How exactly does space/time fabric work?

Doer said:

Finally!! A very interesting post. You are right, I have been quite un-clear as to where you are coming from. Thanks for this. I will delve in and strive to discuss it with you.

I have no rage. Funny comment. I have no beef with you. I like discussion. It's not dry to me it's normal for these topics. I can see what you are saying. But, I think it is more basic. Science seeks to rule things out, right? When we rule out everything, including the idea that light is affected by gravity, then we have some Imponderables.

Mass Compressing Space?
Dark Energy?
Dark Matter?

These are just a few of the current Imponderables. It can't be anything we know about, we have ruled out the idea that photons have mass.

So, it MAY be something in the new Models I listed above. It really has nothing to do with logic. It may have something to do with a Higgs field. MAY have.

Need to test it. We have tested the idea that light could just be experiencing a photonic orbit change. It isn't. We tested the idea that maybe the light is just given a different vector, as you suggest. A refraction?

It isn't. It lens. It magnifies. Imponderable.

We don't know what gravity is. We do see that Mass has the ability to form a concave gradient of magnification.

What dear Dr. forms a magnifier like this? A crystal ball does.

So, unless all these large masses we can see magnification around are encased in a transparent sphere,, what causes the magnification?

You know they are using these gravity lens lined up as ulra powerful telescopes. They can see these black holes plumes in visible light now.

All the space time math predicts this gradient. But, no one is saying space is actually compressible, at this time. It is a Model. Experiments are underway.

So, it's not a right-fight. You are using deductive logic, this is inductive.. Or did i get that backwards?

Click to expand...

and here i was under the impression that light has infinitesimal mass and it therefore subject to the pull of gravitation.

when i was in school photons had no mass at all. but all the latest evidence shows that photons DO have a tiny almost imperceptible mass, and a gravity all their own.

even the latest atomic models discuss the tiny amount of mass contained within the electron shell, so apparently even electrons have some mass and gravity as well.

the conclusion i have drawn from all this is that energy in all it's forms is simply matter in a different state and in motion, gravity is an attracting force that exerts it's power on all things from photons to molecules to massive bodies, attempting to draw everything in to a single giant clump, and the electro-repulsive force is attempting to push everything away from everything else, and when the final score is tallied we may learn which side wins, will the universe collapse into a new pre-big bang mass of whatever the fuck that thing is, or expand into dispersal? either way space still just sits there. i dont see space doing shit, it doesnt work for or against either team, it may just sit on the sidelines not doing shit, and hitting on cheerleaders. like the photographer from the school newspaper.

cannabineer said:

From Wikipedia ... cn

Parting shot / Parthian shot

"Parthian shot" is not to be confused with the phrase "parting shot". The first record of the phrase "parting shot" was by John McCleod, surgeon on board His Majesty's ship Alceste contained in "A narrative of a Voyage to the Yellow Sea" (181:

The consort, firing a parting shot, bore up round the north end of the island, and escaped.
​

In 1828 records in "The Friend, or Advocate of Truth" (a publication of The Religious Society of Friends) used the phrase in the figurative sense:

I think it would be much more becoming..., if you could separate without giving each other a parting shot.
​

The two phrases have rather similar phonetic soundings but are actually separately derived at different times. Although the Parthian archers of old have been famous for their shooting, the term "parthian shot" was recorded for the first time in 1832 by Captain Mundy, ADC to Lord Combermere on a hunting trip in India:

...I made a successful Parthian shot with my favourite Joe Manton (shotgun).
​

The figurative use of the phrase "Parthian shot" appeared later in The Times (1842):

They have probably enough dealt a Parthian shot to British interests...
​

If chronology were to be the source, it would appear that the English usage of "parting shot" preceded the use of the phrase "Parthian shot". "Parthian shot" is less often used. "Parting shot" is far more likely to be encountered.[SUP][2][/SUP][SUP][3][/SUP]

With which Parthian shot he walked away, leaving the two rivals open-mouthed behind him.
—Arthur Conan Doyle, A Study in Scarlet (1886)
​

His Parthian shot reached them as they closed the doors. 'Never mind darlings', they heard him say, 'we can all sleep soundly now Turner's here.'
—John Le Carre, A Small Town in Germany (196

​

Click to expand...

