Do photons age? Do they remain stationary in x4?

[brunoeinstein]

Do photons remain stationary in the fourth dimension?

Do photons age?

Thanks! :)

 

[zhermes]

I've always been interested in that question, but I don't think there's much of an answer because you can't consider the reference frame of the photon itself.

Does QFT have anything more substantial to say?

 

[bcrowell]

FAQ: What does the world look like in a frame of reference moving at the speed of light?

This question has a long and honorable history. As a young student, Einstein tried to imagine what an electromagnetic wave would look like from the point of view of a motorcyclist riding alongside it. But we now know, thanks to Einstein himself, that it really doesn't make sense to talk about such observers.

The most straightforward argument is based on the positivist idea that concepts only mean something if you can define how to measure them operationally. If we accept this philosophical stance (which is by no means compatible with every concept we ever discuss in physics), then we need to be able to physically realize this frame in terms of an observer and measuring devices. But we can't. It would take an infinite amount of energy to accelerate Einstein and his motorcycle to the speed of light.

Since arguments from positivism can often kill off perfectly interesting and reasonable concepts, we might ask whether there are other reasons not to allow such frames. There are. One of the most basic geometrical ideas is intersection. In relativity, we expect that even if different observers disagree about many things, they agree about intersections of world-lines. Either the particles collided or they didn't. The arrow either hit the bull's-eye or it didn't. So although general relativity is far more permissive than Newtonian mechanics about changes of coordinates, there is a restriction that they should be smooth, one-to-one functions. If there was something like a Lorentz transformation for v=c, it wouldn't be one-to-one, so it wouldn't be mathematically compatible with the structure of relativity. (An easy way to see that it can't be one-to-one is that the length contraction would reduce a finite distance to a point.)

What if a system of interacting, massless particles was conscious, and could make observations? The argument given in the preceding paragraph proves that this isn't possible, but let's be more explicit. There are two possibilities. The velocity V of the system's center of mass either moves at c, or it doesn't. If V=c, then all the particles are moving along parallel lines, and therefore they aren't interacting, can't perform computations, and can't be conscious. (This is also consistent with the fact that the proper time s of a particle moving at c is constant, ds=0.) If V is less than c, then the observer's frame of reference isn't moving at c. Either way, we don't get an observer moving at c.

 

[pallidin]

Photons are fascinating to me. Example, as far as I know, photons do not exist when not moving.
And that a photon goes from zero to c instantaneously is equally fascinating, as I thought that nothing could go faster than c. "Instantaneous" is certainly much faster than c.
Much for me to ponder and learn...

 

[brunoeinstein]

well, we can take the limit i suppose

as v approaches c, time slows more and more.

so at 99.9999% the speed of light, t would be very slow.

so at 99.99999999999999999% the speed of light, t would be very, very, very slow.

and at 100%, it will have stopped, i would imagine.

interesting fact:

the velocity of all objects through spacetime is c.

so if an object is moving at c through the three spatial dimensions, its velocity in the fourth dimension is 0.

and vice versa.

brian green talks about this in the elegant universe.

does anyone know the passage or have the book?

please let me know! :)

 

[zhermes]

Photons are fascinating to me. Example, as far as I know, photons do not exist when not moving.
And that a photon goes from zero to c instantaneously is equally fascinating, as I thought that nothing could go faster than c. "Instantaneous" is certainly much faster than c.
Much for me to ponder and learn...

Photons are truly amazing! I want to talk about a few details here because I hear them a lot.
1) Photons don't "go from zero to c." They just start out at c, continue at c, and end at c :)
Which ties into what you said at first: you can't have a photon that isn't moving [at c].

2) You're mixing up acceleration, and velocity. Moving from one point to another instantaneously would mean infinity velocity (faster than c). Accelerating from zero velocity to non-zero velocity instantaneously (although it brings up other serious issues--like infinite force, etc) is very different, and has nothing to do with the speed of light per se.

Hope that helps :)

 

[zhermes]

well, we can take the limit i suppose ... and at 100%, it will have stopped, i would imagine.

