[ExI] Simulations of ‘backwards time travel’ can improve scientific experiments

[BillK]

On Mon, 16 Oct 2023 at 19:55, Adrian Tymes via extropy-chat
<extropy-chat at lists.extropy.org> wrote:
>
> If I read this correctly, they send a bunch of photons and then, after finding out certain criteria, then apply filters to make sure that only the photons matching those criteria make it through.
>
> They seem to confuse "only the correct photons arrive" with "only the correct photons were sent", overlooking that the filtered-out photons were sent too.  The difference between simulated time travel and what they are doing is the fates of the filtered-out photons.  The difference is enough to break the simulation for most meaningful purposes.
>
> I wouldn't call this a "deep dive", nor is this specific to quantum mechanics.  On a macro scale (as in their "gift" analogy), if I know that I will need one of four things but I do not yet know which one, I can pre-arrange that one of each of those four will be where I need it when I need it, and ignore the other three at that time, no temporal shenanigans (simulated or otherwise) involved.
> _______________________________________________


I've been fretting a bit over this, but I think I understand it now.
The article is written in a very click-baity way, making it difficult to follow.

But basically you're correct.

This is a thought experiment they are describing.
They haven't yet done anything practical.
They aren't changing either the past or the future.

The 75% failure rate is due to the probabilistic nature of finding
suitably entangled photons. The thought experiment is a simulation
because it produces this effect probabilistically.
So, there are a certain number of times when it looks like you have
time-traveled, but not every time. The filter is used to actually see
the photons that would appear to have time-traveled.
As you say, they are just selecting the photons they want and
discarding the rest.

My time-traveling DeLorean will have to wait a while!

BillK