Gravitational attraction between two atoms

[Dmitry Tyurev]

The question: Is there a gravitational attraction between two atoms if they are located at a distance of several light years of each other? Or physics does not have the answer to this question yet? )
(Sorry if this question has already been discussed on the forum. Please send a link to the topic then.)

 

[Vanadium 50]

Sure. But it's too small to measure with just two atoms.

 

[Nugatory]

The question: Is there a gravitational attraction between two atoms if they are located at a distance of several light years of each other? Or physics does not have the answer to this question yet? )

It would be a good exercise to calculate the predicted strength of the gravitational force between two atoms several light years apart. The classical Newtonian formula $F_g=Gm_1m_2/r^2$ will work just fine; google will give you $G$ and good ballpark numbers for the masses.

 

[Dmitry Tyurev]

It would be a good exercise to calculate the predicted strength of the gravitational force between two atoms several light years apart. The classical Newtonian formula $F_g=Gm_1m_2/r^2$ will work just fine; google will give you $G$ and good ballpark numbers for the masses.

Correct me if I'm wrong, but this formula can be used only if gravity is not quantized (so the gravitational force can be infinitely small). But if gravity is quantized, then this formula cannot be used. In this case the gravitational attraction of the first atom will act on the second atom only if it will absorb a graviton emitted by first atom. But at such a great distance, none of gravitons emitted by the first atom is unlikely to be absorbed by the second atom. So will not be gravitational interaction between them at all.
Is this right or not?

 

[Vanadium 50]

1. No, it's not right.
2. Classical gravitation is adequate to describe the situation.

 

[Dmitry Tyurev]

1. No, it's not right.
2. Classical gravitation is adequate to describe the situation.

Question A: Whether gravity is quantized or not - it's not known yet. Right?
Question B: If gravity is quantized then my previous post is correct. Right?

 

[Topolfractal]

Picture this gravitons are waves of space time curvature. Propagation of the waves through objects in between the atoms doesn't deter them, it just bends the objects. The graviton waves will reach the other atom. For an example picture wave particle duality as in the earlier days of quantum mechanics.

 

[Topolfractal]

And quantum gravity as it is currently formulated requires the existence of a graviton and therefore a quantization of gravity.

Question A: Whether gravity is quantized or not - it's not known yet. Right?
Question B: If gravity is quantized then my previous post is correct. Right?

 

[Topolfractal]

And for question B no quantization has nothing to do with the calculation due to the g-force between the atoms being more than that of the force of one graviton.

 

[Vanadium 50]

Question A: Whether gravity is quantized or not - it's not known yet. Right?
Question B: If gravity is quantized then my previous post is correct. Right?

"Gravity is quantized" is a string of scientific-sounding words strung together. It is meaningless - it has so many possible interpretations that there is no way to pick one. If you mean "is there a complete quantum theory of gravity", the answer is that is that there is not, but one does not need it to answer this question. And no, your description of quantum gravity is not correct, and I can say that without reservation. Quantum gravity is a quantum field theory, and what you wrote is incorrect for any quantum field theory.

It sounds a lot like you are promoting your own theory here - I would recommend you look at the PF Rules before going any farther in this direction.

 

[rumborak]

I don't understand why you are coming down so hard on the OP just now. While he may not have chosen the most precise terminology, it's rather clear what was meant: He assumes, and not without reason, that just like light, gravity is mediated with quantized particles. So, he makes the reasonable conjecture that unless an object is interacting with a graviton, it will not experience a gravitational pull.
The final *conclusion* is sketchy, but his question is perfectly fine.

His other assertion, that we simply don't know, is not too far off either. I remember reading that at least up until a few years ago, the validity of the regular gravitational law had not been experimentally verified for distances less than a few centimeters.

 

[Topolfractal]

But the law is being applied across light years.

The question: Is there a gravitational attraction between two atoms if they are located at a distance of several light years of each other? Or physics does not have the answer to this question yet? )
(Sorry if this question has already been discussed on the forum. Please send a link to the topic then.)

 

[Mark Sloan]

Like Dmitry, I am interested in the answer to his question.

I might expand on what I understand to be the intent of his question by adding:

“By general relativity, the mass of the first atom will distort space-time so there will be an apparent super tiny force acting on the second atom after that distortion has time (several years) to propagate to the second atom – so there is no limit on how small a gravitational force can be. But if graviton particle exchange (a quantum mechanical idea) is the mechanism that produces gravity, then could the momentum of a single graviton be so large (or so unlikely to be in the area) that no gravitational force at all is felt?”

Dmitry, correct me if I have misunderstood your question.

I also wonder about another possibility, if the gravitational force from gravitons from the other atom is felt only sporadically and only averages over time to the same as the general relativity value – so there is no “on average” limit on how small a gravitational force can be even if gravitons are real and have some quantized minimum momentum.

My question doubtless reveals my ignorance on the subject, but that is why I am asking.

 

[jtbell]

He assumes, and not without reason, that just like light, gravity is mediated with quantized particles. So, he makes the reasonable conjecture that unless an object is interacting with a graviton, it will not experience a gravitational pull.

The proper analogy to make with the gravitational force between two objects, is the electrostatic force between two charges, not the electromagnetic radiation produced by oscillating charges.

