[yor_on]

How Mike?

How does time adapt?
And why would it adapt to a constant?

[yor_on]

A constant is by definition unchanging. You can't have it both unchanging and changing Mike, if you use such a definition then we're not talking about a constant any longer. When we speak about the room time geometry inside a black hole we can define it, depending on whose math we trust and 'mass' as 'infinite'. That doesn't state that time changed its 'speed' to adapt so that we will find the speed of light in a vacuum to fit. It state that the room time geometry is different, the reason why we use room time is because you can't have a 'room' without time and neither can you have a 'time' by itself. But the direct effect for us being inside will be that the room in fact become infinite, not that light as such change speed.

In one way this whole discussion is meaningless as 'speed' is a very shaky definition. The only thing that always seem to have one exact 'duration' when measured by us, invariant in/from all frames, is lights speed in a vacuum. And that goes from anywhere you choose to measure it, inside that black hole or outside it. You can measure it from any frame you like, against any other frame, moving near the speed of light measuring that event horizon for example. You will still find it to have one single 'speed'. But you can have an observer at the same exact 'location' as where you do your measurement, but contrary to you being still relative that black hole. He will be doing the exact same measurement on the same light. And you will both find the speed to be the same, namely 'c'.

The speed of light in a vacuum is invariant. Time does not slow down to adapt the light speed, as shown by our two observers, to fool us. To me it's a question of the geometry of SpaceTime, and it is coupled to mass, motion, and possibly energy?
==

As it seems to me )

In your world everything gets invincible forcefields of 'time' adapting itself so that we won't notice lights speed 'differing' if I understand you right? Whilst in mine there is only one thing that is constant, namely lights speed in a vacuum. I go out from that definition and from there I find the geometry of 'SpaceTime' to change. That also fits with all observation I know of your personal time never differing, no matter if you're at the EV of a black hole, speeding away near light, or just comfortably reclining in your sofa.

Using your definition it becomes trickier it seems.  When it comes to uniform motion you can exchange any motion measured. For example, 'A' will say it moves close to lights speed relative 'B' being still, but, you can as easily exchange that to it being 'B' moving near lights speed relative 'A' being still, or give them both any speeds in between as long as they add up to the number measured relative each other.

In Relativity both statements are true when it comes to uniform motion, and it builds on the equivalence of them, as observed and tested in a 'black box scenario'. If all experiments you can do inside that black box, on each of the ships, gives you the exact same results, then all uniform speeds are the same from that point of view and so speed becomes a meaningless definition. (ignoring tidal forces here)

But it seems to me that if you was right then we would have a way to prove that only one of them was 'moving'. And that would redefine the equivalence principle and theory of relativity to me  And as I see it, for Einstein too if he was here.

[yor_on]

You can, if using my definition, think of time as measured out by lights invariant propagation. Then it will with relative motion (and mass) be found to have different 'distances' to reach. If you're uniformly moving away from the light it will take longer to reach you than if you were moving towards it. That can in a way be translated into time. The geometry you move in is dependent on those light signals, they are the watch that 'ticks', and they 'tick' differently for you moving than for you being still. And they will be normal to you as all 'light ticks' only can have one constant invariant speed, but to the observer being still they will describe another duration as they propagate trough space, moving with you.

And as light is the only true constant, that and the fact that your personal time never changes, then the effect you see in a time dilation suddenly will be found to be placed in the relation between you and the observer. In SpaceTime all time is a definition from lights propagation, and the geometry changes with it too. To you the light clock you have with you always bounce the same amount of 'distance'. But to the observer at rest relative your origin (Earth) that same 'light corn' will bounce a different (longer) path through SpaceTime. And yet you both observe the same light-clock, although it to him will be found to take a longer path through space as you move, but for you, being at rest with it comoving, it will be found to take the exact same path as on Earth.

