Why do scientific laws persist?

Question

Why don’t the laws stop today, or change, or work differently? What is keeping them afloat and consistent? What keeps them constant?

Does this just follow from the fact that laws exist or is this something contingent?

Answer 1

The laws are just human-written descriptions of how the world works.

We have no reason to expect that the world could ever change the way it works. But if it does, we are ready to write new descriptions.

Answer 2

Your question is a radical version of Hume’s problem of induction:

Can we deduce from finitely many observations a general law?

• Each day we observe that the same laws of nature hold. Can we conclude by logical reasoning that they also hold tomorrow and in the future?

  Hume’s answer is clear: There is no logical deduction. It is just a psychological fact that we expect a general law.

• IMO Hume is right. Continuity is the most simple hypothesis as long as we have no facts speaking against this expectation.

Answer 3

Physics has an answer to this one, actually.

Noether's theorem states that every continuous symmetry of the action of a physical system with conservative forces has a corresponding conservation law. That's a lot of jargon, but the basic idea is that if we observe something to be conserved, then there must be some symmetry in the system.

In the case of scientific laws "persisting", that's the same as time-translation symmetry, and the corresponding conservation law is conservation of energy. Phrased alternatively, because we observe conservation of energy, we also expect scientific laws to not be changing. Yet another way to put it is as Wiki does:

Invariance of an isolated system with respect to time translation (i.e. that the laws of physics are the same at all points in time) gives the law of conservation of energy (which states that the total energy of an isolated system is constant)

There are a few other conservation laws, such as conservation of angular momentum <-> there is rotational symmetry (i.e. the laws of physics do not vary depending on which angle you view the experiment).

See also this question on the Physics SE.

Answer 4

I doesn't 'follow' from anything- it is an observed pattern. Indeed, suppose there was a phrase, P, such that you could write a true sentence of the form 'P, therefore the laws of science must persist', you would then be in the same boat, because the obvious next question would be why doesn't P stop today, or change or work differently? Etc etc.

Answer 5

There are a few things going on here.

• There's no escape from faith. The belief that tomorrow will be like today the way that all the yesterdays have been like each other cannot be justified by the fact that one of the ways that all the yesterdays have been like each other is that all the yesterdays have been like each other in those ways. This is a version of the same problem that manifests in "How do we know reason is reasonable?" - it's a priori unanswerable, because you have to grant the conclusion in order to make the argument.

• There are a few things that physicists call laws that do change with time (e.g. Hubble's law, which has "constant" of proportionality that has changed dramatically over the history of the universe) or environment (e.g. Newton's law of Cooling, which has a "constant" of proportionality that changes if you change practically anything about the system under consideration). Others are only valid under certain circumstances which approximate certain idealizations (Ohm's Law, the Ideal Gas Law, etc). Others are just handy, mathematically simple approximations (e.g. Kepler's laws of orbital motion). However, these are distinct from what people mean by "the laws of physics". "So-and-so's Law" means "the widely useful mathematical equation named for so-and-so." "The laws of physics" means "the unknown and possibly unknowable totality of principles that describe the behavior of all natural systems".

• There's a selection bias. The overwhelming majority of true descriptions of reality change rapidly. We just don't describe these as approximations to the laws of physics (or so-and-so's Law, see above), we call them characteristics of particular systems at particular times.

• It's a near certainty that, over the expected future lifetime of the universe, many of the things we now think approximate "the laws of physics" will cease to be good approximations. The universe is already old in a way that defies human intuitions about time. But compared to the age we have attempted for forecast its future characteristics, it's like all the history that has ever been was nothing but a tiny fraction of a second. Whether that means the laws of physics will have changed, or that the real laws of physics were principles which would have described how the approximations would be both now and a trillion trillion universe lifetimes from now and how they would change, depends on your choice of definition.

Answer 6

Scientific laws aren't "real" - by which I mean they do not have existence in reality outside of humanity. They are human descriptions of how the world behaves. Their apparent consistency over time and space is largely a mere brute fact - it is something that is observed rather than something that we can give a definitive reason for.

However, I would posit that there is probably a simple reason: there's no way to change them. Each fundamental thing in the universe (by which I mean electrons, quarks, gravity, whatever actually is if our current understanding hasn't reached the true fundamentals) behaves in a certain way, and the collective effect of all those individual behaviours adds up to the things we describe in our scientific laws. If this is the case, then how would the laws change? They can only do so by changing the behaviour of these innumerable fundamental entities. The consistency of scientific laws then results from the simple lack of anything to change them, rather than because anything is there to preserve them.

