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So, let's say that somewere out past the Oort Cloud, physics just kind of... changes. For whatever reason. Maybe space is magic, or maybe we're just in a weird sort of localized physics bubble. The universe doesn't devolve into boiling plasma, but once you get out far enough, there's a noticeable shift in how things work.

Assuming that these changes don't affect something super obvious like gravity or visible light that we would have noticed during the first 2,000-somewhat years of human history, how do we prove that physics is noticeably different without sending a manned or unmanned probe out that far, and for bonus points, how do we figure out exactly where that physics/not-physics barrier lies?

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    $\begingroup$ This is an interesting question, but can you be a bit more specific as to what the changes are? Otherwise, this is very hard to answer. $\endgroup$ – HDE 226868 Mar 13 '17 at 23:43
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    $\begingroup$ What purpose are you aiming to fulfill by this proof? I wonder if this is maybe a case of the XY problem (meta.stackexchange.com/questions/66377/what-is-the-xy-problem). So, if we know what purpose you're trying to fulfill, we might be able to offer alternatives that are more tractable. $\endgroup$ – Ethan Kaminski Mar 14 '17 at 2:46
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    $\begingroup$ I'm confused here. The title seems to be asking "how do we prove physics is not different outside the solar system", and the body seems to be asking "how do we prove physics is different outside the solar system". Which one is it? $\endgroup$ – Tanner Swett Mar 14 '17 at 13:30
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    $\begingroup$ From a Worldbuilding perspective, Vernor Vinge's "Zones of thought" universe got the idea of a "local bubble" more right than most authors do. Read A Fire upon the Deep, if you haven't already. It made me forget Noether's theorem, at least until I finished the book! $\endgroup$ – nigel222 Mar 14 '17 at 16:06
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    $\begingroup$ I don't see how this question relates to worldbuilding. Can you make that explicit. $\endgroup$ – James K Mar 14 '17 at 19:53

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You do not. Period.

I am not joking. This is the kind of thing science simply does not touch.

Science is rooted in the world of empirical study. If you have a bubble where the laws of physics do not apply but appear to apply in every way shape or form, science simply will not detect this.

A similar experiment is the brain-in-a-jar thought experiment: if everything we know is part of a simulation, how can we find out if we are in a simulation? The answer from Science is "we cannot".

Now this limitation is one reason why science is fanatical about its measurement of the data it has. We measure the light from stars so precisely that we can detect that there is an expansionary tendency in space of $67 \frac{km/s}{Mpc}$. This corresponds to a factor of $0.000 000 000 000 000 002 17 \frac{m/s}{m}$, if we put it on human scales by changing the units. This factor would be completely and utterly undetectable locally. We only detect it because we can do amazing measurements on a universal scale.

This is also the source of the Cartesian Demon, the idea that there could be a malevolent demon who acts with the express purpose of leading you do incorrect assumptions about the world by manipulating your ability to observe the world around you. Descartes could not dispel this demon with science or even empiricism in general. He relied on religion to do so.

