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Comment by drc500free | Hacker News Reader

This article perfectly bookends my abandoned physics degree.

1. This reminds me a bit of the delayed-choice quantum eraser, which is one of the weirdest scientific outcomes and is the sort of thing that inspired me to pursue a physics degree. It implies a certain kind of time travel is possible, in the sense that in the present moment we can cause some past moments to collapse.

2. As my TA, Frank Wilczek successfully scared me off that physics degree by simply being so smart and having complicated things come so easily to him. Being confronted with the kind of horsepower needed to be successful in academic physics was eye-opening.

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Speaking of causality, Wilczek had been a professor for 4 years before the first delayed choice experiment was proposed (1974 vs. 1978), which would normally disqualify him from being a TA/AI. Not doubting your experience, but I don't understand the timeline here. Were you using "delayed choice" to more broadly mean "which way" experiments?

As an aside, Jeff Bezos had a very similar experience with his physics TA: https://youtu.be/eFnV6EM-wzY .

As an outsider who enjoys a certain flavor of conspiracy theories, your confusion about a timeline involving a professor investigating delayed choice experiments tickles me.

Reminds me of Douglas Adams' Dirk Gently Holistic Detective Agency.

He was my recitation instructor at MIT circa 2002/2003. It was very confusing to have a recitation instructor win a Nobel prize a couple years later, I had no idea who he was until 2004.

Thinking back, he was probably just running recitations for fun and to find future phd's, not grading assignments.

Did he act at all like he had already won a Nobel prize? I want to rule out time travel.

Haha, I very much doubt his behavior changed in the slightest. He knew how the universe works at a deep level, and was so excited to have others learn about it too.

Also note that he has become very involved in research into physics (and stem) education in the later parts of his career (and has done some interesting stuff in this space as well).

At MIT in early Physics courses TAs are other professors, not the usual graduate students. Definitely atypical.

1. There is no retrocausality - https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser#... This is an often misunderstood effect and while it’s very weird, it (most probably) doesn’t break causality.

I like Sean Carroll's explanation:

https://www.preposterousuniverse.com/blog/2019/09/21/the-not...

So it basically reinforces the many-world interpretation, which makes perfect sense, and it’s the most mathematically minimal of all too.

Resorting to some kimd of retro-causality mechanism really shows how many people are uncomfortable with many-worlds.

And many-worlds (though likely only scratching the surface of reality) is pretty much in the vein of panpsychism as it mirors the branching-out biology does with life/consciousness. That’s what I call a tasty correspondence of the universe

We need a new mathematical framework that goes beyond spacetime and amplituhedron https://en.m.wikipedia.org/wiki/Amplituhedron (from which more re-interpretations can happen, especially ones that can encapsulate consciousness more than just “an observer” (or worst leading to absurdity like the quantum suicide experiment https://en.m.wikipedia.org/wiki/Quantum_suicide_and_immortal... which definitely played a role in affecting Hugh Everett’s self-abusive lifestyle leading to his very early death at 51, as well as the suicide of his young daughter

> Everett's daughter, Elizabeth, died by suicide in 1996 (saying in her suicide note that she wished her ashes to be thrown out with the garbage so that she might "end up in the correct parallel universe to meet up w[ith] Daddy"),

https://en.m.wikipedia.org/wiki/Hugh_Everett_III

There is no retrocausality exactly because there is time resolution: causality with sort itself out whatever the cost, is what the quantum erasure experiment showed.

There is a series called “dystopia”on Amazon that demonstrates this in a roundabout way IMHO.

Thanks for clarifying this! The best way I've been able to intuitively understand it is that all worlds are internally consistent and causal, but the observation that causes us to split away from some worlds can be after the fact. That doesn't make it possible to come up with a superposition of worlds that breaks causality.

Is that correct(ish)?

When one of my physics class mates told me he was reading topology at the age of 7, I knew I would never make it with my mere hard work. I still love physics but I’m glad I never tried academia. I would have been chewed up

Gotta call the bluff. That's how I ended up a prof.

