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Offline yor_on

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Does gravitational field increase energy of a photon?
« Reply #25 on: 19/07/2011 21:36:25 »
A 'time dilation' is a effect between 'frames of reference'. Your 'frame of reference' is purely conceptual as you observe a rocket speeding away. By that I mean that if you were to take a snap shot of the universe, metaphysically speaking, you would find all 'points' to differ, each one its own 'frame of reference', with its own unique definition of a 'now', relative the 'point' from where you look at that universe.

That means that when we define for example Earth as 'one common inertial frame of reference' relative us living here, we in reality just ignore the 'time dilations' etc as they are too small to be observed by human senses. But they can be, and in fact have been, observed using atomic clocks. So this is a known fact.

Your own 'arrow of time' will always be unchanging though, just as 'c' always will be measured to the exact same standard, no matter from where you measure it, a rocket or Earth. So there is no 'second becoming longer' for you, neither do 'photons' intrinsically change any 'energy' or 'speed' relative gravity.

What you see is a relation between frames of reference, resting upon the relation between the observer and what he observes. If you were to give an 'photon' its own 'frame of reference', quite impossible to do in our reality, except imaginatively as it only can represent one 'tick', of the best clock we have (radiation). But if you were, you would find that photon intrinsically the same at all 'times'. What differs is your observation of it, relative your 'motion' and 'gravity' observed, inside our macroscopic arrow of time, whether the photon is climbing from a planet, or 'falling into' a gravity well.

You can define it as every point in this universe is dynamically changing 'frames of reference' depending on gravity, energy and mass in its objects (planets, etc) motion, relative all other 'points'. With your own 'frame', from where you observe, being the one that always will give you the constant, invariant, definition of 'c', as well as of 'your invariant arrow of time'. And that is true no matter from where, rocket or earth, you will measure it locally . As soon as you start to compare different frames of reference though, you will find 'time dilations' and 'Lorentz contractions'. Although a definite 'time dilation' can be defined, as in the Twin experiment, from where both start from a 'same origin' later to rejoin at that same origin, after one has traveled and so pushed his 'local parameters' relative the universe. You will find that neither of those, at any time, found themselves living any 'slower' or 'faster', as defined from inside their own 'frame of reference'.

The only 'place' where you can define a time dilation, is in the comparison between 'frames of reference', as that rocket relative the twin staying at home. But as you also will find your own 'time', as  well as radiation, to be unchanging locally when measured you can't speak of 'time' being different at 'location x' from 'location y'. Would you to 'instantly teleport' to any of those locations you would find the arrow of time to be the same as always, so also 'c'.

All time dilations are, mostly unmeasurable, except conceptually comparing between 'frames of reference'. And even though your own (intrinsic sort of) measure of life won't change just because you ride a rocket, your relation to all other frames of reference will, creating what we call the Twin paradox.
« Last Edit: 20/07/2011 01:10:18 by yor_on »
 

Offline yor_on

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Does gravitational field increase energy of a photon?
« Reply #26 on: 20/07/2011 03:54:12 »
The biggest mistake I think people do when trying to understand time dilations is to assume that there must be some common 'standard' to it . There is no such thing, the only 'standard' your universe gives you is your own local definition of 'c' and your local 'arrow of time' measuring out your unvarying lifespan. You can extrapolate that standard to include everyone in the universe of course, seeing that we all find 'time' unvarying from our local frame of reference, as well as 'c' always will give us the same definition, if measured directly and locally.

And if you do I agree :) We live as entities in a sea of unvarying radiation. most of us moving 'uniformly' in space. That radiation is a 'clock' of a sorts, it always ticks the same locally. But motion distort the 'room time' it 'ticks' in. And the only way we have defining motion is 'expending energy', aka accelerations. Without knowing who accelerated relative whom, defining a 'time dilation' becomes meaningless.

Any possible time dilation you ever will be able to define must have a common origin, a same 'frame of reference' from where you can set the 'clocks' to being 'approximately' the same. Without a common origin, there is no way to prove who becomes 'time dilated' relative whom.

Imagine a situation where we have two frames both moving uniformly with you looking at both from Earth. Deciding to define Earth as your 'inertial frame', at 'zero' speed, you now are able to give both of those object a unique 'speed' relative your 'newfangled definition' of 'zero'. So you state that 'A' is moving with double the 'speed' of 'B', according to your observation relative earths 'zero', and so must be aging 'slower' than 'B'. And you are right, relative your definition of Earths speed being 'zero'.

