I've been thinking....

[acropolite]

Something to Ponder on the next rainy night :rain:....

One night when laying awake and pondering the answer to life the universe and everything (which of course we know is 42), I started thinking about the theory that gravity is directly related to space/time. Ok let's start with light. The theorists tell us that light is bent by gravity due to the warping of space time.

Given that, consider the following.

Light is energy. We know that because we can use light to produce electricity, cut with lasers and feel heat from infra red.
If light is energy, according to Einstein's :einstein: own theory (e=mc squared), light particles MUST have some mass otherwise they would have no energy.
Gravity is a force which acts on mass, therefore light will bend in a gravitational field simply because of it's mass and can't escape from a black hole, once again simply because it has mass.
Time is a measured interval between events and we don't have any mechanism to measure it other than by something which has mass (light or atomic) ( albiet very small mass) and which moves and is therefore affected by gravity, or the lack of, so any attempt to measure time is doomed to failure because the very mechanism we are using is not constant. So time may not vary in a gravitational field, merely our perception through measurement.
If all the above are correct then light is not bent by space/time effects merely by gravity and gravity need not be related to space time.
All of the above are irrelevant if you accept current theory that light has no mass (which itself contravenes other theories), but if light has no mass why doesn't it contravene Einsteins own theory.

Here's a bit of debate on whether a photon has mass to add to the confusion. http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html and a google search of "mass of light particles" will bring up heaps of material.

What are your thoughts....:whistle:

[[1ponders]]

Interesting Phil.

Here's something to think about from a couple of your statements. Assuming:
1. Light is energy. Therefore 2. That energy released from a disrupted particle/piece of mass in the value of mc sq. ie. the energy we are seeing/measuring is the result of the disrupted mass, not the mass itself. If energy has mass then the equation would mean that mass is converted into another type of mass???

3. Is gravity bending light or is light following the geodesic deformity created in space time by mass produced gravitational fields. Ie the path of least resistance/lower energy cost of its apparently straight line flight. Also isn't light redshifted when it moves through this field implying it costs it energy to escape from it. If e=mc sq then the if the photon had mass to start with it would have less mass after leaving the field as it cost it energy to do so. If it had less mass then it would be less effected by subsequent gravitational field as the force applied to this photon mass by another would less (by the formula F = G m1 m2 / r2) This observationally doesn't apply. Light reacts consistantly with one gravitational field after another. Hence there is no mass loss. But there is energy loss, more red shifting. Therefore light has energy but no mass.

I'll get back to you on the rest.

[acropolite]

Taken from the FAQ in the original link...

[acropolite]

Ponders wrote Don't you mean less energy. If you could fire a marble into space would it have less mass when it got there due to gravity, no, but it would have less energy. Light with less energy = redshift.

[slice of heaven]

What is the actual question???
1. thats correct
2.Incorrect/sort of Photons have no mass as that has to be determined at a state of rest and since they are always in motion and never at rest(they can be stored but not stopped) they basically have none.
3. because of 2. gravity has no effect
4. Time is relative only to the immediate situation
5. see 1 - 4

[slice of heaven]

The best guesstimation of a photons upper limit of mass was calculated at 0.00000000000000000000039 times the mass of an electron,
Pretty close to zero I'd say.

[acropolite]

If that's so then it's (light) got mass and space time may have absolutely nothing to do with gravitational bending...

[slice of heaven]

Thats the assumed upper limit ,that doesnt mean its not zero.

[[1ponders]]

If e=mc2 then aren't they interchangeable, energy is mass and mass is energy, if energy is lost wouldn't mass be lost as well ie m=e/c2, so if energy is lost, this would represent an equivalent loss of mass equal to the amount of energy lost divided by c2. There is no observed deviation of gravitaional effects on light after light experiences a gravity field so there is no loss of mass. IE If a photon had mass then by lossing energy in a gravity field it would also loose mass. If it lost mass then it would be effected differently by subsequent gravity fields by F = G m1 m2 / r2. There is no observed difference so there is no mass.

