# How gravity can attract light?

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I assume light have no mass

also gravitational force only works with mass

and light can be pulled by gravity field.

Those 3 things can be mentioned in scientific documents.

But i see there is a contradiction .Or is there anything i know wrong?

How can i solve this paradox?

Edited by emrekanca
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I assume light have no mass

also gravitational force only works with mass

and light can be pulled by gravity field.

Those 3 things can be mentioned in scientific documents.

But i see there is a contradiction .Or is there anything i know wrong?

How can i solve this paradox?

Gravity is not a force like magnetism so it doesn't pull things in really. Space is visualised as being made of a non-substantive material called spacetime which has a geometry described as 'flat' in the absence of mass (first image). Mass causes the local spacetime geometry to curve in towards itself (second image) and light follows this curvature. Gravity is, in effect, curved spacetime or can also be described as a consequence of the interaction between spacetime and mass.

http://media.wiley.com/Lux/67/183867.image0.jpg

Edited by StringJunky
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Gravity is not a force like magnetism so it doesn't pull things in really. Space is visualised as being made of a non-substantive material called spacetime which has a geometry described as 'flat' in the absence of mass (first image). Mass causes the local spacetime geometry to curve in towards itself (second image) and light follows this curvature. Gravity is, in effect, curved spacetime or can also be described as a consequence of the interaction between spacetime and mass.

http://media.wiley.c...3867.image0.jpg

I got this:Light cant bend the spacetime geometry (cuz it have no mass) but it follows it as everyhing.

I have no question else thanks stringjunky

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I got this:Light cant bend the spacetime geometry (cuz it have no mass) but it follows it as everyhing.

Except that it does — spacetime is bent by energy.

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Except that it does — spacetime is bent by energy.

yea i think its because matter is wave at a very very hi frequency

As we go up in the spectrum it seems to collide more

Radio waves can pass through walls, infrared (Remote control of telly) can pass through flesh easier than visible light (i observe!),as we increase the frequency it even gets worse (it interacts more, it collides and reflects) and at higher it seems to be collide to each other in a small point .

if we accept matter is a wave, what is vibrating? (space time)

Is my observation true

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what intrigues me is the relationship between various things in motion and the spacetime curvature of gravity. For example, why does light bend a certain amount due to gravity while an object with mass moving along the same trajectory will veer more and even fall into the gravity well? According to Newtonianism (and maybe other approaches as well), all objects are supposed to fall at the same rate in the same gravity regardless of mass. Yet, as particles get lighter, they become more likely to escape gravity wells with lower amounts of energy/momentum. So a water molecule can evaporate off the moon, whereas Earth's gravity is too strong for that to happen to water, although it could happen to helium on Earth.

Black holes, then, supposedly have enough gravity to capture and contain light, the way Earth captures and contains heavier molecules with mass. But does matter and light fall into a black hole along the same path? I'm not sure why this question of when the curvature of spacetime is the same or closer to the same for light and matter, but it seems key to me for some reason. For example, in relatively straight paths through spacetime, matter and light easily follow the same path. But as spacetime becomes more curved entering a gravity well, the paths taken by the light and the matter will diverge more, correct, although both will still curve to some extent. Anyway, I know it sounds strange that this interests me but I'm not sure why, but somehow it seems key to the relationship between energy and matter.

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For example, why does light bend a certain amount due to gravity while an object with mass moving along the same trajectory will veer more and even fall into the gravity well?

I guess its because object with mass bents too.But as proportion it may wont work.We have to build an experiment to measure the proporion between mass and light to find out that will mass be attracted more than its expected.

If im on something else than what you wrote sorry.

So a water molecule can evaporate off the moon, whereas Earth's gravity is too strong for that to happen to water, although it could happen to helium on Earth.

I thing its due to atmosphere pressure of the earth.If we could vanish earth's atmosphere,gravity would have no effect on evaporation.Atmospher squashes things (pressure) so its easier to get closer for molecules.

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I assume light have no mass

also gravitational force only works with mass

and light can be pulled by gravity field.

But i see there is a contradiction .Or is there anything i know wrong?