Now be 'B' looking at 'A' . From the point of 'B' moving uniformly you are free to define 'B' as being 'still' too. You then define 'A' as the only one moving, therefore having an even slower clock than the one you found before, using Earth as your 'pivot of change' (only as an example, okay:)

Now be 'A', looking at 'B' moving uniformly. You make the same assumption again and find that it must be 'B' that is the one moving, therefore now having the slowest clock. And all of those definitions are correct.

Why are they correct? Because you do not have a same origin. Without a origin and a clock to set all further 'time dilations' against, any definition you make will be arbitrarily. And if measured looking at the others clock, you will find all clocks to go slower than 'yours', no matter from where you chose to stand looking.

It doesn't mean that the 'arrow of time' is a illusion though. As I see it, it's because of it not being an illusion, instead having a 'clock' of a unvarying 'c' locally that those effects can exist. Think of the radiation between 'frames of reference' as something 'invariantly ticking', the 'room time geometry' contracting or magnifying in your relative motion, versus all other 'frames of reference'.

Also remember that any 'uniform motion' only can exist as a definition (comparison) between 'frames of reference' in Einsteins universe. And he's right there. You need at least two objects, then a space (distance), and a 'clock' ('c') measuring even durations, to find a motion. Your universe gives you one clock 'c', but, with it a indefinite amount of objects, all of them in 'different' uniform motions, as defined from your point of view.

Looking at it from that perspective you will find everything 'time dilated' but, only measurable, when you can define some common origin from where you set your clocks. And there is no way around this, you need a same origin, and you also need to meet up with the twin, to define that 'time dilation'. And, Nota Bene, you now also will have to introduce a acceleration to get that 'time dilation', and with that acceleration you also will introduce 'gravity' in the accelerating frame, and so a locally observable change defining whom the time dilation 'belongs to'.

Although 'time dilations' is a reality, your invariant clock as I define 'c' as, also will be a reality locally. And that fact will give you a same life measure inside your 'frame of reference' no matter where you are, or how fast you go. And that one is extrapolate-able to all other frames too, conceptually.
==

Room time geometry is just the way the room (time) will distort relative the observer. You look at someone traveling finding him 'slower', that I call the travelers 'room time geometry', as defined from you. Defined from him it will be what he observes outside his own 'frame of reference' that is distorting instead. And that's also why I define it as being a 'relation', just as a uniform motion must be.
« Last Edit: 20/07/2011 04:52:52 by yor_on »
 

Offline MikeS

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Does gravitational field increase energy of a photon?
« Reply #27 on: 20/07/2011 14:07:47 »
yor_on

I guess that's why it's called relativity, it's all relative.
For once we pretty much agree on something.

Time dilation is not something we come across in our everyday lives, so some people tend to trivialise it.  I think this is a mistake.  Gravitational time dilation is a major factor in the universe.  When two masses combine time dilates for both of them more than it did for them individually.  As all mass is attracted together, ultimately the universe should grow more clumpier and with time dilating.  A way I like to think of this is all matter is heading toward the black hole at the end of the universe where time would cease to exist.  Time dilation and gravity is the major source of entropy in the universe and entropy is also the arrow of time.
 

Offline yor_on

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Does gravitational field increase energy of a photon?
« Reply #28 on: 20/07/2011 19:39:58 »
Ending up in one big lump, huh?

And where would that 'time dilation' be then?
heh :)
 

Offline JP

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Does gravitational field increase energy of a photon?
« Reply #29 on: 20/07/2011 19:55:12 »

the answer?

http://iopscience.iop.org/1063-7869/42/10/A04

http://www.itep.ru/theor/persons/lab180/okun/em_13.pdf

Interesting articles.  But they only address half of the original question:
Quote
Gravitational field increases frequency of a photon.
What the articles are saying is that to get accurate predictions of the frequency change due to gravity, you need to use GR, not Newtonian gravity.

The second part of the question is:
Quote
Does it increase energy of the photon?   
Yes, it would increase between a camera on an orbiting satellite and a detector stationary on the earth's surface, but...




To really be precise you'd need to specify who's measuring photons and how they're moving.  Energy is proportional to frequency of light, which is increased as a photon travels towards a source of gravity.  But motion of an observer can also effect frequency.  Going back to the above case, if your satellite in orbit were to start moving rapidly towards the source of the light, it could measure a higher energy photon than the detector on the earth's surface.
« Last Edit: 20/07/2011 20:06:19 by JP »
 

Offline MikeS

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Does gravitational field increase energy of a photon?
« Reply #30 on: 21/07/2011 06:32:43 »
Ending up in one big lump, huh?

