How Cn Gravity Affect Light When Light Has No Mass?

[Rhondazvous]

This is the $50 million question

If gravity only affects objects that have mass and photons are massless, why does light curve around a planet or get trapped in a black hole?

[polymath257]

Gravity does affect things with no mass in general relativity. it does so by curving spacetime, which affects anything, whether it has a mass or not.

Also, the converse is true. Anything with energy produces gravity, whether it has mass or not.

[zebo-the-fat]

Gravity does not affect light directly, but it does bend the spce-time that the light is moving in

[polymath257]

Gravity does not affect light directly, but it does bend the spce-time that the light is moving in

In that sense, it doesn't affect *anything* directly. The reason planets orbit the sun is because of the curvature of spacetime the sun produces. It is that curvature that makes the planets move the way they do.

[Anomalocaris]

This is the $50 million question

If gravity only affects objects that have mass and photons are massless, why does light curve around a planet or get trapped in a black hole?

Energy and mass are interchangeable directly, and for the purpose of gravity. Photons have energy, E=MC^2, hence photons have equivalent of mass.  

Think of it this way, by E=MC^2, all forms of energy have equivalent of mass, and therefore are both affected by gravity, and exert their own gravity.    If global warming heat the earth up, the gravity of the earth actually increase because the added kenetic energy of the molecules makes the earth slightly more massive.

If you annihilate a mass particle with its anti-partlcle, the mass of those two particles will convert into photons. If you somehow trap the photons so they don’t speed away, you will find the gravity well around the these photons remains exactly the same as before the annihilation.

[popeyespappy]

General relativity: Mass warps spacetime. Photons travel in spacetime so to an outside observer they follow a warped path when passing an object with mass.

Special relativity: E=MC2. Photons have relative mass even if they don't have resting mass.

[polymath257]

This is the $50 million question

If gravity only affects objects that have mass and photons are massless, why does light curve around a planet or get trapped in a black hole?

Photons have energy, E=MC^2, hence photons have equivalent of mass.  

Think of it this way, by E=MC^2, all forms of energy have equivalent of mass, and therefore are both affected by gravity, and exert their own gravity.    If global warming heat the earth up, the gravity of the earth actually increase because the added kenetic energy of the molecules makes the earth slightly more massive.

One aspect of this that is a bit strange is that massless particles, like the photon, actually move along a different path (a null path) than a massive particle of going very close to the speed of light would. The deflection of the light is *double* what would be expected from a naive equivalence between the mass and energy. that was actually one of the distinguishing experiments differentiating special and general relativity when applied to gravity.

[Rhondazvous]

This is the $50 million question

If gravity only affects objects that have mass and photons are massless, why does light curve around a planet or get trapped in a black hole?

Energy and mass are interchangeable directly, and for the purpose of gravity.   Photons have energy, E=MC^2, hence photons have equivalent of mass.  

Think of it this way, by E=MC^2, all forms of energy have equivalent of mass, and therefore are both affected by gravity, and exert their own gravity.    If global warming heat the earth up, the gravity of the earth actually increase because the added kenetic energy of the molecules makes the earth slightly more massive.  

If you annihilate a mass particle with its anti-partlcle, the mass of those two particles will convert into photons.  If you somehow trap the photons so they don’t speed away, you will find the gravity well around the these photons remains exactly the same as before the annihilation.

This explains a lot, with one nagging caveat. Photons mediate the electromagnetic field. While the mediator of the gravitational field has not yet been discovered. So we have mediators in two separate fields affecting one another. If photons create gravity, then the electromagnetic field is also the mediator for the gravitational field. Is it possible there is no gravitational field? Like heat, maybe gravity is just a property of matter or a property of spacetime when massive or energy particles come close.

---

General relativity: Mass warps spacetime. Photons travel in spacetime so to an outside observer they follow a warped path when passing an object with mass.

Special relativity: E=MC2. Photons have relative mass even if they don't have resting mass.

And this explains why although photons existed before recombination, there was no matter and therefore no gravity to counter the dark energy pushing everything apart. only after things got so apart that they lost energy was the strong force able to bring quanta together to form atoms and then large bodies with measurable gravity.

[The Grand Nudger]

Is it possible there is no gravitational field?

No, even within the context of your proposal you're simply wondering whether or not some other x might effect that grav field...there's a grav field in that proposition all the same.   Regardless of what gravity is a property of, gravity, then, would exist as a property of that x.

To demonstrate this in another context. We don't know whether or not there are gravitons, a hypothetical fundamental particle in qft that mediates the force of gravitation. We've never identified one. Suppose there aren't. There's still gravity, there are still grav fields.

[Anomalocaris]

And this explains why although photons existed before recombination, there was no matter and therefore no gravity to counter the dark energy pushing everything apart. only after things got so apart that they lost energy was the strong force able to bring quanta together to form atoms and then large bodies with measurable gravity.

I don’t believe that is accurate for two reasons:

1.  Recombination refers to electrons pairing up with protons.  They existed separately as ionized plasma before.   So there were matter before recombination, just not electrically neutral matter.
2.  Even if there were not electrons and protons, If there were photons, there were gravity.  Gravity is an artifact of energy in all forms, not just in matter form.   If I am not mistaken, most of the gravity of normal matter is not from the rest mass of the particles with rest mass, but from binding energy that holds These particles together.