Well, sure, that is interesting. But, I thought your contention was a difference in meaning.
"Parting and Parthian shot are distinct concepts. cn "

They have the same meaning and are not necessarily from the same origin. Is that what you meant?
----------
http://www.phrases.org.uk/meanings/parting-shot.html
Having two almost identical terms in the language which mean the same thing has led to the belief that one derives from the other. That may be the case, but there's no real 'smoking gun' evidence to link the two.
----------

It is only perhaps, likely they are from different origins. But, I rightly applied both terms to the same meaning, didn't I?

Doer said:

Well, sure, that is interesting. But, I thought your contention was a difference in meaning.
"Parting and Parthian shot are distinct concepts. cn "

They have the same meaning and are not necessarily from the same origin. Is that what you meant?
----------
http://www.phrases.org.uk/meanings/parting-shot.html
Having two almost identical terms in the language which mean the same thing has led to the belief that one derives from the other. That may be the case, but there's no real 'smoking gun' evidence to link the two.
----------

It is only perhaps, likely they are from different origins. But, I rightly applied both terms to the same meaning, didn't I?

Click to expand...

i gotta side with the polar bear on this one.

the Parthian shot is attack in retreat, considered dishonorable and cheating at the time.

the Parting shot is an act of defiance and a promise that "this aint over motherfucker"

they convey different meanings despite being similar in that they are both attacks from a position of withdrawal.

it was quite the innovation in the peninsular war, when british riflemen would slip shoot and move, working in teams against the bonepart regiments arrayed in line or square.

today of course, firing while withdrawing so an ally can advance is standard practice and no longer considered worthy of a special literary association. we just call it covering fire.

Dr Kynes said:

the crux of the argument is whether Object B and it's mass and gravity acted upon Object A through the interaction of gravitational force (which seems obvious to me) or if Object B modified the fundamental nature of the space around itself to cause Object A's course to be altered through a process that requires the illogical assumption that space can be folded, deformed and altered by objects within it.

Click to expand...

Correct, I also see this as the crux of the problem.

since anything passing through empty space is NOT deflected one can presume that the object's personal gravity is NOT warping the space around it, or it would move in circles.

Click to expand...

This does not follow. If mass warps space, it does so in every direction, in proportion to how the mass is distributed. The models coincide well with Newtonion inertia and motion. The model showing space is warped compared to another model of a field would not make any noticeable difference as far as I can tell. Of course if you have the math to show otherwise, that's all I have been asking for.

the extraordinary claims of space being modified by things passing through it seems not only illogical, but also highly suspect.

Click to expand...

Why? Because it doesn't make sense to you? Argument from ignorance is not a counter to established thought.

if this is actually the case then there has to be a lot of explanation about why space UN-WARPS once the influence of the gravitational feild departs, or a shitload of explanation of how the "warping" follows the gravity around as it moves leaving previously warped space to return to it's normal non-warped status as well as where it gets the energy to un-warp without a new force to provide the energy since it is empty space.

Click to expand...

How much explanation do you need beyond -- this is the nature of how spacetime reacts to a massive object? Of course there are people studying exactly what is the nature of spacetime and maybe in due time we will have the answers you seek. But writing off a theory because it hasn't answered every single objection you have is short sighted.

simple observation that onbjects move in straight lines until another force changes that direction and then its straight lines again when that force expires tells me that FORCES make shit change course, not mysterious warps in space/time, nor do i have to have a PHD to see that things and forces interact with other things and forces, all without the interference of an unseen unmeasurable ever-present additional power that makes shit happen through inscrutable methods that can only be divined by the high priests like Kip Thorne (who stilll has a porn-star name) and their acolytes.

Click to expand...

