Measuring The Relative Velocity Of Light

  1. Anyone attempting to argue the Special Theory of Relativity needs to understand the basics of how light travels, and how we perceive it.


    Einstein wrote that the speed of light does not depend on the speed of the object emitting the light. To prove this, Einstein referred to De Sitter’s observation of the binary stars, which are two stars that are orbiting each other. De Sitter concluded that if the speed of light were dependant on the speed of the star, then the light emitted from the star as it is traveling towards us would eventually catch up to the light that was emitted from the same star when it was traveling away from us.

    That logic is incorrect since relative to the binary stars, they are not moving and we are orbiting the binary stars. By viewing the stars as motionless, it becomes clear that while we orbit the binary stars, we are running into the light of one star as we are running away from the light from the other star. Relative to the binary stars, their light is not approaching us at different speeds; we are approaching the light at different speeds. This proves that the speed of light can be based off the speed of the star without disturbing our perceptual view of the orbits.

    Maxwell stated that all types of light would have a frequency that is inversely proportionate to its wavelength. Einstein believed that an increase in frequency caused by traveling towards the light source would cause an inversely proportionate change in the wavelength. What Maxwell meant was that since all types of light travel from the source at the same speed, than while at rest relative to the source, any light with a high frequency will have a short wavelength, and any light with a low frequency will have a long wavelength since multiplying them together must equal the speed of light. He did not mean that a perceptual change in frequency caused by the observer’s speed would change the wavelength.

    The wavelength of light is not a relative measurement; it is the distance that the light has to travel away from the source in order to complete one wave. That distance is not determined by the observer’s speed, it is the same for all observers traveling at any speed or direction. The frequency of light is a relative measurement; it is the number of wavelengths the observer passes in one second. This number is determined by the speed of the observation and will be different between observers traveling at different speeds relative to the source. The wavelength of light is unaffected by the observers speed, any measured change in wavelength is an error that is caused by not including the distance the observer has traveled relative to the source. When calculating the wavelength, the distance that the light travels from the source in one second must be added to the distance the observer has traveled relative to the source in one second, and then divided by the measured frequency. If the distance the observer has traveled is not included, then the relative speed will never change since the total distance traveled would only include the distance the light has traveled.

    In order to accurately measure the relative speed between two objects, the distance traveled by both objects in the same amount of time must be included. Interferometers and oscilloscopes only account for the distance that the light has traveled, both need to be adjusted to include the distance traveled by the observer relative to the source. An observer using an interferometer moves a mirror a specific amount of distance while counting the number of changes in the pattern of interference fringes. When used to measure wavelengths while in motion relative to the light source, the scale used to measure the distance that the mirror has moved must be adjusted to include the distance the observer has traveled relative to the source. If the observer is traveling towards the source, the same amount of movement of the mirror will represent a larger distance since it now includes the distance the observer has traveled. If the observer’s distance is not included, any increase in frequency caused by the observer’s speed will appear to decrease the wavelength causing the speed to remain unchanged.

    Traveling towards the source will increase the number of waves displayed on the screen of an oscilloscope. Displaying more waves in the same amount of space means the length of each wave displayed on the screen will be reduced. This does not mean that traveling towards the source will reduce the actual length of the waves. The oscilloscope shows the waves closer together because the total distance that the screen represents has been increased to include the distance the observer has traveled relative to the source. Traveling towards the source causes the oscilloscope to use a smaller amount of the screen to represent the same amount of distance. If the distance is not included, any increase in frequency caused by the observer’s speed will appear to decrease the wavelength causing the speed to remain unchanged. While at rest relative to the source, a one second screen of an oscilloscope will represent 186,000 miles. If the oscilloscope is traveling 1,000 miles per second towards the source, then the screen of the oscilloscope must represent 187,000 miles.

    Traveling towards the light does not change the distance that the light has to travel to complete one wave, just as traveling towards an oncoming train does not reduce the length of the boxcars. Traveling towards the train will increase the number of boxcars that are passed and it will increase the relative speed between the observer and the train, but it will not change the length of the boxcars. If the observer plotted the number of boxcars that passed in one minute on a four-inch line, and then did the same thing after increasing speed towards the train, the second experiment would have more marks on the four-inch line and they would be closer together. This does not mean the length of the boxcars have gotten shorter, it means that the four-inch line represents a greater distance while traveling towards the source than it does when not moving relative to the source.

