# Are Laws of nature independent of time? [duplicate]

There are certain laws that govern the universe and these laws make up the fundamentals of any physical observation. But were these laws present the way there are now since the beginning of space time, were they same during inflation or did they change after cosmic inflation?

I can't get how in certain answers to prior similar questions ( here https://physics.stackexchange.com/a/10082/311056 ) they propose the idea that the laws which change were never truly fundamental laws but a special case of a general law, that definitely had to be fundamental. Then how do we describe this "never changing general law", that gives off special cases.

• I'm not sure what kind of answer you're looking for. If we imagine that, say, the fine structure constant changed over time, that would still be the result of unchanging physical laws of the universe as a whole. Whether our models encompass those changes is irrelevant to the actual laws of the universe - the universe is whatever the universe is, and we try our best to model it as precisely (and practically) as possible. Sep 26 at 6:46
• The simple answer no one seems to be pointing out here is that while the actual laws of physics likely never change, our own theories on how the universe works are (highly) incomplete. This means we need to change our human-assigned laws for the universe to make sense over large timeframes. In other words, the knowledge needed to accurately describe the universe over all timeframes does not exist yet. Sep 26 at 21:15

There are two approaches to time dependence in physical laws. One is to say that there could be different laws at different times. Another is to say that there is one "true" unchanging law, which might happen to include a dependence on time (or temperature/energy, or some other parameter). With either approach you get the same outcome - the difference is just a matter of emphasis.

By analogy, we can refer to the three phases of $$H_2O$$ as ice, water and steam, emphasising their different properties. Or we can refer to them as frozen water, liquid water and water vapour, emphasising that they are different arrangements of the same molecule.

• There isn't any concept of H2O if it isn't in any of these form. I.e. if water exists HAS to exist in any of these 3 forms or else there isn't any concept of it. Water is still water, it's same molecule of H2O, nothing changes here! You can't explain or emphasize it's properties if you don't know what it is!? So how are different laws at different times or same unchanged law everytime, even analogous to different forms of water?
– A.M.
Sep 26 at 1:00
• @A.M. That isn't true of you look for a more accurate picture, though. Liquid water is not the "same molecule of H2O". Water spontaneously dissociates, so a certain proportion of liquid water is always H+ + OH-. The same is true of many other "simple" things you take for granted - when you look closer, you'll see a lot more nuance. None of our models cover the universe perfectly (even if we assume there's no unknowns, which decidedly isn't true) - but that doesn't tell you everything about the underlying reality. Sep 26 at 6:54
• The change in forms never change the chemical properties of water! Water is still water whatever may be it's form. Dissociation into H+ and OH- never changes the properties of water, if the properties would change then we CAN'T POSSIBLE deem all 3 as different FORMS of SAME molecule. Isn't it? I am sorry but that really doesn't explain the analogy given in the above answer.
– A.M.
Sep 26 at 10:10

Yes, the laws of nature are independent of time.

That is, when and if we have the 'correct laws' of physics.

It's quite subjective and philosophical as physical laws can't be proved right, only falsified, or proved wrong.

However most scientists would think that if we had a 'law of physics' and it was found to vary with time - then it had been falsified and need improvement/development.

So with these caveats we should aim to find laws of physics that are independent of time and many would believe that the 'true' laws of physics are independent of time.

• We think that the distance between points in space is changing over time (right now, expanding). Does that mean that part of our understanding of physics is wrong? Sep 26 at 0:56
• @DanielWagner Well, that's why physicists had to make up dark energy, and they don't know what it is. Sep 26 at 1:58
• @DanielWagner We know how spacetime can expand - it was already described rather nicely by Einstein. That part of our understanding of physics is fine. The tricky part is what drives that expansion - we have some candidates for the drivers of spacetime expansion at different times in the evolution of the universe, but there's still a lot of unknowns. And of course, the universe is under no obligation to be knowable by us :) Sep 26 at 6:49
• @DanielWagner it's fine for things to change, but according to the answer the underlying physical laws shouldn't. For example a pendulum looks different when viewed at different times, but the underlying rules for it's motion are unchanging (always the force of gravity and the tension towards the point of suspension) Sep 26 at 8:35

As far as we know, the laws of nature have not changed in the 13.7 billion years since the big bang. That is the laws of gravity, E&M, quantum mechanics, and so on applied then as they do now. Furthermore, the strength of the constants that describe the strength of interactions and such, like G, e, and so on, have not changed.

