# How far does gravity reach? **URL:** \ **Category:** Factual Questions\ **Created:** [May 7, 2013, 6:17pm UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726 "2013-05-07T18:17:23Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Gagundathar](https://avatars.discourse-cdn.com/v4/letter/g/a183cd/32.png) [@Gagundathar](https://boards.straightdope.com/u/Gagundathar)\ **Post date:** [May 8, 2013, 7:09pm UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726/21 "2013-05-08T19:09:37Z")
Gravity can be expressed, as far as I can tell, as a warping of space-time. This warping apparently propagates at c and only asymptotically approaches flatness based upon the distance from the gravity well. In other words, all of space-time is warped by ALL matter and energy in the Universe. But, I could be wrong. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [May 8, 2013, 7:10pm UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726/22 "2013-05-08T19:10:18Z")
> [@Mangetout](#): > > That’s easily resolved by expressing it as (1 - 0.999…) > [@moriah](#): > > [Learn! 😃](http://www.youtube.com/watch?v=TINfzxSnnIE) > [@Animastryfe](#): > > Since 0.999…=1, then 1-0.999…=0. **Moderating** I don’t think we need to rehash the nearly infinite previous discussion on this subject here. Let’s stick to the OP. Colibri General Questions Moderator ---
**Author:** ![Derleth](https://avatars.discourse-cdn.com/v4/letter/d/b9e5f3/32.png) [@Derleth](https://boards.straightdope.com/u/Derleth)\ **Post date:** [May 8, 2013, 7:57pm UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726/23 "2013-05-08T19:57:42Z")
> [@Senegoid](#): > > Away back in that not-quite-infinite thread about the value of 0.999… the question came up, about what 0.000…1 would mean. That came from one of the several guys who just could not wrap his head around the idea that 0.999… = 1 and who was arguing that it _must_ always be infinitesimally less than 1. The analogous 0.000…1 was suggested, being always infinitesimally infinitesimal – but never 0. > > I proposed that the notation 0.000…1 _could_ be given a meaningful and sensible definition in a way very similar to the way 0.999… (or any other infinite decimal) is defined. And surprise, surprise! The idea works out, and you can imagine 0.000…1 (with an infinite number of 0’s in there) as having a specific value. Turns out, it’s 0. Huh. And then I confused the issue by bringing up finite infinitesimals in the form of Robinson’s hyperreals, where the notation “0.000 … 1” is still undefined but the concept of “A number strictly less than every positive real number and strictly greater than zero” is given a rigorous definition. So, _in the real numbers_, 0.999… = 1 and (0.999… - 1) = 0. In other systems of numbers, however, it’s possible to give a logically consistent definition to “a number that is infinitesimally less than 1” and do perfectly good math on that foundation. However, in physics, magnitudes (the kinds of values we’re talking about here) are always expressed as real numbers, so all of this is rather academic. ---
**Author:** ![chrisk](https://avatars.discourse-cdn.com/v4/letter/c/6de8d8/32.png) [@chrisk](https://boards.straightdope.com/u/chrisk)\ **Post date:** [May 8, 2013, 8:05pm UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726/24 "2013-05-08T20:05:23Z")
> [@CC](#): > > Yes, but not to a noticeable degree. Even if the universe was not otherwise empty, the answer would be the same. Gravity is a property of matter and doesn’t care if there is other matter around. To me, this brings up the question of what is ‘noticeable’, if there’s nothing else in the universe. No, the specks probably wouldn’t be a millimeter, (or a fraction of their diameter) closer in 100 years, but who says that 100 years is a significant period of time for such a universe. Eventually the attraction between them will have an effect. 😃 ---
**Author:** ![Frazzled](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/frazzled/32/3368_2.png) [@Frazzled](https://boards.straightdope.com/u/Frazzled)\ **Post date:** [May 11, 2013, 7:53pm UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726/25 "2013-05-11T19:53:22Z")
I decided to check out just how much force would be exerted between 2 paperclips placed 4 light years apart. I’m a little rusty so I’ll show my work in case anybody sees something glaringly obvious that I missed. For the force of gravity I used the equation F=(G \* m1 \*m2) / d2 for the mass I used 0.001 kilograms, the size of a large paperclip, and the distance I used 3.78\*10^16 meters. This gave me a total gravitational force between the 2 objects of 4.45\*10^-50 Newtons. Next I plugged this into F=ma to find the acceleration of one of the paperclips. Total acceleration is 4.45\*10^-47 m/s^2 At that rate of acceleration I calculated how much the paperclip would move in 100 billion years, approximately the total lifespan of the universe using the equation d= (a \* t^2) / 2. I used 3.16\*10^18 seconds. So, total distance moved on one paperclip over the lifespan of the universe is: 2.21 \* 10^-10 meters. This translates to just a little over 200 hydrogen atoms distance. So, yes, there is gravitational attraction at that distance but even over the lifespan of the universe it won’t make any difference. ---
