Has a “delayed-choice experiment” been performed from a light source outside our galaxy?
Not a simnply a thought experiment but, the real thing?
Is this a joke?
Worse–it’s quantum physics. But from an extraterrestrial perspective.
My head hurts.
Ahhhh come on this stuff rocks!
It was obviously a jest, but wouldn’t this be a significant experiment (if it could ever actually be performed that is!) This would seem to show that the photons would have to have known whether we would detect them billions of years (depending on it’s source) before our solar system was even formed. If this particular delayed-choice experiment is ever carried out, it would show, incredible as it may seem, that the past of the quantum world is influenced by factors associated with how we choose to conduct our observations now!!!
Am I on the right path? or should I have taken a right at Albuquerque
Help!!!My head is hurting too!!
Now, I sort of understand the principle that proposes that our observations now can impact upon the state of the world in the past, however illogical it seems.
But I have no idea whatsoever what you are on about
Is it possible to have some kind of back story explaining the significance of the question and why it’s being asked? Or, perhaps, a link or two.
I’d be glad to comment on whether I see significance in the endemic infection by Rickettsia of Hydrochoerus senegalensis, but I’d expect that somebody asking such a question have the common decency to explain his terms and his reason for asking such a question in the first place. Same applies here.
Here ya go:
http://physicalworld.org/restless_universe/html/ru_5_15.html
I think this is what he is talking about. Experiments have been done which demonstrate that the outcome of events at the quantum level remain in some sort of indeterminate state UNTIL they are observed. I have no idea how they actually perform these experiments, so I can’t answer the OP’s question. But I believe such experiments measure the deflection of particles, so I suspect that even if one could do so with photons emanating from a distant star, one would still be measuring an event (deflection) here on Earth, and whatever the photon did before that would be irrelevant. I dunno, is that right? I guess we’ll have to wait until someone who knows about quantum physics sees this thread.
Are we talking about the Einstein Podolsky Rosen paradox?
Very VERY briefly:
-
Experimenters produce pair of particles at point X. They fly off in different directions
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Some time later, a measurement is performed on one of the particles at point Y (as far away as you like from X). Then a measurement is performed on the other particle at point Z.
even if points Y and Z are far enough away from each other that there is no time for a signal to travel between them between the two measurement times, the results of the “Z” measurement are different, depending on what you choose to measure at “Y”.
(it’s ‘delayed choice’ because the choice about ‘what to measure’ is delayed until there appears to be no physical way that it could have an effect on the other measurement.)
This is a very freaky result of QM, because it appears to violate the locality principle - it seems that what you do at one point in the universe can affect another point even if they are light years away from each other.
However, it doesn’t imply cause-and-effect working backwards in time. The point is that the two measurements are too far removed from each other for cause-and-effect to (theoretically) work at all - and yet it does!
I believe the experiment has actually been done a number of times (it’s not that tricky, except philosophically) and , yes, it ‘works’.
So … ummm… what was the point of the question again??
I know… let’s have a deliberately exclusive thread which makes most ordinary posters here feel inadequate!!
Great idea!
Just to make sure:
The OP is ludicrously specific, unprovable, and above all vague question. Not having studied Quantum Physics in college yet (or ever), I am left in the dark.
Well, I didn’t study quantum physics, either, but all I did was look up “delayed choice experiment” on Google and read enough of the first couple of hits to know that (a) the OP was about quantum physics or something, (b) I didn’t get it, and © my head hurt.
The OP sez he was joking, anyway, so as there doesn’t seem to be a debate here, maybe some kind mod could move this puppy to the forum For Jokes About Pointless Extraterrestrial Silliness?
Yeah, but I don’t even understand how he’s joking. 
No, it’s not a joke, physicists have thought about this kind of experiment. I’m not sure if it’s been done or not.
An EPR ( Einstein Podolsky Rosen) experiment has two parts.
- Splitting a photon beam
- Recombining it.
QM says that if you measure which path the photon took then you will not see interference when you recombine the beams. If you don’t measure, you will see interference.
The “delayed choice” comes in when you decide whether or not to “measure” after the splitting has already occurred. Since experiments show you still get the same result, you have to conclude that the photon “knows” ahead of time whether to take both paths or just one. (Well, you don’t really, because there are other ways of looking at it. But that’s the popular gee-whiz way of putting it.)
buzz’s OP asks “What if the photon needs to know billions of years ahead of time whether to go both ways or only one?” The problem is, even if you use photons from a distant galaxy, you need to split the beam after they arrive. No reason to expect “old” photons to behave any differently.
Now, if the beam were split by some natural process at or near its source, then the OP would make sense. A possible process is a gravitational lens.
BTW - Welcome to the SDMB, buzzz_kill!
Yeah, that’s a helluva question. Not really a GD, though.
But keep 'em coming. I’d rather debate QM than another damn SUV thread.
“Are SUVs proof that aliens are experimenting on us?”
It seems like a perfectly valid GQ question to me. I think that answer is that it happens all the time, but there’s no way to analyze the results.
Everytime an astronomer fires up his instrument, there is some probability that he will view an image of an extra-galactic object. This probability is 100 percent when he or she actually views another galaxy.
If the photons that make up this image have the possibility of taking multiple paths (like being gravitationally lensed around some other massive object, whereby it could take one path around the object or another path around it) then the experiment is basically executed. QM, as I understand it, says that the photons did not take any single path until a detection system (in this case the astronomer) “sees” the photon.
So, this experiment happens all the time. But how one would actually get measurable data I don’t know.
I just thought, technically the extra-galactic photons of the image could be diverted into an earth-bound two-slit apperatus. Still, I don’t see why these photons should act any diffferently from an earth-bound source.
It’s been done. It’s something I have noticed and wondered about. The scientific term I’ve heard is “Spooky action at a distance.” Heh heh. I suppose that’s more of a layman’s term but it sums it up nicely. Here is an article that describes the whole thing (theory and experiments) in pretty plain english.
Entaglement is a key word here. I’ve never heard of this having the potential to effect the past though . . .
DaLovin’ Dj
I think that entanglement is different from delayed-choice.
So the theory is that nothing will exist (except as probability) as anything unless we observe it, and since we observe the universe, and it took billions of years for everything to get the way it is, our observing it now translated through time and locked in all of those particle interactions? So until awareness came into the picture nothing had been decided and awareness effected the past to allow for its own existence?
Pass the aspirin . . .