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Photons have no mass. Therefore they can emit no gravity.
Remember that, according to General Relativity,the spacetime curvature that we experience as gravity is generated by energy. Rest mass is just a special case of energy; other forms of energy, like electromagnetic fields, also contain energy and hence generate curvature. So the statement that "No MASS = no gravitational force exertion" is not true. The amount of energy in a single photon is so small that the gravity it creates is extremely tiny. We are unable to measure this in the laboratory but there is some hope that we may be able to observe this effect in powerful astrophysical systems known as Gamma Ray Bursts (GRBs). In a GRB, the photon density is so high that we may be able to see a "self-gravity" effect causing a bunching of the photon pulse. Hope that helps!
Originally posted by DragonsDemesne
Well relativity says that an object with nonzero mass needs infinite energy to accelerate to the speed of light. Also, I didn't say photons had mass, I said that photons had energy which is gravitationally equivalent to a mass. (an incredibly tiny mass) That's if I understand it correctly, which may not be so :p
I offered the theory that the universe is not infinite and is in fact contained within another 'object'. The gravitational attraction of the mass outside our universe's bubble is what is causing the increase in rate of expansion of our universe.
Originally posted by DragonsDemesne
reply to post by TurkeyBurgers
I realize it's not a perfect source, but a few minutes on wikipedia suggests that photons do contribute to the mass of a system.
There are also a few other terms, like relativistic mass and so on, so it might be wise to clarify just what you mean, since it would have implications on your theory.
"An upper limit to the photon mass can be inferred through satellite measurements of planetary magnetic fields. The Charge Composition Explorer spacecraft was used to derive an upper limit of 6 × 10-16 eV with high certainty. This was slightly improved in 1998 by Roderic Lakes in a laboratory experiment that looked for anomalous forces on a Cavendish balance. The new limit is 7 × 10-17 eV. Studies of galactic magnetic fields suggest a much better limit of less than 3 × 10-27 eV, but there is some doubt about the validity of this method."
Q: Do photons have mass? If not, why does the gravitational field of a star bend passing light?
A: No, photons do not have mass according the present definition of mass. The modern definition assigns every object just one mass, an invariant quantity that does not depend on velocity, says Dr. Matt Austern a computer scientist at AT&T Labs Research. Under this definition, mass is proportional to the total energy, Eo, of the object at rest.
"A particle like a photon is never at rest and always moves at the speed of light; thus it is massless," says Dr. Michael S. Turner, chair of the Department of Astrophysics at the University of Chicago.
What about experimental evidence? Experiments don't determine exact quantities because of small errors inherent in making measurements. We have, however, put an upper limit on the photon rest mass. In 1994, the Charge Composition Explorer spacecraft measured the Earth's magnetic field and physicists used this data to define an upper limit of 0.0000000000000006 electron volts for the mass of photons, with a high certainty in the results.
This number is close to zero; it is equivalent to 0.00000000000000000000039 times the mass of an electron (the lightest particle), says Turner.
You ask how a star's gravitational field can bend the path of a massless photon. This takes us into the realm of Einstein's general theory of relativity. The mass of the photon isn't attracted to the star's mass under Einstein's theory. Rather, the star's mass distorts space and the photon's path changes because the space is curved, says Paul Hewitt in his book Conceptual Physics.
General relativity uses a geometry that is extremely difficult for we humans who live in three-dimensional space to visualize. This geometry describes not only a curved space but also a curved time. It's a geometry of curved four-dimensional space-time. Gravity is nothing but the bumps, depressions, and warpings of geometrical space-time.
We three-dimensional beings, says Hewitt, can glimpse this distortion by considering a simplified analogy in two dimensions: Think of a heavy, black bowling ball resting in the middle of a king-size water bed. (See the image to the right.) The more massive the ball, the more it dents or warps the bed.
Roll a marble across the bed, well away from the bowling ball. It rolls along a path that's pretty straight. Now, roll the marble across the bed but nearer the bowling ball. It curves in towards the ball as it rolls past it. That's how photons bend as they pass a star. Not because of their mass but because the star has warped the four-dimensional space-time they travel in and we all live in.
A new limit on photon mass, less than 10-51 grams or 7 x 10-19 electron volts, has been established by an experiment in which light is aimed at a sensitive torsion balance; if light had mass, the rotating balance would suffer an additional tiny torque. This represents a 20-fold improvement over previous limits on photon mass.
Photon mass is expected to be zero by most physicists, but this is an assumption which must be checked experimentally. A nonzero mass would make trouble for special relativity, Maxwell's equations, and for Coulomb's inverse-square law for electrical attraction.
The work was carried out by Jun Luo and his colleagues at Huazhong University of Science and Technology in Wuhan, China (email@example.com, 86-27-8755-6653). They have also carried out a measurement of the universal gravitational constant G (Luo et al., Physical Review D, 15 February 1999) and are currently measuring the force of gravity at the sub-millimeter range (a departure from Newton's inverse-square law might suggest the existence of extra spatial dimensions) and are studying the Casimir force, a quantum effect in which nearby parallel plates are drawn together. (Luo et al., Physical Review Letters, 28 February 2003)
Originally posted by TurkeyBurgers
If you could show the place where it mentions ANYTHING about a measurement taken of a photon having mass (and therefore gravity) I would be more than excited to see it. It would destroy my theory instantly.
(edit: external source = the wiki link in my last post that apparently wasn't read)
The energy of a system that emits a photon is decreased by the energy E of the photon as measured in the rest frame of the emitting system, which may result in a reduction in mass in the amount E / c2. Similarly, the mass of a system that absorbs a photon is increased by a corresponding amount. As an application, the energy balance of nuclear reactions involving photons is commonly written in terms of the masses of the nuclei involved, and terms of the form E / c2 for the gamma photons (and for other relevant energies, such as the recoil energy of nuclei).
Since photons contribute to the stress-energy tensor, they exert a gravitational attraction on other objects, according to the theory of general relativity. Conversely, photons are themselves affected by gravity; their normally straight trajectories may be bent by warped spacetime, as in gravitational lensing, and their frequencies may be lowered by moving to a higher gravitational potential, as in the Pound-Rebka experiment. However, these effects are not specific to photons; exactly the same effects would be predicted for classical electromagnetic waves.
The law of conservation of energy states that the total amount of energy in an isolated system remains constant. A consequence of this law is that energy cannot be created nor destroyed. The only thing that can happen with energy in an isolated system is that it can change form, for instance kinetic energy can become thermal energy. Because energy is associated with mass in the Einstein's theory of relativity, the conservation of energy also implies the conservation of mass in isolated systems (that is, the mass of a system cannot change, so long as energy is not permitted to enter or leave the system).