Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: George Voulgaris on 01/06/2011 18:30:02
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George Voulgaris asked the Naked Scientists:
Hello from Australia and thanks for taking the question.
Do photons experience time?
And if not, how is it that light can undergo changes such as becoming redshifted as it moves through space?
Kind regards,
George Voulgaris
Melbourne, Australia
What do you think?
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This is a big point of confusion in special relativity. The theory says that if you have two observers with clocks, and one moves very fast with respect to the other, if they compare their clocks, the fast observer's clock appears to be running slow. The faster he/she goes, the slower the moving clock appears to go, tending to infinite length intervals of time per second of the stationary clock as the observer gets closer an closer to the speed of light.
This seems to indicate that light itself, which always moves at light speed, would have a clock that ran infinitely slow, so it wouldn't experience time. But there's a major flaw in this reasoning. From the point of view of the equations, they apply only to objects with mass that can never reach the speed of light. The theory was developed by treating light in a special way, so the equations don't apply to what light "sees." (Also important: seeing and experiencing requires that we have eyes, which have to have mass to work, and a brain, which has to have mass to work. Photons can't have either nor can anything moving at the speed of light.)
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As JP says, it's really impossible to say. However, there may be a clue in that, as far as we know, light, and all other forms of electromagnetic radiation, do not decay over time. The photons that were released at the birth of our Universe just keep on trucking. That suggests they are "timeless".
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As JP says, it's really impossible to say. However, there may be a clue in that, as far as we know, light, and all other forms of electromagnetic radiation, do not decay over time. The photons that were released at the birth of our Universe just keep on trucking. That suggests they are "timeless".
I'd argue this one with you. ;) Photons released at the birth of our universe can be absorbed and they are also stretched out by the expansion of the universe even if they don't spontaneously decay. If a photon is there one minute and absorbed the next, what does that say? Or if a photon is red-shifted over millions of years, what does that mean?
Mostly, I just don't like the word timeless being applied to photons because it can be taken out of context easily. If you understand well what's going on, as you do, then you can use it without being confused. If you don't understand special relativity well, then you might be tempted to interpret the word timeless to mean that if photons carried clocks, those clocks would stop. I think, and what I believe the theory is saying, is that our human concepts of time as measurable intervals between events doesn't even exist for photons. We can't even define a concept of time for them, so why bother trying to explain their viewpoint in our terms?
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I'd argue this one with you. ;) Photons released at the birth of our universe can be absorbed and they are also stretched out by the expansion of the universe even if they don't spontaneously decay. If a photon is there one minute and absorbed the next, what does that say? Or if a photon is red-shifted over millions of years, what does that mean?
Mostly, I just don't like the word timeless being applied to photons because it can be taken out of context easily. If you understand well what's going on, as you do, then you can use it without being confused. If you don't understand special relativity well, then you might be tempted to interpret the word timeless to mean that if photons carried clocks, those clocks would stop. I think, and what I believe the theory is saying, is that our human concepts of time as measurable intervals between events doesn't even exist for photons. We can't even define a concept of time for them, so why bother trying to explain their viewpoint in our terms?
I knew you would [:D]
My argument probably hinges on whether or not there are other things that don't spontaneously decay. I'm not sure if there are or not.
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I'd argue this one with you. ;) Photons released at the birth of our universe can be absorbed and they are also stretched out by the expansion of the universe even if they don't spontaneously decay. If a photon is there one minute and absorbed the next, what does that say? Or if a photon is red-shifted over millions of years, what does that mean?
Mostly, I just don't like the word timeless being applied to photons because it can be taken out of context easily. If you understand well what's going on, as you do, then you can use it without being confused. If you don't understand special relativity well, then you might be tempted to interpret the word timeless to mean that if photons carried clocks, those clocks would stop. I think, and what I believe the theory is saying, is that our human concepts of time as measurable intervals between events doesn't even exist for photons. We can't even define a concept of time for them, so why bother trying to explain their viewpoint in our terms?
