Why was it specifically 40 years and how does a radio signal get back to you being sent out in space?
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>Why was it specifically 40 years
Not sure I understand this part of the question. That’s just the date when it happened, and it was Nov 1974 so very nearly 50 years ago. The Arecibo telescope sent out our strongest broadcast yet into space, with the goal of showing off humanity’s technological status.
>how does a radio signal get back to you being sent out in space
It doesn’t, it just keeps going out farther and farther into space, moving at the speed of light (radio waves are just a different frequency of electromagnetic waves, which is what light is too). We’re never going to “get this signal back”. We’re thinking someone might receive our transmission and send back *a different radio signal of their own,* because they’d know we’re radio-capable. All we’d receive is what *they* send in our direction, our own broadcast will just keep expanding outwards and onwards into space.
Here’s a page with some more info on the radio transmission, its contents, and other attempts before and since:
[https://www.celestis.com/blog/message-sent-into-space-and-what-we-heard-back/](https://www.celestis.com/blog/message-sent-into-space-and-what-we-heard-back/)
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