Gravity & State of Matter: Does Force Vary?

[russ_watters]

Gravity (i.e., mass or weight) is not a conserved quantity. For example, when a positron annihilates at rest with an electron, the gravity (mass) associated with the 1.02 MeV in rest mass is lost. Some measurements have been made on the gravitational attraction of low Z materials (e.g., carbon, which is half neutrons) vs. high Z (e.g., lead, which is 60% neutrons), but the measurements are not conclusive on neutron vs. proton gravitational attraction.

That's misleading at best. Since mass and energy are related concepts (perhaps two forms of the same thing), conservation of mass really is conservation of energy/mass. In other words, when mass is converted to energy, conservation law applies and is satisfied.

[edit] Dadface addressed this one without quoting it.

 

[gonegahgah]

That would be given by the theory itself, which we lack. I mean, there are two privileged directions when a photon moves: the direction in which it moves and its polarization... In any case, they [gravitons] would escape from it at the... speed of light

If light does create gravity then what about the following?

If the light is traveling at the speed of light and the gravitons are traveling at the speed of light will the gravitons emitted forward arrive at the same time as the photon itself?

That was what I was meaning by does the graviton travel with the photon?

 

[jrlaguna]

They might, for sure, but taking into account special relativity some considerations would be in order... I'd be careful with that.

 

[gonegahgah]

I agree, we do have to be careful with it somehow.

If light is an emitter of gravitons, because it is being stated that energy creates gravity and not mass per se, then the other question is: is it a constant emitter of gravitons; as we know the energy tied up in mass is.

If so then does the photon constantly emit gravitons as it approaches us?
If it does, and if the gravitons can travel no faster than the photon itself towards us, do all the front emitted gravitons, during the travel of the photon, hit us at the same time as the photon itself?

However the gravity wave, and therefore the density of gravitons, does weaken as the as they move out from their point of emission, as do the light wave and photons themselves.

So allowing for this the photon's gravity bow wave (as in like a boat's bow wave) in front of the photon would sum to ∑(i=r→0) f(t_i) ∆i where f(t_i) = graviton / i².

Given this, and even though the waves weaken with distance travelled; but if gravitons are constantly being emitted, then the bow wave would still sum considerably higher for the proportional amount of light energy than it does for gravity created from energy tied up in matter. (See correction to this below).

Exactly the same thing would occur if we considered it from the perspective of gravity wave emission instead of graviton emission. The gravity wave itself would still have to travel towards us at the speed of light; so the bow of the photon emitted gravity waves would move towards us with the photon itself; as the wave can move no faster.

Again the bow wave would keep summing; from the delta of the weakening gravity waves the photon is emitting before it towards us. Still at the end of the photon's journey the amount it would be adding to the sum would be a fairly similar amount.

There is a way to see this as okay however. True the bow wave would increase in size but the overall effect would be no different if the gravity were instantaneous (which it is stated it is not). If it were instantaneous then the later photons to come after the photon reaching us would add their gravitational force anyway. So the net effect would be the same.

So this allows the constant emission of gravitons/gravity waves from the photon/light wave to occur without any problem even though it creates a bow wave before the photon.

The only real difference is that this allows for gravity to turn on and off as in the imaginary scenario where the Sun magically disappears out of existence. The last photons carry their bow gravitons with them along with the last gravity wave of the sun. And 8 minutes later the Earth stops being affected by the gone Sun.

I'm glad I worked that out. I hope it is okay?

The other thing is what this means for space time curvature. It means that the photons travel at the leading edge of their space-time distortion. Kind of like ramming through the space-time fabric leaving the gravity dispersion in their wake.

Any comments on the acceptability of all this?

 

[nuby]

Can a PF Mentor please explain to me how a photon can create gravity / warp space-time?

 

[vebrown]

If so then does the photon constantly emit gravitons as it approaches us?
If it does, and if the gravitons can travel no faster than the photon itself towards us, do all the front emitted gravitons, during the travel of the photon, hit us at the same time as the photon itself?

Since we are just speculating here, why not simplify the system and keep Occum happy. Instead of photons emitting gravitons, why not look to the photon itself. Consider the photon to be composed of electric and magnetic fields. The fields reach saturation amplitude at points moving along the photon's line of travel. The fields occupy a spatial area, diminishing in amplitude away from the points. These diminished fields contribute toward the saturation amplitude of the points of other photons moving through them. The points thus reach saturation at an offset toward increasing field strength.

 

[ZapperZ]

... and these speculations signal the DEMISE of this thread. If you are puzzled by this, re-read the PF Guidelines and figure out if you contributed to its fate.

Zz.