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Assume a science fiction setting. An advanced civilization can change astronomical phenomena. They activate a cosmic string around 10 light-years away from the solar system and break it.

The gravitational waves generated by the break will reach the solar system and tidally tear the sun apart.

Human beings have a cooperative relationship with another advanced civilization, which uses more advanced physical means to help humans offset or avoid gravitational wave destruction disasters.

If we want to protect the solar system objects from damage, how can we avoid the havoc caused by the gravitational wave, assuming similar level scifi tech?

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  • $\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$
    – Community Bot
    Mar 4 at 4:00
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    $\begingroup$ Adding bold text doesn't make the question more clear. Cosmic string are nothing more than fictional objects devised by some people who cannot even agree on a way to verify their theories. You can build all and nothing on them. That said, this sounds like a variation of your previous closed question, with the same fundamental flaw. $\endgroup$
    – L.Dutch
    Mar 4 at 4:20
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    $\begingroup$ I'm not sure I see what's wrong with the question. Besides the fact that gravitational waves from networks of cosmic strings have been well-studied in conjunction with pulsar timing array measurements (e.g. Afzal et al. 2023), some models of cosmic strings do allow them to break, which would subsequently form gravitational waves. $\endgroup$
    – HDE 226868
    Mar 4 at 14:01
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    $\begingroup$ @HDE226868 I don't see what is opinion based, but I don't think the question contains all the information needed to answer it, like what this "gravitational wave destruction disaster" is meant to be or what it would do, what kind of tech level is available to those allies of the humans or what kind of damage the wave would do if not stopped or mitigated. $\endgroup$
    – Trish
    Mar 4 at 14:48
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    $\begingroup$ Another good worldbuilding question beaten down by the physics.lite ideology. This is for a scifi setting. Who cares if cosmic strings are fictional noodles! Thes question should be reopened since it provides ample details as it stands. Let's get creative rather than assume that we must always answer queries as if they were real world questions! $\endgroup$
    – elemtilas
    Mar 5 at 3:06

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What kind of weapon are we dealing with?

A cosmic string is essentially a deformity in spacetime that presents itself as an anisotropy in the spacetime metric; in other words, something left over from the beginning of the Universe that creates a sort of "string" around which circles have fewer than 360 degrees. More specifically, according to the Wikipedia page, "cosmic strings are hypothetical 1-dimensional topological defects which may have formed during a symmetry-breaking phase transition in the early universe when the topology of the vacuum manifold associated to this symmetry breaking was not simply connected."

What does this actually mean for the Solar System if one breaks ten light-years away? It's often said that mass shapes spacetime, but it's actually the reverse: looking at the Einstein field equations,

$$\mathrm{Ric}_{\mu\nu}-\frac{1}{2}Rg_{\mu\nu}+\Lambda g_{\mu\nu}=\frac{8\pi G}{c^4}T_{\mu\nu},$$

it becomes apparent that mass and energy ($T_{\mu\nu}$ is the stress-energy tensor) is actually defined in terms of the deformations of spacetime ($g_{\mu\nu}$ is the metric tensor describing how spacetime curves and $\mathrm{Ric}_{\mu\nu}$ and $R$ are related to the Riemann tensor which describes how much spacetime is different from regular Euclidean spacetime). This is why solving the Einstein field equations is so hard: the intention is to take a metric (a particular configuration of spacetime) and tell you what and where its energy is, not to take a specific arrangement of energy and give you its spacetime metric.

So, what does this mean? That cosmic strings contain a huge amount of energy. In fact, the same Wiki article describing cosmic strings also notes that they contain a large mass: "a circle around the outside of a string would comprise a total angle less than 360° ... From the general theory of relativity such a geometrical defect must be in tension, and would be manifested by mass. Even though cosmic strings are thought to be extremely thin, they would have immense density, and so would represent significant gravitational wave sources. A cosmic string about a kilometer in length may be more massive than the Earth."

So how much power?

So, say a hostile civilization knows about Earth, detests our large-scale production of teddy bears, and decides to break a cosmic string to screw with us. How much energy is released?

Well, this depends on the mass of the string, which is in turn dependent on its length. Here's the thing: they might have practically-infinite length; it's possible that they stretch all the way around the Universe and are thus, for all intents and purposes, infinite.

So, if a civilization is capable of breaking a cosmic string to release its energy in a giant gravitational wave, we might be screwed because they have virtually infinite energy to work with.

So that's an issue. How do we deflect an incoming wave of gargantuan gravitational energy that will instantaneously shred any massive object it comes across? We actually have several options!

How does another advanced civ defend us from it?

