# Tag Info

## New answers tagged metrology

1

If you with your rods and clocks are in free fall (ie: your metric is the Minkowski diag(-1,1,1,1) ) in a vacuum and the light ray passes near you, you will always measure the standard speed c= 2.99792458 E+8 m/sec. However, the speed of light is observed to be different if the observer and his rods and clocks are in a different gravitational environment ...

1

The answer to your question depends on fine definitions. Locally the speed of light is always the same; more precisely, the universal, Lorentz invariant speed $c$ (which is also the maximum speed of a cause-effect relationship and experimentally observed to be the same as the speed of light) is constant. This means that any measurement of light speed in any ...

0

Let's say for argument's sake that light is a speeding car. That's quite a silly analogy, because a car is generally thought of as some thing which can be observed while it's driving along on the road (e.g. being observed by landmarks such as delineators along the road, or by other cars), and which may observe them in turn. A similarity to light is ...

0

the definition of a second wouldn't have an uncertainty when related to the transition of the Cs atom, The definition of the SI unit "second" does not refer to just any given sample of Cs atoms, and specificly, not to transitions between the two hyperfine levels of the ground state of just any given sample of caesium 133 atoms; but it refers to an ...

5

With respect to your question, the immediate thing you need to clarify is: constant with respect to what? How SR answers that question The speed of light is usually held to be constant with respect to reference frames. In other words, if we're both at the same place in outer space, but you're passing by me in your spaceship, then every photon in either of ...

2

Is the speed of light constant or does the math just happen to work out? None of the above. It's a tautology. What happens is that instead of having just one car, you count 9192631770 cars passing you by. See the defiition of the second which involves microwaves passing you by. Then you declare that a second has elapsed. If those cars are going slower, ...

-2

Is speed of light in vacuum always the same value? No. The speed of light varies with gravitational potential. You can see Einstein talking about this in the Einstein digital papers: Also see Shapiro's 4th test of General Relativity along with The Deflection and Delay of Light by Ned Wright and this PhysicsFAQ article by Don Koks: "Einstein talked ...

3

No, in perfect vacuum, photons do not slow down. Although, gravity of massive objects like stars or planets can bend the trajectory of photon (the Theory of General Relativity) like a lense. If you are referring to the fact that Black Hole is black because no photons can escape its massive gravitational force and you thought it is because the gravity of the ...

19

As far as we can tell, the local speed of light in vacuum is indeed constant. Photons don't slow down or speed up as they fall into or rise out of a gravity well. However, just as a massive object's kinetic energy changes as the object falls into or rises out of a gravity well, photons also gain or lose energy. In the case of photons, this energy change ...

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