speedoflight

Why Does C Have a Particular Value, and Can It Change?

Short answer:

Because c (speed of light) has units, its value is what it is only because of our choice of units, and there is no meaningful way to test whether it changes. These questions are more meaningful when posed in terms of the unitless fine structure constant. Nobody knows why the fine structure constant has the value it does, and there are controversial claims that its value may have changed.

Long answer:

The SI was originally set up so that the meter and the second were defined in terms of properties of our planet. The meter was one forty-millionth of the earth’s circumference, and the second was 1/86,400 of a mean solar day. Thus when we express c as 3×108 m/s, we’re basically specifying the factor by which c exceeds the speed at which a point on the equator goes around the center of the earth (with additional conversion factors of 40,000,000 and 86,400 thrown in). Since the properties of our planet are accidental, there is no physical theory that can tell us why c has this value in the original French-Revolutionary version of the SI.

The base units of the SI were redefined over the centuries. Today, the second is defined in terms of an atomic standard, and the meter is defined as 1/299,792,458 of a light-second. Therefore c has a defined value of exactly 299,792,458 m/s. Again, we find that the numerical value of c has no fundamental significance; it is merely a matter of definition. In fact, physicists often choose to work in a non-SI system of units in which c=1 exactly.

One might object that c could have a numerical value that was not merely an accident of natural or human history, if we instead chose to express it in terms of base units of time and distance that were universal. For example, suppose that SETI succeeds, and we initiate two-way radio contact with an alien civilization. We want to know whether the speed of light has the same value in their neighborhood of the galaxy as it does in ours. We agree to use an atomic standard for our base units. As our distance unit, we’ll use the circumference of the electron’s orbit in the ground state of the Bohr model of hydrogen; and as our unit of time, we agree on the corresponding orbital period. In these units, the speed of light equals 137.0359991. But this number is simply the inverse of the fine structure constant, defined as e2/ħc, where e is the fundamental charge and ħ is Planck’s constant over 2π. It now becomes clear that it is not possible for us to find out whether the aliens’ local value of c is or is not the same as ours. If they get 134 instead of 137, it could be because e or ħ is different where they live.

The moral of this story is that it is never meaningful to ask why a universal constant has a particular value, unless that constant is unitless (Duff 2002). Currently, there appear to be about 26 such unitless fundamental constants (Baez 2011). The unitless constant most closely related to c is the fine structure constant. It is meaningful to ask why the fine structure constant has the value it has, but nobody knows the answer.

It has been claimed based on astronomical observations that the fine structure constant actually varies over time, rather than being fixed (Webb 2001). This claim is probably wrong, since later attempts to reproduce the observations failed (Chand 2004). Webb et al. responded with even more extraordinary claims that the fine structure constant varied over the celestial sphere (Webb 2010). Extraordinary claims require extraordinary proof, and Webb et al. have not supplied that; their results are at the margins of statistical significance compared to their random and systematic errors. Even if this claim it is correct, it is not evidence that c varies, as is sometimes stated in the popular press; it is only evidence that the fine structure constant varies.

Further Reading

Duff, “Comment on time-variation of fundamental constants,” http://arxiv.org/abs/hep-th/0208093v3
Baez, Baez, http://math.ucr.edu/home/baez/constants.html
J.K. Webb et al., “Further Evidence for Cosmological Evolution of the fine structure Constant,” Phys. Rev. Lett.87 (2001) 091301,http://arxiv.org/abs/astro-ph/0012539v3
J.K. Webb et al., “Evidence for spatial variation of the fine structure constant,” http://arxiv.org/abs/1008.3907
H. Chand et al., Astron. Astrophys. 417: 853

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  1. PeterDonis says:

    [QUOTE=”Dutchr, post: 5229008, member: 558022″]By resonating the Cesium atoms are continuously cycling between energy levels[/QUOTE]

    No, they aren’t. Each atom undergoes a single transition, from the ground state to a particular excited state.

    [QUOTE=”Dutchr, post: 5229008, member: 558022″]the atomic clock resonates with that frequency…[/QUOTE]

    With what frequency? Even if the Cesium atoms were “oscillating” with some frequency, that would not be the frequency that determined the atomic clock’s frequency. The atomic clock’s frequency is the frequency of photons absorbed by the Cesium atoms when they undergo the transition from the ground state to a particular excited state; it has nothing at all to do with any vibration of the atoms themselves. And the photons themselves aren’t even measured, as Maxila’s explanation makes clear (and even if they were, the “frequency” of a photon does not correspond to any actual vibration in space; photons don’t even have well-defined spatial position operators); the frequency that’s actually measured in the atomic clock is the frequency of the quartz oscillator.

    [QUOTE=”Dutchr, post: 5229008, member: 558022″]there are two energy levels with their own certain orbital distributions involved in the Cesium atom.[/QUOTE]

    You are focusing way too much on the position/momentum representation of quantum states. I realize that many pop science treatments of quantum mechanics do this, because it seems intuitively plausible, but that doesn’t make it right. The position and momentum expectation values, orbital shapes, etc. of the electrons in the Cesium atoms in an atomic clock are irrelevant to the clock’s operation and the time standard it defines; they convey nothing physically meaningful since those observables are never measured.

    [QUOTE=”Dutchr, post: 5229008, member: 558022″]with the Eigenenergy always equal to E = h f.[/QUOTE]

    The energy E = hf, where f is the frequency of the absorbed photon, is not the energy of the electron in a given energy eigenstate. It’s the [I]difference[/I] in the electron energy between two different energy eigenstates (the ground state and the particular excited state used in the atomic clock).

    [QUOTE=”Dutchr, post: 5229008, member: 558022″]There most definitely is a changing position overtime conveyed by electromagnetism.[/QUOTE]

    No, there isn’t. See above. Please take some time to learn more about quantum mechanics and how it models atoms and atomic transitions.

    [QUOTE=”Dutchr, post: 5229008, member: 558022″]Experiments agree with me.[/QUOTE]

    Experiments do agree that ideal clocks of different constructions (for example, an atomic clock and a light clock), at rest relative to each other, will keep the same “rate of time flow” (once corrected for units). Experiments do [I]not[/I] agree with your incorrect understanding of quantum mechanics.

  2. Dutchr says:

    [QUOTE=”Maxila, post: 5228924, member: 366067″]Since both statements regarding Cesium clocks are not entirely correct or complete I’ll add some clarification on the Cesium clock function with links.
    [/QUOTE]

    I wasn’t trying to write a lengthy explanation of an atomic clock in my original comment. I will still stand by what I said that Cesium atoms are oscillating or resonating and changing energy levels releasing light. By resonating the Cesium atoms are continuously cycling between energy levels and yes the atomic clock resonates with that frequency. That frequency is conveyed with electromagnetism and there is a certain frequency and a certain wavelength involved. Just like there are two energy levels with their own certain orbital distributions involved in the Cesium atom. There is no uncertainty concerning the shape of the orbitals only on where we will find the electrons if we look for them. The atom transitions from a certain set of possible momentum/positions to a new set of momentum/positions with the Eigenenergy always equal to E = h f.

