Albrecht said:We know that our measurement tools a cheating us (by dilation and contraction). So it makes sense to ask for the truth. - This was also an argument of Lorentz when he once discussed relativity with Einstein.
You really have a serious misunderstanding of time dilation. You should fix that before you dig a hole any deeper for yourself.Albrecht said:No, because dilation and contraction influence our tools.
No.Albrecht said:No, because dilation and contraction influence our tools.
The information moved between two inequivalent inertial frames; I.e., did not follow a geodesic; I.e., did not maximize proper time. The stationary clock followed a geodesic.A clock moving with a (different) inertial frame is delayed. Take the following experiment:
You have a clock at rest in your system. Then move another clock by linear motion along this clock, and in the moment of passing by the moving clock is synchronized to the clock at rest. Then after a time of motion, another clock may move linearly along this clock into the direction of the clock at rest. And when passing the other clock the new clock shall be synchronized to the first moving clock. Then when the new clock passes the clock at rest compare both clocks. The moving one will show a delayed time, so dilation. All clock in this experiment move linearly, so they are all in inertial frames.
This shows that also clocks in linear motion are dilated.
Minimize the arc length in Minkowski spacetime = maximize proper time. Edit: in the interest of complete transparency, this is true only for timelike separations. (Mentors: This statement is still I-level, right?)What does "maximization of time" mean?
Yes, considering that we're talking flat Minkowski spacetime (that's a sufficient condition, not a necessary one).TeethWhitener said:(Mentors: This statement is still I-level, right?)
You really should read more than just the title. The topic is the speed of light but the actual content of the paper is as I described. It acknowledges that only changes in dimensionless constants are physically meaningful, specifically identifies the fine structure constant as the thing measured, and then simply by fiat attributes any measurable variation in the fine structure constant to a change in c.Albrecht said:And the topic of the paper is clearly the speed of light
You mean that it would explain those things if it (the fine structure constant) did vary. But it doesn’t vary so that isn’t the explanation.Albrecht said:The assumption of a variation has fascinating consequences. It explains directly the (otherwise not understood) cosmological inflation (said by the authors). And even better: The problem of Dark Energy,
I am not very sure about that. I am more certain that believing a counterfactual assumption will not solve the question either.Albrecht said:We can be very sure that the question of Dark Energy will never be solved on the basis of present understanding, i.e. a constancy of c.
I know very well where this line of thought comes from. Please read the forum rules.Albrecht said:We know that our measurement tools a cheating us (by dilation and contraction). So it makes sense to ask for the truth. - This was also an argument of Lorentz when he once discussed relativity with Einstein.
The reason is well known. It has that specific value because the BIPM committee members voted for it to have that value.FactChecker said:Or is it just what it is, with no known reason for that specific value?
I hope we are talking about the same thing. I am not asking about the units of measurement so much as the actual physical movement of the light. So it sounds like there is nothing in physics to set limits or a preference for the particular motion that light has now. So if the light always went twice as far per unit time as it does now (regardless of the units used), that would not have violated any fundamental law of physics as we know it.Dale said:The reason is well known. It has that specific value because the BIPM committee members voted for it to have that value.
If you are not asking about the units then you are asking about dimensionless constants, specifically the fine structure constant.FactChecker said:I am not asking about the units of measurement so much as the actual physical movement of the light.
Yes, there is nothing in known physics which determines the fine structure constant. It is considered to be fundamental.FactChecker said:So it sounds like there is nothing in physics to set limits or a preference for the particular motion that light has now.
rootone said:This is similar to asking why the value of Pi happens to be what it is.
It simply is a universal constant, something which is not disputed.
Arguably Pi, c, and other constants might differ in some interpretation of a 'multiverse', (not something I am keen on),
However. even if that was the case, it makes no difference to the Universe we exist in.
This statement is correct for dimensionless physical constants like the fine structure constant.AgentSmith said:There is a difference between mathematical constants like Pi, and physical constants like c. The latter are experimental, while mathematical constants not.
