Are we push or attracted to a planet?

In summary: Earth. However, this is not what we observe.In summary, according to Mr. Moffat's book, Georges-Louis Le Sage proposed that small particles could exert pressure on a body, but this idea was later discredited by Maxwell and Poincaré. It is difficult to create a push gravity model that is consistent with observation, and people tend to take for granted the direction of the force without any clear evidence.
  • #1
fcycles
5
0
Last year while thinking about it, I thought it will make more sense if we were pushed on our planet rather than being attracted to it. Mathematically, there is no change made to the current equation by reversing the force vector's direction!

While I am read "Reinventing Gravity" from John W. Moffat. I learn that Mr. Georges-Louis Le Sage in 1758 was proposing particules could exert pressure on a body. However, they don't mention why the idea was later consider to be wrong by Maxwell and Poincaré?

So, I am still not convince of the direction of the force? If we are push or attracted on Earth.

If I consider gravity has a space deformation, maybe my question make no sense?

Anyone could clarify it?
 
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  • #2
It is difficult, if not impossible, to make a "push" gravity model that is actually consistent with observation.
 
  • #3
It's all relative. In a coordinate system attached to Earth surface, there is a force of Gravity that pulls everything down. It is a fictitious force, however, resulting from non-inertial coordinate system choice.

In any inertial system, yes, it is Earth's surface that's accelerating outwards, pushing you up, rather than anything pulling you down.
 
  • #4
K^2 said:
It is a fictitious force, however, resulting from non-inertial coordinate system choice.

Is this true?

Imagine a planet that is neither rotating, nor is it's centre of mass accelerating. Then the frame "attached" to the planetary surface WILL be inertial, but the downward gravitational force surely still exists?
 
  • #5
fcycles said:
I learn that Mr. Georges-Louis Le Sage in 1758 was proposing particules could exert pressure on a body. However, they don't mention why the idea was later consider to be wrong by Maxwell and Poincaré?

Le Sage's theory of gravitation (Wikipedia)
 
  • #6
fcycles said:
Last year while thinking about it, I thought it will make more sense if we were pushed on our planet rather than being attracted to it. Mathematically, there is no change made to the current equation by reversing the force vector's direction!

While I am read "Reinventing Gravity" from John W. Moffat. I learn that Mr. Georges-Louis Le Sage in 1758 was proposing particules could exert pressure on a body. However, they don't mention why the idea was later consider to be wrong by Maxwell and Poincaré?

So, I am still not convince of the direction of the force? If we are push or attracted on Earth.

If I consider gravity has a space deformation, maybe my question make no sense?

Anyone could clarify it?
Can there be any doubt about the direction of the force? It must be towards the Earth. You either have to account for this force by the presence of the Earth and its mass (a pull force) or by the 'absence' of the Earth in every other direction and, somehow, that 'absence' produces a push force.
I know which description I'd put my money on.

Furthermore, the closer you are to the Earth, the greater the force - despite that there is less 'no Earth' around you.
 
  • #7
Beeing closer to an object and seeing a force increase does not proof that the source of that force came from the object.

If you think that gravity has many sources caming from different directions. And that force react to matter in a way that it get reduce very slightly after traversing it. Then, considering a force on top of your head and one down below your feet (after passing throught the Earth), the result will be that you will be push down the Earth.

And if you think that sources in the universe are places in a way that they are not symetrical. That was my first guess to invalidate my hypothesis, you might argue that we will see things moving into one direction? Well, no... because it is relative and we are inside that system. We see things moving according to our position in space.

What maked me think this make more sense than having a force pulling you on Earth are:
- Gravity is the weakest force by a large margin;
- If we consider the source of gravity is the Earth and that gravitron is pulling object into the source... I cannot see how particules going into a direction will make an object move into the opposite direction (but rather the direction should follow);
- When we observe galaxy rotating, their speed does not match our current model;
- Base on the current physics models, there is an important missing mass in the universe;
- Everybody seem to take for granted that we are pulled into Earth (I doubt of things which are taked for granted without any proof, hehe!).


That was some clarification I wanted to add to my first post, just to explain better what I was thinking. But, in itself my thought does not convince me of anything... except that now I cannot say if we are pull or push on Earth.


K^2 bring an interesting statement... but I think like lilphil1989 that you will still move into the direction of the massive body. Being pull or push...? ;)

ps: I found the discussion really interesting... thank you all for your posts and I hope we can continue talking about it!
 
