How to know whether A and B is causal or correlated? Is it correct to say that physicists have always been concerned about causation? The laws of physics are stated in terms of equations that have nothing to say about causation. They are correlational laws.

Please give me some reference if possible.

  • Please precise the difference. In general, causality is correlation (two related events), and the understanding of arithmetic equations (qualified by you as correlations: F(x) is related with 2x on the arithmetic statement F(x)=2x) depend on causality (F(x)=2x implies that if x is the cause, the consequence is 2x). In some contexts, it is considered that an equation is causal if its parts are correlated.
    – RodolfoAP
    Aug 7, 2022 at 16:43
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    We observe a correlation but a cause in general is accounted for in the context of a theory. Aug 7, 2022 at 17:44
  • 1
    It helps if there's a story. Every time I flip the light switch the light comes on. Is that just a correlation? Well, there's a compelling story that says that flipping the light switch closes a circuit between the lamp and the power company. I believe it. So it's causation. Now why do I believe that story? I've never personally been to the power plant, nor personally traced the wiring between my room and the power plant. I haven't personally investigated the theory of electricity. So it comes down to epistemology. How do I know what I think I know? What stories do I believe?
    – user4894
    Aug 7, 2022 at 19:08
  • @Mr.White It is the task of the community, not moderators, to handle simple things like closure for being a duplicate. Moderators should, ideally, only intervene where the moderation privileges of members end and intervention is still needed.
    – Philip Klöcking
    Aug 7, 2022 at 19:10
  • One does not need a microscope to see that things are not running so ideally at this place. It might be a time to moderate some more.
    – user14511
    Aug 7, 2022 at 19:13

2 Answers 2


Physics is concerned with causality in the framework of natural law. Causality there is deeply embedded in both the two main fundamental theories: QM & GR. In QM, because time is open and things happen whilst in GR, its proveable that the very structure of spacetime is causal. This is a theorem of Malament who showed that a spacetime could be rebuilt (upto a conformal factor) from a knowledge of its causal structure. This has prompted the development of the causal set programme in Quantum Gravity.

More broadly speaking, as al-Ghazali pointed out, physics is merely correlational, requiring the intervention of the Absolutely Real to make what is wholly unreal, real. But this is outside what is now understood to be physics - if not what was understood traditionally as metaphysics. Of course some physicalists take physics to be the ground but this is not primarily because they are physicists or even interested in physics but because they are a certain tribe of materialists.


Causation in physics goes like this:

  • We have some equations that describe how the state of a system changes over time. These equations typically give the time-derivative of different variables of the system, as a function of the current values of those variables.
  • At time t, we set up some initial conditions for the system.
  • We use the equations of the system to trace how the system changes, based on its initial conditions, to some later conditions at a later time.
  • Then we say that the initial conditions caused the later conditions.

It is true that the equations typically don't inherently say which is the cause and which is the effect, and in this sense you might say they are describing mere correlation. We might use the same equations to trace how the state of the system changes backwards in time. However, by convention, the positive time direction is considered the direction of causation.

Here's another way you can use the equations to talk about causation:

  • You first deduce that initial conditions X at time t lead to later conditions Y at time t2 > t, according to the equations of the system
  • You change the initial conditions, so that instead of X you have X2, slightly different from X. Then you trace from X2 at time t, to later conditions Y2 at time t2 > t.
  • Then you say that the change in initial conditions from X to X2, caused a change in later conditions from Y to Y2. This lets us talk about "but-for" causation: what would have happened, if initial conditions had been different.
  • -1: Actually, Newton used "causal" language is his Principia. For example he said "a particle perseveres in rectilinear motion or at rest". This language was taken out of the Principia by a certain tribe of French mathematical materialists as it offended their notion of what was proper to nature and this has fed into how physics is taught and mathematicians think about physics but not how physicists think about physics. For example take Sorkins "Causal Sets" as a fundamental theory of physics. Notice the word 'Causal' in the name of the theory ... Sep 20, 2022 at 0:11
  • @MoziburUllah You are speaking as if I had said there was something wrong with causal language in physics. I don't think I said anything to that effect. I mean, look at my user name.
    – causative
    Sep 20, 2022 at 0:16
  • Really? You say, "it is true that the equations typically don't inherently say which is the cause and which is the effect, and in this sense you might say they are describing correlation ...". This is why physicists invented the science of thermodynamics to explain why time goes forwards only. Sep 20, 2022 at 0:21
  • @MoziburUllah Yes, in that sense you might say they are describing correlation, and then I go on to describe a different sense in which you might say they are describing causation: "However, by convention, the positive time direction is considered the direction of causation." Furthermore the bullet points, which you must not have read, are entirely about when we can say something caused something else.
    – causative
    Sep 20, 2022 at 0:23
  • No. It's not correlation. It's causal. Why would physicists bother inventing thermodynamics if they didn't think there was a direction to time. You ate confusing physics with mathematics. Mathematics is acausal. Sep 20, 2022 at 0:27

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