There is two ways to look at that phenomena, that light will be found to have a 'longer path' from Earth than as what you perceive traveling aside it. Either you define it as the light clock 'slowing down' as observed by the observer on Earth, now saying that light goes 'slower' inside that ship, and that seems to be your interpretation of it, or you define it as light having one invariant speed and the effect you observe being a result of 'different' room time geometries, the observers and yours, aka 'frames of reference'. But as I also see their 'times arrow' as unchanging in both scenarios, which is my interpretation of it I state that it is the room time geometry that is different for them. And stating that I define the room time geometry as their 'SpaceTimes' being different. Which in a way make me even more heretic than you as I now define them each one to have a unique, different, SpaceTime And that's kind'a weird The only thing that I see binding those SpaceTime's together is 'light'. Radiation is what makes this universe seem seamless to us, that and mass, motion, and possibly 'energy'. It both is what shows us that we're in reality 'divided' at the same time as it 'joins us' And now I'm afraid we soon will have to move us both to 'New Theories'.

Ahem..

And that's why your personal time always is the same, unchanging, and that's why the observer and you will disagree on the 'time taken'. And that's why a time dilation exist. But it weirder than that Because as I said, you can define any uniform motion as being at rest, weightlessly 'drifting', no gravity existent. And that is true, there is no way you will find any gravity inside that black box. And if you measure a light coming from the stern to the aft, it will not 'blue shift' no matter what speed you believe yourself to have relative Earth. Also you can redefine our planetary gravity (Earth) as a constant 'uniform' acceleration at one gravity. And that is the direct equivalence to your spacecraft starting to accelerate a constant one gravity. And if you now watch that light in-falling from the stern you will find it to blue shift, same as on Earth. So it's a tricky business, where it's very easy to get lost in its definitions. But it's a nice idea, although I see it differently.

[Geezer]

Let's try an experiment.

I'm zipping along in my very fast spaceship. So fast in fact that time will be dilated relative to time on Earth. On my spaceship, I happen to have an evacuated tube and a light source that allows me to measure the speed of light in a vacuum. It's really quite a simple setup.

If I understand how this all works, despite any shortening of the tube and local time dilation, the value that I measure in my spaceship will be exactly the same as the value I measure using the same equipment on Earth.

Do we all agree with that, or have I got it wrong somewhere?

[yor_on]

As long as you're uniformly moving that should be correct as I see it It will 'zip away' or 'tick' heh the same as on Earth.
==

Maybe you are thinking of what will happen if you turn it around? In the direction of the motion '|' as for putting it horizontal '-' to the motion. The Lorentz contraction will equalize the difference as I see it. and so the 'ticks'  will be found, from a thought up observer on Earth, to be the same when measured, all of the same duration. And for you being inside the ship, you will be at rest with your equipment and so notice no difference at all.

In a acceleration it becomes trickier for me as there will be a constant accelerating displacement relative the lights path, with a respective red and blue shift noticeable. But as lights speed in a vacuum is a constant, it shouldn't matter for the 'ticks'. Ah, that is for you being inside, at rest with the light source. For our observer at Earth the acceleration will change the durations measured, well as I think. Acceleration is indeed trickier, and very weird to me.
==

Think of bouncing a tennis ball on the floor of a aircraft at 900 km/h. The ball won't care, it will go straight down on the floor and up. But if the floor was made of glass and someone standing on earth could watch that ball bounce he would swear to it taking a curved path down and then a curved path up. Exchange the ball for light, and define it as a constant, always of the same exact 'speed' in a vacuum. Then try to define the shortest durations we can measure. That will be by that same invariant light, won't it? Radiation is the best 'clock' we have.

[Geezer]

Ah! Good. So, what might we conclude?

Well, I think we can say that the speed of light is constant for any observer within their frame of reference. Speed is correct in that sense because it really is the distance travelled in time.

Here's where it might get ugly. We know that the two clocks (the one on the spaceship and the one on earth) are not in agreement. Also, we know that the two vacuum tubes are not really the same length while they have a great difference in relative speed. Soooooo, if you could measure the speed of light on the spaceship using the the Earth clock and the Earth vacuum tube, you would measure a value for c that was different from the official c.


 

[CPT ArkAngel]

The thing is that all measurements you can do by using the earth's clock and tube will be corrected by the speed of light relating you to the earth...

By the way, i agree with Mike about the blueshift, but i suppose it has already been taking in account and it should be quite small. It may be only a drifting of electronics components... They surely cannot measure it...

