# Thread: How should we describe the gravitational redshift effect?

1. Established Member
Join Date
Apr 2004
Posts
588
I'm with Van.

2. Order of Kilopi
Join Date
Nov 2002
Posts
6,235
[quote="Sam5"]
Originally Posted by Van Rijn

Ok, I’m still thinking about your thought experiment. In the mean time, let’s see what Tensor, Sean, and Ricimer think about it. I’m trying to work on a solution now.
I can wait.

3. Order of Kilopi
Join Date
Nov 2003
Posts
6,197
Originally Posted by Ricimer
I'm with Van.

4. Established Member
Join Date
Apr 2004
Posts
588
take your time. I'm quick about it, cause I've been trained to think about such things (and all the physics behind it).

5. Order of Kilopi
Join Date
Nov 2003
Posts
6,197
Originally Posted by Tensor
Originally Posted by Sam5
Originally Posted by Van Rijn

Ok, I’m still thinking about your thought experiment. In the mean time, let’s see what Tensor, Sean, and Ricimer think about it. I’m trying to work on a solution now.
I can wait.

6. Order of Kilopi
Join Date
Nov 2003
Posts
6,197
Van,

Ok, I’m tending to lean in the direction of your solution being correct.

7. Originally Posted by Sam5
Plus you’ve got to consider what is going on inside the eye cones as the observer changes altitude. They are made up of atoms too, and of course they would oscillate more slowly at the bottom than at the top of the tower.
Gosh Sam5, it almost sounds like you're saying that this slowing down of atomic clocks affects everything, almost as if time slows down itself!

You never answered my question about whether or not you think that space is just flat, 3D Euclidean like. The reason I ask this is because, so far, all you've done is argue for a one particular description of gravitational redshift over another with no mention of how the two could be experimentally differentiated. But you have often made remarks about people "mystifying" it with spacetime descriptions. If you really believe that space is flat, then it is more than just a difference in description. You would, presumably, have your own account of Mercury's orbit for instance, given that you don't believe the warped spacetime explanation.

8. Order of Kilopi
Join Date
Nov 2003
Posts
6,197
Originally Posted by worzel
Originally Posted by Sam5
Plus you’ve got to consider what is going on inside the eye cones as the observer changes altitude. They are made up of atoms too, and of course they would oscillate more slowly at the bottom than at the top of the tower.
Gosh Sam5, it almost sounds like you're saying that this slowing down of atomic clocks affects everything, almost as if time slows down itself!
Hey, get out of here, boy! These guys want to talk in term of “time dilation” so I figure I’ll speak their language. If an atom slows down its oscillation rate in a gravity field, that can also be described in plain ol’ classical terms too. If you slow down your photongraph record the sound waves emitted will be lower. I call it tomAto and you call it tomaaahto.

Edit:
*Note to young whippersnappers: A “phonograph” is what we old-timers used before we had CDs. Back in our day, CD meant “Civil Defense”.

9. Originally Posted by worzel
Originally Posted by Sam5
Plus you’ve got to consider what is going on inside the eye cones as the observer changes altitude. They are made up of atoms too, and of course they would oscillate more slowly at the bottom than at the top of the tower.
Gosh Sam5, it almost sounds like you're saying that this slowing down of atomic clocks affects everything, almost as if time slows down itself!
Originally Posted by Sam5
Hey, get out of here, boy! These guys want to talk in term of “time dilation” so I figure I’ll speak their language. If an atom slows down its oscillation rate in a gravity field, that can also be described in plain ol’ classical terms too. If you slow down your photongraph record the sound waves emitted will be lower. I call it tomAto and you call it tomaaahto.
Well, a serious question is actually whether you think this effect is limited to atoms. For example, when we observe spectral lines in the Sun's light, those are caused by atomic transitions, with the frequency governed by the electromagnetic force between the nucleus and the outer electrons. On the other hand, in Pund and Rebka's experiment, their "clocks" were actually nuclear rather than atomic. That is, they were looking at gamma rays emitted from the nuclei of atoms, so in that case the frequency of the radiation is controlled by the energy levels of the nucleus, which is bound instead by the strong force. So these two types of interactions actually have nothing to do with each other as far as the mechanisms involved are concerned. Yet it's interesting that in both cases, the change in frequency is given by the same relationship from general relativity, so the amount that a nuclear "clock" is slowed is precisely the same as the amount an atomic "clock" is slowed.