I knew you would [:D]
My argument probably hinges on whether or not there are other things that don't spontaneously decay. I'm not sure if there are or not.
I agree that you have a good point. :) I just think the word "timeless" has connotations that could confuse a lay person.
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I agree that you have a good point. :) I just think the word "timeless" has connotations that could confuse a lay person.
Could we use something else, like non-decadent perhaps?
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There is an area of highly abstruse physics called gamma-gamma interaction in which photons are placed in a situation in which they interact with each other - this does present the possibility for a photon worldline unlike any we have been able to study before; ie if both the two particles are timeless and unchanging how can they interact?
Non-decadent? Hmm - let's face it soviet era physicists probably had to claim that all the particles of the great mother land were non-decadent.
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It's weird alright.
The redshift you discuss George is related to the observer, that means that any red & blue shift only can exist relative your 'motion' observing. When we come to the cosmic 'red shift' then that is an idea of how space 'expands', like a hill coming up from under the earth (space). If you define your light as a wave then it gets 'stretched out' as the hill tightens it up (rubber band).
But I do not find that good a explanation myself, as you also can see it as 'photons' moving. If you do you might want to define it as those light quanta getting more 'spaced out'.
If the 'cosmological redshift' is correct we will need to find the photons 'spaced out' in time when detecting them, that means that their energy will not have changed but their flux must have changed. There are two ways to reach a redshift, one is the frequency that will change, the other is the flux. They do not state the same. If the frequency (photons energy) is down shifted we will need to redefine redshift.
(The photon flux are the number of photons, per second, relative some 'unit area'. But the intensity of photon(s) is the irradiated power per unit area. Equal to the photon flux times the energy of the emitted photons.) Even though there are a lot of questionable assumptions hiding behind a 'expansion', we do seem to have one.
But the real difficulty lies in that a 'photon', according to mainstream definitions neither has a mass, nor any 'size'. That means that it can't take any place inside what we think of as SpaceTime. So how do you give a position to something not there? The only time you can define a photon, is in its interaction. You have the 'recoil' as it leaves a source, then you have the 'impact' as it delivers its 'kinetic' energy (momentum) and, that's it, as I think of it.
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This is a big point of confusion in special relativity. The theory says that if you have two observers with clocks, and one moves very fast with respect to the other, if they compare their clocks, the fast observer's clock appears to be running slow. The faster he/she goes, the slower the moving clock appears to go, tending to infinite length intervals of time per second of the stationary clock as the observer gets closer an closer to the speed of light.
This seems to indicate that light itself, which always moves at light speed, would have a clock that ran infinitely slow, so it wouldn't experience time. But there's a major flaw in this reasoning. From the point of view of the equations, they apply only to objects with mass that can never reach the speed of light. The theory was developed by treating light in a special way, so the equations don't apply to what light "sees." (Also important: seeing and experiencing requires that we have eyes, which have to have mass to work, and a brain, which has to have mass to work. Photons can't have either nor can anything moving at the speed of light.)
A flaw in photons not experiening time? Even if we cannot measure any true frame for a photon (because frames for photons do not exist in relativity) you must also challenge why a photon does not spontaneously decay in spacetime if it experiences time...
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^I see Geezer made the same point.
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Well, I have a simple definition of photon being a clock of sorts. You just need to do your measurement locally to see that it always will be/give you a 'constant'. The rest is no measurements, it's you assuming that red shift etc gives you a relation that you by Lorentz transformations can relate to the way radiation treat you. And it's correct of course, but if you fail to see that your measurements and transformations only comes to be conceptually as you try to translate it into one coherent definition for radiation you miss the point. Relativity is very simple if you use the local point of view to define it, and there are no misunderstanding of it then.
In a way that confusion tells us more of the way we grow up and learn to treat reality, than about what reality really is. Light have only one beat 'c' as you can measure. When you measure a red shift from the traveler, that light still have only one invariant speed in your measurements.
