Gravity at atomic scale ? ............

[cable]

Newton tells us that gravity exists at any distance with any mass.
But we have no expériment to show that gravity exists at atomic scale:
Earth attracts a single atom. Does a single atom attract earth ?

When light particles/elements gather to form a star, this cannot be due to gravity, kuz it's so weak or perhaps inexistant at atomic scale ?.... There must be other forces to start the formation. Gravity starts from a certain size to finish the job.

Question:
Do you think that gravity exists at atomic scale, or it starts interaction only when mass reaches a certain size ?

[Eta C]

It exists, but due to the small masses involved is a distinctly second order effect compared to EM or the two nuclear forces. As such it can safely be neglected when examining the interactions of atoms with each other. At atomic scales, a full-up quantum theory of gravity will be necessary. However (as some ATM types who will remain nameless will gleefully tell you) there is still no fully satisfactory quantum theory of gravity. Even when one is developed it won't be necessary to invoke it on atomic scales.

[TriangleMan]

Hi cable, haven't seen you around for a year or so, what's happening?

As for gravity, using (G*m1*m2)/r^2 (I hope that's right, I'm doing this off the top of my head) would get some really small numbers at the atomic scale, likely too small to detect. I'd vote for that gravity does exist at an atomic scale but is too small to make a difference. Perhaps someone more knowledgable of cutting-edge physics equipment would know if detection is possible or not.

[Normandy6644]

The force of gravity pales in comparison to all other forces at that level. As Eta C said, even when we do have a full theory of quantum gravity, I'm not sure exactly what it will do to bring gravity into the atomic picture. It will be there, but mostly in the shadows.

[cable]

Hi cable, haven't seen you around for a year or so, what's happening?

Hi TM. That's right. I was on an intergalactic trip, too far from earth. Huh ! :wink:

Back to gravity.
We have to admit that there is no experiment to supprt the existence of gravity at atomic scale.
It's merely an assumption, which may be wrong !

[Eta C]

Hi cable, haven't seen you around for a year or so, what's happening?

Hi TM. That's right. I was on an intergalactic trip, too far from earth. Huh ! :wink:

Back to gravity.
We have to admit that there is no experiment to supprt the existence of gravity at atomic scale.
It's merely an assumption, which may be wrong !

I'll do a search here, but there may have been experiments that have measured the effect. One thing is certain, there have been no experiments that have conclusively ruled out that gravity operates on all distance scales. Therefore, there is no reason not to accept that it operates on atoms the same way it operates on planets. It is not an assumption. That implies something with no basis in observation. Rather, the existence of gravity on atomic scales is the reasonable extrapolation of observed effects which, until evidence to the contrary is found, is acceptable as true.

[Demigrog]

Back to gravity.
We have to admit that there is no experiment to supprt the existence of gravity at atomic scale.
It's merely an assumption, which may be wrong !

1) Earth's gravity pulls in atomic scale particles all the time
2) So does the Sun
3) The effects of gravity on particle beams is quite as expected
4) Etc

So, we do not really have to test for gravity at the atomic level, since we see its effects frequently.

Clearly at sub-atomic distances the rules get a bit muddier. For one thing, the gravitational force is related to the inverse square of radius, which would mean gravity might be significant in particle collisions. Of course, particles do not collide in a Newtonian sense, and I have no idea if they can really get close enough for gravity to become significant relative to other forces. We need a particle physicist to comment.

[Demigrog]

Oops, silly me, I forgot the obvious. The point where gravity becomes equal to the other forces is the Planck Length, or 10^-33 cm. String theory, among other things, predicts that the effects of extra spacial dimensions will cause departures from Newtonian gravity at that scale. Some researchers, IIRC, have predicted abnormalities in the mm distance range, testing using AFM probes, but not found anything yet.