Good point. But even ##\pi##, if it is simply defined as ##\pi = \frac {\text{circle circumference}} {\text{circle diameter}}##, can be experimental and depend on curvature.AgentSmith said:There is a difference between mathematical constants like Pi, and physical constants like c. The latter are experimental, while mathematical constants not.
You can slow down light. You can't change c. The named constant "c" denotes the speed of light in a vacuum. The numeric value of its speed depends on your choice of units. Our conventional choice of units is such that c has a defined value that is not experimentally determined.Gary_T2018 said:You most certainly can slow it down by juggling either medium or temperature.
jbriggs444 said:You can slow down light. You can't change c. The named constant "c" denotes the speed of light in a vacuum. The numeric value of its speed depends on your choice of units. Our conventional choice of units is such that c has a defined value that is not experimentally determined.
Nugatory said:its value was chosen by a committee.
Because the logic of the Special theory of Relativity is based on distortions of space and time, it applies to everything that moves, not just light. There are two systems of geometry which are compatible with some simple assumptions: Galilean and Einsteinian. (see https://arxiv.org/pdf/physics/0302045.pdf ). When experiments showed that the speed of light in a vacuum was always measured the same, the Galilean theory was ruled out. That left only the Einsteinian theory, which includes formulas for adding velocities. With those formulas for adding velocities, nothing will be measured as moving faster than c. Light and all electromagnetic waves move at the maximum measureable velocity, c.Gary_T2018 said:Why at this moment there is no solid theory which supports the possibility of moving faster than the speed of light in vacuum?
You have an additional assumption here, namely that the length of that prototype meter stick is constant.suremarc said:We could measure the discrepancy in the speed of light by comparing the length of a light-second to the prototype meter stick.
Nugatory said:This statement is correct for dimensionless physical constants like the fine structure constant.
However, it's not correct for ##c##; its value was chosen by a committee.
To be precise, it was chosen to fall within the error bars of the previous definition of the meter. There's a conceptual shift here, in that earlier experimental measurements of the speed of light are reinterpreted as measurements of the length of the meter.AgentSmith said:The committee did not pick a value out of thin air. It was ultimately based on experimental values.
Nugatory said:To be precise, it was chosen to fall within the error bars of the previous definition of the meter. There's a conceptual shift here, in that earlier experimental measurements of the speed of light are reinterpreted as measurements of the length of the meter.
No, it didn’t. They chose to have it fit within the error range of previous experimental results, but they most certainly did not have to. They chose to keep it within previous experimental ranges for convenience, but if they had decided to be inconvenient then they could have chosen any arbitrary value whatsoever.AgentSmith said:But still the new definition had to fit within experimental results.
Dale said:No, it didn’t. They chose to have it fit within the error range of previous experimental results, but they most certainly did not have to. They chose to keep it within previous experimental ranges for convenience, but if they had decided to be inconvenient then they could have chosen any arbitrary value whatsoever.
There is simply no way to get an exact value through experiment, and c is an exact value in SI units. It is purely the outcome of a committee.
Me too, thanks!AgentSmith said:No way to get an exact value through experiment. Glad you're here to tell me these things, professor.
Good, you understand. The value of c in SI units is not experimental.AgentSmith said:Of course they could have chosen any value whatsoever,
Sure, there were lots of great reasons to not be stupid. But anyone working with committees knows that they are fully capable of being stupid anyway.AgentSmith said:but that would be pretty d**m stupid. Ya think there is a reason they chose not to be stupid?
AgentSmith said:Glad you're here to tell me these things, professor. Of course they could have chosen any value whatsoever, but that would be pretty d**m stupid. Ya think there is a reason they chose not to be stupid?
Vanadium 50 said:You do know that the 1799 definition of the meter was known to be incompatible with the 1798 definition? So historically there have been examples of "pretty d**m stupid".