# About space and gravity, too long to explain in thread title **URL:** \ **Category:** Factual Questions\ **Tags:** science-math\ **Created:** [December 12, 2024, 3:14pm UTC](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558 "2024-12-12T15:14:46Z")\ **Posts on this page:** 19\ **Page:** 3
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [December 23, 2024, 10:42pm UTC](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558/41 "2024-12-23T22:42:45Z")
Yeah, we’re spoiled here on Earth by having a reaction mass that might as well be infinite; in space Newton’s Third Law is supreme. Even something as massive as an O’Neill colony might be noticeably affected by sufficiently unbalanced activity within. (Do suspension bridges still have to restrict things like marching in step across them?) ---
**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:** [December 23, 2024, 10:56pm UTC](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558/42 "2024-12-23T22:56:42Z")
I know I was at a party in an apartment once where the beat of the music was close to the fundamental frequency of the floor, as (most alarmingly) could be observed as everyone was dancing on it. ---
**Author:** ![Lucas\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lucas_jackson/32/303_2.png) [@Lucas\_Jackson](https://boards.straightdope.com/u/Lucas_Jackson)\ **Post date:** [March 28, 2025, 5:55pm UTC](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558/43 "2025-03-28T17:55:17Z")
> [@HeyHomie](#): > > Let’s say I have a one-meter sphere weighing, say, 1000kg. I’m out in deep DEEP space – as in, light years away from the nearest star or what have you. I also have a one-millimeter sphere weighing, say, one milligram. If I held the smaller sphere a few centimeters from the larger one and let go of it, would the larger sphere’s gravity be enough to pull it towards its center, the way the Earth does with, well, anything? > [@zimaane](#): > > In theory yes the smaller sphere could orbit the larger sphere. In practice, it would depend on the gravitational influence of nearby planets and stars. Sorry to bump this but better than starting a new thread… I was reading about how much the universe is expanding, and thought of this thread. Would the expanding fabric of space have and bearing on this? How far apart would they have to be before expansion over-rode gravitation effects? ---
**Author:** ![mixdenny](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mixdenny/32/2962_2.png) [@mixdenny](https://boards.straightdope.com/u/mixdenny)\ **Post date:** [March 28, 2025, 10:10pm UTC](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558/44 "2025-03-28T22:10:07Z")
Back to pushing that 1000 kg sphere. It would not be hard at all. Just picture it hanging by a rope on earth. You could shove it easily. Heck, I push my 2400 lb Scion frequently without bracing and that has a lot of tire friction to overcome. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [March 28, 2025, 11:20pm UTC](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558/45 "2025-03-28T23:20:13Z")
You could move it with a single finger. The only reason it’s impossible to lift on Earth is gravity; the only reason it would be hard to roll on earth is friction and maybe friction-like mechanical effects where it sinks into the surface on which it is resting. If it’s a 1000kg sphere floating in space, you wouldn’t be able to swing it around as though it’s a beach ball, but there is nothing to attenuate the effect of a small force you apply to it, so pushing it gently with one finger will eventually get it moving - of course you’re pushing yourself in the opposite direction, but if we assume you are magically braced or something, then you can move the thing. If you’re not magically braced, you and the thing both move apart from each other. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [March 29, 2025, 12:27am UTC](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558/46 "2025-03-29T00:27:47Z")
> [@DPRK](#): > > I have a little digital scale which internally measures who-knows-what, but the readout is in grams. Modern, top-loading balances measure weight, but report mass. Cheap ones use a strain gauge-based load cell. Precision/analytical balances, such as those made by Mettler, use an electromagnetic force restoration (EMFR) load cell. These use a light beam and electromagnet. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [March 29, 2025, 2:22am UTC](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558/47 "2025-03-29T02:22:28Z")
