What is the smallest mass proven to have gravity?

[Robittybob1]

I know light paths are bent in a gravitational field but I haven't heard of light being attracted to light. What is the smallest mass proven/known to fall in a G field?

Is it the electron?

Gas molecules combined mass produce atmospheric pressure so even atoms as small as Hydrogen fall due to gravity. So masses smaller than Hydrogen only need to be considered.

This report talks of gravity effect on neutrons: http://www.nature.com/news/bouncing-neutrons-probe-dark-energy-on-a-table-top-1.15062

 

The neutrons bounce off the lower plate, which is a highly polished mirror, while the upper plate is an absorber that creams off those with the highest energies, to leave only neutrons in their lowest quantum state. Neutrons are ideal for these quantum bouncing experiments because they have only weak electrostatic polarization and carry no net electric charge, says study co-author Peter Geltenbort, a physicist at the Laue-Langevin Institute in Grenoble, France, which produced the neutrons for the experiments. “They only really feel gravity,” he says.

....

The team found that the neutrons' energy levels are exactly as if they are being acted on by gravity alone — measured on a scale 100,000 times smaller than ever tested before.

.

Edited March 12, 2016 by Robittybob1

[ajb]

The lightest elements that I know have been tested are hydrogen and antihydrogen (ALPHA at CERN). I am not an expert in these kinds of experiments, but I expect that working with much lighter objects would be very difficult. I am not sure if any experiment has been done that really tests how electrons fall.

Edited March 12, 2016 by ajb

[Strange]

I was going to mention ALPHA as well: http://alpha.web.cern.ch/node/248

[Rajnish Kaushik]

As far as we know, nothing is too small to be affected by gravity. In our current models, even the smallest particles have a gravitational affect on each other.

However, as far as I know, this this has never been checked experimentally. Maybe there is some small gravitational perturbation that can be seen in the collisions of particle accelerators? Someone with more expertise than I could maybe comment on that.

So the current understanding of gravity is given by models that are amazingly accurate in the regimes were we have experimentally checked them. And according to those models, there is nothing too small to be not affected by gravity.

[EdEarl]

As I understand, the Higgs boson affects Fermions, including the electron, which I think means electrons are affected by gravity.

[swansont]

As far as we know, nothing is too small to be affected by gravity. In our current models, even the smallest particles have a gravitational affect on each other.

 

However, as far as I know, this this has never been checked experimentally. Maybe there is some small gravitational perturbation that can be seen in the collisions of particle accelerators? Someone with more expertise than I could maybe comment on that.

 

 

 

Basically what the OP is asking.

[Robittybob1]

As I understand, the Higgs boson affects Fermions, including the electron, which I think means electrons are affected by gravity.

Could you explain your reasons better please? Even if you are wrong it will give me an avenue to look into.

[EdEarl]

Could you explain your reasons better please? Even if you are wrong it will give me an avenue to look into.

As with all quantum "magic", if you aren't confused you don't understand (corollary: be quiet and calculate). See: Finding how certain particles acquire mass

[Strange]

The Higgs mechanism may give things mass but that isn't relevant as to whether small masses are affected by gravity in the same way. We have no reason to doubt it but, for individual particles, no way to test it either.

[swansont]

As I understand, the Higgs boson affects Fermions, including the electron, which I think means electrons are affected by gravity.

 

Electrons have mass, so yes — the Higgs affects it, and so will gravity. The aren't any real particles unaffected by gravity, AFAIK.

[Robittybob1]

 

Electrons have mass, so yes — the Higgs affects it, and so will gravity. The aren't any real particles unaffected by gravity, AFAIK.

Yes even photons are affected by gravity but do they contribute to the gravity? It is probably sufficient to think that protons, neutrons and electrons are affected by gravity and contribute to gravity. Why I wanted to know this was thinking at what level of structure would gravitational radiation come from. Accelerate a kilo of mass, in effect you are accelerating many protons, neutrons and electrons and maybe each unit produces part of the overall radiation.

[EdEarl]

http://profmattstrassler.com/2012/10/15/why-the-higgs-and-gravity-are-unrelated/

[swansont]

Yes even photons are affected by gravity but do they contribute to the gravity?

 

They would contribute to the stress energy tensor in GR. Yes.

 

This also answers your main question, since we know photons are deflected by gravity and they have zero mass.

 

It is probably sufficient to think that protons, neutrons and electrons are affected by gravity and contribute to gravity. Why I wanted to know this was thinking at what level of structure would gravitational radiation come from.

 

GR is not a quantum theory. I doubt it makes any distinction. (Neutrons were not known for another 15 years after GR was proposed, so it could hardly account for them)

 

Accelerate a kilo of mass, in effect you are accelerating many protons, neutrons and electrons and maybe each unit produces part of the overall radiation.

But they are all attracted by much stronger interactions. If a particle unaffected by gravity existed, but it was bound to a normal particle, the composite system would still be affected by gravity. Lots of other physics would fail, though, so ultimately there's nothing to this, but that reasoning alone is not inherently sound.

 

But again, GR is not a quantum theory.

[Strange]

Yes even photons are affected by gravity but do they contribute to the gravity? It is probably sufficient to think that protons, neutrons and electrons are affected by gravity and contribute to gravity. Why I wanted to know this was thinking at what level of structure would gravitational radiation come from. Accelerate a kilo of mass, in effect you are accelerating many protons, neutrons and electrons and maybe each unit produces part of the overall radiation.