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    $\begingroup$ This. Descartes' Meditations is an excellent introduction to how we can ever observe the world and understand it (through science, of course). You might want to consider giving the Cartesian Demon more emphasis here. $\endgroup$ – HDE 226868 Mar 13 '17 at 23:53
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    $\begingroup$ This is not the case. The "laws" of physics are descriptive, not prescriptive. IOW, they are our best attempt to describe how the universe actually works, but the universe is not bound by them. For instance, our ideas of what the laws of physics were underwent radical changes when we started to look at things that are very small (quantum mechanics) or going really fast (relativity). There have been suggestions that the laws may have been different in the beginning, too. So if we do find that physics changes outside our "bubble", then it does :-) $\endgroup$ – jamesqf Mar 14 '17 at 4:23
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    $\begingroup$ @jamesqf: The OP specifies 'without sending a ... probe out that far.', so we simply won't be able to detect the changes and our descriptions will remain as they have always been, unless we can find evidence of the bubble's existence, in which case the laws of physics outside the bubble and inside the bubble can be assumed to still be linked together in a way that is measurable, in which case they're still our laws of physics and we've already measured them and probably tried to wrap weird descriptions like 'dark energy' around them in order to try explain the fundamentally unexplainable. $\endgroup$ – Joe Bloggs Mar 14 '17 at 7:55
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    $\begingroup$ @Nit I thought about using 1/s. It definitely is the simplest unit. I chose not to because Hubble's constant is a measurement of a change in velocity over a distance and when strapping a bunch of zeros to it to argue how ridiculously uninutitively small it is it felt awkward to lose that intuitive connection. That being said, I intended to write it as (m/s)/m not m/(s*m). That was an oversight during an edit converting to mathjax. I've edited it to correct that mistake. Thanks for drawing my attention to it! $\endgroup$ – Cort Ammon - Reinstate Monica Mar 14 '17 at 14:29
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    $\begingroup$ Re "brain in a jar" - what if the "brain" itself is a simulation? How do you tell if your entire being is a simulation in a simulated universe? Again you can't, but I'm just making the point that people get hung up on the brain still being real. Frankly, I think it's much more likely that the brain is a simulation too, because it would be far harder to wire up a brain to artificial input than it would be to just simulate the brain. $\endgroup$ – Bohemian Mar 15 '17 at 15:19
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Occam's Razor applies here. "Among competing hypotheses, the one with the fewest assumptions should be selected"

Until we get out there and have a look we just don't know what lies beyond our bubble.

But does a universe where there are different laws of physics in different solar systems require fewer assumptions than a consistent set of laws across the whole thing? I don't think it can.

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    $\begingroup$ No, Occan's Razor does not apply here. The OP explicitely asks how we would (dis)prove a hypothetical bubble. He does not ask "do we live in a bubble". O.R. would be the philosophically correct answer to the latter; for the first, a technical answer is proper, I feel. $\endgroup$ – AnoE Mar 14 '17 at 16:19
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    $\begingroup$ +1 Science cannot really prove this so philosophy is all we have. I think Newton's flaming laser sword may also apply, because we can't really test the whole universe (it's infinite) so we cannot know whether these bubbles exist $\endgroup$ – Melkor Mar 14 '17 at 22:41
  • $\begingroup$ Well, philosophy has more to offer than just Occam's razor (which would make a lousy academic department). $\endgroup$ – MissMonicaE Mar 15 '17 at 19:31
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You are trying to prove a negative. It's like proving their is no Santa Claus or Tooth Fairy. You can prove he isn't here, or there, or in Trump's bedroom but it leaves the rest of the universe open.

Several sf stories are based on the idea that physics is different in the presence of a gravitational field stronger than X. E.g. Any story that requires some distance from the star to enter hyperspace. A few are explicit, one postulated that the negative results of the Michelson-Morley experiment was due to the experiment being done too deep in a gravitational well.

Another had a crashed spaceship on Earth that still had a running drive. The drive 'froze' the ether locally. Aliens watched from a distance with amazement at the development of relativity.

An effect that was gravitationally threshold dependent would be very difficult to detect. A huge fraction of the radiating mass of the universe is in gravitational wells. If the effect was subtle it might not be apparent from the relatively diffuse radiation from gas clouds.

Some jumping off points for speculation:

  • The missing mass issue: We can measure the rotation rate of galaxies by doppler shifts of different sides, and by measuring the orbital velocity of halo clusters around them. We can add up the mass of the stars. We come up short. By a huge fraction. Currently we have dark matter and dark energy as stand-ins but the properties are vague.

  • The topology issue. Is space singly or multiply connected? Just read a paper (ok, browsed the abstract and got very confused) analyzing the cosmic background radiation. Universe may be a multiply connected hyper dodecahedron. Do a web search for topology and cosmology if you wish to share my confusion.