  • #8
I have to admit that my position on this is rather 'entrenched' but I always try to avoid the question "what is it really?". Things behave as they behave and some models can be used to make reliable predictions while others will let you down.
The 'attracted to' model seems by far the simpler model so that's what I will go with. What is 'really is' is, I think a meaningless concept.
 
  • #9
fcycles said:
That was my first guess to invalidate my hypothesis

It's not your hypothesis. It's Nicolas Fatio's, and it's 380 years old. It's also, as the Wikipedia article points out, completely inconsistent with observation.
 
  • #10
lilphil1989 said:
Imagine a planet that is neither rotating, nor is it's centre of mass accelerating. Then the frame "attached" to the planetary surface WILL be inertial, but the downward gravitational force surely still exists?
No it's not. Surface of massive body is inherently non-inertial due to curvature in the space-time. That's where gravity comes from.

Gravity is always a fictitious force. If you have gravity, you have an accelerating frame of reference. And vice versa, if you found a locally inertial frame of reference, there is no gravity.

If you compute acceleration at Earth's surface, [itex]a = \Nabla_u u[/itex] for [itex]u = (u_t, 0, 0, 0)[/itex], you will get 9.8m/s² out away from center. Earth's surface is accelerating outwards.
 
  • #11
K^2 said:
lilphil1989 said:
Imagine a planet that is neither rotating, nor is it's centre of mass accelerating. Then the frame "attached" to the planetary surface WILL be inertial, but the downward gravitational force surely still exists?
No it's not. Surface of massive body is inherently non-inertial due to curvature in the space-time. That's where gravity comes from.

Gravity is always a fictitious force. If you have gravity, you have an accelerating frame of reference. And vice versa, if you found a locally inertial frame of reference, there is no gravity.

If you compute acceleration at Earth's surface, [itex]a = \nabla_u u[/itex] for [itex]u = (u_t, 0, 0, 0)[/itex], you will get 9.8m/s² out away from center. Earth's surface is accelerating outwards.
Just in case lilphil1989 is confused, K^2 is talking about Einstein's General Theory of Relativity. According to Newton's Law of Gravity, lilphil1989 is correct, but Einstein's theory, which superseded it, takes a different view: the inertial objects are the ones that are falling freely under gravity.
 
  • #12
Vanadium 50 said:
It's not your hypothesis. It's Nicolas Fatio's, and it's 380 years old. It's also, as the Wikipedia article points out, completely inconsistent with observation.

Sorry to dig this one out of the depths, but how exactly is a push theory of gravity "completely inconsistent with observation"?

There are a lot of things out there that would be explained by a push theory of gravity.

Similarly, pull gravity: A completely undiscovered force field, magically generated by "mass" of an object, that pulls on an object at a distance through vacuum, without any known interaction between those two objects. It seems ridiculous to me to claim that gravity "must" be a pull interaction between two objects.
 
  • #13
I think your first step should be to read the references in this thread.
 
  • #14
Barwick said:
Sorry to dig this one out of the depths, but how exactly is a push theory of gravity "completely inconsistent with observation"?

That's easy. Show me even ONE observation that indicates otherwise.
 
  • #15
Vanadium 50 said:
I think your first step should be to read the references in this thread.

I may be too dumb to understand because I read that jtbell linked, and couldn't find anything where it was "completely inconsistent with observation". That's very very possible, I'm not exactly a PhD when it comes to physics, and it's been so long that I probably couldn't do the simple math to derive functions for mechanical interaction of bodies without referencing Google.

On the other hand, there have been experiments where neutrons were isolated from all outside sources of energy, except for obviously gravity. They observed their behavior and the neutrons didn't accelerate at constant velocities, but rather in discrete jumps.

A pull type of gravity would result in a constant, uniform movement of mass in the direction of the other mass.

A push type of gravity (be it from a particle or photons) would have a probability of coming into contact with the mass being "affected" by gravity (the one being observed), and thus result in discrete changes in velocity, rather than constant changes.
 
  • #16
There is no such thing as "push gravity"
Doesn't exist.
It would be an oxymoron on conceptual terms.

Perhaps those whom wish to believe in it believe also in a 9/11 conspiracy. Who knows.
 
  • #17
pallidin said:
There is no such thing as "push gravity"
Doesn't exist.
It would be an oxymoron on conceptual terms.

Perhaps those whom wish to believe in it believe also in a 9/11 conspiracy. Who knows.

Ok, not to turn this into an argument, but now we have a proof by hand waving, and name calling?
 
  • #18
Barwick said:
Ok, not to turn this into an argument, but now we have a proof by hand waving, and name calling?

