Why scientists assumes that nature have laws? Is it possible to have no laws at all? I mean that how nature behaves may vary with space and time but this doesn't mean it is unpredictable at all. It behave in its own way. If I let an object fall from a height then it could drop/explode/do anything. But something must happen. The fact that predicting this behavior is difficult doesn't mean that nature has no laws at all. So why it is considered a priori that nature has laws?
To answer this question you first have to know what physicists mean when they refer to physical laws.
To a physicist, a physical law is a rule which appears to account for the behavior of a physical system in such a manner as to allow the physicist to apply that rule to predict the outcome of an unperformed experiment or to explain the outcome of a performed experiment.
That rule must 1) furnish the correct answer within its range of applicability and 2) always furnish the correct answer every time it is applied, within its range. The rules of greatest utility in this context are those which can be concisely described in the language of mathematics, which means those physical laws are usually written as equations.
Physicists do not automatically or simplistically assume that nature has laws of this sort. They observe the behavior of physical systems and thereby discover regularities in that behavior that hint at the presence of some sort of underlying principle which might then be mathematically expressible as a "law". Because most working physicists believe that the universe they inhabit is causal, they carry an expectation that the universe contains laws that account for effects in terms of causes, and it is their job to uncover those laws.
A universe without physical laws would be one in which for example a planet could exhibit a stable orbit around a star on one day and then on the next day suddenly become unstable for no cause. If the universe were acausal in this regard, it is unlikely it would contain any humans to take note of it because a planet on which life might evolve would be just as likely to fall into the star as it would to be flung away into deep space at any instant in its existence.
A universe without laws would be one in which counting objects would be not just impossible but meaningless, because objects could pop into existence and wink out of existence at any time. Because of this, the discipline of mathematics could not have a meaningful existence in an acausal universe.
If we assume an universe as any possible flow of qualia, then physical laws are not necessary. Take, for instance, the world you find yourself in in the night dreams. There are no physical laws, even mathematics and logic may act differently.
Yet, you still have feelings, thoughts, observe objects and interact with them.
One can imagine worlds which have laws, but not of physical nature. For instance, a world where everything you think is true, is in fact true. Or a world where everything you fear is true. Of a world where everything you desire is true.
Why scientists assumes that nature have laws?
To start, we cannot know nature.
The fact that we perceive colors doesn't mean that nature is colored. Following the same consideration: the fact that we perceive time doesn't mean that nature has time; the fact that we perceive space doesn't mean that nature has space; the fact that we perceive causality doesn't mean that nature follows a causal behavior; etc.
In consequence, we (science) cannot know if nature has rules.
But inside each one's subjectivity, patterns are perceived. For example: things have colors. That's a pattern we perceive. In addition, colors manifest according to specific rules; that is, our subjective experiences tell that colors obey some laws.
Therefore, nature has no laws, but we grant nature of laws, which are biased by our subjectivity. Nature might have no space or time, but within our subjectivity, Einstein's Relativity laws allow a very precise description of the space-time patterns we perceive.
Do not forget that science does not seek for final truth. Science seeks for empirical truth, that is, the truths that are coherent with our experience. That is because metaphysical considerations (knowledge, ontology, perception, causality, etc.) are excluded from science.
Philosophy, on the contrary, seeks for final truths. But the most developed philosophical branches tend all to suggest that everything that exists do so only in our mind; outside of us, something happens, but it seems to be a reality quite different to the one obtained by perception. Read about the empiricists and rationalists debate.
What you are talking about at root, is the problem of induction. Hume suggested skepticism as a response. Popper reckoned induction to be a myth, & evidence turned to only for choosing between explanations.
What is explanatory power? It seems like it is about being able to model something in the world, in an efficient way: capturing dynamics; not 'multiplying entities without necessity'; providing a framework that unifies experiences with a common language, or a versatile model. The hallmarks of good science are about efficient abstraction.