Simple observation can be fooled. For a long time we thought gravity was a fundamental force and you would have a lot of support. However, we have a new model that supports that force is an illusion created by non-Euclidean spacetime. Do you regard centrifugal force real? How about the coriolois effect? These are forces that only appears because of a non-inertial frame. Gravity is merely acceleration. There is no difference between you in a space elevator being pulled up at 9.8m/s^2 and sitting still on the earth. The force you measure is not really from a field. Considering that no one to this day has found any evidence that gravitation is caused by a field force, it seems presumptuous of you to disregard the only other theory that offers explanation for the observations with such great precision to actually be able to predict that massless photons will bend in accordance with the curvature that is measured.

Dr Kynes said:

and here i was under the impression that light has infinitesimal mass and it therefore subject to the pull of gravitation.

when i was in school photons had no mass at all. but all the latest evidence shows that photons DO have a tiny almost imperceptible mass, and a gravity all their own.

Click to expand...

Well, maybe this is where you continue to be misguided. Photons are massless. A massive photon would give us many things to test, not the least of which is it's speed in a vacuum, where a massive photon's speed would vary based on frequency. Coulomb's Law would also be another test for a massive photon. Considering I have already mentioned these two in this thread and you ignored it once, so I guess I don't expect you to pay it any regard.

even the latest atomic models discuss the tiny amount of mass contained within the electron shell, so apparently even electrons have some mass and gravity as well.

Click to expand...

Electrons are not photons. Electrons have a mass.

Who cares...

It is amazing that someone will go thru all this length, (a pun) like seedling to smear something with the most outrageous language.

And why? Because they don't know the difference between space and volume and don't know the difference between charged particles with mass and charge-less particles without mass.

How can we discuss the fine points if there is no fundamental, proved, basis for talks?

You are in the wrong forum section, gentlemen.

mindphuk said:

Correct, I also see this as the crux of the problem.
This does not follow. If mass warps space, it does so in every direction, in proportion to how the mass is distributed. The models coincide well with Newtonion inertia and motion. The model showing space is warped compared to another model of a field would not make any noticeable difference as far as I can tell. Of course if you have the math to show otherwise, that's all I have been asking for.
Why? Because it doesn't make sense to you? Argument from ignorance is not a counter to established thought.

How much explanation do you need beyond -- this is the nature of how spacetime reacts to a massive object? Of course there are people studying exactly what is the nature of spacetime and maybe in due time we will have the answers you seek. But writing off a theory because it hasn't answered every single objection you have is short sighted.
Simple observation can be fooled. For a long time we thought gravity was a fundamental force and you would have a lot of support. However, we have a new model that supports that force is an illusion created by non-Euclidean spacetime. Do you regard centrifugal force real? How about the coriolois effect? These are forces that only appears because of a non-inertial frame. Gravity is merely acceleration. There is no difference between you in a space elevator being pulled up at 9.8m/s^2 and sitting still on the earth. The force you measure is not really from a field. Considering that no one to this day has found any evidence that gravitation is caused by a field force, it seems presumptuous of you to disregard the only other theory that offers explanation for the observations with such great precision to actually be able to predict that massless photons will bend in accordance with the curvature that is measured.

Well, maybe this is where you continue to be misguided. Photons are massless. A massive photon would give us many things to test, not the least of which is it's speed in a vacuum, where a massive photon's speed would vary based on frequency. Coulomb's Law would also be another test for a massive photon. Considering I have already mentioned these two in this thread and you ignored it once, so I guess I don't expect you to pay it any regard.
Electrons are not photons. Electrons have a mass.

Click to expand...

and though you insist that photons have no mass they still react to gravity as if they did, and every place i looked the mass of a photon was described as ZERO in capital letters followed by this: <1×10[SUP]&#8722;18[/SUP] eV/c[SUP]2

which looks like a Non-Zero sum to me. small is not zero. and small shit still responds to gravity.

meanwhile electrons are described as having a mass of :0.510998928(11) MeV/c[SUP]2[/SUP][/SUP][SUP] which would also be a Non-Zero number. a larger one to be sure, but mass is mass, even if it is small, and to my reckoning mass is subject to gravity's pull.

where pray tell am i wrong.
[/SUP]

You are not quite right, yet. When something is going light speed, (it is wave form) it can't have mass, by definition, but has virtual mass due to velocity. Virtual mass is not affect by gravity. An observed Uncertainty is the wave collapses to a particle as an impact, and reflects to become a wave again.

