Hi Pop Worlds

[EDG]

A planet is a planet because it's a large solid or gaseous body that isn't big enough to ignite as a star. None of which has any particular relevance to whether or not it can survive being moved from one orbit to another.

Thats not true at all, a planet is born from a build up in Mass,
Mass = Garvity, hence drawing more Mass, which creates more gravity,
rinse and repeat until, bingo, one planet sized body,

If a body does not have enough mass, then it does not have enough gravity to ignite as a star,

Stars are born the same way, but just get to harvest more mass at birth,

Um... hello? Planetary scientist here. Mass does not "equal" gravity. Gravity is related to mass (and radius). They are not the same thing - if you think that they are then you are mistaken.

What you said later is correct - planets form by accreting mass, and as the accreted core gets more massive it can pull in more material due to its increased gravity (and then it stops growing when it runs out of material that's within range).

But none of what I said was "not true at all". The reason an object is a planet and not a star is because it's not massive enough to be a star.

 

[GypsyComet]

A planet is a planet because it's a large solid or gaseous body that isn't big enough to ignite as a star. None of which has any particular relevance to whether or not it can survive being moved from one orbit to another.

Thats not true at all, a planet is born from a build up in Mass,
Mass = Garvity, hence drawing more Mass, which creates more gravity,
rinse and repeat until, bingo, one planet sized body,

If a body does not have enough mass, then it does not have enough gravity to ignite as a star,

Stars are born the same way, but just get to harvest more mass at birth,

You do realize you're arguing with an astrophysicist, right?

 

[DPSteve]

A planet is a planet because it's a large solid or gaseous body that isn't big enough to ignite as a star. None of which has any particular relevance to whether or not it can survive being moved from one orbit to another.

Thats not true at all, a planet is born from a build up in Mass,
Mass = Garvity, hence drawing more Mass, which creates more gravity,
rinse and repeat until, bingo, one planet sized body,

If a body does not have enough mass, then it does not have enough gravity to ignite as a star,

Stars are born the same way, but just get to harvest more mass at birth,

You do realize you're arguing with an astrophysicist, right?

Shhh. . . . It's getting good *munches on popcorn*

 

[EDG]

He does need to go read some physics and astronomy texts - oaty's understanding of mass, gravity and inertia is rather... flawed. I just noticed he was posting in the artificial grav thread and corrected him there too (and others have as well).

Which is OK, obviously people can have misunderstandings about this sort of thing. Hopefully we've cleared them up for him though.

 

[Tobias]

In my opinion, something more interesting than Ringworlds or Dyson Spheres would be to move planets into shared orbits.

At TLs close to the OTU, this is bound to be just as economically unfeasible as a ringworld is, if not more. Drive systems are expensive.
Furthermore, it's an incredible waste. Constructed habitats are a far better solution because you get a lot more surface area per mass unit.

The bottom line is that even if population pressure were a problem, such methods of solving it would need to be cheaper and more feasible than a) building artificial habitats from readily available materials and b) colonizing other planets.

 

[rust]

The bottom line is that even if population pressure were a problem, such methods of solving it would need to be cheaper and more feasible than a) building artificial habitats from readily available materials and b) colonizing other planets.

Yes, indeed. The only exception I could imagine would be a kind of "White
Elephant" built to demonstrate a civilization's "power", but such a costly
luxury would probably be extremely rare.

 

[Gaidheal]

No "He's a xxx, you know?", please? Appeals to Authority are a great big fail in terms of logic and argument. ;¬)

I second what EDG said about it being fine to not know things but don't argue endlessly when someone corrects you, without at least checking a standard text, please, maybe?

 

[Gaidheal]

I agree with you, rust, I think that sheer scale of the project would mean that in the OTU it is simpler to just colonize another planet, a lot of the time and then you start making artificial habitats around existing 'crowded' planets.

 

[captainjack23]

when you can use the Gas giant as fuel, and start from the idea that whatever happens to the GG is irrelevent. The fact that they are big (which of course I already knew ..... ) is used to advantage.

Can't really see how. Having read your summary (and the responses in the link that say it's pretty much impossible to get any decent acceleration to affect the GG's motion in a non-geological timescale), it's not going to work anyway.

