Bat echolocation is a topic that's very personal to me. My grandpa worked as a researcher in telecommunications and fibreoptics in the 1970s, in East Germany (GDR). This being at the height of the cold war, it was completely prohibited to publish anything relevant to their actual work, so that the "class enemy" wouldn't be the wiser of what they were doing in the lab. When publishing anything, they had to water down the content so much that it became useless to anybody reading it. Also, publishing on data transmission with fibreoptics, while nobody in the country is able to get a telephone line in their homes, wasn't seen as helpful.

It was sometimes possible to travel to western/international conferences - of course only after the Stasi gathered from interviews with all your colleagues and neighbors that you loved your children, and were likely to come back. And even then they were not allowed to make any contact with western scientists at the conferences, making any kind of useful exchange near-impossible.

After finding and reading a book on Bionics, which was a bit of a hype topic at the time, he noticed that the biologists were talking about the inexplicable nature of bats' echolocation. As he had experience with code multiplexing, he wrote a paper on the signal theory behind that, in 1974 [0]. As this topic was considered completely harmless, it was no problem to get this published in the GDR. After a request, it was even published in a journal in West Germany. But then being invited to give a talk on it in Frankfurt/Main, the authorization was given three times by the institute, and then revoked again each time (by higher-ups/Stasi). He was then asked to cease any communication with West-German researchers (who had sent him a book manuscript to review). It was a bitter-sweet thing for him. In later years, he was often asked about bat echolocation, as it made for a good pop science topic. But of course he would have loved to publish, and exchange, on his actual research topics at the time much more.

My grandpa died a couple of years ago. When I travel to international conferences now - being able to present whatever I like, talking to whoever I choose - this history often comes back to mind. Sometimes these stories feel like a very distant past. But then I read about how Linux maintainers are removed just for having a Russian email address, as happened recently. So maybe we haven't come as far as we think. I believe it's important to be conscious of the great freedoms most of us currently enjoy, how precious they are, and how brittle they can be.

[0]: https://link.springer.com/article/10.1007/BF00611870 - paywalled, unfortunately. And German!