It is implied, per QM, that the behavior of subatomic particles cannot be precisely predicted. However, these indeterministic effects do have defined probabilities. By the law of large numbers, they can “average” out and result in approximately deterministic laws.

For this reason, I presume, we can predict with pinpoint accuracy whether or not atleast some kinds of events will happen in the macro scale even if we can’t know their minute details on a subatomic level.

The question then is how fine or loose grained of an event is predictable given all knowledge about antecedent conditions. And how antecedent must these conditions be?

Suppose I woke up today at 9 AM and ate toast for breakfast. If I were to know everything that could be possibly known about the configuration of the universe right after the Big Bang, is this event predictable? Can one say, given that knowledge, with assuredness whether or not this will happen?

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    I like the way you put the question, which to me highlights the absurdity of the determinist claim.
    – Olivier5
    Sep 15, 2023 at 13:12
  • Not an expert, but it would seem to me, that over such a long time there would be 'threshold' influences of quantum/micro events which might tip the scales at macro level, and that over time, these would build into significant diversions from pure determinism; the greater the time, the greater the divergence. Does this make sense? EG: Your eating toast may have been predictable, but then again, you existence at all may not have been predictable, let alone you eating toast. Sep 15, 2023 at 13:16
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    It's absurd to have such simplified causal implication for your eating toast today seemingly actually happened, the Solomon's lemegaton lies in in reality nothing can be said to be actually actualized by some 1-d sequence of a super long causal chain in this Saha world, there're many dynamically entangled worlds where either you are not born yet or eating eggs today instead or what come it may, the ability to predict either one of them in some sense spookily depends on your degree of belief as presentiment of the said event while remembering your past observed consistent histories... Sep 16, 2023 at 6:55
  • I could have predicted you eating toast without knowing anything about the beginning of the universe.
    – Scott Rowe
    Sep 22, 2023 at 18:34

3 Answers 3


No event is predictable from the conditions right after the Big Bang. As far as we can extrapolate, the conditions were extremely simple: There was a singularity with no other properties than its existence. Total information content (complexity) of the Universe was one bit.

All subsequent evolution, the increase in universal complexity and entropy are the results of unpredictable probabilistic events.

The Universe is not deterministic, absolute accuracy is not a thing of reality.

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    Even if the singularity seems to be extremely small just after the Big Bang, it contained a gigantic matter (mass + energy), it was extremly hot and heavy. By consequence, the information that this singularity contained can not be as small as one bit but very high.
    – NN2
    Sep 16, 2023 at 21:22
  • You don't seem to understand the concept of singularity. The whole universe was just one particle with no form. Sep 17, 2023 at 3:25
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    You've come a long way, baryons.
    – Scott Rowe
    Sep 22, 2023 at 18:42

No. We have no theory yet into which to input the data. Even if we imagine a fictional universe without gravity so that we can apply QM to every problem, still no. QM needs somewhere outside of the phenomenon described by the wavefunction to put the physicist, so it can't take whole universes as inputs.

If we take the fictional no-gravity Milky Way ten billion years ago, and we build a really big box with a really high heat capacity around it, and we put a physicist outside of it, and we let that physicist ask his wizard friend for the exact wavefunction of the whole system inside of the box, then the physicist can calculate the probability that a measurement at a certain time ten billion years later in a certain place inside the still-sealed box will return an instance of you eating toast. It will be a vanishingly small probability.

I should note that the physicist may need his wizard friend to do the computation by magic, or to magically summon a computer much bigger than a galaxy in which to run the simulation. Normally simulation works because of simplifying assumptions, but if we magically have the wavefunction of the whole macroscopic system, we have no simplifying assumptions.

  • It takes a universe to simulate a universe.
    – Scott Rowe
    Sep 22, 2023 at 18:36

The question of determinism boils down to: could something else have happened? If there exists a possible world in which you didn't eat toast, how would this world have come to be? If you want to use QM, you will need to answer at which point did a particle bounce to the right and produce the current reality, when it could also have bounced left to produce an alternate reality?

As you say, there are so incredibly many particles that the odds of a meaningful change being effected by QM dice falling the other way is exceptionally low. The law of large numbers effectively means that nothing else could have happened. Yes, you were destined to eat toast.

Obviously, none of this is particularly useful; it is well beyond any supercomputer to know every state and every physics rule.

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    The discovery of chaos being intrinsic to even some very simple math relationships is a refuting test case to your claims about the “Law of large numbers”. SOME of physics is driven by the law of large numbers and is effectively reductionist. Some of physics is chaotic and amplifies quantum indeterminacy. Our universe is therefore indeterminist, and no thinking man was not determined to eat toast.
    – Dcleve
    Sep 18, 2023 at 12:33
  • @Dcleve first of all, something being chaotic only means that it is unpredictable, not that it is non-deterministic. Random Number Generation is chaotic, yet perfectly determined by a simple math formula. Second, if you are going to make the claim that the butterfly effect influences the formation of stars and galaxies, you will need to provide some evidence for that. I have no idea what the Lyapunov exponent would be for the universe, do you?
    – Jumboman
    Sep 19, 2023 at 11:27
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    Your second question is explicitly answered by cosmologists. Their assumed mechanism for galaxy formation IS local density fluctuations at the very beginning of Inflation. This principle that quantum phenomena leverage up is easily established by considering a triple pendulum and the effect of the HUP on the ability to determine its location 10 years later. Note all solid objects oscillate/vibrate, generally with more modes than a triple pendulum. All even macro level interactions have an HUP leveraged up uncertainty.
    – Dcleve
    Sep 19, 2023 at 16:28
  • @Dcleve again, the inability to detemine a pendulum's trajectory is merely a sign of unpredictibility, not a proof of non-determinism. You shouldn't conflate these terms. Neither does the HUP entail that either speed or location are random within a certain range, it only asserts that we cannot know both with absolute certainty at the same time. Quite frankly I think the idea that quantum effects would 'leverage up' rather than cancel each other out is ludicrous. There are 10^27 particles in a normal sized triple pendulum. QM is perfectly negligable at that scale.
    – Jumboman
    Sep 21, 2023 at 7:18
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    Jumboman, the math by which quantum uncertainty leverages up to macro scales is explicit in Chaos theory. Your disbelief in it based on “wish it weren’t so” is a fallacy. And no, the Heisenberg Uncertainty Principle is not some bizarre and inexplicable limit on “what we know” but instead is s limit on what can be real. The efforts to try to recast it as “just” a limit on us, not on the universe, conflict with the physics of quantum mechanics.
    – Dcleve
    Sep 22, 2023 at 23:54

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