    The atomic clock is still resonating with a frequency of a fundamental force. The Quartz crystal and the electronics connected to it convey that resonance frequency to an instrument we can read with yet again electromagnetism. There most definitely is a changing position overtime conveyed by electromagnetism. I still see no fundamental difference between an atomic clock and a light clock. Experiments agree with me.

  3. Maxila says:

    [QUOTE=”PeterDonis, post: 5228948, member: 197831″]Ah, ok, so this is a measurement of the frequency (not the energy) of the transition; the energy of the transition photons themselves isn’t measured, they’re just counted, but maximizing the number of photons counted amounts to measuring the transition frequency using the quartz oscillator.[/QUOTE]

    Exactly, maximum florescence shows the microwave frequency is tuned precisely, which in turn was derived from (and used to tune) the quartz oscillator that provides the output frequency of the clock.

  4. PeterDonis says:

    [QUOTE=”Maxila, post: 5228924, member: 366067″]As the Cesium atoms pass through a microwave cavity a detector is used to produce a feedback signal that continually tunes the quartz oscillator (from which the microwave frequency is being derived) in a way that maximizes the number of state changes (florescence of the Cesium atoms).[/QUOTE]

    Ah, ok, so this is a measurement of the frequency (not the energy) of the transition; the energy of the transition photons themselves isn’t measured, they’re just counted (actually the atoms are counted), but maximizing the number of counts amounts to measuring the transition frequency using the quartz oscillator.

  5. Maxila says:

    [QUOTE=”PeterDonis, post: 5228096, member: 197831″]
    [QUOTE=”Dutchr, post: 5228023, member: 558022″]Time is best measured by calculating how many back and forth vibrations light/fundamental forces do through a distance in some fundamental clock (vibrations of a Cesium atom for example).[/QUOTE]
    …The frequency of the light is measured by measuring its energy and dividing by Planck’s constant. No “vibration through a distance” is involved.[/QUOTE]

    Since both statements regarding Cesium clocks are not entirely correct or complete I’ll add some clarification on the Cesium clock function with links.

    NIST Cesium clocks keep time [B][U]by adjusting a microwave frequency derived from a quartz oscillator to the resonance frequency of the Cesium atom[/U][/B]. As the Cesium atoms pass through a microwave cavity a detector is used to produce a feedback signal that continually tunes the quartz oscillator (from which the microwave frequency is being derived) in a way that maximizes the number of state changes (florescence of the Cesium atoms).When the maximum number of state changes is reached the quartz oscillator is locked and standard output frequencies are derived from it.

    [QUOTE]All time and frequency standards are based on a periodic event that repeats at a constant rate. The device that produces this event is called a resonator…
    [B]Fundamentals of Time and Frequency, Michael A. Lombardi, National Institute of Standards and Technology, 17.3 Time and Frequency Standards [URL]http://tf.nist.gov/general/pdf/1498.pdf[/URL][/B][/QUOTE]

    [URL]http://hyperphysics.phy-astr.gsu.edu/hbase/acloc.html[/URL]

    “Very accurate clocks can be constructed by locking an electronic oscillator to the frequency of an atomic transition.”

    [URL]http://www.nist.gov/pml/div688/grp50/primary-frequency-standards.cfm[/URL]

    “Those atoms whose atomic state were altered by the microwave signal emit light (a state known as fluorescence). The photons, or the tiny packets of light that they emit, are measured by a detector.”

    “This process is repeated many times [U]while the microwave signal in the cavity is tuned to different frequencies. Eventually, a microwave frequency is found that alters the states of most of the cesium atoms and maximizes their fluorescence.[/U] [B]This frequency is the natural resonance frequency of the cesium atom (9,192,631,770 Hz)[/B], or the frequency used to define the second.”

    [URL]http://tf.nist.gov/general/pdf/1498.pdf[/URL]

    [B]Fundamentals of Time and Frequency, Michael A. Lombardi, National Institute of Standards and Technology

    17.3
    Cesium Oscillators
    [/B]
    “Those atoms that changed their energy state while passing through the microwave cavity are allowed to proceed to a detector at the end of the tube. Atoms that did not change state are deflected away from the detector.”

    “[U]The detector produces a feedback signal that continually tunes the quartz oscillator in way that maximizes the number of state changes[/U] so that the greatest number of atoms reaches the detector. [U]Standard output frequencies are derived from the locked quartz oscillator[/U] (Fig. 17.12).”

  6. Dale says:

    For those who are still having trouble understanding the point being made about c and units, let’s suppose that I told you that my car had a top speed of exactly 100 “vrooms”. Now, I ask you, “let’s fix the units of speed to be vrooms, I want to know why is my car’s top speed 100 vrooms and can it change?” You would reasonably respond “well, how is the unit ‘vroom’ defined?” It turns out that the unit 1 vroom is defined as 1/100 th of the top speed of my car. So, now that I have defined my units I can unambiguously state that my car’s top speed cannot change, it will always be exactly 100 vrooms and can never change. Why, because that is how I defined my unit of vrooms.

    That clearly is an unsatisfactory answer, but it winds up being the only possible answer. If I didn’t like 100 vrooms then I could make it 1 flubnubitz or whatever I liked, simply by changing my units. The reason that it is the only possible answer is because the question itself is dimensionful, so the answer inevitably depends on the units chosen to represent those dimensions.

    A more interesting question is how my car’s top speed compares to other speeds, such as the airspeed velocity of an african or european swallow. We can express the ratio of my car’s top speed to the swallow speed as a dimensionless number which will be the same regardless of the units. We can then look at the physics to understand the things that would make a car’s top speed a few times faster than the swallow’s. So the question only becomes an interesting physics question once we start making a dimensionless comparison.

    This is why when someone asks about the speed of light changing they are probably actually asking about the fine structure constant changing.

  7. Dale says:

    [QUOTE=”vanhees71, post: 5228558, member: 260864″]The speed of light is indeed defined by choosing units for spatial and temporal distances. I think we have exhausted this topic by far now![/QUOTE]Agreed!

  8. Alex Kostko says:

    It is constant as it assumes the sun as the emitting source. If the sun’s chemistry doesn’t change then the C remains constant as a combination of various rays in the light’s spectrum.

  9. vanhees71 says:

    [QUOTE=”DaleSpam, post: 5228303, member: 43978″]Probably not, which is why we consistently point out that the question is really asking about the fine structure constant.[/QUOTE]
    The fine-structure constant is related to the electromagnetic coupling constant or the value of the elementary electric charge. This is just a parameter in the Standard Model of elementary particle physics, which has to be taking from experiment. Today there is no more fundamental theory that can explain this value. It has to do with the speed of light, because when using unnatural units, where ##hbar c neq 1## it is given by (in the usual HEP units, which are the Heaviside-Lorentz units):
    $$alpha_{text{em}}=frac{e^2}{4 pi hbar c},$$
    which is a dimensionless quantity. After having fixed the values of ##hbar## and ##c## by choosing your units, it just depends on the coupling electromagnetic coupling constant, ##e##.