I think the idea is great, but the math is very different. There's a huge difference here between the speed of light, and arbitrarily CLOSE to the speed of light. Its the same difference as between a black-hole, and just a really big star... the math gets angry at certain values :P

interesting fact:
the velocity of all objects through spacetime is c.

I find this to be one of the most intriguing ideas in physics, and It feels like the kind of thing that might have deep meaning that no one has yet uncovered.

 

[nismaratwork]

If you consider energy loss with the expansion of space to be "aging"... maybe... but the FAQ is already deeper than that.

 

[DaTario]

Photons are truly amazing! I want to talk about a few details here because I hear them a lot.
1) Photons don't "go from zero to c." They just start out at c, continue at c, and end at c :)
Which ties into what you said at first: you can't have a photon that isn't moving [at c].

Hi Zhermes,

I am curious to hear (read) how do you deal with refraction, created either by material medium or by gravitational (general relativity) effects.
It seems reasonable in these contexts to think of photons accelerating.


Best wishes

DaTario

 

[bcrowell]

I am curious to hear (read) how do you deal with refraction, created either by material medium or by gravitational (general relativity) effects.
It seems reasonable in these contexts to think of photons accelerating.

Photons always move at c. Velocities less than c for an electromagnetic wave are the velocities of the wave formed by the superposition of the incident wave and waves reemitted by the charges oscillating in the medium.

 

[DaTario]

Photons always move at c. Velocities less than c for an electromagnetic wave are the velocities of the wave formed by the superposition of the incident wave and waves reemitted by the charges oscillating in the medium.

I think it is an elegant way to see how this things work. But let me check one thing:

If this is true then if you put a large (1 m thick) slab of glass in front of a photon source, and set a photo-detector after this slab, then you would be able to measure time intervals consistent with c velocity of propagation from the source to the detector, as the main wavefront is always present.

Best Regards,

DaTario

 

[bcrowell]

If this is true then if you put a large (1 m thick) slab of glass in front of a photon source, and set a photo-detector after this slab, then you would be able to measure time intervals consistent with c velocity of propagation from the source to the detector, as the main wavefront is always present.

Nope. The wave pattern does propagate at less than c in the glass. It's just not valid to interpret this as the velocity of photons.

 

[DaTario]

So you see difference between EM field and photon. Is it?

In case you see this difference, do you think photon can accelerate?

Best wishes

DaTario

 

[bkelly]

Our telescopes receive photons that are upwards of 10 billion years old. That seems to indicate they do not age.

According a NASA release found here: http://science.nasa.gov/science-news/science-at-nasa/2002/27mar_stoplight/ photons can be stopped.

Regarding the tests on light to coerce it to be a wave or a photon: I wonder if any has been done in a medium where the lights travels significantly slower than the standard speed?

 

[zhermes]

Our telescopes receive photons that are upwards of 10 billion years old. That seems to indicate they do not age.

If they're 10 billion years old, how do they not age? :P

 

[nismaratwork]

What does it mean for a photon to age in the first place? For a radioactive sample, I would say you measure age in terms of decay, for a photon... what? What is there to age in the first place, when they are bound to a set speed at all times in a given medium?

 

[Fredrik]

For something to actually age, it needs to have an internal structure that can change with time. No elementary particles do, so they can't really age.

For something to really experience the passage of time (or anything else), it needs to be conscious. Things without internal structure certainly can't be conscious.

What we mean when we say that an object or a particle "experiences X" is that in the coordinate system that the standard synchronization procedure associates with the object's world line (or its tangent), some sequence of events is described as "X". That's how the term "experiences" is defined in the context of special and general relativity. The problem is that the standard synchronization procedure doesn't work for null geodesics, i.e. for the curves that can be world lines of massless particles. So the term "experiences" is undefined for photons.

 

[DaTario]

For something to actually age, it needs to have an internal structure that can change with time. No elementary particles do, so they can't really age.

For something to really experience the passage of time (or anything else), it needs to be conscious. Things without internal structure certainly can't be conscious.

The word "certainly" seems to be inappropriate as we don't even know how to define consciousness. And it seems also to be quite risky to assume that the consequence of a particle not having internal structure is its being unable to present complex behavior. It is more a question of words here, as I agree in general with the estimatives you presented.