For world builders, consider the possibility that in addition to cosmic multi-connectedness, there are local multiple connections. SF examples: The wormhole junctions in the Honorverse; in Startrek DS9, in Bujold's Vor universe. the Alderson Tramlines in Pournelle's Co-dominium universe

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  • $\begingroup$ No I think they mean like the concept of gravity itself no longer exists outside this bubble. So like... if you go out past this bubble everything collapses into a 2d universe and you can access an infinite number of them by moving in and out of our universe. That's a weird example, but an example nonetheless. $\endgroup$ – The Great Duck Mar 15 '17 at 8:17
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    $\begingroup$ Yeah, but he had a tag of 'reality check' so I figured the answer had to have at least some rivets. $\endgroup$ – Sherwood Botsford Mar 15 '17 at 13:38
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    $\begingroup$ What sf story is about crashed spaceship? $\endgroup$ – BЈовић Mar 15 '17 at 16:25
  • $\begingroup$ I second that, I want to read that story. $\endgroup$ – Azor Ahai Mar 15 '17 at 17:41
  • $\begingroup$ @SherwoodBotsford I think the reality check was to say what realistic means feasible in our world can be used to determine that physics devolves into pure entropy at 100 ly out. $\endgroup$ – The Great Duck Mar 15 '17 at 18:23
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There are in fact real studies to try and determine if the laws of physics have changed over time, where far away things would show the difference compared to closer things.

For example the fine structure constant

The first experimenters to test whether the fine-structure constant might actually vary examined the spectral lines of distant astronomical objects and the products of radioactive decay in the Oklo natural nuclear fission reactor. Their findings were consistent with no variation in the fine-structure constant between these two vastly separated locations and times.

Improved technology at the dawn of the 21st century made it possible to probe the value of α at much larger distances and to a much greater accuracy. …

Light and the atoms it interacted with 10 to 12 billion light years away (as they appear — they are farther now) operate by the same laws of physics. Absorption spectra and emission spectra are fingerprints of basically all of quantum mechanics and special relativity.

Totally different physics would not show this effect. Very slight differences in fundamental constants would show different detailed spectra.

Meanwhile, stars work. By a great coincedence,

Ordinarily, the probability of the triple alpha process is extremely small. However, the beryllium-8 ground state has almost exactly the energy of two alpha particles. In the second step, 8Be + 4He has almost exactly the energy of an excited state of 12C. This "resonance" greatly increases the probability that an incoming alpha particle will combine with beryllium-8 to form carbon. The existence of this resonance was predicted by Fred Hoyle before its actual observation, based on the physical necessity for it to exist, in order for carbon to be formed in stars. The prediction and then discovery of this energy resonance and process gave very significant support to Hoyle's hypothesis of stellar nucleosynthesis, which posited that all chemical elements had originally been formed from hydrogen, the true primordial substance.

We see the spectra of carbon in far-away parts of the universe. So not only does the atom “work” the same in terms of electron orbitals, but the neuclear energy levels (due to the strong force) must be the same, as well.

In short, everything fits together so observations with high precision checks everything; and it’s all the same as far as we can see.

Now as you go back in time closer to the Big Bang, things do behave differently. But we can chalk that up to heat and pressure, the conditions rather than a fiat change. So the same thing happens under extreme conditions, even today.

More generally, look at inflation: a sudden difference in the rules are not attributed to changing the rules, but a change in state.

And that’s how any future discovery will be modeled: the rules don’t change — they are globally true for all time and space. Rather, there is a larger set of rules and different ones are applicable in different conditions. Even if you have to postulate a previously unknown field just to have a “thing” whose state can vary.

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  • $\begingroup$ To be fair, we can only check back to the first stars, and in some respects to the cosmic microwave background. If things have changed with time, it's most likely that the strangeness manifested itself during the first century, or day, or millisecond, or much shorter interval, after the universe started. $\endgroup$ – nigel222 Mar 14 '17 at 15:57
  • $\begingroup$ @nigel222 There’s Big Bang nucleosynthesis which is quite sensitive. Different physics during the first few moments can simply be chalked up to temperature and pressure — we would suppose that the same thing would happen under similar conditions. $\endgroup$ – JDługosz Mar 14 '17 at 23:11
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How do we prove that there is no porcelain teapot orbiting the Sun?

