What is Doppler effect?

[Bullet51]

There is a LifeWiki page Doppler effect. It's only referenced for one time on LifeWiki: Infinite glider hotel.

The page is about the relationship of the periods and the speed difference of two moving objects. However, there is another interpretation of Doppler effect in cellular automata, pertaining more to the infinite glider hotel and its counterpart in physics:

When a periodic glider stream is 180°-ly reflected by a moving object in the same direction of the gliders, the period of the glider stream increases.

So, what is the intended meaning of "Doppler effect", and how should we edit the LifeWiki page?

[hotdogPi]

I created the page. I was applying its typical meaning (regarding the relative motion of two moving objects) to CA. If there's another example that applies, you can add it.

Note that the opening sentence has changed since I added it; I defined it generically and didn't mention CA until the first header.

[Bullet51]

I created the page. I was applying its typical meaning (regarding the relative motion of two moving objects) to CA. If there's another example that applies, you can add it.

Maybe we should ask GUYTU6J because the only mention of the Doppler effect on LifeWiki is a GUYTU6J edit.

[confocaloid]

[...] When a periodic glider stream is 180°-ly reflected by a moving object in the same direction of the gliders, the period of the glider stream increases. [...]

There is an occurrence of 'doppler effect' in the book Conway's Game of Life: Mathematics and Construction page 335 in a footnote, which says

The speed is 98c/(2(1078 + 98)) instead of just 98c/(2 · 1078) because of a “doppler effect”: the flotillae do not have to travel just 1078 cells per period, but also the extra 98 cells that the still lifes were pushed.

The moving object does not have to reflect gliders back (it suffices to have a periodic interaction between the moving object and the glider stream; e.g. it might fire gliders sideways, or might just eat them), and the moving object does not have to move in the same direction (it can go in the opposite direction). The common idea is that the period of the interaction differs from the period of the glider stream.

[Bullet51]

There is a use of the term "Doppler effect" on collidoscope.com. It refers to a "Diagonal Pattern Broadcast Bomber", i.e. a diagonal-moving pattern giving out diagonal waves in the four directions.

The pattern is

Code: Select all

x = 12, y = 12, rule = 1c3e/23-ce/4
6.2A$5.ABCA$4.AB2C2A$3.ABC2.CBA$2.ABC4.CBA$.ABC3.C.CBA$ABC3.BABA$A2C2.
CA$.2AC2.B$2.AB2CA$3.A2B$4.2A!

[confocaloid]

^^ It is not just "use of the term", but an actual example of the concept. In this case, the moving object is an emitter of the "streams". Measuring periods at stationary points will give different results for the forward, backward and sideways waves.

[...]
The pattern is

Code: Select all

x = 12, y = 12, rule = 1c3e/23-ce/4
6.2A$5.ABCA$4.AB2C2A$3.ABC2.CBA$2.ABC4.CBA$.ABC3.C.CBA$ABC3.BABA$A2C2.
CA$.2AC2.B$2.AB2CA$3.A2B$4.2A!