    The speed of light is indeed defined by choosing units for spatial and temporal distances. I think we have exhausted this topic by far now!

  10. PeterDonis says:

    [QUOTE=”Dutchr, post: 5228443, member: 558022″]Atoms are standing waves mediated by the fundamental forces.[/QUOTE]

    Reference, please?

    [QUOTE=”Dutchr, post: 5228443, member: 558022″]Those atoms will be a certain number of wavelengths across in a particular state.[/QUOTE]

    You appear to have some serious misconceptions about how our quantum mechanical models of atoms work. Atoms don’t have a definite “size”, and there is no one single “wavelength” associated with their states.

    [QUOTE=”Dutchr, post: 5228443, member: 558022″]Measuring the length of an object with a light beam or a collection of atoms laid end to end is equivalent.[/QUOTE]

    No, it isn’t. If I have a particular object that is my standard of length, I can lay it alongside any other object and compare their lengths. I don’t need a light beam or a clock to make such a measurement, so I don’t need any definition or standard of time. But if I measure the length of an object with a light beam, I do need a definition and standard of time.

    [QUOTE=”Dutchr, post: 5228443, member: 558022″]Try defining distance without any notion of time or vice versa.[/QUOTE]

    I already did that, by quoting the former definition of the meter in terms of the length of a standard metal bar. No notion of time is required for such a definition. And the definition of time in terms of the energy/frequency of light emitted in a particular state transition of a particular atom does not require a notion of distance. Your belief that it does is based on an incorrect understanding of quantum mechanics, as I noted above (and see further comments below).

    [QUOTE=”Dutchr, post: 5228443, member: 558022″]there is a vibration through a distance for an atomic clock. The particle goes from a ground state with an radial expectation value of x1 to an excited state with a radial expectation value of x2 and back down again.[/QUOTE]

    Expectation values don’t mean what you appear to think they mean. The electron’s position is not measured during the experiment, so its expectation value is irrelevant. The electron certainly does not move a distance of x2 – x1 during the transition.

    [QUOTE=”Dutchr, post: 5228443, member: 558022″]There is another length involved called the wavelength of the photon.[/QUOTE]

    Which is not a distance between identifiable points, so it doesn’t mean what you are thinking it means.

    [QUOTE=”Dutchr, post: 5228443, member: 558022″]I NEVER said an atomic clock worked like a billiard ball bouncing back and forth.[/QUOTE]

    You didn’t say that explicitly, but whether you realize it or not, that’s what you’re saying. For example, this:

    [QUOTE=”Dutchr, post: 5228443, member: 558022″]the particle goes from one expectation value to another and back again forming a cycle with a distance involved occurring in time t. That’s a vibration.[/QUOTE]

    This is not a correct description of what is happening (see what I said above about the expectation value of position); but it can seem like one if your implicit model is the electron as a little billiard ball bouncing back and forth. You might be thinking of it as a “fuzzy” billiard ball, with an “expectation value” for position instead of a definite position, but you’re still thinking of it as bouncing back and forth, moving through space, and that means you’re thinking of it wrong.

    [QUOTE=”Dutchr, post: 5228443, member: 558022″]I could have just as easily mentioned Einstein’s light clock with a beam of light bouncing between two mirrors.[/QUOTE]

    Sure, it’s certainly [I]possible[/I] to have a clock based on the time it takes light to cover a specific distance. But you are making a much stronger claim: that [I]any[/I] clock must be based on such a principle. That claim is false.

    [QUOTE=”Dutchr, post: 5228443, member: 558022″]identical changes can occur in the fine structure constant AND c can change[/QUOTE]

    I’m not sure what you’re trying to say here. Since ##alpha## and ##c## are related by a particular formula, if either one changes, the other must change too. There’s no way for one to change but not the other, if we’re only looking at those two constants.

    If both ##alpha## and ##hbar## change, it’s possible for ##c## to remain unchanged, if the changes in ##alpha## and ##hbar## exactly compensate for each other. Are you thinking of something like that?

    [QUOTE=”Dutchr, post: 5228443, member: 558022″]I can even give you a quote Einstein said saying that from a non-local observer’s perspective c is not a constant.[/QUOTE]

    Once again, this is irrelevant to the discussion in this thread. We’re talking about ##c##, the value of the speed of light measured locally in an inertial frame. It is true that measurements at a distance can show a changed value of ##c## even if local measurements do not. But these effects are well understood parts of GR and are different from speculations that ##c## can change as measured locally in an inertial frame.

    [QUOTE=”Dutchr, post: 5228443, member: 558022″]No experiment ever done takes place over 0 time or 0 distance.[/QUOTE]

    I wasn’t claiming they do. But the fact that measurements take some finite time and distance does not necessarily mean the results of the measurements are dependent on how we measure time or distance.

    [QUOTE=”Dutchr, post: 5228443, member: 558022″]There’s no reason to think that the constants can’t change together[/QUOTE]

    As I said above, they [I]have[/I] to change together, since they’re related by a specific formula. Unless you’re thinking of a case like the one I mentioned above, where ##alpha## and ##hbar## both change in just the right way to keep ##c## the same.

    [QUOTE=”Dutchr, post: 5228443, member: 558022″]Nothing is said about the speed of light locally or in an inertial reference frame in that question.[/QUOTE]

    Read the rest of this thread for context.

  11. Dutchr says:

    [QUOTE=”PeterDonis, post: 5228096, member: 197831″] This happens to be true now, which is why we currently define the meter in terms of light travel time. But it wasn’t always true (and the meter wasn’t always defined the way it is now–it used to be defined as the length of a standard piece of metal kept in France). So you can’t base a general argument on it. See below. [/QUOTE]

    How the meter is defined does have bearing on the argument. The definition of the meter was chosen after very careful experiments conducted over a period of more than 100 years. I do not need a history lesson on how the meter was defined in the past. How distance was defined well in the past of course did not involve the speed of light. However, I would disagree that our definition of a meter fundamentally changed. Atoms are standing waves mediated by the fundamental forces. Those atoms will be a certain number of wavelengths across in a particular state. Stacking atoms one after another is exactly like stacking standing waves one after another (mediated by the electromagnetic force BTW). Each atom will be a certain number of wavelengths of a certain frequency across (say the expectation value of the atom). Measuring the length of an object with a light beam or a collection of atoms laid end to end is equivalent. This makes sense to me, I don’t see a real difference between the two, and it matches experiment to a high degree. Unless there is an experiment that comes along and disputes this it’s good enough for me.

    [QUOTE=”PeterDonis, post: 5228096, member: 197831″]
    That’s not how atomic clocks work (see below). But even if it were, taking your two definitions together, they are circular, with no content: first you define distance in terms of light travel time, then you define time in terms of light travel distance. See the fundamental problem?