If the science that we have tells us that there is no reason to believe that we live in a bubble, and, more strictly speaking, there is no scientific theory of such bubble, then we must assume that there is no bubble. Otherwise we can not be sure that there is no monster in our closet until we turn on the light and check out the closet.

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  • $\begingroup$ The lack of a "no monster in the closet" assumption is really pretty reasonable, especially considering that the monster could always just turn invisible whenever you look. $\endgroup$ – Devsman Mar 14 '17 at 21:43
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    $\begingroup$ Also, the test you have designed only proves that there is no monster in that one particular closet at that one particular time. It does not prove that there are no monsters, nor does it disprove their preference for hiding in closets. $\endgroup$ – Henry Taylor Mar 15 '17 at 0:48
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We would observe differences. At the moment is an axiom of modern physics that the laws are the same everywhere. When we observe differences between the physics outside the solar system and locally, we come up with other models which might work over both scales, but there is no local evidence for these models.

For example, the rotation of galaxies is different to what the laws of physics as empirically measured on Earth would be. One way of compensating for that is to introduce dark matter, another is to add another term to the inverse square law that is too small to notice on local scales. As either model does not have any effect on local scales, there is no way to prove them empirically.

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  • $\begingroup$ Well, dark matter could be proven empirically by finding a dark matter particle, which we are working on. But until then... $\endgroup$ – Graipher Mar 14 '17 at 15:11
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    $\begingroup$ "The laws are the same everywhere" is not an axiom. It's a working hypothesis, and the simplest (so generally accepted via "Occam's razor"). Also, a violation of this principle would have local consequences, via Noether's theorem. Either conservation of momentum would have to be abandoned, or Lagrangian analysis would not apply to the real universe. Two other pairs: conservation of energy and time-invariant laws, conservation of angular momentum and rotation-invariant laws. $\endgroup$ – nigel222 Mar 14 '17 at 15:52
  • $\begingroup$ @nigel222 I thought Noether's theorem required symmetry, so requires the assumption. $\endgroup$ – Pete Kirkham Mar 14 '17 at 16:09
  • $\begingroup$ Oh, and if the Em-drive is found to actually work.... $\endgroup$ – nigel222 Mar 14 '17 at 16:11
  • $\begingroup$ Yes, it's wrong to say that conservation of momentum is the only possible casualty of laws that are not spatially invariant. But something would have to give, and it's tricky to envisage such a change that would not have any locally testable consequences. $\endgroup$ – nigel222 Mar 14 '17 at 16:15
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In order to prove it you'd need to rationally construct the world from necessarily true first principles in a logically valid manner. This means something like deducing you exist from the fact that you perceive (Descartes "I think therefore I am") and moving from there on into other things. According to some rationalist philosophers you would at some point have encompassed everything.

A particularly salient example of this would be to allow Liebnitz's theodicy that this is the best of all possible worlds. Assuming one could prove the existence of Liebnitz's idea of God, one could then logically deduce from ethical principles the exact nature of reality except for those parts of reality with multiple equally good possibilities. Assuming that the physics bubble could be shown to be a logical necessity of this necessary being's necessary plan, its existence would be proven.

If inferior proofs like abundant empirical evidence and such suffice, you could also use any accepted sufficiently binding metalogical form of reason within the confines of your world. This would make the question unreasonably broad, however.

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Several others pointed out problems with the scenario you've presented. Some have thought your scenario sounded a bit like radical skepticism, ala Descartes's demon. Presumably, those folks were imagining that the rest of the universe looks as if the laws of physics continue to apply, but, per the scenario in the OP, perhaps they do not. This sounds a bit like the Boltzmann brain scenario; if you're not familiar, check out Sean Carroll's recent "Why Boltzmann Brains Are Bad" or his pop-level book From Eternity to Here. Others have pointed out that we can make measurements of objects beyond the solar system and that, to the best of our measurements, the laws of physics continue to hold beyond the solar system. Fair enough.

