An Argument Against Determinism

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Definitions and Goal

Determinism is the notion that all events, including those pertaining to and initiated by conscious beings, are the necessary and inevitable consequences of prior events. This doesn’t necessarily entail materialism, the belief that matter is the fundamental substance in the universe and all phenomena, including mental phenomena, are the result of material interactions, nor does it necessarily entail physicalism, the idea that the real is the physical (that which is composed of physical matter), although the three principles tend to come as a package in our modern, scientific age.

My position on each of these is as follows:

  • I reject determinism in favour of freewill (I am a libertarian)
  • Strictly speaking, I am a materialist. By this, I mean that I am not a substance dualist (like Descartes, probably the most famous substance dualist); i.e. I don’t believe in any mysterious “Mind stuff” or “Spirit” or any other esoteric improbability.
  • I disagree with physicalism. I reject the idea that reality can be reduced to and fully accounted for by a complete physical description of a situation

You may be uneasy about my rejection of physicalism and acceptance of materialism however I don’t think there is a contradiction here. I don’t think there is any “thing” (i.e. substance) in our universe except matter (hence, I am a materialist) but at least one conglomeration of matter in the universe generates a non-physical reality, including thoughts and a subjective, conscious awareness, which is just as real as anything physical (hence, I am a non-physicalist).

Clearly, with what I have said above, I haven’t made any effort to explain how that non-physical reality came to be or how it’s even possible in the first place. Fortunately, we don’t need to provide an account of the origin of a thing in order to note certain characteristics about it. Indeed, having as intimate a relationship with consciousness as we do puts us in the privileged position of being among the only category of entities in the universe that can describe that non-physical reality. Careful reflection on the nature of our conscious experience and sound reasoning ought to give us two reasonably reliable methods of divining something useful about that experience. It is my hope that this article is one example of the latter.

As the title indicates, what I am refuting here is physical determinism, i.e. the idea that all events are the inevitable and necessary consequences of prior causes and the only thing that qualifies as an event or cause is physical matter.



Physical determinism means that all events in the universe are merely the result of the mechanical movements of physical atoms (or strings, or whatever the smallest unit of matter turns out to be). ‘Mechanical’ here simply means governed by natural laws and lacking any independent, conscious volition. So, your uttering a particular word is a physical event caused by the firing of a particular sequence of neurons, which was itself triggered by the soundwaves your ear picked up, which was caused by my lips moving in a certain fashion, etc. And more importantly, this event is no different from what happens when one billiard ball hits another one. Both are examples of physical cause and effect and both appear in a causal chain that extends all the way back to the Big Bang.

If physical determinism is true, then all future (and past) events are knowable with absolute precision. Since all events are reducible to the mechanical movements of physical lumps of matter, in order to predict the future, all we need to do is know the state of every particle in the universe at any given time, know the physical laws governing matter, and have the computing power to perform the relevant calculations.[1]


The Thought Experiment

I manage to acquire a machine that is capable of taking a snapshot of the location and momentum of every particle in the universe at time t and which can also extrapolate from this, using well-understood laws of nature, to calculate the precise location and momentum of any particle (or group of particles) at any time, or series of times, in the future. Since physicalism tells us that all events are nothing more than the interactions of particles over time, my machine also comes equipped with translation software that interprets the raw data and renders it as events understandable to humans.

I turn the machine on and it takes its snapshot. Zooming in, I see a frozen image of myself with my finger on the button. Panning around shows me a picture of you sitting on the couch, a bemused expression on your face. So far, so good.

I notice a box on the screen that says “t”. I navigate the cursor there and enter “t+15”. I also change the display format from “image” to “video”. The picture jumps to life showing you grabbing the remote control and turning the TV on. I wait and sure enough, exactly 15 seconds after I turned the machine on, you reach over, grab the remote and turn the TV on.

I quickly enter “t+40” into the box and the machine shows you getting up and stretching. This time, I decide to tell you what I’ve seen. I tell you that you are going to get up and stretch in exactly 10 seconds (by which time it will be “t+40”). You smile and shake your head as I confidently count down from 10. I get to 1 and look up from my watch as… nothing happens. You sit there as “t+40” comes and goes and refuse to stretch. “Better get a refund,” you say, as you go to bed at “t+45”.


 The Argument

  1. If physical determinism is true then all future states of the universe must be knowable (controlling for non-deterministic physical influences)
  2. But all future states of the universe are subject to change if anyone actually comes to know what those future states will be
  3. Therefore all future states of the universe are NOT knowable
  4. The conclusion in step 3 contradicts the premise in step 1, therefore the premise in step 1 must be incorrect; i.e. physical determinism is false.



What could have gone wrong here? We can see straight away that the machine failed to predict me telling you about what I had seen. In other words, it predicted the future without taking account of my actions. Is this a problem in my description? Suppose it had shown me what actually happened; i.e. the video showed me telling you that you would stretch, you not stretching and then you going to bed. But if it had shown that instead, I could then have decided not to tell you and you would have stretched. Either way, the point is the same. Knowledge of the future makes that future alterable, therefore not determined.


What if there was another being in a higher dimension watching? Let’s call him Laplace. He has his own machine which takes a snapshot of every particle in our dimension and he was watching what would happen at “t+45” as well. Unbeknownst to me, while I was confused about how you could have failed to stretch after I saw it happen on my machine, everything happened exactly as he saw it on his. Determined after all. I just thought I wasn’t.

But this doesn’t actually solve the problem; it just pushes it one dimension higher. Laplace could repeat the same experiment for himself that I just carried out. Instead of watching us, he could try to predict what his friend, Laplace 2, would do, and then intervene just as I did. He would then discover that while our dimension seems to be determined, his own isn’t.


I can only see two ways of avoiding the conclusion that physical determinism is false; neither appear that convincing though:

  1. Refute the first premise; i.e. claim that even if you know the position and momentum of all particles in the universe you still can’t predict the future. Unfortunately this also seems to refute physical determinism. If every event can be reduced to particles whose movements are governed by strict physical laws, it’s hard to see how you could refute the first premise.
  2. Maintain that physical determinism is true and the future is knowable BUT only if you cannot interfere with that future in any way. However, you now have to give a reason for the inclusion of that caveat. What physical principle can you possibly invoke to explain why you can’t come to know any future event which you could interfere with?


The second unconvincing strategy above actually gets right to the heart of the thought experiment; consciousness. Learning about the future and then deciding to thwart it is only possible for a free, conscious being. If we were nothing but the mere lumps of matter physical determinism imagines us to be, the thought experiment would fail before it even begins because then there would be no question of any thing interfering with a determined future. The idea would be ludicrous. But it isn’t. Tell someone what they will do and they may suddenly turn around and do the opposite, because they can. We are free not just because the conclusion of my argument is valid, but because the argument can be made in the first place.


[1] Two things. First, this is clearly impossible in practice, but practicality is irrelevant in a thought experiment. The assumption doesn’t contravene any logical or physical laws, which makes it valid as a thought experiment. Second, I am controlling for any non-deterministic physical influences which may render the future fundamentally unpredictable (such as quantum complications) because they are irrelevant to the issue at hand; i.e. the truth (or falsity) of quantum mechanics says nothing about whether we are free or determined.

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