## Ideal balance of two bodies in orbit

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Aikanaro
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### Ideal balance of two bodies in orbit

Question tied to a complicated issue I've never been quite able to wrap my head around..

Hypothesis: For any two complicated bodies you could create in an otherwise empty universe, there is at least one hypothetical "perfect" combination of distance and relative speed which would allow them to maintain perpetual orbit.

True or false?
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Zohar
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### Re: Ideal balance of two bodies in orbit

In classical physics the answer is definitely yes - choose a large enough distance between the two objects and you can push them quickly enough to orbit each other. I don't know about the general relativity calculations for orbital mechanics, but you can read about them here.
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Aikanaro
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### Re: Ideal balance of two bodies in orbit

Okay, so next question: What if one of the bodies is a planet that contains a lot of oceans? Orbital balance is still possible, right?
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doogly
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### Re: Ideal balance of two bodies in orbit

No, they'll slosh energy away and decay. If you want to go to infinity, you need symmetric perfection. Fluids are not forever.
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Zohar
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### Re: Ideal balance of two bodies in orbit

Also oceans imply liquid water, which adds limits on temperature, gravity, atmosphere, possibly a magnetic field (to keep said atmosphere so water doesn't evaporate), etc.
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Aikanaro
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### Re: Ideal balance of two bodies in orbit

What form will the energy take? Thermal? And couldn't the decay be countered by placing the balance either slightly closet or further?
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Zohar
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### Re: Ideal balance of two bodies in orbit

The energy will dissipate into heat, yes. And no, the system will lose energy no matter how you place it.
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Sandor
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### Re: Ideal balance of two bodies in orbit

Zohar wrote:In classical physics the answer is definitely yes - choose a large enough distance between the two objects and you can push them quickly enough to orbit each other. I don't know about the general relativity calculations for orbital mechanics, but you can read about them here.

See also gravitational waves, which will radiate away from any pair of orbiting bodies, causing them to lose energy and (very slowly) spiral in.

doogly wrote:
Aikanaro wrote:Okay, so next question: What if one of the bodies is a planet that contains a lot of oceans? Orbital balance is still possible, right?

No, they'll slosh energy away and decay. If you want to go to infinity, you need symmetric perfection. Fluids are not forever.

Most of the energy loss will be due to tides. If the two bodies are 1:1 tidally locked to each other (so the same sides are always facing each other), losses due to "sloshing" will be much less.

To expand on "fluids are not forever": for two bodies in an otherwise empty universe, there is no background radiation. The two bodies will be forever radiating away thermal energy, so will be getting closer and closer to absolute zero. In the end everything will end up frozen, and there won't be any oceans.

eternauta3k
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### Re: Ideal balance of two bodies in orbit

Conservation of orbital angular momentum would give you a lower bound for the distance between two rigid bodies. However, I'm not sure that orbital angular momentum is actually conserved here (maybe the bodies torque each other and turn orbital into spin).
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Tal-Seto
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### Re: Ideal balance of two bodies in orbit

The energy-density of two rotating bodies is far too low for a wave.

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### Re: Ideal balance of two bodies in orbit

Ooops! Sorry for inconveniece. This was a side effect from a replay to the past. If you encounter some other artifacts, ignore it.

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Tal-Seto
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### Re: Ideal balance of two bodies in orbit

SCNR
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Tal-Seto
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### Re: Ideal balance of two bodies in orbit

Gravity waves? What sort of thing should that be? What should there "waving"?

What is a wave?

P.S.:
Trust me, the higgs-boson is a hoax.
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gmalivuk
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### Re: Ideal balance of two bodies in orbit

Ah, wonderful. A crackpot.
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Zohar
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### Re: Ideal balance of two bodies in orbit

Tal-Seto wrote:P.S.:
Trust me, the higgs-boson is a hoax.

OK, I'll trust you! You definitely convinced me!
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Tal-Seto
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### Re: Ideal balance of two bodies in orbit

gmalivuk wrote:Ah, wonderful. A crackpot.

With a perfect explanation =:)
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Tal-Seto
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### Re: Ideal balance of two bodies in orbit

And i have some background-info.

The book "Knaur's Buch der modernen Physik"  in a edition of the early seventies, together with some lecture about the history of science, points to my conclusion.

