# How does the whole universe agree on the laws of physics? [duplicate]

How is it possible that the every particle in the universe agrees on the laws of physics?

What enforces those laws? Might the laws change slightly across the universe in the same way the cosmic microwave background radiation (CMBR) does?

Have you perhaps mistaken the meaning of the word "law" in this context? It simply means "pattern" or "regularity". If a given property or behaviour is neither constant nor varying in some regular way, then it would not be a regularity so it would not be a law.

Some parts of the universe are very different from others. E.g. In the middle of a vast inter-galactic void many things are very different from inside a star or near a supernova or something like that. The aspects that are in common (e.g. conservation of momentum, equations of gravity, etc.) we call laws. The aspects that are different we call 'conditions' or something like that.

The evidence for dark matter is a good example of this distinction. For a while it was possible to suggest that rotation curves of galaxies could be explained by a modification of gravity. But further evidence accumulated and now the best hypothesis is dark matter. So we have that different galaxies have the same gravitational laws but different amounts of dark matter obeying those laws.

Having said that, I agree that it is rather wonderful that there can be such a grand scale to the universe. Ultimately there is a certain amount of mystery here. Does it all have to play out on this vast scale, or could it have been smaller (say, millions of galaxies rather than gazillions)? I don't think we know what to make of questions like that.

The hypothesis that the fundamental laws of physics are the same everywhere in the universe and at all times is based on empirical evidence. Detailed observations of distant galaxies confirm that physical constants such as the fine-structure constant, the cosmological constant, the proton to electron mass ratio and the speed of light in vacuum have remained unchanged to a high degree of precision for billions of years - see this Wikipedia article.

Of course, our knowledge of the universe is limited to the observable universe and to the past (we have no knowledge of the future) so the most we can say is that this hypothesis has not yet been contradicted by anything that we know.

Physicists have sometimes considered theories in which one or more of these fundamental constants does change gradually over time - Einstein considered several versions of general relativity where the speed of light is not constant - but so far none of these theories have been confirmed by the available evidence.

On the other hand, if experimental evidence did confirm that some law of physics could change depending on time or location then physicists would seek to replace that law with a more general law that explained the new results. So there is a sense in which the fundamental laws of physics must logically be universal as far as we know, otherwise they would not be fundamental laws.

Let's consider an example of this violation. Consider the electrostatic attraction strength (Coulomb's constant). If we compute it and get some value $$k_1$$ in our labs, we might conclude that it is a law of nature that $$F=k q_1 q_2 /r^2$$. If we look at another part of the universe we might find some $$k_2 \neq k_1$$. Is this a violation?

One might say that this isn't a violation of the laws of physics, because we just found that what we thought was the law was just an approximation. The full theory would have $$k(x)$$ with $$x$$ being positions in space (or maybe space-time to include time-variation). We might not have the full theory, but surely some law exists, which upon giving initial conditions produces the function $$k(x)$$.

In this point of view, the law was never violated. Only our initial idea of a law was violated and was replaced by the true, more general law.

In short, if you can find a spatial variation of some "law", I would assume that you can in principle find the dynamics controlling this variation - and call that the law. That law is not violated in different locations.

• There is another possibility: that $k$ depends on $x$ (or some other parameter) in a completely arbitrary (seemingly random) fashion. Even if $k$ was well-defined at every point of time and space, this wouldn't be what most people would call a "law". Though of course that very idea of physics rests on the assumption that the universe behaves in a more "reasonable" manner. – gardenhead Oct 26 at 22:15
• Option 1: we have areas of constant $k$ with boundaries. I would call that initial conditions+ some dynamic of the boundary which needs to be described (in a relativistic theory the boundary has to be dynamic) Option 2: a smooth variation in space: This would have to be explained in a cosmological theory, simmilar to the CMB. different $k$ would indicate a different energy-distribution Option 3: random $k$ in every point in spacetime- this is option 2 in disguise, as an experiment would give some average value. – Rd Basha Oct 27 at 7:44

You seem to attribute sentience and intention to lifeless particles - which they do not possess (or need not posses to describe the universe in a meaningful way, c.f. Occam's razor).

A "law" in physics is kind of the opposite of a "law" in the legal sense. There isn't any "physics police" enforcing obedience of the Universe, but rather it's the Universe behaving the way it does, and physicists (and everyone else) trying to make sense of that behaviour and describe it as uncomplicated as sensible with what is then called a law.

• @PeterMortensen I used the "wrong" capitalization for narrative effect :P But I guess proper one doesn't hurt 😅 – Tobias Kienzler Oct 27 at 17:04
• Side remark: Typical QFT calculations are harder, both in code complexity and in CPU need, than the average AI calculations. – peterh - Reinstate Monica Oct 28 at 8:23

Suppose "the laws of physics" are, themselves, a quantum object that has existed from the moment the universe came into being, such that every particle in the universe carries a version of that object, and the versions are all consequences of that "object" and therefore entangled at the "laws of physics" level. Although from the perspective of QM, the laws of physics could have any of a near-infinity of different forms, measurement of the laws of physics locally would in that case, through entanglement, firmly determine that the laws of physics that could be inferred from astronomical observations of events distant in space and/or time are exactly the same as the local laws of physics. There's a lot of "suppose" in that, but it's not unreasonable to hypothesize that the laws of physics -at least in the form of a quantum object- existed prior to the existence of matter.

The essential part of all sciences is that they are looking for the laws governing everything, independently from space and time.

The goal is to find (or get to the possible closest) to the set of laws which describe everything. We assume that these laws exist, although believing it is not a requirement.

The scientific method, essentially, is the following:

1. We have our current set of laws.
2. We find cases, where these laws don't work.
3. Create hypotheses where a "tuned" version of the laws describe the reality better.
4. Validate the hypothesis by experiments.
5. Restart from (1).

What enforces these laws, is not a science question. Science is about to find them. Furthermore, there is no warranty if these laws don't exist, or the Universe is not describable by a finite set of laws. Science just tries to find them.

Actually laws are given to explain observed phenomena. Many of which are not even proved.

and it might be possible that those laws fail in any other part of this universe. but the laws that are proved cannot fail anywhere else for surely.

• Your answer is quite misleading. Without proper reasoning it's wrong to give such answer try to explain a bit and if possible put this on comment section. This is seemingly not an answer. – David Oct 26 at 14:53
• actually the question he asked was also misleading. There can be no better answer than this as the laws are experimental and those that are proved are true for any part in universe. – Anonymous Oct 26 at 14:58
• Better question is why do we assume it behaves the same everywhere. – DKNguyen Oct 26 at 15:04
• This is very confused. We believe laws are universal (that's a belief). What we however actually discover, are not laws, but theorems, which aim to describe the laws. Moreover, even the theorems cannot be proved. – user1079505 Oct 27 at 16:58
• i think you have a misconception – Anonymous Oct 29 at 14:24