Comment by Confusion | Hacker News Reader

Comment by Confusion | Hacker News Reader

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What DenisM is describing is not the result of a systemic error. It is not an error at all. 'Something' is travelling faster than light in that experiment. The problem is that the 'something' isn't a physical object.

The common example is the beam of a lighthouse. Suppose a lighthouse revolves once per minute. At one lightyear distance from the lighthouse, the angular velocity of the beam is 2*Pi lightyears per minute, which is much faster than the speed of light. However, this is not a problem: the beam is not a physical entity. There is no single particle actually travelling faster than the speed of light. It's just some construct in our minds to which we assign that velocity.

Something similar is happening in the experiment described by your parent and possibly in the experiment in the linked article.

Perhaps I misinterpreted, but I think DenisM was talking about something completely different. He mentioned that because of a lack of density in the leading photons, the first piece of equipment missed the measurements while the second one picked it up. That would a problem with the system they're measuring with, not at all to do with treating light as a single entity.

As I interpreted it, the critical part of his explanation is the fact that the higher density part shifted from the back to the front. If that change in density would be due to actual photons shifting that way, then those photons would have traveled faster than light (whereas the entire 'blob', on average, traveled exactly at the speed of light).

Could be explained if the photos leaving the source look like this: :::::..... and arrive like this: :::::.::, where the 'tip' folds back on itself to become visible, still before the original bulk of the photon cluster.

At one lightyear distance from the lighthouse, the angular velocity of the beam is 2Pi lightyears per minute*

Actually, that's the linear velocity. The angular velocity would be 2*pi radians per minute and is independent of distance.

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