A .45 slug at the barrel has a virtual impact mass. Heavy slug, 800 fps

A .223 bullet has an impact mass based on velocity

Yet, the same thing that was observed at the tower of Pisa holds true. Both a fired slug and a dropped slug will hit the ground at the same time.

If virtual mass was affected by gravity, there would be an observable effect as it slow and lost virtual mass. It doesn't. The trajectory in the gravity well, remains ballistic. The impact has less energy, is all.

Impact mass, or virtual mass is all that a photon has. It can impart some velocity to a light sail. But, a photon is not subject to gravity.

So, now you know.

Dr Kynes said:

and though you insist that photons have no mass they still react to gravity as if they did, and every place i looked the mass of a photon was described as ZERO in capital letters followed by this: <1×10[SUP]&#8722;18[/SUP] eV/c[SUP]2

which looks like a Non-Zero sum to me. small is not zero. and small shit still responds to gravity.

meanwhile electrons are described as having a mass of :0.510998928(11) MeV/c[SUP]2[/SUP][/SUP][SUP] which would also be a Non-Zero number. a larger one to be sure, but mass is mass, even if it is small, and to my reckoning mass is subject to gravity's pull.

where pray tell am i wrong.
[/SUP]

Click to expand...

for start comparing an electron at rest to a photon that can never be at rest

Doer said:

You are not quite right, yet. When something is going light speed, (it is wave form) it can't have mass, by definition, but has virtual mass due to velocity. Virtual mass is not affect by gravity. An observed Uncertainty is the wave collapses to a particle as an impact, and reflects to become a wave again.

A .45 slug at the barrel has a virtual impact mass. Heavy slug, 800 fps

A .223 bullet has an impact mass based on velocity

Yet, the same thing that was observed at the tower of Piza hold true. Both a fired slug and a dropped slug will hit the ground at the same time.

If virtual mass was affected by gravity, the bullet would drop faster when it is moving faster. As it slowed down it would drop toward the earth slower. It doesn't.

Impact mass, or virtual mass is all that a photon has. It can impart some velocity to a light sail. A photon is not subject to gravity.
So, now you know.

Click to expand...

but still even the best of the poindexters cant actually say a photon has zero mass the best they can do is put a maximum possible value on it, leaving everything between the cap and zero as a possible mass. the cap is pretty fucking low, and zero is not that far below the cap but mas is still mass. and gravity attracts mass equally regardless of it's velocity so i dont see that your gallileo experiment alters the dynamic at all.

big bullets and tiny bullets drop at the same rate, preumably electrons with their tiny mass are attracted by gravity the same as a lump of a nuetron star's matter, so presumably the "as close to zero as we can confidently state" mass of a photon would react to a gravitational pull the same as an electron, a proton, or a brick. to my way of thinking that pretty much concludes that photons have some mass, or at least something that acts like mass which is subject to gravity, and if it acts like mass, and nobody has been able to establish with any certainty that it isnt mass would it not be prudent to at least accept the possibility that photons COULD have mass which would explain a lot of shit without requiring warps in space, dark matter or extra dimensions?

i always reach for the answer that doesnt require extra dimensions. but maybe i'm biased. i really cant accept other dimensions until i see spock's beard.

ginjawarrior said:

for start comparing an electron at rest to a photon that can never be at rest

Click to expand...

first show me an electron at rest.

as far as i know planck, heisenberg einstein hawking and rowdy roddy piper toghether in a handicap match couldnt pin one of those bastards for a three count.

ohh i know heisenberg will claim that it is PROBABLY outside the ring at any given moment, but countouts and disqualifications are not pinfalls.

you cant take the electron's intercontinental belt on a disqualification.

high|hgih said:

I know all the basics like how gravity works and stuff, but is there up/down/left/right? That sort of thing? I'd imagine there is, but it would take some crazy math to calculate a trip somewhere lightyears away taking gravity, axis, location, asteroids, all of that into consideration.