I'm going to take a different tact. It's long been noticed that the galactic rotation curves -- i.e. the velocities of objects as a function of their distance from the center of galaxies -- goes towards a constant for large distances. That's not expected on standard accounts of gravity, given all of the mass we can observe. The standard response is to say that there is more mass than we can observe -- this is one way physicists infer the existence of dark matter. But notice that we could propose a different hypothesis. Perhaps, instead of invoking dark matter, at very large distances, we need to modify the standard equations for gravity. This leads to a view called Modified Newtonian Dynamics (or MOND) in which, at large distances, gravitational physics changes.

What might be of particular interest to you are the so-called "Pioneer Anomalies". There are two objects that have effectively left the solar system -- Pioneer 10 and 11 -- and both exhibited unexpected motions after passing approximately 20 AU (or 2,000,000,000 miles). For some time, physicists thought the Pioneer Anomalies could be due to new physics, as with MOND or other speculative theories. Later, the anomalies were explained by an anisotropic radiation pressure caused by the spacecraft's heat loss -- in other words, not by new physics. But this provides a real world example of what you might have in mind -- new physics might be detected when we leave our solar system, perhaps physics our present day observations only hint at (as with the galactic rotation curves). What this would require is that the effects are consistent with all of our present astronomical observations, but significant enough so that, once one leaves the Sun's gravitational well, one would begin to see something surprising!

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Based on what you ruled out, I'd say:

Space wouldn't be there at all, you can't hide something like that.

I'm in now way an expert, so I might be totally wrong, but:

We know of 4 (might consider them 3) fundamental forces.

  1. Gravitation
  2. Strong nuclear force
  3. Weak nuclear force
  4. Electromagnetism

These forces are what, as far as we know, build up everything around us. You said you wouldn't want to change Gravitation and Light (which essentially means Weak nuclear force & electromagnetism, as I understand it).

This leaves you with the Strong nuclear force that you can change. You can go and read what this force is all about, but essentially it boils down to "keeping everything together", without it particles wouldn't form atoms, and without atoms...well you get the point.

I'm not sure what would happen if you change that force slightly, it might be possible to form atoms that aren't so densely packed? So everything would essentially become bigger, but probably also rather unstable? Even then though, science would have probably noticed.

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    $\begingroup$ We're a lot less sure that we understand Gravitation, and the "dark matter" and "dark energy" needed to make our most widely accepted theory of Gravitation compatible with all observations. However, it is very hard to invent changes to accepted theory which don't immediately imply that the universe as we know it, cannot exist. $\endgroup$ – nigel222 Mar 14 '17 at 16:02
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There are two possible scenarios here, either this happens because somebody is messing with us, or it happens from sort of natural causes.

Somebody messing with us.

We cannot disprove this, period.

Somebody could have set up a computer screen around the solar system showing natural looking stars and galaxies that doesn't really exist. Beyond this screen anything could be happening. Maybe it is a science experiment. Maybe it is a child's toy.

We cannot disprove this in any way. The hypothetical experimenters can fake anything.

Natural causes

This seems unlikely.

We can look at distribution of stars and galaxies and it looks similar in all places we can see. This means gravity probably works the same everywhere.

We can measure the inner lives of stars far away, and the matter there seem to follow the same rules as matter in our laboratories.

This means that the other laws of physics probably work the same here and there.

It is possible to set up some contrived scenario where the laws change in a very coordinated way so that the measurements all come out the same.

But this would be very unlikely... unless somebody is messing with us.

