Instantaneous Particle Decisions: Why Isn't the Property Set Upon Splitting?

[LeeJeffries]

I was watching a lecture by Prof Wolfson, and he said there was an experiment where a particle was split, I can't remember which, and so either charge was positive in one direction and then negative the other, or spin up and spin down, but in any event the two new particles were sent to two different countries in opposite directions, and once one particle had been observed, information about the other was instantly known

Now in my mind the properties of both were decided upon the moment they were split, but the interpretation is somehow wrong (i.e. no one really believes the moon isn't there when no one is looking, or that the cat is both dead and alive at the same time)

My question is why isn't the property of the new particle set when the original is split? Why is it until it is detected hundreds of miles away it is said it hasn't been decided?

 

[phinds]

Lee, I don't understand it either, but it is not only what is theorized by physicists, it has been shown true by observation. I can't give you a specific reference, but I've been reading this stuff heavily for a while now and that one seems to be conclusive. The quantum state is not defined until observed.

Yes, it makes no "sense" at all, just like the fact that you can see my watch moving more slowly than yours, while I see yours moving more slowly than mine. I don't mean the two phenomenon are related, just that modern physics has experimentally proven a number of things that are so contrary to intuition and normal though processes that they are VERY hard to believe.

Some one in a post on this forum recently made the point that human intuition really sucks when looking at QM.

 

[SethHCohen]

I believe that it has to do with the fact that until it is actually observed, certain details about the particle's state is only probabilistic. So that upon observation and confirmation of state the information is obtained or realized.

 

[ZealScience]

Isn't it a similar case to the EPR paradox? Mr Einstein spent great deal of time to come up with this in order to counter the Quantum theory... Actually, Bell or someone else said that it must be true in order to fit what is true, I guess later the experiment was done, and Einstein lost the game. Maybe you should search for EPR paradox...

In my perspective, the observation is not transforming information, just like Copenhagen interpretation, it is like a conjugate system that one of them decides the fate of the other...

PS: I'm freshman here, and I am not professional. Mistakes there might be, please correct the wrong ones

 

[DrChinese]

I was watching a lecture by Prof Wolfson, and he said there was an experiment where a particle was split, I can't remember which, and so either charge was positive in one direction and then negative the other, or spin up and spin down, but in any event the two new particles were sent to two different countries in opposite directions, and once one particle had been observed, information about the other was instantly known

Now in my mind the properties of both were decided upon the moment they were split, but the interpretation is somehow wrong (i.e. no one really believes the moon isn't there when no one is looking, or that the cat is both dead and alive at the same time)

My question is why isn't the property of the new particle set when the original is split? Why is it until it is detected hundreds of miles away it is said it hasn't been decided?

Yes, there are several experiments in which the distance is quite large. To understand the reasoning about the professor's conclusion, you must study Bell's Theorem. Your idea about predetermination has been falsified because it leads to flat out incorrect predictions. This is not obvious at first glance, which is why it was missed for nearly 30 years after EPR.

For the experiment:
http://arxiv.org/abs/quant-ph/9806043
"A Franson-type test of Bell inequalities by photons 10.9 km apart is presented. Energy-time entangled photon-pairs are measured using two-channel analyzers, leading to a violation of the inequalities by 16 standard deviations without subtracting accidental coincidences. Subtracting them, a 2-photon interference visibility of 95.5% is observed, demonstrating that distances up to 10 km have no significant effect on entanglement. "

For Bell:
http://plato.stanford.edu/entries/bell-theorem/

For an overview of the EPR/Bell/Aspect series, I would humbly refer you to a page of mine:
http://www.drchinese.com/Bells_Theorem.htm

-DrC

 

[DrChinese]

Isn't it a similar case to the EPR paradox? Mr Einstein spent great deal of time to come up with this in order to counter the Quantum theory... Actually, Bell or someone else said that it must be true in order to fit what is true, I guess later the experiment was done, and Einstein lost the game. Maybe you should search for EPR paradox...

In my perspective, the observation is not transforming information, just like Copenhagen interpretation, it is like a conjugate system that one of them decides the fate of the other...

Welcome to PhysicsForums, ZealScience!

In a few short sentences, I think you summed it quite nicely.

 

[SpectraCat]

I was watching a lecture by Prof Wolfson, and he said there was an experiment where a particle was split, I can't remember which, and so either charge was positive in one direction and then negative the other, or spin up and spin down, but in any event the two new particles were sent to two different countries in opposite directions, and once one particle had been observed, information about the other was instantly known

Now in my mind the properties of both were decided upon the moment they were split, but the interpretation is somehow wrong (i.e. no one really believes the moon isn't there when no one is looking, or that the cat is both dead and alive at the same time)

My question is why isn't the property of the new particle set when the original is split? Why is it until it is detected hundreds of miles away it is said it hasn't been decided?

The kind of experiment you are describing is only valid for pairs that are "entangled" in the quantum sense. This means that the two particles (call them A & B) are in a coherent superposition of two possible outcomes, one where A is "up" and B is "down", and another where "B" is up and "A" is down. It is impossible to know which result will be obtained until one of the particles is measured. The theory tells us that such a measurement "breaks" the entanglement, so that each particle resolves into a well-defined state (i.e. both A & B now have definite "up" or "down" status). That is why one observer can immediately infer the state of the other particle, once the state of their particle is known.

It is important to realize that there is no violation of special relativity in the above experiment. That is because no information travels between the reference frames of the two observers. In other words, the observer making the measurement may infer based on the laws of physics what the spin of the other particle must be, but that information is confined to his reference frame. The other observer has no knowledge that the measurement has been made, and thus doesn't know anything about the state of the particle in her reference frame. Of course, she is free to do her own measurement, but then she doesn't know whether her measurement is determining the spin of the other particle, or whether the spin of her particle has already been determined by her partner's measurement in another country. In fact, the relative order of the two measurements is frame-dependent, so there is no unique answer to the question of "which measurement came first".

 

[LeeJeffries]

Great answers as usual!