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At the present time, we have a collection of variables and laws that describe, maybe in a non deterministic fashion, the evolution of the universe.

Is it possible that these laws suddenly change? Say, for example, that the sign of an interaction change, and all the other laws are modified coherently.

What would happen in this case? Of course there are apocalyptic scenarios, in which all things disgregate instantaneously. Is there a scenario that would not result in a complete mess?

Edit. Let me clarify that I am not looking for an answer concerning "what we think is a law" or "the knowledge we Have of the actual laws"; this would pertain the subject of pure logic.

Say for example you have a collection of polynomial equations (like are most of the classical laws). For example, the gravitational interaction force for two planets can be written as

$$ F_{12} R^2 = G M_1 M_2 $$

This can be restated as

$$ \frac{d}{d M_1 } \frac{d}{dM_2} ( F_{12} R^2 ) = G = constant $$

In fact with this procedure all the polynonial equations can be restated in terms of something = constant.

A (not small) change in these constants would be a change in the actual physics of the universe, and not only that we knew things in a wrong way. Things would start to interact differently. I don't know if all the laws of physics can be stated as something being constant - as Nielsen noticed, Noether's theorem give us a lot of other candidates to be constant. In any case, maybe I explained myself better!

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    $\begingroup$ A possibility for such a law changing scenario would be the decay of the, possibile, metastable vacuum of the Higgs. There are two really cool papers by Coleman dealing with such scenario, their title is The fate of the false vacuum $\endgroup$ – Davide Morgante Jan 26 at 21:48
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    $\begingroup$ Although true that such papers pertain the metastability of vacuum, they don´t mean in any way a change in the laws themselves. I believe this is dangerously close to becoming non-scientific. $\endgroup$ – ohneVal Jan 27 at 8:13
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    $\begingroup$ You could argue that if the laws of physics changed in a predictable manner you could describe those changes with another law. So actually the laws of physics stay the same because the change was predicted by the laws of physics $\endgroup$ – AccidentalTaylorExpansion Jan 27 at 10:24
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    $\begingroup$ You can also argue that it has happened. The conditions of the universe were different before the inflationary period than after. $\endgroup$ – Barmar Jan 27 at 15:36
  • $\begingroup$ There are important examples that aren't just power laws. In any case, the most general solution of constant $G=\frac{d}{dM_1}\frac{d}{dM_2}(F_{12}R^2)$ is $F_{12}R^2=A(M_1)+B(M_2)+GM_1M_2$ for arbitrary differentiable functions $A,\,B$ for which $A+B+GM_1M_2$ dimensionally consistent. $\endgroup$ – J.G. Jan 27 at 17:06
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There's a difference between the "laws of physics" which are our current best model for how the universe works, and the true laws of physics, the underlying behaviour and nature of the universe.

We could quite easily encounter a situation that defies the former - we already know that our two best models, for astronomical and microscopic scales, don't mesh with each other, so we must be missing something. If we had such an encounter, that doesn't really mean anything about the universe has changed - it just means that our ideas of how it was presumed to work are wrong, and furthermore, always were wrong, although possibly only by a little bit. (It turns out that Newton always had been wrong about the nature of gravity and mechanics, but he was so close to being right that we didn't notice for centuries, and even now we have noticed, we still assume his model because it's close enough. Einstein will probably be discovered to have always been slightly wrong in the same way, but with an even smaller "slightly.")

Considering the "true" laws, it's not obvious what it would mean for them to change. No amount of experimental evidence can rule out a future encounter that breaks your theories, so in practice it's not really possible to distinguish between the true laws changing and you just being mistaken about what they were to begin with.

