# Ives-Stilwell

## Recommended Posts

Above is the Wikipedia Drawing for the Ives-Stilwell test. (I assume there is no copyright problems with taking stuff from Wikipedia.)

I have seen a few (five or six) videos on the Michelson-Morley test that explained the basics either in graphical or simple word form. (I think one of them was by Neil Degrasse Tyson.) Easy to understand. And so, I think I understand the physical makeup of the Michelson-Morley apparatus.

I haven’t had so much luck when looking for easy to understand videos (graphical or verbal) on the physical makeup of the Ives-Stilwell apparatus. Does anyone here know of one? Can anyone here make one? (There is a gap in content on the Internet waiting to be filled.)

Even an easy to understand written description would go a long way in helping me understand what is being claimed in this experiment.

Any help would be greatly appreciated.

I also have two specific questions (based on my limited current Wikipedia level understanding):

1. What are “canal rays”?

2. What is the source of light being used (the sun, a candle)?

Thank you.

##### Share on other sites
Tim88    30

Hi Thales,

I suspect that you think that it's like the Michelson set-up; but it is totally different.

1. the canal rays are explained in the Wikipedia article, inside the very text that accompanies the picture that you copied; and for a more elaborate explanation you should click with your mouse on the blue underlined "Canel rays" text.

2. These hydrogen ions emit light when they return (in flight) to a lower energy state.

##### Share on other sites

Thank you for the response.

Here is what I think I understand so far:

1. There is an additional Doppler shift due to time dilation.

2. This additional Doppler shift is called the “transverse Doppler effect.”

3. Ives-Stilwell is meant to measure the transverse Doppler effect.

3.1 The theoretical idea was to measure the TDE at a right angle.

3.2 Ives-Stilwell figured out how to do this this at a skewed angle.

Do I have the basics correct?

(“Canal rays” are distinct streams of electrons coming out of perforations in the back of the gas filled cathode.)

Above is my drawing of the Ives-Stilwell experiment.

I’m happy to amend it. This is my first attempt at drawing out the Ives-Stilwell experiment (and I don’t know much about the experiment), and so I’m sure I’m way off.

Thank you.

##### Share on other sites
swansont    6208

(“Canal rays” are distinct streams of electrons coming out of perforations in the back of the gas filled cathode.)

Electrons would be cathode rays. Canal/channel rays are positive ions.

##### Share on other sites

Got it. I stand corrected on the distinction between "electrons" and "positive ions" and my incorrect description of the physical layout and physical process of the Ives-Stilwell experiment.

Thank you.

##### Share on other sites

So, does anybody know of a good simple video (History-tv-channel-education-level of a description) explaining the Ives-Stilwell apparatus (as there are simple videos for the Michelson-Morley apparatus)?

Thank you.

##### Share on other sites
Tim88    30

So, does anybody know of a good simple video (History-tv-channel-education-level of a description) explaining the Ives-Stilwell apparatus (as there are simple videos for the Michelson-Morley apparatus)?

Thank you.

I don't know such. However, the basic idea is fairly straightforward. What is called "transverse Doppler" is a misnomer, it's just time dilation. That effect comes on top of the Doppler effect. Wikipedia explains it rather well, the Doppler equations are given; only some info about the set-up is lacking. The basic idea was that one can accurately determine the forward and the backward Doppler shifts, and these relate to each other for a given particle that is going at a certain speed at a given time. But due to time dilation the short wavelengths (high f) are longer than classically expected, and the long wavelengths (low f) are also longer than classically expected. Compared to the Doppler shifted wavelength they are thus both redshifted. And that creates an asymmetry in the frequency shifts that can be measured, as discussed in Wikipedia.

I'll now look up the details of the measurement set-up.

From reading through their paper I got the following understanding of their set-up.

Light coming out of the tube towards the detector consisted of:

- light emitted in the forward direction (to the right in your drawing)

- light emitted in the backward direction but next reflected by the mirror inside the tube.

