Energy and Gravity

[BPHgravity]

It is commonly understood that mass produces the effects of gravity.

 

Is it also the case that energy itself produces gravity?

 

If this is the case, don't gravity fields have energy, and wouldn't these energy fields also produce gravity, and so on for infinity?

 

 

 

[Giles]

ok, i'm speaking as a layman here but...

 

iirc, gravity is defined by energy density, but einstein's famous relation means that a little mass is worth a lot of some other form of energy. So I guess that makes mass 'more important' in the gravitational scheme of things. (i guess matter is also more amenable to accretion than say photons, which prefer spreading out, making it more important in forming large scale structures.)

 

Since gravitational fields are described as 'curved space' in GR, i doubt they have any energy of their own that produces a gravitational field. In any case, if you introduced some kind of carrier particle like the graviton i guess it would have energy, which may be one of the reasons physicists want to quanticize (is that the right term?) gravity. If you couldn't have infinite 'grades' of gravitons the problem would disappear, much like the black body problem.

[alt_f13]

Hmm... well I'll put another simpler spin on it.

 

Gravity is potential energy, and is used when two bodies move towards each other, accellerating and converting the gravitational potential energy into mechanical, thermal etc. but when an energy particle is on its lonesome, it cannot accellerate towards itself, which eliminates that energy output. Thus we do not have infinate ammounts of energy pouring out of everything.

[bigjnorman]

I don't follow you alt, I think that because mass causes the gravity phenomenon, it follows that energy would do the same. The problem arises when you try to test the theory...

 

1) energy is not stable enough, it would immediatly be absorbed into the surrounding matter in some way,

 

2) the amount of energy required exceeds our ability to produce it safely enough (think about testing the gravity associated with the small fraction of mass that contributes to the energy released in an A-bomb), testing the gravitational field associated with that MASS would be difficult enough, not to mention testing the G-field associated with the ENERGY released as a result.

 

later

[newsky]

I think the mass itself contains the gravitational energy but the mass is not energy.

An energy cannot be transformed in gravitational mass.

Maybe the black hole can explain to us how the mass produces the gravitational energy.

[Cap'n Refsmmat]

Energy does not make gravity! A magnetic field can be likened to a gravitational field, but it is not.

[Tom Mattson]

Cap'n Refsmmat said in post # :

Energy does not make gravity!

 

Yes, it does.

 

The field equations of GR are:

 

G^mn=(8pG/c⁴)T^mn

 

The tensor G^mn contains all the information about the curvature of spacetime (the effect we call "gravity"), and the tensor T^mn is the stress-energy tensor, which contains all nonzero contributions to the 4-momentum density (that includes energy).

[Cap'n Refsmmat]

Whatever.

I'd forgotten about that. Mass can be converted to energy, which makes up some of an atom. But that type of energy (that holds atoms together) does not contribute to gravity, unless it has mass.

[Tom Mattson]

Cap'n Refsmmat said in post # :

But that type of energy (that holds atoms together) does not contribute to gravity, unless it has mass.

 

No, that is still wrong. Read what I wrote again:

 

the tensor T^mn is the stress-energy tensor, which contains all nonzero contributions to the 4-momentum density (that includes energy). (emphasis added)

 

When I say "all nonzero contributions", that is precisely what I mean. All rest mass energy, all electromagnetic energy, all kinetic energy, all of it goes into the stress-energy tensor, and all of it works to curve spacetime to give rise to the effect called "gravity".

[greg1917]

which makes up some of an atom

 

I presume your talking about nuclear binding energy there, which Tom has already stated has an effect. Atoms also 'contain' energy in terms of their electron clouds and their relative velocity.

 

He cited a proven mathematical piece of evidence. You didnt. Unless you have some crazy equations physicists have yet to derive.

[newsky]

I think atom has a lot of black holes and the proton itself can have a lot of black holes.

If two black holes are attracted it can explain the force of gravity and the nuclear force.

[JaKiri]

newsky said in post # :

I think atom has a lot of black holes and the proton itself can have a lot of black holes.

If two black holes are attracted it can explain the force of gravity and the nuclear force.

 

hehehhehehehehehehehehehhehehehehehehe

[greg1917]

That doesnt explain anything, much less gravity or the strong or weak nuclear force. Its also completely unfounded, flat out wrong and ridiculous.