[Geezer]

The thing is that all measurements you can do by using the earth's clock and tube will be corrected by the speed of light relating you to the earth...

Actually, they won't  []

If the spaceship was orbiting the Earth, you could send it a signal during every orbit so that the spaceship's clock was continuously synchronized with Earth time. Then you would measure a different value for c on the spaceship.

But that does not violate relativity because, in that situation, you would not be measuring the speed of light using the time within the frame of reference of the observer.

[CPT ArkAngel]

You're cheating, you forgot the tube...  []

[MikeS]

It would seem that I can't stress this enough:-
The speed of light is a constant, is a constant is a constant.

But

The speed of light is a constant because the rate of flow of time is a variable.

Without wishing to get into what time is it has two components, direction and rate of flow.  Obviously time is a product of the universe and its rate of flow must be connected to some particular qualities of the universe, say its a relationship between energy and mass, energy divided by mass.  This ratio is not constant in the universe, nor is it constant on any local volume of space that contains mass.

There is very good reason, known and understood why the speed of light is a constant.  There is nothing that says the rate of flow of time is a constant.  It isn't.  General Relativity states that the passage of time (the rate of flow of time) is relative.  Traveling near to the speed of light or being in a gravity well dilate time.  These are not abstract frame of reference ideas that can't be seen or measured.  Time dilation is real and observable and has been proven to be correct.

"Gravitational time dilation is the effect of time passing at different rates in regions of different gravitational potential; the lower the gravitational potential, the more slowly time passes. Albert Einstein originally predicted this effect in his theory of relativity and it has since been confirmed by tests of general relativity.
This has been demonstrated by noting that atomic clocks at differing altitudes (and thus different gravitational potential) will eventually show different times. The effects detected in such experiments are extremely small, with differences being measured in nanoseconds." http://en.wikipedia.org/wiki/Gravitational_time_dilation
Gravitational time dilation is minute on the Earth because the Earth in cosmological terms contains little mass.

ArkAngel
It would seem reasonable to assume the blue shift has been taken into account as it is predicted by relativity but honestly, I don't believe it has.

Mike

[MikeS]

Further to comment from ArkAngel:-
As I understand it Newtonian Gravity was used as the model when analysing the Pioneer anomaly.  Newtonian Gravity is obviously lacking for this scenario as it does not take into account gravitational time dilation by our solar system.

Mike

[JP]

Further to comment from ArkAngel:-
As I understand it Newtonian Gravity was used as the model when analysing the Pioneer anomaly.  Newtonian Gravity is obviously lacking for this scenario as it does not take into account gravitational time dilation by our solar system.

Mike

It would be extremely embarrassing to physicists if the anomaly was as simple as them not using general relativity to do the calculations.  Interestingly, I can't find any description of the model of gravity used in the original papers on it.  See this one, for example: http://arxiv.org/PS_cache/gr-qc/pdf/9808/9808081v2.pdf 

However, some of the attempted explanations involve using general relativity and assuming dark matter/dark energy http://arxiv.org/PS_cache/gr-qc/pdf/0407/0407023v1.pdf, so I assume the effect has been checked with general relativity.  It would be odd to check the anomaly using general relativity with added dark matter/energy and not notice that general relativity without these additions explains the anomaly.

At any rate, I agree with ArkAngel on this one.  Surely they've checked if GR alone predicts the effect, even if I can't find someone explicitly stating that in an article.

[MikeS]

I agree, it would seem odd if they hadn't considered general relativity.  Einstein, when he came up with these theories based much of his work on thought experiments.  I don't know how he would have translated thought experiments into specific as opposed to general mathematical solutions.  Perhaps relativity needs tweaking.

Apart from the Pioneer anomaly there exists the galaxy and associated quasar red shift anomaly and the galaxy rotation anomaly. I am sure that these anomalies are also based around relativity.  Personally I do not believe in dark matter or dark energy.

Anybody care to comment on the speed of light being a constant because the rate of flow of time is a variable.  I think this is what relativity is telling us and I believe my interpretation of this is correct.  However perhaps you know better?