    As far as how atomic clocks actually work, they measure the frequency of the light emitted when particular atoms undergo particular transitions between states. Any vibration of the atoms themselves is not measured (and indeed needs to be minimized, by cooling the clock to as low a temperature as possible, in order to get accurate readings). The frequency of the light is measured by measuring its energy and dividing by Planck’s constant. No “vibration through a distance” is involved.[/QUOTE]

    I would disagree with your statement completely. First of all many definitions in physics are circular but that’s fine if they also match experiment. We can’t really answer how things “fundamentally” work. We can relate one physical thing to another with equations and use experiments to verify. I think you completely missed why I wrote: “See the fundamental problem?” Do you understand what I meant by that? Try defining distance without any notion of time or vice versa. I can’t and it doesn’t make much sense to do so. This is why time as a fourth dimension makes mathematical sense to me. At some point to measure a distance you need to involve time.

    Also there is a vibration through a distance for an atomic clock. The particle goes from a ground state with an radial expectation value of x1 to an excited state with a radial expectation value of x2 and back down again. The released photon is also a vibration of the electromagnetic field. There is another length involved called the wavelength of the photon. I NEVER said an atomic clock worked like a billiard ball bouncing back and forth. It of course works quantum mechanically. Still the particle goes from one expectation value to another and back again forming a cycle with a distance involved occurring in time t. That’s a vibration. The entire orbital changes shape from one form existing on average a certain distance from the center to another. I have absolutely no idea why you mentioned vibrations of the entire Cesium atom. Of course if the center of mass of the Cesium atom moves around it will cause unwanted Doppler Shifts to the frequency of the released photon causing errors. I could have just as easily mentioned Einstein’s light clock with a beam of light bouncing between two mirrors. That one is a very clear example of a light clock that does not require direct complication of quantum mechanics.

    [QUOTE=”PeterDonis, post: 5228096, member: 197831″]
    Sure, because for that to happen other constants would have to change too–mainly the fine structure constant. And there are ways of measuring those independently of any measurements of time or distance.[/QUOTE]

    No, identical changes can occur in the fine structure constant AND c can change. alpha = e^2/(hbar c) If the value of e proportionally drops for each particle in the interaction as does hbar and c then you have: (e a)^2/(hbar a c a) = e^2/(hbar c). In fact deep in a gravity well time and space warp and I can even give you a quote Einstein said saying that from a non-local observer’s perspective c is not a constant. The warping of space-time having locally flat space only makes sense if the fine structure constant does not change, the constant e does not change, and the constant hbar does not change for the _local_ observer. But then how are those three observed from a distance? If I drop an object a meter wide into a gravity well from my perspective light bouncing back and forth across the box would slow down as would time, the object would appear to shrink (if there was an event horizon eventually squishing onto that), AND if I had placed opposite charges on either side of the box they would take longer to attract across the box. Einstein’s first theory of gravity only varied time which didn’t work. Later he found he had to warp both space and time to get it to work. It’s not inconceivable that all the constants could vary as space-time warps. In fact from the outside viewer’s perspective that’s the observational way it makes sense when looking in on the other frame.

    Now the point I was trying to make was if this was true we would not notice the change in c locally. Only if the constants vary disproportionately would the changes be noticed and a disproportionate change in those constants would change the fine structure constant. A proportionate change in the constants over-time and distances can be detectable (it can even explain all the experiments of GR) but very importantly not locally as a change in c.

    [QUOTE=”PeterDonis, post: 5228096, member: 197831″] And there are ways of measuring those independently of any measurements of time or distance.[/QUOTE]

    Really? I’ve never heard of experiments “independent of time or distance.” No experiment ever done takes place over 0 time or 0 distance. What you mean is that the math we formed has terms proportional in time and/or distance that when written in a denominator and a numerator they cancel. My response to that reasoning is? SO? It’s extreme metaphysical nonsense to suggest any experiment we’ve done is independent of time and distance. If there are proportional changes that proportionally cancel for local observers it hardly helps your case. What experiment does not have time and distance changes in it? It’s also metaphysical to state that changing c must change the fine structure constant. That’s not what the math says at all. There’s no reason to think that the constants can’t change together just like time and space appear to do. All the experiments and math we have shows that even if that did happen we would likely expect that c would still locally be measured as c. Only if the fine structure constant changes (changing the observed fundamental forces) would c not be measured locally as c.

    [QUOTE=”PeterDonis, post: 5228096, member: 197831″]
    This has nothing to do with the topic under discussion in this thread. We are talking about the speed of light as it would be measured locally in an inertial frame.[/QUOTE]

    Really? “[B][SIZE=6][URL=’https://www.physicsforums.com/insights/why-does-c-have-a-particular-value-and-can-it-change/’]Why Does C Have a Particular Value, and Can It Change?[/URL]”[/SIZE][/B]

    That was the original question of this thread. Nothing is said about the speed of light locally or in an inertial reference frame in that question. How light is observed in a moving reference frame and under the influence of gravity is very important to the general understanding of the constant c.

  12. PeterDonis says:

    [QUOTE=”QST, post: 5228192, member: 546890″]If something were to move faster than that would we be able to measure it?[/QUOTE]

    I don’t see why not. We can measure times and distances accurately enough to detect possible “faster than light” objects over distances of a few hundred miles, if not shorter–that was the distance scale involved in the experiments some time back that at first appeared to show neutrinos traveling faster than light. (Of course it turned out that it was an error in the equipment, but the point is that the issue only arose in the first place because our measurements are accurate enough to spot possible faster than light objects at that distance scale.)

  13. Dale says:

    [QUOTE=”QST, post: 5228192, member: 546890″]I do not think that the original questioner was concerned about units of measure or the numerical value of c in varying units. [/QUOTE]Probably not, which is why we consistently point out that the question is really asking about the fine structure constant.

  14. QST says:

    I do not think that the original questioner was concerned about units of measure or the numerical value of c in varying units. He was not interested in whether the speed of light is expressed in m/s or mi/hr or furlongs/fortnight. He was wanting to know why light travels at the speed that it does instead of some other speed expressed in the same units no matter what units you choose. Light travels 1 planck distance in 1 planck time because it is the nature of the universe for it to do so. If something were to move faster than that would we be able to measure it?

  15. PeterDonis says:

    [QUOTE=”Dutchr, post: 5228023, member: 558022″]Distance is best measured by calculating how far a light ray travels in a unit of time.[/QUOTE]

    This happens to be true now, which is why we currently define the meter in terms of light travel time. But it wasn’t always true (and the meter wasn’t always defined the way it is now–it used to be defined as the length of a standard piece of metal kept in France). So you can’t base a general argument on it. See below.

    [QUOTE=”Dutchr, post: 5228023, member: 558022″]Time is best measured by calculating how many back and forth vibrations light/fundamental forces do through a distance in some fundamental clock (vibrations of a Cesium atom for example).[/QUOTE]

    That’s not how atomic clocks work (see below). But even if it were, taking your two definitions together, they are circular, with no content: first you define distance in terms of light travel time, then you define time in terms of light travel distance. See the fundamental problem?