That mirror is an important element that is lacking in the Wikipedia drawing.

- light from unaccelerated gas

All that light went through the slit (shown in the Wikipedia drawing) and was next focused on the spectrometer's metal-glass grating which reflected the light onto a photographic plate (with again a focusing lens). Thanks to the grating, the image of the slit is split in different bands depending on the emission frequency.

For classical theory there is only Doppler and for each rest frequency line there would be equal distance to the Doppler shifted lines. The deviation from that symmetry is a measure of the time dilation.

Edited by Tim88

##### Share on other sites

I am a visual thinker.

I had read about the Michelson-Morley experiment, but it wasn’t until I saw the graphics towards the end of this video that I felt I understood the basic set up of the physical apparatus.

---

Tim88:

“What is called "transverse Doppler" is a misnomer, it's just time dilation. That effect comes on top of the Doppler effect.”

In post #3, I wrote:

“1. There is an additional Doppler shift due to time dilation.

2. This additional Doppler shift is called the “transverse Doppler effect.””

And so, it looks like I got that part right!?! The only difference in logic between your three sentences and my two points is that I simply label the time dilation addition (via the intermediary step of time dilation = additional Doppler shift) as “transverse Doppler effect” while you judge this label, and judge it as negative, in addition to what I’ve said.

I got the above right, right? No?

---

Tim88:

“… only some info about the set-up is lacking.”

For me this is not an aside.

I skimmed over the Wikipedia article again, looking at its drawings and looking for written descriptions of its physical make up, but I couldn’t find much.

Thank you for responding Tim88, and thank you for considering my problem.

For me to understand Ives-Stilwell, for me to understand the mechanics of it, I see to first be able to see a picture of it in my mind. That’s me and how my mind works.

---

This picture is from: http://www.mrelativity.net/MBriefs/Ives_Stilwell_Exp_Flawed_P2.htm (After finding the picture on Google Image Search I then read the opening paragraph on his web page and it has something to do with replacing Einstein with something else. I don’t know about any of that. His drawing seemed better than the other drawings in Google, to me, someone who doesn’t yet understand this experiment, just from a visual simple perspective, and so that’s why I posted it here. Maybe it will help with this discussion.)

This is the original drawing from the 1938 Journal of the Optical Society of America Ives-Stilwell article. (http://spiff.rit.edu/classes/phys314/lectures/doppler/doppler.html)

---

Tim88:

“The basic idea was that one can accurately determine the forward and the backward Doppler shifts”

“- light emitted in the forward direction (to the right in your drawing)

- light emitted in the backward direction but next reflected by the mirror inside the tube.”

I am missing from my drawing (and my description). This is my new drawing:

Tim88:

“That mirror is an important element that is lacking in the Wikipedia drawing.”

In the Einstein-denier’s drawing there is a graphical element labeled “mirror” and in the original drawing, near “C” or perhaps labeled as part of “C”, there is also something that could be a mirror in this same place. I took a shot at it and put a “mirror” into my drawing based on these other two drawings. Please let me know if, in my drawing, it is misplaced or if it misrepresents the setup of the apparatus.

---

Tim88:

“All that light went through the slit (shown in the Wikipedia drawing) and was next focused on the spectrometer's metal-glass grating which reflected the light onto a photographic plate (with again a focusing lens). Thanks to the grating, the image of the slit is split in different bands depending on the emission frequency.”

I put a similar diagonal line with a gap in the middle as used in Wikipedia which I believe must represent the “slit” in the “grate,” but I’m not sure so I didn’t label it in the drawing (yet).

&

I need to go understand how a spectrometer works before I change “detector” to “spectrometer” in my drawing (assuming that’s one of the things I need to change). I understand that the broken diagonal line in the Wikipedia drawing is necessary and will include it but I first need to understand what the detector is doing before, I think, I can then go on to understand what the “slit” and what the “grating” are doing.