And where would that 'time dilation' be then?
heh :)

Well, a little lump actually, the singularity in the last black hole.

"And where would time be then?", uh ultimately dilated?
 

Offline MikeS

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Does gravitational field increase energy of a photon?
« Reply #31 on: 21/07/2011 06:40:38 »
JP

The original question was
Does gravitational field increase energy of a photon?

The answer the paper gave was NO.
 

Offline Geezer

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Does gravitational field increase energy of a photon?
« Reply #32 on: 21/07/2011 07:18:52 »
Seems to me there is something a bit dodgy going on here.

We know (at least I think we do) that photons are affected by the presence of mass (gravitational lensing etc.) so, it would seem that some energy has to be transferred while altering the trajectory of a photon.
 

Offline MikeS

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Does gravitational field increase energy of a photon?
« Reply #33 on: 21/07/2011 10:48:29 »
Seems to me there is something a bit dodgy going on here.

We know (at least I think we do) that photons are affected by the presence of mass (gravitational lensing etc.) so, it would seem that some energy has to be transferred while altering the trajectory of a photon.

Not so.
Photons are not directly affected by mass but space time is.
Gravity bends or warps space.  Photons travels a straight line in curved space.  Gravity bends space but does not alter the path of the photon.  Gravitational lensing is an example of that.  The trajectory of the photon is not altered so there is no transfer of energy.
The photon does not interact in any way.
« Last Edit: 21/07/2011 10:52:04 by MikeS »
 

Offline yor_on

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Does gravitational field increase energy of a photon?
« Reply #34 on: 21/07/2011 13:09:36 »
Mike, couldn't help it, a little joke. If we assume something not perfectly spherical at that 'lump' you still will have time dilations, as I see it. And the arrow should be there, as SpaceTime still would contain a 'size', matter still existent in it. As for photons changing energy on their own? I don't think it happens, except in a 'expansion'. That a gravitational field 'interact' with a photon is correct but as I understand it, the blue shift will still be a relation between the photon and its sink. If it wasn't that way we could forget about 'light quanta' and? But still, we also have those 'virtual ones' that can act as weird as they please, it seems?

As I think of it the 'extra energy' is of a similar kind to what we see in a collision where, depending on relative motion, more or less kinetic energy will be expended. On the other tentacle, lately inertia has confused me, and it keeps on doing it, da*n it :)
 

Offline JP

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Does gravitational field increase energy of a photon?
« Reply #35 on: 21/07/2011 13:27:09 »
JP

The original question was
Does gravitational field increase energy of a photon?

The answer the paper gave was NO.

Before we go into exactly what the paper is and isn't saying, can you answer a simple question for me. 

I have a lab at the earth's surface and one in orbit.  They both catch photons from a high-powered laser far away from the earth so that all photons are emitted with the same frequency.  Do the two labs measure (a) the same frequency or (b) different frequencies for the photons?
 

Offline MikeS

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Does gravitational field increase energy of a photon?
« Reply #36 on: 21/07/2011 15:20:28 »
JP

The original question was
Does gravitational field increase energy of a photon?

The answer the paper gave was NO.

Before we go into exactly what the paper is and isn't saying, can you answer a simple question for me. 

I have a lab at the earth's surface and one in orbit.  They both catch photons from a high-powered laser far away from the earth so that all photons are emitted with the same frequency.  Do the two labs measure (a) the same frequency or (b) different frequencies for the photons?

b)  The lab on earth registers the photons as being more blue shifted as it is deeper within the gravity well where time is more dilated.
 

Offline JP

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Does gravitational field increase energy of a photon?
« Reply #37 on: 21/07/2011 15:22:12 »
Frequency is proportional to energy in their local frame, so they measure different energies in their frames.  If they had a process that required a certain energy, they might be able to do it on earth but not in orbit because of this.

Of course time dilation happens.  So what?  They still measure different energies.
 

Offline yor_on

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Does gravitational field increase energy of a photon?
« Reply #38 on: 21/07/2011 15:32:45 »
JP, allow me to be somewhat cheeky and sort of jump in here.