    As far as how atomic clocks actually work, they measure the frequency of the light emitted when particular atoms undergo particular transitions between states. Any vibration of the atoms themselves is not measured (and indeed needs to be minimized, by cooling the clock to as low a temperature as possible, in order to get accurate readings). The frequency of the light is measured by measuring its energy and dividing by Planck’s constant. No “vibration through a distance” is involved.

    [QUOTE=”Dutchr, post: 5228023, member: 558022″]Could the speed of light even change from an observer’s perspective if say its value were cut in half?[/QUOTE]

    Sure, because for that to happen other constants would have to change too–mainly the fine structure constant. And there are ways of measuring those independently of any measurements of time or distance.

    [QUOTE=”Dutchr, post: 5228023, member: 558022″]The speed of light is also NOT constant in accelerating reference frames and is only constant locally in gravity.[/QUOTE]

    This has nothing to do with the topic under discussion in this thread. We are talking about the speed of light as it would be measured locally in an inertial frame.

  16. PeterDonis says:

    [QUOTE=”Dutchr, post: 5228023, member: 558022″]Distance is best measured by calculating how far a light ray travels in a unit of time.[/QUOTE]

    This happens to be true now, which is why we currently define the meter in terms of light travel time. But it wasn’t always true (and the meter wasn’t always defined the way it is now–it used to be defined as the length of a standard piece of metal kept in France). So you can’t base a general argument on it. See below.

    [QUOTE=”Dutchr, post: 5228023, member: 558022″]Time is best measured by calculating how many back and forth vibrations light/fundamental forces do through a distance in some fundamental clock (vibrations of a Cesium atom for example).[/QUOTE]

    That’s not how atomic clocks work (see below). But even if it were, taking your two definitions together, they are circular, with no content: first you define distance in terms of light travel time, then you define time in terms of light travel distance. See the fundamental problem?

    As far as how atomic clocks actually work, they measure the frequency of the light emitted when particular atoms undergo particular transitions between states. Any vibration of the atoms themselves is not measured (and indeed needs to be minimized, by cooling the clock to as low a temperature as possible, in order to get accurate readings). The frequency of the light is measured by measuring its energy and dividing by Planck’s constant. No “vibrations through a distance” is involved.

    [QUOTE=”Dutchr, post: 5228023, member: 558022″]Could the speed of light even change from an observer’s perspective if say its value were cut in half?[/QUOTE]

    Sure, because for that to happen other constants would have to change too–mainly the fine structure constant. And there are ways of measuring those independently of any measurements of time or distance.

    [QUOTE=”Dutchr, post: 5228023, member: 558022″]The speed of light is also NOT constant in accelerating reference frames and is only constant locally in gravity.[/QUOTE]

    This has nothing to do with the topic under discussion in this thread. We are talking about the speed of light as it would be measured locally in an inertial frame.

  17. Dutchr says:

    The speed of light is a constant because we measure time and distance in the same way.

    Distance is best measured by calculating how far a light ray travels in a unit of time. This is exactly how the meter is defined in physics. Time is best measured by calculating how many back and forth vibrations light/fundamental forces do through a distance in some fundamental clock (vibrations of a Cesium atom for example). To the fundamental forces and to the fields that make up everything time and distance are measured in a very similar way. See the fundamental problem?

    Could the speed of light even change from an observer’s perspective if say its value were cut in half? That’s not a straight forward answer. Because we measure time and distance in a similar way time would slow AND objects would contract proportionately making every reference frame measure the speed of light as c still (Lorentz Transforms do the same procedure and some VSL theories that match GR in all experiments also do). If space itself also contracts then no reference frame could detect any difference. However, if objects contract and time slows but space is static to observers that could look like space is expanding as travel time at any v between unbound objects increases (bound objects shrunk and time slowed). So light could be variable in a sense and match observation but according to all our theories we would never detect that variance locally. If any effect would be observed (like the observed expansion of space) it would not be a variance in c. So varying c globally could have an effect but we would have to call it something else because as observers within the universe we would not witness a variance in c. To say that a variance in c is causing some effect without experimental evidence for that variance would be a metaphysical stance. For example its very much possible that observers warp instead of a “space-time” background warping like in GR and that perspective can match all experiments done. However, science is performed through the looking glass of the observer who does the experiments so we choose that perspective as that’s the best one we have.

    Another way: Now hypothetically say the fundamental forces relative strength’s change (or the fine structure constant changes). Changing the fine structure constant or manipulating the relative strengths of the forces can cause an observed change in the speed of light. This would change the “structure” of all fundamental clocks we have. This could change the observed speed of light.

    The speed of light is also NOT constant in accelerating reference frames and is only constant locally in gravity. The speed of light is locally c because measuring rods and clocks are set locally.

  18. vanhees71 says:

    Well, it’s not that wrong to cite Maxwell in connection with the speed of light, ##c##. In his time the electromagnetic units were similar to what we call Gaussian units nowadays:

    [URL]https://en.wikipedia.org/wiki/Centimetre%E2%80%93gram%E2%80%93second_system_of_unitshttps://en.wikipedia.org/wiki/Centimetre%E2%80%93gram%E2%80%93second_system_of_units[/URL]

    When Maxwell added his famous “displacement current” to the Ampere Law, he realized that this implies the existence of electromagnetic waves, which propagate with the speed of light, ##c##, which brought him to the conclusion that light might in fact be electromagnetic waves, i.e., he did not only unify electricity and magnetism (as well as the local conservation law for the electric charge) into a consistent system of equation but also incorporated optics, the theory of light, into electromagnetism. The direct proof that electromagnetic really exist came then with the famous experiments by H. Hertz in the physics lecture hall in Karlsruhe, where he could do his experiments only in the semester break in order not to disturb the ongoing lectures ;-)).

    Of course again, this history underlines what was said numerous times in this thread: The numerical value of ##c## is arbitrary. From the point of view of relativity, which of course has also been discovered by the careful analysis of the Maxwell equations and experiments concerning the question, whether there exists a preferred inertial reference frame (the “aether rest frame”), there’s no reason to invent different units for length and time intervals. The most natural system of units occurs, when you put all the fundamental natural constants to 1.

    Taking only mechanics and electromagnetism the only fundamental constant is the speed of light. Setting this to 1 and using some arbitrary unit for distances or times and masses, you have already one base unit less than in the CGS system, and you measure space and time intervals in the same unit of length (e.g., light seconds).

    Considering also quantum theory, one more fundamental constant enters, Planck’s modified action, ##hbar##. Setting this also to 1 you have again one base unit less. You can just measure masses (and also energies and momenta) in terms of the inverse length unit. Rationalizing the Maxwell equations and using this units leads to the natural units used in high-energy particle (HEP) physics. Now we have only one base unit left, the length unit (in HEP usually ##1 text{fermi}=1 text{femto metre}=1 text{fm}=10^{-15} mathrm{m}##. All the fundamental constants of the standard model are then dimensionless couplings (for the strong, the weak, and the electromagnetic interaction, and the Yukawa couplings of the quarks and leptons to the Higgs field), and a mass scale (or the vev of the Higgs boson).