Best wishes

DaTario

 

[Mentz114]

The word "certainly" seems to be inappropriate as we don't even know how to define consciousness. And it seems also to be quite risky to assume that the consequence of a particle not having internal structure is its being unable to present complex behavior. It is more a question of words here, as I agree in general with the estimatives you presented.

In our experience we have only found consciousness associated with complex structures, and it is reasonable to assume that billiard balls and photons are not conscious in any sense that the word is usually used.

 

[DaTario]

My claim is that you can of course say that it is reasonable, but you have no basis to infer that with certainty, at least within the scientifical domain, taken in the sense of natural science.

Best wishes

DaTario

 

[Fredrik]

Something that isn't capable of storing information can't be considered conscious, and a physical system that doesn't have distinguishable states can't store information.

 

[DaTario]

Something that isn't capable of storing information can't be considered conscious, and a physical system that doesn't have distinguishable states can't store information.

An alectron for instance has spin, and therefore allows one to store 1 qbit. How much information (classical information) can be stored in 1 qbit. Do you know?

Best Regards,

DaTario

 

[Nisse]

The problem is that the standard synchronization procedure doesn't work for null geodesics, i.e. for the curves that can be world lines of massless particles. So the term "experiences" is undefined for photons.

Would it be fair to infer from this that Relativity is an incomplete theory?

 

[Fredrik]

Would it be fair to infer from this that Relativity is an incomplete theory?

No, not at all. I don't know a definition of the word "incomplete" that would make SR incomplete, except of course "incomplete"="isn't an exact description of all phenomena", but with that definition, all theories are incomplete. SR is as complete as a theory can get.

An alectron for instance has spin, and therefore allows one to store 1 qbit. How much information (classical information) can be stored in 1 qbit. Do you know?

I googled and found at least one person who claimed that the answer is "infinite", so I assume that this is what you had in mind, but I would say that this claim is false. I assume that it comes from the fact that the set of spin-1/2 states can be mapped bijectively onto a sphere. Since there are infinitely many points on a sphere, you could argue that there are infinitely many states that the system can "be" in. But it's not at all obvious that a state can be said to represent the particle's properties. The only thing we can be sure of is that it represents the properties of an ensemble of identically prepared systems.

 

[DaTario]

No, not at all. I don't know a definition of the word "incomplete" that would make SR incomplete, except of course "incomplete"="isn't an exact description of all phenomena", but with that definition, all theories are incomplete. SR is as complete as a theory can get.


I googled and found at least one person who claimed that the answer is "infinite", so I assume that this is what you had in mind, but I would say that this claim is false. I assume that it comes from the fact that the set of spin-1/2 states can be mapped bijectively onto a sphere. Since there are infinitely many points on a sphere, you could argue that there are infinitely many states that the system can "be" in. But it's not at all obvious that a state can be said to represent the particle's properties. The only thing we can be sure of is that it represents the properties of an ensemble of identically prepared systems.

I respect your view of QM. I was just trying to convince you not to use so many certainties. But if you think so, It is OK. For instance, when you said "SR is as complete as a theory can get". Your statement makes one think you have a large experience in investigating completeness of physical theories, for it is a complex field, with so many subtleties. But you certainty is there, talking out loud. If you inserted at least somehing like IMO, it would have sounded better. Or...


Perhaps you do have such astonishing expertise in dealing with philosofical aspects of theories in natural sciences.

But let us focus in some objective debate.

Best Regards

DaTario

 

[Dale]

For something to actually age, it needs to have an internal structure that can change with time. No elementary particles do, so they can't really age.

Well, the unstable ones can decay, so I would say that elementary particles can age. Since the proper time along a photon's worldline is 0 then it could make coordinate-independent sense to say that a photon does not age.

For something to really experience the passage of time (or anything else), it needs to be conscious. Things without internal structure certainly can't be conscious.

What we mean when we say that an object or a particle "experiences X" is that in the coordinate system that the standard synchronization procedure associates with the object's world line (or its tangent), some sequence of events is described as "X". That's how the term "experiences" is defined in the context of special and general relativity. The problem is that the standard synchronization procedure doesn't work for null geodesics, i.e. for the curves that can be world lines of massless particles. So the term "experiences" is undefined for photons.