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    $\begingroup$ Hello and welcome to WorldBuilding.SE! Interesting first answer. It's very clear and I like the length of the answer. It looks similar to the answer from Cort Ammon. Could you edit your answer with the little edit button at the end of the text to provide more information about why your scenario is different from the Cartesian Demon Cort mentions? If you got questions please take the tour and visit the help center. Looking forward to your contributions. Have fun! $\endgroup$ – Sec SE - clear Monica's name Mar 14 '17 at 9:41
  • $\begingroup$ A screen set up around the solar system would be fairly easy to detect. Prior to probes being sent out from the Earth you might be able to argue that the images were constantly updated to fake interstellar distances measured through parallax. However, now that we have eyes scattered across the solar system, such tweaks would be noticeable. Your point that being unable to disprove the existence of omnipotent experimenters is valid though. $\endgroup$ – Michael Richardson Mar 14 '17 at 14:33
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One way would be to see if our theories were wrong. Currently we are unsure exactly what is going on with dark matter and dark energy. We have observed their effects but don't know much else about them. They could hypothetically be due to unknown physics not available in our neighborhood.

In reality this is not particularly likely they may at most be due to hitherto unknown physics but if an idea could be presented that explained them and shown that for example they can be observed from afar but not recreated here then you are starting to build a case.

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Science is about observing, forming ideas what the rules behind the observations are, and coming up with experiments to prove those ideas either right or wrong. (I simplify, but the general idea is about right)

Trying to prove that you are wrong is a very good and valid attempt of proving that you are right. If neither you nor any of your peers can prove you are wrong, it is fairly safe to assume that you might be right. Or right enough for the time being, which is just as well.

So, if you want to prove that you are not inside of your bubble, you can either formulate your ideas how it might be proven that things don't change, or you try to figure out how it might be proven that there are aspects of phsics that do change once you pass your hypothetical boundary.
Of course you discuss your ideas with your peers first, lest you overlooked something important.

Then, when you feel reasonably certain that your idea is viable, you try to come up with (preferrably absurdly expensive) experiments to prove either of your ideas. From the results, you rinse and repeat until you reach a point where there are no more obvious flaws in your idea and/or your experiment.

That would then be the point where you might want to read up on the sights woth seeing in Stockholm, because my crystal ball foresees a voyage there, and you meeting some interesting strangers.

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I'd counter that the observable universe IS our localized physics bubble. If we look deep enough, we hit this wall that is the Cosmic Microwave Background. This is the 'outer limits' of our universe, and represents the time in which the universe was formed. At that time, 'physics' was not 'the same' as it is now. 'Time' itself did not exist as a unique dimension at the beginning of the universe, and the fundamental forces were all merged together. Electromagnetism and Weak Nuclear force were together as the Electroweak, etc.

This is all theoretical, however. We can't really test or prove any of it, because we can't replicate those conditions in the first place.

Similarly, black holes are postulated to 'break' some of the older, basic laws of physics. These would be a practical example of a case where you would be accurate to assert that there are areas of the universe where physics as we understand it does not apply.

But 'physics as we understand it' is the key phrase in all of this. Our physics is far from perfect. The physical universe, as it currently exists, is 'perfect' as far as we can tell, in that there is a coherent set of laws that seem to be guiding everything within it, totally and indiscriminately.

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    $\begingroup$ Welcome to Worldbuilding! While some of the points you raise are good, the question is talking about physics outside of the Oort cloud being different, which is on a scale orders of magnitude smaller than the observable universe, so would you be able to edit your answer to explain localised bubbles on a much smaller scale? Thanks. In addition, I'm also slightly confused about what you mean when you say 'breaking the older laws of physics' and 'physics not being the same' - are you talking about classical physics or just saying that we don't understand all physics? $\endgroup$ – Mithrandir24601 Mar 14 '17 at 21:36
  • $\begingroup$ Thanks happy to be here. In regard to your questions, the CMB is in fact beyond, or outside of, the Oort cloud, and so the condition is met. Does it have to be only a little beyond the Oort cloud? Not 'all the way' so to speak? If so, see the next part about Black Holes, which appear to break the laws of Einsteins Classical Physics at the event horizon. When I said 'physics is not the same' in the first para of my answer, it was a segway into explaining some relevant differences (time not being an independent dimension, electroweak instead of electromagnetism and weak nuclear force). $\endgroup$ – Bango Mar 14 '17 at 21:54
  • $\begingroup$ I see what this answer is hinting at, but the metaphors are mixed up. Black holes don't "break" physics. Rather they're a very special case of the same physics we use and apply every day here on Earth. They can even be predicted (though not fully understood) using nothing but Newtonian physics. If we got enough mass together a black hole could form right next door to Earth. As for the very, very early universe, it's not that the rules are different, but that our model of the universe (ie. physics) has assumptions built into it that are no longer valid; we know our model is wrong there. $\endgroup$ – Schwern Mar 15 '17 at 20:39
  • $\begingroup$ I incorrectly said Classical Physics break down at the event horizon. Rather, the singularity is said to have no volume and infinite mass, which does in fact defy physics as we knew it at one time. But we saw there was a problem, which we eventually resolved with quantum physics, which allowed black holes to have a finite mass (since some black holes are obviously more massive and powerful than others). It goes along with the last part of my answer, that, at any point in our timeframe, physics as we knew, or know it was (is) not perfect, and so to defy physics is to not understand physics. $\endgroup$ – Bango Mar 15 '17 at 20:51
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Observe the stars.

