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Author Topic: How can we be certain about uncertainty?  (Read 4875 times)

Offline qpan

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How can we be certain about uncertainty?
« on: 22/03/2004 22:49:35 »
This has been bugging me for quite a while now- and i still do not know the answer!

Lets take 2 quantumly entangled atoms - and in this case, the quantum state of one of the atoms will always be the opposite of the other (and this is the only criteria - the state of each particular atom will be completely random). Lets call theses states up and down. According to current theory, each atom is in a quantum superposition of both up and down - until one of them is measured in which either the up state or down state will crystallise out of the superposition for one of the atoms and the other atom will assume the other state.

The atoms are lets say 10 light years apart, and 1 scientist measures the state of one of the atoms and 1 nanosecond later another scientist measures the state of the other atom. According to current laws, the instant that the first atom's state is measured, the second atom assumes the other state immediately. For our scenario, whis means that information has travelled 10 light years in under 1 nanosecond (actually, it was instant, but lets take the purely experimental view of the situation), which is a violation of Einstein's theory that nothing (including information) can travel faster than light.

Apparently, there is some loophole (which i forget) which means that it doesn't violate Einstein's laws (if someone knows, please refresh my memory).

But my question is, wouldn't it make a lot more sense and save a lot of trouble if the atoms decided which quantum state they were in from the start?

And what proof is there that this is not the case?


"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe


 

Offline MayoFlyFarmer

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Re: How can we be certain about uncertainty?
« Reply #1 on: 23/03/2004 03:11:19 »
I don't claim to be too up on my quantum theory, but are you sure that it really is considered "information" that is flowing?  As I understanding it there is no communication between the atoms, simply the universe balancing itself out.  and if you think of the universe as one entity you can almost treat the entire universe as one point.  
Wow thats wierd to think about...the entire universe as one point; everything represented as infinately small... hmmmm...

Cut me some slack I'm new around here!
 

Offline qpan

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Re: How can we be certain about uncertainty?
« Reply #2 on: 23/03/2004 11:59:58 »
In quantumly entangled systems, as soon as the state of the first atom is measured, the state of the second is no longer completely random, with a probability extremely close to one of being (in this case) the opposite state. (Extremely close due to the statistical nature of quantum mechanics). Einstein described this as the "spooky action from a distance," and i think the loophole i talked about in my previous post which persuaded him to believe in quantum mechanics was that no useful information could ever be transported purely by the quantumly entagled systems (as the outcome of the first measurement is always completely random).

However, surely the second atom must somehow know what the first atoms measure state is? As before the first atom is measured, the state of both atoms is completely random, whereas as soon as the first state is measured, the element of randomness has disappeared.

Not quite sure what you mean by imagine the universe as a point though, as this problem is only a problem if the quantumly entangled states are spatially separated.

"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe
 

Offline gsmollin

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Re: How can we be certain about uncertainty?
« Reply #3 on: 22/04/2004 04:05:53 »
"I think it's safe to say no one understands quantum mechanics." Richard Feynman (I think)

So how can you or I hope to understand it? Any way, relativity is a classical theory, and does not treat quantum mechanical issues. It's interesting that general relativity is believed to provide clues as to why quantum mechanics remains a microscopic realm. The separated, but entangled particles (atoms are pretty big for quantum mechanics) distort the gravitational field, and borrow energy from the vacuum. After a time, there is a sort of "margin call" and the entangled states must resolve. This is why Schrodinger's cat is either alive or dead, not both, but electrons can remain entangled for lengthy periods.
 

Offline assasin

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Re: How can we be certain about uncertainty?
« Reply #4 on: 22/04/2004 09:17:53 »
quote:
So how can you or I hope to understand it?


I believe Feynman is sometimes attributed with the quote "anyone who claims to understand quantum theory is either lying or crazy" but if he did say it it was most probably a flippant repost to Bohr's better documented "anyone who is not shocked by quantum theory has not understood it"

 It is not true to say that Relativity does not extend to the quantum world. E=Mc2 is a perfect vindication of Planks "wave particle duality", which is equally important to Bohrs interpretation of quantum theory.

 The problem with relativity and quantum theory is that Einstein spent the rest of his life fighting against the Copenhagen interpretation that quantum states where random until observed. He abhored the idea that a system should be able to select which state to manifest itself at a time of it's own choosing.

 Ironically it was Einstein's work trying to discredit the Copenhagen interpreatation that lead to Schrodingers descriptions of entanglement.

 I think your ascertation that "entangled particles borrow energy from the vacum" is mistaken, but the description of a "margin call" when the wave form collapses is true enough. As a waveform interacts with it's environment (be it time or space) the uncertainty is reduced until the waveform ultimately collapses.
 