...while i'm thinking about it, my explanation is completely without math.
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Zohar
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### Re: Ideal balance of two bodies in orbit

That's very impressive. Astounding that so many physicists in the past fifty years have overlooked this. Surely you've published your results and received professorship offers from multiple universities!
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gmalivuk
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### Re: Ideal balance of two bodies in orbit

Tal-Seto wrote:
gmalivuk wrote:Ah, wonderful. A crackpot.

With a perfect explanation =:)

If you posted a picture of a horse and I responded, "Oh look, a horse," would you also complain about the lack of explanation for my statement?
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Copper Bezel
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### Re: Ideal balance of two bodies in orbit

I think they meant that they have an explanation, which they're promoting someone to ask for.
So much depends upon a red wheel barrow (>= XXII) but it is not going to be installed.

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WibblyWobbly
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### Re: Ideal balance of two bodies in orbit

Gee, that's a shame. Anyone have any intention of doing that? No? OK, moving on.

Eebster the Great
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### Re: Ideal balance of two bodies in orbit

I think the problem with this thread is that it's supposed to be about gravity, but it tries to look at real world possibilities, in which everything else gets in the way. You wouldn't need orbiting bodies at all to see that stability is impossible. You could just have a block of cheese sitting in the vacuum, or whatever. Eventually it will evaporate. There isn't really any way around this. Everything evaporates. In the case of orbiting bodies, the vapor will produce drag. Also, the vapor cloud will eventually extend past the other body, thus reducing effective mass. So even in Newtonian physics, even with perfectly rigid and symmetrical bodies, you are going to have problems.

But if you throw all that out and just look at gravity, ignoring other physics, then sure, stable orbits are easily possible in Newtonian physics. In fact, almost all 2-body orbits are stable. The only way for them to be unstable is if both point masses are moving straight towards each other with no perpendicular motion at all, and they crash and form a singularity. Otherwise, you will end up with elliptical, parabolic, or hyperbolic orbits.

Tal-Seto
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### Re: Ideal balance of two bodies in orbit

gmalivuk wrote:
Tal-Seto wrote:
gmalivuk wrote:Ah, wonderful. A crackpot.

With a perfect explanation =:)

If you posted a picture of a horse and I responded, "Oh look, a horse," would you also complain about the lack of explanation for my statement?

Ok, i need a explanation of the principles of a wave from wich i go further.
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Copper Bezel
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### Re: Ideal balance of two bodies in orbit

I don't think anyone's asking that of you, Tai-Seto.
So much depends upon a red wheel barrow (>= XXII) but it is not going to be installed.

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gmalivuk
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### Re: Ideal balance of two bodies in orbit

Tal-Seto wrote:i need a explanation of the principles of a wave

https://en.wikipedia.org/wiki/Gravitational_wave
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Tal-Seto
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### Re: Ideal balance of two bodies in orbit

gmalivuk wrote:
Tal-Seto wrote:i need a explanation of the principles of a wave

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

TL;DR
I suppose you know what you talking about.

I need only a brief explanation of the principles of a wave just to make sure we talk about the same.

At the moment, i won't give such an explanation to avoid manipulation.
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Eebster the Great
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### Re: Ideal balance of two bodies in orbit

This isn't a game where we try to trick you into saying something stupid. This is a thread where nobody is really waiting to here about your brilliant idea because nobody cares and that isn't the subject of the thread.

Tal-Seto
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### Re: Ideal balance of two bodies in orbit

It's not that i think someone here will manipulate my explanations.
It's because of a third person can't argue i manipulate your point of view in my explanation. Yes, i will change it, but don't manipulate.

The math in the standard theory reminds me to an chess- game against a computer, while the operator of the computer is arguing that computers somtime in the future evolve a bigger intellect than a human.

You can't argue thru such an concrete-wall of counting power.

You must communicate directly with the operator because he is ignoring the fact that he must set up the computer to do what he want.

My thoughts are based on a data set wich most of the interestet non-experts are able to recognise.
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gmalivuk
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### Re: Ideal balance of two bodies in orbit

Put up or shut up.

Just get to whatever point you want to make, or stop wasting database space with these posts that don't actually say anything.
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