For example, if you could observe a binary star system through a telescope, and watch the motion of the stars as they interact with eachother via gravity, and if that interaction matches your own model of gravity then you can conclude with a high degree of confidence that gravity was acting the same in that location.

The light emits from plasma forms narrow bands when separated by a prism. In general the type of element can usually be identified by the observed light spectrum. For instance we assume our sun consists of hydrogen and helium because the light it emits matches the spectrum emitted by hydrogen and helium. If you look at a star and the light coming from it looks like the light coming from locally generated plasma then you can conclude that the processes that generated that light are probably similar. Since the process which generates that light is highly dependent on the way that subatomic particles interact with each-other, one could conclude that those particles generating the observed light behave very similar to the ones here.

Of course all of our observations could be an illusion. The odds would be pretty low of having an illusion that so closely matches the rest of reality by pure chance. More likely would be a deliberate illusion.

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  • $\begingroup$ The OP excluded "super obvious" things like light and gravity... $\endgroup$ – AnoE Mar 14 '17 at 16:14
  • $\begingroup$ @AnoE I don't think we should exclude gravity and light as the OP suggests. All physical processes are ultimately described by the four fundamental forces (Electromagnetic, gravitational, weak nuclear, strong nuclear), and quantum mechanics. If you can prove those then you prove the rest of physics. Between gravity and light you can prove almost all of it. $\endgroup$ – user4574 Mar 14 '17 at 18:33
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    $\begingroup$ I'm not arguing; I have the impression that the question, as posed, renders itself unanswerable by its internal logic ("can we detect X by any means except by dectecting X"). Just saying - your answer has as its main point exactly that which was ruled out. $\endgroup$ – AnoE Mar 14 '17 at 21:38
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Wait for an interstellar meteor or comet to arrive, and examine it. The meteor would serve as a sample of what the rest of the universe was made of.

Does the meteor contains elements or isotopes that don't normally exist here? If the types of elements are similar then one could conclude that they may have been created by physical processes similar to those here (for example the fusion process in stars).

Examine the molecular structure. Are the elements arranged in ways that don't normally occur here? Typically the compounds that form are those that are most favorable thermodynamically under some specified conditions. If we see moleculecular structures that normally wouldn't form here then we could conclude either that the surrounding conditions were very different when it was created, or that it was obeying different physical laws during its creation.

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  • $\begingroup$ This doesn't add anything to the conversation. It's very vague. For example, why would examining a comet help understanding a difference in physics beyond our Oort Cloud $\endgroup$ – Paul TIKI Mar 14 '17 at 19:14
  • $\begingroup$ Done that. Nothing bizzare about the atoms or their formation. Also see presolar grains. $\endgroup$ – JDługosz Mar 15 '17 at 22:41
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Dark energy has come up a number of times, and it's a good case study to show that we have looked out into the universe many times and found things that don't obey our current model of the universe. Rather than deciding that our physics is a special case, we revise our model of the universe ever finer and come up with physics that fits both what we observe locally and at a cosmic scale. That we can successfully make predictions with this ever refined model very strongly suggests that physics is the same everywhere.


