# 100% certain physical laws are same in other galaxies? **URL:** \ **Category:** Factual Questions\ **Created:** [October 13, 2014, 7:12pm UTC](https://boards.straightdope.com/t/100-certain-physical-laws-are-same-in-other-galaxies/701230 "2014-10-13T19:12:23Z")\ **Posts on this page:** 10\ **Page:** 2
**Author:** ![Robert163](https://avatars.discourse-cdn.com/v4/letter/r/4af34b/32.png) [@Robert163](https://boards.straightdope.com/u/Robert163)\ **Post date:** [October 14, 2014, 2:43pm UTC](https://boards.straightdope.com/t/100-certain-physical-laws-are-same-in-other-galaxies/701230/21 "2014-10-14T14:43:32Z")
> [@Wendell\_Wagner](#): > > Robert163, does what we’re saying make any sense at all to you? I’m afraid that this thread is going to turn into another one where we get into endless details that are incomprehensible to the person who asked the question. Let’s get back to finding out if what we’re saying here makes sense to you. Well, I was under the assumption that the laws were consistent. But I must admit that the explanation for Dark Matter being a slight change in gravity and speed of light of very long distances is intriguing. ---
**Author:** ![Grrr](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/grrr/32/146_2.png) [@Grrr](https://boards.straightdope.com/u/Grrr)\ **Post date:** [October 14, 2014, 2:43pm UTC](https://boards.straightdope.com/t/100-certain-physical-laws-are-same-in-other-galaxies/701230/22 "2014-10-14T14:43:52Z")
> [@naita](#): > > How is that relevant to the OP or what you posted earlier? First I’m not trying to debate you, I’m just trying to fight my own ignorance. I was under the impression that the four basic forces are a big part of what governs the laws of physics. Is that false? ---
**Author:** ![Hail\_Ants](https://avatars.discourse-cdn.com/v4/letter/h/dc4da7/32.png) [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)\ **Post date:** [October 14, 2014, 2:48pm UTC](https://boards.straightdope.com/t/100-certain-physical-laws-are-same-in-other-galaxies/701230/23 "2014-10-14T14:48:53Z")
Simple answer: Because our Milky Way galaxy is not, repeat, is \*\*NOT \*\*the universe. Hasn’t been since [The Great Debate](http://en.wikipedia.org/wiki/Great_Debate_(astronomy)) in the 1920s. And, _Star Trek_ aside, there is no evidence of any ‘galactic barrier’ outside of which the universe would be any different. It’s the same as asking are we sure gravity obeys the same laws (proportionately of course) on Pluto as it does on Earth. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 14, 2014, 3:39pm UTC](https://boards.straightdope.com/t/100-certain-physical-laws-are-same-in-other-galaxies/701230/24 "2014-10-14T15:39:43Z")
> [@](#): > > Quoth **Robert163** : > > Well, I was under the assumption that the laws were consistent. But I must admit that the explanation for Dark Matter being a slight change in gravity and speed of light of very long distances is intriguing. If Modified Newtonian Dynamics (the model that explains “dark matter” as actually being a slight change to how gravity works) is true, then the laws of physics are still consistent; they’re just slightly different laws than what we thought they were. In fact, the one and only point of evidence in favor of MOND is that the key new parameter in the model appears to be the same for all galaxies. Oh, and we actually know less about the dynamics of our own galaxy than others, not more. It’s a lot harder to measure some of these things by looking from the inside than from the outside. ---
**Author:** ![Robert163](https://avatars.discourse-cdn.com/v4/letter/r/4af34b/32.png) [@Robert163](https://boards.straightdope.com/u/Robert163)\ **Post date:** [October 14, 2014, 3:58pm UTC](https://boards.straightdope.com/t/100-certain-physical-laws-are-same-in-other-galaxies/701230/25 "2014-10-14T15:58:38Z")
> [@Chronos](#): > > In fact, the one and only point of evidence in favor of MOND is that the key new parameter in the model appears to be the same for all galaxies. interesting ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [October 14, 2014, 5:19pm UTC](https://boards.straightdope.com/t/100-certain-physical-laws-are-same-in-other-galaxies/701230/26 "2014-10-14T17:19:42Z")
> [@Shakes](#): > > First I’m not trying to debate you, I’m just trying to fight my own ignorance. > I was under the impression that the four basic forces are a big part of what governs the laws of physics. Is that false? In that case the answer is that the unifications of the forces might have been part of the very start of the Big Bang, but that the [Grand Unified Theories](http://en.wikipedia.org/wiki/Grand_Unified_Theory) (which are only hypotheses so far) that deal with this are way above my physics pay grade. ---