(It’s interesting that the Einstein-denier’s drawing and the original drawing do not include a spectrograph. But, maybe, when I understand this experiment better, this won’t seem interesting at all.)

---

“The basic idea was that one can accurately determine the forward and the backward Doppler shifts, and these relate to each other for a given particle that is going at a certain speed at a given time. But due to time dilation the short wavelengths (high f) are longer than classically expected, and the long wavelengths (low f) are also longer than classically expected. Compared to the Doppler shifted wavelength they are thus both redshifted. And that creates an asymmetry in the frequency shifts that can be measured, as discussed in Wikipedia.

I'll now look up the details of the measurement set-up.”

&

“For classical theory there is only Doppler and for each rest frequency line there would be equal distance to the Doppler shifted lines. The deviation from that symmetry is a measure of the time dilation.”

I don’t understand (yet), but I believe I will be able to understand once I have a picture of the physical device, and the physical process within that device, in my head.

---

Question for you both:

Is the “light emitted in the backward direction” [Time88] also “canal/channel rays” (distinct streams of “positive ions” [swansont]) or have the distinct streams started to diffuse?

Or does my very question demonstrate a misunderstanding of some basic physics?

And please tell me if I need to change my drawing.

Thank you both.

##### Share on other sites
Tim88    30

I am a visual thinker.

I had read about the Michelson-Morley experiment, but it wasn’t until I saw the graphics towards the end of this video that I felt I understood the basic set up of the physical apparatus.

---

Tim88:

“What is called "transverse Doppler" is a misnomer, it's just time dilation. That effect comes on top of the Doppler effect.”

In post #3, I wrote:

“1. There is an additional Doppler shift due to time dilation.

2. This additional Doppler shift is called the “transverse Doppler effect.””

And so, it looks like I got that part right!?! The only difference in logic between your three sentences and my two points is that I simply label the time dilation addition (via the intermediary step of time dilation = additional Doppler shift) as “transverse Doppler effect” while you judge this label, and judge it as negative, in addition to what I’ve said.

I got the above right, right? No?

---

Tim88:

“… only some info about the set-up is lacking.”

For me this is not an aside.

[..]

For me to understand Ives-Stilwell, for me to understand the mechanics of it, I see to first be able to see a picture of it in my mind. That’s me and how my mind works.

Yes, you got that right, but it seems that you missed the connection between what you want to know and what I told you:

- Doppler is functionally not to be confounded with time dilation. That's indeed not directly a visual issue, but it's a conceptual one and you immediately are confronted with it visually if you include drawing the light waves in the picture of the set-up. Then you automatically distinguish between Doppler and time dilation, for Doppler is what happens due to reducing or increasing the number of waves "in flight" and has nothing to do with a difference in frequency standards, while time dilation is just the inverse. Time dilation is independent of direction, contrary to Doppler. It's even that difference of causal principle that is at the heart of the measurement.

- There is nothing "transverse" going on in this set-up, as both directions of observation are approximately parallel to the direction of ion motion. Again it's essential to know that in order to make a correct sketch.

Accurate labeling is therefore helpful for correct visualizing!

More later.

Edited by Tim88

##### Share on other sites
Mordred    886

Just to add one detail to Tim's post. You have three types of redshift. Doppler, gravitational redshift and cosmological redshift.

Out of these three types gravitational redshift is directly related to time dilation while the other aren't.

The first is directional movement, the second is gravitational potential differences. The third is an expanding contracting volume.

Edited by Mordred

##### Share on other sites
Tim88    30

I find the drawings a bit difficult to read, but it looks to me that the mirror is placed somewhat next to the channel rays. Alternatively it could be a mirror with a hole to let the rays through. Essential is to understand, once more (both Swanson T and I mentioned this) that the channel rays are hydrogen ions. They emit light in all directions. These ions are treated as microscopic clocks, as they emit light at precise frequencies (wavelengths).

