<p>See also: <a href="https://physics.stackexchange.com/questions/11614/do-the-laws-of-physics-work-everywhere-in-the-universe">Do the laws of physics work everywhere in the universe?</a></p>
<p><a href="https://en.wikipedia.org/wiki/Noether%27s_theorem" rel="nofollow noreferrer">Noether's theorem</a>, in the context of this question, states that:</p>
<blockquote>
<p>If the laws of physics do not vary with position, then linear momentum is conserved (and vice versa).</p>
</blockquote>
<p>Therefore if we observe conservation of momentum (which we do with exquisite precision) then we do not expect the laws of physics to vary with position. In other words, distant parts of the universe obey the same physical laws.</p>

CC BY-SA 4.0
2020-09-28T05:26:16.227Z
The way it is stated here, this is a non sequitur. "If A then B" does not imply "If B then A".
Guntram Blohm
CC BY-SA 4.0
2020-09-28T06:02:54.107Z
@GuntramBlohmsupportsMonica in formal logic, "If A then B" does not imply "if B then A", but [formal logic does not apply to physics](https://physics.stackexchange.com/questions/472785/does-the-principle-of-explosion-mean-we-can-prove-objects-must-fall-up-because).
Allure
CC BY-SA 4.0
2020-09-28T08:29:28.073Z
@Allure The post you cited: "We don't expect physical theories to be true in any absolute sense of formal logic. We expect them to be good approximations under certain conditions." I find this quite confusing. Within a theory, formal logic has to apply - at least ideally -, just because it is a science. But the theories themselves do not claim to yield perfect descriptions of the entire would, just useful approximations within a certain context. And yes, out of this context, they may yield false statements about reality.
rexkogitans
CC BY-SA 4.0
2020-09-28T10:28:35.090Z
Related: https://physics.stackexchange.com/questions/24596/is-the-converse-of-noethers-first-theorem-true-every-conservation-law-has-a-sy
jpa
CC BY-SA 4.0
2020-09-28T11:28:41.430Z
@Allure well the question remains. You are quoting something like "if A then B" and then saying "B implies A". On what basis are you telling "B implies A" ? The argument of Guntram is basically "you can't justify your assertion with formal logic" and you answer that formal logic doesn't work in this case, but then what kind of logic are you using to go from the first proposition to the second ?
EDIT : I didn't see any justification on your affirmation about formal logic in the link provided
Guiroux
CC BY-SA 4.0
2020-09-28T11:41:12.107Z
@Guiroux See the link by jpa.
Allure
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2020-09-29T04:30:38.343Z
Noether's theorem is a biimplication -- symmetry implies conserved quantity and conserved quantity implies symmetry.  You have only written half of the theorem.
Eric Towers
CC BY-SA 4.0
2020-09-29T04:38:11.780Z
@user253751 : Then LIGO ring-downs would be wildly different.  And exoplanets would be much harder to detect because their orbits would not be periodic.  And globular clusters would not be stable.  And Hubble shift would not be spherically symmetric and radially smoothly increasing.  And the population of type Ia supernovae would not be as uniform as it is.  And pulsar periods would not be stable.  And ... And ... And ...  We have literally millions of observations, any one of which could reject extra-solar conservation of momentum, and all have failed to do so.
Eric Towers
CC BY-SA 4.0
2020-09-29T09:37:42.293Z
@user253751 I don't understand. If rocket ships on Alpha Centauri don't need reaction mass, then the laws of physics would've changed, and we would've seen a violation of conservation of momentum (via experiments done on Earth).
Allure
CC BY-SA 4.0
2020-09-29T11:05:43.897Z
@user253751 again, if the laws of physics are changing between here and Alpha Centauri (and they must be in your scenario, since it requires reaction mass on Earth and not there), then we would not observe conservation of momentum.
Allure
CC BY-SA 4.0
2020-09-29T12:58:18.883Z
@Allure I'm not sure that's entirely true; certainly not obviously so. It seems reasonable to wager, from the non-expert's view, that Noether's theorem essentially implies that if you have translation invariance over a region of spacetime, then in some sub-region you will observe conservation of momentum to a high degree of certainty.  Similarly for approximately translation invariance.  So why are we sure we are not in a well-behaved bubble that prevents us from seeing conservation violations with present instruments? Perhaps that should be a question on physics, if not already.
zibadawa timmy
CC BY-SA 4.0
2020-09-29T14:02:06.780Z
@user253751 : A hypothesis of the form "something behaves differently from everything we have ever measured" requires extraordinary evidence.  Without such evidence the most *paranoid* scientific philosophy is to deny that such questions have answers -- rejecting your hypothesis on foundations.  A parsimonious scientific philosophy is to assume a "small" physics, expanded only when it disagrees with measurement -- rejecting your hypothesis.  To accept your hypothesis is to assume that the Universe is hostile to understanding, which denies utility of reason, so is definitionally unreasonable.
Eric Towers
CC BY-SA 4.0
2020-09-27T23:55:52.987Z
2020-09-29T04:36:06.690Z
2020-09-29T04:36:06.690Z
Allure
<p>The measurements of all astronomical manifestation are currently the same in all directions of the sky, rather than variable by direction and distance.</p>
<p>The CMB temperature is nearly constant with with anisotropy which has been very well studied, there is a dipole variance which indicates that that we are moving at 370 km per second relative to the CMB, travelling with the Galaxy.</p>
<p>Physicists tried to find evidence that gives credence to your suggestions, but the CMB implies that the big bang was the same, 13 billion light years in every Direction.</p>
<p>The same atoms seem to be emitting the same wavelengths, the quasars are the same, the galaxies are the same locally, far away and with dipole variations, the star numbers and distributions are the same, the supernovae are the same. The laws of physics are the same, same hydrogen lines and same rotation speeds.</p>
<p>The visible universe is the invariant, although you can be right about 130 or 500 trillion light years away, there may be some variation in in an unobservable distance of the universe, only that it's beyond what we can see.</p>