> [@Lucas\_Jackson](#): > > How far apart would they have to be before expansion over-rode gravitation effects? There is actually a theory related to this. Tl;dr: it would be bad. > In their paper, the authors consider a hypothetical example with w = −1.5, H0 = 70 km/s/Mpc, and Ωm = 0.3, in which case the Big Rip would happen approximately 22 billion years from the present. In this scenario, galaxies would first be separated from each other about 200 million years before the Big Rip. About 60 million years before the Big Rip, galaxies would begin to disintegrate as gravity becomes too weak to hold them together. Planetary systems like the Solar System would become gravitationally unbound about three months before the Big Rip, and planets would fly off into the rapidly expanding universe. In the last minutes, stars and planets would be torn apart, and the now-dispersed atoms would be destroyed about 10−19 seconds before the end (the atoms will first be ionized as electrons fly off, followed by the dissociation of the atomic nuclei). At the time the Big Rip occurs, even spacetime itself would be ripped apart and the scale factor would be infinity. > **[Big Rip](https://en.wikipedia.org/wiki/Big_Rip)** > > In physical cosmology, the Big Rip is a hypothetical cosmological model concerning the ultimate fate of the universe, in which the matter of the universe, from stars and galaxies to atoms and subatomic particles, and even spacetime itself, is progressively torn apart by the expansion of the universe at a certain time in the future, until distances between particles will infinitely increase. > According to the standard model of cosmology, the scale factor of the universe is accelerating, and, in th... And a Hugo-nominated short story: > **[Last Contact by Stephen Baxter (part 1 of 3)](http://zestfullyblog.blogspot.com/2011/02/last-contact-by-stephen-baxter-part-1.html?m=1)** > > Dark energy (defined as a property of space, a new dynamic fluid, or a new theory of gravity) permeates all of space and tends to increase t... ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [March 29, 2025, 2:26am UTC](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558/48 "2025-03-29T02:26:31Z")
Except if quarks cannot be pulled apart because any force strong enough to do so would simply create new quark-antiquark pairs which then decayed, then wouldn’t the Big Rip result in a spacetime filled with stupendous amounts of energy? Sounds a lot like cosmic inflation to me. ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [March 29, 2025, 3:26am UTC](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558/49 "2025-03-29T03:26:03Z")
> [@Lumpy](#): > > Except if quarks cannot be pulled apart because any force strong enough to do so would simply create new quark-antiquark pairs which then decayed, then wouldn’t the Big Rip result in a spacetime filled with stupendous amounts of energy? It’s not a force as such; it’s space itself getting larger. ---
**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:** [March 29, 2025, 12:51pm UTC](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558/50 "2025-03-29T12:51:37Z")
Hypothetically, the Big Rip would be too fast, and on too fine a scale, for that to keep up. Once you’ve got colors isolated within their cosmological horizon, no amount of new quark generation can change that. ---
**Author:** ![Kedikat](https://avatars.discourse-cdn.com/v4/letter/k/ed655f/32.png) [@Kedikat](https://boards.straightdope.com/u/Kedikat)\ **Post date:** [March 29, 2025, 4:11pm UTC](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558/51 "2025-03-29T16:11:44Z")
A goofy question. Two spheres of equal size and mass exist some distance apart, but alone in the universe. They attract. Build up speed towards each other. Just before they hit. One mass configures into a doughnut shape that allows the other to pass through the hole. Then assumes a sphere shape again. I assume this would be a repeating event. Eventually ending with one mass stationary in the doughnut hole. But not sure. The doughnut mass has a different shaped gravitational field as the other passes through. Would they part ways forever? If it did repeat. Would it matter if they took turns becoming the doughnut? If just one changed, would a drift in a direction of the system develop? ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [March 29, 2025, 4:20pm UTC](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558/52 "2025-03-29T16:20:47Z")
I don’t think it’s necessary to postulate a sphere translating into a torus. If the torus was perfectly face-on to the approaching other mass, then its gravity field would remain symmetrical and it would behave as if its mass was located in the center. The two would simply oscillate back and forth for all eternity, barring complications like quantum effects. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [March 29, 2025, 4:22pm UTC](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558/53 "2025-03-29T16:22:56Z")
> [@Der\_Trihs](#): > > It’s not a force as such; it’s space itself getting larger. Except that if something’s making the quarks move apart when they don’t want to, it has to impart energy to the quarks; more or less the definition of a force. > [@Chronos](#): > > Hypothetically, the Big Rip would be too fast, and on too fine a scale, for that to keep up. Once you’ve got colors isolated within their cosmological horizon, no amount of new quark generation can change that. Once you have an isolated spacetime with a net color (or electric) charge, does that change the properties of spacetime? ---
