does light possess gravity? can it attract things?

Question

well if u say the energy thing ,then why does it bend in a gravitational field. if it responds to a gravitational field then it too must have a field of its own and can attract things. i know it doesnt. but how come its not the other way round. can anybody tell me where the flaw is?

Answer 1

oooh oooh pick me.

Newton's theory of gravity fails us when it comes to things we don't experience in everyday life (i. light bends due to gravity).

Einstein's theory of gravity clearly states that both matter and energy are affected by and produce gravitational fields.

So if you had a high energy density (I mean stupidly high) you would be able to experience a gravitational attraction towards it.

Edit: I'm pretty sure a certain someone who is claiming to have a PhD in physics, doesn't...

Answer 2

Oh yes it can. Energy has weight and the local curvature of space (eg the gravitational force) depends upon the total mass/energy density. There is no flaw.

Edit: Mr. Quark below is incorrect. He is using the Newtonian theory and an inconsistent argument. He may as well be saying that satellites cause no gravitational attraction, because relative to the Earth they are so tiny. In fact, EVERYTHING follows the local curvature. Gravity IS the local curvature. And the local curvature depends on the total mass/energy density tensor.

Another Edit: Poohp, I'm pretty sure I'm correct. Consider the following thought experiment. An electron and a positron are falling along a geodesic in a small mirrored box. They come together and annihilate, emitting two photons. The two photons bounce off the mirrors, come back together and pair produce. Has the mass/energy in the box changed? No. Does the weight of the box change? Again, no. So it must not have changed course. But this course was at once determined by the total mass in the box--therefore the energy of the photons must be acting like mass for this purpose.

The source of the gravitational field is the energy-momentum tensor, and this tensor includes field energy. Just because the curvature due to a photon is small doesn't mean it's nonexistent.

Answer 3

The flaw is that no one really knows. There's no test or model which fully explains light behavior. They (the PhD astro-physicists) are still trying to work out Einstein's theories with Quantum mechanics and the "Big Bang" theory. There is no unified theory yet which makes it all work together. The mathematics don't fully jive between all these theories, particularly at the extreme ends of the theory spectrums.

We know that massive objects such as stars will bend light rays. But there is still a debate as to whether a not light is a particle or wave only. No one clearly knows and tests and models need to be worked up to sort this all out.

There is a possibility that our equipment just isn't sensitive enough or sophisticated enough to sort out exactly what a photon is, whether it has mass or not. Its mass could be so tiny that our instruments don't detect it yet. So this question could be going on for another hundred years or longer, just depends on how good our science is and how good our instrumentation has become.

Of all this, gravity itself is the least understood between the four forces:
1)electro-magnetic
2)weak nuclear
3)strong nuclear
4)gravity

Even neutrinos and neutrons are not yet fully understood, nor is "dark matter". Is light affected by dark matter? Is there more dark matter around gravitational fields? You see? Is this dark matter what is slowing down the light, or is it really gravity, or is it something else? Why do neutrinos pass through objects that photons (apparently) do not? (Even though light supposedly has no mass?)

You see? There are still too many unknowns. I'm not even aware that there is any confirming research on gravitons, even they are still a theory. What is gravity really? (The Big Bang by the way, is still a theory too -- it isn't conclusively proven, the "background radiation" which is being detected could be who knows what. Maybe background radiation is the sum total of gravitational radiation throughout the whole universe, there's a theory for you, LOL.)

The main problem with science is that theories are often assumed to be facts. Many scientists cannot ascertain the difference apparently. Maybe we should start studying that phenomena instead. It would probably be more interesting:

Why do many scientists take theories to be facts and then do research based on theories which haven't been conclusively proven to be true? And then come up with new "facts" based off of unproven theories?

ROFL. (Sorry, I'm not trying to be sarcastic, it just came out that way.) But that all goes nowhere really. We need better methods of doing research.

So for any PhD to tell you that he "knows" and that the other PhD's are wrong, is pure BS. No pun intended. None of them know, because of the reasons I just stated.

How to do research:

Since all these theories don't work together very well yet, the first thing you know is that something isn't right. In other words, you know that you don't know. Many can't do this because it's a self-criticism of sorts -- you have to put yourself down a bit before you can go forward. There are soooo many people who just CAN'T be wrong...

That is the first step -- knowing that you don't know. The next step is to sort out what is known from what isn't, most of these guys have omitted that step, because that first step just didn't go anywhere.

But once you HAVE sorted out what you know from what you don't know, you can then devise models and tests to delve into these unknown areas, but always being careful not to accept an assumption or theory as fact.

Then you can get somewhere in research. Good luck to all of you.

Answer 4

Good question! I think that light does have a gravitational pull, assuming it has mass. It must have mass, because it's affected by other planets and such. But, the gravitational energy light contains is probably very little. It's like me. I am 160 pounds of pure muscle, and I affect the gravitational fields of earth, but so slightly it's practically immeasurable. Light weighs even less than I do. Further more, the energy my be dispersed with speed. For example, I throw a baseball and it flies 20 feet into my partner's glove. In the same fashion, light may travel past a planet and be bent only slightly until it goes beyond the planets pull and continues flying into space.