CC BY-SA 4.0
2021-04-25T03:13:03.800Z
2021-04-25T03:13:03.800Z
bandybabboon
<p>We don't know in general but to the extent we can measure, the laws seem to be the same, even if conditions are not.</p>
<p>For example radioactive decay: We know how fast various elements decay, and we can observe the results of radioactive decay in distant supernovae.  The conclusion is that, for at least some elements, the rate of radioactive decay is the same on Earth as it is in distant supernovae.</p>
<p>After accounting for redshift, spectral emission lines remain unchanged by distance. This implies that the fine-structure constant is indeed constant.</p>
<p>Distant galaxies have gravitational fields, and interactions between galaxies proceeds in the same way in distant galaxies as it does in local ones. Eventually, the justification is philosophical:  There is no observational reason to believe gravity behaves differently in distant parts of the universe, and so we believe that it does not,</p>
<p>In the extreme conditions of the early universe, some physical laws were different.  For example, instead of distinct electromagnetic and weak fields, there was a single Electroweak field.  But this can be described as single &quot;law&quot; with the electromagnetic and weak interactions being just the low energy approximation of the electroweak interaction.</p>
<p>So if it were discovered that Gravity (for example) was working differently in distant parts of the universe, but that there was a consistent pattern or rule for how it varied, then that would simply become the new theory of gravity (with general relativity becoming only the local approximation to this new law).</p>
<p>There is a more fundamental assumption: that the behaviour of matter and energy in the universe can be modelled by &quot;laws&quot;.  There are no angels dancing on pinheads. The justification for this is strictly in the realm of philosophy.</p>

