Tensor, since you gave us the brilliant definition of “time” by saying it was the “duration” between “events”, now you can tell us the physical Doppler mechanics of why a moving observer on the rear of a moving train hears a normal pitch of the moving whistle.

And maybe Russ can give us the history of the “atomic clock” concept, starting with Maxwell’s statement about it, going through the Lorentz concept, the Einstein use of “atomic clocks” and the 1938 Ives paper about “atomic clocks”. He told me earlier they were only invented in the 1950s.

Well, Russ, tell us the history of “atomic clocks”. What did Maxwell say about them in 1873? Lorentz in 1895? Einstein in 1907 and 1911? Steinmetz in 1923? Ives in 1938?

You are an expert on this topic, so tell us about the history of the “atomic clock” concept.

'Tone' refers to sound. However, radio signals are not sent as sound waves. They're sent as radio waves which carry the information that your radio uses to tell the speakers how to reproduce the sound. Radio transmitters send electromagnetic waves - not tones.

Actually, 'cycles per second' would have been correct. No nitpicks would have been needed.

Usually, yes. If one of my students wrote that on an assignment you're darned right I'd point it out - it's incorrect grammar and sloppy composition.

Because the observer in the caboose is in the same reference frame as the whistle on the engine and are at rest relative to each other - or if you prefer they're both moving in the same direction at the same speed. The Doppler effect ONLY occurs when you have observers in two different references frames, one of which is in motion relative to the other. In other words, the listener in the caboose won't hear the whistle's pitch change, but the trainspotter sitting near the enbankment will.

They send “tones” coded into the radio waves. I thought everybody knew that already. The radio waves carry the “tone” as a coded signal in the EM waves. The “tone” comes out your speaker on your radio. How difficult is this to understand?

In the radio and television business, a broadcast “tone” is what a test signal is called. It’s like the old CD test tone. Today the weather emergency tone is a kind of squeal. Maybe none of you have ever worked in radio or TV and don’t know the jargon. Maybe the jargon is changed, but what difference does that make. Your are just trying to distract from my description of how the classical Doppler effect works.

Call it “pulses” if you want. A 1,000 Hz pulse sent by radio.

Is the nitpicking night on the board?

And trust me. If I had said "cycles", someone would have complained because I did not say Hz.

Oh Geez! I don’t believe this!

Tell me the PHYSICAL MECHANICAL DOPPLER MECHANISM. What happes in the air, with the waves and the observer. Forget about that “reference frame” Eisnteinian baloney.

You can’t do it, can you? Because you just don’t know how the classical Doppler effect works.


No! There are TWO DIFFERENT TYPES OF DOPPLER EFFECTS AT WORK in the train example. One cancels each other out. What are they? Describe them.

Didn't you learn this in your university physics classes?

What is the interaction then? The gravitational perturbation on the elctrons?

Is the field in question fixed with respect to the earth, or changing with respect to the earth?

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You made a deliberate mistake, so that beginners would be sure to understand?

That's not the same thing as oversimplifying something so that beginners can understand difficult concepts.

Really? Aren't the "atomic clocks" of Maxwell and Lorentz et al imaginary? I mean, they didn't actually build the atomic clocks mentioned in their papers, did they?

Is there anything about the light pulse clock that violates any physical laws? It could, in principle be built, right? People usually do things this way - plan something using the laws of physics, etc. and then build it.

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The classical Doppler is purely kinematic in origin. Why are you talking about a "physical mechanism"?

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"Why waste time learning, when ignorance is instantaneous?" - Hobbes (Calvin and Hobbes)

"It's all about context!" - Vince Noir (The Mighty Boosh)

"I've never heard of such a brutal and shocking injustice that I cared so little about!" - Zapp Brannigan (Futurama)

"...because the logic of the lines traced from reality is as poor of aesthetic value as it is strict in consistency. " - Paolo Bozzi (Naive Physics - free translation)

They didn’t have to build them. They already existed in nature. They were talking about naturally oscillating and glowing atoms. They measured their wavelengths of light by means of a spectroscope and from the known frequency of the light they calculated the oscillation rates of the atoms. They were natural atomic clocks. Haven’t you read the Ives paper, or Maxwell’s treatises on electricity and magnetism?