Conditions have changed over that time, so the universe looks a lot different now. For example, it is a lot cooler now than immediately after the big bang.

That said, there is a not really mainstream idea that the universe is really big and we can't see all of it. So we have no way of knowing if the laws are the same everywhere. See The Multiverse, Science or Science Fiction? | Sean Carroll

Aristotle argued that one of the major goals of physics was the study of change.

If the laws of physics that we knew of changed with time, then we can ask for the reason behind this change and call that a law of physics instead. If that in turn appeared to change then again we can ask for the reason behind this change. One does not expect this to go on, ad infinitum - eventually it will come to a stop. And we have a physical theory that is independent of time.

Thus we should expect the final theory, the actual laws of physics, should be independent of time.

Whether this means they are in time or ourside of time is an open question. As is the question as to the nature of physical law. These questions are typically not addressed by physicists but by philosophers, especially in todays world (in an older world, one would have expected them to be tackled by natural philosophers - an older name for physicists, biologists etc. This is the term by which Newton called himself).

In my opinion they are an aspect of what the Greeks would have called Ananke or Neccessity. This also explains the famous question put by Wigner about the unreasonable effectiveness of mathematics in physics. Mathematics is also an aspect of Neccesity in a purer form. Hence their close relationship. In a sense, physicists are busy reducing physics to mathematics. And they have been very successful in this programme.

### Yes but...

Many of the "laws" of classical physics are actually rather conditional - they work OK in normal environments, but they tend to break down in extreme cases, like in black holes. As a result, physics has developed a Standard Model of subatomic particles, which interact in non-intuitive ways to produce the classical physics we know.

As an analogy, classical physics says "this train takes 2 hours to get from A to B". Modern physics says "this is how the wheel bearings work, and the engine, and...". If you only need to get from A to B under normal conditions, you're good with the classical model. If you've been hit by a cold snap which freezes the wheel bearings, you need to deal with the extra detail.

The Big Bang definitely qualifies as "extra detail" territory, of course. You can forget about Newtonian physics there. But the Standard Model is still holding up pretty well.

### So those subatomic particles...

We can do experiments on Earth under extreme conditions in particle accelerators, and see how things behave now. Because light (or other emissions) from distant stars represents events in the distant past, we can observe them and compare those ancient cosmic events against what we observe today. (And we can do experiments with light and other radio waves to check how they work right now too.) So far, everything does seem to be to tying up.

That doesn't mean that some other thing couldn't turn up, of course - just that the observations we have so far are matching well enough. As well as we can measure, anyway. Maybe better measurements will show us something new though. And that's why experimental physics gets expensive, because "better" costs money!

### And those "laws"...

In some ways, physics is still at the point of describing how things work without totally understanding it. The point of building a unified field theory is getting to a point where we do understand properly. This is still TBD though.

The definition of a "theory" is that it has to match evidence. So the problem isn't just putting some maths together - it also needs you to design experiments which will show (or not show!) the universe following your idea and not doing something else. Up to now, we haven't been able to do that. (See "expensive"!)

### In short...

The only answer so far is "probably", with boundary values for where this could be different and how much by. But those boundary values represent a very small amount of the universe by space and time.

This subject is not in my area of expertise, but for what it's worth, in the following article titled "Eras of the Big Bang" (https://web.njit.edu/~gary/202/Lecture26.html#:~:text=The%20Planck%20Era%20is%20prior,a%20single%20%22super%22%20force.) the following statement is made: "The first few eras are when the laws of physics were considerably different than they are now".

Hope this helps.

At high energies the laws of nature become different than in lower energies so as we go back in time some laws must have been different.

• That's like claiming the laws were different on the early Earth because it was so hot the surface rock was molten.
– J.G.
Sep 25 at 12:21
• @J.G The early universe was much much hotter and different rules applied to it.Maybe the strong force was much weaker , there wasnt any electromagnetic force ,the electroweak force followed different rules should I continue? Sep 25 at 12:28
• @J.G. the reason why the laws of nature are time dependent is that because the universe is evolving and its temperature changes of time so it is not a direct relationship maybe I should have said that. Sep 25 at 12:39
• You're missing my point. The fundamental laws are the ones you see at high energies; everything below that is an emergent consequence. For example, electromagnetism is what you get past an attometre or so when the energies are too low for three of the four electroweak gauge bosons to propagate.
– J.G.
Sep 25 at 12:45