[alancalverd]

So - as I have been saying for last 3 years, a photon shifts  oppositly to a clock in the gravity potential!

No. The observed shift depends only on the difference in gravitational potential; between the source and the observer. It is exactly the same for all sources, as I said but you refuse to accept.
 

So - what about what Jeff says in post 25?  He is saying that photons do not shift in the gp, and that they only appear shifted as a symptom of clocks being time dilated.Do you share this viewpoint @alancalverd ?

It is the same phenomenon., differently expressed. The fractional change in observed clock frequency is the same as the fractional change in photon energy fore a given difference in gravitational potential because the laws of physics are the same for everyone and everything, everywhere.

[timey]

Wtf @alancalverd ? Yes I do accept that  "The observed shift depends only on the difference in gravitational potential; between the source and the observer. It is exactly the same for all sources".

But the photons (NOT the source of the photons) the photons, ie: electro magnetic radiation, REDSHIFTS (as observed by observer in the higher potential, really don't know why I have to include this, it's obvious, and also the first thing one learns about relativity) as it moves away from a gravitational mass, and a clock, or a photon source BLUESHIFTS (as observed by the blah, blah) when placed in the higher potential)
And a photon IS shifted oppositely to a photon source/clock in the gravity potential.

You say that is the same phenomenon, differently expressed.
Yes, as shown in the physics exchange quote/link in post 39.

However, given that you say that physics is the same for everyone everywhere, it hardly seems possible that light would deem to 'have' a constant energy in one description, yet would deem to gain or lose energy in the other description.

Light/electro magnetic radiation cannot be doing both.

(BTW, my sister and I are looking after grandma Joan, who is 103 years age, for few days. She's great, a real trooper. 103, fancy that aye!)

[jeffreyH]

Well as I said already. I give up.

[timey]

Well as I said already. I give up.

Yes - well that is very boring of you.

[alancalverd]

I'm with Jeffrey. You are incorrigible. Perhaps Grandma Joan will persuade you of the error of your thinking - give her my best wishes.

[Colin2B]

OK, one last try, then I’m with Jeff & Alan

Photons 'do not' behave the same as clocks in the gravity potential.
Remember that when we moved clock G to A, that A observes the clock as blueshifted compared to when it observed clock G on the ground...
So if a photon behaves the same as a clock, then a photon released at G will be observed by A as blueshifted, when it arrives at A...
BUT a photon released at G and observed by A will be REDSHIFTED Colin, won't it?

We are in danger here of not comparing like with like. To move a clock is the equivalent of moving a source, in this case a source of ticks, so let’s clarify.

We have a clock H = highest, above A (I want to avoid ‘far away’ as it has a specific meaning)
We have a clock A = above ground
We have a clock G = on the ground

Let’s say for easy numbers clock H is 2x faster than A which is 2x faster than G, so H is 4 times faster than G.

Clock G thinks it is running at 1s/s but we want to know what H measures it as. So G sets off a light which flashes once every tick =1/second, which we let run for say 20 flashes. H sees those 20 flashes but, because it is running 4x faster, 80s have passed thus the ticks released at G are measured at H as tick rate = 20/80 = 0.25ticks/s ie redshift.
Similarly A measures G as 0.5ticks/s ie redshift, but less so than H measures G.
Also H sees A as 0.5ticks/s. So if G moves to A, H will see it as having same redshift as A.
This is exactly the same behaviour as photons and photon sources.

The point about where the reference clock is in the NIST experiment is that a clock at ground level will always see clocks, sources or photons from above it as blueshifted, unless the clock or source is lowered towards it.

For the benefit of the OP it is also important to note that we can set up G, A and H at any height above the ground and as long as the ratio of Gravitational Potential (GP) between them remains the same we will get the same result. In other words these shifts depend only on difference in GP and not directly on height or distance.

[timey]

I'm with Jeffrey. You are incorrigible. Perhaps Grandma Joan will persuade you of the error of your thinking - give her my best wishes.

