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Copernicus
2012-Jan-27, 04:39 PM
Is it possible that gravity only responds to the part of mass that is associated with charge?

trinitree88
2012-Jan-27, 05:12 PM
Is it possible that gravity only responds to the part of mass that is associated with charge?

Copernicus. Nope. Neutrons have no net electric charge, yet the separation of isotopes in a mass spectrometer depends upon the charge to mass ratio varying. That it does because the additional neutrons increase the nuclides' gravitational mass, and inertial mass, and the arc traced out in the chamber is different for each isotope comensurately. You'd also have to see no change in inertial mass and violate the principle of equivalence....which has always shown them to be the same (otherwise objects don't fall at the same rate in a gravitational field....(or change their weak interaction cross-sections in the neutrino sea). pete


SEE:http://en.wikipedia.org/wiki/Mass_spectrometry

SEE ALSO:http://www.google.com/imgres?q=mass+spectrograph&hl=en&biw=1014&bih=683&gbv=2&tbm=isch&tbnid=7Vfg9zShD-037M:&imgrefurl=http://www.mhhe.com/physsci/chemistry/carey/student/olc/ch13ms.html&docid=BpibIH6rQPqi6M&imgurl=http://www.mhhe.com/physsci/chemistry/carey/student/olc/graphics/carey04oc/ch13/figures/1334.gif&w=762&h=446&ei=h9siT-jGE8Ph0QHa4f3nCA&zoom=1&iact=hc&vpx=98&vpy=149&dur=78&hovh=172&hovw=294&tx=187&ty=94&sig=101622641883108794792&page=3&tbnh=125&tbnw=213&start=30&ndsp=18&ved=1t:429,r:5,s:30

SEE:http://www.worsleyschool.net/science/files/mass/spectrograph.html

antoniseb
2012-Jan-27, 05:26 PM
Nope. Neutrons have no net electric charge, yet the separation of isotopes in a mass spectrometer depends upon the charge to mass ratio varying...

I don't yet see how limiting gravity to charge bearing particles would be detectable, given that there are no neutral quarks, so even neutrons are made of charge carriers. However, I don't see how that could be a useful for any cosmological theory either. Would you care to elaborate?

caveman1917
2012-Jan-27, 05:27 PM
Is it possible that gravity only responds to the part of mass that is associated with charge?

Good question. Theoretically the answer is no. Practically, you might say neutrons are neutral but they are made up of charged quarks, so the only examples i can think of would be neutrino's (but it's still debated whether they actually have mass) and Z bosons (but those are so short-lived as to make it very hard to go and check).

However that would make most explanations of dark matter impossible, since that is electrically neutral mass (at least in the most popular speculations).

Strange
2012-Jan-27, 06:09 PM
Is it possible that gravity only responds to the part of mass that is associated with charge?

I'm not sure what you mean; what does "gravity responds to mean? Do you mean, is gravity only caused by charged particles? Or do you mean, are only charged particles affected by gravity?

John Jaksich
2012-Jan-27, 07:21 PM
I would speculate that there is confusion between the gravitational field--itself-- and the effect of a gravitational field upon the mass bearing the charge.---to put it another way?

phunk
2012-Jan-27, 08:31 PM
I don't yet see how limiting gravity to charge bearing particles would be detectable, given that there are no neutral quarks, so even neutrons are made of charge carriers.

There are elementary particles without charge, the obvious example being the photon. We know these are affected by gravity.

antoniseb
2012-Jan-27, 08:37 PM
... the photon. We know these are affected by gravity.
D'Oh... I was thinking about having mass, but you're absolutely right.

caveman1917
2012-Jan-27, 09:17 PM
There are elementary particles without charge, the obvious example being the photon. We know these are affected by gravity.

Sure, but the question seems to be phrased the other way around. It says "gravity responds to mass", not "mass responds to gravity", ie whether the only mass that causes gravity is charged mass. Since photons have no mass, they would not answer the question. As far as i know we only have neutrino's and Z bosons that fit.

Strange
2012-Jan-27, 09:24 PM
But as energy causes gravity just as much as mass does, wouldn't this include photons?

caveman1917
2012-Jan-27, 09:38 PM
But as energy causes gravity just as much as mass does, wouldn't this include photons?

Yes, however the question seems to specify 'mass' specifically. The way i interpreted the question was "of all forms of mass, does only mass associated with charge cause gravity?". But maybe i'm just interpreting too strictly, or perhaps i'm just interpreting it that way because that makes the question most interesting (other interpretations are easily answered) :)

Copernicus
2012-Jan-27, 09:50 PM
I'm not sure what you mean; what does "gravity responds to mean? Do you mean, is gravity only caused by charged particles? Or do you mean, are only charged particles affected by gravity?

I was referring to neutrons as being charged as well because they carry quarks.

Nick Theodorakis
2012-Jan-27, 09:51 PM
If WIMPs are real and a source of Dark Matter, would they be an example of a non-charged particle that can both react to and cause gravity?

Nick

Copernicus
2012-Jan-27, 09:53 PM
I know this sounds dumb, but since light is electromagnetic, would it have some sort of charge equivalence?