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    $\begingroup$ From a logical point of view, "true laws" cannot change, because if a property $P$ change at time $t_0$ then the "true law" would just be "$P$ holds until $t_0$". What I mean could be alternatively said in this way: our theories depends on a finite number of constants. Can these constants change upon time? In case of equations involving only sums, multiplications and quotients, this is equivalent to my original question. $\endgroup$ – Andrea Marino Jan 26 at 22:32
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    $\begingroup$ @AndreaMarino you've effectively ansewered your own question there if you posit that the constants having the values they do are logical properties. They could, but you can't distinguish that from a true law that says it was always variable and you just hadn't seen it vary before $\endgroup$ – redroid Jan 26 at 22:36
  • $\begingroup$ That's why I also put a second part in my question: what would happen if these constants instantly change? I made the example of a sign reversion since it has a qualitative effect on the dynamics $\endgroup$ – Andrea Marino Jan 26 at 22:38
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    $\begingroup$ This is basically the "grue and bleen" philosophy problem. $\endgroup$ – Barmar Jan 27 at 15:33
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One way to think of laws of physics is as update rules for some set of states, a bit like how a computer has an operating system allowing various applications to interact with each other in particular ways. From this perspective, where the laws of physics are not inherent in the physical states themselves, anything could happen. The operating system could after all have a hidden rule that after next Tuesday the allowed interactions would be something completely different, and there would be no way to determine this since we can only observe the past regularities of interactions (as far as we have data... and that data could in principle have been faked at the last reset). There is no way of limiting how often or how radically physics could change in this case.

Another way of thinking about laws of physics is to think of them as the patterns we see in repeated experiments or observations that describe or predict natural phenomena. The complete set of physical laws would be what we would know if we did every possible observation and constructed the best model possible from them. This is the "inside" perspective, and it does not and can not give evidence for any radical changes. We cannot exist in a reality with different coupling constants or number of spatial dimensions, so observed laws (as observed by us) cannot change fundamentally.

Note that small changes may be survivable and memorable - if several dimensionless physical constants changed together in a minor way (see Victor Stenger's critique of "fine tuning") life would go on but measurements may reliably tell that something really weird happened. That would force the models in the second approach to incorporate the possibility of such weird changes somehow.

In the end the main answer is anything could happen, but what we really care about is prediction ability: what can we predict given what we know (or could know)? Random physics changes is mostly decision-irrelevant since we cannot predict it. One could argue it should set our long-term discount rate of the future to the expected rate of physics change, but constructing a sensible prior without any evidence likely ends up with a scale-free prior for the rate of physics change, which implies some rather weird hyperbolic discounting.

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  • $\begingroup$ The second part is a good point and I didn't know about the possibility of minor changes happening without humans to be destroyed. About the third part, I do not agree is not important: lately science is seen as an absolute thing, but I have the impression not much people is conscious of the fact that science is just a bunch of (very well organized) observations. It is then important to know that we can't actually expect to predict things, it's just we have been lucky for a few (billions of?) years. $\endgroup$ – Andrea Marino Jan 27 at 10:46
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    $\begingroup$ The comment about data being faked at the last reset reminded me of this Douglas Adams quote: "There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another theory which states that this has already happened." $\endgroup$ – IMSoP Jan 27 at 12:58
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At the time I am adding this, there are some good answers, but none that make the following statement completely clearly and upfront:

the 'laws' that science deals in are descriptive, not imperative

That is to say, a 'law of nature' is simply some observed regularity in natural phenomena. The observed regularity gets called a 'law' when it is of sufficiently wide occurrence or relevance. Asking whether the laws can change is no more and no less than asking whether regularities which have been observed up till now might not be quite as universal as was thought. The answer to that is yes. For example, it was thought for a long time that there was a law of conservation of mass. It turns out that was wrong, but not entirely wrong. Once we understand the relationship between mass and energy then the mass conservation 'law' is seen to be the form that conservation of energy takes in some circumstances.

In chemistry it was thought that the chemical elements were immutable, and then radioactivity was discovered which shows that there are processes which change one element into another.

It was also thought for a long time that if one connects three points with lines of minimal distance, then the triangle thus formed will have internal angles summing to 180 degrees (i.e. half a full rotation). Up until about 1917 this would have been said to be a very concrete and universal regularity of nature. It turns out it is not in fact true in general; it is just approximately true in ordinary circumstances.