I am completely with you here both in terms of consciousness and experience. Attributing consciousness to fundamental particles is just an absurd thing to do in physics (how would you experimentally test that), and the usual meaning of experience is undefined for null worldlines.

 

[Fredrik]

Well, the unstable ones can decay, so I would say that elementary particles can age.

I would say that the measured decay rates are the strongest evidence we have for the particles not aging. If the properties of a particle don't change with time, the probability that it will decay during the next second must be independent of how much time has passed since the particle's creation. This implies an exponential decay rate. So the theory that particles don't age (i.e. the theory that particles don't have any properties that can change with time) predicts the correct decay rates.

 

[jtbell]

Well, the unstable ones can decay, so I would say that elementary particles can age.

[putting Fredrik's response in different words]

For a given type of particle, the probability that it will decay during the next second does not depend on the time that the particle has already "lived." It is constant. As far as we know, there is no difference between a muon that was created one microsecond ago, versus one that was created one second ago, or one that was created one hour ago. (assuming of course that it still exists)

 

[nismaratwork]

Seems the questions I raised in the last page have been answered with: No, they do not age, because they don't participate in any standard definition or standard by which aging can be measured.

 

[Naty1]

Brian Greene Elegant Universe:

pg 49

...in the majority of circumstances (slow speeds) most of an objects motion is thru time, not space...the maximum speed through space occurs if all of an objects motion through time is diverted to motion through space...thus light does not get old; a photon that emerged fromthe big bangis the same age today as it was then.

In note 6 for Chapter 2, he explains how the proper time d(tau²) can be interpretated in terms of velocity and position four vectors to reflect the idea in the above quote... or...per

Dalespam
".. Since the proper time along a photon's worldline is 0 then it could make coordinate-independent sense to say that a photon does not age.

So the simplistic idea is that a photon does not age...whether that's technically correct is debatable... as Crowell posted...

 

[Naty1]

For something to actually age, it needs to have an internal structure that can change with time.

I disagree...an object without internal structure CAN age...maybe it doesn't change, however...so trying to measure the passage of time utilizing such "something" that does not change would be futile.

 

[Fredrik]

I disagree...an object without internal structure CAN age...maybe it doesn't change, however...so trying to measure the passage of time utilizing such "something" that does not change would be futile.

How do you define "age" when the "older" version of the same thing is indistinguishable from the younger?

 

[Dale]

I would say that the measured decay rates are the strongest evidence we have for the particles not aging. If the properties of a particle don't change with time, the probability that it will decay during the next second must be independent of how much time has passed since the particle's creation. This implies an exponential decay rate. So the theory that particles don't age (i.e. the theory that particles don't have any properties that can change with time) predicts the correct decay rates.

Very good point. I certainly had not considered it that way. The lifetime of people is not governed by an exponential law precisely because they do age, meaning that the likelihood of decay in the next year changes as a function of the number of years since birth.

So, although you can say that the proper time along a photon's path is 0 you cannot associate that with aging one way or the other.

 

[Naty1]

So, although you can say that the proper time along a photon's path is 0 you cannot associate that with aging one way or the other.

Brian Greene says you can as I noted in my previous post.

 

[brunoeinstein]

I found more discussion on Brian Greene's writings here:

http://www.fqxi.org/community/forum/topic/511

MDT & Brian Greene’s Elegant Universe:

In An Elegant Universe, Brian Greene almost characterizes Moving Dimensions Theory’s deeper reality:

“Einstein found that precisely this idea—the sharing of motion between different dimensions—underlies all of the remarkable physics of special relativity, so long as we realize that not only can spatial dimensions share an object’s motion, but the time dimension can share this motion as well. In fact, in the majority of circumstances, most of an object’s motion is through time, not space. Let’s see what this means.” Space, Time, and the Eye of the Beholder, An Elegant Universe, Brian Greene, p. 49

Right here Brian almost grasps MDT. But time is not a dimension. Time is an emergent phenomenon that arises because the fourth dimension is expanding relative to the three spatial dimensions at the rate of c. Let’s rewrite Brian’s paragraph with MDT's insights:

