#### I was with you right up to...

"A group of physicists at the University of Glasgow is claiming a first"

But, hoorah for science!

A group of physicists at the University of Glasgow is claiming a first: taking photos of entangled photons. In this paper in Nature (hooray for free access!), they explain that their 201 x 201 pixel images captured around 2,500 different entangled quantum states. The entangled photons were imaged using different lens …

"A group of physicists at the University of Glasgow is claiming a first"

But, hoorah for science!

to Nature for allowing us ordinary mortals to read the paper, and not least, to Richard for giving us a heads-up !...

Henri

"allowing us ordinary mortals to read the paper"

Which is grand. Sadly without a plain English explanation it is beyond my dismal A level physics.

> "“state” information in entangled quanta propagates faster than the speed of light."

"State information" does not propagate - and neither does it go back wards in time. If I win in the lottery, there is nothing that propagates to the lottery tickets of the other players making them instantly worthless. The whole lottery ticket system just needs to be considered as a single system. Sure, QM has the added benefit of the complex-valued probability density function which allows you to do MORE MAGIC and is somehow MORE EPISTEMOLOGICALLY REAL than the real-valued probability density functions of classical probability calculus, which after all just express SUBJECTIVE UNCERTAINTY whereas here we have OBJECTIVE UNCERTAINTY buy COMPLEX-VALUED AND INTERFERING and the lottery numbers such as they are are not actually real in any classical sense UNTIL YOU RENDER THE INFORMATION CLASSICAL BY LOOKING AT THE TICKET!

WHAT DID YOU JUST DO, THE CAT DIED ON ITS ARSE IN THE BOX! OMG!

Yeah, it's a kind of maths trick.

Take two playing cards - an ace and a two, shuffle them randomly so you don't know which you have.

Take one to Australia leaving the other one at home in a yurt on the Mongolian steppe and once you get there turn it over.

Hey presto, you now know what the other one was. OMFG! Faster than light!!!!

IANAS (i am not a scientist)

Your example is flawed IIRC the quantum entanglement bit (more than happy to be corrected).

For your example to work when you turn over the card in Australia, at exactly the same time, the card in a yurt on the Mongolian steppe would turn over as well.

The difference being that you could, if you wanted to, post the one card to Australia in two envelopes half the size of an ordinary playing card, so long as you keep it face down. But once it gets there, and two half-envelopes arrive on someone's doormat and they take out the one card and look at it, you're essentially right about the disappointing lack of trick, or mis-reporting of faster-than-light information transfer. As none of this actually proves that the state wasn't determined all along. And (as we went over last time) none of this allows anyone to manually insert information to be transferred.

With the playing cards, they really are the ace and two; you just don't know which one you've got. Entangled quantum particles are different. Until you measure the state, they're not in one state or the other and the measurement collapses the waveform. The other particle of the pair is then guaranteed to give the corresponding result, no matter how far away it is and how soon after the first measurement it's checked.

The cards are an example of a hidden variable theory - i.e. the value you're measuring is already set and just waiting to be measured. There are experiments that can tell the difference between hidden variables and the quantum weirdness described above; when these experiments are done, quantum weirdness wins. In fact it's been shown that no local hidden variable theory (one without FTL transfer) can explain observed results.

I suspect any simple explanation in real-world terms is probably wrong.

"I suspect any simple explanation in real-world terms is probably wrong."

Maybe it is, and maybe it isn't.

That's the difference between physical objects and information.

> Until you measure the state, they're not in one state or the other

This is an artefact of the model, they are actually in one state or the other.

In the same way that the cat is actually alive or dead, it is not both alive and dead even

if we can treat it like that mathematically and achieve the same result.

No, it's a property of the model. And the kicker is that in something like a hundred years nobody has been able to demonstrate that there is any more to reality than the model describes. Or to put it another way, the hidden variables that "common sense" demands have become increasing conspicuous by their absence.

Nothing is "propagating" faster than the speed of light. From the universe's perspective, both photons are the same "thing," it's only from our perspective that they aren't and if you can measure stuff you aren't supposed to because "our" view allows that then I can't really see what the hoo-ha is all about. The universe is as dumb as a box of dead cats when it comes to small stuff.

if the many worlds interpretation is valid and when particles are entangled, all possible pair state permutations will exist, but in separate universe branches. henceforth, when the state of one of the entangled pair is measured and the appropriate correlated value is found to exist in the other, the observer is in fact discovering which of these universes he/she is in. no faster than light propagating required.

Emmanuel Goldstein: "the observer is in fact discovering which of these universes he/she is in. no faster than light propagating required."

In fact you can prove this (but only to yourself) by becoming Shroedinger's cat yourself. You get in the box, subject yourself to a 50% quantum risk of death, get out, rinse, repeat. After you have survived 22 times you've hit 5 sigma (I think, maybe someone can check my maths) certainty.

Of course, there are now something over 4 million universes where people are tutting to themselves as they get a dead physicist out of a box.

Except that if you're doing that maths, you're chances of surviving that 5 Sigma event were precisely 1. Because you're there to do the maths.

Go, go anthropomorphic principle! A great thing to talk to people about who tell you that God is real, because the chances of us existing are so infinitesimal, he must have made us.

Good luck with your quantum immortatility, struldbrug. I just hope you like cats...

Not since I found out what mass-murdering bastards they were yesterday, thanks to El Reg.

I've been thinking about that and I don't quite agree (although it wasn't me that downvoted you). Every time you get in the box you run a 50% risk of dying. As you survive more and more times, it appears obvious that *something* is defeating the risk. That something could be (if the equipment isn't broken) that you find yourself in a particular universe where the history is of, say 20 successful survivals, and not in one of the 2^20-1 universes where you died.

This actually gives you a counter-argument to the God people - that there are gazillions of universes out there where nothing has happened at all. We live in the one where we developed like this. But the difference between that argument and my strategy is that (if the equipment works) you can exactly quantify the chance that you would have survived, whereas we have no realistic measurements for the chance of abiogenesis.

...to think that taking a photograph of a single photon is quite an amazing feat in itself?

The human retina can respond to single photon events. But these don't make it as far as your brain - otherwise it would be swamped with noise in low light.

Yebbut surely to photograph a quantum you have to bounce other quanta of light off it, which then in turn have to end up in the camera. Isn't that what's slightly weird about this? What does the uncertainty principle have to say about that?

Indeed 1 (and only 1) photon triggers 1 photoreceptor ( which is a modified G-protein coupled receptor). Certainly the retinal cells are capable of truly extraordinary sensitivity.

Imagine photographing the camera that you are taking the photograph with

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