Edit: Found a link on the subject: http://www.aip.org/pt/vol-53/iss-9/p22.html

[Eta C]

Hah! particle physicist to the rescue. Found the evidence I was talking about. This was part of the work that led to the 1997 Nobel Prize in Physics awarded to Chu, Cohen-Tannoudji, and Phillips. They found a way to trap atoms in what they called "optical molasses." Basically, they trapped sodium and cesium atoms between intersecting laser beams. By varying the frequency to match the emission modes of the atoms, they were able to confine them in space and cool them to ultra-low temperature. One of the many effects they were able to study was a so-called "atomic fountain." They were able to give some of atoms a small upward kick and observe their ballistic trajectory as they fell back under the influence of gravity. This effect was described in Chu's Nobel Lecture (accessable via the link above) as well as in an article in Physical Review Letters (Kasevich, et al. PhysRevLett V63 P612, 1989).

So, the effect of gravity on individual atoms has been experimentally observed and verified. Sorry Cable, not an assumption, not an extrapolation, it's a fact.

[papageno]

Bound states of neutrons in Earth's gravitational potential well have been observed:

NATURE, VOL 415, 17 JANUARY 2002, p. 297.

[Normandy6644]

Oops, silly me, I forgot the obvious. The point where gravity becomes equal to the other forces is the Planck Length, or 10^-33 cm. String theory, among other things, predicts that the effects of extra spacial dimensions will cause departures from Newtonian gravity at that scale. Some researchers, IIRC, have predicted abnormalities in the mm distance range, testing using AFM probes, but not found anything yet.

Edit: Found a link on the subject: http://www.aip.org/pt/vol-53/iss-9/p22.html

One really cool idea to explain why the gravitational force is so weak compared to the others is that it is not bound to a single membrane (i.e., "universe"), but rather it is able to move freely within any number of parallel membranes. By "it" I mean the graviton.

[Brady Yoon]

Yes. Gravity is always there, no matter how small the masses or how far apart they are. Two neutrinos on the opposite ends of the universe would be attracted. (Not very much, of course. :P )

[cable]

So, the effect of gravity on individual atoms has been experimentally observed and verified. Sorry Cable, not an assumption, not an extrapolation, it's a fact.

The experiment of the Nobel prize you're talking about, is about interaction of the mass of earth with a particle. ie. gravity between earth and a particle
I have no doubt it can be proven experimentally.

My question was about gravity between a particle/atom and another particle/atom, that's what I'm calling "gravity at atomic scale". To make it simpler, consider the 2 particles at a distance higher than Planck's.

[Demigrog]

Yes. Gravity is always there, no matter how small the masses or how far apart they are. Two neutrinos on the opposite ends of the universe would be attracted. (Not very much, of course. :P )

I'm not sure it is as clear cut as that; boundary conditions like very small mass, very large mass, very small distance, and very large distance are all beyond our current capabilities to produce in experiments. There are reasonable theories (string theory for one) that predict different behaviors at these boundaries, and are mathematically as valid as assuming newtonian gravity holds in all conditions.

[Eta C]

So, the effect of gravity on individual atoms has been experimentally observed and verified. Sorry Cable, not an assumption, not an extrapolation, it's a fact.

The experiment of the Nobel prize you're talking about, is about interaction of the mass of earth with a particle. ie. gravity between earth and a particle
I have no doubt it can be proven experimentally.

My question was about gravity between a particle/atom and another particle/atom, that's what I'm calling "gravity at atomic scale". To make it simpler, consider the 2 particles at a distance higher than Planck's.

If earth can attract an atom, that atom has mass. If atoms have mass, they attract each other gravitationally. It's as simple as that. As I said in my first post in reply, that force is small compared to other forces on an atomic scale, but it's always there. In stellar formation EM may play a role in the initial clumping of atoms, but once the objects get to a size slightly larger than dust particles, gravity becomes overwhelming. That's because we're beyond the range of the nuclear forces and matter, as a whole becomes electrically neutral (this inlcudes plasmas, by the way).