Well I'm with @evan_au

- A photon loses energy as it climbs out of a gravitational well
- If a photon loses energy, its frequency is lower: This is gravitational redshift for escaping photons.

...and with them's that are over at physics stack exchange:
https://physics.stackexchange.com/questions/172854/do-photons-lose-energy-due-to-gravitational-redshift-if-so-where-does-the-lost

Honestly Alan, sometimes I wonder if you purchased your physics degree off that dodgy dude round back of Kings Cross station (chuckle)
(For the benefit of OP who might not be used to mine and Alan's banter, that was a joke)

And while I'm at it, you know how sometimes a person can have more than one profile? Well there have been times when I have, just very briefly, wondered if you actually are Jeff, lol.

I will most certainly shout your best wishes to Joan. She's a tad hard of hearing, doesn't get about too much anymore, but loves her food, and is excellent company for short times between long sleeps.

Very good evening to you, don't know why, absolutely no reason for it, but I'm in a f'ing brilliant mood tonight.

[timey]

@Colin2B I don't know why you have to complicate the matter. Einstein himself said that light (not a light source) loses energy climbing out of a gravitational well. If the light has lost energy, it is redshifted.

So imagine now a light source placed on ground producing a continuous stream of photons that are escaping the gravitational well.
Place 10 clocks at 1 metre elevation apart in the gravity potential, and at each elevation the clock there will tick faster than the clock below. ie: blueshifted.
So at each position of elevation in the gravity potential the clock at that position is blueshifted, and at each position of elevation in the gravity potential, when the light arrives there, the light is redshifted.

Now tell me that light that is escaping a gravitational well behaves the same as a clock placed at elevation in the gravity potential of a gravity well.  I double, triple, dare you. (Chuckle)

However, what I really want to discuss is the fact that the elevated clocks are ticking faster, and that this affects the measurement of the observation of the arriving light. And I want to discuss this in relation to how this affects the fact of light losing energy when climbing out of a gravity well.

[alancalverd]

Well I'm with @evan_au

- A photon loses energy as it climbs out of a gravitational well
- If a photon loses energy, its frequency is lower: This is gravitational redshift for escaping photons.

...Alan, sometimes I wonder if you purchased your physics degree off that dodgy dude round back of Kings Cross station (chuckle)

Exactly the point. Kings Cross being the lowest potential point on the route, the train that leaves KX uses a lot of energy to get to Cambridge.

The train that leaves from Stevenage only uses half as much energy to get here, so on arrival it's blueshifted compared with the KX train.

The dodgy degree I got from the bloke  in Cambridge market has a genuine Cantab attached. I think it was from Carlsberg Export (only the best at High Table), but it was an official seal. 

[timey]

Alan, surely no matter if you are travelling from Kings Cross, or Stevenage, your sharp eye would be checking the clock at every station, noting that each is running faster than the last, and you will be scratching your head as to how much energy your train has actually lost?

I didn't know they sold degrees in Cambridge Market.  Good to hear Kings Cross doesn't have the monopoly, and a genuine cantab to boot. Sounds like you've 'probably' got the best degree in the world (or was that Heineken?)

[alancalverd]

Alan, surely no matter if you are travelling from Kings Cross, or Stevenage, your sharp eye would be checking the clock at every station, noting that each is running faster than the last, and you will be scratching your head as to how much energy your train has actually lost?

No. As the station clock is always at the same gravitational potential as my watch, there will be no difference in tick rate.

[timey]

Well we'd better invoke the far away clock then.

[alancalverd]

By all means. Seen from Cambridge, the KX clock will be ticking slower than the STV  clock, which will be ticking slower than the CAM clock. And the 21 cm hydrogen line photon from a lamp at KX will have a greater red shift than one emitted from STV. Exactly as observed in laboratories and observatories, and predicted by general relativity,  for the last several years.

[guest45734]

don't know why you have to complicate the matter. Einstein himself said that light (not a light source) loses energy climbing out of a gravitational well. If the light has lost energy, it is redshifted.

