In the beginning

Intelligent falling, of course.

Quote from: TheCat on September 21, 2008, 08:13:09 AM

Well, it's more of a question than a point, really.

When the DE is gone and stops pushing the Earth upward, will the earth then start falling back down the way it's come? On the way will it heat up again?

Why would it go back the other way?

Because DE is no longer pushing it up I assume there'd be nothing to stop it tumbling back down because it would have potential energy, as you agreed a few posts back

Because DE is no longer pushing it up I assume there'd be nothing to stop it tumbling back down because it would have potential energy, as you agreed a few posts back

I meant "yes" to kinetic energy, not potential energy.

ΣF = ma

Acceleration is always in the same direction as force. What is the force that would cause the Earth to accelerate back where it came from?

Quote from: TheCat on September 21, 2008, 03:03:47 PM

Because DE is no longer pushing it up I assume there'd be nothing to stop it tumbling back down because it would have potential energy, as you agreed a few posts back

I meant "yes" to kinetic energy, not potential energy.

ΣF = ma

Acceleration is always in the same direction as force. What is the force that would cause the Earth to accelerate back where it came from?

Oh - hang on. When the dark energy stops pushing the earth, then the kinetic energy of the earth will do what? I assumed that it would become potential energy. But are you saying that it'll just stop and the kinetic energy won't change into anything else? Or if it will change into something else (which I assume it should), then what will it change into?

DE doesn't "push" the Earth.

Oh - hang on. When the dark energy stops pushing the earth, then the kinetic energy of the earth will do what? I assumed that it would become potential energy. But are you saying that it'll just stop and the kinetic energy won't change into anything else? Or if it will change into something else (which I assume it should), then what will it change into?

When you throw a ball, does the kinetic energy in it become something else when you let it go, or does it fly off in the direction you threw it?

.... a large region in front of it, extending for millions of kilometres, was shielded from the Dark Energy, allowing for spherical bodies to form ....

... at which point the Earth will be left to slowly cool and eventually collapse into a sphere ...

So in the flat earth universe, if a gathering of matter (such as makes up the earth) isn't being affected by DE, it collapses into spherical bodies? Why would it do that if, as you argue, there's no gravity?

So in the flat earth universe, if a gathering of matter (such as makes up the earth) isn't being affected by DE, it collapses into spherical bodies? Why would it do that if, as you argue, there's no gravity?

Gravitation.

Gravitation.

... for the nation ... lol - you seem to be the king of short answers!

How do things exhibit 'gravitation' without 'gravity'? Apologies if that's a dumb question (seriously! - I'm no expert in these matters), but if something makes the spheres form when some material is left floating in a vacuum without external forces against it (i.e. no DE) then surely it's evidence of gravity?

... for the nation ... lol - you seem to be the king of short answers!

How do things exhibit 'gravitation' without 'gravity'? Apologies if that's a dumb question (seriously! - I'm no expert in these matters), but if something makes the spheres form when some material is left floating in a vacuum without external forces against it (i.e. no DE) then surely it's evidence of gravity?

A lot of people ask that question. This thread explains all.

Okay, I've read it (as much as I can - it's a HUUGE thread), but as far as I can understand it from the initial post the theory is that 'gravity' is simply the perceived effect of inertia against an accelerating surface, and 'gravitation' is what is actually being felt?

If that's a correct understanding of 'gravitation' then I still don't understand why matter 'free floating' in space without DE affecting it would form spheres? That suggests 'free floating' matter would accelerate towards other matter with no force making it so? Why would the earth collapse into a sphere and not just continue 'up' but without accelerating any more (and just become a lot of 'loose' material moving through space at the same speed)?

If my understanding of gravitation's way off mark here there then I'm probably better leaving this particular topic alone, since the whole physics behind it is way over my head to be honest.

In General Relativity, gravity doesn't exist as a force. But for most purposes, you can consider what is commonly referred to as "gravity" to do exactly the same thing as gravitation does in General Relativity.

DE doesn't "push" the Earth.

Sorry, wrong terminology but you knew what I meant.

When you throw a ball, does the kinetic energy in it become something else when you let it go, or does it fly off in the direction you threw it?

I thought that kinetic energy changed to potential energy at the point where the ball stops going upwards and before it starts falling abck down again.

I thought that energy doesn't ever just disappear but changes from one form to another so I'm trying to understand what happens to the kinetic energy of the earth when it stops being propelled or accelerated (or whatever I'm supposed to call it) by DE.

Please can you help me understand this?

Quote from: OBL

When you throw a ball, does the kinetic energy in it become something else when you let it go, or does it fly off in the direction you threw it?

I thought that kinetic energy changed to potential energy at the point where the ball stops going upwards and before it starts falling abck down again.

I thought that energy doesn't ever just disappear but changes from one form to another so I'm trying to understand what happens to the kinetic energy of the earth when it stops being propelled or accelerated (or whatever I'm supposed to call it) by DE.

Please can you help me understand this?

If you throw a ball up, then its kinetic energy gets converted to gravitational potential energy because it is moving away from the Earth. Then as it falls back to Earth, that potential energy gets converted back into kinetic energy. The key thing to keep in mind here is that the ball is being attracted to the Earth by gravitation. Kinetic energy does not just turn into potential energy for no reason at all. The formula for kinetic energy is:

E_k = 1/2 * mv²

So the Earth's kinetic energy depends only on its mass and velocity, and not on its acceleration. Therefore, when Dark Energy stops pushing it, it just keeps moving with constant velocity.

... so why would it then collapse into a sphere instead of becoming just a mass of material moving at a uniform 'velocity'?

If it did collapse into a sphere because of attraction caused my mass bending spacetime (did I get that right?), then it becomes a 'spherical' planet surely? If that happened, how would it differ from the RE model?