In Einstein’s 1907 paper, “On the Relativity Principle and the Conclusions Drawn From It,” (“Collected Papers”, paperback Volume 2, page 307), he states,:

“There exist ‘clocks’ that are present at locations of different gravitational potentials and whose rates can be controlled with great precision; these are the producers of spectral lines. It can be concluded from the aforesaid that the wave length of light coming from the sun’s surface, which originates from such a producer, is larger by about one part in two millionth than that of light produced by the same substance on earth.”

In the “light pulse” clock, if the clock is stationary on earth, and a guy drives by it, he is going to see the light pulse go up and down and hit the mirror and the receiver just as the guy on the ground does.

If the observer is stationary with the ground and a guy drives by with a “light pulse” clock, left to right, and if his laser is aimed straight “up”, the pulse will miss the mirror, so he will have to tilt the laser a little to the right so the pulse will hit the mirror. And both guys will see the light pulse travel the same distance, which will be a slightly longer distance than if the guy with the laser were stationary with the ground.

It helps to visualize the classical Doppler effects if you work the mechanics out on graph paper. When the whistle moves through the air, it emits a stretched out sound wave to the rear of the whistle. The wavelength is physically longer as it travels through the air, yet it still travels at the speed of sound in air, about 1,100 fps. So why does the guy riding on the rear of the moving train hear a normal pitch of the longer wave, rather than a redshifted lower pitch?

The rate of the atomic clock is affected by its motion through the earth’s gravity field (Lorentz theory), and it is also affected by its altitude (its distance from the center of the earth) (GR theory).

The classical Doppler effect is as I described it earlier. The “relativistic” Doppler effect is the classical effect plus any real effect on the rate of an atomic clock due to its motion through gravity fields and due to the gravitational potential where it is located.

Of course there are other environmental conditions that can make the rate of an atomic clock unstable, but these are generally not called “relativistic” effects.

I’ve read some papers that say the earth’s gravity field does not rotate with the earth but travels through space with the earth. When the spacecraft reaches a certain distance away from the earth, the sun’s gravity field has more influence on the Lorentz effect than the earth’s field.

Sam, with all this radio talk you're spouting, do you actually know how a radio works? I mean, the whole mechanism of the LRC circuit, resonance frequency, and the like?

If the emitter and the receiver have the same velocity, there is no Doppler effect (the guy on the train is at rest with respect to the whistle, therefore he does not observe a "stretched out" wave).
By the way, one must be careful with Doppler effect: one has to take into account the relative velocity of emitter and receiver and their velocity with respect to the medium. You might get different results for an open train and a closed one.

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"Why waste time learning, when ignorance is instantaneous?" - Hobbes (Calvin and Hobbes)

"It's all about context!" - Vince Noir (The Mighty Boosh)

"I've never heard of such a brutal and shocking injustice that I cared so little about!" - Zapp Brannigan (Futurama)

"...because the logic of the lines traced from reality is as poor of aesthetic value as it is strict in consistency. " - Paolo Bozzi (Naive Physics - free translation)

There are two Doppler effects at work in my example. I am assuming an open car at the end of the train or an open window. The guy hears the whistle through the outside air. One Doppler effect cancels out the other Doppler effect. Describe the mechanics of both of them.

How do you know which one is moving? Two people, A and B, each with a light pulse clock, are moving relative to each other. No tilting of lasers or anything. No other interactions.


A sees the light pulse hit the mirror in his clock. B sees the light pulse hit the mirror in his clock. What happens when they look at the other's clock? According to your explanation above, it sounds like the light misses. How can one person see the pulse hit, and the other sees it miss?

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Hz/s isn’t meaningless—it would measure a rate of change in frequency. That makes this particular misuse a bit worse, as a reader quickly skimming the thread (ie, me) might get confused for a while. It is a bit of a nitpick though.

So, am I right in thinking that classical Doppler does not work out with electromagnetic waves because the propagation speed is constant, c? In a physical system, the wave medium is actually in motion altering the relative propagation speed of the wave, whereas light has no physical medium to move.