Some of the posts, anyway. The second one, in fact . Because it assumes a drive with a paltry billion Newtons thrust. This project assumes Hyper Macro engineering just below a level with Dyson construction.

You basically burn up the gas giant, sure, but one of the last posts suggests a scenario where it could be done excessively in a century, less so for several centuries. ( a long time, but bit better than geological timespan, it seems to me...); plus, if one is willing to compltely evaporate the GG and tolerate all the assorted problems with the exhaust, one can speed it up some.

That said, do you see any other reason that it wouldn't work ? Would there be significant tidal streses on the planet captured ?

 

[captainjack23]

I was just surprised that EDG didn't seem to be.

It helps if you don't assume that your readers know things that you know.
I'm not actually that familiar with Niven - all I've read is Ringworld and its first sequel. And some of his short stories (in Inconstant Moon).

Well, fair enough. But given that you were quite knowlegeably discussing Ringworld, and read a fair amount of SF , perhaps I can be forgiven....

And I did suggest googling it if you were curious.... 8)

 

[captainjack23]

I agree with you, rust, I think that sheer scale of the project would mean that in the OTU it is simpler to just colonize another planet, a lot of the time and then you start making artificial habitats around existing 'crowded' planets.

I think that that's where this discussion has gotten me, also.

 

[Oaty_bars]

Um... hello? Planetary scientist here. Mass does not "equal" gravity. Gravity is related to mass (and radius). They are not the same thing - if you think that they are then you are mistaken.

Gravity comes from Mass, the area of effect of that gravity is raduis

What you said later is correct - planets form by accreting mass, and as the accreted core gets more massive it can pull in more material due to its increased gravity (and then it stops growing when it runs out of material that's within range).

Hello!, thats what I said,

But none of what I said was "not true at all". The reason an object is a planet and not a star is because it's not massive enough to be a star.

Again, Hello?, and how does it acquire mass?
its the gravity that make the star
both in its mass and later ignition

Without the attraction of gravity, no Planet, no Stars,

 

[GypsyComet]

Would there be significant tidal streses on the planet captured ?

Depends on the time frame of the moving gravity field. Earth spins within the Sun's gravity field every day, and aside from all the water sloshing around (which is mostly the Moon's fault), the stresses on Earth are not all that obvious.

Moving a gas giant elsewhere in the system and letting the rest of the system adjust won't cause tidal issues, but orbits will shift, even if only in ways that would worry NASA and no one else.

Bring up a gas giant close enough to pluck the Earth out of its orbit and move it elsewhere and the results might be different, depending on how deep into the gas giant's pull you'd have to get the plucked planet before it followed the gas giant vs just being knocked around.

Tidal forces on a planet in non-orbital, non-rotational motion might be more direct. Blish's "Cities in Flight" does this. They "candle" the south pole and move all the populace north, since the oceans are quite literally heading south.

 

[EDG]

No "He's a xxx, you know?", please? Appeals to Authority are a great big fail in terms of logic and argument. ;¬)

Do you assume what your mechanic tells you is true if he tells you how your car engine just died (assuming you know nothing about cars)? He's an authority on the subject, not you. Logic and argument are all very well, but if someone wants to argue about a subject with someone who has had all the training and experience on the subject that they lack, then they're just wasting everyone's time.

"Appeals to Authority" doesn't mean that authority is infallible - it does however mean that they darn well know what they are talking about, so others would be well adviced to take note of what they say.

 

[EDG]

Gravity comes from Mass, the area of effect of that gravity is raduis

No. No no no no no. And again, no.

The "area of effect" where gravity has an influence is the gravitational field. The radius is merely the distance from the centre of mass.

Seriously, you need to read some physics books. Your understanding even of the basic concepts here is way off.

Hello!, thats what I said

Which is why I said it was correct .

Without the attraction of gravity, no Planet, no Stars,

I'm not disputing that at all. I don't know why you think I am, but you said that what I said was "not true at all" when it was actually very true and even in agreement with what you said.

 

[Gaidheal]

EDG - I don't engage in discussion with my mechanic, I take my car to him and satisfy myself of his credentials before I pay him for services. Your analogy is flawed and any appeal to authority is a waste of space and whilst it doesn't actually weaken a point, technically, it tends to shade the maker of that point in a rather poor light.