Try that way of looking at it and the pieces will fall in place.
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Well, I have a simple definition of photon being a clock of sorts. You just need to do your measurement locally to see that it always will be/give you a 'constant'. The rest is no measurements, it's you assuming that red shift etc gives you a relation that you by Lorentz transformations can relate to the way radiation treat you. And it's correct of course, but if you fail to see that your measurements and transformations only comes to be conceptually as you try to translate it into one coherent definition for radiation you miss the point. Relativity is very simple if you use the local point of view to define it, and there are no misunderstanding of it then.
In a way that confusion tells us more of the way we grow up and learn to treat reality, than about what reality really is. Light have only one beat 'c' as you can measure. When you measure a red shift from the traveler, that light still have only one invariant speed in your measurements.
Try that way of looking at it and the pieces will fall in place.
No, photons are not clocks. Not a relativistic clock, where you can measure the rate of a passage of time for events in spacetime. Relativity does not simply allow this.
Pure gravity solutions - where there exists no matter fields in the Hamiltonian of the universe - is analogous to accepting a pure energy solution, just like a photon gas for instance - in one universe alone. Since there are no frames of reference given to a photon in relativity, you will fail to define them in a universe with a passage of time, no matter how many photons you have.
They cannot act like observers that experience real time. They exist neither in imaginary time.
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You're doing what I defined as wrong, comparing frames of reference there, Mr. Data. If you define if from locality instead, as I, then all experiments you can do have one same invariant speed of light. It has to do with your definitions of 'reality'. If you define 'reality' from what you see conceptually then 'relativistic effects' becomes confusing and reality becomes complicated. If you define it locally you will find that this 'invariant speed' of light is what defines and explains 'relativistic phenomena'. The invariant 'clock' as I call lights constant, is what defines those measurements you do, and there is no way you ever will get another beat from a direct measurement.
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You're doing what I defined as wrong, comparing frames of reference there, Mr. Data. If you define if from locality instead, as I, then all experiments you can do have one same invariant speed of light. It has to do with your definitions of 'reality'. If you define 'reality' from what you see conceptually then 'relativistic effects' becomes confusing and reality becomes complicated. If you define it locally you will find that this 'invariant speed' of light is what defines and explains 'relativistic phenomena'. The invariant 'clock' as I call lights constant, is what defines those measurements you do, and there is no way you ever will get another beat from a direct measurement.
No ... read what I said again please. The whole point of my post states that photons do not have a frame of reference, so a photon-only universe do not have a relativistic clock to measure difference. Everything remains the same, completely immutable. In fact, if quantum theory is correct, it would simply just be a gas state in a superpositioned state in every space which can be occupied; smeared out by the wave function. Nothing truely would ever change. No energy content would change, no time as a seperation between objects would also negate it's existence philosophically-speaking.
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A lot of the confusion about locality raises from 'frames of reference'. A often used example for 'proving' that light have different 'speeds' is by using clocks and rulers to define a speed inside a accelerating frame, as your spacecraft accelerating. If you define two points in the direction of your propulsion inside that ship, 'A' and 'B', separated by a distance. Then you put clocks that first gets synchronized at one common point at those two locations. Then you measure lights speed relative those two points/clocks, finding that when you compare your measurements 'A' against 'B', they will give you a different speed for that light, depending on the direction from which you measured it. That's a 'conceptual' comparison as I see it.
But it has a simple explanation in that gravity will blue and red shift light (radiation), and also, later when comparing clocks, seem to slow 'time', depending on gravitational potential. But, in both measurements they will show you the same invariant 'speed' of light, relative that clock you measured it from. The confusion raises when you compare those two 'frames of reference' to each other. And as shown by our 'atomic clocks' experiment on that table. When one is moved to the floor the same thing happens, one clock will go 'slower' than the other.