Why not consider space to be flowing towards mass (gravity), or expanding in between masses/galaxies (Dark energy). What is the obsession with gravity wells and acceleration in 4 D space time. Why not add additional dimensions ?D space time.

[alancalverd]

1. KISS

2. Facts.

[timey]

By all means. Seen from Cambridge, the KX clock will be ticking slower than the STV  clock, which will be ticking slower than the CAM clock. And the 21 cm hydrogen line photon from a lamp at KX will have a greater red shift than one emitted from STV. Exactly as observed in laboratories and observatories, and predicted by general relativity,  for the last several years.

Yes exactly!
So the train (light) travelling from KX, to CAM, via STV, is losing energy.  At each station the train is observed as redshifted according to the blueshifted clock at that station, by remit of measuring the train's (light's) frequency via the faster ticking clock.

So - is the redshifted train losing energy, or is the redshifted train's energy constant?

[alancalverd]

Redshift = less energy.

And just to get ahead of your next posting: the energy loss equals the gravitational potential difference between the source (KX) and the observer (STV or CAM).  An identical train starting from STV would have less redshift on arrival at CAM because it started with the same amount of fuel but further up the track.

Actually it's a crap analogy as the line is almost horizontal. Think of the Snowdon mountain railway starting from Llanberis (LL) and seen from Halfway (HW) and the top (SN) , compared with one that starts at HW.

[timey]

Yes " the energy loss equals the gravitational potential difference between the source (KX) and the observer (STV or CAM)", but the blueshifted clocks at the stations are also equal to the gravitational potential difference.  But note that the redshift of the light (train) is 'measured' via the clock at the station.

As things stand, we are now making a double usage of a singular gravitational potential difference.  That is like saying 1+1=1. 
If you can accept this as fact Alan, then we can start talking in terms of special relativity and flat space..

[alancalverd]

Yes " the energy loss equals the gravitational potential difference between the source (KX) and the observer (STV or CAM)", but the blueshifted clocks at the stations are also equal to the gravitational potential difference.  But note that the redshift of the light (train) is 'measured' via the clock at the station.

as is the redshift of the clock at the lower potential, when seen from the higher potential. It doesn't matter whether you send me a photon, a train, or a carrier pigeon: if you are at a lower gp than me, it will be redshifted on arrival compared with a carrier pigeon born in Cambridge. 

[guest45734]

1. KISS

2. Facts.

1 KISS: it is easy to envisage at the noddy level space as membrane being absorbed by mass/flowing towards it, and in the absence of mass space expanding. This gives a noddy level understanding of gravity and dark energy, it also helps when viewing red/blue shift near gravity wells if the 3 dimensional medium the light is oscillating through is moving.

2 FACTS: Space time can be said to be the multi dimensional framework within which we locate events and describe the relationships between them in terms of space and time. The concept of space time follows from the observation that the speed of light is invariant. The equations of GR describe gravity as simply geometry which is altered in the presence of mass. Space time can be warped, twisted curved, and have gravitational waves. We observe distant galaxies and stars lensed by the geometry and curvature of space time.

How and why spacetime curvature isn't considered in relativity. BUT for a noddy level appreciation of space time if space is assumed to be a multidimensional membrane or sheet that contracts as it moves towards mass and expands in the absence of mass. I find it helps to explain time dilation, and Muon lifetimes, and many other effects of space time, including Gravitational lensing, and frame dragging for example. If you add to this the general statement that quantum fluctuations are the cause of the expansion and contraction of the membrane of space, and possibly include an additional dimension to explain the effects of non locality and entanglement. Then I suspect you have a basic idea of the Hows and Whys of space time.  One does not need to focus on the type of quantum fluctuation when dealing in generalities such as I have stated here. The theoretical virtual graviton is a spin 2 boson, which is a quantum fluctuation.

Red shift and blue shift of photons is easy to explain using the flowing space concept. I trying to help apologies