Gravity & State of Matter: Does Force Vary?

[cragar]

Is this true? Light creates gravity?

Yes it is , let's say we have matter and anti-matter in a globe , they both have weight so the create a gravitational field when we collide the matter and anti-matter they produce photons the gravitational field is still there it didn't go anywhere. Another way we can show this is if we bend light in a strong gravitational field , using Newton’s laws fore every action there is an equal but opposite reaction so if we are pulling on the light it must pull back with an equal but opposite force.

 

[jrlaguna]

A source of confusion here is between Newtonian gravity and Einstein's general relativity... According to the first, it is a force felt by mass alone. So, light is out of the equation. But now we know better :) According to Einstein, both mass and energy "curve" space-time, and also mass and energy move in this curved space-time. Light also, of course: it is both affected by the curvature and creates curvature.

About the speed at which gravity "travels", it is c, the speed of light, according to Einstein's theory. How do we know? OK, we solve the equations: make a perturbation in the mass of the sun and see how long it takes to reach the Earth. If you're asking for an experimental proof, I can tell you one (although indirect), but only if you're really interested :)

 

[gonegahgah]

So if light creates gravity, and we seek to cede to QM, then is the photon an emitter of gravitons?

If it is a graviton emitter, does the photon carry its graviton(s) along with it or does it emit them in all directions like mass does?

 

[fatra2]

Hi there,

What cragar is saying, without going anywhere close to anti-matter, but going very close to two friends of mine, Schrödinger and Einstein.

Shcrödinger's equation proves the duality between matter and energy. One of the best effects of this is the transformation of matter into energy, and vice-versa. This means that at anytime light can be interpreted as pure energy, from a normal wave-function, and as "matter-like" particle, from the photon point-of-view.

Therefore, light reacts to the gravitational pull. The effect on its trajectory is very limited, unless passing next to a very massing object, and bit bigger than a whale. Some of the effects of light curvature can be observed in the universe, and you can google for "Einstein's cross" to see a bit mor of this.

Cheers

 

[fatra2]

Hi again,

You posted your post just before mine, and I would like to add to

is the photon an emitter of gravitons?

Gravitons have not yet been observed experimentally. They have been postulated by theoretical physics, which would go into the idea of a symmetric universe. But their existence is still an open question.

Cheers

 

[jrlaguna]

So if light creates gravity, and we seek to cede to QM, then is the photon an emitter of gravitons?

If it is a graviton emitter, does the photon carry its graviton(s) along with it or does it emit them in all directions like mass does?

Yes, if ever we have a nice theory unifying QM and GR, and if it does not differ too much from what we have now, then the photon will emit gravitons. In order to emit them, the photon does not need a graviton bag (funny concept, btw). Electromagnetic force between an electron and a proton is due to their interchanging photons. Although, they don't have a "photon bag". They're just... ehm... somehow created. I'm sorry I can't be more precise, neither is QM. I can tell you how to compute, but not where do the photons (or the gravitons for that sake) come from.

 

[gonegahgah]

Thanks guys.

Upon rereading my post I can understand why you mentioned the bag of gravitons.

I didn't mean it that way; I meant it how you said. Silly me.

That particular part of my post was specifically meant to ask in what direction a graviton would travel away from the photon i.e. in all directions away from the photon or stays with the photon itself on its journey?

 

[jrlaguna]

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 would escape from it at the... speed of light

 

[nuby]

Yes it is , let's say we have matter and anti-matter in a globe , they both have weight so the create a gravitational field when we collide the matter and anti-matter they produce photons the gravitational field is still there it didn't go anywhere. Another way we can show this is if we bend light in a strong gravitational field , using Newton’s laws fore every action there is an equal but opposite reaction so if we are pulling on the light it must pull back with an equal but opposite force.

Do you have a reference?

 

[cragar]

not really , you don't believe it , are you saying that light doesn't create gravity.

 

[nuby]

not really , you don't believe it , are you saying that light doesn't create gravity.

I'm not sure. That's why I asked, but a good reference explaining how a photon (with 0 mass) can create gravity would be interesting.

 

[Archosaur]

Almost everyone who has replied to this topic has said something awfully wrong. I don't even know what to say.

 

[nuby]

Almost everyone who has replied to this topic has said something awfully wrong. I don't even know what to say.

Seriously.. Are the moderators all on vacation?

 

[gonegahgah]

I think pervect is a moderator? Or at least is considered reputable.

Here was his take:

Mass is the source of gravity in Newtonian theory, but not in GR.

Any sort of energy can be said to "gravitate" in GR. Massive particles are different from photons, but as they both contain energy, they both contribute to gravity, since it is energy that causes gravity (along with the other things I mentioned).

This quote is from the following thread: https://www.physicsforums.com/showthread.php?t=154391&page=2"

Though an actual reference or two would indeed be welcome to help tie this up...

 

[Dadface]

:

Almost everyone who has replied to this topic has said something awfully wrong. I don't even know what to say.

Why not chip in with some constructive comments?

 

[nuby]

Massive particles are different from photons, but as they both contain energy, they both contribute to gravity, since it is energy that causes gravity (along with the other things I mentioned).

Does this mean photons with different energies have different trajectories through space around planets? How would you calculate this?

 

[Archosaur]

:
Why not chip in with some constructive comments?

Okydoke.

does the effect of gravitational force vary with state of matter,i.e
the force is most felt in gases?right.

No

then moon's gravitational pull has to affect gases also,only the water bodies are affected causing tides,why ?

Because they aren't

Gravity could be thought of as a type of energy, but a force is simply a perpetual energy exerter.

This is the opposite of true.

yes light is affected by gravity it also creates gravity.

...

now when the moon exerts its gravitational pull on earth,it is the gases that need to
be affected first,rather the liquid bodies.but tides are being created whille atmosphere
seems to be intact.

Failure.

 

[russ_watters]

Seriously.. Are the moderators all on vacation?

The thread moved fast and got away from me...i'll answer a few more...

...however, Archosaur, your post is "the opposite of"/"faulure"/"no" constructive. Please do better.

 

[russ_watters]

A compressed spring has potential energy and has more mass when compressed .

That's true, but that isn't what was being claimed. It is the difference between saying 'a spring can store energy' and 'a spring is energy'. Gravity (and a spring) is not a type of energy, doesn't ever consume energy continuously, and doesn't always even have energy as a component of what is being analyzed with it (ie, "energy" not a concept that applies to a constant spring force or gravitational force).

 

[russ_watters]

now when the moon exerts its gravitational pull on earth,it is the gases that need to
be affected first,rather the liquid bodies.but tides are being created whille atmosphere
seems to be intact.

This was somewhat addressed before, but just to be a little more explicit, "seems to" isn't scientific. Gravity, including tidal forces, most certainly does affect gases. The solid surface of the Earth is also distorted by the tidal forces.

well," first", i meant in priority,gravitational pull would be more over gases or liquids?
according to the formula,does increase in mass mean increase in force of gravity?

First? Priority? These concepts have no meaning here. Gravity acts on an object in proportion to its mass, as the formula says, period.

 

[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.