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#43207 04/16/12 01:43 PM
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Bill S. Offline OP
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Re-reading an old NS article (10.06.06) (Yes, that's June) I was puzzled by the following:

"If one half of a pair of entangled particles were to cross the event horizon [of a BH] and disappear into the singularity while the other did not, then this entanglement would be destroyed, and that is forbidden by quantum theory."

It's just the last bit that bothers me, because I thought that entanglement was a fragile thing that could be destroyed at the drop of a hat-ron.


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Old school QM thought entanglement was fragile turns out it isn't just hard to measure through the vibrational noise.

There is a big difference between fragile and hard to measure :-)

QM information can not be destroyed by any normal physical means we have been able to test, it only collapses (Decoherence) by observation.

You have to stop thinking of QM in normal physics ways it simply doesn't exist in that realm the ultra-cold etc are just needed to measure it.

For example to measure temperature for reporting on the news the thermometer is placed in a box to stop wind and rain etc affecting the reading. It's not that temperature exists only in the box it's just you need to isolate out other factors to get an accurate reading.

Infact we have lately found ways to test entanglement at room temperature and on macroscopic objects km's apart
http://phys.org/news/2012-03-crystals-linked-quantum-physics.html

The development of a camera like device capable of seeing QM and entanglement is also close to a reality
http://phys.org/news/2012-01-quantum-mechanics-naked-eye.html


I believe in "Evil, Bad, Ungodly fantasy science and maths", so I am undoubtedly wrong to you.
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Bill S I ran across a very good radio discussion from British physics professor Brian Cox. It's not deep or complicated but the message is very much that which should be taught

http://news.bbc.co.uk/today/hi/today/newsid_9622000/9622751.stm


It is interesting that people now readily accept that we are controlled by these tiny DNA sequences that creates and shapes what we are, yet struggle with the idea that our physical seemingly solid world comes out of this tiny very non solid fabric structure.

We should also add one last final piece from this year in that the speed of propogation of QM information has recently been experimentally tested and it is alot less than the speed of light. This is going to have very profound consequences to some previous thought QM ideas (http://www.wired.com/wiredscience/2012/01/quantum-information-speed)

Last edited by Orac; 04/17/12 04:24 PM.

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Thanks for the comments and links, Orac.

I've listened to the radio Prog. Great!

I've printed the others so I can read them while doing other things. smile


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Originally Posted By: link 2
Building microscopic cavities which tightly trap light into the vicinity of electrons within the chip....


Does this imply that individual photons are trapped?
Is the trapped light stationary?


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No the light and photons are most definitely moving they are creating standing waves in the cavity

This is the wikipedia reference => http://en.wikipedia.org/wiki/Optical_lattice

But probably a better understanding is gained from looking at standing waves created in water

Sort of general standing wave in a tank
http://www.youtube.com/watch?v=NpEevfOU4Z8

Much closer to the sort of thing the chip optical latice does
http://www.youtube.com/watch?v=ewIr4lO4408


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OK with the standing wave bit. I now have a mental image of a trapped photon jiggling in a confined space.


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“These polaritons overwhelmingly prefer to march in step with each other, entangling themselves quantum mechanically.”

Is this another of those measurement things, or are we saying that entanglement can be created but not destroyed?


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The fact you have realized the above question underlies your deductive skill Bill S and does you great credit.

Up until 1993 we would have said that we create and destroy entanglement. We viewed entanglement as a manifestation that we created by allowing subatomic particles to directly react together in controlled ways. All known ways to create entanglement required the particles to be bought into sort of direct contact.

In 1993 Charles Bennett (http://en.wikipedia.org/wiki/Charles_H._Bennett_(computer_scientist)) published a paper because his mathematical calculations showed that QM could only be correctly explained if it was already present and we were simply unmasking it.

The direct result of his work was in 1997 the report of the first quantum teleportation (http://en.wikipedia.org/wiki/Quantum_teleportation#Entanglement_swapping)

There is no direct connection between the two particles and yet they become entangled.

That is the moment everything changed in QM because it means every subatomic particle in the universe is inherently entangled.

The fact this was discovered by someone working with information and encrypting as a background and viewing QM as information not physical was also most interesting to me :-)

The answer to what it means that every sub atomic particle in the universe is inherently entangled is an open book being written now. I don't have answers only many questions probably the same as you.

But the answer to your question we still call it creating entanglement but actually the answer is we control the background noise and the entanglement emerges which is what is happening in the above example.

I should throw in two very recent links to ponder as you consider our solid world and where QM goes from here
http://phys.org/news/2012-04-electrons.html
http://phys.org/news/2012-04-kind-quantum-junction.html

Last edited by Orac; 04/19/12 04:03 AM.

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“After a first system that allows them to verify that they've actually managed to release one, and only one, photon, a condition essential to the success of the experiment, a second device "slices" this particle in two. This splitting allows the researchers to obtain two entangled photon halves.”

I thought a quantum was indivisible. However, one of your latest links talks of splitting the electron, so I guess I could be quite out of date here.


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OK, so we now have two photon halves; but later in the experiment:
"the two photons that we captured exiting the crystals...."

Suddenly we have two photons. I expect the maths of QM to elude me, but am I losing my grip on the basic arithmetic, or just being pedantic?


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To answer I will point to a more recent publication of a delayed choice experiment or so called "Gedankenexperiment"

http://phys.org/news/2012-04-quantum-physics-mimics-spooky-action.html

How many raindbows can you count?
If I see a rainbow here and there are they the same rainbow or two different rainbows?

You keep trying to put a physical interpretation on a photon you can not as alice or bob :=).


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Another good link, thanks, Orac.

One thing I particularly like is the fact that Zeilinger does not try to interpret this as past directed TT.

"Within a naïve classical word view, quantum mechanics can even mimic an influence of future actions on past events", says Anton Zeilinger."


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Yes what is weird that the future can affect the past but only if it was unobserved and that does not involve time travel of any form it is a quantum effect.

Modern QM is actually clearing alot of the old QM paradoxes because most of those paradoxes arise because of a failure to understand QM properly.

I love the grandfather paradox which modern QM would actually say is impossible ... well within your current reality :-)


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Quote:
the future can affect the past but only if it was unobserved


Could we be moving towards an understanding of reality in which time has meaning only in terms of our limited observations.


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That is very much what QM says Bill

"the act of observation changes reality, even after the fact."

A reasonable argument of the current position for QM
http://phys.org/news/2012-04-quantum-function-reality.html

Last edited by Orac; 04/27/12 01:04 AM.

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Quote:
In one view, the wave function corresponds to an element of reality that objectively exists whether or not an observer is measuring it. In an alternative view, the wave function does not represent reality but instead represents an observer's subjective state of knowledge about some underlying reality


This seems to be saying that QM recognises an underlying reality about which we can really know nothing. An observation causes an aspect of this reality to become perceivable within our reality.


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That would be an accurate assessment .. or we know very little of at the moment because of our fixation with a solid world.

Last edited by Orac; 04/28/12 02:06 PM.

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No doubt evolution and the exigencies of survival programmed us to have a fixation with the solid world.
Prior to QM God would have occupied the non-solid bit. (Look at that, God has crept into this thread as well; without his tildes!)


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