But even if the above is true I see no way that it could be directly proven so, I suspect, like many mysteries it will lie beyond the realm of provable human knowledge.

Answer 7

I believe it is important when thinking about such questions to have a good understanding of what the observed and understood physical laws really are.

Modern theoretical physics has shown beyond all reasonable doubt that the matter we are made out of is described on relevant scales by a quantum field theory known as the Standard Model which is minimally coupled to Einstein General Relativity. Of course the real citations here are a certain corpus of papers and a few textbooks, I do quite like Sean Carroll's explanation for philosophers.

So the answer to your question as understood by modern physics is simply that we have seen no evidence for time variation of the 'laws of physics', being 'the parameters of our fundamental theory of the composition and dynamical evolution of matter'. And so we have no reason to believe they change with time.

But really that is not to say that they cannot change with time. For example, it is possible that some of the parameters of the Standard Model derive at even smaller distances from the sizes and shapes of some compact internal dimensions. Then in general it's certainly possible the background values of the dilaton modes of these extra dimensions change with time. Slowly, because they're on some very nearly flat potential, or possibly rapidly due to a phase transition. But we've seen no evidence of this so far.

You don't even need to go to extra dimensions to do this. Write down some effective operators in the Standard Model with a new neutral scalar which has some background value, like φFF (F is the field strength). Or non-minimally couple a scalar to gravity with φR (R is the Ricci scalar). If the vacuum expectation value of this scalar changes with time, then the strength of respectively electromagnetism or gravity changes. Sometimes people suggest maybe these sorts of phenomena could be used to explain puzzles like the cosmological lithium problem.

These are all perfectly possible, but it's not clear we should think they are needed by a theory of fundamental physics. And we do lots of tests including using cosmological observables to look for these possibilities. Everything we have observed is instead consistent with the fundamental 'laws of physics' being the same since a few seconds after the big bang. As probed sensitively by nuclear physics + particle physics + cosmology in our understanding of Big Bang Nucleosynthesis. In fact these observations give us incredibly good constraints on theories that would predict variations of the fundamental physics.

It is still possible that earlier than that, at even hotter temperatures, the fundamental laws of physics change. In fact in some senses we believe this should be true. At temperatures a couple orders of magnitudes hotter we think quantum chromodynamics underwent a confinement phase transition, and at earlier times would have been in a deconfined phase. Another three orders of magnitude even earlier and the electroweak sector may have dynamically undergone a spontaneous symmetry breaking phase transition, in which case at earlier times we would be in a electroweak symmetric phase (the Higgs boson would not yet have condensed). In either of these cases the laws of physics would be quite different from the way we know they are today. A variety of well motivated theories Beyond the Standard Model predict even further variation of the physics at earlier times.

I really do think it is important to understand that we know a remarkable amount about how the world works at very small distances. And so the philosophy really must accord with what we have understood about fundamental physics. The philosophy is important too, I agree. But the answers are much more well-constrained now than they were a hundred years ago.

Answer 8

I don't think the answer to "why?" can be answered since "why?" looks for the final cause, the purpose.

But your perplexity is understandable, and it can be handled by looking at the situation differently. I am not a professional philosopher, so please correct me if I make any mistake.

One possible answer is that we choose them to be a scientific law because they have persisted. There is no reason why a law can't stop working today; every day it persists is beautiful. But the day it stops working, we will be curious about what happened and why it stopped, and we will no longer consider the law. Usually, we look for higher-order laws/patterns where we can also accommodate that change in the previous law.

I have talked about the cognitive experience of these laws. But If you really looking for the answer to this question

Does this just follow from the fact that laws exist, or is this something contingent?

So, before answering this, let's look at some naive possibilities of answering "Yes, law exists" or "No, it's contingent".

But these answers themselves come under the laws.

"yes, law exists": good to go. "no, it is contingent.": means that my answer is itself contingent. And hens it is subject to change, which will bring us to "yes, laws exist"

Answer: "Yes, some laws exist. We can't deny it. Since you're breathing."

Answer 9

The distinction of "today" and "tomorrow" is not separate from those laws.

This question succumbs to the Anthropic Principle.

Perhaps there exist numerous universes in which laws change. However, those universes are unlikely to be stable enough to develop intelligent life forms which make scientific observations.

In other words, the laws in our universe are stable because it's the kind of universe in which an Earth-like planet can evolve intelligent life, which then investigates and documents the laws. If the laws weren't stable, things wouldn't get that far and you and I wouldn't be here to discuss the opposite question: why is it that the laws are changing?

