If there is no gravity in space

[David-J-Franks]

The Lagrange points are not zero gravity points. The gravitational attraction of the Earth stretches out to them. There is a net zero force due to the counter acting gravity of the Sun and or the Moon, but gravity is still present just balanced.

General relativity describes gravity as a distortion of space-time and not an actual force like electromagnetic or the weak and strong nuclear forces. So if there is a net-zero force, force being the wrong word possibly, doesn't that mean all the warping of space has been straightened out, i.e. all those bent lines you see in diagrams has been straightened out so effectively does that mean no gravity?

Also, according to the equivalence principle, acceleration and gravity are equivalent, so if I'm experiencing no acceleration then there is also no gravity?

Just my first thoughts on seeing your post, I am out of my depth with relativity, so any comments are welcome, thank you.

 

[vincenzosassone]

Also, according to the equivalence principle, acceleration and gravity are equivalent, so if I'm experiencing no acceleration then there is also no gravity?

Excuse me if I only reply this, but this is something I know.
As far as I know, gravity is a force (even if gravity is more a property of the space-time we can talk about it as a force to exemplify everything), and every force cause an acceleration. So, acceleration and gravity are equivalent in a certain sense. Anyway, in no places of the Universe you can experience this, since the entire Universe is full of mass and energy (mass=energy). Even though they aren't evenly distributed, every place in the Universe is warped by an object.
In our solar system, for instance, you can't be motionless, we have the Sun, so you'll move around it with a certain constant speed in order not to fall into it. Now you can easily tell me that a constant speed presents zero acceleration, but this isn't true since we are moving in a circolar motion, so there is a centripedal acceleration.
I hope I gave you something important

 

[Catastrophe]

If there is no gravity in space

"General relativity describes gravity as a distortion of space-time and not an actual force like electromagnetic or the weak and strong nuclear forces. So if there is a net-zero force, force being the wrong word possibly, doesn't that mean all the warping of space has been straightened out, i.e. all those bent lines you see in diagrams has been straightened out so effectively does that mean no gravity? "

I agree with David.

No gravity would be no distortion of space time. No mass. No black holes.

Cat

 

[Helio]

If we ignore special circumstances (e.g. time dilation), for us to calculate how an object will move in space, one can use a force model or a GR model. Newton's laws are the primary laws used in practice as they are the superior model due to their simplicity vs. GR.

GR has been verified over and over, thus the model that uses the warping of the spacetime fabric to determine things like orbital motion is necessary to get to more decimal places. But, since we prefer the force model to explain motion, perhaps it helps to consider the idea that gravitons (still hypothetical) are the cause.

If one choses to use either the idea that gravitons emitted by all matter (thus obey the inv. sq. law) directly interact with other matter to force attractive motion, or the idea that graviton density warps spacetime, causing this motion, does it matter which it is? [AFAIK, I don't think I've ever seen this stated, so feel free to throw any darts you have at it. ]

 

[David-J-Franks]

Excuse me if I only reply this, but this is something I know.
As far as I know, gravity is a force (even if gravity is more a property of the space-time we can talk about it as a force to exemplify everything), and every force cause an acceleration. So, acceleration and gravity are equivalent in a certain sense. Anyway, in no places of the Universe you can experience this, since the entire Universe is full of mass and energy (mass=energy). Even though they aren't evenly distributed, every place in the Universe is warped by an object.
In our solar system, for instance, you can't be motionless, we have the Sun, so you'll move around it with a certain constant speed in order not to fall into it. Now you can easily tell me that a constant speed presents zero acceleration, but this isn't true since we are moving in a circolar motion, so there is a centripedal acceleration.
I hope I gave you something important

Thanks for your reply and also support from Catastrophe.

but this is something I know.

This is something I don't know, I'm making it up as I go along

As usual on this forum, something simple quickly turns complicated.

As far as I know, gravity is a force

Current thinking still holds Einstein's views as correct, which means - General relativity describes gravity as a distortion of space-time and not an actual force. So until someone comes along and discover's gravitons or unites gravity with quantum field theory or quantum loop gravity, gravity is currently not a force.

I would like to agree with you, I personally think gravity is a force. I don't like the analogy of gravity depicted as a bowling ball on a trampoline with graph lines on it. In that analogy, the ball has somewhere to fall but in 3D space where does a bowling ball fall to? 4D space? So if mass distorts space I still think you need a force to distort the space since the bowling ball is not falling anywhere in 3d space. It also helps to think about space as something tangible, for example, quantum foam or quantum fields, then it's easier to imagine it being distorted.

So, acceleration and gravity are equivalent in a certain sense.