It is a weird thing JP, gravity do blueshift a infalling photon, same as it will raise the kinetic energy of a particle of rest mass. And you're perfectly correct in your example. As for why it happens? A photons 'acceleration' is a blue-shift, its 'deceleration' a red-shift. But it can't be the 'photon' itself that change energy, not as I understands it, But for how it happens?

I've seen it explained with 'clocks', where we can set a clock for, say, each kilometer it falls, then we translate the different readings of those clocks, that will differ with distance from the surface (gravity), into a 'energy' of that said photon. But that seems to me to be a circular proof. I like Einsteins definition better in where he discuss 'conservation of energy' and uses much the same argument that I started with. The equivalence to a 'rest mass' falling into a gravity well. It was you that gave me the sweet symmetry in a photons recoil JP :) and if that one holds, so must this.

Symmetries is amongst the most intriguing aspects of life, the universe and all, that I know of. Symmetries and symmetry breaks.

Is that the way you think of it too?
Or do you define it otherwise?
 

Offline MikeS

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Does gravitational field increase energy of a photon?
« Reply #39 on: 21/07/2011 15:33:30 »
Mike, couldn't help it, a little joke. If we assume something not perfectly spherical at that 'lump' you still will have time dilations, as I see it. And the arrow should be there, as SpaceTime still would contain a 'size', matter still existent in it. As for photons changing energy on their own? I don't think it happens, except in a 'expansion'. That a gravitational field 'interact' with a photon is correct but as I understand it, the blue shift will still be a relation between the photon and its sink. If it wasn't that way we could forget about 'light quanta' and? But still, we also have those 'virtual ones' that can act as weird as they please, it seems?

As I think of it the 'extra energy' is of a similar kind to what we see in a collision where, depending on relative motion, more or less kinetic energy will be expended. On the other tentacle, lately inertia has confused me, and it keeps on doing it, da*n it :)

I don't understand that.  To the best of my knowledge a photon once created can not change its energy level or be directly affected by gravity in any way.

That's true in as much as for the photons to be blue shifted they must be entering a gravity well but it is time that has been affected not the photons.
 

Offline yor_on

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Does gravitational field increase energy of a photon?
« Reply #40 on: 21/07/2011 15:45:37 »
In a gravitational field all 'clocks' hung up in the sky will give a observer on the surface (earth) different readings, and you're perfectly correct in that you can translate those readings to a 'frequency'. Although we're discussing a photon here, and that one should only have a energy, not a frequency. But I still like 'conservation of energy' better Mike, where the equivalence, as I understands it, becomes one similar to what you see when it's matter dropping in from the sky.

It's the 'game rules', sort of :)
==

But it is weird though. Because it's still, again as I see it, a effect between the observer and what he observes.
« Last Edit: 21/07/2011 15:47:31 by yor_on »
 

Offline MikeS

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Does gravitational field increase energy of a photon?
« Reply #41 on: 21/07/2011 15:47:45 »
Frequency is proportional to energy in their local frame, so they measure different energies in their frames.  If they had a process that required a certain energy, they might be able to do it on earth but not in orbit because of this.

Of course time dilation happens.  So what?  They still measure different energies.

It can be shown that when you run certain experiments under redshift energy change or redshift time dilation they yield different results.  Therefore they are not equivalent and only one can be right.  It makes no sense to me at all that a photon, a massless particle can change its energy level or momentum.

Yes, I agree they do.  If you look at the situation from the viewpoint of time dilation it's all relative, surely that's the point.  If we imagine the reference frame of the photon it never gravitationally interacts with anything, its energy level remains the same.
« Last Edit: 21/07/2011 15:51:53 by MikeS »
 

Offline imatfaal

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Does gravitational field increase energy of a photon?
« Reply #42 on: 21/07/2011 15:48:05 »
Mike - you are flogging a dead horse, please stop as you are way out of your depth.  Einsteinien relativity is amazingly powerful but it is not simple - your concentration on a small aspect of GR is blinkering you
 

Offline yor_on

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Does gravitational field increase energy of a photon?
« Reply #43 on: 21/07/2011 15:58:55 »
And yeah, a expansion only make sense when you think of it as 'waves'. But the duality we see seems to be a result of the surroundings also, meaning that the 'photon' somehow 'know' when to be a wave or 'photon'. And if one look at it that way then the 'expansion' must be a 'place' where the 'wave attribute' takes precedence. And that also makes it a little easier to see why so many physicists change their definitions midstream, from a wave to a particle to a wave again. Although I have this feeling that if it is this way, then the 'duality' must be 'more' than what we define it as, as something just 'propagating' I mean.
 