    Finally, also considering gravitation and General Relativity, you have one more fundamental dimensionful unit left, Newton’s coupling constant of gravity. This can be used to eliminate the last remaining base unit, and you are working in fundamental Planck units. All quantities are then given in dimensionless numbers.

    In fact, what’s done in an international effort concerning the SI is to do exactly such a program. One tries to trace back the values of all the base units of the SI to the fundamental constants of nature. This has been already done for space-time units by defining the speed of light to a certain value and define the unit of length via the very accurately representable unit of time (the second) and this value of the speed of light.

    I guess, it won’t take too long, until the unit of mass, kg, is redefined in the one or the other way: either one uses the “Watt balance” and fixes Planck’s constant in terms of the SI units or by defining Avogadro’s constant and the atomic weight of a certain isotope-clean element (most probably silicon-28).

    [URL]https://en.wikipedia.org/wiki/Kilogram[/URL]

  19. bcrowell says:

    [QUOTE=”Nugatory, post: 5227042, member: 382138″]When you use the laws of electricity and magnetism to calculate (as Maxwell first did in 1861) the speed at which electromagnetic radiation propagates through a vacuum, that’s the value you get.[/QUOTE]
    I disagree both with the factuality and the spirit of this statement.

    First off, this simply incorrect. If you write Maxwell’s equations in a sensible system of units where c=1, they predict that light travels at speed 1. Maxwell’s equations are not predicting anything about the speed of light that you didn’t put in by hand. The fact that the value of c was put in by hand just happens to be obscured by one of the common ways of writing them, with epsilon-noughts and mu-noughts.

    Second, this statement makes it sound as though c was defined as the speed of light. It’s not. So appealing to Maxwell’s equations to explain c is backwards.

    [QUOTE=”Nugatory, post: 5227042, member: 382138″]Of course you could ask why the laws of E&M are what they are and not something else… but if we answered that question, the answer would just lead to another “Why?” question, and the regress will never end.[/QUOTE]

    Not true. We understand quite well, based on more fundamental considerations, why Maxwell’s equations predict that light travels at the universal speed c. They predict it because light is massless, and SR says that massless things travel at c. Furthermore, we understand quite well, based on more fundamental considerations, why there is a universal speed c in SR: [URL]https://www.physicsforums.com/threads/why-is-the-speed-of-light-same-in-all-reference-frames.445032/#post-2970609[/URL]

    DaleSpam’s explanation is both necessary and sufficient: c has the numerical value it does in a particular system of units simply because we chose that system of units.

  20. Nugatory says:

    [QUOTE=”Murdstone, post: 5226785, member: 380515″]
    e.g. – c = 186,000 mi/sec Why is c not more or less than this value.[/QUOTE]

    When you use the laws of electricity and magnetism to calculate (as Maxwell first did in 1861) the speed at which electromagnetic radiation propagates through a vacuum, that’s the value you get.

    Of course you could ask why the laws of E&M are what they are and not something else… but if we answered that question, the answer would just lead to another “Why?” question, and the regress will never end.

    As DaleSpam as pointed out, the essential fact about the laws of E&M that lead to the speed of light being what it is is the value of the fine structure constant – and that’s a experimental fact about the universe we live in.

  21. Dale says:

    [QUOTE=”Murdstone, post: 5226785, member: 380515″]Sure you can alter the value of c by changing the units of measurement. However, once your choice of units has been determined the question is why does it take on the value that it does.[/QUOTE]Because of your choice of units. There is no additional explanation needed or possible. The choice of units wholly accounts for the value of C.

    [QUOTE=”Murdstone, post: 5226785, member: 380515″]e.g. – c = 186,000 mi/sec Why is c not more or less than this value.[/QUOTE]c is 186000 mi/s because of the length you chose to call 1 mi and the duration you chose to call 1 s.

    Again, if you dig down to the question that you probably actually want to know, it is most likely a question about the fine structure constant.

  22. Murdstone says:

    Sure you can alter the value of c by changing the units of measurement. However, once your choice of units has been determined the question is why does it take on the value that it does.

    e.g. – c = 186,000 mi/sec Why is c not more or less than this value.

  23. Dale says:

    [QUOTE=”Murdstone, post: 5226550, member: 380515″]What constrains C to have the value that it has? The value of C is not arbitrary. – [B]Why Does C Have a Particular Value?[/B]

    c=f(xi) i =1,2,…n Where xi is a constraint on the value of c. [B]Can It Change?[/B] If you could change the value of one of the constraints then you should be able to change the value of c. For a constant c the implication is the constraints are also constant.

    Unfortunately, to date, we do not know what constrains c.[/QUOTE]We know exactly what constrains c to have the value that it has: our choice of units. The value of c can change if we change our units. Because we can change it by changing our units we often use units where c=1.

    You probably mean the fine structure constant, not c.

  24. vanhees71 says:

    There’s not so much more to say about this issue. It’s a fundamental law that spacetime is best described by relativistic spacetime continua of nature. It’s a very well established basic empirical fact. In this sense you can set ##c=1## and measure spatial distances and temporal durations in the same unit. In principle that’s what’s realized in the SI of units, because ##c## has a fixed value and is just a conversion between distance and time units in order to have convenient numbers in everyday life. The choice of this value is arbitrary and was done in a way to reproduce the previously defined units of length, metre, and time, second.

  25. Murdstone says:

    Everyone seems far adrift from the original question of the OP.
    [SIZE=6][B]Why Does C Have a Particular Value, and Can It Change?[/B][/SIZE]

    C has a finite value. It is fast but not amazingly fast. What constrains C to have the value that it has? The value of C is not arbitrary. – [B]Why Does C Have a Particular Value?[/B]

    c=f(xi) i =1,2,…n Where xi is a constraint on the value of c. [B]Can It Change?[/B] If you could change the value of one of the constraints then you should be able to change the value of c. For a constant c the implication is the constraints are also constant.

    Unfortunately, to date, we do not know what constrains c. We can measure c but know little else about how this value is coming about.

    This relates to Newton’s gravity. Gravity was assumed and all that was actually done was measure its effects.

  26. vanhees71 says:

    And as far as I know, it’s historically wrong that Planck was sceptical about Einstein’s work on gravity. Planck was very much in favor for getting Einstein to Berlin, which was not so easy an endeaver, because Einstein was a bit reluctant to come back to Germany after he escaped from the German (Bavarian) Gymnasium in Munich at an age of 16, abandoning his German (Baden-Wurttembergian) citizen ship. But then he could not resist the very attractive offer by Planck, von Laue, and other Berlin physicists (no teaching obligations but a professor title at the university, director of the Kaiser-Wilhelm-Institut für Theoretische Physik, and last but not least a very good salary). In Planck’s recommendation for Einstein to the academy of sciences he was full of praise about Einstein’s work on relativity, and he had been an early advocate for Einstein’s point of view concerning special relativity as soon as the famous paper of 1905 appeared. He was only a bit sceptical about Einstein’s work on quantum theory, particularly the idea of particle aspects of light (and last but not least he was very right with this). Finally, one must also not forget that the final work on General Relativity was done within his first 2 years in Berlin (1914-1916) with an important exchange with Hilbert in Göttingen. Also General Relativity was received enthusiastically at least by the theorists of his time, particularly von Laue and Planck (Berlin), Sommerfeld (Munich), and Born (Göttingen).

