Now, I am not a physisist... can't even spell the word, but last night, something occured to me.

The universe, by modern standards, is what, 4.6 billion years old, correct? If that is the case, why is it we still have planets?

This is what I was thinking about...

There are two things keeping our solar system together: the sun's gravity, and the speed of which the planets revolve around the sun. The planets try to move in a straight line, but the gravitational pull of the sun keeps pulling them back in (thus, an orbit). The speed of the planet keeps it moving away, but the pull keeps it in place. But what I don't understand is this:

Every day, a planet looses a bit of it's momentum, due to the effect of the sun pulling on it, right? But at what point would the planet loose enough forward momentum to counter the sun drawing it in?

Then I pictured our solar system as a great big whirlpool. The innermost planets move faster than the outer... as would be expected with the sun's gravity. The sun's pull is drawing the inner planets in faster and faster, creating the downward spiral, whereas the outer planets are barely effected.

Which then makes me think, foolishly or not, why we still have planets.

Wouldn't the inner planets have been drawn in while the outer escaped?

It's amazing what being outside all day, coupled with lack of sleep, can do to one's mind...

Any thoughts?

Actually
the universe is thought to be at least 12 billion years old.. the earth alone is 6...
It's either the universe or the solar system that is 12 billion years old... probably the former

The planets dont lose momentum, they are still technically accelerating (Velocity is a vector function, and as such, a change indirection means acceleration), so they are still accelerating and as such, they continue to have an increase in momentum

some outer planets do escape, scientists have found them floating around in space, star-less
it has however, been postulated that they do get sucked in and absorbed by the sun, it is speculated by some that there was a planet to which this happened in our solarsystem... There's a thread called The Fifth Planet somewhere

Lol, there's a reason why you're not a physicist. The current age of the universe is estimated to be at AROUND 14 billion years old. The earth is estimated to be around 4.6 billion. No, the planets do not get sucked in to the sun, lol.

Originally posted by soothsayer
But hey, I could of used the religious number of... what was it... 4000 (?) years old.

oops! that would be 6000 years

Originally posted by Kano
A larger cause for the Earth to be moving away from the sun is because the sun's mass is shrinking as it burns off its fuel. Don't panic though, even this isn't a particularly large effect.

Yeah... and it takes billions of years before sun "cookes" earth so there's still plenty of time.
Unless mankind self-terminates itself or "cosmic billiard" throws "planet killer" to collision course.

That's right. If I'm not wrong, and obviously if there is no big collision, earth can still safely rotate around the sun in similar conditions as today for several billions of years. So no panic needed. I'm sure by then, if something will happen, we would have been able for ages to move to a better place...

To answer your question, no, the earth is not slowing down. It will not slow down unless acted upon by an outside force i.e. a collision, another stars gravitation, etc. This is because there is no friction in a vacuum, which space is. If a car and a feather were placed in a vacuum with a gravitational force pulling down, both would fall at the same rate.

STREPULSION-PHYSICS:
I have gone through the website www.srepulsion.com and also followed Nasa-Ads on strepulsion-Physics. I feel -one to four centuries old theories and laws of Galileo,Newton and Einstein need major corrections and modifications. Newton's law of Gravitation is no more universal. The sun and stars exerts Stellar Termonuclear Repulsion force in short STREPULSION-FORCE(SRF), not gravitation. Gravitation is limited to nonstellar bodies as planets, which are free from thermonuclear reaction. In the solar system, the sun exerts REPULSION while planets exerts Gravitation. So planets neither fall into the sun by gravitation nor flungaway by Repulsion. Both reverse forces counterbalance each other at orbital distance. So planets remain in orbit. If the sun realy exerted gravitation - all planets and satellites should have collepsed into the sun billions of years ago. This is because mass of the sun is 99.9% of the solar system.The existence of system proves the sun exerts REPULSION,not gravitation. Stellar mass under thermonuclear reaction converted into radiating energy(20%)that is in form of light and heat and rest 80%mass converted into Stellar thermonuclear Repulsion force. So active force exerted by the sun and stars is REPULSION, NOT GRAVITATION.
The universe is balanced by REPULSION and GRAVITATIONAL FORCES and in spherical motion by Retraction or REVOLTATION force which is generated by interaction of Repulsion and gravitation.SORLOD SPACE SYSTEM (SSS) is new space navigational system under Strepulsion-Physics
having strength to lead present space programs ahead by a century. Strepulsion and Revoltation forces are discovered by Dr.Navinchandra K.Shah and Prof.pankaj N.Jain of Hubli 580020,India and Strepulsion-Physics is established by the same scientists.

Prof.John N.Wills, E-mail: astrophysics@rocketmail.com, Indiana,USA.

Originally posted by Soylent Green Is People
The stuff that makes up our 4.5 Billion year old solar system HAD to have come from an ancient star (or stars) that exploded long before our solar system existed.

It also means that all of us are made from 'star dust'

and, ultimately, we will also end up as stars/star dust once again.