Obviously the variation in itself of constants like c, h, G or ε[sub]0[/sub] which have dimensions has no physical implications because time-dependency of the constant could equally be seen as time-dependency of the units that they are measured.
There was an interesting paper that Half Man Half Wit posted recently though about a model for a varying c that could (at least on the face of it) recreate the standard cosmological model. I strongly suspect though that when you can derive the same physics from two different models, what you generally doing is illustrating a certain mathematical equivalence between the two models.
How do you know it changes? You measure it against an outside standard, which will eventually fall back to a universal constant such as the speed of light.
Specialists have an obligation to the rest of us to say if a position they take is generally accepted, and if it is not to at least mention that there are competing views.
So you’re saying that tomorrow, the equation 1 = 0.9999999896 will hold? We’re not talking about something that’s measured as 1, here: We’re talking about something that is 1.
Yes, exactly, and that’s why it doesn’t make sense to speak of c changing.
This position is generally accepted, except that that makes it sound like it was once a contentious issue, which it wasn’t. Nature doesn’t know about (can’t know about) things like meters or seconds. Those are human constructs. See dimensionless physical constants for more. The language surrounding all this has evolved over the years, but the mathematical understanding of how units are defined and behave is quite old.
Physicists are humans, though, so human constructs (e.g., units) do play a role. This is also why it feels natural to say something like “The speed of light is changing” when really that means “The speed of light and some other quantity, with units of speed and calculated using other unit-ful ‘constants’, are changing relative to one another, but I can’t tell you which is actually the one changing.” Alternatively, it could mean “The speed of light is changing, and to make this statement, I’m secretly assuming that anything I need to define speed, such as other unit-ful ‘constants’, are all unchanging.”
There’s also the matter that even if the specialists do understand something, often the science journalists who are writing about it for the general public don’t. Take, for instance, that research on the Fine Structure Constant: The original papers all just talked about the Fine Structure Constant changing. And the speed of light is one of the constants that gets tossed into the mix to come up with the fine structure constant. For some reason, though, when it got reported in the popular press, all the accounts said that it was the speed of light changing. It’d be at least as valid to say that the charge of the electron is changing, or Coulomb’s constant is changing (or most valid of all, just to say that one of them was changing but it was impossible to say which), but for whatever reason, none of the popular accounts phrased it that way.
We can measure time with chronometers (clocks) with such accuracy as to know that the length of the year changes. We also know this from astronomical observations.
Nope; I’m saying that it is circular reasoning to declare “the charge on the electron is defined as 1.0” and then claim that it cannot change. The charge on the electron, as measured by instruments that observe the repulsive force on negatively charged objects, might change. (It probably doesn’t, but that’s not the issue.)
Simply saying, “It’s equal to one” and “one can’t change” is bad reasoning. I gave two examples – the earth’s year and the earth’s mass – of physical “constants” that actually do change. Merely defining them as equal to one won’t help: if you do that, then the length of the second and the value of the kilogram would have to change to accomodate them.
The Earth’s year and the Earth’s mass aren’t the same type of quantity as the speed of light, though. The speed of light, as it’s currently understood, really is 1, and only appears to have units because we made a silly choice of units way back when. It’s like asking whether the quantity “2.54 cm per inch” could change.
Yes, but how does a super-accurate clock measure time? By counting the number of vibrations a particular atom makes. If a rubidium atom vibrates 27 jillion times, we define that a “1 time unit”. Next we notice that last year it took the earth 342 time units to circle the sun, this year it took 341.
But is the Earth speeding up, or are atoms vibrating faster?
Or, it yesterday it took 4.5 years for a light beam to reach Alpha Centauri, and today it takes 4.2 years, is the speed of light decreasing or is the distance between Alpha Centauri and Earth decreasing?
How do you measure whether length is decreasing if the decrease also affects the ruler you are using to measure the decrease?
It sounds like circular reasoning, but it isn’t, and its deeper than this.
This gets us back to the nature of time and space, and the duality between them. Chronos wrote “The speed of light, as it’s currently understood”. This is a way of saying - the nature of spacetime as it is currently understood. Time travels at a rate of one second per second. Light travels at one light second per second. Light therefore travels at one light.
To say that the speed of light changes is to say that the fundamental nature of spacetime varies. Ergo, that the currently understood laws of relativity can vary. We don’t know of any way this can happen, or what it would mean if it did. Although the instant of the big bang tends have the problem that no laws of any kind apply in any way that we understand, once the universe has begun, the clock starts running, and runs at one second per second thereafter. So light runs at one light second per second, or to avoid silly units c = 1.
