# COMMUNITY : FORUMS : SCIENCE

## EPR (Einstein Podolsky Rosen) paradox

. Following a link in one of kelseymh's posts, I started reading the Wikipedia page on Bell's Theorem. Before I got through the first sentence of the Overview, I got sidetracked on the EPR paradox (read about it before, but found I had forgotten or misunderstood a lot of it). A lot of it still doesn't make sense. They didn't teach us a lot a quantum physics back in the '70s. heehee
. Looks to me like I need to understand EPR before I try to go any further. Any volunteers to try to explain it so that Joe Plumber can understand?
. TIA

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NachoMahma (author) 8 years ago
. Whew! I been reading Bell's Theorem. Meas in QM, Copenhagen interpretation, and misc others at Wikipedia.
. I'm having trouble getting my brain wrapped around wavefunction and collapse. Is wavefunction only a convenient way to say it's located somewhere close to here, but we're not sure exactly where until we measure it? Observer may not know if S's cat is dead or not, but the cat is definitely one or the other (and the cat knows)?
. At any particular point in time/space the object is in a definite spot with a definite set of properties, but we can only make a reasonable guess?
. Time for more aspirin.
8 years ago
Hey, NM, sorry I missed this post of yours. I'm going to try to write a reply here, but it ought to be a separate Physics topic (sigh...). ... Yup, it got way too long. See my Physics topic instead.
NachoMahma (author)  kelseymh8 years ago
. Thanks
8 years ago
You're welcome! I tried to include both arm-waving conceptual stuff, and some concrete mathematics.

If you've played with diffraction gratings, interference fringes, or even standing waves in water, I think that's enough to give you a vague mental picture of wavefunctions.

For some mental imagery on how they can "also behave like particles," I recommend reading up on solitons.
V-Man7378 years ago
Did you mean Zeke the Plumber?
Lithium Rain8 years ago
This may be the stupidest idea ever, but what if "spooky action at at distance" is a reflection somehow? Not in the sense of one particle being an illusion, but almost like your reflection in a mirror, except that unlike the reflection of yourself in the morning, it has mass and can move and affect its "sister" particle. Or is that totally crackpot and nonsensical?
8 years ago
That is actually not a bad "classical metaphor" for what's going on. The two "parts" of an entangled system are as tightly and inextricably bound as you and your reflection.

The "weird" quantum mechanics part is that the binding is (apparently) instantaneous. For a real reflection in a mirror, there is a delay between your motion and your perception of the reflection's motion, dictated by the round-trip time for the light from you to the mirror and back again.

The Nature article I had cited elsewhere was explcitly testing that instantaneity for a system of two entangled photons, separated by some 20 km.
Goodhart8 years ago
Oh cool, I just stumbled on ths why didn't anyone tell me ? :-) I have got to take some time and read through this more carefully....I have done a cursory reading of all the posts, but not the links. I love this stuff, or at least, what amount of it I can grasp ( sadly my math skills are VERY lacking in this area).
8 years ago
You wrote, "I love this stuff ... (my math skills are ... lacking in this area)." I would highly recommend Feynman's ''QED: The Strange Theory of Light and Matter. He was able to describe wavefunctions, interference, etc., without any mathematical equations.
8 years ago
Thanks, I will look into that.

It isn't just this stuff as it were, that I love though....I like to stretch my thinking in lots of ways, including the imagination thing I mentioned in another forum (Hawking? ;-)

I was once asked if I could "see" in my mind's eye, a mobius strip, then I was asked to cut it length wise, and then again. The second (or was it the third?) cut, caught me by surprise.
Then I was asked to imagine a "2 dimensional" mobius strip. That took awhile and I am not sure I had it quite right when he showed me his rendition (drawn). I would love to be able to see a 3-d version of a mobius strip (that is, a structure that is twisted in each of the 3 dimensions).
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