**Author:** ![Enola\_Straight](https://avatars.discourse-cdn.com/v4/letter/e/dec6dc/32.png) [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)\ **Post date:** [May 12, 2013, 6:50pm UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726/26 "2013-05-12T18:50:04Z")
According to newtonian gravity and general relativity…continuum mechanics…gravity has an inverse square geometry dropping off to infinity. Do EM, strong and weak nuclear forces with known quantum mechanical geometries of force strength, drop off to zero at a finite range? ---
**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:** [May 12, 2013, 7:07pm UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726/27 "2013-05-12T19:07:48Z")
No theory predicts any of the fundamental forces falling off to zero at any finite range. In fact, the raw color force (of which the effective strong force is only a higher-order residual) is believed to remain constant at large ranges, not diminishing at all. The weak force and the residual strong force, however, approach zero very rapidly, for any macroscopic distance. ---
**Author:** ![toofs](https://avatars.discourse-cdn.com/v4/letter/t/4491bb/32.png) [@toofs](https://boards.straightdope.com/u/toofs)\ **Post date:** [May 12, 2013, 7:34pm UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726/28 "2013-05-12T19:34:51Z")
In regards to the specks at each end of an otherwise empty universe, I have read that our universe is expanding away from the point of the big bang at an ever increasing rate. Wouldn’t gravity’s infinite reach ultimately slow the rate of expansion, eventually causing all matter in the universe to reverse direction and meet once again at the point of origin? Is there a conflict between the theory of the infinite reach of gravity and the observation that the speed of the big bang expansion is increasing? ---
**Author:** ![eltro102](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@eltro102](https://boards.straightdope.com/u/eltro102)\ **Post date:** [May 12, 2013, 7:46pm UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726/29 "2013-05-12T19:46:13Z")
> [@davekhps](#): > > Hmmm, hadn’t heard that before. Does that mean that gravity is potentially a stronger force, just in higher dimensions? well one of the main reasons we know that we live in a 3 (spatial) dimension universe is that stable orbits can exist - if humans (and the planets and…) existed in 4D then gravity would be marginally stronger - and stable orbits couldn’t exist ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [May 12, 2013, 8:09pm UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726/30 "2013-05-12T20:09:32Z")
> [@toofs](#): > > In regards to the specks at each end of an otherwise empty universe, I have read that our universe is expanding away from the point of the big bang at an ever increasing rate. Wouldn’t gravity’s infinite reach ultimately slow the rate of expansion, eventually causing all matter in the universe to reverse direction and meet once again at the point of origin? Is there a conflict between the theory of the infinite reach of gravity and the observation that the speed of the big bang expansion is increasing? Density (as well as pressure) acts decelerates t expansion i.e. the denser the and it’s possible that the rate slows down so much it becomes negative (i.e. the Universe re-collapses), on the other hand it may only decelerate it so that it approaches some non-negative constant rate as the density approaches zero. And that’s not even considering dark energy. There’s no conflict between expansion and gravity: expansion comes from general relativity which is a gravitational theory, however it’s not really correct to think of it as gravitational force pulling against expansion (though it is often stated that way) as general relativity doesn’t model gravity as a force and the way that density acts against expansion doesn’t have a Newtonian limit in which it can be approximated as a force. ---
**Author:** ![Thudlow\_Boink](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/thudlow_boink/32/320_2.png) [@Thudlow\_Boink](https://boards.straightdope.com/u/Thudlow_Boink)\ **Post date:** [May 12, 2013, 8:37pm UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726/31 "2013-05-12T20:37:28Z")
> [@Frazzled](#): > > I decided to check out just how much force would be exerted between 2 paperclips placed 4 light years apart. After reading this first sentence, I was expecting you to tell us what happened when you got 2 paperclips and placed them 4 light years apart. ☹🙂 ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [May 12, 2013, 9:11pm UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726/32 "2013-05-12T21:11:42Z")
> [@toofs](#): > > In regards to the specks at each end of an otherwise empty universe, I have read that our universe is expanding away from the point of the big bang at an ever increasing rate. Wouldn’t gravity’s infinite reach ultimately slow the rate of expansion, eventually causing all matter in the universe to reverse direction and meet once again at the point of origin? Is there a conflict between the theory of the infinite reach of gravity and the observation that the speed of the big bang expansion is increasing? I believe that one of the current issues in cosmology today is the observation that the expansion of the universe is\* not \*slowing down, as one would expect from the effects of gravity, but is, instead, increasing (!) - contrary to what used to be common sense. This has supported the idea of dark matter and dark energy and has caused some degree of upheaval in the field. Clearly, some of those here who know this topic well can weigh in, but I think I have the right notion. ---