CC BY-SA 4.0
2020-09-27T14:59:36.373Z
After accounting for redshift, spectral emission lines remain unchanged by distance. This implies that the fine-structure constant is unchanged by distance: https://en.wikipedia.org/wiki/Fine_structure
Wayfaring Stranger
CC BY-SA 4.0
2020-09-27T16:06:56.067Z
Lets bring a hypothesis, a start at a very distant part of the universe which in reality emmits 500% more light compare to what we observed by our equations because the physical laws was different at the point it emits and hence the luminosity decreased. How can we disprove that hypothesis? @Stranger
Sazzad Hissain Khan
CC BY-SA 4.0
2020-09-27T18:44:23.033Z
@SazzadHissainKhan we don't have to disprove any and every hypothesis. A hypothesis which makes unusual claims needs means to positively verify its predictions. There simply is no way to disprove my hypothesis that in a far far part of the universe a planet exists where dragons rule and atoms weigh twice what they do here. Yet there simply is no indication that this hypothesis should be true as all we see seems to confirm that the universe behaves the same as here. Occams razor applies: the simplest solution is assumed in the absence of proof to the contrary
planetmaker
CC BY-SA 4.0
2020-09-27T19:36:46.607Z
@planetmaker I have to voice the usual Humean skepticism. You seem to be saying that nature is uniform because we observe its uniformity. But observable uniformity only implies that that uniformity extends to the unobserved if we assume that nature is uniform. Because the logic is circular, we don't get to apply Occam's razor. Better to say that we take it on faith that nature is uniform. Or, if you've spent a lot of time reading Kant (not me!), you might say that the uniformity of nature is an inextricable feature of the thinkable world (as opposed to the physical world).
Charles Hudgins
CC BY-SA 4.0
2020-09-27T19:48:13.487Z
@planetmaker why it wouldn’t be a positive claim that the physical laws work uniformly at the distant part of the universe even without any single empirical evidence then? Also why don’t scientists apply the same arguments and confirm that the un observable universe has the same principle?
Sazzad Hissain Khan
CC BY-SA 4.0
2020-09-27T20:47:15.143Z
I think this ultimately comes down to Occam's Razor. We assume uniformity because it's simpler, and we haven't detected anything that contradicts it yet.
Barmar
CC BY-SA 4.0
2020-09-27T21:22:13.183Z
Science tries to find things which are not known, and thus also which contradict current theories. But as long as there is not proof to the contrary, the simplest solution is to be assumed. A theory never is reality but only a description of realiy - the simplest possible one. And if something unexplicable with current theory is found, we adjust theory to explain that fact, too - of course that may and will mean that the overall picture gets more complicated. But little point in making it more complicated than necessary to explain all observations
planetmaker
CC BY-SA 4.0
2020-09-27T23:16:12.070Z
@SazzadHissainKhan "why don’t scientists apply the same arguments and confirm that the unobservable universe has the same principle" - how exactly do you propose to confirm anything about something unobservable?
IMil
CC BY-SA 4.0
2020-09-28T02:02:13.237Z
@IMil look here the point is not about observability instead knowledge. If we can assume that the laws applicable for what we have no knowledge by the argument “simplest solution needs to be considered” then why we can’t apply same principle to something non observable (in other words, completely unknown)?
Sazzad Hissain Khan
CC BY-SA 4.0
2020-09-29T13:10:34.567Z
@SazzadHissainKhan: You can feel free to make any hypothesis you want. But what distinguishes a scientific hypothesis from a nonscientific one is that a scientific hypothesis is *disprovable*, meaning that you can in principle design an experiment based on observation of the physical which will distinguish between truth and falsity of the hypothesis. So as soon as you say "the point is not about observability", you have left the realm of science and entered, I dunno, the world of science fiction?
Lee Mosher
CC BY-SA 4.0
2020-09-29T15:10:12.407Z