Just so you know, you shouldn't listen to me at all. I have no idea about quantum physics. The subject, including this question, amazes me completely, and I didn't want to lose track of this question. By answering, I keep a link to this subject in my profile and it's always a few mouse clicks away so I can read all the answers. These other guys are way smarter in this subject than I am. Listen to them. I answered for selfish reasons(plus, 2 points)!

Answer 5

Nothing, not even light, POSSESSES gravity. Gravity, defined as the tendency of objects with mass to accelerate toward each other, affects light when it (and anything else) responds to a gravitational field. Now, light does possess mass, and that mass responds to a gravitational field, just as yours and mine does. But it's got no magnetic properties; light can't attract things any more than we can without artificial aid.

Perhaps this article on mass (particularly passive and active gravitational mass) will explain it a little more clearly than I'm doing.

Answer 6

Let me see if I can make any sense of this at all. E=MCC, so M=E/CC or E/34596000000 making M extremely small, but not zero. Therefore, I would say that light does have a gravitational field but too small and fast to be detected.
I know that they teach that gravity bends the fabric of space, but I find that much more difficult to believe. I was taught that space is an absolute vacuum and void. Then someone needs to explain what "fabric" there is to bend. I believe the appearance of space bending around a black hole singularity is an optical illusion. Just like a good artist can make a perfectly flat canvas appear to have curved surfaces on it. Now stick that canvas a few million light years away in the darkness of space and then try to tell me that the "fabric" of space is being bent?? I think light being bent is thousands of times more plausible.

Answer 7

Light (photons) are massless and do not have
gravity. However, mass produces curvature of
space-time which affects everything that travels
through it (which is everything, of course). Light
must follow the curvature, too. This is the point
of General Relativity.

Here is a thought experiment my Gravitation professor
showed us a long time ago:

We know energy and mass are interchangeable (E=mc^2),
so imagine a mass with rest energy 1 (units don't matter)
falls from a fixed height, gains 1 energy unit of kinetic energy from the fall and at the bottom hits a target where it transforms to pure energy... a photon with energy 2. This recoils up
against gravity and losses no energy since gravity won't
affect it (massless). At the top we turn the 2 energy units back
into mass with rest energy 2. You can see the violation that happens here as you create energy and matter from nothing if you assume no mass means no effect from gravity.

EDIT:
Benjamin, with all due respect, is somewhat incorrect also.
Energy due to photons does not have a gravitational
pull (except in the moments after the big bang). Photons
and gravitons in our current universe mediate two
separate forces and are completely decoupled.

Answer 8

Yes, light exerts a gravitational influence on things. It must, because if not, momentum would not be globally conserved. Light carries momentum. If light is deflected, the momentum vector changes, and so something, somewhere, must have its momentum changed in order to conserve momentum globally. One can make a similar argument with energy when light is deflected by a moving massive object.

In general relativity, the gravitational field is produced by the stress-energy tensor. There are components in that tensor for energy and momentum fluxes. Contrary to other opinions offered here, light bends space, and light could, in principle, attract other light.

In fact, gravitoelectric and gravitomagnetic forces exactly cancel for two beams of light travelling parallel to one another, so two parallel beams of light don't attract or repel each other under general relativity. Antiparallel beams, or other beams not exactly parallel, do exert a gravitational attraction.

Answer 9

Does electromagnetic energy posess gravity? Let's take a look at what forms a gravitational field and see if there is anything in it that would directly equate to that of the force of gravity.

The force of gravity is a product of heat energy and mass. The equation for this force is part of the physics trilogy: E = mc2, m = E/c2, and c2 = E/m. It is the last we have an interest in.

As the energy value within a mass increases so, also, does the field of energy. Were all the energy within our planet to disappear, then our gravitational field would do the same. This is also true for our sun. The force of gravity is due to a particular form of energy.

All matter is formed of electromagnetic energy, this being formed into electrons, and these into neutrons and protons. When gravitons form, they are tiny bits of energy that are forced to leave the mass they were part of. They move at the speed of light and are an equivalence of the kinetic energy retained within the host mass. What this leads us to, is that gravitons have as their origin a segment of electromagnetic energy, but they do not directly attract other masses as we think of that term. They leave a location in space where they pass through, that mass and energy entering that location, must seek to adjust their speed/direction to account for the existence of the passing graviton.

It is impossible to go through this quickly. You might go to http://timebones.blogspot.com and scroll through that.

Answer 10

The general misunderstanding of special relativity leading to this common misconception comes, in part, from using the simplified form of Einstein's equation, E=mc^2. This is only true for particles at rest (m is the particle's rest mass). The full equation is E=sqrt((mc^2)^2 + (pc)^2). Photons have no mass; their energy comes from momentum (the p in the equation).

It's true that in theory light cannot escape a black hole, this is explained by general relativity, not special relativity, and involves the "bending" of space-time. The light follows space-time in a straight line, however if the space-time is curved, the light bends round - like if you draw straight lines on a trampoline and then stand on it near the line, it becomes curved.

Answer 11

Well according to Einstein's theory about black holes, specifically, that even light cannot escape its gravitational pull, then yes, it does. Unless gravity has some unknown property that specifically effects energy and light, which would be pretty interesting. Oh by the way, did you know Einstein had 15 girlfriends at one time without wanting any of them? Proof to show that even geniuses can be pimps lol