It looks like you're using an Ad Blocker.
Please white-list or disable AboveTopSecret.com in your ad-blocking tool.
Thank you.
Some features of ATS will be disabled while you continue to use an ad-blocker.
Originally posted by Rasobasi420
That would suck for you, the time traveler, but we'd be okay here in our timeline.
Originally posted by Springer
Originally posted by disownedsky
This is a pathetic, cringeworthy example of cargo cult physics abuse. The writer neither understand relativity or even basic physics. I'd waste no further time on it.
[edit on 7-3-2007 by disownedsky]
Just out of curiosity, how many peer reviewed publications do you have to your credit? I am not trying to be snide here, I am trying to discover if you are a genuine expert in physics or someone simply "popping off" at something he doesn't really understand.
Springer...
Originally posted by Neon Haze
Simply put, light has no mass and so regardless of how much of it there may be it will never be able to deform space-time. In fact we physicists often use the exact opposite when calculating the location of objects in space.
Originally posted by Tom Bedlam
As much as I hate to support Dr Mallett here, while it is true that photons have no rest mass, they do have an equivalent mass (which used to be called the relativistic mass) which is related to their energy. This effective mass of a photon is given by hv/c^2.
Energy does exhibit gravitational attraction. There are a number of papers by Dr Wheeler dealing with it. If you check out the two papers I put links to, you'll find that Mallett is using the energy-momentum tensor of electromagnetic radiation in the GR equations in just this way.
Originally posted by Tom Bedlam
As much as I hate to support Dr Mallett here, while it is true that photons have no rest mass, they do have an equivalent mass (which used to be called the relativistic mass) which is related to their energy. This effective mass of a photon is given by hv/c^2.
If the particle is at rest, then p = 0, and E = mrestc2.
If we set the rest mass equal to zero (regardless of whether or not that's a reasonable thing to do), then E = pc.
In classical electromagnetic theory, light turns out to have energy E and momentum p, and these happen to be related by E = pc. Quantum mechanics introduces the idea that light can be viewed as a collection of "particles"--photons. Even though these photons cannot be brought to rest, and so the idea of rest mass doesn't really apply to them, we can certainly bring these "particles" of light into the fold of equation (1) by just considering them to have no rest mass. That way, equation (1) gives the correct expression for light, E = pc, and no harm has been done. Equation (1) is now able to be applied to particles of matter and "particles" of light. It can now be used as a fully general equation, and that makes it very useful.
Because the energy of a particle just equals its relativistic mass times c2, physicists have learned to economise the language by only ever referring to a particle's energy. When they use the term "mass", they mean rest mass. This is purely a linguistic convention. When the two sorts of mass are referred to together, relativistic mass is usually written m and rest mass is written m0. But when only rest mass is being used, then the word "mass" is assumed to mean rest mass, and it tends to be written simply as m.
One reason why the term relativistic mass is sometimes avoided is because there is actually a directional dependence to a particle's resistance to being accelerated; it's much easier to push a fast-moving particle sideways than it is to alter its speed in its direction of motion. Another reason is that physicists do not want anyone thinking that relativistic mass can be used in the newtonian relations F = ma and F = G m1 m2 /r2. There is no definition of mass for which these equations are true relativistically; they must be generalised. The generalisations are more straightforward using the idea of rest mass, as opposed to using relativistic mass. For more discussion of the term "relativistic mass"
Energy does exhibit gravitational attraction. There are a number of papers by Dr Wheeler dealing with it. If you check out the two papers I put links to, you'll find that Mallett is using the energy-momentum tensor of electromagnetic radiation in the GR equations in just this way.
In fact objects do not have any increased tendency to form black holes due to their extra energy of motion. In a frame of reference stationary with respect to the object, it has only rest mass energy and will not form a black hole unless its rest mass is sufficient. If it is not a black hole in one reference frame, then it cannot be a black hole in any other reference frame.
