[andreareina]

Paper: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.13...

> We construct a metrology experiment in which the metrologist can sometimes amend the input state by simulating a closed timelike curve, a worldline that travels backward in time. The existence of closed timelike curves is hypothetical. Nevertheless, they can be simulated probabilistically by quantum-teleportation circuits. We leverage such simulations to pinpoint a counterintuitive nonclassical advantage achievable with entanglement. Our experiment echoes a common information-processing task: A metrologist must prepare probes to input into an unknown quantum interaction. The goal is to infer as much information per probe as possible. If the input is optimal, the information gained per probe can exceed any value achievable classically. The problem is that, only after the interaction does the metrologist learn which input would have been optimal. The metrologist can attempt to change the input by effectively teleporting the optimal input back in time, via entanglement manipulation. The effective time travel sometimes fails but ensures that, summed over trials, the metrologist’s winnings are positive. Our Gedankenexperiment demonstrates that entanglement can generate operational advantages forbidden in classical chronology-respecting theories.

[pama]

There is a nice explanation at the end of the letter: “While PCTC simulations do not allow you to go back and alter your past, they do allow you to create a better tomorrow by fixing yesterday’s problems today.”

[dvaletin]

Basically, having infinite budget you can send any gift you can imagine to your friend via Amazon at day-1 and cancel irrelevant orders at day-0 except correct one to make your friend happy at his BD, which is day+1. Make better future correcting your past decisions based on today information. Now the question is: how to get enough money?

[DaveSchmindel]

Interesting. Isn't that just problem solving? If yesterday's problems are unsolved by today, aren't they just today's problems?

[gerad]

I read it as:

- Today, I need to predict tomorrow’s weather.

- Yesterday I made some measurements of the (temperature, pressure, etc) conditions that I need for today’s prediction.

- Yesterday it was impossible to know what measurements I’d optimally need to take for today’s forecast.

- Today, I can (quantumly, probabilisticly) go back in time and make sure I have the optimal set of measurements for today’s prediction.

- I can’t change anything that happened between yesterday and today, but I now have better information I can use to change tomorrow.

[xwdv]

If you already know the optimal set of measurements why not skip the whole traveling back in time part and just change tomorrow today?

[gerad]

> The problem is that, only after the interaction does the metrologist learn which input would have been optimal.

[goodluckchuck]

So you can measure the past, but not change it?

[chrisweekly]

"Our Gedankenexperiment demonstrates that..."

"Gedankenexperiment" sounds an awful lot like "thought experiment".

[forgotusername6]

This has just unlocked a childhood memory of mine. I read a book as a young child about a girl and her grandfather who did experiments about space and time. The girl's name was Gedanken. It explored some of Einstein's theories in the form of short adventures. I've been struggling to find the name of the book. Does anyone else remember this book?

[trulyunruly]

”The book you're remembering is likely "Mr. Tompkins" by George Gamow. The series features the character Mr. Tompkins, but in "Mr. Tompkins in Paperback" (which combines "Mr. Tompkins in Wonderland" and "Mr. Tompkins Explores the Atom"), he has a daughter named Gedanken. The stories are known for their accessible exploration of advanced scientific concepts, including those related to Einstein's theories, through fantastical adventures.” - GPT-4

[omnicognate]

AFAICT there is no character named "Gedanken" in that book. The correct book was findable in a few seconds with a traditional search engine: The Time and Space of Uncle Albert by Russell Stannard [1].

[1] https://books.google.co.uk/books/about/The_Time_and_Space_of...

[paulrouget]

Incredible book.

In french it's Les Trous Noirs Et L'Oncle Albert.

I read that book when I was ~14 years old. I can't overstate how incredible that book was. Having a grasp of what special relativity was at that age really made me feel like I could learn anything just by reading the right books. I never stopped reading about astrophysics since then. And I'm now 40+.

[forgotusername6]

Thanks for finding it! I guess my traditional search engine skills aren't that great these days. Searching either returned booked on Einstein or German titles.

[trulyunruly]

Cunningham's Law:) I was only hoping to provide some direction. But thank you for finding the right answer.

[omnicognate]

I found and posted the answer in parallel with you, and then deleted my direct response when I replied to yours (at greater length as I initially posted only the link, which was sufficient for merely answering the question).

I don't think the posting of unverified ChatGPT snippets in response to factual questions on HN has value.

[kadoban]

That's the translation, yeah. They're a very important tool in physics for exploring the consequences of known or hypothsized physical principles.

[fodkodrasz]

With the main difference that it sound way cooler.

[mdekkers]

That’s literally what it means, and it’s a minor nitpick I have - it’s an English paper, just use English. Using the German word here just increases noise.

[galaxyLogic]

I think it comes from Einstein whose Gedanken Experiments lead to the discovery of relativity. Einstein came from a German-speaking country.

So what the authors are saying is "We're basically doing a similar thing as Einstein did". Jargon is to be avoided but this is more like a tribute to the great physicist Einstein.

[dr_kiszonka]

A less charitable interpretation would be that is a form of self-aggrandizement.

[corney91]

It's a pretty standard word used in quantum physics.

Source: I did a masters in the subject and remember reading it a lot.

[galaxyLogic]

There is something to it. If you say it is a "thought experiment" the interpretation is "of it's juts your thoughts right?" When you say "Gedanken ... " it means this is part of real research in physics (since E did it this way)

[77pt77]

It's both.

[euroderf]

Sort of like wrapping yourself in the flag.

Of Einstein.

[Yoric]

It's a pretty common word in research. After all, "thought experiment" is actually a translation from German.