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Gravitational waves should permanently distort space-time
- mrkramer 5y agoJust like sea waves which are permanently changing(shaping) the structure of rocks they are hitting[0]. [0] https://en.wikipedia.org/wiki/Wave_pounding https://en.wikipedia.org/wiki/Wave_pounding
- LegitShady 5y agoI’m not sure that’s a good analogy. Spacetime isn’t necessarily pounding anything - it could be Spacetime itself that is distorted and curved by such a phenomonon. If spacetime is the medium of the waves, why are these waves hitting anything, and what?
- mrkramer 5y ago>If spacetime is the medium of the waves, why are these waves hitting anything, and what? "Gravitational waves are disturbances in the curvature of spacetime, generated by accelerated masses, that propagate as waves outward from their source at the speed of light." [0] They are hitting everything what is on their way just like sea waves are. [0] https://en.wikipedia.org/wiki/Gravitational_wave https://en.wikipedia.org/wiki/Gravitational_wave
- LegitShady 5y agoIt depends what “everything” is though. We exist in spacetime, so we are as much the medium of the wave as everything else is. What are the ‘rocks’ in the analogy? What’s ‘wearing’ like the rocks? We don’t know enough about the spacetime or what’s out of spacetime to say.
- mrkramer 5y agoI'm not a physicist but it doesn't seem hard to understand: "Water waves, sound waves, and electromagnetic waves are able to carry energy, momentum, and angular momentum and by doing so they carry those away from the source. Gravitational waves perform the same function[0]." So as water wave is hitting rock or any other object(mass/energy) on its way gravitational waves should hit also everything and anything on their way until they lose energy and collapse. "Gravitational waves are constantly passing Earth; however, even the strongest have a minuscule effect and their sources are generally at a great distance. For example, the waves given off by the cataclysmic final merger of GW150914 reached Earth after travelling over a billion light-years, as a ripple in spacetime that changed the length of a 4 km LIGO* arm by a thousandth of the width of a proton, proportionally equivalent to changing the distance to the nearest star outside the Solar System by one hair's width[0]." Gravitational waves are all around us but they have minimal impact whatsoever unless I suppose some large event(source) propagates strong gravitational waves near us. *Laser Interferometer Gravitational-Wave Observatory [0] https://en.wikipedia.org/wiki/Gravitational_wave https://en.wikipedia.org/wiki/Gravitational_wave
- pomian 5y ago"I'm not a physicist but"... You should be. That was a nice postulation.
- galaxyLogic 5y agoWhen we have a sound-wave it means air-pressure changes along the peaks and troughs of the wave. When we have a gravitational wave what measurable quantity changes?
- mrkramer 5y agoAsk a physicist but as far as I understood gravitational waves are dents in spacetime[0] and as they travel their energy, momentum, and angular momentum change over time because of interaction and collision with other "stuff" in space. Idk how you can measure any of that. [0]https://www.esa.int/Science_Exploration/Space_Science/Gravitational_waves_dents_in_spacetime https://www.esa.int/Science_Exploration/Space_Science/Gravit...
- goldenkey 5y agoCorrect, it's all just spacetime. This is what Einstein was after in the last years of his life - a unified geometric theory, where mass was not separate from the sheet, but rather, part of it - a deformation of it. [1] https://www.arxiv.org/pdf/0706.0190v2 https://www.arxiv.org/pdf/0706.0190v2 Water waves can crash into eachother. There's no reason that spacetime waves cannot either. You can get some hint of this if you look at the oscillations that comprise the Higgs field. The negative curvature of gravitation should be cancelled out by the positive curvature of matter and energy. https://en.wikipedia.org/wiki/Zero-energy_universe https://en.wikipedia.org/wiki/Zero-energy_universe
- jjk166 5y agoWe, and everything else, are stuff floating in the sea of spacetime. Just as a ship would bob up and down as an ocean wave passed along but is not itself part of the wave, so too are we affected by gravitational waves as the pass through spacetime. The difference is instead of up and down motion, the distance between two points in space and time expands and contracts.