In part the misunderstanding arises because of the use of the concept of relativistic mass in the equation E = mc2. Relativistic mass, which increases with the velocity and kinetic energy of an object, cannot be blindly substituted into formulae such as the one that gives the radius for a black hole in terms of its mass. One way to avoid this is to not speak about relativistic mass and think only in terms of invariant rest mass
Because the energy of a particle just equals its relativistic mass times c2, physicists have learned to economise the language by only ever referring to a particle's energy. When they use the term "mass", they mean rest mass. This is purely a linguistic convention. When the two sorts of mass are referred to together, relativistic mass is usually written m and rest mass is written m0. But when only rest mass is being used, then the word "mass" is assumed to mean rest mass, and it tends to be written simply as m.
Of course, electromagnetic waves are classically regarded as linear, meaning that photons don't ordinarily interfere with each other (directly). As Dirac said, "each photon interferes only with itself... interference between two different photons never occurs". However, the non-linear field equations of general relativity enable photons to interact gravitationally with each other.
Originally posted by Urn
heres a video about this very same guy...i saw a video that was WAY longer, but it seems to have disapeared from youtube...so this is the best that i can find...
www.youtube.com...
pretty interesting stuff, i must say...
Originally posted by Tom Bedlam
Dumse comments: "In GR, it is mass-energy that gravitates, and not just mass. Even photons (and even pressure!) participate. If you put two photons in a mirror box, its mass would increase (a tiny, but non-zero, amount). Fill
the mirrored box with many photons, and externally, you can't tell the
difference between the box with photons in it and the box with an
equivalent mass."
Originally posted by Neon Haze
I'm sorry but I am in total disagreement with your analysis.
I question your motives as you appear to be stating that a light bulb in a box of mirrors will eventually create a black hole.....
You obviously have not read the links I provided and have totally ignored the main point of my post.
Come on.... you know some of us here at ATS actually have already achieved a PHD and may also be in the class room but not as students!!
Best regards,
NeoN HaZe
Einstein's equation can be expressed as a statement about the relative acceleration of very close test particles in free fall. Let us clarify these terms a bit. A `test particle' is an idealized point particle with energy and momentum so small that its effects on spacetime curvature are negligible.
This equation says that positive energy density and positive pressure curve spacetime in a way that makes a freely falling ball of point particles tend to shrink. Since E = mc2 and we are working in units where c = 1, ordinary mass density counts as a form of energy density. Thus a massive object will make a swarm of freely falling particles at rest around it start to shrink. In short: gravity attracts.
Another remarkable feature of Einstein's equation is the pressure term: it says that not only energy density but also pressure causes gravitational attraction.
As Nathan Urban has replied, two parallel beams of light
will not attract each other. Two antiparallel beams,
on the other hand, will attract each other with twice
the relative acceleration you would expect from ascribing
each of them a mass of E/c^2.
As others have remarked, it's really the stress-energy tensor
that affects spacetime in general relativity. This is a
complicated object that includes masses, energies, pressures,
and stresses.
It's sometimes a good approximation, though, to consider
"relativistic mass" as the mass that creates and responds to
gravity. Specifically, if you have a small bound system in a
weak gravitational field, to a first approximation it behaves
as if it had a gravitational mass E/c^2 in Newtonian gravity.
For example, if you have a mirror-sided box of light (so the
light is trapped, and the system is thus bound), then on the
average you'll have as many photons moving in one direction
as the opposite direction, and the two effects I described
above average to an effective mass of E/c^2.
The principle of equivalence—the exact equality of inertial and gravitational mass—is a cornerstone of general relativity, and experimental tests of the universality of free fall provide a large set of data that must be explained by any theory of gravitation. But the implication that energy contributes to gravitational mass can be rather counterintuitive. Students are often willing to accept the idea that potential energy has weight—after all, potential energy is a rather mysterious quantity to begin with—but many balk at the application to kinetic energy. Can it really be true that a hot brick weighs more than a cold brick?
Originally posted by jbondo
I would think that if in fact light is made of particles and waves then it would have mass or weight, no?
In section 2 Einstein uses this expression by assigning mass to the energy of radiation. Einstein makes the substitution of the energy density of radiation with a mass density when he stated that If we assign the electromagnetic field too a mass density ...
Originally posted by Tom Bedlam
The stress-energy tensor, which, oddly you seem unfamiliar with: math.ucr.edu...
So, let's see how you explain away Einstein, Wheeler, Carlip, Mallett, Olum, Baez, Gerlach et al. Dude, this is low level first semester Intro to GR.