The funny thing is that all of these three statements can either be correct or wrong, depending on how you interpret them. In the mainstream answer, the key to your problem is the 2nd statement: a gravitational field influences a body in a way that does not depend on the mass. You even have that in classical mechanics: a gravitational potential $\phi$ creates causes a force $\vec F = -m \nabla \phi$ on an object with mass m. This causes an acceleration $\vec a = \vec F / m = - \nabla \phi$, i.e. an acceleration that is independent of the mass. If you take the intermediate step seriously then you run into problems when m=0, but you could imagine forgetting about forces and just make $\vec a = -\nabla \phi$ the basic principle of gravitational action. Indeed, forces as you might know them are usually not used in modern physics (i.e. new fundamental physics developed in the last 100 years). In Relativity it actually is the case that you (sometimes) make the extension of $\vec a = -\nabla \phi$ the basic equation for the impact of a gravitational field on an object and don't run into any special case for m=0, then. That's of course only the formal dropping of an intermediate principle; the justification comes from seeing that nature indeed seems to follow that rule.

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I guess its because object with mass bents too.But as proportion it may wont work.We have to build an experiment to measure the proporion between mass and light to find out that will mass be attracted more than its expected.

If im on something else than what you wrote sorry.

I don't think an experiment to measure anything is necessary, unless current knowledge and formulas are flawed. What would interest me is to know how much a particle at a certain velocity changes course through a certain trajectory of a gravity-well and how to compare that with light on the same trajectory. After all, how do you measure how much light is bending due to gravity? I mean, no matter how much it may bend it always make the object you see appear to have a straight line path between you and the source.

I thing its due to atmosphere pressure of the earth.If we could vanish earth's atmosphere,gravity would have no effect on evaporation.Atmospher squashes things (pressure) so its easier to get closer for molecules.

It's not strange. It's just a fact. But it is noteworthy that whether a particle gets trapped in a gravity-well is a function of its mass and its energy/velocity verses gravity. If the sun was much hotter, for example, I think all water could boil off the Earth's surface and float away with the solar wind. On the other hand, if Earth was more massive and/or more compact a higher energy atmosphere would still fail to eject as many gases beyond the gravity well. Similarly, I would guess there are nearly black-hole density neutron stars that bend light quite a bit before the light gets through and moves on. I also think that higher frequencies of light bend less than lower ones with less energy, but I may be remembering that wrong.

It would seem that any given gravity-well has a certain ratio between the energy-level of a particle or object and the velocity needed to achieve a closed orbit (circular or elliptical). So, for example, a black hole requires massless photons traveling at the speed of light to achieve closed orbit at a certain proximity. A slightly less dense neutron star might only be able to sustain a certain masses of particles in its orbit, depending on what happens to those and other particles as they approach the near-C speeds required to sustain orbit. I'm guess that at some point close to the speed of light, particles of matter get converted completely into light/radiation, but someone with more expertise should confirm or reject that since I don't know much about how particles breakdown in accelerators, etc.

Edited by lemur
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what intrigues me is the relationship between various things in motion and the spacetime curvature of gravity. For example, why does light bend a certain amount due to gravity while an object with mass moving along the same trajectory will veer more and even fall into the gravity well? According to Newtonianism (and maybe other approaches as well), all objects are supposed to fall at the same rate in the same gravity regardless of mass. Yet, as particles get lighter, they become more likely to escape gravity wells with lower amounts of energy/momentum. So a water molecule can evaporate off the moon, whereas Earth's gravity is too strong for that to happen to water, although it could happen to helium on Earth.

Black holes, then, supposedly have enough gravity to capture and contain light, the way Earth captures and contains heavier molecules with mass. But does matter and light fall into a black hole along the same path? I'm not sure why this question of when the curvature of spacetime is the same or closer to the same for light and matter, but it seems key to me for some reason. For example, in relatively straight paths through spacetime, matter and light easily follow the same path. But as spacetime becomes more curved entering a gravity well, the paths taken by the light and the matter will diverge more, correct, although both will still curve to some extent. Anyway, I know it sounds strange that this interests me but I'm not sure why, but somehow it seems key to the relationship between energy and matter.