10. Originally Posted by Sam5
Originally Posted by worzel
Originally Posted by Sam5
Plus you’ve got to consider what is going on inside the eye cones as the observer changes altitude. They are made up of atoms too, and of course they would oscillate more slowly at the bottom than at the top of the tower.
Gosh Sam5, it almost sounds like you're saying that this slowing down of atomic clocks affects everything, almost as if time slows down itself!
Hey, get out of here, boy! These guys want to talk in term of “time dilation” so I figure I’ll speak their language. If an atom slows down its oscillation rate in a gravity field, that can also be described in plain ol’ classical terms too. If you slow down your photongraph record the sound waves emitted will be lower. I call it tomAto and you call it tomaaahto.
You are, as ever, as clear as mud. One the one hand it is just a case of tomAtoes verses tomaaahtoes, and yet on the other, time dialation is somehow analogous to paying your 45 at 33. And apologies if it was a stupid one, but you still didn't answer my question.

11. Order of Kilopi
Join Date
Nov 2003
Posts
6,197
Originally Posted by Grey

Well, a serious question is actually whether you think this effect is limited to atoms. For example, when we observe spectral lines in the Sun's light, those are caused by atomic transitions, with the frequency governed by the electromagnetic force between the nucleus and the outer electrons. On the other hand, in Pund and Rebka's experiment, their "clocks" were actually nuclear rather than atomic. That is, they were looking at gamma rays emitted from the nuclei of atoms, so in that case the frequency of the radiation is controlled by the energy levels of the nucleus, which is bound instead by the strong force. So these two types of interactions actually have nothing to do with each other as far as the mechanisms involved are concerned. Yet it's interesting that in both cases, the change in frequency is given by the same relationship from general relativity, so the amount that a nuclear "clock" is slowed is precisely the same as the amount an atomic "clock" is slowed.

Interesting, thanks for the description.

12. Established Member
Join Date
Mar 2005
Posts
290
Originally Posted by Grey
Well, a serious question is actually whether you think this effect is limited to atoms.
Another question is whether we think the effect depends on the gravitational forces being experienced by the atom/nucleus. Here is a thought experiment, and we can try the two explanations Sam5 has provided. Unfortunately, I can't think of a good way to conduct the experiment in reality.

Imagine something emitting photons at a constant frequency. It could be from electrons dropping through well defined energy levels in an atom or it could be from well defined excitation states of a nucleus.

Suppose we place such an emitter somewhere in a very high Earth orbit, and we also place an identical emitter at the center of the Earth, or in the center of any shell of matter, with a little hole for the photons to get out.

The total gravitational force experienced at the center of the Earth, or in the high orbit, is zero.

The photons emitted from the center of the Earth are then received in the high orbit, and compared with the photons produced by an identical emitter in orbit.

• Question 1. Will the photons from the center of the Earth will be redshifted?

I think they will be redshifted. I guess Sam5 might agree. I know Grey will agree.

There are two explanations for this. The one I prefer goes as follows:

• Explanation 1: We can calculate the time dilation of the emitter with respect to the receiver by applying relativity and considering paths from the emitter to the receiver. The emitter is running in exactly the same way as it does anywhere else, producing photons of a fixed characteristic frequency at the emitter. Due to differences in the passage of time at the emitter, and at the receiver, this frequency relative to the receiver is lower: a redshift. The receiver observes the photons with this redshift arising from time dilation.