The 1kHz tone is carried on a higher frequency carrier wave. If the frequency of the carrier wave changes due to redshifting, the 1kHz tone will be redshifted by the same ratio. So, it is reasonable to say you are transmitting a 1kHz tone, though it does needlessly distract (obviously) from the main argument.

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Not entirely. The speed of any wave, including sound, is a property of the medium through which it travels and is independent of the motion of the source and receiver. In classical terms, one way of measuring motion through a medium is to compare the observed speed of a wave to the known propagation speed of that wave in the medium. An observer who is stationary with respect to the medium (again in classical terms) will see the same propagation speed regardless of the source's motion. An observer in front of a car going 60 mph will not measure the speed of sound from the car's horn as 850 mph (if the speed of sound is 790 mph) in front of the car and 730 mph behind it.

Now light doesn't require a physical medium. Rather its speed is determined by the electromagnetic properties of the vacuum, or of any physical medium it travels through. It differs from sound in that all observers observe it's speed as the same regardless of their motion. Thus you can't determine your motion in relation to some medium (call it aether if you want) by measuring the speed of light. This, in effect is what the null result of the MM experiment showed. This, together with the relativistic effects of time dilation and space contraction, complicate the relativitstic doppler effect although the basic idea is the same. Wavefronts are compressed in front of a moving source (blue shift) and lengthened behind it (red shift). You need relativity to determine the precise value correctly.

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"If it was so, it might be, and if it were so, it would be, but as it isn't, it ain't. That's logic!" - Tweedledee

This isn't right. This isn't even wrong. - Wolfgang Pauli

One of the things that causes confusion about the constancy of c is that light exhibits particle behavior as well as wave behavior. The parallel with sound waves, and the constancy of the speed of sound in air regadless of the motion of the source, works fine when you think of light as strictly a wave phenomenon (and ignore the issue of the observer's speed w/r/t the "ether").

However, the parallel doesn't work at all when you think of light as a stream of photons - or "little bullets". Our intuition, based on everyday experience, tells us those photons should go faster "in front of" a moving source, and slower "behind" it.

That's not a parallel, is it? After all, for light, each observer would measure the same speed. That's not true for sound.
Maybe it doesn't work at all, period.

It is if you read EtaC's original scenario carefully. He's talking about an observer who is stationary with the medium (air), and comparing the speed of sound he measures from a source that's moving (i.e. approaching vs. receding). In that case, the observer would measure the same speed of sound in both cases, but a shift in frequency between the two cases.

However, the restriction that the observer must be stationary w/r/t the medium makes it a limited analogy, since that is not a requirement in SR or GR. Lightspeed is always measured the same, regardless of any motion of observer or source.

Are you kidding? Every night is nitpicking night, here at the BABB. 8)
Yes and no. I'd complain, and will complain even now, that you said "cycles" instead of "cycles per second", when the post to which you were responding was clearly and unambiguously speaking of "cycles per second". You're the only one who wants to bring raw, unadorned "cycles" into it, after bringing up "Herz per second" before.
You don't state that these mirror-bearing spacecraft are moving at the same rate as the transmitting spacecraft, but it would be a reasonable assumption for anyone attempting to learn anything here. So, for their benefit, I'd point out that if they were travelling at the same velocity, Earth would receive first approximately 998 Hz (not per second) as it travels away from Earth, then approximately 1002 Hz on the return trip.
Were it otherwise, you could try to argue your way out of your next speeding ticket by telling the judge that the radar gun manufacturers make radar guns that read twice your actual speed. :wink:

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d 2022,
I'm working on it. He's got a couple of things within his equations that I have no idea why they are there. He has also referenced something near the end that I'm trying to track down. Bear with me.

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I was responding to the "The parallel with sound waves, and the constancy of the speed of sound in air regadless of the motion of the source, works fine" part. It seems to me that the parallel doesn't work fine at all, there.