Now it will be said that the question asked is not about human misunderstanding about laws of nature, but the laws themselves. Let's translate that. It is asking "can the regularities of nature themselves change?" But if they change then they were not regularities after all! Well not universal ones anyway. So if they were universal, describing phenomena equally well at one time as another, then by definition they cannot change.

Philosophers of science have of course given a good deal of thought to all this, and a very common conclusion is that one cannot give a good definition of "laws of nature" except the working definition "our best summary so far of the regularities which have been perceived". The whole of science is based on induction, which amounts to saying it is based on the reasonable conjecture that the universe will carry on being like it has been in the past, just changing over very long timescales. For example, the values of some of the parameters that physics normally treats as constant might possibly change over many billions of years. Experimental searches for such effects have been carried out, taking advantage of the precision of atomic clocks and the long time-scales offered by astronomy.

Just as we have no guarantee, when venturing out for a walk, that some calamity might not happen, such as a rock fall or an earthquake, equally we have no absolute guarantee that the fabric of the universe will not undergo some profound change which it has been building up to, all unknown to us. So what shall we do? Better accept the uncertainty and go out for that walk, and also carry on with all our other efforts to do something creative.

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  • $\begingroup$ Thanks. I think your answer is the one that I find more convincing, I feel like you got my point. $\endgroup$ – Andrea Marino Jan 27 at 16:12
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If any of the fundamental laws of physics suddenly became invalid, mayhem would ensue and carnage would result on all fronts- and the universe as we know it would end, and so would we.

But be not dismayed. One of the most basic laws governing the universe is the conservation of energy, which requires that all the rest of the laws of nature cannot simply stop working at any time. In other words, if the laws DID quit on us, energy would not be conserved anymore- and magic would become real, because magic is based on energy nonconservation!

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    $\begingroup$ @redroid, Ah, but it does. Look up noether's theorem, which proves that for energy conservation laws to hold, there can be no time dependence of the laws of nature. $\endgroup$ – niels nielsen Jan 26 at 22:19
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    $\begingroup$ I don't think energy conservation implies the laws of physics can't change; certainly Noether's theorem says nothing of the sort. But even if this were true, who says the law of conservation of energy itself couldn't change? $\endgroup$ – d_b Jan 26 at 22:56
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    $\begingroup$ @d_b, it says exactly this: The fact that the laws of nature do not change when you move your lab across the street implies that linear momentum is conserved. The fact that the laws of nature do not change when you rotate your lab around any angle implies that angular momentum is conserved. The fact that the laws of nature do not change when you reset your clocks by an hour implies that energy is conserved. $\endgroup$ – niels nielsen Jan 26 at 23:22
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    $\begingroup$ @nielsnielsen My understanding would be the opposite. Energy is precisely constructed to be a constant of motion for time-independent Hamilton's equations. Make the equations time-dependent, and I think one could redefine the energy by adding a term and have it conserved again. $\endgroup$ – Wouter Jan 27 at 10:56
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    $\begingroup$ @nielsnielsen I think you are overextending the philosophy of Noether's Theorem. First, there do exist systems whose energy is not conserved, does this then mean that the laws of nature are changing for those systems? I would say no; it just means that the Hamiltonian is time dependent. Additionally, what does it even mean for the laws of physics to change as you move in space and time? Certainly any variations in space or time is described by some law of nature that says it should do so. Noether's theorem is about symmetries of the system, not about the underlying laws of nature themselves. $\endgroup$ – BioPhysicist Jan 27 at 14:21
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This is an interesting question, and as has been stated, our known laws are often approximations of more fundamental laws of physics. It is obviously impossible to know if any of our known laws is a "fundamental" according to mother nature, or even if the concept is sensible.

As Anders touched in his answer, constants with dimensions (like gravitational constant) are not very good probes for changes in laws of physics. All such "constants" as measurements of something against a known measuring stick. How would you know it was not the stick that changed?

There are dimensionless constants, the fine structure constant alpha as the best example. These would probably be better probes.

Any kind of conclusive answer would be the discovery of a fundamental no-free-parameters-theory. Such a theory would require no tuning, or experimental measurements, and there would be no arbitrary natural constants! Everything would just somehow pull itself out of pure mathematics. The universe would be how it is, because to exist is to be identical to it. It's hard to imagine how one would even begin such a theory.