Some other people here prefer a different explanation, which really corresponds to using a different co-ordinate system in GR.

• Explanation 2: The emitter is running in exactly the same way as it does anywhere else, producing photons of a fixed characteristic frequency at the emitter. As the photons travel from the emitter to the receiver, up through the gravitational field, they lose energy and their frequency drops. By the time they arrive at the receiver, they have the redshift that we can calculate by GR.

My preference for the first explanation is subjective. The second explanation is not really wrong. I'm inclined to think it can lead to confusions; but this thread has certainly shown me that the first explanation can lead to confusions as well! In any case, GR comes with the tools and techniques for mapping between co-ordinate systems, and giving a precise transformation from one explanation into the other.

Now as I understand the matter, Sam5 has a third explanation. However, I am not sure that Sam5 would agree, and he is welcome to correct my understanding of his position. The following explanation is my own wording, not that of Sam5.

• Explanation 3. The emitter actually behaves differently when at the center of the Earth, and the photons emitted have a different frequency. This frequency corresponds to the redshift seen by the observer.

Sam5 may confirm this, or not. If he confirms it, there is a problem… what physical laws can be used to calculate the emitter frequency? What are the variables involved? The emitter is weightless in both cases, so it can’t simply be the force experienced.

Cheers -- Sylas

13. Originally Posted by Sam5
Originally Posted by Tensor
Originally Posted by Sam5
The question is, in a strong gravity field, where they oscillate more slowly, do they emit light of a lower frequency than the frequency of light they emit in a weaker gravity field? I say yes they do. And I believe the original gravitational redshift theory says “yes” they do.
Sam5, I really don't see a problem with you looking at it this way, for a single observer. However, the problem with this view is if you have two different observers, at two different heights, each will see a different frequency. The higher the observer (the lower the gravity), the more of a red shift they will see. In this case, it's easier (at least for me) to think of it as a wavelegth getting longer as the light climbs out of the higher gravity, which is the same as losing energy.
Well, it seems to me that if you say the wavelength gets longer as the light climbs out of the gravity field, that seems like a “tired light” theory, and if we admit to a tired light theory then that leaves open the tired light theory of the redshifts of the distant galaxies.
Except that the typical "tired light" theories assume that light is losing energy due to some interaction, not because it was emitted in a gravitational potential different form the observer.

Originally Posted by Sam5
In other words someone could say that the galaxies are fixed relative to us, and are not moving, but the light from them just gradually redshifts as it moves toward us over long distances, and the further the distances the more it redshifts.

And also, your approach would assume that the light is emitted at a normal standard frequency, even though the oscillation rate of the atoms is slowed down in a gravity field.
The emission of light is not due to oscillations.
Are you confusing emission of light with old-type atomic clocks?
Emission of light comes from electrons changing between states with different energy.
Old-type atomic clocks used molecules where one atom oscillates between two positions.

The gravitational red-shift is observed over the whole range of frequencies for EM emission, even those that have nothing to do with "atomic lock oscillation rates" or electronic transitions.
The tower experiment used gamma-radiation, which is produced by nuclear transitions in radioactive Fe nuclei (nothing to do with electrons).

Originally Posted by Sam5
Well, what if the oscillation of the atoms stops under certain conditions, such as inside a black hole. Will it continue to emit light of a “normal” frequency even though it has stopped oscillating?
Yep, you are confused.

Originally Posted by Sam5
The best explanation I’ve seen for this is what Steinmetz wrote about it: “every incandescent hydrogen atom, for instance, is an accurate clock, vibrating at rate definitely fixed by the electrical constants of the hydrogen atom and showing us the exact rate of its vibration in the spectroscope by the wave length or frequency of its spectrum lines. Thus in a strong gravitational field the frequency of luminous vibrations of the atoms should be found slowed down; in other words, the spectrum lines should be shifted towards the red end of the spectrum.”