Something not changing is, also, a simpler situation than change. Change is an extra process that has to have some sort of cause. Perhaps another law is underneath it; perhaps one that does not change. If you identify a pattern in how the laws are changing, and that pattern doesn't change, you are back to unchanging laws.

Answer 10

Every scientific laws can be viewed as an attempt to compress a description of reality. Can you describe 'useful' information about a situation without fully describing the situation?

If it is possible to describe useful information about a situation without fully describing the situation, then you are going to have "scientific laws" that can be discovered. Those laws are just relationships between the limited description of a situation, and the useful information you get out of it.

In our universe, it appears that you can describe parts of a situation with words like "mass", "velocity", "charge", and using those parts you can predict (some of) what will happen (to a certain degree of accuracy) next in a wide variety of situations.

Those laws not changing rapidly (ie, at a pace we can notice) is something we have noticed that tends to be true, that we can drop the "when this happened" from the description of the scenario and the compression still works.

This compression of describing the universe happens even at really low levels, far lower than physics: the idea that "sheep" is a word that has meaning happens because there are a pile of "sheep" scenarios that are similar enough that using the same label on both has some use. Because we have lots of stuff that tends to be possible to label in such a way, counting turns out to be a useful form of compression - "two" would be meaningless if the universe didn't have more than one of anything that was like another thing.

From this argument, the laws of physics don't change because the universe is a relatively simple place with lots of patterns, and most of those patterns don't change over time.

In addition, as we appear to be patterns of stuff in this universe, and amazingly complex ones at that, if the rules by which the patterns behave changed rapidly, we would probably not be around afterwards to notice it happening.

It seems plausible that a universe without something like stable laws of physics - without stable patterns - wouldn't have intelligent beings in that universe looking at the universe to write the laws of physics; that the intelligent being is built out of the patterns in the universe, if those patterns aren't stable it seems implausible that you'd get something smart enough to describe the patterns.

We can look at what a universe without much in the way of patterns would look like, given our understanding of the universe. After 10^1000 years, the universe we are in plausibly is going to be full of nothing but non-interacting photons. "Mass" as a concept stops being a useful concept, as you can't predict any events when there aren't any events to predict.

The photons don't mutually interact, and their QM-state becomes nothing but a smear. All baryons have decayed. Black holes have all evaporated. White dwarfs have cooled to black dwarfs, then iron stars, then exploded - their fragments in turn have all decayed.

So most of todays laws of physics is blathering nonsense that don't predict or describe anything in that scenario.

Answer 11

This is a consequence of what we categorize as a "law." If we cannot described predictably a particular phenomenon, and its relationship with other things appears to vary from day to day, we just don't classify any description of that phenomenon as a "law."

If we do describe a phenomenon according to a law, but then it turns out that tomorrow, the phenomenon deviates from that description, that is simply a revelation that we were wrong.

Answer 12

Physics has no answer to the question: Why are there physical laws?

That said, time invariance of laws is rather fundamental in physics. A lot would unravel if that weren't true. There is space-time mixing and also CPT-invariance. (No doubt there is a horde of physicists out there who can flesh this out.) It's an aspect of the question: Why are the laws of physics the way they are?

So I wouldn't worry about this happening.

One argument that has been given is that human brains simply don't have the cognitive capacity to understand certain things, just as the brains of rats cannot comprehend differential equations.

Answer 13

I think this is a great question, however most answers focus on the natural science aspect of this and not the philosophical part.

From a scientific point of view we have to assume a priori that natural laws (or natural processes) don't change. I.e. that the world will be the same tomorrow as today and that it's the same 10 billion lightyears from here. This matches with our observations, but we don't have any explanation from within the natural sciences to assume that (also see below the part on parallel universes).

This understanding is pivotal to doing science and comes from your world-view. For example, if you assume that a God (e.g. Zeus or Thor) is responsible for the weather, then there's no point in studying the weather. Conversely, if we assume that the world was created by a rational being who vows for continuity, then only it makes sense to study nature.

This is among the reasons why science arose in the christian world and not so much in others (speaking here from a historic point of view, not that this would neccessarily be the case, but this is what has happened, for more info see here). So for me personally, I believe in constant laws because of the one who made the laws.

A natural question then becomes do we really need somebody who keeps them constant? Kind of. You may have heard of the many-world interpretation of quantum physics, but even if not, you are probably familiar with the idea of infinite alternative universes, where all possible universis that can exist do exist. From a purely scientific point of view these probably exist (otherwise you run into the issue of finetuning). However, if all possible universes that can exist do exist, then this would/could imply that some/many universes with non-constant laws exist. So from a scientific point of view, for every possible universe with constant laws we could also have one with non-constant laws? If that's the case, we might potentially even have much more universes with non-constant laws? So the fact that you, and essentially everybody else believes in constant laws of nature is actually a hint at the fact that you don't really believe in (infinitely many) alternative universes (not talking about the fact that they do or not exist. More about the fact that you don't believe they exist).