“Einstein found that precisely this idea—the sharing of motion between different dimensions—underlies all of the remarkable physics of special relativity, so long as we realize that not only can the three spatial dimensions share an object’s motion, but the fourth dimension, which is moving relative to the three spatial dimensions, can share this motion as well. In fact, in the majority of circumstances, most of an object’s motion is through the fourth dimension, not the three spatial dimensions. Let’s see what this means.” Space, Time, and the Eye of the Beholder, An Elegant Universe, Brian Greene, p. 49

Most objects are traveling far less than c through the three spatial dimensions. Thus most objects are traveling close to the rate of c through the fourth dimension. To be stationary in the three spatial dimensions implies a velocity of c through the fourth dimension. Ergo the fourth dimension is expanding relative to the three spatial dimensions. To be stationary in the fourth expandning dimension, as is the timeless, ageless, nonlocal photon, implies a velocity of c through the three spatial dimensions. Ergo the fourth dimension is expanding relative to the three spatial dimensions.

dx(4)/dt = ic

Brian Greene continues:

“Motion through space is a concept we learn about early in life. Although we often don’t think of things in such terms, we also learn that we, our friends, our belongings, and so forth all move through time, as well. When we look at a clock or a wristwatch, even while we idly sit and watch TV, the reading on the watch is constantly changing, constantly “moving forward in time.” We and everything around us are aging, inevitably passing from one moment of time to the next. In fact, the mathematician Hermann Minkowski, and ultimately Einstein as well, advocated thinking about time as another dimension of the universe—the fourth dimension—in some ways quite similar to the three spatial dimensions in which we find ourselves immersed.” Space, Time, and the Eye of the Beholder, An Elegant Universe, Brian Greene, p. 49

What Greene misses is that the time measured on your watch—the ticking seconds—is not the fourth dimension, but it is a phenomenon that emerges because the fourth dimension is expanding relative to the three spatial dimensions. The time measured on a clock or watch relies on the emission and propagation of photons, be it in the context of an unwinding clock spring or an oscillating quartz crystal, or even the beating of a heart. And photons are matter that surf the fourth expanding dimension. As time is so inextricably wed to the emission and propagation of photons, and as photons are matter caught in the fourth expanding dimension, our notion of “time” inherits properties of the fourth expanding dimension. But the fact is that time emerges from a deeper physical reality—a fourth dimension that is expanding relative to the three spatial dimensions.

Brian Green continues on, heading off in the wrong direction that just misses the central postulate of MDT:

“Although it sounds abstract, the notion of time as a dimension is actually concrete.”

But it is not. Can you move to where your watch reads three seconds back in time? Or can you move to where your watch reads an hour back in time? We can walk left or right. We can climb up or down. We can move forwards or backwards. But we can’t move through time like we can through the three spatial dimensions. This is because time, as measured on our watch, is not the fourth dimension, but it is a construct we have devised which is based on the fundamental fact that the fourth dimension is expanding relative to the three spatial dimensions, governing the emission and propagation of photons, by which time is known and measured on our watches.

Brian Green continues on,

“When we want to meet someone, we tell them where “in space” we will expect to see them—for instance, the 9th floor of the building on the corner of 53rd Street and 7th avenue. There are three pieces of information here (9th floor, 53rd Street, 7th avenue) reflecting a particular location in the three spatial dimensions of the universe. Equally important, however, is our expectation of when we expect to meet them—for instance, at 3 PM. This piece of information tells us where “in time” our meeting will take place. Events are therefore specified by four pieces of information: three in space and one in time. Such data, it is said, specifies the location of the event in space and in time, or in spacetime, for short. In this sense, time is another dimension.”

But again, time is different from the three spatial dimensions. Time is inextricably wed to our sense of the past—the order stored in our memory, long with our ability to imagine and dream of future events. The present is where we put our dreams into action. However, the time defined by past, present, and future is not a dimension akin to the three spatial dimensions, but rather it is a phenomenon that emerges because the fourth dimension is expanding relative to the three spatial dimensions, at the rate of c.