Back in the 19th century evidence was mounting that the Earth was billions of years old. This presented many problems, not the least of which was how did the Sun manage to shine that long? No known fuel source at the time could sustain such a fire for billions of years. Even nuclear fission couldn't explain it.

The debate raged back and forth, and evidence mounted that yes, the Earth was billions of years old, so something is wrong with our understanding of the Sun. Eventually nuclear fusion was discovered and that resolved the paradox.


Fast forward to the 21st century and we have new problem with gravity at a galactic scale. We're observing that galaxies are accelerating away from each other rather than slowing down as we'd expect. We've given this accelerating force a name, "dark energy", even though we know very, very little about it.

Again, evidence is mounting that this is real. And, again, it's likely not that our local physics is different, but that dark energy is so weak it only has an effect on a galactic scale. Much like how gravity is so weak you don't notice its force until you get a few trillion kilograms of matter together; there's so many stronger forces interfering with your observations.

The density of dark energy is estimated to be roughly 7e−30 g/cm3. That's roughly the same as matter, but unlike matter which clumps up in galaxies, it is evenly distributed across the universe. And, unlike matter, it only interacts via gravity. Physics (probably definitely) works the same everywhere, but we have to look out into space (and back in time) to get observations on the necessary scale.

The other option, that our understanding of gravity is wrong, so far doesn't work. All of the alternative theories of gravity people have tried to explain dark energy fail to match other observations. Like trying to fit a wrong sized carpet into a room, fit one corner and the other pops out.

We could say "well I guess physics is just different in all those other places", but exceptions like that result in inelegant messes that, and this is very important, offer no predictive power. It's not just that it's inelegant, but it also results in a model of the universe that is less useful. Physicists measure how good their model of the universe is by how well it matches existing observations, but also how well it predicts future observations. "Gravity just works different around Somewheretarius 5" doesn't tell us anything about the rest of space, whereas dark energy as a cosmological constant neatly explains and predicts across the whole universe.


Another reason to believe that we're not in a local physics bubble is so many of our predictions about the universe at very large scales come out correct. This is the heart of science: come up with a theory about how the world works, make some predictions based on it, see if they turn out correct. If they do, your theory is strengthened! If they don't, back to the drawing board.

The two biggest examples in recent memory are the Cosmic Microwave Background (CMB) and Gravitational Waves. Both rely heavily on the assumption that physics is homogeneous across the entire universe.

A prediction was made both about what the CMB would look like, and what gravitational waves the merger of two black holes would make. WMAP's observations of the CMB and LIGO's observation of a black hole merger match those predictions extremely closely.

These results mean our physics is correct at the scale of the entire history of the universe and even for crazy things like black holes. We don't have to pepper our physical laws with exceptions and special cases, instead we refine them ever more, all from our little ball of mud.

The WMAP result is so spectacular that xkcd crowed "Science. It works, bitches." with a graph of the predicted and observed CMB black body radiation.

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I'm not sure you could "prove" that the solar system isn't inside of a localized physics bubble--that seems outside the realm of science. However, you could come up with some pretty creative ways to come closer to an answer.

For example, suppose that you engaged in a massive propaganda campaign, convincing everyone on earth that you'd discovered a method for testing the laws of physics outside the solar system, then claimed that you would proceed to do the testing in one month's time. Then, suppose you set up a prediction market for each of the "tested" laws of physics. Under this essentially economic framework, you'd be able to find humanity's absolute best prior probability for whether individual laws of physics hold outside the solar system. Then just announce it was a giant prank--there is no such method for testing the laws of physics--and record the prices of each of the futures in each prediction market.

Would this work? Probably not. It assumes that prediction markets are perfect information aggregators, and that somehow the people most informed about the laws of physics buy into your propaganda campaign without reformulating their understanding of the laws of physics in light of the knowledge that you can somehow test the laws of physics at extreme distances; this miiiiight pose a teeny problem. But at least its an interesting idea.

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