 

You are, as is so often the case, overthinking things.

 

Gravity is caused by the total mass and energy (plus some other things) of the system. There is no need to think about the fundamental particles.

[Robittybob1]

 

You are, as is so often the case, overthinking things.

 

Gravity is caused by the total mass and energy (plus some other things) of the system. There is no need to think about the fundamental particles.

But if I want to relate gravity back to fundamental particles is there anything wrong with that? Bremsstrahlung radiation seems to be an effect of electrons acting on protons even though the result of that you do get more tangible effects like an x-ray beam. So why not do the same thing for analogous gravitational radiation? Why not go back and look at the smallest everyday subatomic particles and see if they are the source of gravity? You might even see the similarity to magnetism, they relate magnetism to the alignment of atomic nuclei, so why not do something similar for gravity?

 

They would contribute to the stress energy tensor in GR. Yes.

 

This also answers your main question, since we know photons are deflected by gravity and they have zero mass.

 

 

GR is not a quantum theory. I doubt it makes any distinction. (Neutrons were not known for another 15 years after GR was proposed, so it could hardly account for them)

.....

Would there be some theoretical physicists trying to make it a quantum theory? If they were to discover a graviton would this alter your views?

Edited March 13, 2016 by Robittybob1

[ajb]

However, as far as I know, this this has never been checked experimentally. Maybe there is some small gravitational perturbation that can be seen in the collisions of particle accelerators? Someone with more expertise than I could maybe comment on that.[/size]

One can calculate the kinds of processes you would expect, at least up to one loop in perturbation theory. You will see that the contributions due to gravity are swamped by contributions from the standard model. There is little hope of discovering gravitational physics in collider experiments...

 

Unless we have large extra dimensions, meaning that the true scale of quantum gravity is far lower than the 4-dimensional Planck scale. It maybe possible to detect these extra dimensions via gravitons carrying off energy into these higher dimensions. So far nothing like that has been seen.

[swansont]

It's actually an interesting question.

Imagine, for example, that the electron has inertial mass, but not gravitational mass.

How would you know?

All determinations of the gravitational constant G are made using macroscopic lumps of uncharged matter.

So every electron is accompanied by several thousand times its mass of nucleons.

 

It's not clear how we could tell if all the "G" we measure is due to the heavy bits.

 

We can measure the inertial mass of electrons (etc) with a mass spectrometer- but that's got nothing to do with the determination of their tendency to "fall" under gravity.

 

 

One of the most precise things I can think of is the e/m ratio measurements made in a Penning trap (Gabrielse), but I can't find any mention of gravitational effects, possibly because the confining field is large enough to render them moot.

 

If you have a trap potential of 10V and a trap size of 1 mm, the electron can see 10 eV of electrostatic PE, but gravitational PE over the size of the trap is about 10^-13 eV. OoM calc: (~10^-30kg*10m/s^2*10^-3m)/(10^-19J/eV)

[John Cuthber]

I can't see a way round the problem. If you have enough charge that you have a meaningful excess (or deficit) of electrons to weigh, then you have a relatively huge electrostatic effect.

 

An electron, on a table in the lab is subject (we presume) to a gravitational pull of about 10^-31 N

And it's electrostatically attracted to the Earth (assumed to be conducting , a metre away, and near enough flat to make the maths easy) by a force of

about 0.6x10^-28 N

And it's attracted to just about everything else (for example, the experimenter) by a comparable force

 

And that's assuming you can "stop" a single electron in the middle of a vacuum chamber a metre or so across (you would probably need to go with something like the middle of a 100 metre vacuum chamber to get the charge effects significantly smaller than the gravitational ones.)

 

Even with a (much heavier) proton, you still have a huge problem because gravity is such a small force.

[Robittybob1]

Could you use neutrons as in #1?

[John Cuthber]

It's difficult to know what neutrons are up to since they fall apart and aren't affected by electromagnetic fields.

[swansont]

It's difficult to know what neutrons are up to since they fall apart and aren't affected by electromagnetic fields.

 

 

Not quite. Neutrons have a small magnetic moment, and have been magnetically trapped

http://www.nature.com/nature/journal/v403/n6765/abs/403062a0.html

http://www.nist.gov/public_affairs/releases/n00-01.cfm

 

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Moderator Note

 

I've split off the discussion of the ramifications of an electron not having inertial mass to a separate thread.

http://www.scienceforums.net/topic/93942-ramifications-of-electrons-not-having-gravitational-mass-split/

 

[Robittybob1]

can we see gravitational attraction between two neutrons as between two neutron stars? Would they tend to clump together? Would we have a problem of getting rid of their gravitational potential energy?

Edited March 13, 2016 by Robittybob1

[swansont]

can we see gravitational attraction between two neutrons as between two neutron stars? Would they tend to clump together? Would we have a problem of getting rid of their gravitational potential energy?

 

 

The stars, or the neutrons?

[Robittybob1]

 

 

The stars, or the neutrons?

Individual Neutrons. it seems like you can have a very dense object quite close to another

F = G m^2 / ( r^2 ). R^2 would be a very small number so can the force be measured?

Edited March 14, 2016 by Robittybob1

[Robittybob1]

Force came out to 2.93E-34 Newtons. If they were gravitationally bound could we use another force to move them to confirm they were bound?

Unbound ones should be easier to move, is that right?