The marble wouldn't loose any mass as the energy it lost in its ejection into space is the energy applied to it to get it there in the first place. If we were able to get the marble to self propell itself into space then yes it would loose mass.

Another thing to think about it that experimentally it has been shown that as objects increase in velocity they increase in mass. The closer to light speed the larger the mass increase. So at light speed an object would have infinite mass. And would require infinite energy to get it there. It could be simplistically argued that the energy is being converted into mass. Then why doesn't a photon have infinite mass. It is travelling at lightspeed. :shrug:

[[1ponders]]

For 4. above. It has been argued that there are a number of differnt "types" of time. There is the percieved time you mentioned at the top, and there is for want of a better word "intrinsic" time. There is a belief among some physicist that not only are there gravitons or gravitational waves (as per photons and light waves) but also intrinsic units of time and temporal waves (AKA star trek). That the 4th dimension of time is both particulate (as in photons and gravitons (which are yet to be proved :) ) and "experiential", simialar to our familiar 3 dimensions. If this is the case then as gravity may well have an effect on time, based on similar principles to the effect it has on photons.

[acropolite]

Approach the subject from a logical viewpoint. Paul suggests that if light had mass and was influenced by a gravitational field then it would lose mass i.e. becomes lighter, but, as he states later in the post the marble shot into space would not lose mass... but neither would the photon. Photons of light can't be propelling themselves otherwise they would be accelerating (or they've got cruise control) and therefore must have been ejected from whence they came (we might have to call this the marble theory), therefore they would not lose any mass (if they had any to start with). Focus on the key aspect does light have mass. If light has any mass (EVEN INFINITESIMALLY SMALL MASS) then our assumptions of space and time bending light are not necessarily correct.

[[1ponders]]

Ah but I was arguing that the marble wouldn't loose mass because the energy it was loosing would be the energy of impetus applied by an external force for it to achieve escape velocity. The photons energy, speed and direction are an integral part of its generation. Nothing has been applied to it to get it moving on its way.

Another way of looking at it might be to consider the effect a black hole has on a photon of light. If from you arguement Phil we accept that light has mass then would it not also have dimensions of volume. If that's is the case then close to a black hole the photons of light would be physically stretched from the effects of different field strengths of gravity at one end of the photon compared to the other, stretching to infinity as one end of the light gets closer to the black hole and the other end reaches our recording equipment (at the other end of the universe). My thoughs are that if this were the case then wouldn't the photon light frequency remain the same but the intensity would diminish, whereas what we do see is a loss of energy through the increased red shift of the light.

Hyperthetically that is :)

[slice of heaven]

Phil , if light had mass the effect of gravity would be to draw the light towards the object creating the gravity force, not around it as happens when gravity bends the space/time.
2 links below of Einstein's cross, which explain the situation, and an image of it from a 10"

http://www.astronomynotes.com/relativity/s4.htm

http://voltaire.csun.edu/roland/cross.html
Einstein's Cross with an AP 10 inch f/14.6 Maksutov-Cassegrain

The gravity of a black hole is so great that the escape velocity is faster than the speed of light, whether a photon has mass or not, the photon still cannot travel fast enough to escape.

[acropolite]

The photon's energy speed and direction are the result of it's generation just as the energy, speed and direction of the marble are the result of its launch. I haven't done any physics for 30+ years but I seem to remember that the photon is ejected as a result of electrons moving from one energy state to another within a molecule. It is incorrect to say that nothing has been applied to get the photon moving on it's way; for example in the case of lasers, energy has been applied, just as energy was applied to the marble. In a star, chemical reactions (producing energy) are causing the photons to be ejected. Pressure is exerted by photons and can be measured, and varies accordingly if the light is reflected. How can this occur if light has no mass. http://en.wikipedia.org/wiki/Radiation_pressure

[[1ponders]]

Yes Slice, once the photon reaches the event horizon. But before it reaches the point of no return the differential tidal forces at different distances from the black hole would stretch the photon if it had dimensions. ie stronger grav force 1 meter from the EH as opposed to 1.0000000000001 meters causing the photon to elongate.

I should point out that I am arguing strictly from a laymans point of view using my perception and admittedly limited understanding of quantum mechanics.