What really matters is the velocity of the object. Objects of different masses moving at the same velocity will follow the same path, objects of the same mass moving at different velocities will follow different paths. An object traveling at nearly the speed of light will curve almost the same as light.

As far as molecules escaping the Earth or any other body is concerned, it is still just the velocity that matters. The reason that less massive molecules escape more readily than more massive ones is that they are moving faster and a higher percentage exceed escape velocity. They move faster because the temperature of a gas is a measure of the average kinetic energy of the gas molecules, and in order for lighter helium atoms to have the same kinetic energy as water molecules at the same temp and pressure, they have to have a higher velocity.

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What really matters is the velocity of the object. Objects of different masses moving at the same velocity will follow the same path, objects of the same mass moving at different velocities will follow different paths. An object traveling at nearly the speed of light will curve almost the same as light.

And this convergence makes me wonder about possible further ramifications. In this solar system, for example, there is a very marked distinction between the behavior of matter w/ inertia and that of light/radiation. As a solar system approaches the mass/gravitation of a black hole, however, I am guessing that distinction becomes less. Stars themselves, whose gravity is sufficiently large to render matter into a plasma phase, probably give some indication of what it means for matter to approach pure energy. If I'm correct, the plasma phase of matter itself involves a collapse of the distinction between heavy particles (protons & neutrons) and electrons. I.e. we are accustomed to electron shielding of atomic nuclei and other electron-energy phenomena at our level of gravitational intensity, which causes the nuclei to function only as anchors for the orbiting and free electrons to act as energy-carriers. However, when unshielded the larger particles seem to begin acting as their own energy-carriers while all the energy that is potential in the electron-shielded state is transformed into pure energy (i.e. radiation).

I would also guess that looking at increasingly massive stars would reveal ever larger proton/neutron configurations behaving as lighter energy-carrying particles. It's as though the higher gravity gets, the less distinct matter gets from pure energy. Is it coincidence that the effects of gravity on light/energy vs. matter in terms of trajectories through spacetime also become more similar as gravity and/or speed increases?

Could pure energy/radiation itself be a phase of matter? I.e. radiation is to plasma what gas is to liquid? This also makes me wonder if radiation/light could go through condensation-type phase changes when subject to the gravity levels of a black hole. The core issue in all this, to me, involves energy density as a function of gravitation because pure energy is ultimately the capacity to radiate in the straightest line possible at the highest speed possible, which translates into the least dense energy-expression. The more light curves, the smaller total volume its energy takes up, so it could be said to be densifying with higher gravity, no? I'm guess this means that in a black hole, matter and energy have converged into an undifferentiated primordial-type substance that doesn't exhibit differentiation in terms of how we normally think of light and matter behaving in different ways and interacting with each other in terms of inertia and momentum. Is it possible that there could be a third state of matter-energy that transcends the common distinction/differentiation between the two?

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I'm guess that at some point close to the speed of light, particles of matter get converted completely into light/radiation, but someone with more expertise should confirm or reject that since I don't know much about how particles breakdown in accelerators, etc.

Could pure energy/radiation itself be a phase of matter? I.e. radiation is to plasma what gas is to liquid?

Short answer is no. Most matter with which we are familiar is either baryons (neutrons and protons) or leptons (electrons), and both baryon number and lepton number are conserved quantities. The photon is neither, so while photons can be created, matter does not just turn into photons. You would have to start with the total baryon or lepton number at zero, e.g. matter/antimatter annihilation.

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Short answer is no. Most matter with which we are familiar is either baryons (neutrons and protons) or leptons (electrons), and both baryon number and lepton number are conserved quantities. The photon is neither, so while photons can be created, matter does not just turn into photons. You would have to start with the total baryon or lepton number at zero, e.g. matter/antimatter annihilation.

What does the lost mass in a fission reaction turn into if not photons which I have up to now assumed?

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What does the lost mass in a fission reaction turn into if not photons which I have up to now assumed?

Matter and mass are not to be used synonymously.