So a 'frame of reference' is in reality a abstract thing, very hard to pinpoint. I define it as each point of SpaceTime will have a own 'frame of reference' myself. But it's a dynamic relation defined from relative motion, mass, and possibly the idea of 'energy'.
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A photonic universe?
If you by that mean that you doubt my definition of 'locality' you must also doubt lights invariant speed in a vacuum?
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A lot of the confusion about locality raises from 'frames of reference'. A often used example for 'proving' that light have different 'speeds' is by using clocks and rulers to define a speed inside a accelerating frame, as your spacecraft accelerating. If you define two points in the direction of your propulsion inside that ship, 'A' and 'B', separated by a distance. Then you put clocks that are synchronized at one common point at those locations. Then you measure lights speed relative those two points/clocks, finding that when you compare your measurements 'A' against 'B' they will give you a different speed for that light depending on the direction you measured it. That's a 'conceptual' comparison as I see it. But it has a simple explanation in that gravity will blue and red shift light, and also, later when comparing clocks, seem to slow 'time' depending on gravitational potential. But, in both measurements they will show you the same invariant 'speed' of light relative that clock you measured it from. The confusion raises when you compare those two 'frames of reference' to each other. And as shown by out 'atomic clocks' on that table. When one is moved to the floor the same thing happens, one clock will go 'slower' than the other.
So a 'frame of reference' is in reality a abstract thing, very hard to pinpoint. I define it as each point of SpaceTime will have a own 'frame of reference' myself.
Frame of reference is what you make it: Look, I know this stuff is hard to understand, which is why I am going to say, I know where you are coming from (I think). You can provide information that two photons are moving relative to each other, but this is not the case in the photon-only universe (for some reason) we have been relentlessly talking about. Not even the remedial human observer is there. So who is there is measure anything, if photons do not experience a time? The universe is self-consistent, meaning everything the universe is concerned with, only happens within itself: If this is true, then even the universe as a system exists with reference to nothing! The universe, to have a defined energy, one which is measurable would require an observer to sit outside it's horizon. But there are problems with this, as relativity states there is nothing outside the universe. So if no one is there to measure the system in question, how can the universe have any rate of change?
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A photonic universe?
If you by that mean that you doubt my definition of 'locality' you must also doubt lights invariant speed in a vacuum?
Just a universe with [photons] I do believe it was you with this thought-analogy, no?
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No, I don't need it. I use a constant for defining the 'clock'. And I'm sorry if you can't see my definitions. I try to keep them simple, but if you don't get it I may be failing in that.
A photonic universe is a very strange idea :) And as I said, I use a constant, defining it as Einstein did, of a unvarying speed in, and from, all frames possible. If you don't see it I can only draw the conclusion that you have other definitions of it?
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No, I don't need it. I use a constant for defining the 'clock'. And I'm sorry if you can't see my definitions. I try to keep them simple, but if you don't get it I may be failing in that.
A photonic universe is a very strange idea :) And as I said, I use a constant, defining it as Einstein did, of a unvarying speed in, and from, all frames possible. If you don't see it I can only draw the conclusion that you have other definitions of it?
But a photon experiences no constants. You can only have a constant number if your equations satisfy a number to begin with... photons cannot be ascribed any numbers, because they don't experience anything to begin with.
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I'm sorry Mr Data. You will need to look up the definition of lights speed in a vacuum to see, then you better check Einsteins 1905 paper over SR, and from there go to GR. In the 1905 paper he defined light as being a 'constant' and from there he built Special Relativity. That is the 'constant' I'm using and that one always hold true locally. That you from comparing another frame of reference to yours, presuming that they all are the same 'locally', as you find a Lorentz transformation needed to equalize your observations, actually build on that constant. Without it there can be no Lorentz transformations to define as we then would have a variable 'speed' and 'time'. And that was what I was wondering about, I've seen some try to define it that way, but if doing so you're no longer building on SR and GR.