  27. Vanadium 50 says:

    Let me tell you why I find the Webb result unconvincing.
    [LIST]
    [*]It’s Webb. Whenever there is a positive effect, it seems that his name is there. That doesn’t mean I would never believe anything he said, but it does mean that I consider his track record when evaluating his results? Is this scientific? Who knows – but it is nevertheless a good idea.
    [*]The statistics are not convincing. There are a few hundred possible directions in the sky the dipole might be pointing. But when this is considered it doesn’t change the p-value by a factor of 100. It changes it by less than a factor of 2. What I would have liked to see is a test where the sources are placed randomly on the sky many times, and the fraction of times a random placement is at least this significant reported.
    [*]There are even more significant results that I am unconvinced by. DAMA/LIBRA has a 9 sigma signal with 7 cycles. I am absolutely convinced they see a modulation. I, like much of the community, is unconvinced that dark matter is responsible.
    [*]At 10^-5 (their reported signal) all sorts of systematics start showing up. For example, with room-temperature spectroscopy, that’s where thermal expansion of your instrument starts to limit you. At that level, I’d want to see not just analysis of data, but contributions from the people who built and operate the instrument, explaining how they have addressed this.
    [/LIST]

  28. Dale says:

    This is really going off topic. Let’s keep further discussion focused on the speed of light or the fine structure constant and not a referendum on GR or dark matter.

  29. Dale says:

    [QUOTE=”Maxila, post: 5225315, member: 366067″]Einstein told Max Planck of his intention to work on gravity he said, “You will not succeed, and even if you succeed, no one will believe you.” The latter part is why I agree with the importance of Dr. Courtney’s point.[/QUOTE]I am not sure what point you are trying to make, but that example seems to work completely against Dr Courtney’s point. You have identified an example where the claim was extraordinary and the scientific community was open minded enough to change their opinion once correspondingly extraordinary evidence was produced.

  30. PAllen says:

    [QUOTE=”Maxila, post: 5225407, member: 366067″]This is a good example of my point as GR now requires us to postulate:

    1. “Dark Energy?” to account for the unexpected dimness of SN at a given GR predicted red-shift due to the expansion of space.
    2. GR is incompatible with Quantum Mechanics.

    Yet it’s likely many established physicists would give a similar response to a peer attempting to redo gravity theory.[/QUOTE]
    On the contrary, I know of no physicist except Roger Penrose who thinks GR does not need fundamental change, [I]precisely for these reasons[/I]. (Well, less so, the first, because GR can readily be interpreted to [I]predict[/I] dark energy in that to avoid you need need some reason to set a constant of integration to zero). However, this still leaves open the issue of what sets the value, and GR is irrefutably in conflict with quantum mechanics.

  31. Maxila says:

    [QUOTE=”PAllen, post: 5225355, member: 275028″]That is actually a poor example. When Einstein started working on gravity, two things were well known:

    – there was at least one very well established observation (extraordinary evidence) that Newtonian gravity could not account for (perihelion advance)
    – Newtonian gravity was incompatible with special relativity.

    As a result, the almost universal view at the time was that a new theory of gravity was required, but everyone other than Einstein was looking at at smaller changes.[/QUOTE]

    This is a good example of my point as GR now requires us to postulate:

    1. “Dark Energy?” to account for the unexpected dimness of SN at a given GR predicted red-shift due to the expansion of space.
    2. GR is incompatible with Quantum Mechanics.

    Yet it’s likely many established physicists would give a similar response to a peer attempting to redo gravity theory.

  32. PAllen says:

    [QUOTE=”Maxila, post: 5225315, member: 366067″]I couldn’t agree more with your main point. I recently read in Scientific American (September 2015 issue) that when Einstein told Max Planck of his intention to work on gravity he said, “You will not succeed, and even if you succeed, no one will believe you.” The latter part is why I agree with the importance of Dr. Courtney’s point. There is no problem with the scientific method however; history is strewn with examples of many problems with human’s application of it, one of them is being too confident in what they believe they already know.[/QUOTE]

    That is actually a poor example. When Einstein started working on gravity, two things were well known:

    – there was at least one very well established observation (extraordinary evidence) that Newtonian gravity could not account for (perihelion advance)
    – Newtonian gravity was incompatible with special relativity.

    As a result, the almost universal view at the time was that a new theory of gravity was required, but everyone other than Einstein was looking at at smaller changes.

  33. Maxila says:

    [QUOTE=”Dr. Courtney, post: 5225103, member: 117790″]You left out the one that I have actually been advocating which is “keep an open mind.”[/QUOTE]

    I couldn’t agree more with your main point. I recently read in Scientific American (September 2015 issue) that when Einstein told Max Planck of his intention to work on gravity he said, “You will not succeed, and even if you succeed, no one will believe you.” The latter part is why I agree with the importance of Dr. Courtney’s point. There is no problem with the scientific method however; history is strewn with examples of many problems with human’s application of it, one of them is being too confident in what they believe they already know.

  34. harrylin says:

    It appears to me to be the wrong answer to a slightly ambiguously or imprecisely asked question… People asking such a question are not likely to care if c is expressed in m/s, miles/h or “natural” units.

  35. Dale says:

    [QUOTE=”Dr. Courtney, post: 5225103, member: 117790″]This is a false trichotomy. You left out the one that I have actually been advocating which is “keep an open mind.”

    I do not see a need to accept or reject claims when the data is incomplete. [/QUOTE]The data is ALWAYS incomplete. That is the whole point of inductive reasoning.

    “Keep an open mind” doesn’t mean “pretend you have no data” nor does it mean “pretend you are incapable of making inferences based on the incomplete data that you do have”. It simply means that you should be willing to update your reasoning in the light of new information as it becomes available.

  36. PAllen says:

    So, do you really think each new claim of a perpetual motion machine should be treated as an open question until disproven?

    Whether and how much ‘extroardinary claims’ should apply to this case (variation in fine structure constant) depends how strongly established one takes the theory behind its constancy. This is where I can see legitimate difference of opinion, and where the case can be more constructively argued – as scientific theory discussion rather than disputing methods of logic that everyone uses in real life.

  37. Dr. Courtney says:

    [QUOTE=”DaleSpam, post: 5225071, member: 43978″]
    The contrary philosophical preferences, “accept extraordinary claims without extraordinary evidence” and “accept more complicated claims than needed” are also philosophical preferences, but not well founded.[/QUOTE]

    This is a false trichotomy. You left out the one that I have actually been advocating which is “keep an open mind.”