[newsky]

my opinion is not to underestimate it because a black hole has a great force even if they are very small, and in a atom there is the space between protons and the space between protons and electrons that can make the difference between nuclear force and force of gravity.

 

 

[YT2095]

as far as I know (and was taught) it`s a bit like satelites that orbit Earth. if they had no velocity they would fall back to earth, but it`s the play between their wanting to go in a straight line off into space and gravity that keeps them in situ.

if the electrons didn`t "buzz around" so fast as to be almost a cloud, then they would surely fall into the nucleus as opposites attract and likes repel.

 

I don`t honestly think it`s anything to do with subatomic black holes, I think the answer if far more simple than that

[greg1917]

The answer is not subatomic blackholes because thats beyond preposterous. Orbitting electrons can be characterised as waves, leading to orbittal shapes and associated regions of probability. Not black holes. They have nothing whatsoever to do with this thread. nothing.

[Tom Mattson]

newsky said in post # :

my opinion is not to underestimate it because a black hole has a great force even if they are very small, and in a atom there is the space between protons and the space between protons and electrons

(snip)

 

Yes, there is space, but is there precisely the right amount of space?

 

This is a pretty simple problem to figure out. You take the mass of the object and calculate its Schwarzchild radius. If the object is smaller than that, then it is a black hole.

 

Let's estimate the Schwarzchild radius for an atom.

 

G~10^-10Nm²/kg²

M~10^-27kg

c²~10¹⁷m²/s²

 

Using those estimates, I get something in the ballpark of:

 

R=2GM/c²~2*10^-54m,

 

which is 29 orders of magnitude smaller than the Planck length.

 

So no, there is no black hole in an atom.

 

Let us never speak of it again. :nono:

[JaKiri]

Good response :up:

[newsky]

Tom

 

in this moment I cannot calculate the difference between those spaces but I don't think it's that

 

distance electron-proton

---------------------------- :neq: 29

distance proton-proton

 

 

it's much more! :scratch:

[Tom Mattson]

newsky said in post # :

 

 

in this moment I cannot calculate the difference between those spaces but I don't think it's that

 

distance electron-proton

---------------------------- :neq: 29

distance proton-proton

 

I didn't say it was "29" (what unit is that in, by the way?). I said that the Schwarzchild radius of an atom is 29 orders of magnitude smaller than the Planck length.

 

As far as the e-p distance in an atom goes, it is on the order of 10^-11m (roughly the Bohr radius). And the p-p distance in the nucleus is somewhere in the ballpark of 10^-15m, or 1 Fermi.

 

it's much more!

 

That is precisely my point!

 

The matter in an atom--or even in a nucleus--is not confined to anywhere near small enough a space to form a black hole.

 

Got it now?

 

edit: typo

[deamonstar]

gravity is a psuedo-force much in the same way that centrifugal force is a psuedo-force. it is caused by the temporal inertia of mass (its tendancy to remain at rest in a given moment in time) being accelerated through space-time.

the acceleration is provided by the accelerated expansion of the universe. as a body of mass exists in space, the 'outward' expansion of space tries to push the body of mass through time as well. as space expands, it encounters resistance from the temporal inertia of the body of mass resulting in a curvature of space-time around it.

other bodies of mass are not actually 'pulled' towards another body of mass, so much as space-time is expanding around them. 'realatively' speaking, the distance between the bodies of mass will become less... in a sense, it is the function of a percentage of the realative distances between the two bodies of mass as compared to the mean volume of space at a given moment in time. (of course, other factors such as total mass and velocity and trajectory influence the behaviours of the various bodies of mass which interact with each other.)

 

for further reading follow this link...

gravity

[Crash]

hmm i thought gravitons caused\are the reason for the observed gravity properties, Gravitons (gravity waves) are emitted from accelerating masses just as photons (electromagnetic waves) are emitted by accelerating electrical charges The particular wavelengths of electromagnetic waves depend on the source- radio transmitters, lasers, etc. The same would hold for gravity waves- the wavelength depends on how the mass in the source is accelerating around.

 

could be just me ofcourse

[JaKiri]

Acceleration is utterly irrelevent (apart from it being indistinguishable from gravity, but that's another story)

[Radical Edward]

YT2095 said in post # :

if the electrons didn`t "buzz around" so fast as to be almost a cloud, then they would surely fall into the nucleus as opposites attract and likes repel.

 

the reason electrons stay around the atom, is because they have to - quantum mechanics.