Years ago I spent a significant amount of time to examine and reexamine the experiments that confirmed the kinematic relativistic effects with the hope to demonstrate that those experiments do not prove the reality of spacetime, i.e., the four-dimensionality of the world, because real spacetime means no free will. Unfortunately, the result was the opposite and I painfully realized why Minkowski was so certain that what is real is, as he called it, the World (with time as the fourth dimension), i.e., spacetime.
As Minkowski's arguments have not been refuted (they have been only ignored) I think it would be indeed scientifically and intellectually dishonest to behave as if the greatest challenge to free will (coming from physics) did not exist. Regarding this challenge, I believe we should be guided by what we do in science - a challenge is faced, not ignored (and, who knows, someone might succeed in disproving the reality of spacetime).
2. A note to those who ignore any arguments if they question the existence of free will:Imagine watching an old movie in which the main character is so outraged when he / she reads that the theory of relativity rules out the existence of free will that he / she starts jumping around and saying "I do not care what that bizarre theory claims. As you see I can do whatever I decide right now." We can only smile at the genuine confidence of the main character since we know that what is being projected on the screen is fully predetermined because it is entirely given on the film strip.