Don't worry, another advanced civilization is on the way to save us! They have several options as to how they can prevent the gravitational wave emitted from the broken string from pulverizing our Sun and Earth:

Generate an equal-and-opposite wave in the opposite direction

We actually know something about the aggressor civ that wasn't explicitly stated: they are capable of channeling gravitational waves like lasers channel light. How do we know this? Well, if they were to break a cosmic string without being able to do so, they would be hit with a wave just as strong as the one reaching us. "But what if they aren't an aggressor and wanted to do it for science reasons?" you may ask. My response is that any civilization capable of breaking cosmic strings is probably also capable of detecting bio signatures on nearby stars, so unless they're fine with just annihilating themselves and an entire other species that they know to exist, we can assume that they're an aggressor. Or maybe it was done remotely; still, in that situation, this "aggressor" civ has technology more than powerful enough to channel gravitational waves.

If our "savior" civilization has roughly the same level of technology, there shouldn't be any reason they can't just launch another gravitational wave towards the first. Of course, the issue with that is that they would need to have faster-than-light travel to even be aware of it; gravitational waves like the one the cosmic string emits travel at the speed of light, so from an Earthbound observer watching the string, it breaks and then an instant later everything goes to hell.

So, solution 1: have one of the savior civ's ships get caught in the wave or otherwise detect it, have them jump FTL to our Solar System, and then have them activate another cosmic string and break it, channeling all the gravitational waves towards the first wave. Since energy and momentum are directly related, the two colliding waves will have to conserve their momentum and will therefore turn into a greatly-reduced wave going in either direction. It will probably still be noticeable, but if our savior civ's wave is powerful enough, it might just cancel out the other wave.

Wrap the solar system in an Alcubierre-style bubble

Here's another possible solution: just let the Solar System bypass the wave entirely. Our savior civ, if it is on-par with the aggressor civ, probably has the ability to manipulate spacetime on fundamental levels. If they can generate an Alcubierre-style warp bubble around the entire Solar System, then the very edge of the bubble will absorb much of the incoming gravitational wave's energy.

This is an actual phenomenon of the warp bubble that I personally have studied extensively; near the edge of the bubble, spacetime becomes so deformed that time and space stop having much physical meaning, which causes any and all energy going through it to be shredded at the most fundamental level. If the warp bubble is powerful enough, it can actually withstand perturbation from external gravitational wave sources; the bubble would act kind of like a 99.999%-reflective mirror, absorbing the brunt of the gravitational wave in the very edge of the bubble and allowing only a safe amount of energy through (for some definition of "safe").

If the Alcubierre drive is powerful enough, it would be destabilized by the incoming wave instead of allowing much of it through; the energy density around the edge of the warp bubble would have to be changed to account for the wave, but what it allows the savior civ to do is to take the excess wave energy from one end of the warp bubble and deposit it at the other end to keep the bubble stable and to disperse the wave. If transfer is sufficiently fast, the wave can be circumvented entirely, with the warp bubble acting as a kind of "shield" that allows the wave to flow around it by creating a potential barrier that the wave can move around but not through.

Use a DEW to disrupt the wave before it arrives

Here's another option: use a massive directed energy weapon (DEW) to divert a huge volume of energy from various points across the Solar System's diameter at the gravitational wave. Why? Because in the right configurations, these energy beams will act as interference slits (see the double slit experiment) and cause the incoming gravitational wave to interfere with itself. We don't actually need to stop the whole thing; we just need not to be affected. But why from across the diameter of the Solar System? Well, in order to affect the wave, the beams would have to be comparable in energy, and if they're comparable in energy, then having them all clumped up in one spot would produce a similar effect to the wave itself and be very counterproductive. Simply station energy beams at various points throughout the System and have them converge at the incoming gravitational wave so that their effects are localized there, very far away from us.

With enough energy and precise timing, what happens is that the Solar System can be made to fit inside one of the interference fringes and doesn't feel anything from the gravitational wave. Most of the wave's energy is diffracted outwards, so anyone behind us is still screwed, but honestly we just saved an entire species with a Solar System-sized Death Star so... Still, on astronomical distances, the Solar System will easily fit inside the gravitational wave's interference fringe, so that on either side of us will be Sun-destroying mind-bogglingly-powerful gravitational radiation while everything from Pluto to Mercury will be calm and safe.

Just get out of there

All other options be damned, in order to be aware of the inbound catastrophe our savior civ has to be capable of FTL travel, so they can - as a last-ditch effort to save Humanity - load everyone onto a space yacht and book it away from the Solar System.

Certainly not ideal, but hey, at least Humanity survived.