It's the light from the moving ions that is measured, and it's necessary to let them pass the mirror so that one can reflect the backward sent light forward.

For spectroscopy, see:

https://en.wikipedia.org/wiki/Spectrometer#Optical_spectrometer

and the link from there: https://en.wikipedia.org/wiki/Diffraction_grating

##### Share on other sites

Tim88:

“It's the light from the moving ions that is measured, and it's necessary to let them pass the mirror so that one can reflect the backward sent light forward.”

Ah hah! All this time I was thinking the mirror was facing away from the spectrometer when it is facing the spectrometer. Progress.

I didn’t notice before the arrows in the Einstein’s denier’s drawing. He has a double headed arrow between the spectrometer and the mirror and he has another arrow pointing from the mirror to the spectrometer.

Here is my current, abstract, simple, understand of the Ives-Stilwell setup:

“Alternatively it could be a mirror with a hole to let the rays through.” – Tim88

I’m guessing the Einstein-denier’s double headed arrow might be misleading in that it looks like it originates at the mirror when it more likely originates at the source (line a).

After encountering the spectrometer, it then moves back to the mirror (line b).

And then it is reflected back by the mirror (line c).

Is this right? No?

---

Tim88, you have given me a lot of good information, that I need to, want to, respond to, but I’m not there yet. I don’t even understand the basic physical layout and movement. (And thanks for starting to answer my last question of diffusion, and thanks for the spectrometer link.)

---

This is from Wikipedia, and this this aspect of the “mirror” seems like, down the line of this discussion, it will be really important to understand:

“Ives and Stilwell used a concave mirror that allowed them to simultaneously observe a nearly longitudinal direct beam (blue) and its reflected image (red).”

---

Thank you all.

And, if you have the time, please let me know if my “lines” are getting closer (or further) from what this setup is all about?

##### Share on other sites
zztop    11

In the Einstein-denier’s drawing there is a graphical element labeled “mirror” and in the original drawing, near “C” or perhaps labeled as part of “C”, there is also something that could be a mirror in this same place. I took a shot at it and put a “mirror” into my drawing based on these other two drawings. Please let me know if, in my drawing, it is misplaced or if it misrepresents the setup of the apparatus.

---

The author of the paper (the owner of the Mrelativity website) is a well known crackpot, you can ignore what he's saying.

The IS experiment is brilliantly simple:

-the ions emit light DIRECTLY towards the receiver with frequency $f_s$

-the light arrives redshifted at the receiver:

$f_s=\gamma f_r (1-\frac{v}{c} cos \alpha_r)$

-the ions also emit light AWAY from the receiver, towards a mirror located at the opposite end from the receiver in the cathode tube that emitted the ions in the first place

-the light is reflected by the mirror and arrives at the receiver blueshifted:

$f_s=\gamma f_b (1-\frac{v}{c} cos \alpha_b)=\gamma f_b (1+\frac{v}{c} cos \alpha_r)$

because $\alpha_b=\pi-\alpha_r$ (the beams are anti-parallel)

The experimenters measure $f_r, f_b$. From the measurements, they determine the transverse Doppler effect as the part of the shift that is direction independent, by simply taking the average of the two measured frequencies:

$\frac{f_r+f_b}{2}=\frac{f_s}{\gamma}$

It is a brilliant experiment. The person suggesting it was........Einstein.

51 years later (!), there was a DIRECT test of transverse Doppler effect:

Hasselkamp et al., Z. Physik A289 (1989), pg 151.

Edited by zztop

##### Share on other sites
Strange    2479

PS: I do not know why Latex is not working

This site requires the tag [ latex] rather than [tex]: $\frac{f_r+f_b}{2}=\gamma f_s$

• 1

##### Share on other sites

Line a:

“-the ions emit light DIRECTLY towards the receiver”

“-the light arrives redshifted at the receiver:”

Line b:

“-the ions also emit light AWAY from the receiver, towards a mirror located at the opposite end from the receiver in the cathode tube that emitted the ions in the first place”

Line c:

“-the light is reflected by the mirror and arrives at the receiver blueshifted”

Correct? Am I correct so far? (I realize there are things missing from my drawing right now, like the interaction with the grating, but first things first.)