"Ouch! The concept of `relativistic mass' is subject to misunderstanding. That's why we don't use it. First, it applies the name mass--belonging to the magnitude of a four-vector--to a very different concept, the time component of a four-vector. Second, it makes increase of energy of an object with velocity or momentum appear to be connected with some change in internal structure of the object. In reality, the increase of energy with velocity originates not in the object but in the geometric properties of space-time itself."
source: Spacetime Physics Second Edition - Edwin F Taylor
John Archibald Wheeler
Originally posted by Neon Haze
Firstly where exactly have I refuted or stated in opposition to The Einstein field equations?? though I will openly admit right here that I think they only scratch the surface of the reality of reality
Simply put, light has no mass and so regardless of how much of it there may be it will never be able to deform space-time.
Secondly and this is the crunch..... Tom are you trying to say that photons in a box of mirrors will eventually warp space-time and create a black hole or worm hole where you can travel through time ????
Cause that is the premise of the OP's post and you appear to be attempting to argue for.
Look I'm a quantum physists so I am never going to agree with you on your use of relativistic mass.
I have no need or desire to explain away any of the scientist you quote. I may not agree with all of their conclusions though as you should know science builds upon conjecture.
Originally posted by Tom Bedlam
The stress-energy tensor in GR says that they do. Not because they have mass, but because they have energy.[\quote]
As far as warping space-time, since photons have energy, even one is enough, by the stress-energy tensor in GR. This is the substance of Einstein's paper, and Carlip's, among several others which I cited above.
As far as photons being able to cause a singularity, Wheeler certainly thought so, but only at hell's own energy density. This is the center of his geon work.
You seem to be quibbling over this "relativistic mass" term. Chuck it right out. Ok, now you still have to deal with the fact that photons DO have this behavior, due to the stress-energy tensor, and I think I've cited many a reference to it, all the way back to Einstein's 1906 paper.
The fact that the scientific "establishment" believes that freely moving light in vacuum (space) produces a gravitational field continues to be a major conceptual roadblock in their ongoing effort to unify gravitation with the other forces. This is a major (and crucial) point of difference between my theory of gravity's origin and "established" physics. Of course, when captured by the electron shell of an atom, light loses its intrinsic motion and symmetric non-local energy state, and in this bound condition its energy contributes to the atom's overall gravitational field. But it is no longer light or free energy, it is bound energy with a specifiable location - the atom's center of mass.
The error apparently goes back to Einstein, one of his very few (his denial of the validity of quantum mechanics and his "cosmological constant" are others - unlike the Pope, Einstein was humanly fallible). The problem seems to begin with E = mcc; from this justly famous equation it seems everyone assumed, including Einstein, that light has mass and so produces a gravitational field. But light obviously does not have mass, it has momentum and energy which is equivalent to mass, not mass itself. Light is manifestly different from bowling balls: light has intrinsic motion c, light is two-dimensional, light has a zero Interval; bowling balls have a time dimension and are four-dimensional with a positive Interval. And the fact that light is "bent" by a gravitational field does not mean it produces a gravitational field. Light follows the geodesic paths of spacetime, and is a co-mover with spacetime, like every other form of energy which spacetime carries. But light does not "warp" spacetime nor produce a gravitational field; light is the primordial symmetric state of electromagnetic energy. Gravitational fields and the time dimension they produce are only associated with secondary, massive, asymmetric forms of energy, derived from light.
Originally posted by Neon Haze
This is where I believe you have it all wrong, and I'm not alone.
Does Light Produce a Gravitational Field?
As far as photons being able to cause a singularity, Wheeler certainly thought so, but only at hell's own energy density. This is the center of his geon work.
This is absolute nonsense. I can tell you without a shadow of a doubt that a photon could never increase in energy.
If I may be blunt I would also state that the term Photon is not an actual particle but moreover a unit of measurement.
You and everyone else in the field will hear a lot more about LQG after Cern makes an announcement that the Higgs Boson isn't the mass propagator so many people thought it was.
Mark my words…
all the best,
NeoN HaZe.
Originally posted by Tom Bedlam
Ah, what to say here. Yes, photons do increase in energy, decrease as well, and one way is by interacting with gravitational wells. Further, are you trying to say that all photons have the same energy?