[slice of heaven]

Is the photon actually being stretched Paul???
Its the spacetime that the photon is occupying thats being affected , not the photon. Our perception of it might be that it is being stretched, but physically is that the case.

[[1ponders]]

No, my arguement was that if the photon had mass then it would also have to have dimensions (the exception being a singularity, but then does a singularity have mass ?????). If it had dimensions then it is feasible that when experiencing differing gravitational fields then it would be stretched.

[acropolite]

Slice said The effect of gravity on light is exactly the same as it's effect on a body with mass, i.e. it deflects towards the gravitational field. The concept of light bending around a gravitational field is no different to that of a satellite, asteroid or any other body slingshotting around the gravitational field of our sun for example. Just because it's attracted by gravity doesn't mean it has to make a beeline (and collide with) that object. But let me shoot the light has mass theory in the foot. If light has mass, then why does a body continually absorbing light not increase in mass, and why does the body that emits the light not decrease in mass. But it's probably easy to accept that light can have mass without decreasing the mass of the body that emits (or absorbs) it if you accept the big bang theory.

[[1ponders]]

Beat me to the punch Phil. That was going to be my Coup de Tat :D :lol:

The other one is if certain atoms absorb light energy and not the mass as per your arguement above, and raise electrons to higher orbits and then re- emit that light at a specific wavelength when the electrons "fall" back, after all the photonic light energy has been absorbed and re-emitted, what happens to the supposed mass that is left over from the photon. Does it just hang around as an energyless massicle?

Fun debate guys. Yep I'll be the first to admit I drew a long bow on a lot of my arguements :whistle: , but fun and mind exercising all the same, without getting too bogged down in the mathematics of it all. :thumbsup:

[acropolite]

I'm not comfortable with the concept that light has no mass; nor am I comfortable with the concept that it does have mass. Somehow I don't think we'll know the answer in our lifetime. Theory, after all, is something we invent to explain what we don't know. Good fun all the same.....

[[1ponders]]

It'll be interesting to see how they finally do it, if they ever do.

[netwolf]

As i understand it Light is on the E side of the equation E = MC squared. Hence it has no mass. I dont see any contradiction there. Light photons are emited, when electrons move from a higher orbit to a lower more stable orbit. The photo electric effect is the inverse process.

The thoughts i have on the matter are that

1. Gravity of star increases the refractive index of space such that light curves.
2. The Refractive index is porpertional to the distance from the mass generating it. And hence falls away sharply. And hence you have a curved path for light around the Gravity field.

I could be wrong..

[[1ponders]]

I like that idea netwolf. The refractive index of space(/time?). Proportional :confuse3: Distance squared, cubed to the fourth???

But, you could be right :)

[netwolf]

I recall one of my High School asignment that I did on Principle of Equivalence. I had just read at that time the book called "Relativity and Common Sense" By Herman Bondi. A very intresting read, and simple explanations to complex theories. But if you consider it Einstiens postualtions all came from his infamous gendaken "Thought Experiments". The train, the twins. Principle of Equivalence by comparing an Elevator and a Space craft.

Perhaps the fingerprint of the universe is within the mind, and it only requires thought to draw it out.

[[1ponders]]

Ah now we come to the thought shaping the universe we live in. Being considered quite seriously in some circles these days.

[netwolf]

Hizenberg Uncertainty principle, the observer affects the observerd. Time is also affected by our consiousness of it, hence the old saying time flies when your having fun. I think we have moved the discussions into the relms of Metaphysics.. However no Science will withstand that does not asscess the bias of the observer.

[Sausageman]

Can I take you back to Einstien's gravitational lensing?
If light is travelling in all directions, why do we see Einstien's Cross and not a halo effect around the star?
Surely the gravitational effect would affect light from every direction, not just from 4 points. Result: a halo.

Mike

[netwolf]

The Quasar may not be exactly in line with the Galaxy in line with earth. The symetry may not be perfect.