---

You might really think I’m dumb when I ask this question, but I’ve reread the Wikipedia article, and I still don’t know what physical element is “in motion” in this experiment in order for there to be “time dilation due to relative motion.”

I assume the container of gas itself is not in motion. Or is it?

Is it the moving ions themselves that are the “moving” element?

I don’t know.

Thank you for helping me.

(zztop, I realize I only address a fraction of what you responded with. Thank you for all of the information. I will need to work through it all. Right now, I’m just trying to figure out the very basic basics.)

##### Share on other sites
zztop    11

Line a:

“-the ions emit light DIRECTLY towards the receiver”

“-the light arrives redshifted at the receiver:”

Line b:

“-the ions also emit light AWAY from the receiver, towards a mirror located at the opposite end from the receiver in the cathode tube that emitted the ions in the first place”

Line c:

“-the light is reflected by the mirror and arrives at the receiver blueshifted”

Correct? Am I correct so far? (I realize there are things missing from my drawing right now, like the interaction with the grating, but first things first.)

correct

You might really think I’m dumb when I ask this question, but I’ve reread the Wikipedia article, and I still don’t know what physical element is “in motion” in this experiment in order for there to be “time dilation due to relative motion.”

I assume the container of gas itself is not in motion. Or is it?

Is it the moving ions themselves that are the “moving” element?

I don’t know.

Thank you for helping me.

(zztop, I realize I only address a fraction of what you responded with. Thank you for all of the information. I will need to work through it all. Right now, I’m just trying to figure out the very basic basics.)

The "moving element" is the light emitting ions. (the wiki article is terrible)

Edited by zztop

##### Share on other sites

zztop,I reread post #13, and if I’m reading it correctly now, that means I misread it before. This is what I’m now thinking. Please correct me where I’m wrong.

---

Positive ions move from the gas filled cathode towards the spectrometer.

The ions emit electromagnetic waves (light). Some of these move towards the spectrometer. And some of these move in the other direction towards the mirror.

The waves that have come directly from the moving ion (the waves that were emitted in the same direction as the moving ion) arrive at the spectrometer red shifted.

And the waves that first bounce off of the mirror (the waves that were emitted in the opposite direction as the moving ion) arrive at the spectrometer blue shifted.

The amounts of red and blue shift are measured and compared.

The amount of red and blue shift from the Doppler effect from the velocity of the moving source can be calculated.

If this calculated amount is removed from the measured amounts, then what we are left with is the amount of additional red shift due to relativistic time dilation.

---

Do I have this right?

And thank all of you for helping me with my problem.

##### Share on other sites
zztop    11

zztop,I reread post #13, and if I’m reading it correctly now, that means I misread it before. This is what I’m now thinking. Please correct me where I’m wrong.

---

Positive ions move from the gas filled cathode towards the spectrometer.

The ions emit electromagnetic waves (light). Some of these move towards the spectrometer. And some of these move in the other direction towards the mirror.

The waves that have come directly from the moving ion (the waves that were emitted in the same direction as the moving ion) arrive at the spectrometer red shifted.

And the waves that first bounce off of the mirror (the waves that were emitted in the opposite direction as the moving ion) arrive at the spectrometer blue shifted.

The amounts of red and blue shift are measured and compared.

The amount of red and blue shift from the Doppler effect from the velocity of the moving source can be calculated.

If this calculated amount is removed from the measured amounts, then what we are left with is the amount of additional red shift due to relativistic time dilation.

---

Do I have this right?

And thank all of you for helping me with my problem.

You have it right

##### Share on other sites

Cool. More progress.