Of course I could be wrong about this, but I don’t think so, and there are a few physicists who have written papers about this and a couple of university physics department websites that agree with my point of view that the light is emitted from a slowly oscillating atom at a lower frequency and at a higher frequency from a more rapidly oscillating atom.
The light emitted is not the result of pendulum-like oscillations in atoms.
And the effect is not restricted to light.

14. Member
Join Date
Feb 2005
Posts
97
Originally Posted by Sam5
But that doesn’t mean your biological clock has “slowed down” the same amount at sea level
I think this is your fundamental misunderstanding. (We *are* talking GR here, right, not some sort of against-the-mainstream modification?)

15. Originally Posted by jnik
Originally Posted by Sam5
But that doesn’t mean your biological clock has “slowed down” the same amount at sea level
I think this is your fundamental misunderstanding. (We *are* talking GR here, right, not some sort of against-the-mainstream modification?)
Most of us are talking about GR. Sam5's talking about some sort of against-the-mainstream modification.

16. Order of Kilopi
Join Date
Nov 2003
Posts
6,197
Originally Posted by jnik
Originally Posted by Sam5
But that doesn’t mean your biological clock has “slowed down” the same amount at sea level
I think this is your fundamental misunderstanding. (We *are* talking GR here, right, not some sort of against-the-mainstream modification?)

Well, there was a brief discussion about biological time (thermodynamic time) on this board a couple of weeks ago:
HERE.

From the CNN source, (here):

“It works, essentially, like hypothermia. Recall those miraculous cases of people who fall into icy ponds and appear dead but recover after they're warmed up? The extreme cold preserves their brain cells from the certain death that would otherwise quickly follow oxygen deprivation.

---

Within minutes of inhaling the gas, the mice appeared unconscious. Their body temperature plummeted from the normal 98 degrees down to 59 degrees and their respiration slowed to fewer than 10 breaths a minute, down from a normal 120 breaths a minute, Roth reported.

Overall, their metabolic rate dropped by 90 percent -- meaning normal cellular activity slowed to almost a standstill, thus reducing the need for oxygen.”

I brought this very subject up here more than a year ago, and I tried to explain how it works. Some people might remember my “frozen embryo” posts. But the SR and GR relativists here didn’t like the idea since Einstein never mentioned it, so I just dropped the subject. You might want to look it up in biology books.

This basic idea is still ATM in the field of physics, but it has been very mainstream in the field of biology for many decades.

17. Weeks? Seems to me it's been years since you first brought up cryogenics in a relativity-related discussion on this BB.

And after all this time, you still don't understand that it's got nothing to do with it. Absolutely nothing.

18. Order of Kilopi
Join Date
Nov 2003
Posts
6,197
Originally Posted by SeanF
And after all this time, you still don't understand that it's got nothing to do with it. Absolutely nothing.
Actually, I think it was a “time” related thread. I tried to explain the difference between the physics view of time, being mostly based on atomic time, and the biological view of time, being a thermodynamic phenomenon such as explained in the CNN news story. But nobody here seemed interested because Einstein never said much of anything about biological time.

Remember how I tried to explain to you that Hawking was wrong about this, because he was thinking in terms of physics atomic time instead of biological thermodynamic time:

“Newton’s laws of motion put an end to the idea of absolute position in space. The theory of relativity gets rid of absolute time. Consider a pair of twins. Suppose that one twin goes to live on the top of a mountain while the other stays at sea level. The first twin would age faster than the second.”

19. Originally Posted by Sam5
Actually, I think it was a “time” related thread. I tried to explain the difference between the physics view of time, being mostly based on atomic time, and the biological view of time, being a thermodynamic phenomenon such as explained in the CNN news story. But nobody here seemed interested because Einstein never said much of anything about biological time.
A slowing down of biological time, as you call it, is a process actually slowing down. That is, the process takes longer. Time dilation in relativity is the slowing of time itself in one frame as viewed from another. You can measure the former in its own frame. You cannot measure the latter in your own frame, indeed the concept of time dilation in your own frame has no meaning.