@LeeMosher, yes I agree scientific hypotheses require falsifiability. Now if you think deeply all current hypotheses on observable universe in reality makes falsifiability model which is dependent to totally unknown (as I already pointed out far reality is actually unknown in post). Then whats problem to make hypotheses on non observable universe? In fact many scientific hypotheses on non observable stuffs, i.e. multiverses etc. What are the distinction points? That question might not come if science could make local these laws as hypotheses for distant universe, but they described as theory.
Sazzad Hissain Khan
CC BY-SA 4.0
2020-09-29T20:43:36.267Z
@SazzadHissainKhan's comment seems a bit hard to understand; I will try to rewrite it as well as I can, so that this interesting discussion can continue. Here goes: // Yes, I agree that scientific theories need to be falsifiable. However, if you examine the current state of astrophysics in depth, you will see that even falsifiable theories that use data from the 'observable' universe [presumably to extrapolate to 'unobservable' regions] use models that depend on the unknown, since 'reality' is by definition not attainable. So how are hypotheses on the 'non-observable' universe different? ...
Timm
CC BY-SA 4.0
2020-09-29T20:54:16.010Z
... The last sentence is quite a poser, but I'll try anyway. // The question might not arise if physical models could be applied to the distant [i.e. 'non-observable'] universe; however, they are "described as theory" [perhaps he sees 'theory' as armchair guessing?].
Timm
CC BY-SA 4.0
2020-09-29T21:30:49.317Z
Now my reply to @SazzadHissainKhan's comment. You seem to be mixing physics and philosophy here. Physics is concerned with facts that can, in principle, be verified by others. The notion of reality as a hidden 'true' or 'as is' world was postulated by Descartes, Kant and Hegel, but it never lost its metaphysical trait and graduated to a verifiable theory or even hypothesis. Your question is about physical laws. The  difference between falsifiable laws or hypotheses of physics and 'reality' (_really_ unknown) is moot. Be a little more humble. "We don't know; we only guess." (Raimund Popper)
Timm
CC BY-SA 4.0
2020-09-29T21:53:42.953Z
@Timm first of all thanks a lot for translating my obscure comment into a sensible form which was exactly what I meant. Sorry for my bad nonnative language. I clearly understood your reply and I totally agree with you. I just tried to express the reason of this post as a reply to someone’s question. However, after reading the answers and comments its now clear to me. I also believe its humble to say ‘we don’t know’ instead of justification with vague arguments. Thanks you again.
Sazzad Hissain Khan
CC BY-SA 4.0
2020-09-30T02:20:18.617Z
Remarkably,  after this long comment thread,  it seems that we have returned to my actual answer.  Read the first three words of my answer!
James K
CC BY-SA 4.0
2020-09-27T11:50:59.377Z
2020-09-28T07:12:07.710Z
2020-09-28T07:12:07.710Z
James K
<p><strong>How do scientists know that distant parts of the universe obey the physical laws exactly as we observe around us?</strong></p>
<p>The question might look a bit odd but I am really stuck on my head. We know, scientists (with tools) explored physically only our solar system and some parts of our galaxy which is really a tiny part of the observable universe. And now they are constantly using these knowledge base along with 'tested physical laws' to measure the properties of distant parts of our universe.</p>
<p>For example, we tested and found the speed of the light is constant within our local periphery many times (within our Earth and Space around Earth). But yet we presume that the speed of the light is constant even at the farthest part of our universe. Certainly we did not test it in the other distant part of the universe because we have no way until now. Not only light but also the other physical properties like, luminosity, gravity, and etc related physical laws are agreed upon based on tests within our solar system. And based on these laws we deduced the properties of other parts of the universe (<em>i.e.</em> age, distance, mass, luminosity of stars in millions/billions light years away).</p>
<p>My question is, how do we know that these physical laws which we tested within a tiny area of the universe are consistently working in the distant parts of it? Is there any probability that the distant part of our universe obeys physical laws differently and our prediction based on applied physical laws gave us an unreal illusion of the actual reality, yet consistently?</p>