Offline gsmollin

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Re: How can we be certain about uncertainty?
« Reply #5 on: 22/04/2004 12:32:17 »
Actually, it's not my ascertion. I wouldn't ascertain anything about quantum mechanics, because I don't understand it, although I do sometimes use it. I will find the reference, if I'm lucky. The energy being borrowed is gravitational binding energy, between the two entangled particles. We all know how weak gravity is, so at the elementary particle level, the amount of borrowed energy can exist, just like the particles, in two states. As the mass grows, the gravitational binding energy grows, and the allowed time for the borowed energy to exist becomes short. Schrodinger's cat doesn't last long, but an electron can last for long periods.

Relativity does not require quantization of anything, so I fail to see it as a quantum theory. In fact, the dichotomy of QM and R is a major problem in physiscs, and the issues above are part of the effort to resolve this.
 

Offline assasin

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Re: How can we be certain about uncertainty?
« Reply #6 on: 22/04/2004 13:44:35 »
quote:
Actually, it's not my ascertion


 No, and sorry my choice of words was poor, I'll rephrase it: "I find it difficult to accept that entangled states borrow energy from a vaccum"

 The idea that they may share some gravitional binding energy is more palatable to me.

 
quote:
In fact, the dichotomy of QM and R is a major problem in physiscs


 Agreed, and in fact Einstein's claim that QM was an incomplete theory may well prove to be ironic, and QM may show that relativity is an incomplete theory.
 

Offline gsmollin

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Re: How can we be certain about uncertainty?
« Reply #7 on: 23/04/2004 23:52:43 »
The reference work is "Quantum Conscienciousness" by Roger Penrose. Here I quote a review by John Horgan of Scientific American.

"But Penrose takes a new approach. He notes that as the various superposed states of a quantum-level system evolve over time, the distribution of matter and energy within them begins to diverge. At some level-intermediate between the quantum and classical realms-the differences between the superposed states become gravitationally significant; the states then collapse into the single state that physicists can measure. Seen this way, it is the gravitational influence of the measuring apparatus-and not the abstract presence of an observer that causes the superposed states to collapse. Penrosian quantum gravity can also help account for what are known as non-local effects, in which events in one region affect events in another simultaneously. The famous Einstein-Podoisky-Rosen thought experiment first indicated how nonlocality could occur: if a decaying particle simultaneously emits two photons in opposite directions, then measuring the spin of one photon instantaneously 'fixes" the spin of the other, even if it is light-years away. Penrose thinks quasicrystals may involve nonlocal effects as well. Ordinary crystals, he explains, grow serially, one atom at a time, but the complexity of quasicrystals suggests a more global phenomenon: each atom seems to sense what a number of other atoms are doing as they fall into place in concert. This process resembles that required for laying down Penrose tiles; the proper placement of one tile often depends on the positioning of other tiles that are several tiles removed."

The review can be found at http://www.dhushara.com/book/quantcos/penrose/penr.htm

There's more on the internet than this, but I have not been able to resurrect a browsing chain from months ago. I shall keep looking.
 

Offline gsmollin

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Re: How can we be certain about uncertainty?
« Reply #8 on: 24/04/2004 04:59:02 »
Here is some more on the subject. Exerpted from "A Chat with Penrose" by John Baez.

"He said that he had come up with a better idea than the "one graviton" notion. It goes roughly like this. Consider a superposition of 2 quantum states, and consider the difference of mass density functions in these two states. Calculate the gravitational self-energy of this difference (after taking absolute values, presumably - though he didn't say this); the reciprocal of this energy gives a time, and this time should represent the lifetime after which collapse should occur, leaving the system in one or the other state."

ref: http://math.ucr.edu/home/baez/penrose.html

 

Offline gsmollin

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Re: How can we be certain about uncertainty?
« Reply #9 on: 24/04/2004 05:18:00 »
Here are some more references:

http://www.consciousness.arizona.edu/hameroff/slide%20show/slideshow_5.htm

http://www.consciousness.arizona.edu/hameroff/papers/Quantum_vitalism/Quantum%20vitalism.htm

And at last I have found the original reference, that I read, about this subject. If you read this carefully, you will see where I got the idea that the superimposed quantum states are borrowing energy from the vacuum. It's not stated explicitly, but since there is clearly an energy uncertainty, the uncertainty energy can come from the vacuum, much like a virtual particle. Whether this is true or not, I cannot "ascertain". In fact, on the subject of quantum mechanics, I frequently see red, just as Michaelson did.

http://www.newscientist.com/hottopics/quantum/quantum.jsp?id=23334400

 

Offline gsmollin

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Re: How can we be certain about uncertainty?
« Reply #10 on: 24/04/2004 11:48:44 »
* Actually, it was relativity that made Michaelson "see red". I have to wonder what color quantum mechanics would have made him see?
 

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Re: How can we be certain about uncertainty?
« Reply #10 on: 24/04/2004 11:48:44 »

 

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