Mike

[MikeS]

"ANOMALOUS GRAVITATIONAL FORCE

A discussion of this phenomenon appears in the 4 October 1999 issue of Newsweek magazine (See also the December 1998 issue of Scientific American.) The mystery of the tiny acceleration towards the sun in the motion of the Pioneer 10, Pioneer 11 and Ulysses spacecraft remains unexplained as of 2006. A team of planetary scientists and physicists led by John Anderson (Pioneer 10 Principal Investigator for Celestial Mechanics) has identified a tiny unexplained acceleration towards the sun in the motion of the Pioneer 10, Pioneer 11, and Ulysses spacecraft. The anomalous acceleration - about 10 billion times smaller than the acceleration we feel from Earth's gravitational pull - was identified after detailed analyses of radio data from the spacecraft. A variety of possible causes were considered including: perturbations from the gravitational attraction of planets and smaller bodies in the solar system; radiation pressure, the tiny transfer of momentum when photons impact the spacecraft; general relativity; interactions between the solar wind and the spacecraft; possible corruption to the radio Doppler data; wobbles and other changes in Earth's rotation; outgassing or thermal radiation from the spacecraft; and the possible influence of non-ordinary or dark matter. After exhausting the list of explanations deemed most plausible, the researchers examined possible modification to the force of gravity as explained by Newton's law with the sun being the dominant gravitational force. "Clearly, more analysis, observation, and theoretical work are called for," the researchers concluded. The scientists expect the explanation when found will involve conventional physics. An article in http://www.space.com/scienceastronomy/mystery_monday_041018.html discusses the current thinking on the acceleration anomaly." 
http://www.nasa.gov/centers/ames/missions/archive/pioneer.html

Although it mentions general relativity, it talks about modification to Newtons law. We are now talking about three spacecraft with the same anomaly.  One of which is a different design.  It's a very small but consistent anomaly. 

I am absolutely certain that my original explanation is correct.  Either they haven't used general relativity, or they have done the sums wrong or general relativity needs tweaking.

Mike

[MikeS]

Iv'e just sent an e.mail to Slava Turyshev at NASA's Jet Propulsion Laboratory who is handling the enquiry.  If I get a rely I will post.

Mike

[JP]

I am absolutely certain that my original explanation is correct.  Either they haven't used general relativity, or they have done the sums wrong or general relativity needs tweaking.

Absolute certainty is a huge leap of faith.  Is it backed up by science?  What evidence makes you so certain that your explanation is right?  

I do happen to agree with you that the idea that GR might need tweaking is a very interesting possibility.  I don't think there's any reason to be certain that it does, though.

By the way, as yor_on posted there was a recent paper claiming that the anomaly could be explained by thermal radiation off an antenna.  It hasn't been double checked.

------------------

As for the speed of light being constant because time is variable, it's usually put the other way.  The speed of light is constant for all observers.  This is from experimental evidence.  In order for that to be correct, the geometry of space-time has to depend on the velocity of observers which means that clocks and measuring sticks moving at different speeds don't match up.

You could come at it the other way, I think.  That clocks and measuring sticks of moving observers don't agree and from measuring exactly how they disagree you could come to the conclusion that the speed of light is constant. 

It's harder to motivate GR that way, though, since you'd have to take a lot of measurements of clocks and measuring sticks in different gravitational situations to construct the theory.  

[imatfaal]

In the Naked Astronomy podcast (or possible another sci-cast) they mentioned that the recent ideas about a(nother) directional source of thermal radiation causing the anomaly  would cause problems for those who were using the anomaly to tweak GR in their own special way - if they were modifying GR I think you can be certain that they were using GR/SR in their initial calcs.   The JPL orbital calculational engine definitely takes into account some relativistic effects.