Click to expand...

I find it amusing how little we actually know about any g'damn thing, and yet, the collective "we" talk so much shit about how "bad ass" we are as a species.

Naked apes is all we are, and I would argue we are actually DUMBER than the apes we consider so "savage" and "dumb". EVERY other species on the planet works WITH their environment to survive, except "us". We do just the opposite, and try to create our OWN environment, and then bitch when we fuck it all up. Not so smart IMO.

We don't know shit, and will probably be long dead before we can ever figure out the workings of the universe our particular rock happens to be flying through.

I don't think there are extra dimension involved, until we get to Dark Matter. And as a circle, a tiny one one, there is one exception proposed.

There is no evidence that this mass is any more or less real than a photon itself. Uncertainty. But, when mass is stated in eV that is mass of velocity. Electron Volts. We are looking for the Higgs bosun, for example, in a very high energy range, measured in eV. The energy of impact of mass into mass at relativistic velocity. Atom smashing. It's charged particle. Controlled by magnets, yes?

A photon has no charge. IAC, smashing massless particles makes no real sense. We can't capture most of them, at all. Most are barely known to exist.

But, it is possible to calculate what the eV of a photon is at a limit. We can math out the max possible from the impact velocity. There's your answer. A photon is not affected by gravity. That is the current Understanding.

Dark Matter can be Modeled to be photons that in a tight orbit in a dimension next to the volumetric.
It's not going anywhere, trapped in a light speed orbit, incredibly small, but stable and left over from the Big Bang and the galaxy formation. Not quite condensed, not quite Light.

But, not going anywhere and so constitutes a gravity source from it's light speed circular mometum. So, full circle, indeed.

Doer said:

I don't think there are extra dimension involved, until we get to Dark Matter. And as a circle, a tiny one one, there is one exception proposed.

There is no evidence that this mass is any more or less real than a photon itself. Uncertainty. But, when mass is stated in eV that is mass of velocity. Electron Volts. We are looking for the Higgs bosun, for example, in a very high energy range, measured in eV. The energy of impact of mass into mass at relativistic velocity. Atom smashing. It's charged particle. Controlled by magnets, yes?

A photon has no charge. IAC, smashing massless particles makes no real sense. We can't capture most of them, at all. Most are barely known to exist.

But, it is possible to calculate what the eV of a photon is at a limit. We can math out the max possible from the impact velocity. There's your answer. A photon is not affected by gravity. That is the current Understanding.

Dark Matter can be Modeled to be photons that in a tight orbit in a dimension next to the volumetric.
It's not going anywhere, trapped in a light speed orbit, incredibly small, but stable and left over from the Big Bang and the galaxy formation. Not quite condensed, not quite Light.

But, not going anywhere and so constitutes a gravity source. So, full circle.

Click to expand...

ohh i see where youre coming from, and from your perspective a massles "particle" that does shit, can be observed, is effected by gravity, mass, solid objects and other shit might seem sensible. but from hwere i sit, if it walks like a duck, quacks like a duck, it probably also lives in oregon and votes democrat.

Dr Kynes said:

and though you insist that photons have no mass they still react to gravity as if they did, and every place i looked the mass of a photon was described as ZERO in capital letters followed by this: <1×10[SUP]&#8722;18[/SUP] eV/c[SUP]2

which looks like a Non-Zero sum to me. small is not zero. and small shit still responds to gravity.

meanwhile electrons are described as having a mass of :0.510998928(11) MeV/c[SUP]2[/SUP][/SUP][SUP] which would also be a Non-Zero number. a larger one to be sure, but mass is mass, even if it is small, and to my reckoning mass is subject to gravity's pull.

where pray tell am i wrong.
[/SUP]

Click to expand...

the rest mass of a photon is zero. A moving photon has momentum. Since the photon is always moving, the experiments designed to demonstrate a rest mass will have limits. Currently those upper limits are in the order of 1×10[SUP]&#8722;18[/SUP] eV/c[SUP]2 [/SUP]I hope you can realize how small this is. Even if this was a real mass, what we observe, the amount that light bends does not follow a mass-mass attraction of F(G)=GM1M2/r2 but does exactly follow the geodesic predicted by Einstein's stress-energy tensor equations. How do you explain this except for describing light as following the path of the geodesic?