    The increase in measured frequency caused by the observer’s speed is equal to the distance the observer has traveled (in one-second) towards the source, divided by the known wavelength. When calculating the wavelength using the measured frequency, it must be divided into the sum of “the distance light has traveled away from the source in one second” plus “the distance the observer has traveled towards the source in one second”. When measuring the wavelength, the scale of the tool used to measure the length must account for the distance the observer has traveled relative to the source. While in motion relative to the source, the wavelength or frequency will always be divided into a number that is greater than or less than 186,000 miles, but never equal to 186,000 miles. The frequency multiplied by the wavelength must equal the sum of “the distance that the observer has traveled relative to the source in one second” plus “the distance the light has traveled relative to the source in one second”.

    The speed of light is not constant to all observers, and it is not the universal speed limit. Traveling at relativistic speeds will not alter time, lengths, or mass. The Doppler effect is not a stretching or compressing of the wavelengths; it is an increase or decrease in frequency and relative speed. The only way the speed of light can be measured constant between observers traveling at different speeds is to measure a change in the length of the wave. The only way to measure a change in wavelength caused by the observer’s speed is by not including the distance the observer has traveled relative to the source. If the distance the observer has traveled is not included when measuring the speed of the train, then the speed of the train will never change. If the distance the observer has traveled is not included when measuring the speed of the light, then the speed of the light will never change. The Special Theory of Relativity is interesting, but incorrect.

    In my opinion, Einstein created the Special Theory of Relativity because he misunderstood the following facts. Frequency and wavelength are only inversely proportionate when measured at rest relative to the source. When measuring the relative speed of light, the distance the observer has traveled relative to the source must be included with the distance that the light has traveled away from the source in the same amount of time. Light travels at about 186,000 miles per second relative to the source. Relative to the orbiting binary stars, we are circling them and are running into the light at different speeds (actually different distances), which explains why we don’t see multiple images of the same star. The wavelength, or the distance light travels away from the source in order to complete one cycle, is not a relative measurement and it cannot be altered by changing speed or direction. Traveling past a wavelength at a faster rate does not mean the light has traveled a shorter distance from the source to complete one cycle. Changing speed relative to the source can only change the number of wavelengths passed and the relative speed of light, not the distance the light has traveled relative to the source. It is not the speed of light that remains constant it’s the wavelength.
     
  2. jcsd
  3. Tom Mattson

    Tom Mattson 5,539
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    Anyone attempting to argue the Special Theory of Relativity does understand those things, because they are required to study classical electrodynamics in the process.

    That's not all. Einstein opened his case by referring to the observation that, if Galileo's relativity were correct, then the electrodynamics of moving bodies should result in "asymmetries which do not appear to be inherent in the phenomena". That is, Galileo and Maxwell could not both be right.

    With you so far.

    No, the logic is just fine. The binary stars are orbiting each other, and it is this relative motion that DeSitter had in mind. You can't simply transform that relative motion away with a change of reference frames, because the motion is accelerated.

    No, it doesn't, because you can't fix both stars simultaneously.

    He didn't just "believe" it, it is a consequence of his postulates, which by the way are required to explain the apparent paradoxes in Maxwell's EM theory. One such paradox is that, if Galilean relativity were correct, EM waves would not even appear as EM waves in any frame moving relative to the source.

    Everyone knows that Einstein's view was an extrapolation of Maxwell's.

    That is only true if you assume Galilean relativity in the first place. Since that model is now long defunct, there is no reason to assume it. SR has successfully overthrown it, on both theoretical and experimental grounds.

    The next 6 paragraphs are based on the same faulty assumption, so I'm going to skip them.

    In my opinion, you reject relativity because you either misunderstand or are simply unaware of the following facts:

    1. The speed of light has actually been measured to be independent of the speed of the source in pion decay experiments.
    2. Time dilation has actually been measured in muon decay experiments.
    3. Rejecting SR necessarily means rejecting Maxwell's electrodynamics, because Maxwell is only frame-independent under SR.
    4. Injecting SR into quantum theory makes it much more accurate, not less so. Indeed, QED (the marriage of quantum theory and SR) is the most accurate theory ever devised by man.

    You need to take some courses in physics, especially electrodynamics.
     
  4. Can you estimate the correction to the MM experiments when the earth velocity is added?
     
  5. Geistkiesel Wrote: Can you estimate the correction to the MM experiments when the earth velocity is added?


    What type of correction are you looking for? Since there is no ether (at least none with resistance), the velocity of the earth or the source is not important. Light travels in all directions at the same speed. The Michelson-Morley experiment was designed to show the resistance light encountered while traveling with or against the ether. Since there is no resistance, the experiment failed to detect it. The only reason a correction would be needed is to sustain the belief in the resistance, such as the Lorentz-Fitzgerald contraction. No matter how fast the earth is traveling, any ray of light used in the experiment will travel the same speed going straight as it would if reflected 90-degrees.
     