The mass difference is due to the binding energy of a composite bound system. The potential energy of a bound system is lower than that of the free constituents. Thus the mass of a bound system is less than that of the free constituents.

The "missing mass" in any reaction is transformed into excited states or is removed as the energy carried by photons.

Note that although mass is not conserved, matter is via the conservation laws of the standard model i.e. baryon number and lepton number as stated by swansont.

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Matter and mass are not to be used synonymously.

The mass difference is due to the binding energy of a composite bound system. The potential energy of a bound system is lower than that of the free constituents. Thus the mass of a bound system is less than that of the free constituents.

The "missing mass" in any reaction is transformed into excited states or is removed as the energy carried by photons.

Note that although mass is not conserved, matter is via the conservation laws of the standard model i.e. baryon number and lepton number as stated by swansont.

OK got that. Thanks.

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Matter and mass are not to be used synonymously.

The mass difference is due to the binding energy of a composite bound system. The potential energy of a bound system is lower than that of the free constituents. Thus the mass of a bound system is less than that of the free constituents.

The "missing mass" in any reaction is transformed into excited states or is removed as the energy carried by photons.

Note that although mass is not conserved, matter is via the conservation laws of the standard model i.e. baryon number and lepton number as stated by swansont.

If the mass of a bound system is less than that of the free constituents, then how could fission result in a net gain of mass AND gain of energy? Also, does this mean that matter is not ultimately reducible to pure energy? Are these particles truly elementary?

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For fission to result in a release of energy the total binding energy of the resulting elements has to be lower than the total binding energy of the starting element.

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For fission to result in a release of energy the total binding energy of the resulting elements has to be lower than the total binding energy of the starting element.

Quite so. See the Binding Energy Per Nucleon curve.

Up until about Iron, the binding energy increases as the total number of nucleons increases. That means that fission would typically cause a release of energy.

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If the mass of a bound system is less than that of the free constituents, then how could fission result in a net gain of mass AND gain of energy?

It doesn't. Mass decreases in fission of heavy isotopes and fusion of light ones.

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And this convergence makes me wonder about possible further ramifications. In this solar system, for example, there is a very marked distinction between the behavior of matter w/ inertia and that of light/radiation. As a solar system approaches the mass/gravitation of a black hole, however, I am guessing that distinction becomes less. Stars themselves, whose gravity is sufficiently large to render matter into a plasma phase, probably give some indication of what it means for matter to approach pure energy. If I'm correct, the plasma phase of matter itself involves a collapse of the distinction between heavy particles (protons & neutrons) and electrons. I.e. we are accustomed to electron shielding of atomic nuclei and other electron-energy phenomena at our level of gravitational intensity, which causes the nuclei to function only as anchors for the orbiting and free electrons to act as energy-carriers. However, when unshielded the larger particles seem to begin acting as their own energy-carriers while all the energy that is potential in the electron-shielded state is transformed into pure energy (i.e. radiation).

A plasma is simply a gas that has been sufficiently ionized so that it becomes a current carrier and responds strongly to electromagnetic fields. It has nothing to do with nucleons and electrons losing their distinction, and definitely doesn't involve electron transforming to energy.

I would also guess that looking at increasingly massive stars would reveal ever larger proton/neutron configurations behaving as lighter energy-carrying particles. It's as though the higher gravity gets, the less distinct matter gets from pure energy. Is it coincidence that the effects of gravity on light/energy vs. matter in terms of trajectories through spacetime also become more similar as gravity and/or speed increases?

Trajectories converging as velocities converge is just a matter of orbital mechanics, it has nothing to do with matter becoming more "light-like".
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It doesn't. Mass decreases in fission of heavy isotopes and fusion of light ones.

That's what I would have thought before post #14.

A plasma is simply a gas that has been sufficiently ionized so that it becomes a current carrier and responds strongly to electromagnetic fields. It has nothing to do with nucleons and electrons losing their distinction, and definitely doesn't involve electron transforming to energy.Trajectories converging as velocities converge is just a matter of orbital mechanics, it has nothing to do with matter becoming more "light-like".