Now the interesting thin is there are some good arguments against the Einsteinian view of spacetime curvature but you haven't presented any. Most of them have to do with the speed of propagation of gravity. I am certainly open to hearing good arguments that challenge the prevailing view but your whining and crying about Kip Thorne and accusations of thoughtless cheerleading for current theory certainly doesn't help your position.

I plainly said, only in that special case of that Model dreamed up to support Dark Matter. You are attempting to right-fight again.

So, ask yourself, Dr. K. Do all ducks quack or just the stupid ones?

I don't really care.

Dr Kynes said:

religion and dogma require and demand acceptance.

Click to expand...

They have to because their theories cannot stand on their own merit. Other credible theories, like evolution, can.

Dr Kynes said:

real science does not require consensus, the belief of the masses, or acceptance by any particular person. i can feel free to disbelieve any of a number of theories with no effect on reality whatsoever.

Click to expand...

That is absolutely untrue. Disregard germ theory and modern medicine and watch how quickly you die. Disregard relativity and watch your gps system no longer work. These theories are accepted for good reason. Not because anyone demands or forces it.

Dr Kynes said:

what you are describing is theocracy with heavier textbooks, not science, fact, reality or truth.

to this day nobody can tell you what your appendix actually does. it remains a mystery. yet you still have one. that to me is pretty sure proof that "intelligent design" is bullshit since nobody installs parts that dont do shit except kill the user.

if the jeesans insist on claiming their god created us in his image, all i can say is he has a fucked up design team, and somebody is making a packet supplying non-functional appendixes to his assembly line. maybe we should ask the christians for an investigation into this scandal...

if one wishes to believe the earth is flat, and bordered on the rim by a massive wall of ice (to keep the oceans in) thats cool, you could believe the fuck out of that. that doesnt mean its not crazy. some people even vote democrat.

some people want to believe that kwanza is a traditional african holiday. that also does not bother me. it's stupid, since i remember when kwanza was invented right here in america, but thats fine. people can be as wacky as they want. fuck i worship a god that has never been nailed to a tree and doesnt demand sacrifices or tell me who to hate. and THAT'S wacky.

meanwhile in the dark ages, the geocentric model was rigorously tested using the finest biblical research available, conducted by the most eminent theologians in italy, and they were so persuasive that Galileo recanted cuz his earth revolving around the sun theory was obviously flawed. they totally proved him wrong, and THATS good science!

ohh wait no it's not.

science is not proving the other guy wrong, or demanding that you be proved wrong or the other guy should STFU, science s the search for truth and fact. the truth may be odd, may be counter to currently held beliefs or it could be that the truth was hidden in a nugget of folklore from 700 years ago that everybody else dismissed as magical thinking from the peasantry.

case in point: within the pages of Prior John's "Secrets of the Common Weal" (a book banned by papal edict specifically) in among the love potions, curse, hexes and other pagan beliefs of the peasantry in the 900ad-ish timeframe was the claim that a silver coin in a pail of milk kept the milk from spoiling for several days.

well it turns out it's true. totally 100% true as a motherfucker

sometimes even hedge witches stumble upon science, even if they dont feel the need to prove anybody else wrong.

Click to expand...

How does not knowing the function of the appendix change the facts and evidence of any of the accepted theories brought up this far?

Biblical research. Stop being disingenuous you festering anal wart. If you don't understand the fundamental difference between real evidence and the garbage you are spewing then you are too stupid to converse with.

Dr Kynes said:

and though you insist that photons have no mass they still react to gravity as if they did, and every place i looked the mass of a photon was described as ZERO in capital letters followed by this: <1×10[SUP]&#8722;18[/SUP] eV/c[SUP]2

which looks like a Non-Zero sum to me. small is not zero. and small shit still responds to gravity.

meanwhile electrons are described as having a mass of :0.510998928(11) MeV/c[SUP]2[/SUP][/SUP][SUP] which would also be a Non-Zero number. a larger one to be sure, but mass is mass, even if it is small, and to my reckoning mass is subject to gravity's pull.

where pray tell am i wrong.
[/SUP]

Click to expand...