Mike - can you actually DO the sums required?  If so, do them and show they are wrong - ie for a start what is the time dilation caused by the gravitational potential of the sun at the position of the earth's orbit, mars', jupiter's etc.  This would at least give you an idea if you were talking in the right magnitude

edit here is a quote giving a rough idea of the methodology used

The ephemeris programs use equations for point-mass relativistic gravitational accelerations. They are derived from the variation of a time-dependent, Lagrangian action integral that is referenced to a non-rotating, solarsystem, barycentric, coordinate frame. In addition to modeling point-mass interactions, the ephemeris programs contain equations of motion that model terrestrial and lunar figure effects, Earth tides, and lunar physical librations . The programs treat the Sun, the Moon, and the nine planets as point masses in the isotropic, parameterized post-Newtonian, N-body metric with Newtonian gravitational perturbations from large, main-belt asteroid

This is from this paper produced by JPL and others http://arxiv.org/PS_cache/gr-qc/pdf/0104/0104064v5.pdf  I think even this snippet makes it clear that the calculations are not based on solely Newtonian physics.

[MikeS]

JP.  I agree, there is nothing scientific about being absolutely certain  but it is still how I feel.
The explanation that I gave, is, the simplest explanation, requires no assumptions, does not require anything new and is the one predicted by general relativity.

"As for the speed of light being constant because time is variable, it's usually put the other way.  The speed of light is constant for all observers.  This is from experimental evidence.  In order for that to be correct, the geometry of space-time has to depend on the velocity of observers which means that clocks and measuring sticks moving at different speeds don't match up"

Yes, I agree but in this instance we are considering gravitational time dilation which is predicted by general relativity and is a proven fact.  Gravity slows down the rate of flow of time. Or to put it another way the speed of light is a constant because the rate of flow of time is a variable.

I have just found this:-
This is an extract from a paper about the pioneer anomaly written by Slava G. Turyshev, Viktor T. Toth
Slava G. Turyshev is the person investigating the anomaly at JPL Pasadena.
"This apparent violation of the Newton's gravitational inverse-square law has become known as the Pioneer anomaly; the nature of this anomaly remains unexplained."

"While most of the modern experiments in the solar system do not show disagreements with
general relativity, there are puzzles that require further investigation. One such puzzle was presented by the Pioneer 10 and 11 spacecraft. The radiometric tracking data received from these
spacecraft while they were at heliocentric distances of 20 – 70 astronomical units (AU) have consistently indicated the presence of a small, anomalous, Doppler frequency drift. The drift was
interpreted as a constant sunward acceleration of aP = (8.74 ± 1.33) × 10
−10 m/s
2
experienced by
both spacecraft [15, 18, 391]. This apparent violation of the inverse-square law has become known
as the Pioneer anomaly; the nature of this anomaly remains unexplained."

"Before Pioneer 10 and 11, Newtonian gravity was not measured with great precision over great
distances and was therefore never confirmed. The unique “built-in” navigation capabilities of the
two Pioneers allowed them to reach the levels of ∼ 10
−10 m/s
2
in acceleration sensitivity. Such an
exceptional sensitivity allowed researchers to use Pioneer 10 and 11 to test the gravitational inverse
square law in the largest-scale gravity experiment ever conducted. However, the experiment failed
to confirm the validity of this fundamental law of Newtonian gravity in the outer regions of the
solar system. Thus, the nagging question remains: Just how well do we know gravity?"

"One can demonstrate that beyond 15 AU the difference between the predictions of Newton
and Einstein are negligible. So, at the moment, two forces seem to be at play in deep space:
Newton’s law of gravity and the Pioneer anomaly. Until the anomaly is thoroughly accounted
3for by conventional causes, and can therefore be eliminated from consideration, the validity of
Newton’s laws in the outer solar system will remain in doubt. This fact justifies the importance
of the investigation of the nature of the Pioneer anomaly"
http://arxiv.org/PS_cache/arxiv/pdf/1001/1001.3686v2.pdf

It would appear that the problem has been analysed from the standpoint of Newtonian gravity and surprise, surprise ..."the validity of Newton’s laws in the outer solar system will remain in doubt."  Let's face it they haven't taken into account gravitational time dilation by mass have they?

