The Secret Life of Time | Hacker News Reader

The Secret Life of Time

newyorker.com

109 pointssergeant320 comments

It might be interesting to consider how and whether time is relevant to computation. For example-- does time have an arrow on a computer?

It does, for at least two reasons: 1) Computation physically produces heat and increases entropy. 2) Many operations lose information -- for example XOR's can't be run backwards to reproduce the original inputs.

People have tried to tackle both issues with reversible computing. https://en.wikipedia.org/wiki/Reversible_computing

Someone even wrote a programming language that was (logically) time-reversible:

https://en.wikipedia.org/wiki/Janus_(time-reversible_computi...

Does having a time-reversible programming language mean that if you start with the output of a given program, you can run the program backwards and get the input?

This would be useful outside of research. Though, I expect the memory usage will be ridiculous.

Isn't that already a thing, if you really want it? [1,2,3]

[1] https://en.wikipedia.org/wiki/Retroactive_data_structures

[2] https://www.youtube.com/watch?v=T0yzrZL1py0

[3] https://www.youtube.com/watch?v=WqCWghETNDc

https://sourceware.org/gdb/wiki/ReverseDebug

http://rr-project.org/

XORs only lose information if you overwrite the input values.

In that way everything is trivially "reversible", so this is not a meaningful category. What is meant by reversible operation is that you can get its input from just the output.

It is a weird choice of irreversible CPU operation, though. Something like MOV / LD etc. would probably be a better choice.

There is a branch of computing called zero energy computing. It overlaps with time reversible computing.

With power demands for exabyte data centers and exaflop computers well into megawatts, there is interest in low energy computing.

One scheme Ive heard pairs a forward circuirt with an inverse circuit to reduce energy, despite it appears to double the computation.

Still working through the article, but it reminded me of the presumable fact that everything that happened before the first conscious entity existed in the Universe was essentially instantaneous. Same goes for time's forward direction. Without consciousness, i.e. with a perfect form of stasis, one could time travel to just before the heat death of the Universe in an instant.

John Archibald Wheeler took this idea even further with the PAP, the Participatory Anthropic Principle.

You are asserting that "the Universe" can exist without a "conscious entity".

are you suggesting it can't?

[oops]

I assume you meant "can't"? I think the parent simply made a poor choice of words, "a perfect form of stasis" fits a lot better than "without consciousness"

I actually assert this! But that is because I say the word "exist" is meaningless without a conscious observer. I would claim that existence requires consciousness and vice versa.

A Whale, of course.

Or a potted plant.

The passage of time is an emergent property of quantum entanglement. Yes, I know that sounds like new-age hooey, but it's actually based on solid science:

http://blog.rongarret.info/2014/10/parallel-universes-and-ar...

[UPDATE] I would really appreciate if those of you who are downvoting this comment would tell me why.

“Where is it, this present? It has melted in our grasp, fled ere we could touch it, gone in the instant of becoming.”

It might be a stretch, but this seems like a small glimpse of the concept of a time differential ('dt'), a thousand years before the math existed to describe it explicitly.

Most ideas don't have explicit mathematical descriptions. Why would this one be more notable than any other?

Fascinating article. Great, long read.

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