Destroying a star

[factotum]

That page you linked to is also using Kepler's Third Law, like I did, but it notes this near the bottom of the first section:

"The time to traverse half the distance R, which is the infall time from R along an eccentric orbit, is the Kepler time for a circular orbit of R/2 (not R), which is (1/32)1/2 times the period P of the circular orbit at R. For example, the time for an object in the orbit of the Earth around the Sun, to fall into the Sun if it were suddenly stopped in orbit, would be P / 32 {\displaystyle P/{\sqrt {32}}} P/{\sqrt {32}}, where P is one year. This is about 64.6 days."

I'm not sure I understand what that means, but it suggests my calculation was essentially correct but I used the wrong multiplication factor--so this is saying that our hypothetical Persephone would take 126.5 years to fall in with its orbital period of 716 years, still *way* longer than the timescale implied in the novel.

@halfeye: Kepler works just as well for circular orbits as for ellipses. The semimajor axis of a perfectly circular orbit is just its radius.

[DavidSh]

I'm not sure I understand what that means, but it suggests my calculation was essentially correct but I used the wrong multiplication factor--so this is saying that our hypothetical Persephone would take 126.5 years to fall in with its orbital period of 716 years, still *way* longer than the timescale implied in the novel.

If I remember the novel correctly, they had a couple of different methods for "immortality". So a war that takes centuries to resolve isn't ruled out.

[Traab]

If I remember the novel correctly, they had a couple of different methods for "immortality". So a war that takes centuries to resolve isn't ruled out.

Even so you have to admit, "GASP! We only have 126 years to stop our sun from exploding! We are all going to die!" Doesnt seem very.... likely.

[warty goblin]

Maybe I'm missing something, but if I can stop a planet, and want to kill everybody on a planet, wouldn't I just stop that planet?

[Mechalich]

Maybe I'm missing something, but if I can stop a planet, and want to kill everybody on a planet, wouldn't I just stop that planet?

Range.

Again, the 'dark forest' hypothesis for alien relationships requires that species be able to destroy each other immediately upon detection. The central idea is that if it becomes known that some sapient species exists around a star they will be destroyed as soon as the speed of light permits said destruction to occur. However, depending upon how far away you are a planet may well be invisible no matter how good your instruments, but the star's position is quite obvious. So you attack the star.

[Aeson]

Maybe I'm missing something, but if I can stop a planet, and want to kill everybody on a planet, wouldn't I just stop that planet?

I'm not familiar with the story in question, but I'd think that the people who lived on the planet might be able to do something about that - sounds to me like the story essentially has somebody strapping a giant rocket to the planet and then firing the rocket in such a manner as to cancel out the planet's orbital velocity and maybe give it a push towards the sun, which might be the kind of thing that you can't really do in the face of organized opposition.

[factotum]

The giant rocket in question was using the atmosphere of the gas giant as fuel. It wouldn't really be possible to do that on a habitable planet. (OK, realistically it wouldn't be possible in a gas giant either because regular hydrogen is actually really, really difficult to fuse into helium, but it's less of a stretch than trying to fuse *oxygen*).

[warty goblin]

Range.

Again, the 'dark forest' hypothesis for alien relationships requires that species be able to destroy each other immediately upon detection. The central idea is that if it becomes known that some sapient species exists around a star they will be destroyed as soon as the speed of light permits said destruction to occur. However, depending upon how far away you are a planet may well be invisible no matter how good your instruments, but the star's position is quite obvious. So you attack the star.

It seems to me that if you can launch a projectile at a star from across interstellar space, you can launch something that has an antenna hooked up to a computer that does a little bit of processing and aims at the planet with all the radio signals. Hell, launch a lot of them; rendering a planet utterly uninhabitable requires a lot less oomph than blowing up a star. Add a bit of coordination between your projectiles, and you can probably smash every reasonably large rocky body in the system into a twisted hellscape. Compared to the tech level necessary to fire a weapon between solar systems in the first place, this seems like kindergarten level stuff.

