gravitons

Originally posted by @moonbus
Nothing causes gravity. Nothing causes electricity either.

Nothing can't cause gravity (or electricity) because nothing doesn't cause anything.

( I'm not sure about what's happening in this thread... are we agreeing to disagree, or disagreeing to agree? )

There is a built-in semantical problem in saying nothing causes gravity.
If gravity exists, but it has no cause, then by definition gravity is self existent. But according to BB theory gravity came into existence shortly after the expansion began. Saying nothing causes gravity is the same as saying gravity has no cause, but it clearly must have a cause if it didn't exist prior to the BB event.

Originally posted by @lemon-lime
Nothing can't cause gravity (or electricity) because nothing doesn't cause anything.

( I'm not sure about what's happening in this thread... are we agreeing to disagree, or disagreeing to agree? )

There is a built-in semantical problem in saying nothing causes gravity.
If gravity exists, but it has no cause, then by definition gravity is se ...[text shortened]... gravity has no cause, but it clearly must have a cause if it didn't exist prior to the BB event.

I've got problems with your use of the word "caused". Gravity is a property of space-time. Space-time came into existence at the moment the big bang started and, since gravity is a property of space-time, there was no delay. The word "cause" is usually associated with an event correlated and necessary for a later event known as the effect. The key word here is "later" - since space-time to all intents and purposes has always existed and gravity along with it I don't think there is a cause.

I'm intrigued as to why you think there was some delay between the earliest moment and gravity being switched on, so to speak.

Originally posted by @metal-brain
My guess is that you are right.

If space/time is discrete there might be no need for the graviton to explain gravity. My theory is that gravity is caused by the displacement of space/time by matter.

So the space/timeatron is displaced?

Originally posted by @deepthought
I've got problems with your use of the word "caused". Gravity is a property of space-time. Space-time came into existence at the moment the big bang started and, since gravity is a property of space-time, there was no delay. The word "cause" is usually associated with an event correlated and necessary for a later event known as the effect. The key w ...[text shortened]... ink there was some delay between the earliest moment and gravity being switched on, so to speak.

I'm intrigued as to why you think there was some delay between the earliest moment and gravity being switched on, so to speak.
I'm assuming gravity did not exist until the formation of elemental mass... mass that could bend spacetime.

"After the initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles, and later simple atoms. Giant clouds of these primordial elements later coalesced through gravity in halos of dark matter, eventually forming the stars and galaxies visible today."
https://en.m.wikipedia.org/wiki/Big_Bang

Space-time came into existence at the moment the big bang started and, since gravity is a property of space-time, there was no delay.
Before there was any mass how could spacetime exhibit the property of gravity? It's not as though gravity was already there, and waiting for mass to appear before showing itself. If gravity is mass bending spacetime then how do we define gravity in the absence of mass?

Originally posted by @deepthought
I've got problems with your use of the word "caused". Gravity is a property of space-time. Space-time came into existence at the moment the big bang started and, since gravity is a property of space-time, there was no delay. The word "cause" is usually associated with an event correlated and necessary for a later event known as the effect. The key w ...[text shortened]... ink there was some delay between the earliest moment and gravity being switched on, so to speak.

Before the formation of mass gravity was a potential property of spacetime.... not an actual (existing) property.

Darn it, I forgot about this and it seems to completely trash my gravity argument.

"Planck Epic
Planck time, the smallest theoretically observable unit of time and the time before which science is unable to describe the universe. At this point, the force of gravity separated from the e!ectronuclear force."

Does this mean gravity existed before spacetime?
I still don't see how gravity as we know it today could exist before matter existed. Imagine a stretched out flat sheet with nothing (no ball) on it... where's the gravity?

Originally posted by @lemon-lime

Before there was any mass how could ...

You do know the singularity that expanded to form the big bang is supposed to have mass, right?

Originally posted by @deepthought
I've got problems with your use of the word "caused". Gravity is a property of space-time. Space-time came into existence at the moment the big bang started and, since gravity is a property of space-time, there was no delay. The word "cause" is usually associated with an event correlated and necessary for a later event known as the effect. The key w ...[text shortened]... ink there was some delay between the earliest moment and gravity being switched on, so to speak.

I agree the is no delay between the bending of spacetime and gravity (because no evidence for such a delay and not even sure if such a 'delay' would make sense).
However, there is a delay between a change in mass and the change of bending of spacetime. The fact that gravity waves and gammer rays have been detected from the same (violent) source shows that, in that sense, gravity travels at the 'speed of light' because the influence of a sudden change in mass on the resulting bending of spacetime (which in turn immediately changes gravity) radiates out as an expanding sphere expanding out at the speed of light.

Originally posted by @humy
..bending of spacetime..

sorry, shouldn't have said "bending of spacetime" but rather "spacetime curvature", which is the correct term.

Originally posted by @humy
You do know the singularity that expanded to form the big bang is supposed to have mass, right?