CC BY-SA 4.0
2020-09-28T06:07:26.687Z
1/2 This is an important philosophy of science issue. The thing is, nothing prevents anyone from posing the hypothesis that physical laws are different in other parts of the universe. As you say, because we haven't been there yet, it's impossible to prove or disprove. Problem is, by posing this hypothesis we would give up all possibility of understanding what we see when observing there: if anything goes, there is no point in trying to make sense of the astronomical phenomenons we do observe.
armand
CC BY-SA 4.0
2020-09-28T06:12:50.787Z
2/2 It has happened that observation of events far away led us to reconsider how things work here. For example, Newtonian physics worked on earth but could not explain the orbit of Mercury. Then the theory of relativity came and managed to explain how gravity works differently near the giganornous mass of the Sun, while still being consistent with what we observe on Earth and thus extended the Newtonian theory.
armand
CC BY-SA 4.0
2020-09-28T06:21:47.997Z
@armand my point is same. Just like we found Newtonian laws did not work outside our Earth periphery and we needed to update with Einsteinian laws. Now with same argument how we can be sure that Einstienian laws work in the whole Universe uniformly until we reach to the farthest part. Pretty much a deviation of Occams razor theory.
Sazzad Hissain Khan
CC BY-SA 4.0
2020-09-28T08:50:37.803Z
Note that if the laws of physics would be different from the known laws of physics far away but in such a way that the laws of physics change in an analytic way as a function of position, then this means that the laws of physics as they are valid right here would be different and knowing the correct laws of physics would allow us to describe the difference in the approximate laws of physics as observed here and in far away regions.
Count Iblis
CC BY-SA 4.0
2020-09-28T11:57:05.533Z
@Sazzad Hissain Khan: we can't be sure. But as long as we don't have a compelling reason to think the physics are different in other places, we have to work under the hypothesis that they are, otherwise its only speculation. Einstein could prove his theory by explaining with extreme precision observations that were impossible according to Newtonian physics. Young Earth creationists often posit that the speed of light decreased over time to explain how the universe can be 6000 years old while we can see stars millions of light years away, but they have no evidence that it is in fact the case.
armand
CC BY-SA 4.0
2020-09-28T12:27:16.853Z
@armand I agree with you. Young Earth creationists claim sounds absurd to me. From my empirical perspective I am just trying to understand the philosophical aspects of science especially in that concern. Anyway, thanks for your time. I think I got the answer.
Sazzad Hissain Khan
CC BY-SA 4.0
2020-09-28T13:26:53.447Z
Isn't the definition of 'our universe' simply all the stuff around us that obeys the same rules
Strawberry
CC BY-SA 4.0
2020-09-29T02:55:49.117Z
Your next to last comment is incorrect.  It is true that Newton's laws were an approximation to relativity, but we can measure and test relativity here on earth.  We do it all the time in particle accelerators and GPS satellites.  The only things we cannot test are those where we cannot create the proper conditions.  In this context, that is extreme density over a large region.  We have done it with gravitational redshift experiments and Gravity Probe B.
Ross Millikan
CC BY-SA 4.0
2020-09-29T18:03:00.980Z
The physics of today is inadequate to explain the inside a black hole.
MaxW
CC BY-SA 4.0
2020-09-29T22:13:13.250Z
@RossMillikan it seems a non sequitur. ‘but we can measure and test relativity here on earth’. I agree. My point was different. Just like Einstein refined the Newtonian laws considering velocity aspect, thus how can we be sure that some other laws can’t have scope to refine Einsteinian laws considering other aspect (which we don’t know)? Until then we are confidently using that laws to calculate other unknowns of the universe. I just raised question about such big confidence, nothing else. However, I agree, thats how science works. Heard of Occams razor for the first time and got more insight.
Sazzad Hissain Khan
CC BY-SA 4.0
2020-10-14T13:57:51.403Z
Which laws though? If a given set of laws is not universally applicable, then they aren't really laws, and we would seek a generalization that is universally applicable, which we would then call "the physical laws of the universe", like relativity generalized classical physics.
Museful
<astrophysics><universe><space-time><observable-universe>
How do scientists know that the distant parts of the universe obey the physical laws exactly as we observe around us?
Sazzad Hissain Khan
# How do scientists know that the distant parts of the universe obey the physical laws exactly as we observe around us?