[Demigrog]

My question was about gravity between a particle/atom and another particle/atom, that's what I'm calling "gravity at atomic scale". To make it simpler, consider the 2 particles at a distance higher than Planck's.

Obviously, it would be no simple task to develop such an experiment. Possibly gas chamber studies of particle collisions at high speeds might show gravitational effects, but I'm in over my head already. Single-atom interaction with another single atom would approach the kind of boundary condition I mentioned previously; I think you are correct in that we cannot be sure whether it would match Newtonian predictions. However, I suspect (with no facts to support me at the moment) that any atom has sufficient mass to be well above the boundary conditions where Newtonian gravity fails. There are plenty of particles far less massive than Protons.

[TriangleMan]

If earth can attract an atom, that atom has mass. If atoms have mass, they attract each other gravitationally. It's as simple as that.

Layman question:

Aren't some scientists trying to find a graviton particle? If such a particle exists would individual particles such as neutrons be affected by them? Not that there is any reason why a graviton couldn't it's just that if such a particle existed then could there possibly be a lower limit of mass under which it will not be affected by a graviton?

[Eta C]

If earth can attract an atom, that atom has mass. If atoms have mass, they attract each other gravitationally. It's as simple as that.

Layman question:

Aren't some scientists trying to find a graviton particle?

Yes, gravitons would be the force carrying particle of gravity analagous to photons for the EM force, W and Z for weak nuclear, and gluons for the stron nuclear force. This would put gravity onto the same theoretical basis as the other three forces. Such a theory would be consistent with general relativity, the current theory of gravity. We know some properties the graviton must have. It will be massless (gravity has an infinite range) and will have a spin of 2 (the reasons here are a bit more esoteric).

If such a particle exists would individual particles such as neutrons be affected by them?

Sure. On the subatomic level, forces are carried by the exchange of particles. Individual particles would couple to the graviton with a strength proportional to their mass. It's just that the coupling is weak compared to other forces. What makes gravity strong over macroscopic distances is its infinite range (the nuclear forces are strong, but extremely short-ranged) and it's lack of any charge shielding effect (EM is limited by the fact that bulk matter is electrically neutral). I'm talking in terms of standard gravitational theories here, various dark energy theories and cosmological models posit a time when gravity had a repulsive effect as well as an attractive one (no bad puns, please :roll: )

Not that there is any reason why a graviton couldn't it's just that if such a particle existed then could there possibly be a lower limit of mass under which it will not be affected by a graviton?

Possible, but not likely. Such a cut-off would impose complications in the theory. Besides, as I've said before, there is no evidence for such a cut-off (Plank-length limits aside). After all, photons are affected by gravity, and they are massless.

[cable]

Yes, gravitons would be the force carrying particle of gravity analagous to photons for the EM force, W and Z for weak nuclear, and gluons for the stron nuclear force. This would put gravity onto the same theoretical basis as the other three forces.

Perhaps it's a mistake to consider gravity the same way we consider all other 3 forces.
It's more mysterious and much weaker.

If we can show experimentally that there is no such a gravity ( and/or no inerty ) at atomic scale, then the graviton doesn't exist. A pure fiction.
Why ?
if garviton exists then he must interact at atomic scale ( over Planck's distance ), same way as his peers in EM, gluon etc ...

Back to the old Bohr's model.
Wa are told we cannot consider electron circling nucleii like earth/sun, kuz at this scale, it doesn't match experiment. we have to use QM.
Perhaps the reason is different: there's no gravity nor inerty at this atomic scale.

And remember , graviton is one the most wanted entity since long time ago. Not found yet.
I suggest it doesn't exist.

[Normandy6644]

Yes, gravitons would be the force carrying particle of gravity analagous to photons for the EM force, W and Z for weak nuclear, and gluons for the stron nuclear force. This would put gravity onto the same theoretical basis as the other three forces.