You seem to not know shit.

http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html

[h=1]What is the mass of a photon?[/h] This question falls into two parts:
[h=2]Does the photon have mass? After all, it has energy and energy is equivalent to mass.[/h] Photons are traditionally said to be massless. This is a figure of speech that physicists use to describe something about how a photon's particle-like properties are described by the language of special relativity.
The logic can be constructed in many ways, and the following is one such. Take an isolated system (called a "particle") and accelerate it to some velocity v (a vector). Newton defined the "momentum" p of this particle (also a vector), such that p behaves in a simple way when the particle is accelerated, or when it's involved in a collision. For this simple behaviour to hold, it turns out that p must be proportional to v. The proportionality constant is called the particle's "mass" m, so that p = mv.
In special relativity, it turns out that we are still able to define a particle's momentum p such that it behaves in well-defined ways that are an extension of the newtonian case. Although p and v still point in the same direction, it turns out that they are no longer proportional; the best we can do is relate them via the particle's "relativistic mass" m[SUB]rel[/SUB]. Thus
p = m[SUB]rel[/SUB]v . When the particle is at rest, its relativistic mass has a minimum value called the "rest mass" m[SUB]rest[/SUB]. The rest mass is always the same for the same type of particle. For example, all protons, electrons, and neutrons have the same rest mass; it's something that can be looked up in a table. As the particle is accelerated to ever higher speeds, its relativistic mass increases without limit.
It also turns out that in special relativity, we are able to define the concept of "energy" E, such that E has simple and well-defined properties just like those it has in newtonian mechanics. When a particle has been accelerated so that it has some momentum p (the length of the vector p) and relativistic mass m[SUB]rel[/SUB], then its energy E turns out to be given by
E = m[SUB]rel[/SUB]c[SUP]2[/SUP] , and also E[SUP]2[/SUP] = p[SUP]2[/SUP]c[SUP]2[/SUP] + m[SUP]2[/SUP][SUB]rest[/SUB]c[SUP]4[/SUP] . (1) There are two interesting cases of this last equation:

1. If the particle is at rest, then p = 0, and E = m[SUB]rest[/SUB]c[SUP]2[/SUP].
2. 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.
[h=2]Is there any experimental evidence that the photon has zero rest mass?[/h] Alternative theories of the photon include a term that behaves like a mass, and this gives rise to the very advanced idea of a "massive photon". If the rest mass of the photon were non-zero, the theory of quantum electrodynamics would be "in trouble" primarily through loss of gauge invariance, which would make it non-renormalisable; also, charge conservation would no longer be absolutely guaranteed, as it is if photons have zero rest mass. But regardless of what any theory might predict, it is still necessary to check this prediction by doing an experiment.
It is almost certainly impossible to do any experiment that would establish the photon rest mass to be exactly zero. The best we can hope to do is place limits on it. A non-zero rest mass would introduce a small damping factor in the inverse square Coulomb law of electrostatic forces. That means the electrostatic force would be weaker over very large distances.
Likewise, the behavior of static magnetic fields would be modified. 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[SUP]&#8722;16[/SUP] 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[SUP]&#8722;17[/SUP] eV. Studies of galactic magnetic fields suggest a much better limit of less than 3 × 10[SUP]&#8722;27[/SUP] eV, but there is some doubt about the validity of this method.

guy incognito said:

When the particle is at rest, its relativistic mass has a minimum value called the "rest mass" m[SUB]rest[/SUB]. The rest mass is always the same for the same type of particle.

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At rest compared to what?

At rest in the reference frame, of course. We can capture an electron magnetically and hold it at rest in the frame. It is still subject to Momentum Conservation of the Universal Inertia frame, as it is also in orbit with the reference frame.

It is called the rest mass? Called? You see?

Seedling said:

At rest compared to what?

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You must be trolling.