- mrkramer 5y ago>We, and everything else, are stuff floating in the sea of spacetime. Just as a ship would bob up and down as an ocean wave passed along but is not itself part of the wave, so too are we affected by gravitational waves as the pass through spacetime. Exactly it's called Frame-dragging[0]: "Frame-dragging is an effect on spacetime, predicted by Albert Einstein's general theory of relativity, that is due to non-static stationary distributions of mass–energy. A stationary field is one that is in a steady state, but the masses causing that field may be non-static -rotating, for instance." [0] https://en.wikipedia.org/wiki/Frame-dragging https://en.wikipedia.org/wiki/Frame-dragging
- akomtu 5y agoI'll make a guess that matter is like bubbles in spacetime. For some reason the bubbles remain stable and due to cleverness of equations governing spacetime, it allows to form stable complex structures around those bubbles. This is even a verifyable hypothesis: check what happens with GR equations in topologies with tiny spherical holes.
- drran 5y agoBubbles + thermal noise. Noise causes vibration, vibration makes bubbles stable. Vibration also causes bubbles to stick together due to Casimir effect.
- LegitShady 5y agoI guess the question is what is spacetime made of, which is the big problem in physics right now. Whether it's loop quantum gravity, string theory, or one of the many other theories that exist, the question of what is spacetime is what people are trying to solve to figure out quantum gravity. What is spacetime made of? Nobody knows yet.
- andrewflnr 5y agoMore like the sea itself doesn't go completely flat after the wave passes. If the water is space, a rock is more like a break in space.
- denton-scratch 5y ago> But a gravitational wave has a longer reach than the force of gravity. That can't be right - surely the gravitational field permeates the whole of space; and surely the wave and the force are the same thing?
- cobaltoxide 5y ago> the wave and the force are the same thing? Nope. This is a common misconception. The difference between gravitational waves and gravity is a little bit like the difference between electromagnetic waves (emitted by an accelerating charge) and the electrostatic force (caused by a net charge at rest). It's not possible to detect the effect of a charge far away, but easy to detect the propagating electromagnetic wave (light, ratio, etc).
- denton-scratch 5y agoThanks - I can see the comparison with electromagnetism.
- anotheraccount9 5y agoI'm no expert in the field, but if that's true, the space-time fabric must be quite irregular, and will become more so in the future.
- errcorrectcode 5y agoSo I wonder if spacetime has a kind of "entropy" where it can be stretched-out but never put back exactly how it was. Possibly explaining inflation.
- xwolfi 5y agoNo inflation is very different, it's pervasive in every direction, it's not localized like your idea would mean. Plus, it's not like galaxies are temporarily pulling on a memory foam, before releasing the pressure, so I m not sure why you think inflation (such a bad name, people think balloon) is so close to that model.
- goohle 5y agoIt looks like Big Shrink (BS) theory is easier to understand: we are shrinking, our rulers are shrinking, so cosmic distances are looking bigger in every direction. It explains why our Universe is flat and why we cannot find a Universe-big source of energy for expanding of the Universe.
- msk-lywenn 5y agoBut what energy is making us shrink?
- klyrs 5y agoFrom the article: > “The memory is nothing but the change in the gravitational potential,” said Thorne, “but it’s a relativistic gravitational potential.” The energy of a passing gravitational wave creates a change in the gravitational potential; that change in potential distorts space-time, even after the wave has passed. Gravitational waves are that energy.
- contravariant 5y agoConservation of energy gets a bit screwy with these kinds of cosmic models. Partially because there isn't a single direction of 'time', but also because all kinds of energy gets stored in the fabric of space-time which can cancel out all kinds of things. Not to mention that there's no reason to assume conservation of energy still holds if the laws of physics simply change over time (which would be the case in the simplest possible theory were all interaction distances simply shrink over time).
- eli_gottlieb 5y agoHow can you change space-time? It's already got a time dimension, so you'd need another time dimension with respect to which to take the derivative. Or is the real claim here that gravitational waves distort space as part of their temporal dynamics?
- LegitShady 5y agoWe already know that spacetime has local curvature, so it’s possible that spacetimes curvature isn’t static. How this affects or interacts with time isn’t clear, since we don’t really understand what spacetime is or how it comes to be.
- cinquemb 5y agoI think if both of you aren't aware, this talk on the concept of time orientability might be interesting exploration on this: https://yewtu.be/watch?v=Mk7vkhT0UCM https://yewtu.be/watch?v=Mk7vkhT0UCM
- paulpauper 5y agoIt's interesting how two posts recently about Newton's Method went viral here. it shows how despite how Quanta Magazine focuses on the most cutting edge of theoretical math, that applied math is still very important.
- kevinconroy 5y agoCue "Three Body Problem" trilogy references
- ASalazarMX 5y agoGravitational waves in the series are only mentioned briefly, as a telecommunication medium. IMO communicating with gravity waves is excessive, and they're not faster than electromagnetic radiation.