(Asked by: username_0 on 2020-09-27)

**How do scientists know that distant parts of the universe obey the physical laws exactly as we observe around us?**

The question might look a bit odd but I am really stuck on my head. We know, scientists (with tools) explored physically only our solar system and some parts of our galaxy which is really a tiny part of the observable universe. And now they are constantly using these knowledge base along with 'tested physical laws' to measure the properties of distant parts of our universe.

For example, we tested and found the speed of the light is constant within our local periphery many times (within our Earth and Space around Earth). But yet we presume that the speed of the light is constant even at the farthest part of our universe. Certainly we did not test it in the other distant part of the universe because we have no way until now. Not only light but also the other physical properties like, luminosity, gravity, and etc related physical laws are agreed upon based on tests within our solar system. And based on these laws we deduced the properties of other parts of the universe (*i.e.* age, distance, mass, luminosity of stars in millions/billions light years away).

My question is, how do we know that these physical laws which we tested within a tiny area of the universe are consistently working in the distant parts of it? Is there any probability that the distant part of our universe obeys physical laws differently and our prediction based on applied physical laws gave us an unreal illusion of the actual reality, yet consistently?

**Tags:** astrophysics, universe, space-time, observable-universe
> **Comments:**
> **username_1**: 1/2 This is an important philosophy of science issue. The thing is, nothing prevents anyone from posing the hypothesis that physical laws are different in other parts of the universe. As you say, because we haven't been there yet, it's impossible to prove or disprove. Problem is, by posing this hypothesis we would give up all possibility of understanding what we see when observing there: if anything goes, there is no point in trying to make sense of the astronomical phenomenons we do observe.  
> **username_1**: 2/2 It has happened that observation of events far away led us to reconsider how things work here. For example, Newtonian physics worked on earth but could not explain the orbit of Mercury. Then the theory of relativity came and managed to explain how gravity works differently near the giganornous mass of the Sun, while still being consistent with what we observe on Earth and thus extended the Newtonian theory.  
> **username_0**: @armand my point is same. Just like we found Newtonian laws did not work outside our Earth periphery and we needed to update with Einsteinian laws. Now with same argument how we can be sure that Einstienian laws work in the whole Universe uniformly until we reach to the farthest part. Pretty much a deviation of Occams razor theory.  
> **username_2**: Note that if the laws of physics would be different from the known laws of physics far away but in such a way that the laws of physics change in an analytic way as a function of position, then this means that the laws of physics as they are valid right here would be different and knowing the correct laws of physics would allow us to describe the difference in the approximate laws of physics as observed here and in far away regions.  
> **username_1**: @Sazzad Hissain Khan: we can't be sure. But as long as we don't have a compelling reason to think the physics are different in other places, we have to work under the hypothesis that they are, otherwise its only speculation. Einstein could prove his theory by explaining with extreme precision observations that were impossible according to Newtonian physics. Young Earth creationists often posit that the speed of light decreased over time to explain how the universe can be 6000 years old while we can see stars millions of light years away, but they have no evidence that it is in fact the case.  
> **username_0**: @armand I agree with you. Young Earth creationists claim sounds absurd to me. From my empirical perspective I am just trying to understand the philosophical aspects of science especially in that concern. Anyway, thanks for your time. I think I got the answer.  
> **username_3**: Isn't the definition of 'our universe' simply all the stuff around us that obeys the same rules  
> **username_4**: Your next to last comment is incorrect.  It is true that Newton's laws were an approximation to relativity, but we can measure and test relativity here on earth.  We do it all the time in particle accelerators and GPS satellites.  The only things we cannot test are those where we cannot create the proper conditions.  In this context, that is extreme density over a large region.  We have done it with gravitational redshift experiments and Gravity Probe B.  
> **username_5**: The physics of today is inadequate to explain the inside a black hole.  
> **username_0**: @RossMillikan it seems a non sequitur. ‘but we can measure and test relativity here on earth’. I agree. My point was different. Just like Einstein refined the Newtonian laws considering velocity aspect, thus how can we be sure that some other laws can’t have scope to refine Einsteinian laws considering other aspect (which we don’t know)? Until then we are confidently using that laws to calculate other unknowns of the universe. I just raised question about such big confidence, nothing else. However, I agree, thats how science works. Heard of Occams razor for the first time and got more insight.  
> **username_6**: Which laws though? If a given set of laws is not universally applicable, then they aren't really laws, and we would seek a generalization that is universally applicable, which we would then call "the physical laws of the universe", like relativity generalized classical physics.  

---

## 3 answers

### Answer by username_15 on 2020-09-27. Score: 54 | Accepted answer

We don't know in general but to the extent we can measure, the laws seem to be the same, even if conditions are not.

For example radioactive decay: We know how fast various elements decay, and we can observe the results of radioactive decay in distant supernovae. The conclusion is that, for at least some elements, the rate of radioactive decay is the same on Earth as it is in distant supernovae.

After accounting for redshift, spectral emission lines remain unchanged by distance. This implies that the fine-structure constant is indeed constant.

Distant galaxies have gravitational fields, and interactions between galaxies proceeds in the same way in distant galaxies as it does in local ones. Eventually, the justification is philosophical: There is no observational reason to believe gravity behaves differently in distant parts of the universe, and so we believe that it does not,

In the extreme conditions of the early universe, some physical laws were different. For example, instead of distinct electromagnetic and weak fields, there was a single Electroweak field. But this can be described as single "law" with the electromagnetic and weak interactions being just the low energy approximation of the electroweak interaction.

So if it were discovered that Gravity (for example) was working differently in distant parts of the universe, but that there was a consistent pattern or rule for how it varied, then that would simply become the new theory of gravity (with general relativity becoming only the local approximation to this new law).

There is a more fundamental assumption: that the behaviour of matter and energy in the universe can be modelled by "laws". There are no angels dancing on pinheads. The justification for this is strictly in the realm of philosophy.