Arguing on a topic where you know next to nothing is a waste of time anyway, no matter with whom you argue.

In other words, don't make appeals to authority or indeed any other of a long list of wellknown and rightly derided rhetorical tricks and logical fallacies unless you want to be taken a lot less seriously by anyone but the naive and easily impressed.

All that said, I don't think you and I have an argument here, do we? Unless you want to be really picky about my shorthand equation of mass to gravity in contexts where there was no point exploring the inverse-square nature of the gravitational field?

 

[captainjack23]

Would there be significant tidal streses on the planet captured ?

<snip>.

Bring up a gas giant close enough to pluck the Earth out of its orbit and move it elsewhere and the results might be different, depending on how deep into the gas giant's pull you'd have to get the plucked planet before it followed the gas giant vs just being knocked around.

Yes. Thats the basic question I was hoping could be answered. Thanks for deciphering my posing .

I'm assuming that detatching the planet from the GG after moving it might be traumatic; and if so, probably too the grabbing ?

I don't know enough about this to answer either question.

 

[EDG]

In other words, don't make appeals to authority or indeed any other of a long list of wellknown and rightly derided rhetorical tricks and logical fallacies unless you want to be taken a lot less seriously by anyone but the naive and easily impressed.

*shrug*. I have a PhD in the subject. It took a long time to get it and I worked damned hard for it, so when the subject that I studied comes up in discussion here (because god knows it's hardly ever going to be relevant anywhere else ), I'll tell people that it's a field that I know a lot about. Whether they respect that or are impressed by that is up to them.

If someone comes along claiming they know better than I do about it, then I'll listen to them if they can cite relevant research to me (it's quite possible that I'm not fully up to speed on some things).

I don't expect people to be impressed by qualifications (be they mine or anyone else's), but I do expect them to at least pay attention to people who have qualifications in a subject. Maybe you listen to your mechanic only because you pay him, but the way I see it I'm spending a lot of time here giving away my very specialised knowledge away for free here when I explain stuff to people. I don't have to do that, I do it because I choose to. But I do expect people to listen to what I say and acknowledge that I may actually know better than them about the relevant topics.

If that sticks in peoples' craw, or if people mistake that for "arrogance" then sorry. I'm just confident in what I know.

All that said, I don't think you and I have an argument here, do we?

Nope .

 

[Gaidheal]

Heh, no you won't get flame from me for speaking with authority on a topic you know about (and I can understand being proud of the Ph.D. too, having only recently seen my then-girlfriend get hers after some really hard work and even tears, at times [mostly frustration with it all]), however, appealing to that authority rather than arguing a point from logic (which is what an appeal to authority is) will not cut it, even with a Ph.D.

I'm not saying you did that, I simply asked people to not do it, as you hopefully recall. It was you who then took that as something to shoot at, although I can understand why.

As for your, undoubted expertise, which you share here, well, I feel similarly and there comes a time when I simply ignore people who are not genuinely interested in benefitting from others and only address those whom I think might be.

I listen to my mechanic because I've already checked that his qualifications are sound and if what he says is plausible and seems reasonable, then I say "go ahead and do that then" - usually, he's already shown me what he is talking about (if yours doesn't, get a better mechanic) and I'm no idiot so I have a rough idea myself of what might need work. I then pay him when the job is done and I am satisfied. This is not the same as a board discussing cars where someone says "I am right, I know because I am a mechanic", that would be an appeal to authority and will cause me to say "So what? You've still failed to make a case for ... being ..."

 

[EDG]

Heh, no you won't get flame from me for speaking with authority on a topic you know about (and I can understand being proud of the Ph.D. too, having only recently seen my then-girlfriend get hers after some really hard work and even tears, at times [mostly frustration with it all]), however, appealing to that authority rather than arguing a point from logic (which is what an appeal to authority is) will not cut it, even with a Ph.D.

Gotcha. Sure, I mean, I'll definitely go more with the facts I present than just say "I have a PhD so listen to me". Problem is, people who don't know stuff about a subject can present themselves as being authoritative too (heck, you don't even know for sure that I really have a PhD , but I do).