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I'm sorry Mr Data. You will need to look up the definition of lights speed in a vacuum to see, then you better check Einsteins 1905 paper over SR, and from there go to GR. In the 1905 paper he defined light as being a 'constant' and from there he built Special Relativity. That is the 'constant' I'm using and that one always hold true locally. That you from comparing another frame of reference to yours, presuming that they all are the same 'locally', as you find a Lorentz transformation needed to equalize your observations, actually build on that constant. Without it there can be no Lorentz transformations to define as we then would have a variable 'speed' and 'time'. And that was what I was wondering about, I've seen some try to define it that way, but if doing so you're no longer building on SR and GR.
You are now mixing up the idea of photons speed as a constant, with what frame of reference means to a photon... in which case, it does not have one, which I have explained more than once now.
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No, I don't mix anything Mr Data. I'm describing frames of reference as simple as I can to present why people mix their definitions up. There is only one frame of reference in where you measure/observe. Your own, that we commonly define for example Earth to be one same 'frame of reference' is, strictly defined, wrong. But we don't notice the variations as they are so extremely small, and that's why it's only at relativistic 'speeds' you will find them becoming obvious, around 0.4-5 'c' where our commonly seen Doppler effect 'lose out' to the relativistic Lorentz contraction, and relativistic blue shift, that then will raise very quick as you accelerate further.
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You can't understand what a frame of reference means for a photon... are you arguing this case or not?
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I'm not discussing a photons 'frame of reference' at all? You just don't seem to read what I write here? I define light as a constant, then I define what a frame of reference is, all to explain why I'm defining 'locality' as the proper perspective for understanding relativity. As for your question? There is no 'frame of reference' from a photons perspective. If you mean the 'clock' I'm discussing, then that can be defined as lights invariant speed in a vacuum.
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'Frames of reference' build on lights speed in a vacuum too. That's why they exist, and it has taken me some pondering to understand them properly. You can see them as something that exist up to 'c'. At 'c' we have no proper definitions for them, as that is a limit of our understanding. It's a 'singularity' of sorts, in that we can't define what happens pass that limit, other as a theoretical guess. FTL and taychons may be called theories, but as they have no experimental evidence I know of, I would call them hypothesis's myself.
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I'm not discussing a photons 'frame of reference' at all? You just don't seem to read what I write here? I define light as a constant, then I define what a frame of reference is, all to explain why I'm defining 'locality' as the proper perspective for understanding relativity. As for your question? There is no 'frame of reference' from a photons perspective. If you mean the 'clock' I'm discussing, then that can be defined as lights invariant speed in a vacuum.
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'Frames of reference' build on lights speed in a vacuum too. That's why they exist, and it has taken me some pondering to understand them properly. You can see them as something that exist up to 'c'. At 'c' we have no proper definitions for them, as that is a limit of our understanding. It's a 'singularity' of sorts, in that we can't define what happens pass that limit, other as a theoretical guess. FTL and taychons may be called theories, but as they have no experimental evidence I know of, I would call them hypothesis's myself.
You led me to the path we discuss. If you are making a mockery of this, forget my participation from now on.
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...and by the way, tachyons are completely irrevelent to our topic as they cannot exist in nature due to tachyon condensation.
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I think you're right Mr Data, we've gotten astray from the subject. When we define a speed to photons we do it relative 'time' and 'distance'. So we observe them as defined from that perspective, but from a photons perspective the idea of 'time' and 'distance' becomes a meaningless definition. And that's another way to define why a photons 'frame of reference' becomes impossible to define. If I define it as a clock, with each beat locally being a photon annihilating at your retina, then trying to look at it from the perspective of being one single photon stops the 'clock'. And having no arrow to define a causality in, there is nothing to measure.
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Hence why we have a subject focused on human observation. Just because we are stuck in illusionary mesh of time, does not mean all objects in the universe are.