> When one of my physics class mates told me he was reading topology at the age of 7

Oh man, everybody with a physics degree met a guy like that, the sort who claims to have learned differential geometry at 2 or some such bs.

don't worry, Richard Feynman read Trigonometric functions when he is 7 years old. that's guy better than Feynman!

I was also reading topology around that age, doesn't mean I understood much if it, lol. In all likelihood you are far smarter than I am.

How does one end up reading topology at age 7? Were your parents math professors or something? Or were you just a very mathematically curious 7 year old?

It was a picture book of donuts.

this is the most amazing and inspiring comment i have read on hackernews, and it just made my day

thank you

I learnt to use a computer very early and I had few friends, so I would spend my days reading Wikipedia. The maths and physics articles for some reason drew me in particularly, and some times I'd also look at other sources. But really, I didn't understand most of it.

Ahh. I can relate, in that case. I thought you meant that you were seriously studying from topology textbooks.

Not same commenter, but we just went to the library as a family every 3 weeks. Around that age I was bored with the childrens section, so I tended to pick books on computing and quantum field theories :)

I ditched the math side soon for the computing section though.

I read Aha Gotcha at about that age, if I recall. It was sitting around my house.

> This reminds me a bit of the delayed-choice quantum eraser, which is one of the weirdest scientific outcomes and is the sort of thing that inspired me to pursue a physics degree. It implies a certain kind of time travel is possible, in the sense that in the present moment we can cause some past moments to collapse.

Only if you assert the copenhagen interpretation. If you instead assert that the experimenter merely becomes entangled with one part of a superposition on measurement, causality is just fine.

I think you’ve got to call the bluff and try to level up. Progress through Physics isn’t monotonic and a bit like the speeding cars of the freeway, you’ll probably meet those going faster at the traffic lights due to the throughout bottleneck of your environment.

Grinding is a separate super power — few can grind at an elite level.

2. Seems sad to me, his job was to make sure you are inspired, or at least informed to make a wise choice, but not scared off. But maybe he didn't know.

He definitely didn't know (he was just excited about showing us Einstein summation notation), and he definitely informed me to make a wise choice. Not every degree program is about ensuring the best median performance, some are only concerned with picking out the world-changers. And that's okay.

As a disillusioned phd I appreciate your response here. For years I’ve beaten myself up for not doing noteworthy science. For some reason your words have washed away a lot of guilt.

Glad it helped! It was a bit crushing at the time (and TBH I am still working through residual shame here and there), but it was kind of like washing out of Navy SEAL training. There's no shame in not hitting the very top of the mountain. Hardly anyone does.

Sounds like “informed to make a wise choice” still applies? I had a similar experience with mathematics, having been “good at maths” in high school and then making friends in university with people who are ACTUALLY good at maths.

Sometimes complicated things are just bad abstractions: you dont have a clearer framework yet.

Yeah, it's the dog calculus thing

"delayed-choice quantum eraser" is so mind-boggling that I don't see any comprehensible explanations to me, a beautiful enigma that locks one of deepest secrets of our universe. And my brain simply refuses to accept any violation of causality - I consider causality possibly the most fundamental rules of physics, if it conflicts with others, I can only consider other rules to not hold.

The Wikipedia article [0] has a fairly accessible introduction to non-physicists like me.

[0] https://en.m.wikipedia.org/wiki/Delayed-choice_quantum_erase...

Reading about these kinds of experiments always fills me with lots of little questions like "well what if we did THIS" or "what if we tweaked THAT slightly". I have the urge to try and "catch reality out", to expose the trick.

Makes me wish you could do these experiments with a laser pointer and a piece of paper instead of needing lots of very expensive machinery and a research grant. Everyone should have the chance to play around with quantum weirdness.

This one is for you then: http://www.quantenkoffer.com/en/

It certainly seems like a mind blower - Perhaps causality is not violated if the concept of causality is actually orthogonal to the concept of time. We perceive causality to be time-dependent, but could this be an illusory constraint from our frame of consciousness?

My feeling is that ultimately causality will turn out to be the same as “absence of contradiction”, and that time is just an emergent phenomenon in the causal network of all possibilities.

It all makes perfect sense in the many-worlds interpretation.

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