Okay, in my drawings the grate and the spectrograph are left pretty much untouched/unexplained. I want to get to their description, but I still have a question about what has been said up to this point.

I have a question about what is in my drawings in post #17:

I show the light coming from the ion and to the receiver as red-shifted and I show the light coming from the ion and to the mirror (and then to the receiver) as blue-shifted. But shouldn’t it be the other way around?

Shouldn’t it be that the light coming from the ion and moving in the same direction as the ion is blue-shifted and the light coming from the ion and moving in the opposite direction as the ion is red-shifted? No?

Thank you!

##### Share on other sites
zztop    11

Cool. More progress.

Okay, in my drawings the grate and the spectrograph are left pretty much untouched/unexplained. I want to get to their description, but I still have a question about what has been said up to this point.

I have a question about what is in my drawings in post #17:

I show the light coming from the ion and to the receiver as red-shifted and I show the light coming from the ion and to the mirror (and then to the receiver) as blue-shifted. But shouldn’t it be the other way around?

Shouldn’t it be that the light coming from the ion and moving in the same direction as the ion is blue-shifted and the light coming from the ion and moving in the opposite direction as the ion is red-shifted? No?

Thank you!

It is correct the way you have it. Let me explain:

1. Light coming directly from the ion is redshifted because the source (the ion) is moving AWAY from the receiver

2. Light going into the mirror has the same frequency as the light reflected from the mirror (due to the energy conservation). So, light reflected by the mirror into the receiver is blueshifted because the source (the ion) is moving TOWARD the mirror.

The IS experiment is a very clever one.

##### Share on other sites

zztop:

This is my current drawing:

In my drawing the positive ion moves from the container on the left to the spectrometer on the right.

However, you said:

“1. Light coming directly from the ion is redshifted because the source (the ion) is moving AWAY from the receiver

2. Light going into the mirror has the same frequency as the light reflected from the mirror (due to the energy conservation). So, light reflected by the mirror into the receiver is blueshifted because the source (the ion) is moving TOWARD the mirror.”

And so I’ve changed my drawing:

(I changed the arrow on the moving ion from left to right to right to left)

Is this now right?

If so, then this clears up my red-shift/blue-shift confusion. Cool.

But, then … if this is correct … my basic understanding that the ion comes out of the container of gas … and so would then move from left to right is all askew.

My question (simple, like all of my previous ones): how does the ion end up moving from right to left? (This is so simple, I know it must be dumb.)

Thank you.

##### Share on other sites
zztop    11

zztop:

This is my current drawing:

In my drawing the positive ion moves from the container on the left to the spectrometer on the right.

However, you said:

“1. Light coming directly from the ion is redshifted because the source (the ion) is moving AWAY from the receiver

2. Light going into the mirror has the same frequency as the light reflected from the mirror (due to the energy conservation). So, light reflected by the mirror into the receiver is blueshifted because the source (the ion) is moving TOWARD the mirror.”

And so I’ve changed my drawing:

(I changed the arrow on the moving ion from left to right to right to left)

Is this now right?

If so, then this clears up my red-shift/blue-shift confusion. Cool.

But, then … if this is correct … my basic understanding that the ion comes out of the container of gas … and so would then move from left to right is all askew.

My question (simple, like all of my previous ones): how does the ion end up moving from right to left? (This is so simple, I know it must be dumb.)

Thank you.

The ions are accelerated by a very strong electrostatic potential (of the order of 50000V)

##### Share on other sites

Okay.

I think I'm starting to get it.

Thank you all for helping me out!

##### Share on other sites
zztop    11

Okay.

I think I'm starting to get it.

Thank you all for helping me out!

you are welcome

##### Share on other sites

This thread ended a long time ago.

But I found a page that includes a pretty good description of what is physically happening in the Ives-Stilwell experiment.

http://spiff.rit.edu/classes/phys314/lectures/doppler/doppler.html

And so I figured I'd post it here if anyone is interested.

Cheers!