- bigodbiel 5y agoObviously not the graviational waves, but I was also thinking abouth the warp bubbles used in FTL travelling (and its abuse) distorting space time forever
- ASalazarMX 5y agoBut all space travel in "The Three Body Problem" is subluminical? I can't even recall a single Liu Cixin story with FTL space travel. The closest situation I can think of is ST TNG "Force of Nature", where warp travel was damaging subspace.
- bigodbiel 5y agoDamn! True, sorry about that!
- SavantIdiot 5y agoI read that whole article and all I came away with was, "Gravitational waves bend space time a little in a phenomenon called gravitational memory." I still have no idea by what mechanism though, other than guesses at some deeper super symmetry. Can anyone dumb this down a little more for me? What holds on to the deformation? If spacetime can be deformed by a gravitational wave, then how can its original be entirely decided by the amount of and the arrangement of matter nearby. Meaning: if a wave passes by, unless it impacts the arrangement of matter in the locality, then what "holds" the deformation?
- goohle 5y agoSpacetime is just 4D array: [x,y,z;t]. "Bending of spacetime" means that you need to apply a shader to this array. If you want to talk about physics of the process, then you need to pick up a physical medium first, not an array of measurements.
- jcun4128 5y agoI don't get in many depictions they show this planet/ball over a grid that's deforming downwards. I can understand how another mass would want to "fall" into that but is it actually that shape (has up/down) or it some kind of sphere. I also believe with regard to mass clumping, gravity is strongest near the surface of the Earth vs. inside where you could say it's equal/0 except the oblique part.
- ben_w 5y agoThe rubber sheet analogy is criticised for this exact reason. Here’s a different visualisation that starts with what’s wrong with the rubber sheet: https://youtu.be/wrwgIjBUYVc https://youtu.be/wrwgIjBUYVc
- jcun4128 5y agoOh yeah I can see the 3D sinking inwards that's a neat video haven't seen that slicing idea before
- pdonis 5y agoThe Wikipedia page on gravitational memory effect [1] gives links to some actual papers, which might be more illuminating than the rather garbled description in this article. https://en.wikipedia.org/wiki/Gravitational_memory_effect https://en.wikipedia.org/wiki/Gravitational_memory_effect
- p1mrx 5y ago"persistent changes in the relative position of pairs of points in space due to the passing of a gravitational wave." So the idea isn't that space itself is storing information, just that a gravitational wave doesn't put everything back where it found it. Presumably if you cleared out all the stuff, there would be no memory left behind.
- pdonis 5y agoThat's my understanding, yes. So the "permanently distort spacetime" part in the article's title is misleading.
- zuminator 5y agoWhat you are both saying seems incompatible not just merely the title but also with the text of the article, where is states, "Earth’s gravitational pull also tends to restore LIGO’s mirrors to their original position, erasing its memory. So even though the kinks in space-time are permanent, the changes in the mirror position — which enables us to measure the kinks — are not." In other words, the article is claiming that there are two things being affected, spacetime itself, and the objects embedded in spacetime, but only the objects are temporarily displaced, spacetime itself is permanently displaced. At least, that's my reading. But I wonder, notwithstanding the article's assertion, are objects really completely restored back to their former position in spacetime? Spatial coordinates, sure, but timewise? I don't claim to know the answer, just posing this as a question, but imagine a really powerful gravitational wave going through a large object. Wouldn't it create some kind of timewise interference pattern in the object where at the peaks of oscillation, the constituent subatomic particles would feel a stronger gravitational force and age more slowly than the particles at the troughs of oscillation? So after the wave had passed, you'd be left with an object that has areas of divergent age? I mean even with standard GR we experience aging on a gradient, in that our feet are somewhat younger than our heads thanks to the gravitational pull of the Earth. ( https://www.theatlantic.com/technology/archive/2010/09/study-your-head-is-older-than-your-feet/63539/ https://www.theatlantic.com/technology/archive/2010/09/study... )
- p00tst00t 5y agoSpace-time doesn't exist. Space is innert. Counter-space however is another story. Matter is relative, it cares not for "spacetime"
- codingclaws 5y agoI've had that theory. Gravity wells remain for a time after the responsible mass has moved on. Maybe that explains dark matter/energy.
- edgan 5y agoI like your theory, but it doesn't explain galaxies that don't seem to have any dark matter.