[Tvtyrant]

I've been saying for years that science fiction is dead. There's only space fantasy now.

I think the reason is that once upon a time we were more optimistic about the possibility of space travel. It is increasingly obvious we aren't leaving, and things that were science fiction are now clearly impossible.

[Mechalich]

It seems to me that if you can launch a projectile at a star from across interstellar space, you can launch something that has an antenna hooked up to a computer that does a little bit of processing and aims at the planet with all the radio signals. Hell, launch a lot of them; rendering a planet utterly uninhabitable requires a lot less oomph than blowing up a star. Add a bit of coordination between your projectiles, and you can probably smash every reasonably large rocky body in the system into a twisted hellscape. Compared to the tech level necessary to fire a weapon between solar systems in the first place, this seems like kindergarten level stuff.

The ability to make effective course corrections while traveling at relativistic velocities is somewhat tricky. But yes, it is still probably viable to kill the planets with a proper engineering fix and requiring far less overall energy expenditure, but Cixin Liu needed stars to blow up as part of a plot point in The Dark Forest that blowing up planets wouldn't have fulfilled, so he blew up some stars.

I think the reason is that once upon a time we were more optimistic about the possibility of space travel. It is increasingly obvious we aren't leaving, and things that were science fiction are now clearly impossible.

There's still plenty of science fiction being written, much of its quite good. Heck, The Martian was written only a few years ago. It's just not as popular or perhaps as approachable as it used to be. Science fiction of the mid to late 20th century mostly focused on questions related to changes in the human condition that might be produced by macro-engineering technologies, of which space flight was merely the most prominent. However, recent development has moved toward micro-engineering products such as information technology and biotechnology and all their implications. These offer the potential to change the human condition on a considerably more fundamental level than the old technologies, and a considerable portion of the potential audience reacts to these possibilities with distaste and trepidation.

For example, it is still quite possible that we will go to the stars, but it's becoming fairly clear that if we do so it won't be as flesh and blood entities. Instead it will be as brains in jars or digital people or perhaps it will be our AI creations that inherit the cosmos. This sort of thing appears to be far less appealing than tales of heroic daring by otherwise recognizable humans in the 'final frontier.' The accessibility level of something like Greg Egan's Diaspora is much, much lower than Star Trek, even though both are ultimately about exploring the cosmos and seeking to solve its mysteries.

[Excession]

Blowing up a planet does not stop a space-faring civilisation from shooting back. In fact it pretty much guarantees that they will try to. The trick then is changing a single relativistic projectile into something that scorches the whole system. You don't want to miss a few asteroid habitats, or you'll be facing return fire in a few centuries.

The idea, it seems, is to hit the star hard enough, and in the right way, to stop fusion in the core briefly. The outer layers of the star will then start falling inward. By the time fusion restarts the inertia of those layers means it will start big. The resulting nova then cleanses the whole system for you.

On the bright side, if this was happening I suspect we would see it. The explosion would be bright, but noticeably smaller than we could explain with physics.

[factotum]

For example, it is still quite possible that we will go to the stars, but it's becoming fairly clear that if we do so it won't be as flesh and blood entities.

That's been fairly clear ever since Einstein formulated his theories of relativity more than a century ago now. Any time an SF writer invoked hyperspace, warp drive, wormholes or whatever they're using something known to be impossible. I think this is why the likes of the Expanse is set entirely within the Solar System, because that's more realistic (even if it requires impossibly efficient fusion drives to make the whole thing work).

[Chen]

That's been fairly clear ever since Einstein formulated his theories of relativity more than a century ago now. Any time an SF writer invoked hyperspace, warp drive, wormholes or whatever they're using something known to be impossible. I think this is why the likes of the Expanse is set entirely within the Solar System, because that's more realistic (even if it requires impossibly efficient fusion drives to make the whole thing work).