In a very real way, efficient abstraction has to be possible for intelligence, for self-consciousness. We have to be able to make a model of the world, and of ourselves, that is less complicated than the reality, but captures it's dynamics enough to navigate between possible outcomes. We call 'being more intelligent' being better at making abstractions, & so better at choosing among possible outcomes.
We are meat-robots driven by genes, to manipulate our environment. Now with a socio-cultural intelligence or meme-sphere, driven by language, and including tools & technology. When we say 'that's a rule' or a law, it provides a constraint that helps us have to think less. A salience landscape, focusing us on things we can act on. But also hiding the complexity and chaos of the world from us, to save processing power.
I think Newton started this trend (continued until our time, in full force since the 20th century) of realizing that our mathematical models/theories for how nature works do not equal how nature actually works. In other words, one must separate actual nature and the universe we inhabit from our description of it, or even from our ability to describe it. There are then no "natural laws"; instead, what we have is different species with an ability to perceive some regularity in some aspects, and maybe even to be able to make predictions, but this says a lot about the organism doing the modeling, and little about the universe.
To address your point of what would nature look like with no laws, a good example one can take is the mind. It seems like problems concerning understanding our own minds (or even those of much more basic animals) are completely out of reach to us. It is very conceivable that a more advanced species could look at the workings of human minds and to them things could appear regular enough to formulate predictions, etc., but to us things look completely incomprehensible. I suppose this is what our ability to predict planetary motion must look like to cats, for example. In any case, our ability to formulate certain phenomena in theories that allow us to make predictions seem restricted to certain phenomena, and highly species-specific, so I definitely wouldn't call these properties of nature.
A simpler illustrative question is whether there is such a thing as 'sanity'. We all prefer to think of ourselves as being 'sane', but immediate problems arise if a definition is examined: 'The ability to think and behave in a normal and rational manner; sound mental health."
Which raises further problems of what is 'normal', what is 'rational', and what constitutes 'sound mental health'. To illustrate, it is obvious that one of today's biggest problems is environmental degradation, especially that caused by industrial waste and the enormous amounts of non-degradable plastics in EVERYTHING. These in turn derive from modern consumer society and the billions of eager 'consumers' ultimately responsible. The obvious solution is to reduce consumers to a manageable number, perhaps by killing ninety percent of the world's human population. This is simple, obvious, and rational, and so should count as an acceptable conclusion; i.e. as a sane recommendation.
From this it is obvious that mere 'rational thinking' - sc. sequential logical deduction - does not necessarily meet the commonly accepted notions of 'sanity'. Physical laws result from applying sequential logical deduction to observations of natural processes, and are carefully worded to ensure consistency of interpretation; but if continued beyond a certain point, their conclusions eventually become meaningless, and then absurd.
A good example is the Standard Model of so-called 'sub-atomic particles'. Protons are fine: we can bang them about in particle accelerators with great confidence. Neutrons, being uncharged, are a bit more problematic, but do enough 'banging about' to convince us of their reality. Electrons are still more problematic since they appear to have no mass (other than the energy-equivalence of their charge) but are far too useful to dismiss as illusory - think the heater with 'electricity' running through it that's keeping your feet warm.
The REAL problems start with quarks. The most useful - indeed ESSENTIAL - of their properties is that they can never be observed in isolation: it's IMPOSSIBLE to observe - sc. detect - individual quarks. Now science is founded on observation: anything that cannot be observed cannot be real - scientifically. So quarks cannot be real - SCIENTIFICALLY.
Here, then, is one boundary of Physical Law: anything 'smaller' than quarks in the Standard Model is SCIENTIFICALLY NON-EXISTENT. There are other boundaries of Physical Law equally unrecognized, but phenomena beyond them are accepted as real to prevent confusion, and so enable more papers to be published about them. And without ever more papers, where WOULD today's 'Science' be?