- legohead 5y agoSo as I was trying to imagine this I came up with an example that I think fits, can someone confirm my thoughts? My idea is a square piece of fabric (space). You cut a single strand of fabric somewhere, which is the origin of the wave event. This affects the whole fabric as the destruction ripples throughout, and also results is a permanent scar/distortion on the fabric as a whole.
- TheOtherHobbes 5y agoMy understanding was more that spacetime isn't perfectly elastic, so when it's distorted by a gravitational wave it stores the equivalent of a gravitational charge - a bit like a piezoelectric crystal that stays very slightly permanently polarised after you stop squeezing it. This would be amazing if true because spacetime would be rough on very tiny scales because of all the waves that passed through it. Speculating wildly, this might even have observable quantum-level effects.
- akomtu 5y agoOfftopic. This would be a precursor for the typical generator in the future: a stone on a rope inside a stone cavity that resonates with gravity waves, converts the piezoelectric tension of spacetime into vibration, heats up as a result and boils a rusty cup of water.
- nsxwolf 5y agoCould this mean the possibility of stable wormholes that don't require any "exotic matter" to keep them from collapsing?
- k2xl 5y agoCould this prove/disprove whether there have been "prior" universes? In other words, the theory that after the heat death of the universe another universe will form... If gravitational waves permanently distort space time would that allow us to observe evidence of previous universes?
- deleted 5y ago[deleted]
- VLM 5y agoEarth-Sun system should radiate about 200 watts of gravitational waves continuously. One 20th that should be 10 watts of permanent deformation. Bad news is 10 watts is not much, spread thru a large volume. Good news is its "easy" to measure the infra red radiation from Pioneer and Voyager space probes running less than a KW point source of energy. I wonder if the gravity probe A and B missions would show those permanent deformations in their data. Permanent deformation should be detected in large scale long term orbits, eventually?
- galaxyLogic 5y agoWhat does this deformation mean physically? I thought matter makes space curve. Does the deformation mean the curvature get changed?
- dokem 5y agoCan we make memristors with this info?
- ststephen88 5y agoThis is clear evidence, these are angels, be not afraid.
- nybsop 5y agoSo were talking about magnetic monopoles except with gravity this time?
- CoastalCoder 5y agoLayman's question: are gravitational waves really "waves"? When I think of waves, I think of systems governed by the wave equation [0]. But IIUC that requires a restoring force. I'm not sure what that would mean in the case of gravity. E.g., if the moon suddenly lurched towards the Earth, we'd perceive an increase in gravity between the two. But that would be a semi-permanent change in the strength of that attraction between the two objects; not what I'd think of as a wave-like fluctuation. [0] https://en.wikipedia.org/wiki/Wave_equation https://en.wikipedia.org/wiki/Wave_equation
- joe__f 5y agoYes, gravitational wave are governed by the wave equation. A standard way to treat them is as a small perturbation around a known spacetime geometry. Then the metric would be $g = g_0 + \epsilon h$, where $g_0$ is the background, $\epsilon$ is a small parameter and $h$ is the perturbation. In general Einstein's field equations govern the dynamics of $g$, and if you take the first order behaviour in $\epsilon$ around $g_0$ as flat space, then you recover the wave equation for $h$ as in the article you linked, with propagation speed $c$ the speed of light. (There are some additional subtleties about choice of gauge, but this is not physical). I'm not sure what you mean with your moon example.
- CoastalCoder 5y agoThanks! I'm not ready to understand your explanation, but I can clarify the moon example at least. Suppose the gravitational attraction between the earth and moon is 2e20 Newtons. Now imagine something forces that attraction to strengthen from 2e20N to 3e20N. E.g. the Earth and moon get closer to each other, or the moon gets more massive somehow. When we talk about "detecting gravity waves", I understand that to mean that on Earth we've managed to detect that increase from 2e20N to 3e20N. My point was: perhaps that looks like the rising edge of a wave phenomenon, but it's not actually cyclic like I expect from a traditional "wave". So I couldn't understand why it's called a gravity wave.
- Beldin 5y ago
- mikewarot 5y agoThe detectors we have are just sensitive enough to detect the spin down when two objects 50+ times the size of the sun merge into a single new object. The gravity in the direction of the objects decreases permanently by the delta of the mass expended creating gravity waves, which is shift too small to measure. I expect it may be possible in the future to confirm this, very small, persistent shift in spacetime, but not in my lifetime.
- cobaltoxide 5y agoGravitational wave detectors can only detect oscillatory signals, not static ones.
