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Comment by vasco | Hacker News Reader

In another way it's really cool to be able to "see the past" even if all we see is always the past. At this level it is like a super power. If only some aliens had put a mirror somewhere far so we could see ourselves too. Or multiple mirrors at different distances.

With enough mirrors and light bouncing around the size of the universe itself can be a "storage media" of the past with different photons all around carrying "how this location looked X years ago". "All" you have to do to know what happened is find the right photon to see whatever it is you want to see.

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For prior art in this field, see:

https://github.com/yarrick/pingfs

"pingfs is a filesystem where the data is stored only in the Internet itself, as ICMP Echo packets (pings) travelling from you to remote servers and back again."

Also https://en.wikipedia.org/wiki/Delay-line_memory

Storing data as acoustic waves gave a higher capacity in practice, as propagation is slower thus fitting a larger number of symbol per time unit.

From chainsaws to ICMP echo packets (and more)

http://tom7.org/harder/

In theory, couldn't we focus on a perfect spot near a black hole where the light has been warped 180 degrees around it... i.e. if the black hole is 100 light years away, you'd see ( with perfect zoom, of course ) a picture of the earth 200 years ago...?

I understand that we'd have to account for the movement of objects, of course, but with computers, seems like a small hurdle...

You don't need mirrors, you just need to get in front of the photons. A time machine or warp drive will do :)

Also the past is the only thing you can perceive, there effectively is no now.

Is there a science fiction universe that explores a hypothetical warp drive that lets you travel very far relatively quickly, but the travel is only possible with simultaneous backwards time travel that's proportionate to the distance traversed? So you can hop across star systems but can't do a roundtrip A -> B -> A without significantly shifting time from the point of view of A backwards (irreversibly from the point of view of the traveler).

Consider:

- I leave Earth and travel 1ly at speed c

- I arrive one year later

- An Earth telescope will see the destination as it was when I left

- It will take another year to see me arrive

So in a way that's already happening because I'm traveling quite quickly - twice as fast as it seems from Earth's perspective - and I arrive in what appears from Earth to be the past.

Relativity is so hard to wrap you head around.

Well that sounds like a good premise for a scifi book or movie.

https://en.wikipedia.org/wiki/The_Hundred_Light-Year_Diary

By Greg Egan, so highly recommended.

You should check out Three Body Problem (the book, not the mediocre netflix adaptation).

I love that book

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