You write, "So I don't think Einstein and Minkowski went far enough. They covered measurement, and how events in one reference frame would appear to an observer in another reference frame. That is quite useful in itself, but the real picture seems to be fundamentally much larger than what they covered. We need to go beyond Einstein and include temporal motion, which in turn requires a consideration of non-directional motion, speeds greater than light, non-locality, and so forth. Even better, we need to learn how to think in terms of "motional dimensions" directly, instead of space and time dimensions."

Yes! Feynman sought this mechanism for the ever constant motion of time! He sought source of time's arrows and assymmetries!

And MDT provides this *physical* mechanism for time and all change, and a while host of other physical phenomena.

Indeed, MDT finally provides, in Feyman's words, "the thing that makes the whole phenomena of the world seem to go one way." Time has a definitive arrow because the dx4/dt=ic, or the fourth dimension is expanding relative to the three spatial dimensions at the rate of c. Ergo radiation, which is but matter caught upon the expanding nonlocality of the fourth exapnding dimension, expands outward, but never inward. Ergo time and all its arrows and asymmetries, as well as entropy, as more fully elaborated on in my paper.

Feynman stated, "Now if the world of nature is made of atoms, and we too are made of atoms and obey physical laws, the most obvious interpretation of this evident distinction between past and future, and this irreversibility of all phenomena, would be that some laws, some of the motion laws of the atoms, are going one way – that the atom laws are not such that they can go either way. There should be somewhere in the works some kind of principle that uxles only make wuxles, and never vice versa, and so the world is turning away from uxley character to wuxley character all the time – and this one-way business of the interactions of things should be the thing that makes the whole phenomena of the world seem to go one way. But we have not found this yet. That is, in all the laws of physics that we have found so far there does not seem to be any distinction between the past and the future. The moving picture should work the same going both ways, and the physicist who looks at it should not laugh."--(The Distinction of Past and Future, from The Character of Physical Law, Richard Feynman, 1965)

MDT has finally found "the thing that makes the whole phenomena of the world seem to go one way."

To be stationary in a lab means to move at c through the fourth dimension. So it is that absolute rest may be defined as maximal aging, but this can never be ascertained in an inertial frame cutoff from the surrounding environment, as time is measured relative to the velocity of light and distance, which are ultimately measured relative to time. This tautological definition of time and the velocity of light and the velocity of light and time is something Einstein noted.



Dr. E (The Real McCoy)

http://www.fqxi.org/community/forum/topic/511

 

[yossell]

`Biological age' should be distinguished from `chronological age'. The former tracks the wear and tear of an organism over time, the latter the amount of time that has passed for an organism. While 'biological age' clearly refers to organisms, its use could be extended to other systems, to track their changes too.

Biological age clearly must involve change. A forty year old man in a sixteen year old's body implies that certain changes have gone slowly for him and also is illegal in some countries. Chronological age does not so obviously require change (though if time necessarily requires some kind of change, it may) and it's theoretically possible for periodic system to `experience' time, in that it goes through a sequence of changes, yet returning to exactly the same qualitative state.

(Perhaps, then, here I disagree with Fredrik's last post )

It seems to me that the argument that the decay rate of fundamental particles shows that their `biological' age does not change - they are intrinsically the same for the whole of their lifetime. But the notion of time passed, and in particular, relativistic time dilation, also makes sense for muons - they do have a half life, which is a function of the proper time, and fast traveling muons live longer.

By contrast, traveling on light-cones, not even this much can be said for photons.

 

[brunoeinstein]

As Brian Greene points out in the Appendix to Chapter 2 of The Elegant
Universe, we note that from the space-time position 4-vector
x=(ct,x1,x2,x3), we can create the velocity 4-vector u=dx/d(tau),
where tau is the proper time defined by
d(tau)^2=dt^2-c^-2(dx1^2+dx2^2+dx3^2). Then the "speed through
space-time" is the magnitude of the 4-vector u,
((c^2dt^2-dx^2)/(dt^2-c^-2dx^2))^(1/2), which is identically the speed
of light c. Now, we can rearrange the equation
c^2(dt/d(tau))^2-(dx/d(tau))^2=c^2 to be c^2(d(tau)/dt))^2
+(dx/d(tau))^2=c^2. This shows that an increase of an object's speed
through space, (dx/d(tau))^2)^(1/2)= dx/d(tau) must be accompanied by
a decrease in d(tau)/dt which is the object's speed through time,
which also may be considered the rate at which time elapses on it's
own clock d(tau) or the proper time, as compared with that on our
stationary clock dt.