- tejtm 5y agoWould not be surprised if this cues some Expansion of the universe due to gravity lost in waves. headlines. But the distance scales and force magnitudes are so far out of my experience that even with the help of math I would be hard pressed to be convinced one way or another.
- mrfusion 5y agoI never understood how gravity waves can go through anything and not be weakened? If the wave imparts energy on an object and makes it move, how is that energy still available for the next object the wave goes through?
- neophyt3 5y agoI never understood how gravity waves propagate Mass causes gravity then what are these waves then? Is it dark matter thats not visible, not measurable and yet it has mass which causes ripple in space fabric
- p1mrx 5y agoIt's possible to move an object, and return it to its original location, without expending energy. Ocean waves do this all the time. Based on conservation of energy, I would assume that friction can weaken a gravitational wave by turning some of its energy into heat. Though if we're talking about permanently changing the location of an object, that theoretically requires a negligible amount of energy... reminds me of the magic drive in https://qntm.org/frontier https://qntm.org/frontier
- cobaltoxide 5y ago> Based on conservation of energy It turns out that energy is not conserved globally in General Relativity. https://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html https://math.ucr.edu/home/baez/physics/Relativity/GR/energy_...
- cobaltoxide 5y ago> If the wave imparts energy on an object and makes it move The objects don't move. The space between them stretches and compresses. Now, if the gravitational wave moves through a large massive object like a star or planet, the electromagnetic forces of the "stuff" in the object will cause it to resist this stretching or compressing. I think this does cause a very very very tiny "backreaction" to the gravitational wave, weakening it slightly.
- thehappypm 5y agoThis is cool. Maybe it’s an explanation for mass. When you’re at rest (or at a constant velocity) you’re constantly making a dent in spacetime, that closes up eventually behind you. Go faster, the dent grows, so you need a force to push through that initial resistance of making the dent bigger.
- vmception 5y agommm haven't seen Apophysis fractal art in a long time!
- zelphirkalt 5y agoThe title reminded me of that Star Trek episode, in which they realize, that warp drive usage has a permanent effect on space time and can tear terrible rifts open, which could destroy basically everything and then decided, that throughout the whole federation there would be speed limits or so.
- perl4ever 5y ago>which could destroy basically everything https://en.wikipedia.org/wiki/False_vacuum_decay https://en.wikipedia.org/wiki/False_vacuum_decay I guess it's not worth worrying about, because if it happened, it would happen at the speed of light and be impossible to see coming.
- 8bitsrule 5y agoLots of questionable assertions in this very speculative article. "According to general relativity, every gravitational wave should leave an indelible imprint on the structure of space-time...." All kinds of possibilities can be found in equations. The derivation of possibilities is no guarantee that they correspond with physical realities. An earthquake leaves an undelible imprint on some matter in space-time. Different thing. The presence of stars is said to 'warp' space-time. Never saw a suggestion that the warp is permanent. Do stars orbiting a galactic center 'permanently warp' the space-time they pass through? "How, exactly, will a passing wave distort space-time? The possibilities are literally infinite, and, puzzlingly, these possibilities are also equivalent to one another...." Literally infinite? Colorful language, no math, no hint of why the possibilities are non-zero. "While detecting the memory effect caused by a single gravitational wave is infeasible with current technology...." Maybe so much speculative fiction based on no empirical evidence is no fit way to conduct science.
- AnimalMuppet 5y ago> Maybe so much speculative fiction based on no empirical evidence is no fit way to conduct science. Well, if they can make predictions that could in principle be measured, then LIGO or some future version may become good enough to measure them (or observe their absence). That's actually one of the ways that science is conducted.
- mason_dev 5y agoWhat are the implications of this?
- kazinator 5y agoIf we step back and think about it, everything that happens changes the content of space-time; the universe does not cycle back to prior state (excluding, of course, certain concepts and time scales like going from a big bang to a big crunch).
- thamer 5y agoThe article talks about the limitations of LIGO that make it impossible (currently) to detect such a small effect, but would the proposed Laser Interferometer Space Antenna[1] (LISA) probe be sensitive enough to measure this memory effect? The proposal is to arrange three spacecrafts in an equilateral triangle with sides measuring 2.5 million km (for comparison, each "arm" of LIGO is 4 km long). [1] https://en.wikipedia.org/wiki/Laser_Interferometer_Space_Antenna https://en.wikipedia.org/wiki/Laser_Interferometer_Space_Ant...