Offline MikeS

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Does gravitational field increase energy of a photon?
« Reply #44 on: 21/07/2011 16:10:51 »
Mike - you are flogging a dead horse, please stop as you are way out of your depth.  Einsteinien relativity is amazingly powerful but it is not simple - your concentration on a small aspect of GR is blinkering you

Never the less nobody has yet shown me that I have been wrong when interpreting the aspects of GR that I have concentrated on, quite the contrary in fact.  In all of the debates that I have taken part in I have yet to be proven wrong.  I have answered all questions put to me, successfully I think.  I find these debates help to clarify ones thoughts but they have yet to make me change my mind on any of the fundamental principles that I believe in but they have helped me to refine them.

I find your attitude amazingly condescending.
 

Offline JP

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Does gravitational field increase energy of a photon?
« Reply #45 on: 21/07/2011 16:28:24 »
We've proven you wrong plenty of times, Mike, as is evident to those who have physics training.  The problem is that you apparently don't understand a lot of the physics involved, and that your own view of these debates boils down too some variation of:

 It makes no sense to me at all that a photon, a massless particle can change its energy level or momentum.

You have major gaps in your understanding of basic physics and of general relativity, so of course our physics-based explanations don't make sense to you!  But rather than try to learn from these mistakes, you just take your own lack of understanding to mean that you're wrong. 

This isn't condescension on my part, but rather annoyance that you are misleading other posters on the forum by mis-representing physics and frustration that you are happy to state your incorrect opinion of how physics should work, but show no inclination to learn enough physics to have a debate on actual physical grounds
« Last Edit: 21/07/2011 16:30:58 by JP »
 

Offline yor_on

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Offline MikeS

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Does gravitational field increase energy of a photon?
« Reply #47 on: 22/07/2011 07:56:53 »

Einstein's 1911 paper, 'On the Influence of Gravitation on the Propagation of Light' might shed some light on how he thought of it.

I think this particular paper muddies the issue somewhat because he is primarily interested in experiments being carried out to verify that gravity bends light.  What he does not say in this paper is that space is curved.  By omitting to say that does not imply space is not curved, he was simply talking about something else.

"Light travels along the shortest path between two points in spacetime (a geodesic). If the geodesic is curved, then the path of light is curved. Einstein proposed in his General Relativity theory that what is called gravity is really the result of curved spacetime."
http://www.astronomynotes.com/relativity/s3.htm

"Einstein introduced the idea of four-dimensional space, a universe that is not fixed and is constantly changing. If Fermat's Principle is used with this in mind, light then travels instead in a geodesic, which is a straight line but on a curved surface."
Read more: Does Light Travel in a Straight Line? | eHow.com http://www.ehow.com/how-does_4569984_does-light-travel-straight-line.html#ixzz1SoVwnnjw

"Light travels in straight lines. However, 'straight' ain't what it used to be. Our current understanding of the universe suggests that mass causes a localized distortion in space time, effectively curving space around itself. As a beam of light approaches a massive object, it can be affected in this way as it passes through the curved space. From outsie, it appears to travel in a curved path, but as far as the light is concerned, it's moving in a straight line -- it's just that the straight line exists in a curved reality, if you follow me."
Read more: http://wiki.answers.com/Q/Dose_light_travel_in_stright_or_curved_lines#ixzz1SoWNyXU7
 

Offline PhysBang

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Does gravitational field increase energy of a photon?
« Reply #48 on: 22/07/2011 14:15:50 »
Never the less nobody has yet shown me that I have been wrong when interpreting the aspects of GR that I have concentrated on, quite the contrary in fact.
This is because you are almost entirely ignorant of General Relativity. You keep writing the phrase, "the reference frame of the photon," a phrase which is entirely without meaning in physics. Nobody can use such a reference frame in a consistent manner. Given that you don't understand the theory, when people say things that make sense, you do not understand that they have provided a refutation of your claims.
 

Offline PhysBang

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Does gravitational field increase energy of a photon?
« Reply #49 on: 22/07/2011 14:18:46 »
I think this particular paper muddies the issue somewhat because he is primarily interested in experiments being carried out to verify that gravity bends light.  What he does not say in this paper is that space is curved.  By omitting to say that does not imply space is not curved, he was simply talking about something else.
The 1911 paper was written before Einstein developed general relativity and well before physicists began using "curved spacetime" language.
 

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