So it seems that as an object propagates at c through the three spatial dimensions, it must propagate at 0 through the fourth dimension.

Hence it would seem that photons remain stationary in the fourth dimension. For if they moved at all in the fourth dimension, their velocity would be greater than c, which is impossible.

 

[Dale]

So it seems that as an object propagates at c through the three spatial dimensions, it must propagate at 0 through the fourth dimension.

Hence it would seem that photons remain stationary in the fourth dimension.

This is certainly not correct. The fact that the proper time along a lightlike worldline is 0 does not imply that the worldline does not go through coordinate time.

Btw, although the four velocity of any timelike particle has a magnitude of c, the four velocity of a lightlike particle is undefined.

 

[Dale]

`Biological age' should be distinguished from `chronological age'.

I guess I would use "age" to refer to the former and "proper time" to refer to the latter.

 

[brunoeinstein]

This is certainly not correct. The fact that the proper time along a lightlike worldline is 0 does not imply that the worldline does not go through coordinate time.

yes dale,

indeed our watches would continue ticking as photons zoom on by.

i assume that you are picturing a space-time diagram and a light cone. the time on that space-time diagram is in our frame.

what brian greene is saying is that the photon is moving along with the fourth dimension, as it is staying stationary in x4. as the velocity of all objects through space-time is c, and as all of a photon's velocity is directed through space (x1, x2, x3), it must thus be stationary in the fourth dimension (x4).

that is what the math is saying.

best. :)

 

[Dale]

what brian greene is saying is that the photon is moving along with the fourth dimension, as it is staying stationary in x4. as the velocity of all objects through space-time is c, and as all of a photon's velocity is directed through space (x1, x2, x3), it must thus be stationary in the fourth dimension (x4).

that is what the math is saying.

No, from your comments about the fourth dimension you are clearly referring to coordinate time and a photon clearly is not stationary in coordinate time.

Also, your references to the four-velocity apply only for timelike particles, not lightlike particles. The four-velocity is not defined for a photon's worldline (division by 0). That is why you have to use an affine parameter instead of proper time for a photon.

 

[brunoeinstein]

No, from your comments about the fourth dimension you are clearly referring to coordinate time and a photon clearly is not stationary in coordinate time.

Also, your references to the four-velocity apply only for timelike particles, not lightlike particles. The four-velocity is not defined for a photon's worldline (division by 0). That is why you have to use an affine parameter instead of proper time for a photon.

Indeed a photon is not stationary in time as we measure it on our watches.

But too, a photon does not age.

Or are you saying that Brian Greene is wrong? "Brian Greene writes in the Elegant Universe:

pg 49

...in the majority of circumstances (slow speeds) most of an objects motion is thru time, not space...the maximum speed through space occurs if all of an objects motion through time is diverted to motion through space...thus light does not get old; a photon that emerged from the big bangis the same age today as it was then.

"

Greene states "thus light does not get old; a photon that emerged from the big bang is the same age today as it was then."

This is true.

 

[Kitesurfer]

Do photons age?
Time has no meaning in photon rest frame, nor for any zero mass particle moving at c. Time is "experienced" only by mass particles. Therefore, only interaction of photon and a mass particle yields information about time.

 

[brunoeinstein]

Do photons age?
Time has no meaning in photon rest frame, nor for any zero mass particle moving at c. Time is "experienced" only by mass particles. Therefore, only interaction of photon and a mass particle yields information about time.

so you agree with brian greene i take it?

Greene states "thus light does not get old; a photon that emerged from the big bang is the same age today as it was then."

This is true.

 

[Kitesurfer]

so you agree with brian greene i take it?

Greene states "thus light does not get old; a photon that emerged from the big bang is the same age today as it was then."

This is true.

Yes.
A photon that was emitted 13 plus billions years ago, right after the initial condensation of electrons / protons that made the universe transparent to photons and enabled its propagation without scattering on mass particles (circa 300 thousands years after the big bang), is received by our detector via its interaction with a mass particle in the detector. Only then a time is recorded, i.e. it has a meaning.