Yeah, my bad. I'm usually more professional. Sorry.
Anyway, for any theory that counters accepted theory, one must provide "acceptable" evidence that the new theory is worthy of further thought.

What would be interesting is if you could use your undoubtedly creative mind to design an experiment that supports this theory. Not that you have to build it, as it might be prohibitively expensive for an individual, but properly propose it for others to MAYBE take it up.
 
  • #19
what is the point of threads like this? anyone who posts anything that considers a model of gravity that relies on pushing instead of pulling will be accused of speculation and disciplined according to forum rules.
 
  • #20
That Le Sage theory is really cute. Wonder if virtual particle mediated attraction can be re-expressed in this kind of way..
 
  • #21
The reason that gravity doesn't push us away from Earth is due to the anthropic principle; if it did, we couldn't exist!
 
  • #22
I was trying to think of a single sentence that could somewhat explain gravity to a layman. Anyone have any suggestions? This is the best I could come up with:

The bigger something is, the more likely another thing will fall towards it.
 
  • #23
cr45 said:
I was trying to think of a single sentence that could somewhat explain gravity to a layman. Anyone have any suggestions? This is the best I could come up with:

The bigger something is, the more likely another thing will fall towards it.

I'd say its more like "The bigger something is, the faster another thing will fall towards it."
 
  • #24
The more massive something is, the more it pulls on everything else?
 
  • #25
cesiumfrog said:
The more massive something is, the more it pulls on everything else?

Yes. Something like a black hole exerts an enormous pull on everything around it, while something like the moon is so less massive that it only causes us to weigh 1/6th of what we normally do on earth.

Also, the denser something is, the stronger its gravity is. If i compacted the Earth into the size of a baseball, the gravity at say 1 foot away from it would be enormous. Way more than what we have on the surface of the Earth now. But if i were in orbit of the Earth when it is compressed, i wouldn't notice a difference in the gravitational pull.

This is how a black hole can form out of supermassive stars. Once the star cannot fuse any more elements at its core, there is no more outward pressure to counteract gravity. The rest of the star starts to collapse inwards towards the core and in a complicated series of events, the star explodes in a supernova and leaves behind a very very dense core of material in the form of a black hole. Theoretically i could compress the Earth so much that it would form a black hole if i had the means.
 
  • #26
Drakkith said:
Theoretically i could compress the Earth so much that it would form a black hole if i had the means.

Hello. My name is Bond, James Bond, and I must stop you... :biggrin:
 
  • #27
planck42 said:
The reason that gravity doesn't push us away from Earth is due to the anthropic principle; if it did, we couldn't exist!

Nobody's saying Earth pushes us away. See below.

pallidin said:
Yeah, my bad. I'm usually more professional. Sorry.
Anyway, for any theory that counters accepted theory, one must provide "acceptable" evidence that the new theory is worthy of further thought.

What would be interesting is if you could use your undoubtedly creative mind to design an experiment that supports this theory. Not that you have to build it, as it might be prohibitively expensive for an individual, but properly propose it for others to MAYBE take it up.

In my mind, Newton, Einstein, and others never committed to a pull or push theory of gravity, they simply weren't sure. I'm not a historian when it comes to Physics, but I don't know that pull gravity has shown any more evidence than push theories. They'd behave mostly the same.

I know, this is all speculation, but that's what science does, it thinks, looks at evidence, makes predictions, tests those, thinks again, etc... I'm just thinking, I really have no stake in the subject, beyond the fact that I kinda like gravity, it's a handy dandy thing to have in this universe.

As for a test, it would be a prohibitively expensive test, or likely would require incredibly sensitive equipment. But if a push theory of gravity is true, there's a few things that would hold true. But first let me state a few assumptions I'm making:
1) Pushing would be done by something, as yet unknown. Particle or radiation, I don't know, but I would lean towards radiation, not going to get into it right now, it's all speculation.
2) The source of the "pushing" objects is mostly uniform throughout the universe, and replenishes itself somehow (if radiation, it absorbs radiation that other source objects emitted previously). Again, all speculation, but just stating the presumptions.
3) Mass and matter (or the most fundamental objects of matter) would absorb a very small fraction of this energy, most of it would simply pass through.
4) Since some of it is absorbed, that has the effect of "lessening" gravity to all objects on the "shaded" side of any object. The more massive object, the more it "shades", hence, why we are attracted or pushed to the earth.