Mike

[JP]

"One can demonstrate that beyond 15 AU the difference between the predictions of Newton
and Einstein are negligible. So, at the moment, two forces seem to be at play in deep space:
Newton’s law of gravity and the Pioneer anomaly. Until the anomaly is thoroughly accounted
3for by conventional causes, and can therefore be eliminated from consideration, the validity of
Newton’s laws in the outer solar system will remain in doubt. This fact justifies the importance
of the investigation of the nature of the Pioneer anomaly"
http://arxiv.org/PS_cache/arxiv/pdf/1001/1001.3686v2.pdf

It would appear that the problem has been analysed from the standpoint of Newtonian gravity and surprise, surprise ..."the validity of Newton’s laws in the outer solar system will remain in doubt."  Let's face it they haven't taken into account gravitational time dilation by mass have they?

Actually, if you read the bolded part above, they did account for general relativity, and noted that the differences from Newtonian gravity is negligible at those distances.  So they ignored time dilation because they considered it and found that it isn't important here. 

[MikeS]

imatfaal,

No, I can’t do the maths I wish I could. 

Mathematics  is just another language, the one mostly used by the scientific community.  It is frequently used to prove some theory or another.  There are countless theories on just about everything that can be represented by mathematics, most of them wrong.  Whilst mathematics are capable of telling ultimate truths they are just as capable of deceit, unwitting or otherwise. 

I am always reminded of this quote.
“Any intelligent fool can make things bigger and more complex... It takes a touch of genius - and a lot of courage to move in the opposite direction”.
Albert Einstein

I don’t need to do the maths to know that I am “talking in the right magnitude”.  The anomaly is extremely small but real, just the kind of adjustment that gravitational time dilation should predict.

These are quotes from the paper you mention

“It is also possible to infer the position in the sky of a spacecraft from the Doppler data. This is accomplished by examining the diurnal variation imparted to the Doppler shift by the Earth’s rotation. As the ground station rotates underneath a spacecraft, the Doppler shift is modulated by a sinusoid. The sinusoid’s amplitude depends on the declination angle of the spacecraft and its phase depends upon the right ascension. These angles can therefore be estimated from a record of the Doppler shift that is (at least) of several days duration. This allows for a determination of the distance to the spacecraft through the dynamics of spacecraft motion using standard orbit theory contained in the orbit determination programs”
http://arxiv.org/PS_cache/gr-qc/pdf/0104/0104064v5.pdf

The above programs were written obviously for spacecraft in orbit within the solar system.  It is highly probable that when they were written they did not take into account that they would be used on spacecraft leaving the solar System

“Is there any evidence that some kind of “time acceleration”
http://arxiv.org/PS_cache/gr-qc/pdf/0104/0104064v5.pdf

Although “time acceleration” is mentioned in, the above paper and various methods proposed and discounted.  I could not find any reference to relativistic, gravitational time dilation being seriously considered.

Although the anomaly being discussed is about Pioneers 10 & 11 it seems there may be a total of four that are “probably” affected in the same manner, possibly more.  The anomaly only becomes apparent when spacecraft are leaving the Solar System.  Most explanations have been proposed and discounted.  Gravitational time dilation of photons entering the Solar System remains the simplest and most likely explanation.

JP wrote.

"One can demonstrate that beyond 15 AU the difference between the predictions of Newton
and Einstein are negligible. So, at the moment, two forces seem to be at play in deep space:
Newton’s law of gravity and the Pioneer anomaly. Until the anomaly is thoroughly accounted
3for by conventional causes, and can therefore be eliminated from consideration, the validity of
Newton’s laws in the outer solar system will remain in doubt. This fact justifies the importance
of the investigation of the nature of the Pioneer anomaly"
http://arxiv.org/PS_cache/arxiv/pdf/1001/1001.3686v2.pdf



"One can demonstrate that beyond 15 AU the difference between the predictions of Newton and Einstein are negligible.

In other word below 15AU they are significant right?  The photons from 20AU are being gradually red shifted the closer they get to Earth.

“Actually, if you read the bolded part above, they did account for general relativity, and noted that the differences from Newtonian gravity is negligible at those distances.  So they ignored time dilation because they considered it and found that it isn't important here.”

“So they ignored time dilation because they considered it and found that it isn't important here.”

This should read:-

“So they ignored time dilation because they didn’t understand it.  See Above

Mike