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  • $\begingroup$ What level of "safe" would the bubble likely give? When I did a bit of searching earlier I saw that gravitation waves do pass through earth somewhat routinely (although much weaker than these ones) so would it comparable to those or still much stronger? $\endgroup$
    – Informer
    Mar 25 at 13:04
  • $\begingroup$ If the Alcubierre drive is powerful enough, it would be destabilized by the incoming GW instead of allowing much of it through; the energy density around the edge of the warp bubble would have to be changed to account for the GW, but what it allows the savior civ to do is to take the excess GW energy from one end of the warp bubble and deposit it at the other end to keep the bubble stable and to disperse the GW. If transfer is sufficiently fast, the GW can be circumvented entirely (also assuming enough energy to activate so huge a warp bubble). [Good point, I'll edit my answer!] $\endgroup$ Mar 25 at 13:07
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The super-aliens just negate the whole wave with a counter-wave offset by pi. The whole thing is just a one-off mention to drive home how fragile and helpless humanity really is; humanity never even knew they were in danger. One of the aliens who is in communication with a human explains how they saved humanity from extinction that one time in the 70s when everybody felt dizzy for a quarter of a second and went on with their lives.

The super-aliens collect the whole solar system in a bubble and zap it off to the Endangered Species Reservation, a star cluster in the depths of intergalactic space reserved for star systems with life (not necessarily intelligent) that would be threatened by the intergalactic civil war. The intergalactic civil war was just a setup for getting humanity within a few light years of a few other intelligent technological civilizations and thousands of life-sustaining planets.

The super-aliens race against time to splice the string back together by diverting auxiliary power to the tetryon cascade dynamic manifold generator and routing the isometric flux through the pentatonic quantum dilithium matrix inverter after gathering the antiprotons emitted from the original string-rift. As a surprise twist, the antiprotons are intelligent energy creatures whose wellbeing must be taken into consideration, too. One of them has sex with super-alien Commander Riker.

Humans are on their own except for the help of one eccentric alien who tried to bring them a piece of technology that would allow them to go back in time and fight the super-powered aliens who approved Earth for destruction in 1999. Unfortunately, the alien's ship crash-lands and is found by five teenagers with attitude, who get sucked back in time and given special powers. They must now save the world using costumed karate, all while trying to blend in by attending late-90s American high school.

The super-aliens have the solution, and it's to bring the shiny macguffin to the other shiny macguffin. Unfortunately, the good super-aliens all have computer chips in their brains that make them incapable of violence, and there are bad guy aliens guarding the other shiny macguffin. It's up to Senior Chief Master Sergeant Lee Grizzle of the SAS and Captain Mollie Foxx of the US Air Force to lead simultaneous space-suited infantry and space fighter pilot assaults on the bad alien stronghold in this paperback military sci-fi banger published by Baen books.

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  • $\begingroup$ I wonder why the down vote? A 180-degree offsetting wave would work just fine (pi being the way to say that in radians). Maybe they were set off by the colorful answer! Frankly, I'm a fan. $\endgroup$
    – JBH
    Mar 25 at 23:36
  • $\begingroup$ Not sure myself - this is a list of valid answers, I particularly enjoy the one involving zipping the entire star system away, it would be fun to watch scientists panic for eight seconds while they lose track of all the constellations - xkcd.com/2469/ $\endgroup$ Mar 26 at 0:09
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So... my answer assumes you have the ability to displace black hole equivalent gravity lenses into space. So no worries, eh?

The idea is basically phase-array antenna. They can redirect waves, bundle them into a direction- and thus calm other directions down.

https://www.youtube.com/watch?v=2i293tUjYbI

Now think about black holes, bending the wave around them, distorting them, delaying them, amplifying them by overlaying them. If you place a ton of black holes in the right path- you should be able to redirect the gravitational tsunami towards another direction.

https://en.wikipedia.org/wiki/Phased_array

Is this realistic? Is this a useful answer? Do i misunderstand the gravity of the situation?

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Our current understanding of gravity is that there isn't a way to shield or mitigate it. So no, you they are not going to neutralize the gravity wave without using any fictional scientific principles. The only way would be to escape it. Which would require faster-than-light travel. Another thing that would require fictional scientific principles to make work.

But you didn't flag this question as "science-based", so you can simply make something up that fits the requirements of your plot.

For example:

  • An "anti-gravity counter-wave" that cancels out the gravity wave headed for Earth and is timed to arrive at the exact same time.
  • A "gravity shield" that protects the solar system from the gravity wave
  • Shift the solar system into a parallel universe for a day while the gravity wave moves by
  • Time-travel the solar system a day into the future so it skips the time when the gravity wave is traveling through it
  • Time-travel back into the past to prevent the aliens from breaking the cosmic string
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