You obviously don't believe this, and think instead that time dilation is just the slowing down of some atomic process, but that is not what relativity says. If you accept that the speed of light is c in all intertial frames (and not just "appears to be") then how do you explain that without length contraction and time dilation?

20. Originally Posted by Sam5
Actually, I think it was a “time” related thread. I tried to explain the difference between the physics view of time, being mostly based on atomic time, ...
Please, do not confuse metrology with physics.
Metrology searches for standards of units, and having good standards does help.

Originally Posted by Sam5
... and the biological view of time, being a thermodynamic phenomenon such as explained in the CNN news story. But nobody here seemed interested because Einstein never said much of anything about biological time.
If biological time is based on thermodynamics, it is already included in physics.
When we say in Relativity that time slows down, it affects every physical process, including thermodynamic ones.

21. Order of Kilopi
Join Date
Nov 2003
Posts
6,197
Originally Posted by papageno
When we say in Relativity that time slows down, it affects every physical process, including thermodynamic ones.
So both of the two relatively moving twins in SR see each other freeze?

22. Order of Kilopi
Join Date
Nov 2003
Posts
6,197
Originally Posted by worzel
Originally Posted by Sam5
Actually, I think it was a “time” related thread. I tried to explain the difference between the physics view of time, being mostly based on atomic time, and the biological view of time, being a thermodynamic phenomenon such as explained in the CNN news story. But nobody here seemed interested because Einstein never said much of anything about biological time.
A slowing down of biological time, as you call it, is a process actually slowing down. That is, the process takes longer. Time dilation in relativity is the slowing of time itself in one frame as viewed from another. You can measure the former in its own frame. You cannot measure the latter in your own frame, indeed the concept of time dilation in your own frame has no meaning.
Then how can the traveled clock in the “peculiar consequence” thought experiment in the SR theory “lag behind” the “stationary” clock when they unite? Wouldn’t the observer that traveled with the clock that traveled notice, in his own frame, that his own clock “lags behind” the other and therefore ran slow? And wouldn’t he actually notice that the other clock seemed to him to run fast during his travel?

23. Originally Posted by Sam5
Originally Posted by papageno
When we say in Relativity that time slows down, it affects every physical process, including thermodynamic ones.
So both of the two relatively moving twins in SR see each other freeze?
Have a look at this.

24. Originally Posted by Sam5
Then how can the traveled clock in the “peculiar consequence” thought experiment in the SR theory “lag behind” the “stationary” clock when they unite? Wouldn’t the observer that traveled with the clock that traveled notice, in his own frame, that his own clock “lags behind” the other and therefore ran slow? And wouldn’t he actually notice that the other clock seemed to him to run fast during his travel?
The observer who travelled with the clock would not notice that his clock ran slowly, only that the other clock ran fast. The observer who didn't travel would not notice that his clock ran fast, only that the other clock ran slow.

25. Order of Kilopi
Join Date
Nov 2003
Posts
6,197
Originally Posted by worzel
Originally Posted by Sam5
Then how can the traveled clock in the “peculiar consequence” thought experiment in the SR theory “lag behind” the “stationary” clock when they unite? Wouldn’t the observer that traveled with the clock that traveled notice, in his own frame, that his own clock “lags behind” the other and therefore ran slow? And wouldn’t he actually notice that the other clock seemed to him to run fast during his travel?
The observer who travelled with the clock would not notice that his clock ran slowly, only that the other clock ran fast. The observer who didn't travel would not notice that his clock ran fast, only that the other clock ran slow.
No, in SR theory both of two relatively moving observers see each other’s clocks run slow, with no exceptions.

