How can gravity over power the strong and weak nuclear forces?

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How can gravity over power the strong and weak nuclear forces?

Postby tibbert » Sat Sep 18, 2010 4:30 pm

When black holes or neutron stars are formed, am i right in thinking the elecrons are forced into the nucleus? How is this possible, I was thinking the more mass an object had would mean the number of particles it contained would also increase- would the nuclear forces not increase too and resist the gravity as more and more particles were added?

It hurts to be a curious layperson!!! HELP!

cheers guys!
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RE: How can gravity over power the strong and weak nuclear forces?

Postby brianb » Sat Sep 18, 2010 5:36 pm

[quote]When black holes or neutron stars are formed, am i right in thinking the elecrons are forced into the nucleus? How is this possible[/quote]
Yes, under conditions of sufficiently high pressure, electrons and protons combine to form neutrons. It is wrong to think of a neutron star as being composed of neutrons, though, the central portions really consist of a single giant nucleus.

When a neutron star is formed, the reduction in the number of particles causes further gravitational collapse ... if sufficient mass is present, even the neutron degeneracy pressure is insufficient to prevent the collapse continuing, which is how a black hole may be formed.

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RE: How can gravity over power the strong and weak nuclear forces?

Postby tibbert » Sat Sep 18, 2010 11:43 pm

if there was a reduction of particles wouldn't that lower the gravity? if mass and gravity are linked?
people always say that compared the nuclear forces gravity is very weak... does this mean that when mass reaches a certain level gravity overtakes the nuclear forces?
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RE: How can gravity over power the strong and weak nuclear forces?

Postby brianb » Sun Sep 19, 2010 10:50 am

[quote]if there was a reduction of particles wouldn't that lower the gravity? if mass and gravity are linked? [/quote]
The point is that when an electron and a proton are forced together to form a single particle, the mass is essentially unchanged. The effect of gravity actually becomes much stronger as the interaction cross-section of a neutron is much, much smaller than that of an atom ... the usual analogy is that of a mosquito in St Paul's Cathedral ... as usual, the analogy is imperfect because quantum physics is somewhat counter-intuitive.

The effect of the strong nuclear force falls off more quickly with distance than that of gravity ... consequently for large, massive objects, gravity wins. Neither the strong nuclear force nor electrostatic repulsion can prevent an apple from falling to the earth, though the strong nuclear force is sufficient to bind the protons and neutrons in the nuclei of the atoms in the apple together, and electrostatic repulsion between the electron shells in the atoms is sufficient to stop the nuclei colliding - unless the temperature and pressure is raised to a point similar to those which exist in stellar cores.

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RE: How can gravity over power the strong and weak nuclear forces?

Postby keith m » Tue Sep 21, 2010 9:26 pm

On a similar tack, here''s a random thought . . .

E =mc2

This relates to the equivalence of mass and energy, however energy has no gravity associated with it, but mass does. So, by this equation if you convert mass to energy you destroy gravity. So I suggest the equation should really be something like . . .

E + g = mc2

Shoot me down now?
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RE: How can gravity over power the strong and weak nuclear forces?

Postby brianb » Tue Sep 21, 2010 11:06 pm

[quote]energy has no gravity associated with it, but mass does.[/quote]
Wrong. Energy, like the presence of mass, warps the space/time manifold, causing the illusion of gravity.

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RE: How can gravity over power the strong and weak nuclear forces?

Postby arthur dent » Wed Sep 22, 2010 10:30 am

Keith,

Mass [b][i][color="#cc9900"]is caused[/color][/i][/b] by the [b][color="#cc9900"]Higgs Field[/color][/b] - the associatied particle to confirm this theory - the [color="#cc9900"][b]HIGGS BOSON[/b][/color] is being sought at the Large Hardron Collider (LHC) at CERN.

All masses attract all other masses with an attractive force named Gravity. The bigger the masses involved, the bigger the force. The closer the masses involved, the bigger the force. Unlike the weak and strong nuclear forces (which are [color="#cc9900"][b]very short-range[/b][/color]) gravity (and also electro-magnetism) have infinite range (in theory). Like Briabn said, the presence of mass distorts the fabric of space-time and causes objects to be attracted together.

The strong nuclear force (the force that holds atoms together against electro-static repulsion) is so short range - of the order of 10-14m. Now 10-14m is the sort of diameter of atomic nuclei and this is the reason that there is a limit on the size (or masses) of atoms. When atoms get too big - with so many protons & neutrons in their nucleus, the strong nuclear force cannot "[color="#cc9900"][b][i]stretch[/i][/b][/color]" across the nucleus to hold all the particles in, so there is a kind of "maximum size" for atoms which we are approaching now. In other words, don't expect to see atoms much above an Atomic Number of 116.

Gravity is like a kind of "by-product" of an object posessing mass. Mass itself is effectively energy (the two are interchangeable).

The theory of the Higgs Field may be wrong and the Higgs Particle (the so-called "God Particle") may not actually exist.

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RE: How can gravity over power the strong and weak nuclear forces?

Postby keith m » Wed Sep 22, 2010 9:36 pm


[quote]Wrong. Energy, like the presence of mass, warps the space/time manifold, causing the illusion of gravity.[/quote]

Mmm, not conviced of this. Light for instance follows the contour of the curvature of a gravitational well but I don't think it creates a gravitational well of its own.

Will need to ponder this one further. Art, thanks, but while "gravity is a by product of mass" may be true, we actually cannot fit gravity into the existing theories. The point of my posting was to say suggest that if "gravity is not also a by product of energy" then there is an imbalance in the famous equation. I suspect that somewhere in this problem of gravity lies the route to a new theory of cosmology, needed as the existing ones are falling apart like phlogiston.

K
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RE: How can gravity over power the strong and weak nuclear forces?

Postby brianb » Thu Sep 23, 2010 12:40 am

[quote]Light for instance follows the contour of the curvature of a gravitational well but I don't think it creates a gravitational well of its own. [/quote]
It's just not a very deep one ... the energy associated with a single photon of light is tiny and the associated mass is smaller still, by a factor of the square of the velocity of light.

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RE: How can gravity over power the strong and weak nuclear forces?

Postby keith m » Fri Sep 24, 2010 9:43 am

Ha! Hunting around on some physics forums to bring myself a bit more up-to-speed. This is the full equation taken from a posting there:

[i]The correct statement of special relativity is that energy (E), mass (m) and momentum (p) are inter-related. They are connected by formula
E= sqrt{m^2c^4 + p^2c^2}
Thus:
If a massive body is at rest (p=0), then you'll get the famous energy-mass relationship
If a body has zero mass (like photons), then another famous relationship follows
So, massless particles can have non-zero energy. [/i]

So, perhaps I was niaively expressing, but there is another term in that equation. Just looking around the HEP theories now though, despite their cleverness, you can see the underlying mess they are in, same as cosmology I suppose. Same thing really?

I think I'll go back to my solid state / optics roots now :-)

K
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