  6. TOM MATTSON


    Can I pick your brain again?

    Is it that you don’t believe the number of cycle on the screen of an oscilloscope will increase as you increase speed towards the source?

    Or is it that you don’t believe the distance the observer has traveled has to be included when making relative measurements?
     
  7. russ_watters

    Staff: Mentor

    An oscilloscope has nothing to do with the speed of light. When moving toward a source, there is a red-shift, and if its enough, you would see more cycles on the oscilloscope, but that doesn't tell you anything about C.
     
  8. your hypothesis about light and wavelengths is incorrect i think. i'm not going to go into what "I" personally believe on the matter, because i already have alot of stuff on my plate at the moment <grin>

    the frequency of the wave is not merely the wave length, although that is one way to look at it. it is how often the wave completes a cycle in a given time, say 1 second.

    now suppose you're stationary looking towards a light source with your eyes open. you're taking in that light as a specific frequency meaning let's say arbitrarily 5 waves per second.

    moving TOWARDS the light, you're catching them as you approach, meaning at extremely high speeds you're catching more waves per second. if you moved at a velocity equal to 1/2 lightspeed second towards the source you'd catch 1/2 as many more waves than you would if you were stationary.

    of course you wouldn't KNOW you were moving towards the lightsource in an SR relativistic frame, so you would just "perceive" light as being a different wavelength/frequency in that "reality"
     
  9. Tom Mattson

    Tom Mattson 5,539
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    Not at all. If you move towards a source, you will definitely see that the frequency of the radiation is Doppler shifted such that the frequency increases.

    The distance traveled by the observer only has to be taken into account when we want to translate the data taken from measurements to actual coordinates of events in spacetime. This is because it takes a finite time for information to propagate from an event to an observer.
     
  10. When measuring the relative speed between two objects wouldn't the distance traveled by both objects in the same amount of time always have to be included?

    An observer traveling towards a source of light will measure an increase in frequency. We call this Doppler shift, which is cause by passing the wavelengths (the full lengths) at a faster rate. We also measure a decrease in wavelength, which is said to be an effect of the relativity.

    What I see is that the only reason we measure a decrease in the wavelength is because we are not including the distance the observer has traveled.

    If the distance the observer has traveled relative to the source is included, then the wavelength will not change and the speed of light will not be constant. The only reason we measure the speed of light to be constant is because we measure a change in the wavelength.

    Run some real or theoretical experiments with the formulas below and see what you find.

    Change in frequency:
    The amount of change in the measured frequency caused by the observer’s speed relative to the source is equal to the distance the observer has traveled relative to the source in one second (“positive when traveling towards the source” “negative when traveling away from the source”), divided by the known wavelength.


    Observer’s speed:
    The speed of the observer (relative to the source) equals the measured frequency multiplied by the known wavelength, minus the speed of light.

    Measured frequency:
    The measured frequency equals the speed of light added to the speed of the observer relative to the source (“positive when traveling towards the source” “negative when traveling away from the source”), divided by the known wavelength.


    True wavelength:
    The wavelength (relative to everyone) equals the speed of the observer relative to the source (“positive when traveling towards the source” “negative when traveling away from the source”) added to the speed of light, divided by the measured frequency.
     
  11. Tom Mattson

    Tom Mattson 5,539
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    I was taking the observer's speed to be an independent variable. If you determine the speed by determining the distance traveled and the time elapsed, then yes you need to know the distance.

    OK

    But from the observer's point of view (the one who is measuring the wavelength), he hasn't moved at all. It's the source that is moving towards him.

    But the speed of light will be constant. It has been measured to be independent of the motion of the source in measurements from the decay of fast particles.

    This is nonsense. A change in frequency cannot be equal to the change in the observer's distance. The two quantities don't even have the same units.

    This is also nonsense. The frequency times the wavelength is the speed of light. Your formula says that, no matter what, the speed of the observer relative to the source is zero.

    Which "known wavelength" is that? The one measured by the observer, or the one measured by someone at rest relative to the source?

    There is no "true wavelength, relative to everyone".
     
  12. TOM MATTSON wrote:
    Then you must include the distance the source has moved towards the observer, it doesn't matter.