26. Order of Kilopi
Join Date
Nov 2003
Posts
6,197
Originally Posted by papageno

Have a look at this.
I can sum it up more simply. First, just “relative motion” alone can’t slow down any clock. In the original SR theory, all motion is just “relative”, with no gravity or acceleration. All the SR stories about a traveling twin “aging more slowly” than a twin that “stays at home” is a lot of hokum, fable, and urban legend. It doesn’t happen. In the SR theory, both clocks are always inside “inertial frames” and the motion between the two clocks is just “relative”.

However, in GR theory, atomic clocks really do slow down in a gravity field and when accelerated, but the slow-down is so slight it can’t possibly ever affect human biological time. If an atomic-time slow-down occurred so much it began to affect human biological time, the human would be crushed to death by the extreme gravity/acceleration long before any biological time dilation effect would be noticed.

On the other hand, biological heat-time metabolism slow-downs are caused by temperature factors over just a slight change in temperature.

27. Originally Posted by Sam5
Originally Posted by papageno
Have a look at this.
I can sum it up more simply. First, just “relative motion” alone can’t slow down any clock.
It is clear now that you do not grasp the concept of frame of reference and observer.

Originally Posted by Sam5
In the original SR theory, all motion is just “relative”, with no gravity or acceleration.
Motion is "relative" also in the "original" Newtonian mechanics...

Originally Posted by Sam5
All the SR stories about a traveling twin “aging more slowly” than a twin that “stays at home” is a lot of hokum, fable, and urban legend. It doesn’t happen. In the SR theory, both clocks are always inside “inertial frames” and the motion between the two clocks is just “relative”.
But the frames of reference do not coincide, which is why transformations of coordinates are needed..

Originally Posted by Sam5
However, in GR theory, atomic clocks really do slow down in a gravity field and when accelerated, but the slow-down is so slight it can’t possibly ever affect human biological time.
I don't remember anybody claiming that it has been observed in biological process in humans. If somebody did, feel free to provide references.
By the way, it does not work only for atomic clocks.

Originally Posted by Sam5
If an atomic-time slow-down occurred so much it began to affect human biological time, the human would be crushed to death by the extreme gravity/acceleration long before any biological time dilation effect would be noticed.
So, it does not mean that it would not happen in principle.

Originally Posted by Sam5
On the other hand, biological heat-time metabolism slow-downs are caused by temperature factors over just a slight change in temperature.
So, what is the point? What does this have to do with gravitational redshift?
Biological processes depend on chemical and thermodynamic processes, which do depend on temperature (thermo-, as in thermometer).
Why did you bring up "biological time"?

28. Order of Kilopi
Join Date
Nov 2003
Posts
6,197
Originally Posted by papageno
Why did you bring up "biological time"?
Because of all the silly thought experiments about “traveling twins” aging more slowly. These are fantasies, sci-fi stories.

29. Originally Posted by Sam5
[Snip!]I can sum it up more simply. First, just “relative motion” alone can’t slow down any clock. In the original SR theory, all motion is just “relative”, with no gravity or acceleration. All the SR stories about a traveling twin “aging more slowly” than a twin that “stays at home” is a lot of hokum, fable, and urban legend. It doesn’t happen. In the SR theory, both clocks are always inside “inertial frames” and the motion between the two clocks is just “relative”.[Snip!]
Sorry, but there are a lot of people at CERN, Fermilab, Brookhaven, Stanford, Dubna, Serpukhov, Hamburg, etc. who see this every day at their particle accelerators. It is no "urban legend". [-(

30. Order of Kilopi
Join Date
Nov 2003
Posts
6,197
Originally Posted by Celestial Mechanic
Sorry, but there are a lot of people at CERN, Fermilab, Brookhaven, Stanford, Dubna, Serpukhov, Hamburg, etc. who see this every day at their particle accelerators. It is no "urban legend". [-(
The keyword in your post is “accelerator”. I’ve already mentioned acceleration effects.

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•