I think acceleration and gravity are equivalent in all senses under all circumstances. This is due to the 'equivalence principle' (Einstien again?) and there is currently absolutely no way to distinguish any difference between acceleration and gravity (if you can't see what's causing the acceleration).

so there is a centripedal acceleration.

No, I don't think so. the minute you enter a LaGrange point there is close to zero gravity so there is no centripetal force acting on you. What I think will happen is that when you enter the zero-gravity space there will be no forces acting on you so your circular motion will change to linear motion as per Newton's first law of motion.

You will then leave the Lagrange point in a straight line and then come under the influence of the earth's gravity and start to orbit the earth.

The catch here is that in reality a 'LaGrange point' is just that, a 'point'. It's a mathematical solution to an equation. A point has no volume so therefore there is no volume in space where there is zero gravity. The best we can say is that it's close to zero-gravity (as I emphasised in my first post about this topic) around that point. So strictly speaking I think it's still fair to say that there is nowhere in the observable universe where there is zero gravity only close to zero gravity.

Even more strictly strictly strictly speaking these LaGrange points will jiggle about a bit due to tidal effects on the earth and convection currents in the sun etc.

Last-minute thought, is there zero gravity in the middle of a planet or a star? probably close to zero I think.

 

[Clovis]

In the movie Interstellar, gravity was determined to be the most powerful force in the universe. A lot of people didn't understand that movie. But it was simple if you thought about it. And it explained how a worm hole might exist. Look at the gravitational power surrounding a Black Hole. Once sucked in, where did all that mass and matter end up?

Matter can not created nor destroyed, only altered.

 

[IG2007]

most powerful force in the universe.

Well, it depends if you are talking about the micro level or the macro level. Gravity is, certainly, not the most powerful force in the micro level, it is the weakest of the four fundamental forces (although I guess I shouldn't really call it a force, but, eh, simplification is cool). That is why a magnet can easily attract a magnetic object towards it and easily defeat the gravity of this entire planet. But, the other three forces are only strong in the micro level as their spheres of influence are limited. But, that's not the case with gravity as it is a result of space-time conjectures.

Last-minute thought, is there zero gravity in the middle of a planet or a star? probably close to zero I think.

Relative to the planet or star, probably. Relative to the Observable Universe, no.

 

[vincenzosassone]

I must say that I agree with you, David, but only in the first half of your speech:

gravity is currently not a force.

Of course, it isn't. "Gravity is a property of the space-time" was an important sentence of Einstein if I'm not mistaken.

No, I don't think so. the minute you enter a LaGrange point there is close to zero gravity so there is no centripetal force acting on you.

Mhh... Let's state that a LaGrange point really happens to be zero, absolute zero, between Earth and Moon. We are always attracted by the Sun (on the other hand, there is always the possibility to find an asteroid-like object ready to put into crisis this perfect balance).
No places in the Universe are completely free from gravity, unless we talk about the deep vacuum (even though sometimes there could be found some galaxies inside).

As usual on this forum, something simple quickly turns complicated.

I couldn't agree more...

 

[vincenzosassone]

The catch here is that in reality a 'LaGrange point' is just that, a 'point'.

BTW, what is a point for you? Sometimes this concept is ignored, but there is a lot to say about it.
I remember we were talking about Black Holes in a thread of this forum. We were close to agree that singularity was a point with mass, so infinty density!

 

[David-J-Franks]

I must say that I agree with you, David, but only in the first half of your speech:

Of course, it isn't. "Gravity is a property of the space-time" was an important sentence of Einstein if I'm not mistaken.

Mhh... Let's state that a LaGrange point really happens to be zero, absolute zero, between Earth and Moon. We are always attracted by the Sun (on the other hand, there is always the possibility to find an asteroid-like object ready to put into crisis this perfect balance).
No places in the Universe are completely free from gravity, unless we talk about the deep vacuum (even though sometimes there could be found some galaxies inside).

I couldn't agree more...

First, in all my posts, I've said close to zero-gravity not zero-gravity, so yes, there is no place in the universe where it is completely free from gravity.

It looks like we've not been singing from the same hymn sheet. You have been thinking about the LaGrange point between the earth and the moon and I am thinking about the LaGrange point L1 between the sun and earth. So in your case, I would agree with you that the sun is always providing gravity in that case.

I thought the point of the discussion was to see if there's anywhere with zero gravity, which is why I chose the LaGrange point L1 between the sun and earth. I thought there might be close to zero gravity there.

If so, then I can also stand by my proposition that there isn't any centripetal force acting on any object at point L1. It's gravity that provides any centripetal force so if there's almost no gravity, how can there be any centripetal force? If there are no forces acting on an object there, then it will continue in a straight line temporarily and will therefore leave the LaGrange point, yes?