This may serve to introduce a completely different perspective on the question. Modern Western Science believes that the Universe resulted from the 'Big Bang': a gigantic explosion of sorts creating a state of total chaos. Out of this maelstrom arose the tightly-ordered Universe we observe today, apparently because pre-existing 'Laws' of some sort forced matter and energy to behave in certain pre-defined ways. And all of this is the result simply of chance, completely without premeditation, meaning or purpose.
Buried deeply in some of the oldest literature on the planet are the fragmented remnants of an ancient Science of Consciousness that, when reconstructed, offers an entirely different explanation. In this view the most fundamental property of the Cosmos is consciousness; NOT human consciousness which is a much later development, but a primitive awareness imbued with a creative urge and capability. Its first attempts do not produce 'things', merely 'tendencies' so to speak. Most are transient and formless, but eventually some take various shapes and survive for a time. These 'tendencies' are themselves conscious, and so attempt to form creations of their own.
The Reader is invited to extrapolate this idea through the aeons of time needed to create the gigantic swirls of debris that form galaxies, then stars, finally planets and the many life-forms that eventually take shape in and on them, including humans.
From this point of view, the original question is both true and false, and also meaningless. Yes, in a free-will Universe, all attempts at creation are permitted; but a creation without form or structure - 'Laws' if you prefer - has nothing to offer, and even if created will soon disappear.
From this can be seen that the question is NOT about the reality we inhabit, but about certain concepts in Modern Western Science, which is well overdue for critical examination, and preferably replacement with something less absurd.
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Your particle-physics ontology us positively Victorian.
Let's look at REALITY. A quark star is a HYPOTHETICAL exotic star wherein extremely high temperature and pressure form quark matter. Note that it's HYPOTHETICAL. So if I go out and look at the night sky, I might see a faint pin-prick that is CERTAINLY a quark star; but only if it's close enough to see, and emitting visible light. Otherwise it's completely invisible even if it DOES exist.
For a few millionths of a second after the Big Bang, the universe supposedly consisted of a hot soup of elementary particles known as quark-gluon plasma. So if I went back to the first few microseconds of the Universe, I could take a luxurious bubble bath in quark-gluon plasma. YUMMM! Getting back that far might be a problem, though, and microsecond baths have never been a favourite - WAY too short!
Black holes are another popular fantasy of modern scientists. Whether locked up safely in the stable or roaming around on the loose, there's no proof whatever of their REAL existence.
The most convenient feature of everything you've described is being so far away in space, time or both that nothing about them can be tested, least of all their existence, so you're on safe (but imaginary) ground. Like all modern scientists, you've spent so long cultivating favourite fantasies inside your head that they're now more real than reality. All of those things are merely mathematical constructs in the minds of scientists and have no bearing on reality.
Yep! I'm so old-fashioned that I prefer reality to fantasy. As Einstein put it:
"As far as the propositions of mathematics refer to reality, they are not certain; and as far as they are certain, they do not refer to reality."
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It seems like problems concerning understanding our own minds ... are completely out of reach to us.
Well thought and worded. Ultimately, ALL we ever have is our own consciousness. Many only realize this on their death-bed. HOW we interpret reality is FAR more relevant than "what is reality", which we can never truly know.
Speaking in the language of World Semantics (The model theory for modal logical systems), a world without physical laws would be a world that is, for example at one point a 4 dimensional lorentzian spacetime and then, without cause, fully transforms into a 18 dimensional newtonian spacetime. That's still logically possible, mathematically possible (Well, if you interpret "transform" freely enough), yet for our world physically impossible.
Let's assume you take away the logical and mathematical laws as well. A world, let's say one like ours, could collapse without reason into an abstract concept like the number 3 and turns into an unicorn simultaneously. See where this goes? "Where" (Referring to a world) there are no longer physical laws required, anything not violating the logical possible can still happen. I suppose in some way the logical laws could, in a mathematical realist sense, interpreted as minimal necessary metaphysical laws for a world. Where even mathematics and logic no longer apply, anything goes. These type of worlds have a very fitting name, "Impossible Worlds"