RSR on Veritasium, Jason Lisle, and the One-Way Speed of Light


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RSR on Veritasium, Jason Lisle, and the One-Way Speed of Light

This is the show from Friday, July 23rd, 2021


Real Science Radio hosts Bob Enyart and Fred Williams discuss excerpts from the Veritasium/Derek Muller YouTube video, "Why no one has measured the speed of light". Einstein stipulated that the speed of light in one direction is the same as light's roundtrip speed, decreeing this by definition, rather than measuring it, because measuring the one-way speed of light has been technically impossible and many argue that it is even theoretically impossible. Einstein then observed (as discussed on Veritasium) that the one-way speed of light might be infinite in one direction and half its agreed-upon speed in the reverse direction, averaging to what we refer to as c, or about 300,000 kilometers per second. Astrophysicist Jason Lisle uses this to negate the atheists' objection to a young earth, that light from distance stars could not get to Earth in less than 10,000 years, by pointing out that the light could be traveling at infinite speed, and arriving here from the most distant galaxies instantly, so that we observe the heavens in real time. This is Dr. Lisle's Anisotropic Synchrony Convention. The the guys ask listeners to try to falsify a diagram on a suggested experiment for measuring the one-way speed of light, at


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Well I can't say this rises to the level of falsification, but I gather that the use of a milky liquid and water-vapor is to slow down the light so that it can be measured by the high-speed cameras. The cameras even with their impressively high shutter speeds couldn't be fast enough to capture light traveling at a speed of c, so slowing the light down is necessary. But if the purpose of the experiment is to determine whether the ASC might reflect physics, slowing down the light could have unintended consequences and would seem to defeat the purpose of the experiment. One consequence would likely be that the light, having already been slowed down on the first trip, would be slowed even more on the second trip, possibly leading some to draw the conclusion that the speed of light in a vacuum is different in different directions.

These problems aren't unique to this experiment, of course. Any measurement of light requires interfering with the light to somehow redirect it to a measuring apparatus. I'm not sure it's even theoretically possible to measure the speed of light definitively, one-way or otherwise.