Warping space (say via wormhole or Alcubierre metric) still presents theoretical possibilities for faster than light travel.

[Tvtyrant]

Warping space (say via wormhole or Alcubierre metric) still presents theoretical possibilities for faster than light travel.

So does time travel if it is possible. Go back in time, space moves back as far as it was, move a bit, move forward in time to when the thing you want to get to will be there.

[factotum]

Warping space (say via wormhole or Alcubierre metric) still presents theoretical possibilities for faster than light travel.

Any actual FTL travel, regardless of the means it is achieved, is not possible per Relativity because it would then be possible to set up a reference frame in which causality was violated (e.g. the cause of an event occurs after said event).

[Radar]

Any actual FTL travel, regardless of the means it is achieved, is not possible per Relativity because it would then be possible to set up a reference frame in which causality was violated (e.g. the cause of an event occurs after said event).

Not quite: causality will still work just in a way that makes you have a headache. There are even publications explicitly solving simplified versions of grandfather paradox for example (ball is thrown into a wormhole and hits itself off the course so it never enters the portal in the first place). Those situations only show that you cannot find the solution in an iterative manner but they still exist. Worse yet: one of the most elegant interpretations of quantum electrodynamics requires you to consider antimatter as regular matter moving back in time and in this case virtual particles are simply ontological loops (they exist, because they made themselves exist in the past).

[HandofShadows]

That's been fairly clear ever since Einstein formulated his theories of relativity more than a century ago now. Any time an SF writer invoked hyperspace, warp drive, wormholes or whatever they're using something known to be impossible. I think this is why the likes of the Expanse is set entirely within the Solar System, because that's more realistic (even if it requires impossibly efficient fusion drives to make the whole thing work).

Um, you do know that the Expanse has branched out into other star systems using alien created wormholes, right?

Not quite: causality will still work just in a way that makes you have a headache. There are even publications explicitly solving simplified versions of grandfather paradox for example (ball is thrown into a wormhole and hits itself off the course so it never enters the portal in the first place). Those situations only show that you cannot find the solution in an iterative manner but they still exist. Worse yet: one of the most elegant interpretations of quantum electrodynamics requires you to consider antimatter as regular matter moving back in time and in this case virtual particles are simply ontological loops (they exist, because they made themselves exist in the past).

Some of the tests they have been doing with the double slit experiment have really been playing games with quantum physics (even worse than normal). The Delayed Choice Double Slit experiment gave results that the particles acted as if they were being observed before they actually were observed. (Result of an action being taken before action the action took place.) The Delayed Choice Quantum Eraser Double Slit gave results that indicate the particles "chose" the path they took after they ended the journey. No such thing as time?

[Forum Explorer]

No such thing as time?

I'd believe that. I mean, everything we use to observe time is just motion and/or entropy.

[Kaptin Keen]

I'd believe that. I mean, everything we use to observe time is just motion and/or entropy.

Obviously, there is such a thing as time. Only the term we use to describe it - 'time' - doesn't describe seconds and hours, but rather motion, entropy, our accumulation of memories and the inexorable march towards becoming fertilizer.

[sktarq]

Some of the tests they have been doing with the double slit experiment have really been playing games with quantum physics (even worse than norma)... The Delayed Choice Quantum Eraser Double Slit gave results that indicate the particles "chose" the path they took after they ended the journey. No such thing as time?

Step two technology technology test for the infinite probability drive IMO.

Step one being hot tea.


As for destroying a star. Compressed star plasma is phenomenally dense....like slows light down to the point of taking 10K years to make it the radius of our sun distance (very very not a straight line).
Hiting it with a relativistic object could make a powerful energy event at the surface of the star which could well mess up civilizations, but unless your object is, say a black or brown dwarf I'm not seeing how that would work.

