Gravity and the Expanding Universe

[JohnF]

Could gravity just be an effect from the expanding universe?

 

Since the universe occupied such a small space at the start then it would seem that the space between each particle has increased. If this is true then wouldn't the space between particles still be increasing?

 

So in effect every particle is accelerating away from every other particle and in doing so distorts space/time and causes the effect we call gravity. The more massive the object is the more accelerating particles it has and so the greater the distortion on space/time.

[thedarkshade]

You can refer to gravity as a characteristic of any object that has mass! It's the classical view but meaningful enough. And gravity is supposed to bring stuff together not push them apart.

 

By the way, there are plenty of threads on the subject so a search might have answered your question!

[JohnF]

You can refer to gravity as a characteristic of any object that has mass! It's the classical view but meaningful enough. And gravity is supposed to bring stuff together not push them apart.

 

By the way, there are plenty of threads on the subject so a search might have answered your question!

 

What I'm suggesting is that gravity is the same as the force felt when in a vehicle accelerating at 1G not that we are being pushed apart. We have gravity because the Universe is accelerating and so we feel the effect. On this basis, if the Universe stopped expanding we would have no gravity; or perhaps if the Universe continued to expand at a constant rate, rather than an increasing rate, we would have no gravity.

 

So when the Universe was at it's smallest, before expansion began, there was no gravity.

[thedarkshade]

OK, but from what you're saying I get an impression that as the universe is suffering an accelerated expansion, as a result we feel the effect of gravity! Right? But the universe in accelerating (not expanding in a constant rate like you said), so the gravity value ,by this definition, should change too, since the expansion rate is changing. Now, as far as I know, the gravitational attraction rate has been [math]9.81\frac{m}{s^2}[/math] since it was first determined!

 

Gravity is just an occurring phenomenon between particles with mass, just like the attraction or repulsion that occurs between charged spheres!

[JohnF]

I'm not suggesting the Universe is expanding at a constant rate or that it is the expansion that causes gravity.

 

What I'm suggesting is that the acceleration of the expansion is the cause for gravity. And if the acceleration continues at the present rate, then gravity will remain the same.

[thedarkshade]

What I'm suggesting is that the acceleration of the expansion is the cause for gravity. And if the acceleration continues at the present rate, then gravity will remain the same.

OK, fair enough! Universe expansion is speeding up, the acceleration is increasing at a constant rate. And now we believe that the universe will go on forever, so that acceleration increase will go on forever, of course at a constant rate. And if it goes on forever, then at some point it will reach the speed of light (digression: I mentioned that in another thread, Martin probably remembers), and when that happens, then what about gravity?

[JohnF]

OK, fair enough! Universe expansion is speeding up, the acceleration is increasing at a constant rate. And now we believe that the universe will go on forever, so that acceleration increase will go on forever, of course at a constant rate. And if it goes on forever, then at some point it will reach the speed of light (digression: I mentioned that in another thread, Martin probably remembers), and when that happens, then what about gravity?

 

I wouldn't expect it to make any difference. Light is a part of this expanding Universe. The gravity we feel is as a result of our acceleration through space time or something yet to be determined (whatever is outside of the Universe).

 

Is it important what happens to gravity at that point?

[Klaynos]

OK, fair enough! Universe expansion is speeding up, the acceleration is increasing at a constant rate. And now we believe that the universe will go on forever, so that acceleration increase will go on forever, of course at a constant rate. And if it goes on forever, then at some point it will reach the speed of light (digression: I mentioned that in another thread, Martin probably remembers), and when that happens, then what about gravity?

 

Urmmmm you're scenario there universe expanding indefinitely with a constant rate of acceleration is only one possible option that most cosmologists would tell you if asked, others they'd state would be the acceleration slows then reverses and we get an equilibrium, or possibly that we get an imploding universe...

 

What I'm suggesting is that the acceleration of the expansion is the cause for gravity. And if the acceleration continues at the present rate, then gravity will remain the same.

 

How would this work?

 

Also it should be noted that the distance between particles is not increasing, on a local level weak, strong, EM and gravity forces overrule the expansion...

[JohnF]

Also it should be noted that the distance between particles is not increasing, on a local level weak, strong, EM and gravity forces overrule the expansion...

 

I have assumed that if all the matter in the Universe was compressed in to a very small volume at, or just after, the big bang then the space between particles must have increased.

 

Also, a very simple analogy, if the plank of wood and the ruler you use to measure it are expanding at the same rate then the plank will never be longer than expected; all particles are expanding.

 

I suppose that if Earth was outside of the gravitation effect of the sun then gravity would be different on Earth since at the moment Earth is accelerating through space time distorted by the sun.

[thedarkshade]

Urmmmm you're scenario there universe expanding indefinitely with a constant rate of acceleration is only one possible option that most cosmologists would tell you if asked, others they'd state would be the acceleration slows then reverses and we get an equilibrium, or possibly that we get an imploding universe...

If any cosmologist would answer me this way, I'd consider that as a "not to get stuck" answer!

[Royston]

So in effect every particle is accelerating away from every other particle and in doing so distorts space/time and causes the effect we call gravity. The more massive the object is the more accelerating particles it has and so the greater the distortion on space/time.

 

Unless you're simplifying galaxies as point particles, you realize expansion doesn't happen between particles ?

 

The other problem I see with this, is that the acceleration observed isn't synonymous with the acceleration felt on bodies, you can't think of distant galaxies hurtling away from each other FTL, it's just the distant between is accelerating...from the frame of reference of a distant galaxy, they're not hurtling away anywhere.

[thedarkshade]

Also, a very simple analogy, if the plank of wood and the ruler you use to measure it are expanding at the same rate then the plank will never be longer than expected; all particles are expanding.