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The actual laws of physics can’t change — by assumption, they are valid at all times and in all places. But our knowledge of the laws may be (almost certainly is) sufficiently defective that something happens to change our understanding of them. Just for example, parity conservation was one of the presumed laws of physics until 1957, when an experimental result changed that law.

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  • $\begingroup$ So, for example, you don't believe that at a certain moment gravity could become repulsive? $\endgroup$ – Andrea Marino Jan 27 at 10:27
  • $\begingroup$ As of now, this answer is not within the scope of the question. The question is about the actual laws changing, not our knowledge about them changing. $\endgroup$ – I'm with Monica Jan 27 at 10:51
  • $\begingroup$ @AndreaMarino If gravity suddenly became repulsive, that wouldn’t mean that the laws of physics had changed, but rather that our understanding of them up that point was incomplete. We’d need a new law that encompassed gravity’s behaviour before and after the apparent change. $\endgroup$ – Mike Scott Jan 27 at 10:55
  • $\begingroup$ @MikeScott: this is actually about our knowledge of the laws, but the example I made is substantially different from a "tuning of the known laws", as happened for Newton's laws. $\endgroup$ – Andrea Marino Jan 27 at 11:03
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    $\begingroup$ @AndreaMarino The point Mike Scott is making is that if the sign of gravity suddenly changed it would not violate physics because that sign change is determined by the physics of gravity. This answer doesn't rely on interpretations, rather it says that the true laws of physics are independent of our interpretation and understanding. $\endgroup$ – BioPhysicist Jan 27 at 14:02
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We cannot prove that the laws of physics can't change

This is a branch of the philosophy of science explored by Nelson Goodman and David Hume, referred to as the Problem of Induction. Essentially we can't experimentally differentiate between statements like "This emerald is green" and "This emerald is grue", with grue being defined as a colour that changes from green to blue at time X. This generalises to laws of physics. We think that we're in a universe where F=MA, but we could be in a universe where F=MA before time X. Then after time X; F=MA^2

https://existentialcomics.com/comic/2

https://plato.stanford.edu/entries/induction-problem/#GruParNewRidInd

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This is an interesting question. I do not know much about the law of physics, but I believe what you are suggesting, in some sense, happens continuously in the social realms. In the latter realm, there is no "complete mess" scenario, up to a relatively conservative view regarding what "a complete mess" is (are world wars a complete mess?). What I mean specifically is the following.

I guess there could be two views about the "causal foundations" of social phenomena. They could be described by stochastic laws, which probably are more volatile than physics laws, or alternatively, there are no laws which describe it. In the second case, I guess there is sign reversion all the time. In the first scenario, there is also sign reversion. People may react qualitatively differently to different stimuli, meaning that laws are stochastic at the individual level, but not in the aggregate (I guess this is different in physics). In none of these cases the outcome is a complete mess.

Hence, my point is twofold:

  1. A brave analogy between the social and the physical realm could lead us to conclude that sign reversion may not imply necessarily complete destruction.

  2. A vision according to which the social realm is just a more complicated physical realm could point in the direction that what we believe are interactions with a constant sign are only a realisation of aggregate stochasticity of which we do not view the other side. In this case, I guess everything is fine.

Sorry for the probably meaningless philosophical diversion.

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  • $\begingroup$ There's a whole lot of philosophy implied behind the original question. The Laws of Physics seem concrete (I mean they are Laws right?). But when you dig down into it, they are really just our best current models for how we percieve the world to work. If the actual underlying 'Laws of Physics' were indeed changing in some subtle, perhaps random, way over time, would it be possible to ascribe any 'Laws' at all once we discovered that fundamental chaos? $\endgroup$ – ouflak Jan 27 at 10:45
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    $\begingroup$ This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review $\endgroup$ – Bill N Jan 27 at 16:26
  • $\begingroup$ @BillN : honestly I find this answer perfectly fine :) it broadens my perspectives $\endgroup$ – Andrea Marino Jan 27 at 18:35

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