> **Comments:**
> **username_16**: After accounting for redshift, spectral emission lines remain unchanged by distance. This implies that the fine-structure constant is unchanged by distance: https://en.wikipedia.org/wiki/Fine_structure  
> **username_0**: Lets bring a hypothesis, a start at a very distant part of the universe which in reality emmits 500% more light compare to what we observed by our equations because the physical laws was different at the point it emits and hence the luminosity decreased. How can we disprove that hypothesis? @Stranger  
> **username_17**: @SazzadHissainKhan we don't have to disprove any and every hypothesis. A hypothesis which makes unusual claims needs means to positively verify its predictions. There simply is no way to disprove my hypothesis that in a far far part of the universe a planet exists where dragons rule and atoms weigh twice what they do here. Yet there simply is no indication that this hypothesis should be true as all we see seems to confirm that the universe behaves the same as here. Occams razor applies: the simplest solution is assumed in the absence of proof to the contrary  
> **username_18**: @planetmaker I have to voice the usual Humean skepticism. You seem to be saying that nature is uniform because we observe its uniformity. But observable uniformity only implies that that uniformity extends to the unobserved if we assume that nature is uniform. Because the logic is circular, we don't get to apply Occam's razor. Better to say that we take it on faith that nature is uniform. Or, if you've spent a lot of time reading Kant (not me!), you might say that the uniformity of nature is an inextricable feature of the thinkable world (as opposed to the physical world).  
> **username_0**: @planetmaker why it wouldn’t be a positive claim that the physical laws work uniformly at the distant part of the universe even without any single empirical evidence then? Also why don’t scientists apply the same arguments and confirm that the un observable universe has the same principle?  
> **username_19**: I think this ultimately comes down to Occam's Razor. We assume uniformity because it's simpler, and we haven't detected anything that contradicts it yet.  
> **username_17**: Science tries to find things which are not known, and thus also which contradict current theories. But as long as there is not proof to the contrary, the simplest solution is to be assumed. A theory never is reality but only a description of realiy - the simplest possible one. And if something unexplicable with current theory is found, we adjust theory to explain that fact, too - of course that may and will mean that the overall picture gets more complicated. But little point in making it more complicated than necessary to explain all observations  
> **username_20**: @SazzadHissainKhan "why don’t scientists apply the same arguments and confirm that the unobservable universe has the same principle" - how exactly do you propose to confirm anything about something unobservable?  
> **username_0**: @IMil look here the point is not about observability instead knowledge. If we can assume that the laws applicable for what we have no knowledge by the argument “simplest solution needs to be considered” then why we can’t apply same principle to something non observable (in other words, completely unknown)?  
> **username_21**: @SazzadHissainKhan: You can feel free to make any hypothesis you want. But what distinguishes a scientific hypothesis from a nonscientific one is that a scientific hypothesis is *disprovable*, meaning that you can in principle design an experiment based on observation of the physical which will distinguish between truth and falsity of the hypothesis. So as soon as you say "the point is not about observability", you have left the realm of science and entered, I dunno, the world of science fiction?  
> **username_0**: @LeeMosher, yes I agree scientific hypotheses require falsifiability. Now if you think deeply all current hypotheses on observable universe in reality makes falsifiability model which is dependent to totally unknown (as I already pointed out far reality is actually unknown in post). Then whats problem to make hypotheses on non observable universe? In fact many scientific hypotheses on non observable stuffs, i.e. multiverses etc. What are the distinction points? That question might not come if science could make local these laws as hypotheses for distant universe, but they described as theory.  
> **username_22**: @SazzadHissainKhan's comment seems a bit hard to understand; I will try to rewrite it as well as I can, so that this interesting discussion can continue. Here goes: // Yes, I agree that scientific theories need to be falsifiable. However, if you examine the current state of astrophysics in depth, you will see that even falsifiable theories that use data from the 'observable' universe [presumably to extrapolate to 'unobservable' regions] use models that depend on the unknown, since 'reality' is by definition not attainable. So how are hypotheses on the 'non-observable' universe different? ...  
> **username_22**: ... The last sentence is quite a poser, but I'll try anyway. // The question might not arise if physical models could be applied to the distant [i.e. 'non-observable'] universe; however, they are "described as theory" [perhaps he sees 'theory' as armchair guessing?].  
> **username_22**: Now my reply to @SazzadHissainKhan's comment. You seem to be mixing physics and philosophy here. Physics is concerned with facts that can, in principle, be verified by others. The notion of reality as a hidden 'true' or 'as is' world was postulated by Descartes, Kant and Hegel, but it never lost its metaphysical trait and graduated to a verifiable theory or even hypothesis. Your question is about physical laws. The  difference between falsifiable laws or hypotheses of physics and 'reality' (_really_ unknown) is moot. Be a little more humble. "We don't know; we only guess." (Raimund Popper)  
> **username_0**: @Timm first of all thanks a lot for translating my obscure comment into a sensible form which was exactly what I meant. Sorry for my bad nonnative language. I clearly understood your reply and I totally agree with you. I just tried to express the reason of this post as a reply to someone’s question. However, after reading the answers and comments its now clear to me. I also believe its humble to say ‘we don’t know’ instead of justification with vague arguments. Thanks you again.  
> **username_15**: Remarkably,  after this long comment thread,  it seems that we have returned to my actual answer.  Read the first three words of my answer!  

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### Answer by username_7 on 2020-09-27. Score: 8

See also: [Do the laws of physics work everywhere in the universe?](https://physics.stackexchange.com/questions/11614/do-the-laws-of-physics-work-everywhere-in-the-universe)

[Noether's theorem](https://en.wikipedia.org/wiki/Noether%27s_theorem), in the context of this question, states that:

> If the laws of physics do not vary with position, then linear momentum is conserved (and vice versa).