People often describe the electrostatic force as being mediated by virtual photons, especially in the popular literature and maybe low-level introductory textbooks. However, virtual photons are not in fact necessary for this. One can analyze electrostatic interactions in QED without using virtual photons at all. A former poster here named Tom Stoer, and probably some other people, have discussed this repeatedly on PF, although I can't lay my fingers on a specific post just now.

 

[Vanadium 50]

But the law is being applied across light years.

Yes, and? There is no asterisk after either gravitational or electrostatic force laws saying "except when things are separated by light-years".

 

[rumborak]

I think that exact limit is what he's interested in, and whether it still holds. I mean, duh, of course he can plug just a large distance value into the usual gravity formula and just get a very small value out.
The question is no different than asking "A radio tower is sending a regular radio wave from Earth; at what distance does one need to consider singular photons and whether they hit my receiver on Alpha Centauri?"

 

[Topolfractal]

But the law is being applied across light years.

I don't understand why you are coming down so hard on the OP just now. While he may not have chosen the most precise terminology, it's rather clear what was meant: He assumes, and not without reason, that just like light, gravity is mediated with quantized particles. So, he makes the reasonable conjecture that unless an object is interacting with a graviton, it will not experience a gravitational pull.
The final *conclusion* is sketchy, but his question is perfectly fine.

His other assertion, that we simply don't know, is not too far off either. I remember reading that at least up until a few years ago, the validity of the regular gravitational law had not been experimentally verified for distances less than a few centimeters.

 

[Topolfractal]

The Rumborack post is what I meant to quote before.

 

[Mark Sloan]

Here is a relevant FAQ link about virtual particles suggested by anorlunda in a recent thread https://www.physicsforums.com/threads/particles-vs-virtual-particles-vs-fields.817640/#post-5132361

Link is http://math.ucr.edu/home/baez/physics/Quantum/virtual_particles.html

I see that virtual particles as the carriers of force are not as real as I, and perhaps Dmitry, assumed.

And from the link, “Quantum gravity is not yet a complete, established theory, so gravitons are still speculative. It is also unlikely that individual gravitons will be detected any time in the near future.”

 

[Keith]

The question: Is there a gravitational attraction between two atoms if they are located at a distance of several light years of each other? Or physics does not have the answer to this question yet? )
(Sorry if this question has already been discussed on the forum. Please send a link to the topic then.)

Yes.
Things are gravitationally attracted to each other out to infinity

 

[Vanadium 50]

The question is no different than asking "A radio tower is sending a regular radio wave from Earth; at what distance does one need to consider singular photons and whether they hit my receiver on Alpha Centauri?"

Yes it is. In one case you have real quanta and in the other only virtual quanta. Gravity is not caused by streams of gravitons emitted by massive objects.

 

[Drakkith]

Correct me if I'm wrong, but this formula can be used only if gravity is not quantized (so the gravitational force can be infinitely small). But if gravity is quantized, then this formula cannot be used. In this case the gravitational attraction of the first atom will act on the second atom only if it will absorb a graviton emitted by first atom. But at such a great distance, none of gravitons emitted by the first atom is unlikely to be absorbed by the second atom. So will not be gravitational interaction between them at all.
Is this right or not?

No, it isn't right, as V50 explained. As I understand it, the electrostatic force on a charged particle can be any amount, even though electromagnetism is quantized. As you increase the distance between two charged particles, the force exerted on each particle falls smoothly and continuously, despite quantization. This is very different from something like an EM wave, which will interact via real photons and can be described similarly to what you've posted here. Similarly, the gravitational force should fall off smoothly and continuously as the distance between two objects increases, regardless of quantization.

As has been touched on already, virtual particles cannot be said to be emitted by an emitter, travel across space, and then be absorbed by a receiving particle in the same way that real particles can.

 

[Dmitry Tyurev]

Picture this gravitons are waves of space time curvature. Propagation of the waves through objects in between the atoms doesn't deter them, it just bends the objects. The graviton waves will reach the other atom.

So, one atom will have a gravitational pull on the other atom at ANY distance even if gravity is quantized?

 

[Dmitry Tyurev]

And for question B no quantization has nothing to do with the calculation due to the g-force between the atoms being more than that of the force of one graviton.

Can the g-force between two atoms be arbitrarily small? Or there can exist a (quantum) limit?

 

[Dmitry Tyurev]

He assumes, and not without reason, that just like light, gravity is mediated with quantized particles. So, he makes the reasonable conjecture that unless an object is interacting with a graviton, it will not experience a gravitational pull.

Thanks, you are absolutely right. I meant exactly that. )
So what modern physics says about this? Can it be that "unless an object is interacting with a graviton, it will not experience a gravitational pull"?

 

[Drakkith]

Thanks, you are absolutely right. I meant exactly that. )
So what modern physics says about this? Can it be that "unless an object is interacting with a graviton, it will not experience a gravitational pull"?

I believe the rest of the thread explains this.

 

[Dmitry Tyurev]

Dmitry, correct me if I have misunderstood your question.

You have absolutely correctly understood my question. )

I also wonder about another possibility, if the gravitational force from gravitons from the other atom is felt only sporadically and only averages over time to the same as the general relativity value – so there is no “on average” limit on how small a gravitational force can be even if gravitons are real and have some quantized minimum momentum..

In this case, the gravitational force will be felt not permanent, but as a separate events.