Transactional Physics

Not sure if this experiment is old news, but has anyone explained it? — TiredThinker

It's been around for decades and as far as I can tell most physicists still don't believe in time travel. A quick google search and look at the Wiki page gave me that information so I'm not sure why this is being asked here.

Rather than debating on the existence of time travel, we already had a discussion regarding the paradox if time travel would exist after all.
If you are interested, here is the thread: Time Travel Paradoxes

Yeah I'm well aware of the grandfather paradox and whatnot, but this thread is about physics and implied time travel.

Surprised so few have approached this experiment like Sabina. So basically the data is interpreted wrong? Sensors 3 and 4 are wrongly not considered together for comparison?

I think Sabina actually did do a video suggesting that reverse time travel at least for information might be possible without causing paradox.

The Grandfather paradox is the biggy. Here's my take on the subject: You go back in time and kill your grandfather before he procreates. Instantly the world you came from vanishes and is replaced by an alternate reality in which you don't exist. So you disappear and there is no way to tell time travel has occurred. It's a suicide mission.

On the other hand, suppose you go back in time and don't do any real damage. Then the minor alterations you might cause in the time stream are absorbed and normalized. I don't subscribe to a butterfly chaos, rather what Stanislaw Lem saw as a series of effects that peter out and vanish over a time.

Surprised so few have approached this experiment like Sabina. So basically the data is interpreted wrong? Sensors 3 and 4 are wrongly not considered together for comparison? — TiredThinker

I have found a serious unrelated error in another video of Hossenfelder's, so my trust is broken, and I find myself questioning this dismissal.

The two light paths to the signal detector D0 are the same length every time regardless of which detector gets the idler photon. If they interfere, there will be a bars always at the same locations, never out of phase. Sabine says that the pattern from photons detected at say D4 are out of phase and when combined with the D3 bars, results in no interference pattern. That means that for the idler going to at least one of the detectors, the signal light going up to the 'screen' is out of phase from it's counterpart, which cannot happen if nothing has moved. It cannot happen if the path lengths are the same each time.

Am I missing something? Has there been a peer review of Hossenfelder's video?

this thread is about physics and implied time travel. — Mr Bee

There is no information that can be sent to the past or FTL in any of these experiments. None of it constitutes time travel in any way. There are plenty of interpretations that explain the quantum eraser and explain entangled behavior in ways that obey the laws of locality and forward causation. It's only the counterfactual interpretations that need FTL explanations for these things, and even those don't propose information transfer to the past.
The topic is thus unrelated to time travel.

The Grandfather paradox is the biggy. Here's my take on the subject: You go back in time and kill your grandfather before he procreates. Instantly the world you came from vanishes and is replaced by an alternate reality in which you don't exist. So you disappear and there is no way to tell time travel has occurred. It's a suicide mission. — jgill

The paradox is that, if you do that, and are therefore never born, you cannot go back and kill your grandfather before he procreates. So he does procreate, and you are born. So you do go back and kill him. So he doesn't procreate...

On the other hand, suppose you go back in time and don't do any real damage. Then the minor alterations you might cause in the time stream are absorbed and normalized. I don't subscribe to a butterfly chaos, rather what Stanislaw Lem saw as a series of effects that peter out and vanish over a time. — jgill

I never considered this. It seems to me it depends on how long after your visit you look for alterations. The shorter the time, the less likely you'll see alterations. If the fate of a butterfly that lived today was reversed, that one lost butterfly wouldn't be noticable tomorrow. Even it one animal that survived by eating it ends up dying today instead, that wouldn't be noticed.

But that butterfly is going to be responsible for offspring. And it's offspring will have offspring. Go a few thousand years in the future, and quite a few butterflies that existed in the original timeline no longer do. And quite a few animals the should have lived didn't. And others that shouldn't have lived did, because the predators that killed them never came into being, because their parents didn't get to eat the things that ate the butterflies that should have lived but didn't.

At point does the altered food chain become noticable? When and where are the lives and deaths of people changed? Sure, overall, things will have the same balance. But there will be differences that are noticable to people who know what it should have looked like.

But there will be differences that are noticable to people who know what it should have looked like. — Patterner

How could they have known? Any minor changes in the timestream will actually be what they are accustomed to.

The Grandfather paradox shows how a trip to the past could shift alternate realities in the present in such a way no one would notice. Suppose someone has actually gone back in time and done some major damage. Then we would be in an alternate reality and could not distinguish the differences - there would simply be none. That person, who existed in one reality, would not exist in the present reality.

Well, yes. It would, off course, depend on people/beings outside of time. Superobservers.

Well, yes. It would, off course, depend on people/beings outside of time. Superobservers. — Patterner

Yes, to distinguish differences in realities. I wonder, do we shift realities, never realizing? The very idea spoils a sense of adventure a time traveler might have. Best not to engage in the practice.

I wonder, do we shift realities, never realizing? — jgill

I'm certain I switch realities almost daily. I get red lights like you can't imagine. Even as a passenger I can affect the lights to the point that a driver said, "What the heck is going on?!? I can't believe how many red lights in getting!" Of course, I apologized, and explained it was because of me.

Another person folds me of a light he knew of on his 15-mile commute to college that was always green, asked even I couldn't get red. When I drove to the town his college is in some days later, as we were sitting at the red light, he said, "Wow. You're good."

I don't generally explain that God gets a laugh out of screwing with me by switching me to alternate realities where the lights I'm approaching will be red when I get to them.

To rub salt in the wound, the traffic facing me at the red light gets a green arrow to turn in front of me before I get my green light. But when I make the return drive, and am at that same red light, but facing the other direction, the people in the same position I was in earlier now get the green arrow to turn in front of me before I get my green light.

So yes, I, at least, shift realities. And when I'm dead, God and I are gonna sit down and have a little chat.