    But did they include the distance that our measuring equipment has traveled relative to the source of the light? Or put another way, did they include the distance the source traveled relative to the test equipment?

    The amount of change in the measured frequency caused by the observer’s speed relative to the source is equal to the distance the observer has traveled relative to the source in one second (“positive when traveling towards the source” “negative when traveling away from the source”), divided by the known wavelength.

    The answer is the number of additional cycle measured per second, or the reduction.

    The speed of the observer (relative to the source) equals the measured frequency (measured by the observer) multiplied by the known wavelength, minus the speed of light.


    The known wavelength is the wavelength measured while at rest compared to the source.


    The only way to measure a changing wavelength is by not including the distance the observer has traveled towards the source, or the distance the source has traveled towards the observer.
     
  13. Tom Mattson

    Tom Mattson 5,539
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    Even so, there is still a measurable change in wavelength.

    Yes.

    Right, I hit "send" before going back to complete that sentence. So, it's a distance divided by a distance, which sets a frequency equal to a quantity with no units at all. Unless, of course, you mean to say that it is not the distance divided by a wavelength, but a speed divided by a wavelength.

    Is that it?

    But why should we combine those quantities to form a speed? A main point of SR is that we cannot take it for granted that we can combine quantities taken from different inertial frames.

    No, you measure a changing wavelength simply by measuring the wavelength of light when you are in different states of motion relative to the source. Taking the motion of the source relative to the observer into account doesn't give you the "real" wavelength in your frame, it gives you the wavelength in the rest frame of the source.
     
    Last edited: Jun 15, 2004
  14. Tom Mattson

    Tom Mattson 5,539
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    I'm guessing that the following idea of yours is what is most preventing you from accepting SR.

    And I responded thusly:

    To that I will add that you could make your claim about any measurable quantitiy that varies from frame to frame. You could say that the only way that time dilates is because we don't include the relative motion between muons and our laboratory. Thus, they don't really take longer to decay, and we can prove that if we just calculate back to what the muon lifetime is in its own frame.

    Well no kidding!

    Yes, you can always calculate proper times, lengths, wavelengths and frequencies by transforming back to the rest frame of the object under study, be it a muon, a meter stick, or a light source. But just because we can go back and calculate the values of those quantities, it does not imply that those values are somehow more "real" than the ones we measure.

    You seem to be trying to get me to consider a universe in which SR is false. There's no need: I've already done it (I had to, as part of my studies). What you don't understand here is that you need to consider such a universe.

    A universe in which Maxwell's equations look different in every frame.

    A universe in which the momentum of a photon (which is inversely proportional to its wavelength) is independent of the state of motion of particles with which it collides.

    A universe in which measurements of microscopic systems agree with relativistic qunantum theories vastly better than they do with nonrelativistic qunantum theories.

    The longer you look at a "Universe without SR", the more you'll see that it is an illusion, and it is most definitely not the universe we live in. Do yourself a favor: Study some physics. You'll be the better for it.
     

  15. The reason I believe that is because of the following:

    If the width of the screen of an oscilloscope represents a one-second-time period, then it will also represent 186,000 miles since that is the distance light travels in ones second. Right?

    The number of cycles displayed on the screen is the number of cycles that has passed by in one second. If you take 186,000 miles and divide it by the number of cycles on the screen, it will equal the length of each cycle. Right?

    If the width of the screen is six inches long, then six inches represents 186,000 miles, and 3 inches would represent 93,000 miles. Doing this we can apply a scale to the screen and measure the length of each cycle. Right? Although it would be difficult.

    If the oscilloscope increases speed towards the source, the number of cycles displayed on the screen (relative frequency) will increase, and the length of each wave (relative wavelength) will decrease. And this is why you believe the wavelength has changed right?

    The frequency increases because traveling towards the source has increased the total relative distance traveled in one second. The new frequency must be divided into the sum of 186,000 miles plus the distance the oscilloscope has traveled. Right? Relative speed divided by relative frequency equals relative wavelength, right?

    The cycles appear closer together on the screen because the screen represents a greater area(the relative speed, or distance per second). It’s only by not adjusting the scale of the screen to represent the total distance traveled by the light and the observer that a change in wavelength can occur. If we do adjust the scale, the wavelength never changes. Do you think the scale of an oscilloscope needs to be adjusted when measuring light while in motion relative to the source?
     
  16. Tom

    If you used an oscilloscope to measure a pulse emitted from the front of each boxcar as a train passes by you, the number of pulses on the screen will increase if the train speeds up or if you increase speed towards the train. The individual pulses will also be closer together on the screen, this does not mean the length of the boxcars has changed; it means the distance that the screen represents has been increased.

