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Comment by katabasis | Hacker News Reader

If "zero worlds" means there is no unified single reality that all physical systems relate to (just like there is no universal frame of reference for motion according to relativity) then I think we're in similar territory.

I'm not familiar with Garret, but Rovelli's book contains a great discussion of the "quantum eraser" experiment in that blog post, where quantum interference causes a split laser beam to recombine in different ways whether or not a detector is present. This is something you can observe with tabletop equipment apparently, a pretty visceral demonstration that quantum phenomena are a real part of our world.

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I read Helgoland at the weekend (in a hammock at a glamping lodge in the jungle) and have been meaning since to buy some prisms to see if I can replicate that experiment. Do you happen to know if it's as simple as he describes it, or is there a trick to making it work?

Unless you have a light source that can emit a beam consisting of only a few photons (and precise enough detectors to see them on the other side) you won't see the effect. Otherwise, the quantum interference demonstrated by the experiment will break down due to what is called "decoherence" – too many things interacting with one another will cancel out the phenomenon you want to observe. This is why we don't see quantum weirdness in our every day experience.

Interesting. How precise a laser would you need? And typing "photon detector" into amazon is not exactly yielding anything promising - is there equipment obtainable by somebody who's casually interested, or is this prohibitively expensive?

In Rovelli's book he talks about going to Anton Zeilinger's laboratory to see the experiment in person. I assume you'd need a proper lab with carefully calibrated equipment for something like this, but I'm not a physicist.

Even so, an effect that can be demonstrated with tabletop equipment in a lab seems more intuitively real to me than something that requires a giant particle accelerator...

100 or 200 years ago a more or less average person could set up cutting-edge scientific experiments with basic equipment and patient observation – this was the modus operandi of Michael Faraday[1] for example. Sadly it seems like those days are mostly behind us now.

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

100 years ago, to do the Michelson Morely experiment (imho the most important scientific experiment done yet, except perhaps LIGO) required heroics and could not have been done by mere mortals. It required floating a massive appartus on a bed of mercury in a subbasement and was still hard to run during the day due to horse-based deliveries a few buildings over.

My friend did the experiment in an afternoon Physics lab (princeton), almost all of of this is due to innovations in precision manufacturing and material science.

If you want to do a basic quantum eraser, the simplest path is this: https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=69....

A good physics undergrad could assemble this and demonstrate it successfully in a day. It's really a Mach Zender interferometer (https://en.wikipedia.org/wiki/Mach%E2%80%93Zehnder_interfero...) which is one of the nicest designs for doing quantum information experiments.

The laser they use isn't anything super-special, although it isn't like what you'd get if you bought a laser pointer or a cheap laser engraver. The beam size is very fine and the beam shape is round. Most of the other parts are fairly generic but precisely made. The most exciting part is the beamsplitters, https://en.wikipedia.org/wiki/Beam_splitter since they are key to assembling the interferometer itself.

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