Now, to the test(s). If a push theory were true:
1) There would be a theoretical maximum weight of an object. At some point, all the "pushing" material coming from one direction would be absorbed by a sufficiently massive object. This may be an incredibly massive object (no clue how large, maybe a planet made of heavy elements the same diameter of Antares, I don't know...) If this were true, adding additional mass to the supermassive object would not increase the apparent weight of any object being attracted to it. How to test this, no clue.

2) With current pull theories, during a solar eclipse, the gravitational effect in the direction of the sun would be effectively the gravitational effect of the Sun + Moon. With a push theory, the effective gravitational effect would be slightly smaller than the combined effect of the Sun + Moon. This effect would be even more pronounced (if even so miniscule) during a solar eclipse if you were to test the effect from the exact opposite side of the Earth that is witnessing the eclipse. In this case, pull gravity would be Sun + Moon + Earth. With a push theory, it would be slightly less than that sum. How much less I have no clue.

3) With sufficiently sensitive equipment, and a sufficiently long rod, this theory would also be testable: A long, thin rod would weigh more laying on its side than it weighs standing up. Let's say a rod 1 cm in diameter and 1 km long. If this is large enough to verify, or what level of sensitivity of equipment is required I have no clue. On its side, it would weigh a certain amount. Standing up, it would weigh slightly less, maybe 10^-15 percent less, who knows, but in a push gravity theory, that would be the case.

The reason #2 and #3 would show those effect is because at any given point, there is a certain amount of pushing objects/energy going into that object. If the object were "shadowed" by a kilometer of metal directly above it, then only 99.99999999999999999% (pick a number) of those pushing objects/energy are available to push on the object, leaving a slightly lower probability of interaction than if it were at the top (or on its side), and hence weighing slightly less.

Testing #2 or #3, if these effects were seen, would in my mind lean towards a push theory of gravity. However, not seeing these effects wouldn't necessarily prove that the effect isn't there, it simply may mean the equipment or the objects weren't sensitive or massive enough respectively.
 
  • #28
So what kind of roof would I need to get to create a push-gravity shadow that will let me float around inside?
 
  • #29
brainstorm said:
So what kind of roof would I need to get to create a push-gravity shadow that will let me float around inside?

A *really* really big one :) Most likely the same mass as you would need to create artificial gravity in a pull scenario.
 
  • #30
Barwick said:
A *really* really big one :) Most likely the same mass as you would need to create artificial gravity in a pull scenario.

So you're conceptualizing this push-gravity as a type of radiation that is blocked by mass where more mass = more blockage?
 
  • #31
Barwick said:
I don't know that pull gravity has shown any more evidence than push theories. They'd behave mostly the same.
What about the drag force mentioned on WP?
 
  • #32
brainstorm said:
So you're conceptualizing this push-gravity as a type of radiation that is blocked by mass where more mass = more blockage?

Essentially. I'd lean towards the most elementary particles being the ones that absorb it to some degree, or are affected by it. Whether it's the radiation actually running into matter, or possibly just interacting with it by passing close enough by, I don't know. Just thinking out loud.
 
  • #33
Sorry. Just making sure I'm not having a nightmare.

PF is entertaining discussions on push gravity?

What's next? Calls for submissions of PMMs?
 
  • #34
Barwick said:
I know, this is all speculation, but that's what science does, it thinks, looks at evidence, makes predictions, tests those, thinks again, etc...
True, but that's not what PF does. We don't generate new science, we teach existing science. Thread locked.
 

1. What causes us to be pushed or attracted to a planet?

The force of gravity is what causes us to be pushed or attracted to a planet. Every object with mass has a gravitational pull, and the larger the object, the stronger the pull. Planets have a significant amount of mass, which is why their gravitational pull is strong enough to affect objects, like humans, on Earth.

2. How does the distance from a planet affect the force of gravity?

The force of gravity decreases as the distance between two objects increases. This means that the closer we are to a planet, the stronger its gravitational pull on us will be. As we move farther away, the force of gravity decreases.

3. Are we always being pushed or attracted to a planet?

Yes, we are always being pushed or attracted to a planet due to its gravitational pull. However, other forces, such as the Earth's rotation and our own movements, can counteract this force and make us feel like we are not being pushed or attracted.

4. Can we be pushed or attracted to multiple planets at the same time?

Yes, we can be pushed or attracted to multiple planets at the same time. The force of gravity from each planet will act on us simultaneously, and the overall effect will depend on the distance and mass of each planet.

5. Is there a difference between being pushed and attracted to a planet?

Being pushed and being attracted to a planet are two ways of describing the same phenomenon. The force of gravity is what causes us to be pushed towards a planet, but it can also be described as being attracted to the planet's mass.

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