All LaGrange points are not created equal!

 

[David-J-Franks]

BTW, what is a point for you? Sometimes this concept is ignored, but there is a lot to say about it.
I remember we were talking about Black Holes in a thread of this forum. We were close to agree that singularity was a point with mass, so infinty density!

I think a point is just a mathematical concept, an abstract thought. As such it has no surface area or volume, so, it does not manifest itself in reality.

In the case of a Lagrange point, that is a coordinate from an equation, which is a point. Theoretically gravity tends towards zero as you get closer to the point and is only zero at the point. Now since the point has no volume it means there is no volume in this region with zero gravity. Make of that what you will

I think the idea of a singularity with infinite density is a completely absurd notion. I'm under the impression that scientists have not believed this for more than 40 years since the inflation theory. I think it's a concept which has largely stuck with the public?

I think 'density' requires a numerical value or a statement of low or high relative to something else, infinite is not a number, it has no value?

It seems perfectly sensible to me that you can only compress matter/energy so far until the pressure stops any more compression regadles what any equations may say.

The idea that all the contents of a black hole or the universe can fit into a point which has 0 volume is crazy, I'm surprised why clever scientists came up with it.

 

[vincenzosassone]

I think a point is just a mathematical concept, an abstract thought. As such it has no surface area or volume, so, it does not manifest itself in reality.

In the case of a Lagrange point, that is a coordinate from an equation, which is a point. Theoretically gravity tends towards zero as you get closer to the point and is only zero at the point. Now since the point has no volume it means there is no volume in this region with zero gravity. Make of that what you will

I think the idea of a singularity with infinite density is a completely absurd notion. I'm under the impression that scientists have not believed this for more than 40 years since the inflation theory. I think it's a concept which has largely stuck with the public?

I think 'density' requires a numerical value or a statement of low or high relative to something else, infinite is not a number, it has no value?

It seems perfectly sensible to me that you can only compress matter/energy so far until the pressure stops any more compression regadles what any equations may say.

The idea that all the contents of a black hole or the universe can fit into a point which has 0 volume is crazy, I'm surprised why clever scientists came up with it.

Outstanding! I agree with you!

infinite is not a number, it has no value?

That's the conundrum. I remember that, when I was a child, our teacher told us that two parallel straight lines never touch, so they touch themselves at the "infinite point" (that means never).

I thought the point of the discussion was to see if there's anywhere with zero gravity, which is why I chose the LaGrange point L1 between the sun and earth. I thought there might be close to zero gravity there.

Of course, this is correct. Anyway, this is correct if the system we've chosen is the solar system, otherwise it isn't. We have Albert Einstein again, followed by Galileo Galilei this time. They managed to think in an alternative way. Galilei invented relativity, Einstein brought it to an upper level, extending it to all systems.
In the previous case, for instance, we are experiencing no gravity in our solar system, but even the Sun is moving around the center of our Galaxy. Most importantly, even our galaxy moves, the problem is that I don't know wheather it's moving in a round motion or in a straight one. I know, this is exhausting...

 

[David-J-Franks]

Outstanding! I agree with you!

That's the conundrum. I remember that, when I was a child, our teacher told us that two parallel straight lines never touch, so they touch themselves at the "infinite point" (that means never).

Of course, this is correct. Anyway, this is correct if the system we've chosen is the solar system, otherwise it isn't. We have Albert Einstein again, followed by Galileo Galilei this time. They managed to think in an alternative way. Galilei invented relativity, Einstein brought it to an upper level, extending it to all systems.
In the previous case, for instance, we are experiencing no gravity in our solar system, but even the Sun is moving around the center of our Galaxy. Most importantly, even our galaxy moves, the problem is that I don't know wheather it's moving in a round motion or in a straight one. I know, this is exhausting...

but even the Sun is moving around the center of our Galaxy.

Good point, I forgot about the rest of the galaxy. Yes, the gravity that keeps our sun orbiting the galaxy will permeate through all the LaGrange points, but it's not very strong though.

Most importantly, even our galaxy moves, the problem is that I don't know wheather it's moving in a round motion or in a straight one.

Since the universe is on average expanding, galaxies, in general, are moving apart, so I guess they are mostly going in a straight line away from each other. However, I think most galaxies belong to clusters of galaxies. While the clusters are all moving away from each other, some of the galaxies within them are being attracted to each other. This is the case with our galaxy, it belongs to a cluster called the Local group. Some of the galaxies in the Local group have a blue shift indicating that we are moving towards each other, and in fact, we are due to collide with the Andromeda galaxy in 4-5 billion years!