[slice of heaven]

http://spiff.rit.edu/classes/phys240/lectures/grav_lens/grav_lens.html
Explains it fairly well

[netwolf]

Ok so here you go a near perfect ring.
http://www.universetoday.com/am/publish/perfect_einstein_ring.html

And another one from Huble..
http://antwrp.gsfc.nasa.gov/apod/ap980330.html

[janoskiss]

Great thread guys. A lot of topics touched on. Just a couple of quick points:

Light does "bend" due to gravity in the flat spacetime approximation suggested by our immediate experience, but in the spacetime of General Relativity, it merely follows the curvature of spacetime itself.

A body absorbing light will increase in mass, though the increase will be small. All forms of energy have mass; e.g., (all else being equal) a hotter body weighs more than a colder one, two hydrogen atoms have more mass than a helium atom (despite being made of the same particles), a moving car has (ever so slightly) more mass than a stationary one, etc...

[netwolf]

I like that litle saying all else being equal.. never worked out what should be equal to what..

The curvurture of space is analogus to the curvurture of the earth, it can not immedietly be seen it has to be understood. Our 5 senses are limiting in what they provide, but our brain has far more ability than we can fathom..

[janoskiss]

Let me try to clarify with an example... Take a rock or some other macroscopic object. Measure its mass without disturbing it (e.g., measure its gravitational pull on something very small). Now heat the object whilst making sure it neither loses nor gains material (e.g., irradiate it with infrared or microwave light). Measure the mass again. If the measurements are precise enough, the second measurement will yield a larger mass than the first. The difference in mass will be equal to the heat energy gained by the object, as per E=mc^2.

"All else being equal" means simply that besides the temperature of the object being higher during the second measurement, nothing else is different; i.e., you have the same object and same amount of material; you didn't melt or boil the stuff (then its mass would be even more), it's the same arrangement of atoms but they're moving a bit more briskly.

Precision in language usually gets tedious and people tend to ignore me after a while most times I attempt it. So I often resort to somewhat vague expressions such as "all else being equal". ;)

[netwolf]

Here is something to think about..
If the Solar system moves around the Galaxy, would it be possible to see the past Earth?
I mean to say if we have moved significantly from our location, could wee see our old light?? even as a woble around the sun..

[RAJAH235]

Steve, there's only one thing wrong with your eg. & that is, that every time you try to MEASURE anything,(electron's position etc), you influence the outcome, simply by introducing that external source/device. :shrug: :D L.

[janoskiss]

That's why I said "macroscopic" object, L. :) ... system is large enough so that the uncertainty principle has no detectable consequence. The same energy-mass equivalence principle would still apply in the quantum world though, but that gets more tedious to explain and understand since us humans are not small enough to appreciate the weirdness quantum world directly. It all looks very deterministic from up here... :D :D

[slice of heaven]

Steve and Phil
You've both stated light can be affected by gravity other than the effect gravity has on space/time.
Can you give us proof of this ?
I'm not saying it doesn't or cant, as gravity does have an effect on massless objects.
Space and time are both massless (as long as the space is empty) and are affected by gravity.
Any examples??????

[netwolf]

Slice,

Have a look at this.. see examples at the end specificaly "Precessing Orbit of Mercury".
And also the bending of light was confirmed durin a Solar Eclipse in 1919, this was a prediction of Einstein's theory or spacetime curvurture caused by Gravity.

http://www-astronomy.mps.ohio-state.edu/~pogge/Ast162/Unit5/gr.html

[janoskiss]

Slice, One cannot really say that gravity affects spacetime, because there is no gravitational field or force in the classical Newtonian sense. In general relativity (which is the best description we have of gravitation and the large scale structure of the universe), space is no longer the canvas on which the world is painted. Instead the mass and energy content of the universe defines spacetime and determines its geometric structure. The resulting curvature of spacetime is what we experience and normally think of as a gravitational force one massive object exerts on another, but that is just a simplification useful in the reasonably flat spacetime of our immediate experience. To say space and time are massless is akin to saying something like verbs and nouns are odourless, or lengths are colourless. All true I guess but not very useful. :D Here is the Wikipedia entry on general relativity:
http://en.wikipedia.org/wiki/General_relativity... Lots more info there. :thumbsup: