Why do Planets have elliptical orbits ,AND

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Discussion Overview

The discussion revolves around the nature of planetary orbits, specifically why planets have elliptical orbits instead of circular ones, and the implications of dark matter and dark energy on the universe's expansion. Participants explore concepts related to gravitational forces, energy, and momentum in the context of celestial mechanics and cosmology.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant compares the solar system to a marble rolling on a rubber sheet, questioning whether planets will eventually clump together or be thrown into space.
  • Another participant states that the orbits of planets are primarily circular, with Mercury being an exception, attributing this to the energy and momentum of the planets at formation.
  • Some participants suggest that gravitational interactions between neighboring planets influence whether orbits are circular or elliptical.
  • There is a discussion about the acceleration of the universe's expansion, with some noting that it should slow down if only ordinary matter is considered, but dark matter and dark energy complicate this view.
  • Several participants express uncertainty regarding the nature of dark matter and dark energy, with one mentioning various hypotheses about dark matter and the lack of understanding surrounding dark energy.
  • A participant mentions that true circular orbits are unstable and can become elliptical due to perturbations from other objects or solar tides.
  • Another participant introduces the dark fluid theory, proposing a link between dark matter and dark energy.

Areas of Agreement / Disagreement

Participants express a range of views on the nature of planetary orbits and the role of dark matter and dark energy. There is no consensus on the explanations for elliptical orbits or the properties of dark matter and dark energy, indicating multiple competing perspectives and unresolved questions.

Contextual Notes

Some claims depend on assumptions about gravitational interactions and the nature of dark matter and dark energy, which remain poorly understood. The discussion reflects ongoing debates in astrophysics without definitive conclusions.

gttjohn
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why do Planets have elliptical orbits ,why do they just not have circular orbits ,I understand that the sun is like a bowling ball on a sheet of rubber and the planets in our solar system orbit the bowling ball as if i got a marble and rolled it onto the sheet of rubber but after a while the marble would have a circular orbit ,are we still at the stage where the marble was just thrown onto the rubber sheet ,and will we eventually all clump together towards the sun and burn up or will the sun eventually loose its gravity and we will be thrown into outer space


also why is the universe accelerating should it not be slowing down as the energy from the big bang looses strength
 
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Sorry all i have just looked at the two stickys above my post but in laymans terms they are impossible for me to understand
 
It just depends on the energy and momentum the planets possessed when they formed.
But they actually all have orbits which are very close to being circular, except for Mercury.

And yes, the expanse of the Universe *should* be slowing down if we only consider ordinary matter.
But there is also dark matter (and dark energy) to take into account, and that's what is causing the expansion of the Universe to accelerate.
Why, we do not know.
 
Some planets have circular orbits while some have elliptical orbits based on the grvitational forces that exit between the neighbring planets. Planets that are strong enough to exceed the gravitaional pull of a planet with follow a circular path unlike a plat that is to weak to exceed the gravitational force between another plaet will fall out and follow an elliptical orbit
 
thankyou
 
do we know what dark matter and dark energy is yet
 
I dare say we don't have a clue.
 
gttjohn said:
do we know what dark matter and dark energy is yet

We have some hypotheses for what dark matter is, such as axions, WIMPs and other exotic particles, such as scalar particles and axinos, but experimentally we aren't sure which is correct, WIMPs and axions are the most looked for thus far, and we have reasonably well known upper limits on density and mass for these as a result. It is also possible that the mechanics of large objects behave differently at large scales, which is called MOdified Newtonian Dynamics, or MOND however it doesn't apply itself particularly well to forming large scale structures, of the order of galactic clusters or larger.

Dark energy is completely unrelated to dark matter, but is named similarly due to the fact we don't know what it is, and thus it is 'dark', as far as I am aware, there is very little known about what dark energy actually is, which is a bit frustrating seeing as dark matter makes up about 71% of the Universe.
 
IIRC, a true circular orbit is unstable to perturbation: Any third-object interaction, or even solar tides, will make the orbit slightly elliptical...
...
IMHO, that exasperating ~70% of dark matter may be revised downwards as more galaxies are found to have larger, dusty halos and thrice the expected number of red-dwarf stars. If we're looking for super-sym particles etc, we're into 'new physics' so, like finding neutrinos *do* have non-zero rest mass, it could up-end a lot of theory...
 
  • #10
Those solar tides and or even third object interactions i agree wiould cause the orbit to become slightly elliptical but isn't that the same as saying the gravitational pulls of oter forces, particularly other planets?

and what is non-zero-rest mass anyway?
 
  • #11
Vagn said:
Dark energy is completely unrelated to dark matter

what about the dark fluid theory?
doesnt it propose that Dark Matter and Dark Energy are not separate physical phenomena but that they are linked together.
 
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