Copernicus
2012-Jan-27, 09:54 PM
Don't know that wimps really exist!

Copernicus
2012-Jan-27, 09:57 PM
I probably know the answer, but, have we ever measured the gravitational force between and electron, neutron, or proton with the earth or some other massive enough object? What is the smallest object we have been able to measure gravity with. How many grams or portion of grams?

Copernicus
2012-Jan-27, 09:58 PM
I was referring to charged particles being affected by the gravitational field.

caveman1917
2012-Jan-27, 10:00 PM
I know this sounds dumb, but since light is electromagnetic, would it have some sort of charge equivalence?

No it doesn't. So if your question was about affected by gravity then the answer is, as phunk pointed out, no. If your question is about causing gravity then the answer is in theory no, but experimental verification would be pretty much impossible.

caveman1917
2012-Jan-27, 10:03 PM
I was referring to charged particles being affected by the gravitational field.

In that case, everything is affected by the gravitational field, irrespective of charge or not, because the gravitational field really is just a "background geometry" and everything "follows" that geometry.

Copernicus
2012-Jan-28, 06:11 AM
No it doesn't. So if your question was about affected by gravity then the answer is, as phunk pointed out, no. If your question is about causing gravity then the answer is in theory no, but experimental verification would be pretty much impossible.

Is it possible to count one atom at a time until there are enough atoms, put them in a bag, and then measure the gravitational force to determine if theory matches experiment?

phunk
2012-Jan-28, 06:33 AM
Sure, but the question seems to be phrased the other way around. It says "gravity responds to mass", not "mass responds to gravity", ie whether the only mass that causes gravity is charged mass. Since photons have no mass, they would not answer the question. As far as i know we only have neutrino's and Z bosons that fit.

I think it would have to work both ways, or there's no more conservation of momentum.

Jeff Root
2012-Jan-28, 07:32 AM
Is it possible to count one atom at a time until there are enough
atoms, put them in a bag, and then measure the gravitational
force to determine if theory matches experiment?
The first part of that proceedure is unnecessary, because
it has already been done. The number of atoms in any
volume of any given isotope in a liquid or a crystalline
solid can easily be calculated from numbers you can look
up, which came from careful measurements and counts
of atoms. Just specify the volume, isotope, temperature,
and pressure, and anyone can look up the factor required
to calculate the total number of atoms.

So you just get a measured volume of a known isotope at
a measured temperature and pressure, and measure the
gravitational force between it and the Earth, which is done
all the time, or between it and another mass, which is
done pretty rarely, but has been done with a variety of
different isotopes.

-- Jeff, in Minneapolis

caveman1917
2012-Jan-28, 07:52 AM
Is it possible to count one atom at a time until there are enough atoms, put them in a bag, and then measure the gravitational force to determine if theory matches experiment?

In principle yes, in practice that's quite another matter of course :)

caveman1917
2012-Jan-28, 07:56 AM
I think it would have to work both ways, or there's no more conservation of momentum.

There are subtle effects in general relativity that make passive gravitational mass unequal to active gravitational mass. Since the stress-energy tensor also takes pressure into account, you'll have a greater active gravitational mass than passive gravitational mass for certain matter configurations depending on its state. Another way to think of this is as momentum being carried away by the gravitational field itself.

However when we take those effects into account momentum is indeed conserved and both are equal, so in theory the answer is definitely no. The question is how to experimentally verify that when you only got neutrino's and Z bosons to work with.

papageno
2012-Jan-28, 09:24 AM
I probably know the answer, but, have we ever measured the gravitational force between and electron, neutron, or proton with the earth or some other massive enough object? What is the smallest object we have been able to measure gravity with. How many grams or portion of grams?

Maybe this:
Quantum states of neutrons in the Earth's gravitational field (http://www.nature.com/nature/journal/v415/n6869/abs/415297a.html)



Here we report experimental evidence for gravitational quantum bound states of neutrons. The particles are allowed to fall towards a horizontal mirror which, together with the Earth's gravitational field, provides the necessary confining potential well. Under such conditions, the falling neutrons do not move continuously along the vertical direction, but rather jump from one height to another, as predicted by quantum theory.

Strange
2012-Jan-28, 02:43 PM
Maybe this:
Quantum states of neutrons in the Earth's gravitational field (http://www.nature.com/nature/journal/v415/n6869/abs/415297a.html)

That is very cool. There is a more readable (for mugs like me) discussion of the experiment here: http://backreaction.blogspot.com/2007/06/bouncing-neutrons-in-gravitational.html

Copernicus
2012-Jan-28, 06:48 PM
I think it would have to work both ways, or there's no more conservation of momentum.

You are right, I said it backwards.

Copernicus
2012-Jan-28, 06:51 PM
Maybe this:
Quantum states of neutrons in the Earth's gravitational field (http://www.nature.com/nature/journal/v415/n6869/abs/415297a.html)

That is cool!

Tensor
2012-Jan-29, 04:25 AM
The actual paper of Measurement of quantum states of neutrons in the Earth’s gravitational field (http://arxiv.org/pdf/hep-ph/0306198v1.pdf) published in Physical Review D on 13 May, 2003.