# The Naked Scientists Forum

### Author Topic: Why do we orbit the sun if space is not flat?  (Read 2123 times)

#### acecharly

• Sr. Member
• Posts: 171
##### Why do we orbit the sun if space is not flat?
« on: 15/03/2012 22:58:32 »
Hi

Because the sun has such a large mass it creates a warp in spacetime which means we appear to be traveling in an elipse when were really traveling in a straight line through space that is curved.

I understand the above idea but im confused.

Ive seen a demonstration somewhere that showed a stretched out peice of rubber with a heavy ball representing the sun in the centre, whilst the dent in the rubber it made showed the warp in the surrounding space another smaller ball representing the Earth was pushed and for a short while it circles the pretend sun as you would expect.

This would only work if space like the rubber sheet were flat otherwise there would be just as much gravity at work pulling the space the opposite way as gravity works upside down aswell as all angles id have thought. I.e. imagine the gravity effects of the rubber sheet being upside down and it should cancel out  any warp. I hope this makes sense

Any Ideas would be great

Cheers
Ace

#### MikeS

• Neilep Level Member
• Posts: 1044
##### Re: Why do we orbit the sun if space is not flat?
« Reply #1 on: 16/03/2012 07:36:03 »
To visualize what is actually happening you would have to be able to see different gravitational gradients and different time dilation gradients.  This is not possible.  What we can do is use an analogy.

The rubber sheet is an analogy.  It's a way of visualizing something in three dimensions (two of space one of time) that is impossible to visualize in four.  The problem comes about because it is not a perfect analogy.  It's just an approximation.

#### Soul Surfer

• Neilep Level Member
• Posts: 3345
• keep banging the rocks together
##### Re: Why do we orbit the sun if space is not flat?
« Reply #2 on: 16/03/2012 08:20:04 »
The simplest answer to this question is that it orbits the sun because space is warped to ensure that it is always downhill when you are moving towards the sun or any other massive object in exactly the same way that it is always downhill when you are walking on a path that is getting closer to the centre of the earth.

#### acecharly

• Sr. Member
• Posts: 171
##### Re: Why do we orbit the sun if space is not flat?
« Reply #3 on: 16/03/2012 08:28:55 »
Every hill ive ever walked down i got to the bottom, so we must eventually get to the  bottom of this hill an walk into the sun?

In 4.6 billion years at a 67.000 mph thats one hell of a hill.

#### MikeS

• Neilep Level Member
• Posts: 1044
##### Re: Why do we orbit the sun if space is not flat?
« Reply #4 on: 16/03/2012 09:51:01 »
As Soul Surver said it's always down hill.

Gravity is acceleration but continuous acceleration is a concept that we are not normally familiar with.  It's not particularly intuitive but never the less correct.

#### Cheese2001

• Jr. Member
• Posts: 27
##### Re: Why do we orbit the sun if space is not flat?
« Reply #5 on: 17/03/2012 04:46:42 »
This is likely not a perfect analogy, but it is one that works for me.

Have you seen the coin whirlpool wishing wells?you drop a coin onto a giant funnel down a ramp that imparts an initial velocity around the funnel. A bit like an orbital velocity. The coin rolls along and maintains the velocity by falling down the funnel. As the coin rolls along, the angle around the surface of the funnel is dictated by the forward (orbital) velocity and the velocity due to acceleration toward the bottom of the funnel.  If you took away friction, the coins velocity would dictate an orbital path around the hole, and would be elliptical if the path was not perpendicular to the slope of the surface.

That's the way the earth orbits the sun. In a near frictionless environment, the amount the earth falls toward the sun is exactly offset by the amount of forward motion as it falls, keeping the earth at nearly the same distance from the sun. Obviously, the earth's orbit is an ellipse, so it speeds up near the minor axis and slows near the major.  Just like the coins whose frictionless path around the wishing well is not exactly perpendicular to the local "downhill" slope of the wishing well.

A famous depiction by Newton illustrates the body moving forward offsetting falling toward the Earth is the same as the Earth orbiting the sun:  http://www.askamathematician.com/wp-content/uploads/2012/01/newtmtn.jpg [nofollow]
« Last Edit: 17/03/2012 04:52:35 by Cheese2001 »

#### The Naked Scientists Forum

##### Re: Why do we orbit the sun if space is not flat?
« Reply #5 on: 17/03/2012 04:46:42 »