So you don't think that the interdynamics of electrons and their nuclei stabilize the atoms in a way that destabilizes in the plasma state? My impression was that stable atoms are stable because their volume is much greater than the nuclei. I thought the high-energy interactions in plasma was due to the nuclei coming into closer proximity and being able to move more fluidly than when the electrons are intact.

All I meant by matter becoming more "light-like" is that the trajectory of a photon through a given gravitational field results in less deviation from straight-line motion than for particles/objects with mass. So, as the speed of the particle increases, its trajectory approaches the straightness of a photon and, likewise, when light is emitted closer to black-hole levels of gravity, it can curve at levels closer to that of particles of matter. So is there not convergence between the gravitational responses of matter and light as gravity and/or velocity increases?

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That's what I would have thought before post #14.

That post is perfectly consistent — the system becomes more tightly bound, energy is released and the mass decreases.

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That's what I would have thought before post #14.

So you don't think that the interdynamics of electrons and their nuclei stabilize the atoms in a way that destabilizes in the plasma state? My impression was that stable atoms are stable because their volume is much greater than the nuclei. I thought the high-energy interactions in plasma was due to the nuclei coming into closer proximity and being able to move more fluidly than when the electrons are intact.

How are you defining "stable"? A stable atom can be one that does undergo radioactive decay, or one that is electrically neutral. Neither one relies on the relative size of the nucleus to the atom as a whole.

A Plasma is a mixture of ions(positive charge) and free electrons.(Actually, as little as 1% of the atoms need to be ionized for a plasma to exist) The ions being of the same charge would tend to repel each other, not move closer together. What distinguishes a plasma from a regular gas is that electromagnetic effects dominate in a plasma.

All I meant by matter becoming more "light-like" is that the trajectory of a photon through a given gravitational field results in less deviation from straight-line motion than for particles/objects with mass. So, as the speed of the particle increases, its trajectory approaches the straightness of a photon and,

Again, nothing more than what would be predicted by orbital mechanics, and nothing special of note.

likewise, when light is emitted closer to black-hole levels of gravity, it can curve at levels closer to that of particles of matter.

Near a Black hole particles of matter moving at less than c would curve more than light. A particle passing a black hole at 0.5c will deflect much more than a light beam would, so it is not a matter of light curving at level close to particles.

So is there not convergence between the gravitational responses of matter and light as gravity and/or velocity increases?

No.

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How are you defining "stable"? A stable atom can be one that does undergo radioactive decay, or one that is electrically neutral. Neither one relies on the relative size of the nucleus to the atom as a whole.

That's not the kind of stability I'm talking about. I'm talking about the relative integrity of the electron shielding of the nucleus. I was under the impression that in sub-plasma phases, atoms behave more or less like basketballs where the electrons determine the relative volume and pressure of the ball. I thought that becoming plasma (in the high gravity/pressure/temperature of fusion, e.g. in a star) the electron shielding gives way and the nuclei interact at a closer proximity and with more interaction between the attractive and repulsive forces between the protons & neutrons themselves. I can't remember the source that gave me this impression, though, so maybe I misunderstood.

A particle passing a black hole at 0.5c will deflect much more than a light beam would, so it is not a matter of light curving at level close to particles.

I was thinking more in terms of a particle/object gradually spiraling into the BH in a way that it would have time to accelerate to near-C. In that case, there would be an orbital path at some area of the gravitational field where both light and matter would orbit at almost C, no? This is assuming that matter wouldn't simply convert into radiation from the high levels of energy it would attain by accelerating close to C. This is just my impression, though, on the basis that particles have to approach infinite energy to accelerate close to C. It seems like if gravity was causing them to keep accelerating at such high velocities, they would start losing mass/inertia by converting it into massless radiation. That doesn't seem logical to you?

Edited by lemur
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• 2 years later...

Gravity does not just attract things with mass; but also things with energy. Therefore, anything with mass of Energy can be affected by gravity. The Stress-Energy tensor specifies that. Otherwise, yes, Gravity is actually a manifestation of curved spacetime.

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