Applying relativty, if lets we were to be able to make 2 clumps of protons together without using nuetrons, just raw protons and form 2 masses with them and have one being bigger then the other in mass, would the effect of "gravity" kick in and they would be attracted to each other? Or is this something only nuetron pull off? In other words I am wondering if nuetrons are the real key source to "gravitons" ************************************************* 05-22-06, 07:18 PM methos Anything with mass will attract anything else with mass, but this attraction is very weak.
How weak? It takes something as massive as the Earth to hold you down, but a (relatively) thin material, such as a chair, can hold you up. What's holding that chair together and preventing you from passing through it? The electromagnetic force.
Gravity is so much weaker than the electromagnetic force that it doesn't stand a chance of holding two protons together, whether there are neutrons there or not. So what does hold them together? A third force, the strong force. As the name suggests, it's strong, stronger even than the electromagnetic force at short distances. Distance is the key, though. The strong force falls off quickly with distance. The electromagnetic force falls off less quickly.
So why do neutrons matter? Neutrons, like protons, experience the strong force, so they add to the force holding the nucleus together. Unlike protons, they don't experience the electromagnetic force, so they don't push the nucleus apart.
It's not actually as simple as more neutrons being better, though. Too many neutrons can make a nucleus unstable. It's really a matter of quantum mechanics. It's somewhat like the stability of atoms - certain numbers of electrons are more stable than others because of the way they fill quantum mechanical energy levels. The same, more or less, goes for protons and neutrons in the nucleus.
At any rate, gravity has almost nothing to do with holding the nucleus together, it's just too weak of a force to matter on those scales.
05-22-06, 10:35 PM Professor To amplify methos's answer, I would add that compared to the electromagnetic force, gravity isn't just very weak, it's spectacularly, mind-bogglingly weak. Consider the forces between two electrons. There is (1) repulsion by the electromagnetic force (like charges repel) and (2) attraction by gravity (two masses attract). At any given distance between them, the electromagnetic force is greater than the gravitational force by a factor of about 4x1042!! That's a 4 followed by 42 zeroes. (Reference: Feynman's Lectures in Physics, Vol. I, p. 7-10)
Indeed, gravity is so weak that it takes exquisitely sensitive and well-designed experiments just to measure the gravitational attraction of small masses. The first such experiment was done by Eötvös in the early 20th C.
Down here on earth, at the human scale, we perceive gravity as "strong" only because the nuclear forces don't operate at large distances (as methos explained) and because electrical charges are almost perfectly neutralized for most objects.
Here's another illustration: Take a small refrigerator magnet and pick up a paper clip with it. The wimpy little magnet (magnetism is a form of electomagnetic interaction) has overcome the gravitational effect of the entire mass of the earth pulling on the paper clip.
By the way, relativity has nothing to do with this discussion.
05-28-06, 03:03 PM Kainchild I understand repelling forces of protons would prevent gravity from occurring, I mean if that force was weaker then gravity would gravity even exsist in protons? What I am trying to propose is the possibility that gravity might be a phenomenon that only happens from neutrons or when they interact with other particles, but in turn this effect occurs on all other forms of matter. So far theres no evidence other then neutrons stars that show sub-atomical particles effects on gravity to same sub-atomical particles.
05-28-06, 07:59 PM methos No, you do not appear to understand.
The repelling electromagnetic force does not "prevent gravity from occuring." It doesn't affect gravity at all. It's just that it is so strong and gravity is so weak that gravity is irrelevant on nuclear scales. It's like an ant pushing against a truck. The truck doesn't change the force with which the ant pushes, it is just so much stronger that the ant is irrelevant.
I don't know what this nonsense about neutrons being the only particles with gravity is, or where you get the idea that it hasn't been observed without neutrons present. New stars are nearly entirely protons and electrons (i.e., very few neutrons), and we observe their gravity. Older stars also have far fewer neutrons than protons. Our sun, for example, has more than 6 times as many protons as neutrons.
Even without resorting to stars, we can see that protons have gravity. Carbon, with its 6 protons and 6 neutrons has an atomic mass of 12, twice what could be accounted for by just the neutrons. We can measure this mass by measuring the gravity that pulls on it.
05-29-06, 06:03 AM Kainchild That's what I needed to know, thanks. Didn't know of the make up of new stars were of just electrons and protons with few neutrons. I thought even new stars had a balance of sub-atmoical particles.
05-29-06, 09:10 AM methos New stars are mostly hydrogen (only traces of other elements). An atom of hydrogen is one proton and one electron. As they age, they turn some of the hydrogen into helium (2 protons, 2 electrons, 2 neutrons). As they get even older, they start making more elements, but they still remain largely hydrogen.