That wouldn't look like that to an outside observer! What you are mentioning here is Lorentz contraction ([math]l=l_0\sqrt{1-\beta^2}[/math]), a vague relation to your proposed model!

[JohnF]

Unless you're simplifying galaxies as point particles, you realize expansion doesn't happen between particles ?

 

The other problem I see with this, is that the acceleration observed isn't synonymous with the acceleration felt on bodies, you can't think of distant galaxies hurtling away from each other FTL, it's just the distant between is accelerating...from the frame of reference of a distant galaxy, they're not hurtling away anywhere.

 

I don't see the expansion in space, distance between galaxies, as the cause of this effect. The expansion in space is how we observe the acceleration through space time. All particles are accelerating through space time but some are moving faster. The more massive an object is the more distortion all it's particles cause and so the faster it travels. There's a resistance in space time to the expansion. I suppose you could even think of gravity as a force pushing us towards a massive object; the pressure of space time's resistance to the expansion.

[Klaynos]

The distance between galaxies is increasing.

 

If you where to measure this with a ruler (HAR!) you would be able to measure it, as the particles in the ruler are held together by the em force with over the range of a ruler is stronger than the expansion...

 

The ruler is not expanding...

[JohnF]

The question I'm asking here is, could gravity be caused by our acceleration through another medium?

 

If there was a civilisation sized spacecraft hurtling through inter-galactic space under a constant acceleration then the occupants of that spaceship would have 'gravity'. They could look for ever to find a particle, force, graviton or whatever to explain their 'gravity' but unless they could figure out they were in an accelerating space craft they would never find the answer.

[thedarkshade]

Once again John, the classical view and my personal opinion is that gravity is a characteristic of an object, just like mass, height, width etc.

 

And how that works? Well, GR gives a fine explanation I believe and if you find a place in GR where what you're saying fits in, then you have a reason to debate!

[losfomot]

Once again John, the classical view and my personal opinion is that gravity is a characteristic of an object, just like mass, height, width etc.

 

And how that works? Well, GR gives a fine explanation I believe and if you find a place in GR where what you're saying fits in, then you have a reason to debate!

 

I would replace the word 'explanation' with the word 'description'

[thedarkshade]

I would replace the word 'explanation' with the word 'description'

I think the word "description" is used more for physical features, while "explanation" can me applied to any occurring phenomenon.

 

Besides, "description" means how it's happening while "explanation" means why it is happening.

 

Any strong reason for your proposal?

[losfomot]

I think the word "description" is used more for physical features, while "explanation" can me applied to any occurring phenomenon.

 

Besides, "description" means how it's happening while "explanation" means why it is happening.

 

Any strong reason for your proposal?

 

I would say 'description' gives you a 'picture or idea' of what is happening.

 

While 'explanation' implies a 'mechanism' for what is happening... which GR does not supply.

 

That's just how I saw the words... it is silly and I should have just kept my fingers still.

[thedarkshade]

I would say 'description' gives you a 'picture or idea' of what is happening.

 

While 'explanation' implies a 'mechanism' for what is happening... which GR does not supply.

Then an explanation shows why did you get that idea and how it's happening! Why did you picture it the way you pictured it!

That's just how I saw the words... it is silly and I should have just kept my fingers still.

Feel free to do this anytime! We're always intending toward perfection:cool:!

 

Cheers

[JohnF]

Once again John, the classical view and my personal opinion is that gravity is a characteristic of an object, just like mass, height, width etc.

 

And how that works? Well, GR gives a fine explanation I believe and if you find a place in GR where what you're saying fits in, then you have a reason to debate!

 

I understand what you're saying but as I understand it, gravity is associated with an object and until the mechanism of gravity is fully understood it can only be an association.

 

So from my point of view gravity could be any of the following...

 

1. A 'force' that attracts.

2. A difference in pressure in space/time caused by a massive object

3. An effect of acceleration through another medium.

[lucaspa]

What I'm suggesting is that gravity is the same as the force felt when in a vehicle accelerating at 1G not that we are being pushed apart. We have gravity because the Universe is accelerating and so we feel the effect.

 

This is apples and oranges. In a car, you are moving thru space. But in the expansion of the universe, it is space itself that is expanding. Because you are being carried in space, you don't feel any acceleration. All the molecules within you and around you are changing velocity at the same time as space expands, therefore no "force" that is felt.

 

And yes, Einstein showed that you cannot distinguish between acceleration thru space and gravity.

 

Also, if you think about it, if gravity is simply based on the expansion of space, then gravity should be the same no matter where you are: earth or Jupiter. But that isn't the case, is it? If you relate it to the "number of particles", then you are simply restating classical views of gravity as linked to mass.

[JohnF]

As you say, it is space itself that is expanding. But what is it expanding within?

 

On your other point, I am linking gravity to mass but I am not suggesting classical views of this effect are wrong. I'm suggesting that the search for a field, graviton etc. might be wrong.

 

Since the exact same effect can be experienced in what appears to be two completely different ways then perhaps only one of the events is the real cause of gravity. Perhaps we just don't know we are accelerating. As far as I know there isn't any direct evidence of a 'gravity particle' and so why restrict the search to just that?

[Royston]

As you say, it is space itself that is expanding. But what is it expanding within?

 

You might want to check the links provided by Martin...

 

http://www.scienceforums.net/forum/showpost.php?p=386171&postcount=1

[thedarkshade]

So from my point of view gravity could be any of the following...

 

1. A 'force' that attracts.

2. A difference in pressure in space/time caused by a massive object

3. An effect of acceleration through another medium.

1. Yes, the simplest definition possible, although I personally think not complete!

 

And you know, in this world there is nothing but possibilities!