**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:** [May 12, 2013, 10:01pm UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726/33 "2013-05-12T22:01:58Z")
Basically, if ordinary gravity acting on ordinary matter were all that was at play in the Universe, the expansion would indeed be slowing down. It might eventually reverse, or if it’s going fast enough you might get an escape speed-like phenomenon where it asymptotically approaches some speed. But either way, it should be slowing down. It isn’t. The logical conclusion is that there’s something other than ordinary gravity or ordinary matter at play. It can be described in terms of either, but the current trend among cosmologists is to describe it in terms of a sort of “stuff” that isn’t ordinary matter, called “dark energy”. In fact, this mysterious dark energy stuff appears to make up over 70% of all of the stuff in the Universe. ---
**Author:** ![Frazzled](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/frazzled/32/3368_2.png) [@Frazzled](https://boards.straightdope.com/u/Frazzled)\ **Post date:** [May 12, 2013, 10:41pm UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726/34 "2013-05-12T22:41:31Z")
Our experiences tells us that the space between objects, if neither object is moving relative to one another, is finite and unchanging. However, on the very large scale of the universe we have learned that new space is constantly being created between these 2 objects and gives the appearance that the 2 objects are moving away from each other. The further away the object is the more space is being created and the faster it appears to be moving away (detectable to us as a redshift). In our own universe the galaxies we see furthest away from us appear to be receeding at a very large percentage of the speed of light! But locally they’re not moving anywhere near that fast, and neither are we. It’s just the expansion happening between us that makes it appear that way which is why this doesn’t violate relativity. In fact, there is an edge to the universe beyond which we will never be able to see. Galaxies that may very well exist there are moving (from our point of view) faster than the speed of light away from us so we’ll never see them. ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [May 12, 2013, 11:04pm UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726/35 "2013-05-12T23:04:02Z")
In fact the furthest objects we see in the observable Universe are in fact receding away from us faster than the speed of light (up to just over 3 times the speed of light in the favoured Lambda-CDM concordance model of the Universe). In fact there are even objects in the observable Universe which were receding from us faster than c when the light we currently see from them was emitted! ---
**Author:** ![Frazzled](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/frazzled/32/3368_2.png) [@Frazzled](https://boards.straightdope.com/u/Frazzled)\ **Post date:** [May 12, 2013, 11:47pm UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726/36 "2013-05-12T23:47:27Z")
Incidentally, this is the answer to the OP - the gravity of an object cannot reach past the visible edge of the universe. So that’s how far it can reach. ---
**Author:** ![My\_Lord](https://avatars.discourse-cdn.com/v4/letter/m/e480ec/32.png) [@My\_Lord](https://boards.straightdope.com/u/My_Lord)\ **Post date:** [May 12, 2013, 11:51pm UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726/37 "2013-05-12T23:51:36Z")
What about the super earths? ---
**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:** [May 13, 2013, 2:06am UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726/38 "2013-05-13T02:06:15Z")
What about them? They’re bigger than our planet, but they’re still pretty small compared to gas giant planets (or stars, or star clusters, or galaxies…). ---
**Author:** ![drewtwo99](https://avatars.discourse-cdn.com/v4/letter/d/d07c76/32.png) [@drewtwo99](https://boards.straightdope.com/u/drewtwo99)\ **Post date:** [May 13, 2013, 2:51am UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726/39 "2013-05-13T02:51:13Z")
What about yo’ mama? Yo mama’s so fat, her gravitational pull extends infinitely at the speed of light. ---
**Author:** ![Frazzled](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/frazzled/32/3368_2.png) [@Frazzled](https://boards.straightdope.com/u/Frazzled)\ **Post date:** [May 13, 2013, 3:40am UTC](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726/40 "2013-05-13T03:40:08Z")
> [@drewtwo99](#): > > What about yo’ mama? > > Yo mama’s so fat, her gravitational pull extends infinitely at the speed of light. Yo mama so fat she attracts galaxies in _every_ dimension! [Previous page](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726.md?page=1) [Next page](https://boards.straightdope.com/t/how-far-does-gravity-reach/657726.md?page=3)