It is certainly possible to work with a system where the mass of the earth and length of the year are defined to be equal to one, and the mass of everything else does change to accommodate. It’s not terribly convenient, but it is possible.
Well, yes and no. My only point here is that you can’t say, “It’s defined as one, and therefore it can’t change.” The speed of light doesn’t seem to change, nor does the gravitational constant, nor the charge on the electron. We have astronomical evidence suggesting these haven’t changed in billions of years.
We even have evidence that some of them are tied up in the very nature of space-time itself.
But you can’t say, “It’s equal to one, and one never changes.” That fails with some kinds of constants, and is not a good argument even with those that don’t change.
We calibrate against other tests, such as the orbits of Jupiter’s moons, the orbit of Mars, etc.
We calibrate by speed-of-light measurements on earth, between distant mountaintops and other laboratory measurements.
It’s actually a fair question, in a universal sense. In practical terms, however, such changes have ways of being observed and checked against other constants. Obviously, if both the speed of light and the length of the meter were decreasing in exactly the same proportion, we’d never know it: we couldn’t. If the speed of light and the duration of the second were changing in exactly the same proportions, ditto. But that’s an argument from ignorance.
Only when constants vary with respect to one another can we make measurements. If the length of the second, only, were changing, we’d detect it by the change in the speed of light, the change in the length of the earth’s year, the change in the number of vibrations in atomic clocks, etc.
(The fact that we actually do detect such changes due to relativity is…reassuring.)
Sort of. When we say “the speed of light is constant in all inertial frames of reference” was can translate that to mean precisely c = 1.
No measurements, no anything extra. If our understanding of the nature of the fabric of our universe is correct, c = 1. Not by definition, but by deduction.
It is, as far as we know, meaningless to say “both the speed of light and the length of the meter were decreasing in exactly the same proportion”. You can’t come up with a way of defining what it means, because the fundamental components are locked into the manner in which the universe works.
The cite below describes a paper published (ca. 2002) by Nature which explicitly endorses the position that a change in c is solely responsible for a change in the FSC, so the position was not settled as of then. Also, the cite could be taken to mean that the units issue was not prominently enunciated until after the Nature paper was published.
The cite also contradicts your last sentence: the researchers “provide an argument”. Secret assumptions are are not the kind of “argument” that could get past peer review, I hope.
Yes, exactly. And whenever you have two quantities of interest with the same units, and one of them is changing, what you have is that the dimensionless ratio between them is changing. Which, as I said, is something that can be meaningfully discussed.
The cite describes a Nature “Brief Communications” letter which speculates on how new theories about black holes might behave if you vary e instead of c. More specifically, they suggest that it might be possible, depending on how these new theories look, to argue that there is a 2nd law violation with black holes if you vary e. Of course, if you vary c, there is a violation of Lorentz invariance. It just depends what you are willing to give up, and what the new theory looks like.
The spike in thinking about all this in the early 2000’s stemmed from the experimental data suggesting that maybe the fine-structure constant is varying. This is a common trajectory in physics research, and it is mirrored by many issues. Off the top of my head, here are a few examples that fit the common pattern of: It is generally accepted that <aspect of nature> is true, but due to <new observation> throwing up curious data, there has been a spike in thinking about <things that might explain it>.
<generally accepted thing> / <observation> / <sparked a lot of thinking about>
general relativity works on the scale of the solar system / Pioneer anomaly / modified Newonian dynamics and models that give up the equivalence principle
there are three neutrinos / anomalous neutrino oscillation data / sterile neutrinos
isotropic universe / cold spot in the CMB / cosmologies with preferred directions
nothing goes faster than c / evidence for faster-than-c neutrinos / how to evade other experimental bounds and Lorentz invariance issues
charge radius of proton independent of probe used to measure it / new muon-based measurement in tension with electron measurements / a million ideas, from new particles to solutions involving quantum gravity
The flurry of out-of-the-box theoretical work that follows an anomalous observation is a central part of the research endeavor. Sometimes it bears fruit and leads to a dramatic change in thinking, and this could happen with any of the above items (except faster-than-c neutrinos ). Other times it amounts to wheel-spinning until the experimental situation is clarified. But either way, the presence of this activity doesn’t mean things that were generally accepted suddenly aren’t. It just means they get more attention, deservedly, given the unexpected data.
In fact, usually, it turns out to just be wheel-spinning. That’s why the accepted wisdom is accepted, after all. But occasionally, it turns out to be real, which is why we pursue it, just in case.
). Other times it amounts to wheel-spinning until the experimental situation is clarified. But either way, the presence of this activity doesn’t mean things that were generally accepted suddenly aren’t. It just means they get more attention, deservedly, given the unexpected data.