"After the initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles, and later simple atoms."
https://en.m.wikipedia.org/wiki/Big_Bang

I know it started out with something, but according to the above quote it was not 'mass' in the form of subatomic particles and simple atoms... these did not appear until after the universe sufficiently cooled to allow for their formation.
Apparently gravity existed (as a force) and split off from the other forces before the smallest of elemental particles were formed. But as someone else here has pointed out scientists are moving away from the idea of gravity being a force, and towards the idea of it simply being a property of spacetime.

I'm not implying it wasn't always a property of spacetime. What I'm suggesting is gravity is not a true force commensurate with other forces, and its apparent weakness (as a force) is simply due to it being perceived as such.

Originally posted by @lemon-lime
"After the initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles, and later simple atoms."
https://en.m.wikipedia.org/wiki/Big_Bang

I know it started out with something, but according to the above quote it was not 'mass' in the form of subatomic particles and simple atoms... these did not appear unt ...[text shortened]... ther forces, and its apparent weakness (as a force) is simply due to it being perceived as such.

Spacetime would immediately exist, because there was both motion (time) and space when the expansion began. Gravity as a potential property of spacetime then becomes realized after the formation of the first elemental particles.

By the way, I'm not trying to explain BB theory as it presently stands. Because as it presently stands gravity is viewed as a force commensurate with other forces.

Originally posted by @lemon-lime
[b]I'm intrigued as to why you think there was some delay between the earliest moment and gravity being switched on, so to speak.
I'm assuming gravity did not exist until the formation of elemental mass... mass that could bend spacetime.

"After the initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles, ...[text shortened]... self. If gravity is mass bending spacetime then how do we define gravity in the absence of mass?[/b]

The Einstein field equations are of the form R(i, k) - 1/2 g(i, k)R = (8πG/c^4) T(i, k). The terms on the left are curvature terms and describe space time. The right hand side is a constant times the energy momentum stress tensor. What this all means is that it is energy and not mass that gravitates, since the energy of any given object is dominated by its mass, most discussions tend to focus on it.

So provided there is plenty of energy around the existence of massive particles is not a requirement for gravitation.

I think we are using the word slightly differently - by gravitation you mean the attraction of massive objects. I mean the effect of energy on space-time - so I tend to think of it in terms of the underlying theory rather than the empirical effect. So for me it is enough that it can happen, whether it does or not.

I put that equation in from memory and may have details wrong, especially the constant. Also, i and k should really be subscripts, rather than in brackets. The basic idea - geometric curvature is proportional to energy density - is what matters for this discussion.

Originally posted by @deepthought
The Einstein field equations are of the form R(i, k) - 1/2 g(i, k)R = (8πG/c^4) T(i, k). The terms on the left are curvature terms and describe space time. The right hand side is a constant times the energy momentum stress tensor. What this all means is that it is energy and not mass that gravitates, since the energy of any given object is dominated ...[text shortened]... a - geometric curvature is proportional to energy density - is what matters for this discussion.

I think we are using the word slightly differently - by gravitation you mean the attraction of massive objects. I mean the effect of energy on space-time - so I tend to think of it in terms of the underlying theory rather than the empirical effect. So for me it is enough that it can happen, whether it does or not.

I think of gravity as mass having an effect on the time part of space-time, with the space part of it being the unaffected (but necessary) medium. When time was thought to be constant, space was seen as a 3D grid of straight lines only (no curvatures).
As I see it gravity is both real (it can be observed) and an illusion... the illusion of attraction, or sensation of being pulled.

I'm not sure if this is a good example of what I mean, but what if we used time (and only time) as a tool for measuring distance. Let's say you travel one mile at a speed of one mile per hour. The elapsed time is sixty minutes. Travel the same mile at 3 miles per hour and the elapsed time is now 20 minutes. Keeping in mind we are only using (elapsed) time for measuring distance, in the first example the length of a mile is 60, but in the second example the length of that same mile is only 20. By using elapsed time as our only tool for measuring distance we can then describe a mile as being longer or shorter. This is what I see time doing to what would otherwise be nothing but straight lines in 3D space.

Originally posted by @lemon-lime
[b]I think we are using the word slightly differently - by gravitation you mean the attraction of massive objects. I mean the effect of energy on space-time - so I tend to think of it in terms of the underlying theory rather than the empirical effect. So for me it is enough that it can happen, whether it does or not.

I think of gravity as mass hav ...[text shortened]... This is what I see time doing to what would otherwise be nothing but straight lines in 3D space.[/b]

"I think of gravity as mass having an effect on the time part of space-time,"

I agree. Time dilation is gravity, not a result of gravity. I think of time dilation in the same way as a low pressure area. Things move toward a slower passage of time because it is the shortest path in time.

Originally posted by @moonbus
Nothing causes gravity. Nothing causes electricity either.

In the grandest sense the BB 'caused' electricity. But saying nothing causes electricity is saying nothing causes floods.
You are just playing with semantics.