Therefore if we observe conservation of momentum (which we do with exquisite precision) then we do not expect the laws of physics to vary with position. In other words, distant parts of the universe obey the same physical laws.

> **Comments:**
> **username_8**: The way it is stated here, this is a non sequitur. "If A then B" does not imply "If B then A".  
> **username_7**: @GuntramBlohmsupportsMonica in formal logic, "If A then B" does not imply "if B then A", but [formal logic does not apply to physics](https://physics.stackexchange.com/questions/472785/does-the-principle-of-explosion-mean-we-can-prove-objects-must-fall-up-because).  
> **username_9**: @Allure The post you cited: "We don't expect physical theories to be true in any absolute sense of formal logic. We expect them to be good approximations under certain conditions." I find this quite confusing. Within a theory, formal logic has to apply - at least ideally -, just because it is a science. But the theories themselves do not claim to yield perfect descriptions of the entire would, just useful approximations within a certain context. And yes, out of this context, they may yield false statements about reality.  
> **username_10**: Related: https://physics.stackexchange.com/questions/24596/is-the-converse-of-noethers-first-theorem-true-every-conservation-law-has-a-sy  
> **username_11**: @Allure well the question remains. You are quoting something like "if A then B" and then saying "B implies A". On what basis are you telling "B implies A" ? The argument of Guntram is basically "you can't justify your assertion with formal logic" and you answer that formal logic doesn't work in this case, but then what kind of logic are you using to go from the first proposition to the second ? EDIT : I didn't see any justification on your affirmation about formal logic in the link provided  
> **username_7**: @Guiroux See the link by jpa.  
> **username_12**: Noether's theorem is a biimplication -- symmetry implies conserved quantity and conserved quantity implies symmetry.  You have only written half of the theorem.  
> **username_12**: @user253751 : Then LIGO ring-downs would be wildly different.  And exoplanets would be much harder to detect because their orbits would not be periodic.  And globular clusters would not be stable.  And Hubble shift would not be spherically symmetric and radially smoothly increasing.  And the population of type Ia supernovae would not be as uniform as it is.  And pulsar periods would not be stable.  And ... And ... And ...  We have literally millions of observations, any one of which could reject extra-solar conservation of momentum, and all have failed to do so.  
> **username_7**: @user253751 I don't understand. If rocket ships on Alpha Centauri don't need reaction mass, then the laws of physics would've changed, and we would've seen a violation of conservation of momentum (via experiments done on Earth).  
> **username_7**: @user253751 again, if the laws of physics are changing between here and Alpha Centauri (and they must be in your scenario, since it requires reaction mass on Earth and not there), then we would not observe conservation of momentum.  
> **username_13**: @Allure I'm not sure that's entirely true; certainly not obviously so. It seems reasonable to wager, from the non-expert's view, that Noether's theorem essentially implies that if you have translation invariance over a region of spacetime, then in some sub-region you will observe conservation of momentum to a high degree of certainty.  Similarly for approximately translation invariance.  So why are we sure we are not in a well-behaved bubble that prevents us from seeing conservation violations with present instruments? Perhaps that should be a question on physics, if not already.  
> **username_12**: @user253751 : A hypothesis of the form "something behaves differently from everything we have ever measured" requires extraordinary evidence.  Without such evidence the most *paranoid* scientific philosophy is to deny that such questions have answers -- rejecting your hypothesis on foundations.  A parsimonious scientific philosophy is to assume a "small" physics, expanded only when it disagrees with measurement -- rejecting your hypothesis.  To accept your hypothesis is to assume that the Universe is hostile to understanding, which denies utility of reason, so is definitionally unreasonable.  

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### Answer by username_14 on 2021-04-25. Score: 1

The measurements of all astronomical manifestation are currently the same in all directions of the sky, rather than variable by direction and distance.

The CMB temperature is nearly constant with with anisotropy which has been very well studied, there is a dipole variance which indicates that that we are moving at 370 km per second relative to the CMB, travelling with the Galaxy.

Physicists tried to find evidence that gives credence to your suggestions, but the CMB implies that the big bang was the same, 13 billion light years in every Direction.

The same atoms seem to be emitting the same wavelengths, the quasars are the same, the galaxies are the same locally, far away and with dipole variations, the star numbers and distributions are the same, the supernovae are the same. The laws of physics are the same, same hydrogen lines and same rotation speeds.

The visible universe is the invariant, although you can be right about 130 or 500 trillion light years away, there may be some variation in in an unobservable distance of the universe, only that it's beyond what we can see.


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