[Forum Explorer]

Obviously, there is such a thing as time. Only the term we use to describe it - 'time' - doesn't describe seconds and hours, but rather motion, entropy, our accumulation of memories and the inexorable march towards becoming fertilizer.

I suppose the question is; is there a difference between time and the motion of particles? All of the physical changes in the world seem to ultimately boil down to particles being in different locations and/or types.

[GloatingSwine]

You fool. You insolent coward. The only way to kill a star simply and quickly is to maneuver a Cosmic Candle Snuffer into place, and the star's fires will run out of oxygen.

I mean you're not actually wrong.

If you could introduce a sufficient mass of iron into a star you'd interrupt the fusion process and it would go out (quite violently).

Of course "a sufficient mass" would be ~8 times the mass of the star (for a main sequence G class like our sun).

[Chen]

I mean you're not actually wrong.

If you could introduce a sufficient mass of iron into a star you'd interrupt the fusion process and it would go out (quite violently).

Of course "a sufficient mass" would be ~8 times the mass of the star (for a main sequence G class like our sun).

I guess if you put enough 9s in your fraction of light speed you could get an object's mass that high....course if you could actually do that presumably you have much simpler ways of destroying a civilization.

[Lord Torath]

Of course "a sufficient mass" would be ~8 times the mass of the star (for a main sequence G class like our sun).

A you sure about that being 8 solar masses of iron required to shut down fusion? I'm pretty sure if you gathered only 3 solar masses of iron into a sphere you'd have a black hole in short order, without the need to introduce it to a star.

Edit: Wikipedia tells me the maximum mass for a neutron star is only 2.16 solar masses. Anything more than that will collapse into a black hole unless it's got fusion (or something else) going on in its core to provide enough energy to prevent it.

[Sermil]

So I've been reading Cixin Liu's Rememberance of Earth trilogy (The Three Body Problem, The Dark Forest, Death's End) and was wondering about some of the science in it.

At several instances in the trilogy extremely high veloctity objects are used to destroy stars (and the planetary systems around them). Essentially extremely fast relativistic kinetic kill vehicles, but targetted at the solar system's stars rather than a planet directly. It mentions when one of these objects impacted the star it "tore a hole through the photosphere and the convection zone" that was ~50k km in diameter. In the end it resulted in lower pressure in the core (stuff was being expelled from this "hole") and eventually lead to collapse and stellar explosion.

I'm wondering if this is actually what would happen? Is it just somewhat technobabble or could it really occur?

At a basic level, all stars are trying to destroy themselves constantly. They're not finely-tuned machines, they're completely chaotic messes of gas and plasma that are forced into their current shape by the fact that even the ridiculously high energy fluctuations of a stellar core can't get over the energy barrier to a different state.

So to really, significantly change what a star looks like is going to require energy levels and/or mass at least on the same order of magnitude as the stellar output. Even Jupiter is only 1/1000 of the Sun's mass; you'd either need something far larger than Jupiter using gravity, or you'd need an accelerator that had solar-levels of energy inputs.

[rcom12]

At a basic level, all stars are trying to destroy themselves constantly. They're not finely-tuned machines, they're completely chaotic messes of gas and plasma that are forced into their current shape by the fact that even the ridiculously high energy fluctuations of a stellar core can't get over the energy barrier to a different state.

So to really, significantly change what a star looks like is going to require energy levels and/or mass at least on the same order of magnitude as the stellar output. Even Jupiter is only 1/1000 of the Sun's mass; you'd either need something far larger than Jupiter using gravity, or you'd need an accelerator that had solar-levels of energy inputs.

After they self-destruct, where are the pieces? Are they still in the universe?The latter fell to earth.

[Yora]

Exploding stars turn into an enormous cloud of gas that expands and becomes thinner as it spreads out until it's barely detectable. The core of the star remains behind as either a white dwarf, neutron star, or black hole, depending on how much mass it has.
When the star explodes in a supernova, it also converts a significant amount of mass into pure energy in the form of an extremely bright flash of light.