Perhaps it's a mistake to consider gravity the same way we consider all other 3 forces.
It's more mysterious and much weaker.

If we can show experimentally that there is no such a gravity ( and/or no inerty ) at atomic scale, then the graviton doesn't exist. A pure fiction.
Why ?
if garviton exists then he must interact at atomic scale ( over Planck's distance ), same way as his peers in EM, gluon etc ...

Back to the old Bohr's model.
Wa are told we cannot consider electron circling nucleii like earth/sun, kuz at this scale, it doesn't match experiment. we have to use QM.
Perhaps the reason is different: there's no gravity nor inerty at this atomic scale.

And remember , graviton is one the most wanted entity since long time ago. Not found yet.
I suggest it doesn't exist.

The graviton has to exist for much of modern particle physics to be correct. THe difficulty is in detecting in, but new labs (Large Hadron Collider for one) will have the capability of detecting them eventually. Also, I don't know how you could show experimentally that there is no gravity at the atomic level, since the effects (in this membrane anyway) would be minimal.

[Eta C]

A small confession and a comment on Cable's post above.

One is regarding my comment on gravity affecting massless photons. On reflection this is a naive comment and I'm somewhat embaressed I made it. In a relativistic theory, gravity couples to the full energy-momentum 4-vector rather than just the rest mass of object. Mea culpa, won't happen again, don't bother to point this out endlessly, etc.

Now to the comment. The other three forces have very successfully been described in terms of quantum field theories (QED, QCD, Weinbeg-Salaam's electroweak theory). Having three forces described one way and the fourth another is dissatisfying. Physicists believe that we should be able to put gravity into the same theoretical framework as the other three (that is as a quantum field theory with the graviton as the force carrying particle). Although we haven't directly observed gravitons yet, there is nothing so far to suggest that we won't eventually do so.

In a more general sense, I believe that the four forces will eventually be unified in one theoretical structure. Right now the best candidate is a quantum field theory. If bringing gravity into that fold, however, proves to be too intractable (although it's too soon to make that judgement) this structure may be something other than a quantum field theory.

[Eta C]

If we can show experimentally that there is no such a gravity ( and/or no inerty ) at atomic scale, then the graviton doesn't exist. A pure fiction.

If. Gravitons may not have been directly detected yet, but there is no experimental result that excludes their existence.

remember , graviton is one the most wanted entity since long time ago. Not found yet.
I suggest it doesn't exist.

Not to be snide, but most practicing physicists would consider your suggestion premature.

[papageno]

Back to the old Bohr's model.
Wa are told we cannot consider electron circling nucleii like earth/sun, kuz at this scale, it doesn't match experiment. we have to use QM.
Perhaps the reason is different: there's no gravity nor inerty at this atomic scale.

Even in Bohr's model, the electron is bound to the nucleus due to electromagnetic interaction, not due to gravity.

The reason why it does not work, is because at that scale electrons and nuclei do not behave like classical particles, not because gravity does not work there.

Indeed, the experiment with neutrons shows clearly that quantum particles are affected by gravity.

[Tensor]

A small confession and a comment on Cable's post above.

One is regarding my comment on gravity affecting massless photons. On reflection this is a naive comment and I'm somewhat embaressed I made it. In a relativistic theory, gravity couples to the full energy-momentum 4-vector rather than just the rest mass of object. Mea culpa, won't happen again, don't bother to point this out endlessly, etc.

Eta C, in reality, how many people here do you think really thought about the coupling of gravity with the EM 4 vector (much less caught the error?)? Your initial post was close enough to be understood by almost everyone here, without the technically correct explanation.

Physicists believe that we should be able to put gravity into the same theoretical framework as the other three (that is as a quantum field theory with the graviton as the force carrying particle). Although we haven't directly observed gravitons yet, there is nothing so far to suggest that we won't eventually do so.