I'm not sure whether there are any galaxies on their own, perhaps rod knows that

I don't think clusters are rotating much though.

 

[David-J-Franks]

If we ignore special circumstances (e.g. time dilation), for us to calculate how an object will move in space, one can use a force model or a GR model. Newton's laws are the primary laws used in practice as they are the superior model due to their simplicity vs. GR.

GR has been verified over and over, thus the model that uses the warping of the spacetime fabric to determine things like orbital motion is necessary to get to more decimal places. But, since we prefer the force model to explain motion, perhaps it helps to consider the idea that gravitons (still hypothetical) are the cause.

If one choses to use either the idea that gravitons emitted by all matter (thus obey the inv. sq. law) directly interact with other matter to force attractive motion, or the idea that graviton density warps spacetime, causing this motion, does it matter which it is? [AFAIK, I don't think I've ever seen this stated, so feel free to throw any darts you have at it. ]

does it matter which it is?

Interesting thoughts. I think it matters just from the knowledge point, but you're right in that it makes no difference to any outcomes in reality.

Atlan found an article about space-time in the thread https://forums.space.com/threads/what-was-is.45573/ It's nice to know somebody's on the case as there' not much research about space-time. Be warned though, I think only genuine theoretical physicist professors will understand it though.

I also came across this today - Is gravity truly a quantum force? https://www.techexplorist.com/gravity-truly-quantum-force/41099/

 

[voidpotentialenergy]

Casimir effect - Wikipedia
https://en.wikipedia.org › wiki › Casimir_effect

In quantum field theory, the Casimir effect is a physical force acting on the macroscopic boundaries of a confined space which arises from the quantum ...
‎Derivation of Casimir effect assuming zeta-regularization · ‎Dynamical Casimir effect

"In quantum field theory . . . . . . . . . "

Cat

I always wondered if the Casimir effect of quantum fluctuation couldn't be used to propel a ship.
2 plates placed close together will be forced together with more activity on the outside of plates than the inside.
If we made 1 plate of pyramid cones the Casimir effect should have more force on the flat plate at the bottom than the pyramid cones on the top.
Tiny effect for sure but free and making large stacked plates of cone pyramids not real difficult.
A tiny effect X million plates might be useful and persistent acceleration?

A drop of water on a flat plate takes it's full force but a drop of water hitting a cone pyramid wastes most of it's energy in side motion that will be canceled out.

 

[vincenzosassone]

Good point, I forgot about the rest of the galaxy. Yes, the gravity that keeps our sun orbiting the galaxy will permeate through all the LaGrange points, but it's not very strong though.
Since the universe is on average expanding, galaxies, in general, are moving apart, so I guess they are mostly going in a straight line away from each other. However, I think most galaxies belong to clusters of galaxies. While the clusters are all moving away from each other, some of the galaxies within them are being attracted to each other. This is the case with our galaxy, it belongs to a cluster called the Local group. Some of the galaxies in the Local group have a blue shift indicating that we are moving towards each other, and in fact, we are due to collide with the Andromeda galaxy in 4-5 billion years!

I'm not sure whether there are any galaxies on their own, perhaps rod knows that

I don't think clusters are rotating much though.

Thank you, now I get it!

 

[Pogo]

I think that here we've realized there is no zero gravity anywhere except in a theoretical empty universe. However, we can experience something like zero gravity all over the place here. I think the correct term may be 'neutral gravity'. If an object is in a location where the gravity from all sources are exactly balanced or located such that gravity sources are balanced by the object's acceleration, then the object can experience neutral gravity.
So, if you drop a ball on the moon from a height, it experiences neutral gravity be virtue of its acceleration toward the Moon until it hits the surface. Dropping the ball on the Earth, it will experience neutral gravity until it experiences atmospheric drag very quickly. An astronaut in training experiences neutral gravity for a few seconds aboard the 'Vomit Comet', and experiances neutral gravity all the time aboard the ISS. An object in orbit will experience neutral gravity by virtue of its acceleration due to gravity being balanced by its forward velocity in orbit (inertia). An object at Lagrange points will experience near neutral gravity, but since the two major bodies are in motion, it will likely soon move away from that L point since the L point moves in a non-regular fashion and there is no reliable force to keep it in place. Even the Jupiter Trojans wander about the L4 and L5 points. Place that object in the middle of a void in a galactic group far away from anything it will begin at rest, until something moves. Since pretty much everything moves, it will soon begin to move in the direction of the greater imbalance of gravitational attractions, albeit ever so slowly.
Neutral gravity can be experienced which will seem like zero gravity, but, it won't last forever in any location or any trajectory due to everything in motion; it just may not notice it for a very long time.