... so why would it then collapse into a sphere instead of becoming just a mass of material moving at a uniform 'velocity'?

Because of its gravitational attraction to itself.

If it did collapse into a sphere because of attraction caused my mass bending spacetime (did I get that right?), then it becomes a 'spherical' planet surely? If that happened, how would it differ from the RE model?

The fact that the Sun would be long dead by then and the Earth would be very cold.

True, true ...

Laws-of-physics wise though, this makes RE a possibility in a 'post DE' universe then, even based on the FE beliefs?
Earth would be spherical 'planet' with a gravitational attraction, look like the RE model of earth, the horizon would appear as RE model says it does just now, distance, orbits etc... would all be as RE model says they are just now.

True, true ...

Laws-of-physics wise though, this makes RE a possibility in a 'post DE' universe then, even based on the FE beliefs?
Earth would be spherical 'planet' with a gravitational attraction, look like the RE model of earth, the horizon would appear as RE model says it does just now, distance, orbits etc... would all be as RE model says they are just now.

If you can find another Sun, then yes.

Quote from: TheCat on September 22, 2008, 11:30:39 AM

Quote from: OBL

When you throw a ball, does the kinetic energy in it become something else when you let it go, or does it fly off in the direction you threw it?

I thought that kinetic energy changed to potential energy at the point where the ball stops going upwards and before it starts falling abck down again.

I thought that energy doesn't ever just disappear but changes from one form to another so I'm trying to understand what happens to the kinetic energy of the earth when it stops being propelled or accelerated (or whatever I'm supposed to call it) by DE.

Please can you help me understand this?

If you throw a ball up, then its kinetic energy gets converted to gravitational potential energy because it is moving away from the Earth. Then as it falls back to Earth, that potential energy gets converted back into kinetic energy. The key thing to keep in mind here is that the ball is being attracted to the Earth by gravitation. Kinetic energy does not just turn into potential energy for no reason at all. The formula for kinetic energy is:

E_k = 1/2 * mv²

So the Earth's kinetic energy depends only on its mass and velocity, and not on its acceleration. Therefore, when Dark Energy stops pushing it, it just keeps moving with constant velocity.

Ok thanks. That makes sense.

But I still can't work out where the energy has gone - it can't just dissapear can it? Doesn't it have to turn into another form of energy like heat or light or something?

Ok thanks. That makes sense.

But I still can't work out where the energy has gone - it can't just dissapear can it? Doesn't it have to turn into another form of energy like heat or light or something?

No, the energy has gone into motion. All things that move have energy. That is what the term "kinetic energy" means - "energy of motion".

Quote from: TheCat on September 22, 2008, 01:17:08 PM

Ok thanks. That makes sense.

But I still can't work out where the energy has gone - it can't just dissapear can it? Doesn't it have to turn into another form of energy like heat or light or something?

No, the energy has gone into motion. All things that move have energy. That is what the term "kinetic energy" means - "energy of motion".

Yes I knew that but when it stops being kinetic energy - when it stops moving - what's happened to the energy then? I thought it had to change to another form not just sort of fizzle out. Sorry, my physics is a bit rusty as you can tell - also I've got a shite memory!

Yes I knew that but when it stops being kinetic energy - when it stops moving - what's happened to the energy then? I thought it had to change to another form not just sort of fizzle out. Sorry, my physics is a bit rusty as you can tell - also I've got a shite memory!

It doesn't stop moving. Like I said before, when you throw a ball (horizontally, so you can ignore the gravitational effect on the motion you give it), does it stop moving when it leaves your hand or does it keep going in the direction you threw it (ignoring air friction)?

Quote from: TheCat on September 23, 2008, 01:49:06 PM

Yes I knew that but when it stops being kinetic energy - when it stops moving - what's happened to the energy then? I thought it had to change to another form not just sort of fizzle out. Sorry, my physics is a bit rusty as you can tell - also I've got a shite memory!

It doesn't stop moving. Like I said before, when you throw a ball (horizontally, so you can ignore the gravitational effect on the motion you give it), does it stop moving when it leaves your hand or does it keep going in the direction you threw it (ignoring air friction)?

So then if the DE stops propelling the Earth upwards it'll still keep going by itself? For ever?

So then if the DE stops propelling the Earth upwards it'll still keep going by itself? For ever?

Yes.

http://en.wikipedia.org/wiki/Newton's_laws_of_motion#Newton.27s_first_law:_law_of_inertia

Quote from: TheCat on September 25, 2008, 02:05:43 PM

So then if the DE stops propelling the Earth upwards it'll still keep going by itself? For ever?

Yes.

http://en.wikipedia.org/wiki/Newton's_laws_of_motion#Newton.27s_first_law:_law_of_inertia

At the same speed?

At the same speed?

Yes.

Dark Energy is still becoming less rigid and less powerful, so in a few billion years we will likely be accelerating much more slowly, and more of the upper atmoplane will have stopped being shielded from Dark Energy and will escape into space, causing much lower air pressure at the surface. The oceans will eventually evaporate due to low pressure, creating an uncontrollable greenhouse effect and the Earth will overheat before Dark Energy spills over the ice wall and acceleration stops altogether, at which point the Earth will be left to slowly cool and eventually collapse into a sphere.

I don't get it

Acceleration and velocity are not the same thing.

Acceleration and velocity are not the same thing.

So when I asked if the earth will still be travelling at the same speed after DE is gone, and you said yes, did that not mean that the earth would be moving through space pretty much the same as it is now? Or are you saying that at the moment it's travelling through space faster and faster and faster all the time?

When DE dies out, there will be no more force accelerating FE.  However, since there'll be no opposing force to slow it down (for example, friction).  It shall remain at a constant velocity.