    I do not see a need to accept or reject claims when the data is incomplete. Science need not favor a given viewpoint until the data is compelling for rejecting a given hypothesis. Is the data compelling for rejecting the hypothesis that the value of the fine structure constant is not so constant after all? I do not think so, and neither do the two PRLs that were cited in the Insights article. Is the data compelling for rejecting the hypothesis that the fine structure constant is really constant? I don’t think so, but it does cast reasonable doubt.

  38. Dale says:

    [QUOTE=”Dr. Courtney, post: 5224887, member: 117790″]Like Occam’s Razor, rigid adherence to Bayesian stats is an epistemological preference, not an inherent or essential feature of the scientific method.[/QUOTE]Sure, it is a philosophical preference, but it is also one which is well founded and logically follows from the axioms of probability. Any modern scientific study uses probability. Occhams razor also naturally falls out of Bayesian inference.

    The contrary philosophical preferences, “accept extraordinary claims without extraordinary evidence” and “accept more complicated claims than needed” are also philosophical preferences, but not well founded. Furthermore, the contrary preferences are not in keeping with professional scientific practice, even when not strictly using Bayesian inference.

    [QUOTE=”Dr. Courtney, post: 5224887, member: 117790″]Even if we accept that “extraordinary claims” require extraordinary evidence, we should recognize that there is extraordinary proof in this case.[/QUOTE]If you believe that then this is the point you should argue. Complaining about legitimate scientific standards makes it seem like you do not believe that the data is strong.

    [QUOTE=”Dr. Courtney, post: 5224887, member: 117790″]I see no advantage in biasing scientists that one hypothesis is more likely than another to eventually be rejected as future data becomes available. Better to wait for the data.[/QUOTE]Nobody is claiming what will or will not be shown in future data, only how to judge current data. It is very weird that you simultaneously want to claim that a given piece of data is strong, and also that we should ignore it for now. We always will want more data and we will never be done collecting data, so we need to have a method to reason based on all available data and to update our reasoning as new data becomes available.

  39. PeterDonis says:

    [QUOTE=”Dr. Courtney, post: 5224887, member: 117790″]The variation in the fine structure constant actually fits a spatial dipole at a 4.2 sigma significance level.[/QUOTE]

    Reference, please?

  40. Dr. Courtney says:

    Even if we accept that “extraordinary claims” require extraordinary evidence, we should recognize that there is extraordinary proof in this case.

    In many scientific questions, a 95% confidence level (1.95 Sigma) is accepted as significant supporting evidence worthy of publication.

    The variation in the fine structure constant actually fits a spatial dipole at a 4.2 sigma significance level.

    Like Occam’s Razor, rigid adherence to Bayesian stats is an epistemological preference, not an inherent or essential feature of the scientific method.

    I see no advantage in biasing scientists that one hypothesis is more likely than another to eventually be rejected as future data becomes available. Better to wait for the data.

    The scientific method only needs two kinds of hypotheses: falsified and not falsified.

  41. Dale says:

    [QUOTE=”Dr. Courtney, post: 5224564, member: 117790″]”Extraodinary claims require extraordinary proof” seems to me only a way to favor one hypothesis over another based on popular consensus.[/QUOTE]Actually, it is the correct way for rational individuals to reason in the face of uncertainty and incomplete evidence. This idea of extraordinary claims requiring extraordinary evidence can be formalized in Bayesian inference which allows you to calculate how strong a given piece of evidence is and how much it should change your belief in a hypothesis.
    [QUOTE=”Dr. Courtney, post: 5224564, member: 117790″]There was a time in the history of science when claims of invariance were the extraordinary claims, and claims of variance were more ordinary.[/QUOTE]And the claims of invariance were accepted after being supported by the requisite extraordinary evidence.

    Edit: I see that PAllen beat me to it! I should have read before replying.

  42. PAllen says:

    [QUOTE=”HomogenousCow, post: 5224779, member: 435628″]What is the difference between a constant which can be “made unitless” like c and h-bar, and units which are “inherently unitless” such as the fine structure constant?
    It’s always bothered me that we can just measure time in units of length due to c. I get that since c is universal we can naturally relate one arbitrary unit of distance to a unit of time, however it doesn’t seem immediately obvious to me that this warrants equating the two quantities.[/QUOTE]
    The process of making c unitless is equivalent to the process of selecting an inherently unitless constant. Both entail the feature that you lose the ability to state whether a change in the unitless value is attributable to a change in a particular constant with dimensions.

  43. PAllen says:

    “Extraodinary claims require extraordinary proof” is just Bayesian logic. If I say to you: “jump out the second story window, there is a fire on the first floor” versus “jump out the second story window, there is a 15 foot spider on the first floor”, would you really say there is no difference between your acceptance threshold between these? Rejecting “Extraodinary claims require extraordinary proof” is tantamount to saying there is no such thing as an apriori unlikely claim, and is the basis for crank reasoning.

  44. Dr. Courtney says:

    “Extraodinary claims require extraordinary proof” seems to me only a way to favor one hypothesis over another based on popular consensus.

    There was a time in the history of science when claims of invariance were the extraordinary claims, and claims of variance were more ordinary.

    The turning of the tide of consensus is more a matter of human opinion.

    Hypotheses should only be ruled out based on data: hard data. In principle, the claim of a changing fine structure constant is falsifiable to within much smaller uncertainties than the reported changes. I prefer to keep an open mind until technologies catch up to do the experiment and provide the data. I tend to be skeptical when epistemological preferences get used to malign one view and favor another while waiting on the data.

  45. Macrocompassion says:

    This question has been wrongly understood. It is really about the existence of any speed for light and how the particular value of it comes about regardless of the units. How might we calculate this speed from other constants in physics?

  46. Quantomg says:

    The original poster and all other commenters should read this paper recently published on Academia.edu: Redimensioning of Momentum Space and Quanto-Geometric Derivation of the Speed of Light [c]. Right on the money.

  47. Skilroyishere says:

    No. C is constant. The variable lies in the conditions in which this standard is influenced. All the constants that we have established to this point are based on our unique  (base) perspective. The reality of the physical properties that we observe and postulate are slightly skewed. Accepting the fact that all constants are subject to the effects of the properties and/or restrictions of any environmental variables that may alter that constant. We now understand that the constant is not our own  perspective. The constant that exists is with out. The constant is 0. A very cold 0,  It has no variables. Our perspective tells us the symbol g has relative standard. The numerical value for the acceleration of gravity, most accurately known as 9.8 m/s/s. This also is subject to the variables of a its surroundings. Now that we have established that all constants are measurable by: wave, speed, density, strength, length, resonance or all of the above.   A constant does not mean it cannot change. It simply means it is a scale to measure inconsistencies.

  48. HomogenousCow says:

    What is the difference between a constant which can be "made unitless" like c and h-bar, and units which are "inherently unitless" such as the fine structure constant? It's always bothered me that we can just measure time in units of length due to c. I get that since c is universal we can naturally relate one arbitrary unit of distance to a unit of time, however it doesn't seem immediately obvious to me that this warrants equating the two quantities.

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