Are you talking about this?

edited
In the same link the author gives the reason why no ether was detected.
Because than "the test results cannot prove or disprove the existence of an ether... only whether or not the Earth is moving relative to such an ether."
quote:
In essence, what Michelson, Morley, Einstein, and many other scientists have said is that the M-M test showed the velocity of light was not affected by the Earth's orbital motion. "Therefore" they have said, "we have one of two conclusions to draw":

1) The Earth is orbiting the Sun and there is no ether, or,

2) The Earth is not orbiting the Sun and there is an ether but since the earth is not moving through the ether, the ether "wind" cannot be detected. Obviously, this conclusion is negated by Earth's observed helio-centric orbit.

However, their reasoning should also have incorporated a third option:

3) The Earth is orbiting Ihe Sun and so is the ether; therefore, no ether wind could be detected in the orbital vector immediately in the vicinity of Earth.

In other words, the test results cannot prove or disprove the existence of an ether... only whether or not the Earth is moving relative to such an ether.

RELATIVISTS DISCARD EVIDENCE

By the time the ether wind was proven to exist, Einstein's theories were already winning strong support on the merits of celestial observations which closely agreed with Einstein's predicted values. As a result, the scientific community decided to explain the ether wind phenomenon as a result of Earth's spinning in its own ether blanket which Earth was apparently dragging through space. No explanation was ever agreed upon as to the origin or extent of this ether blanket. It was simply a way to sweep a discrepancy under the carpet.

EINSTEIN ADMITS ERROR...
[quote]
In a biography written just before his death, Professor Einstein is quoted as admitting he had a fundamental error in Relativity. It was, he said, one which-when corrected-will explain how light - an obvious wave form - can be propagated across an apparently non-inertial space. Einstein also stated that the discovery of the solution to this error would probably be the result of some serendipitous discovery in the sixties. However, before he died, Einstein did manage to partially correct his error. With the help of the well-known Dr. Erwin Schrödinger, Dr. Einstein was able to construct a 'total theory' for existence. It was called the "Unified Field Theory". Although Dr. Einstein was able to lay the basic framework before his death, it is reasonably certain that a more readily-usable version of the "Unified Field Theory" was only completed by other physicists after Einstein had died.

One of the more promising contributions toward a usable unified field theory was offered by Dr. Stanley Deser and Dr. Richard Arnowitt (see Appendix 4 of The Gravities Situation in Appendix (3) of this book). They took the General Theory of Relativity which Einstein had devised and constructed a "bridge" or "creation tensor" to link the energy of nuclear fields with that of gravitational fields by co-variant matrices. The basic relationship of General Relativity which they used as a basis for their system is:

discuted in your last post above.

Problem: If the ether can't be detected by any experiment we do (we've done thousands, both on and off the surface of the earth), how is it ok to assume it exists? All I keep seeing is that as the various ether theories are proven wrong by new evidence, the theories get more and more convoluted to account for the new evidence. Never is there any positive evidence of an ether, just evidence that doesn't quite rule it out. Its epicycles all over again. What exactly is the evidence that there is an ether?

Remember again: evidence must be positive, ie, if it can be explained without resorting to an ether, it is not evidence for an ether. That's the way science works.

Presumably this ether is also spinning with the earth (so that all spots on the earth surface, whether on the day side or the night side) are motionless with respect to the ether--this is fairly peculiar, as this means that the ether near the earth's surface is moving at much less than earth orbital velocity.

This ether is peculiar stuff. It is apparently orbiting the sun in the plane of the ecliptic in the direction of motion of the planets, so, presumably, as long as the planet had a zero inclination zero eccentricity orbit it would be motionless with respect to the ether (well, provided it was rotating in the same direction as the rest of the planets). It's not too clear what happens outside the ecliptic--is there no ether there? Regardless, planets with measurable eccentricities (such as Mercury) should never be motionless with regard to the ether wind, so MM experiments there should show a positive result. Similarly, interplanetary probes on elliptical orbits (and especially those with highly inclined orbits) should show unexpected shifts in frequency due to their having a non-zero velocity with respect to the ether wind. I haven't worked through the numbers here, but it might be that some of these results would be measurable.

But the ultimate test must be done far away of the vinicity of the Earth based on option 3
3) The Earth is orbiting Ihe Sun and so is the ether; therefore, no ether wind could be detected in the orbital vector immediately in the vicinity of Earth.