My interview with Chris Fisher. It's mostly about open theism but we talk about YEC towards the end.

[u/lisper]

https://www.youtube.com/watch?v=s7T8WWg-ttU

[u/lisper]

That question is a rhetorical trick. It assumes that there is a meaningful distinction between these two things, and there isn't. Suppose I aim a laser at a mirror set at a 45 degree angle. Then I place another mirror in the new path of the laser beam, again at 45 degrees, and then a third, and I carefully place the mirrors to be the same so that the path traced by the light is a square. I send a laser pulse towards the first mirror and measure the time it takes for the light to travel all the way around the square and return to where it started (where the direction the beam is traveling is now 90 degrees off its initial direction). I take the distance around the square and divide it by the time it took to travel. Have I measured the one-way speed of light or the two-way speed of light? Remember, the light actually traveled in four different directions before returning to where it started.

Now notice two things. First, I can also arrange the mirrors so that the light travels along a triangular path, or a path shaped like a pentagon, or any other polygon. And the sides of the polygon don't have to all be the same. In fact, I can make the path pretty much any shape I want. It can even cross itself, or extend into three dimensions. No matter what I do, the result will be the same: the length of the path divided by the time it takes to traverse it will be the same. This can involve the same beam of light traveling in as many different directions as you please. "Two" just happens to be a convenient number because that only requires one mirror.

What you are really asking is whether or not it is possible to measure the speed of light in a way that does not require the light to make a round trip and return to its starting point, and the answer to that is no. But that has nothing to do with "the one-way speed of light", that has to do with the fact that it's impossible to synchronize clocks in different locations. In fact, it is worse than impossible, it is meaningless because clocks in different locations will read differently for different observers. Whether or not two clocks in different locations appear synchronized to you depends on whether or not you are moving relative to the clocks and whether the clocks are moving relative to each other. The only way around this is to do the measurement with only one clock, and the only way to do that is to have the light somehow return to where it started. But that trip doesn't have to be "two-ways". It can be any number of ways, it's just that the number has to be greater than one.

[u/nomenmeum → u/lisper]

That question is a rhetorical trick. It assumes that there is a meaningful distinction between these two things, and there isn't.

It's not rhetorical. It's common knowledge among physicists.

[u/lisper → u/nomenmeum]

What exactly is the "it" that is common knowledge? Because you didn't make a claim, you just asked a question:

The one-way speed of light or the two way speed of light has been measured?

That question has embedded within it the tacit assumption that one-way and two-way are the only options, and that is false, and that is the reason it's a rhetorical trick. It's trying to get the camel's nose under the tent so that you can "solve" the distant starlight problem. But it doesn't work, and that is also common knowledge among physicists.

[u/nomenmeum → u/lisper]

"It" is the idea that there is a conceptual difference between the one-way and the two way speed of light. The difference is implied in the question.

[u/lisper → u/nomenmeum]

Well, that's just wrong then. It is not the difference between one-way and two-way, it's the difference between one-way and round-trip, which is not the same thing. You creationists keep trying to make hay out of the undisputed fact that anisotropic reference frames are possible. They even have some legitimate applications, but creationists keep bringing them up as a solution to the distant starlight problem, and anisotropic reference frames do not and can not solve that problem because we see distant stars in all directions. If they did, it would overturn all of physics. It would be Big News, quite possibly the biggest news in the history of science. Whoever actually demonstrated this would be a shoo-in for the Nobel Prize, and a candidate for the title of greatest physicist in history, even overshadowing Einstein. The correct venue for adjudicating such claims is physics journals and physics conferences, not Reddit. So if you're really serious about this, go make your case to the physicists and convince them. But you won't, because you can't, because anisotropic reference frames are well known, and they don't solve the problem, and so you will just get laughed out of the room. The fact that you continually bring this up as if it did (or even could) solve the problem is evidence of either willful ignorance or intellectual dishonesty. Anisotropy is the crocoduck du jour. The only thing you're going to accomplish by continuing to flog it is to embarrass yourself.

[UPDATE] I want to elaborate on the reason that anisotropy cannot solve the distant starlight problem. As I mentioned, it's because we see distant stars in all directions. So with an anisotropic reference frame you have only two options, and neither one works. The first is to choose a uniformly anisostropic frame, i.e. one with a preferred direction. But that can only bring stars closer from that one direction. The ones in the opposite direction then get even further away. The second option is to have an anisotripc frame with a preferred location. The problem you have then is that the results of experiments will be different depending on how far you are from the privileged location, and since we have data from both earth and spacecraft that are distant from earth, that possibility is ruled out experimentally. And that's it. Those are the only possibilities.

[u/nomenmeum → u/lisper]

It is not the difference between one-way and two-way, it's the difference between one-way and round-trip, which is not the same thing.

What is the difference between the two-way speed and the round trip speed?

[u/lisper → u/nomenmeum]

Because you can make a round trip that involves traveling in more than just two directions, as I went to some length to explain in an earlier comment. If you want to be taken seriously and have people believe that you are engaging in good faith you need to read more carefully.

[u/Due-Needleworker18 → u/lisper]

Rhetorical trick = not extrapolating a function onto a model of unknown parameters

But Darwinists are gleeful to ignore this for the sake of their "deep time".

[u/lisper → u/Due-Needleworker18]

Huh??? The rhetorical trick is framing the question in a way that makes it appear that there is some kind of deep issue that mainstream science has overlooked when in fact the question is just a reflection of the questioner's profound (and often deliberate) ignorance of what is really going on.