**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\ **Post date:** [March 29, 2025, 7:46pm UTC](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558/54 "2025-03-29T19:46:50Z")
> [@Lumpy](#): > > The two would simply oscillate back and forth for all eternity, barring complications like quantum effects. Gravitational radiation would sap the system’s energy, damping out the oscillation over time. > [@Lumpy](#): > > Except if quarks cannot be pulled apart because any force strong enough to do so would simply create new quark-antiquark pairs which then decayed, then wouldn’t the Big Rip result in a spacetime filled with stupendous amounts of energy? > [@Lumpy](#): > > Once you have an isolated spacetime with a net color (or electric) charge, does that change the properties of spacetime? This is “unstoppable force meets immovable object” territory, and to settle the battle, one needs to solve a lot of unsolved problems in physics. Or, in brief, nobody knows. Note that even relatively pedestrian questions like “How do color-bound objects behave near a black hole?” remain open. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [March 29, 2025, 11:23pm UTC](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558/55 "2025-03-29T23:23:24Z")
About that Big Rip. A recent result from [DESI](https://www.desi.lbl.gov/) indicates that dark energy may be weakening. Which, if true, would indicate there won’t be a Big Rip. However, it’s not confirmed. We’re waiting on results from other instruments that are still in the building stage. This blog has more details than most people want: > **[Is dark energy weakening? DESI's results are ambiguous](https://bigthink.com/starts-with-a-bang/dark-energy-weakening-desi-results/)** > > DESI, by mapping galaxies, has claimed they see evidence for dark energy evolving by getting weaker. But that's only one interpretation. ---
**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:** [March 29, 2025, 11:34pm UTC](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558/56 "2025-03-29T23:34:10Z")
> [@Lumpy](#): > > The two would simply oscillate back and forth for all eternity, barring complications like quantum effects. With the caveat that the system would be unstable, and so if the alignment were off by even the slightest amount, eventually (and fairly quickly) the sphere would end up sliding agains the edge of the donut and you’d get friction. > [@Lumpy](#): > > Once you have an isolated spacetime with a net color (or electric) charge, does that change the properties of spacetime? Almost certainly, and in ways that we can’t fully understand without a working theory of quantum gravity. But from the vague tentative approximations we have, it looks like this effect would actually accelerate the ripping. > [@dtilque](#): > > About that Big Rip. A recent result from [DESI](https://www.desi.lbl.gov/) indicates that dark energy may be weakening. All of the measurements we have of the rate of change of the dark energy are consistent with that rate of change being zero. Since that’s the simplest assumption, it’s what most mainstream cosmologists assume. And you can never actually completely rule out the possibility of it being nonzero, just set tighter and tighter bounds around zero. But, since we can’t rule out the possibility of it being nonzero, people do explore the possible consequences of that. ---
**Author:** ![Zakalwe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zakalwe/32/270_2.png) [@Zakalwe](https://boards.straightdope.com/u/Zakalwe)\ **Post date:** [March 30, 2025, 12:53am UTC](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558/57 "2025-03-30T00:53:14Z")
> [@Lumpy](#): > > Except that if something’s making the quarks move apart when they don’t want to, it has to impart energy to the quarks; more or less the definition of a force. The quarks aren’t moving in any meaningful sense of the word. They are simply spreading apart as the ‘fabric’ on which they lay stretches out. To the quark, there is no sense of movement. Just like you and I don’t feel the current expansion of the universe. ---
**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\ **Post date:** [March 30, 2025, 1:00am UTC](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558/58 "2025-03-30T01:00:42Z")
> [@Chronos](#): > > it looks like this effect would actually accelerate the ripping. Do you have a reference for this? > [@Chronos](#): > > All of the measurements we have of the rate of change of the dark energy are consistent with that rate of change being zero. All the measurements we have to date show tension in a number of aspects of the simplest \Lambda\rm{CDM} model, so one can’t really make a statement that measurements are consistent at all. Whether that’s due to new physics or just unappreciated subtleties in the measurements remains unknown. If it’s the former, then a time-varying dark energy offers some (but not complete) help in making sense of the data, and it’s the avenue that DESI has looked at using their latest data. ---
**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:** [March 30, 2025, 1:08am UTC](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558/59 "2025-03-30T01:08:59Z")
> [@Pasta](#): > > Do you have a reference for this? I have a memory of my grad school advisor mentioning that some of his previous students had looked into it and found that result. Nothing more concrete than that, I’m afraid. Of course, even if I did have the reference, it’s a very weak result, based only on semiclassical considerations (and to the extent that semiclassical results are valid at all, they would surely have broken down by the time you get to Big Rip conditions). As you said, we really don’t know. [Previous page](https://boards.straightdope.com/t/about-space-and-gravity-too-long-to-explain-in-thread-title/1011558.md?page=2)