Answer 14

My 0.5 cents.

If the universe is relational, in a certain sense, then change and constancy are necessarily related through each other.

What does it mean for the universe to be relational? It means, in this case, that properties and processes are defined only in relation to other properties and processes and vice versa.

So in a relational universe change can only happen and be defined when there is something constant with respect to which change happens. Similarly, something constant only exists and is defined through something changing.

So if the universe changes something must be constant about that change, and, vice versa, if the universe is constant it is so only with respect to something changing.

So what is constant about change in the universe can be taken as a kind of persisting physical law related to this change. QED.

The only constant is change.

-- Heraclitus

Answer 15

1. Scientific laws describe nature; if nature appears to be static, so are scientific laws.

This is an evident rule. If nature is static, natural laws are static. If free fall occurs always following the same rules, the free-fall rule are static.

While it appears that nature is static, everything changes constantly.

2. Nature is in fact not static, everything changes permanently.

But wait: nature is not static. You are not the same person you were one second ago (every atom in you has changed).

So, how come natural laws be static?

3. Nature is dynamic, perception makes it static.

Nature changes constantly, but our mind makes it appear as static phenomena.

The simplest way to understand it is with this rule: The river is never the same. It changes permanently. However, for our mind, it is the same.

In fact, our mind is able to abstract selected features from reality, and make them appear as static.

4. Nature is dynamic, but natural phenomena appears static, that's why scientific laws come to be static.

What is a river? It is a huge amount of atoms interacting, something that can't be measured, observed or described with a formula. But the mind can abstract it: it is essentially water (a material abstraction) that follows a curved line (a mathematical abstraction), surrounded by soil (another material abstraction), that moves (a motion abstraction), etc. The river, for a mind is that, but physically is quite far from that.

So, while our mind can abstract natural intuitions to make them static phenomena (which includes scientific laws), reality is that nature is dynamic and everything changes permanently. If we would need a physical law to describe a river in detail, no mind would be able to understand it.

Answer 16

One possibility is, we live in some kind of mathematical or computational structure, so there are structural reasons why our universe seems to conform to consistent rules. The so-called laws that physicists discover would thus be mathematical descriptions of certain regularities within that structure.

Answer 17

Why don’t the laws stop today, or change, or work differently? What is keeping them afloat and consistent? What keeps them constant?

This is a question with a built-in contradiction.

Laws - by definition - are statements to describe phenomena that generally hold true over their range of definition, i.e. a period of time or under certain conditions.

Thus laws are things that - observedly at least - do not change.

So your real question should therefore be something like: why don't natural phenomena explained by these laws change, e.g why don't we find occasions where adding chemicals A and B together (say at ambient temperature and pressure) no longer do what they used to do, e.g react to form two new substances, C and D, but actually form to other compounds, E and F, or G and H, or I and J, or . . . ?

Obviously if the products of combining A and B under identical conditions were to vary then so would the products of many other substances put together, as we now know that earthly matter is composed of atoms with a similar type of structure. Our whole planet and solar system - maybe universe - might be in eternal flux and never be "together (in the hip sense)" enough for any form of life (life as we know it, at any rate) to emerge.

But it's observed repeatedly that natural processes only proceed in a certain direction - that dictated by maximum entropy (or by minimal potential energy) under the prevailing conditions. This the famed second law of thermodynamics.

Were a process to proceed into more than one possible final state, we would conclude that the final states had similar entropy and potential energy. That way the law still holds true though its external manifestation might appear anomalous.

The conclusion here is that a Nature is a closed collection of phenomena that exist and change according to certain underlying physical laws.

No underlying laws, no Nature.

No Nature, no underlying laws.

Why not a Nature that is lawless ? I can't prove it but I doubt if the multiplicity of outcomes to its phenomena would allow it to remain closed even if it could remain in existence.

Answer 18

Physical laws persist because that's part of their definition. Your question is a tautology.

For example, there is no law that things stay forever where they are. There are Newton's laws that describe the way small-ish, slow-ish things bounce off each other; that they generally stay where they are is simply not one of those laws because it is not true over time. In a way, there is an evolution of physical laws: Only those which adapt and survive remain.

That said, because the future has not happened yet it is unknown, potentially including "unknown unknowns" (Rumsfeld), for example events that make clear that anything we thought we knew was utterly wrong.