 

[brunoeinstein]

Yes.
A photon that was emitted 13 plus billions years ago, right after the initial condensation of electrons / protons that made the universe transparent to photons and enabled its propagation without scattering on mass particles (circa 300 thousands years after the big bang), is received by our detector via its interaction with a mass particle in the detector. Only then a time is recorded, i.e. it has a meaning.

More from Brian Greene & Einstein,

"Einstein proclaimed that all objects in the universe are always traveling at one fixed speed--that of light. . . We now see that time slows down when an object moves relative to us because this diverts some of its motion through time into motion through space. The speed of an object through space is thus merely a reflection of how much of its motion through time is diverted." -- p. 50, THE ELEGANT UNIVERSE (read it for yourself if you log in @ https://www.amazon.com/dp/0375708111/?tag=pfamazon01-20)

1. "Einstein proclaimed that all objects in the universe are always traveling at one fixed speed--that of light." --Brian Greene

2. Fact: A photon travels at c through the three spatial dimensions.

3. "The speed of an object through space is thus merely a reflection of how much of its motion through time is diverted." --Brian Greene

4. Because a photon moves at c through the three spatial dimensions, a photon's "motion through time must be entirely diverted."

5. Ergo, a photon has no velocity component in the fourth dimension.

6. Ergo a photon stays at the same place in the fourth dimension, as it has no motion in the fourth dimension, all its "motion through time being diverted," as Brian Greene and Einstein state.
B.E.

 

[Fredrik]

I found more discussion on Brian Greene's writings here:

This was only your third post in this forum, and you're already quoting a crackpot who keeps creating new accounts here just to be able to post his "moving dimensions" nonsense. (No, not Greene). It's not hard to guess who you are. And linking to crackpot stuff is against the forum rules, no matter who you are.

More from Brian Greene & Einstein,

I think Greene's explanation of SR is really bad, so I wouldn't recommend anyone to try to learn SR from his writings.

 

[brunoeinstein]

This was only your third post in this forum, and you're already quoting a crackpot who keeps creating new accounts here just to be able to post his "moving dimensions" nonsense. (No, not Greene).

sorry about that!

i was searching for greene's passage on photons not aging nor traveling through x4, and came across the passage.

perhaps we should stick to greene's text which i found at amazon.com: https://www.amazon.com/dp/0375708111/?tag=pfamazon01-20

if you log in, it will let you read it directly as they have made that page available. or, perhaps you have the book.

More from Brian Greene & Einstein,

"Einstein proclaimed that all objects in the universe are always traveling at one fixed speed--that of light. . . We now see that time slows down when an object moves relative to us because this diverts some of its motion through time into motion through space. The speed of an object through space is thus merely a reflection of how much of its motion through time is diverted." -- p. 50, THE ELEGANT UNIVERSE (read it for yourself if you log in @ https://www.amazon.com/dp/0375708111/?tag=pfamazon01-20)

1. "Einstein proclaimed that all objects in the universe are always traveling at one fixed speed--that of light." --Brian Greene

2. Fact: A photon travels at c through the three spatial dimensions.

3. "The speed of an object through space is thus merely a reflection of how much of its motion through time is diverted." --Brian Greene

4. Because a photon moves at c through the three spatial dimensions, a photon's "motion through time must be entirely diverted."

5. Ergo, a photon has no velocity component in the fourth dimension.

6. Ergo a photon stays at the same place in the fourth dimension, as it has no motion in the fourth dimension, all its "motion through time being diverted," as Brian Greene and Einstein state.



B.E.

 

[brunoeinstein]

I think Greene's explanation of SR is really bad, so I wouldn't recommend anyone to try to learn SR from his writings.

What, specifically, do you find "really bad" about Greene's explanations of SR?

Are you saying that he is wrong? If so, how so, specifically?

It is not enough in life nor education to criticize others in an ad hominem manner, but one must always a) qualify one's statements, and b) suggest the better path for everyone's elucidation.

Who do you suggest we learn SR from?

Thanks in advance!

:) BR

 

[yossell]

but one must always a) qualify one's statements,

Practice what you preach much?