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [October 15, 2014, 4:02am UTC](https://boards.straightdope.com/t/100-certain-physical-laws-are-same-in-other-galaxies/701230/27 "2014-10-15T04:02:26Z")
Here’s my take on this, and I have no illusions of it being rational: Our universe is both object-centric and action-centric. A rock must first exist, in order for forces to act on it. And the rock, itself, is the result of actions. So I pick up a rock and drop it, here on earth, and it falls to the ground. I then travel to Galaxy XYZ, pick up an identical rock and drop it . . . and it bursts into fireworks and sings the Star Spangled Banner . . . it’s not because of different physical laws, it’s because different forced are acting on it, and different forces created it. My own short-sightedness identified it as identical to the Earth-rock, only because I was ignoring its context. If the two rocks in fact are identical, with identical contexts, it would be impossible for them to act differently. It is the nature of rocks to obey the laws of physics . . . like everything else. The issue of dark matter: If it in fact exists, and if it makes things act strangely . . . we only think they are acting strangely, following different physical laws, because we don’t have dark matter here. If we did, we’d see that even dark matter follows the same laws as everything else. I think this issue belongs in the discipline of Philosophy, rather than the science of Physics. ---
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [October 15, 2014, 4:53am UTC](https://boards.straightdope.com/t/100-certain-physical-laws-are-same-in-other-galaxies/701230/28 "2014-10-15T04:53:28Z")
Here’s the central issue of dark matter. The normal matter we’re familiar with is affected by radiation. Most of it emits radiation but the rest of it absorbs, reflects, and re-emits radiation. So you can study the radiation coming from a place and get a pretty good idea how much matter is present in that location. Another way to detect matter is to look for its gravitational effect. All matter affects the movement of matter through gravity. The more mass matter has, the greater its gravitational effect. So astronomers can look at distant galaxies and get an idea of how much matter there is in them by measuring the radiation they emit and the gravitational effect they have on other galaxies. Ideally, these two measurements would give you the same answer. Unfortunately, they don’t. For some reason, the amount of gravitational effect that’s observed would indicate distant galaxies have about five times as much matter as the radiation they produce would account for. So this is where the possibility of dark matter steps in. It’s a hypothesis that there is a form of matter that has mass but is somehow completely unaffected by radiation. It doesn’t emit any form of radiation (including light) and all forms of radiation pass through it without any effect. ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [October 15, 2014, 5:04am UTC](https://boards.straightdope.com/t/100-certain-physical-laws-are-same-in-other-galaxies/701230/29 "2014-10-15T05:04:21Z")
Well there are likely _phenomena_ that are present in some galaxies but not others. e.g. maybe some galaxies don’t have a supermassive black hole in their center. But beyond things like that, from what we currently can observe and predict about galaxies, there doesn’t seem to be much need / room for them to be very different. ---
**Author:** ![Wendell\_Wagner](https://avatars.discourse-cdn.com/v4/letter/w/8491ac/32.png) [@Wendell\_Wagner](https://boards.straightdope.com/u/Wendell_Wagner)\ **Post date:** [October 15, 2014, 8:23am UTC](https://boards.straightdope.com/t/100-certain-physical-laws-are-same-in-other-galaxies/701230/30 "2014-10-15T08:23:26Z")
Dark matter, as I understand, has nothing to do with any possible difference between physical laws in our galaxy and other galaxies. Dark matter is necessary to explain things like the rotational speed of stars in galaxies. It’s just as much necessary to explain such things in our galaxy as it is in other galaxy. So if there are phenomena that would require having different physical laws in other galaxies as in our galaxy, they have nothing to do (as far as we know) with dark matter. [Previous page](https://boards.straightdope.com/t/100-certain-physical-laws-are-same-in-other-galaxies/701230.md?page=1)