05-29-06, 10:44 PM Professor Neutrons and protons (nucleons: particles that compose the nucleus of an atom) are "heavy" particles (baryons) in the sense that their rest mass is some 2000 times the mass of the electron.
Protons and electrons have equal and opposite electric charges (+1 and -1) despite the fact that the proton is so much heavier. Perhaps this is a source of confusion. Charge and mass are apparently independent properties, one having nothing to do with the other. From the standpoint of charge protons and electrons are on equal footing, while neutrons don't even participate in the interaction because they have neutral (zero) charge.
Although protons and neutrons are much heavier than electrons, they differ slightly in mass. It turns out that their mass differs by roughly the mass of an electron*, about one part in 2000. From the standpoint of gravitation this puts protons and neutrons are on equal footing, while electrons play a very minor role, despite the fact that they are just as numerous as the protons in ordinary neutral matter. This may be another source of confusion.
* Indeed it's possible for a neutron to decay into a proton and electron. This occurs via the "weak" nuclear force and creates other neutrally charged light particles to balance the books. Yet I think it's best not to think of a neutron as a proton-electron pair, but rather as a separate particle.
Most atomic nuclei find stability with roughly equal numbers of protons and neutrons, as in methos's example of Carbon-12 having six protons and six neutrons, making 12 mass units. Of course in extremely hot plasmas such as the millions of degrees inside a star, where it's too hot for atoms to form, protons far outnumber neutrons. I don't know exactly why Red Face though I suspect it's related to the weak-mediated decay mentioned above. In neutron stars I think it's the opposite: the crushing gravitational pressure leaves electrons nowhere to go but to combine with protons to make neutrons.
The point is that in bulk matter, whether icebergs or solar systems, gravitational mass is dermined by the combined number of protons and neutrons.
05-30-06, 09:00 AM methos Regarding protons & neutrons in stars... The reason stars, especially when first formed, are primarily protons is because they are primarily hydrogen. They are primarily hydrogen because the universe is primarily hydrogen (something like 3/4).
So why do we have neutrons at all? The large mass of stars means that there is a lot of pressure at their centers due to gravity. This pressure provides the energy for nuclear reaction, which turn the hydrogen into helium and then the helium into heavier elements. Because of this, stars become more neutron-rich as they age.
So, it's not the hot plasma that prevents the neutrons from being there. In fact, it's the hot plasma that creates the neutrons.
Neutron star formation is something interesting. As stars get old, they have less hydrogen and other light elements at their centers to act as fuel for nuclear reactions. (Even these old stars have a lot of hydrogen outside of their cores, though.) At their cores, these old stars are iron, which is the most stable element, and can't act as fuel. Without the nuclear reactions, there is less to push against the gravitational pressure and the star starts to collapse. There is something called electron degeneracy, which basically says that only one electron can occupy a given state. This results in an effective pressure pushing back against gravity, keeping the star from collapsing further. If the star is too heavy, though, this can be overcome, but not directly. The protons and electrons collapse into neutrons (releasing neutrinos). The collapse then continues until another sort of degeneracy, neutron degeneracy, stops it. At this point, you have a neutron star. If there is so much mass that even neutron degeneracy is not enough to prevent collapse, then a black hole forms.
06-02-06, 07:40 PM Kainchild The basic construction of a neutron is interesting. It almost sounds like its some sort of "third pole" in a magnet of sub atomics.
Another question from what you say if both a young star and a neutron star of the same mass would then both also give off the same gravity? There is proof of this I take it in astronomy observations?
06-02-06, 08:54 PM methos Yes, they would.
Leaving aside the specific case of stars, for the moment at least - they are divorced enough from our everyday experience that they were perhaps a poor example.
Drop two objects of different masses from the same height. If air resistance isn't a factor, they will hit the ground at the same time. At first, this might not make sense - we know that gravity pulls more strongly on objects with more mass (if it didn't we could lift the heaviest object as easily as the lightest). So what's going on? Heavier object also resist changes to their movement more. If a heavy object is moving, it takes more force to stop it. Think of a car rolling along vs. a skateboard rolling along at the same speed (imagine, in this case, that the cars engine is off). Which would you rather be standing in front of? The skateboard, of course.
We can measure this same inertial mass on the atomic scale by setting atoms in motion and trying to change their motion. The motion of the light atoms changes more easily than the motion of the heavy atoms. This is something that I have actually done. I can tell you from experience that protons have mass. Given that mass measured via inertia matches mass measured by gravity, this means that protons feel, and cause, gravity.
This message has been edited. Last edited by: DorianGreyed,
I mean do you got anymore information on the subject then what the page provides.
I was wondering how close are we to finding out gravity's effect on anti-matter. I understand we got a long way to go till we get a good amount of anti-matter but was wodnering how much are we going to need to see the effects.