    If you do not adjust the scale of the screen, then the relative speed of the train will never change.
     
  17. russ_watters

    Staff: Mentor

    What, you've never heard of length contraction? Well, if you don't buy time dilation, I doubt you'll buy length contraction either, but....

    ...an observer in a moving boxcar will indeed measure the boxcar to be a different length than an observer on the ground.

    Like Tom said, what you are doing is assigning a "proper" length in order to calculate speed. Sorry, but you can't do that. For the person in the boxcar, time and distance are what he measures them to be and for the person on the ground, time and distance are what he measures them to be. And they will not necessarily agree on the time and distance involved with the same event.

    I must emphasize again that though it may seem counterintuitive to you, these phenomena have actually been observed to occur. They are reality.
     
  18. Tom Mattson

    Tom Mattson 5,539
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    The reason you believe that is because you don't know anything about physics.


    Take a few courses, and try to learn something. Either that, or open up to learning something about real physics here at Physics Forums, whether or not it defies your intuition.

    If not, then you're just going to be another crackpot around here.
     
    Last edited: Jun 15, 2004
  19. The rejection of SR


    You use the lack of formally gathered knowledge "about the real physics" as a priest uses his call to faith. You are only superior in your own perception, a legend in your own mind only. I reject SR for philosophic reasons, primarily becasuse SR and SR spokes agents such as yourself, talk silly, deferentially,with the superiority of mathematical supremeacy. I reject SR and refuse to study the essence of the insanity for the same reason I don't put my finger in fires tio find out how hot it may be. Do you understand? All of your references to experimental proof of SR are understoof by myself as mantras of idiots.

    Do you understand? I consider you a scientific clown. I want not what you have to offer.

    I do not need your pemission to scrutinize any offered theory, nor do I need you permission, or support, to offer my own ideas, even though you and I both know, my ideas are guaranteed to remain unambiguosly contradictory to your ideas.

    I reject your totality of expression, your scientific methods, your authoritative persona, I reject your smug educator's personality, I reject your mentorial status as having any useful significant additions to the exchange of ideas and the progress of science, I reject your every manifest breath, I reject your efforts to maintain the status quo in a state of blind obedient sleep-walking darkness.

    I reject your contnued insistance that I have something owed to you.

    Your reference to the "proof" that mass moving at .99c measured a value of c for the velocity difference of itself and light was ignored, unread.

    You have a huge theoretical abyss to consider:
    1. Either pull up the drawbridge and defend the castle, or [*]*demonstrate how moving toward oncoming photons shortens the wave length of the light, by demonstrating that the increase in frequency is other than your eye moving faster over the oncoming wave lengths and,
      [*] justification of suppressing the addition of the distance traveled by an observer to the wave length of the oncoming photons in the analysis of data from experiments measuring the constancy of the speed of light, and [*] direct experimental results disproving the *Grounded claim in 2.) and 3.) above.

    * See Grounded's Post #1 in this thread.
     
  20. Hurkyl

    Hurkyl 16,090
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    Pot to kettle

    What about your own faith, Geistkiesel? It must be pretty strong for you to continue to have your unwavering belief in the incorrectness of Special Relativity.

    I mean, if I had a strong conviction against learning something, I would resign myself to the fact that I don't know that thing.

    But here you are, steadfastly refusing to learn Special Relativity, refusing to hear evidence confirming it, and you are able to stick to your conviction that it cannot possibly be anywhere close to valid!


    Wait, I'm wrong, you're not so much sticking to your convictions; you never face any scrutiny because you denounce anyone who would scrutinize you as being in a "state of blind obedient sleep-walking darkness".

    You still have your blind faith, but you don't have the confidence in your faith, so you need to belittle those who might erode your faith in order to maintain it.


    You liken learning SR to putting a finger in a fire. Why? Putting your finger in a fire can cause physical pain and injury; are you suggesting that you will suffer mental pain and injury if you tried to learn SR? Are you really that afraid you might be wrong?
     
  21. Tom Mattson

    Tom Mattson 5,539
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    That's just it: Nothing about SR is "understood by yourself".

    The experimental and theoretical arguments in support of SR are overwhelming, and furthermore they are available for anyone to examine. How you can say, on the one hand, that I lack the formal knowledge of physics, and then on the other hand that you refuse even to look at SR seriously, is hypocritical beyond belief.

    You're just another idiot with an internet connection, a bad attitude, and too much time on his hands.
     
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