But, while I got you, in the geometrical model of gravity, it is spacetime that is curved by a mass. With the graviton model, would it be the path of a particle is curved, because of the interaction of the particle with the graviton? Or is the graviton interacting with spacetime, causing it to be curved with the particle just following the curve?

In a more general sense, I believe that the four forces will eventually be unified in one theoretical structure. Right now the best candidate is a quantum field theory. If bringing gravity into that fold, however, proves to be too intractable (although it's too soon to make that judgement) this structure may be something other than a quantum field theory.

The various QM theories are time reversable, which seems to indicate that the force particles do not interact with time. The graviton would seem to have to interact with time, due to the changes in time gravity can cause. Is there any current thought on how the graviton would interact with time? Or am I way off base here?

[cyrek1]

cyrek1 comment

I believe gravity is a manisfestation of EMF. A slight imbalance caused by proton flips to attract rather to repel.

There are THREE reasons for this.
Both forces weaken as the inverse souare to distance.
Both extend to infinity.
Both travel at the velocity of light.

This should be reasonably good evidence to consider.

I wrote a couple of papers on this board that would require the search engine ti find.
One is 'A New GUT theory'. The other is 'Electromagnetic Gravity' or EM Gravity.

[papageno]

I believe gravity is a manisfestation of EMF. A slight imbalance caused by proton flips to attract rather to repel.

There are THREE reasons for this.
Both forces weaken as the inverse souare to distance.
Both extend to infinity.
Both travel at the velocity of light.

This should be reasonably good evidence to consider.

I wrote a couple of papers on this board that would require the search engine ti find.
One is 'A New GUT theory'. The other is 'Electromagnetic Gravity' or EM Gravity.

What about neutrons?

[Gullible Jones]

:roll:

[cable]

But, while I got you, in the geometrical model of gravity, it is spacetime that is curved by a mass. With the graviton model, would it be the path of a particle is curved, because of the interaction of the particle with the graviton? Or is the graviton interacting with spacetime, causing it to be curved with the particle just following the curve?

Good question.

As I understand it, graviton is what 2 masses exchange to make them attractive to each other. ie. they have to exchange the gravition - if it exists - to get closer to each other. That's enough to make gravity attraction , why should it curvate s-t. ?

Considering space-time is not empty kuz we know that what we call vacuum is in fact filled with something.
They call it energy of vacuum.
Could it be that the distribution of that energy that is affected by the presence of mass, not the geodesic of s-t. ?
The result still the same: light path is curved .

[Normandy6644]

But, while I got you, in the geometrical model of gravity, it is spacetime that is curved by a mass. With the graviton model, would it be the path of a particle is curved, because of the interaction of the particle with the graviton? Or is the graviton interacting with spacetime, causing it to be curved with the particle just following the curve?

Good question.

As I understand it, graviton is what 2 masses exchange to make them attractive to each other. ie. they have to exchange the gravition - if it exists - to get closer to each other. That's enough to make gravity attraction , why should it curvate s-t. ?

That's the classical picture of gravity. The "attractive" nature of it is only a consequence of motion along a curved manifold, i.e., the geodesic. The graviton (to my recollection) is the particle that causes the curvature (someone correct me if I am wrong here).

Considering space-time is not empty kuz we know that what we call vacuum is in fact filled with something.
They call it energy of vacuum.

Right, as well as quantum field fluctuations on the Planck level.

Could it be that the distribution of that energy that is affected by the presence of mass, not the geodesic of s-t. ?
The result still the same: light path is curved .

Not a bad thought, but I'm not sure how that works with general relativity.

[cable]

Both ( EM and Gravity ) travel at the velocity of light.

True for EM.
As for Gravity, it's pure assumption. This has to be proven by detecting a gravitational wave. We don't know if it's a wave, let alone it's velocity.

You say that gravity must be of EM origin.
What makes this doubtful is the fact that gravity force is toooo small compared to EMF. A factor of 10^35 or so.

And as Papageno told you, neutrons contribute to garvity, not only protons as you said.