Emilio Santos joins the dark side :)

DrChinese

Emilio Santos, one of the most vocal local realists, appears to have finally lined up against EPR and joined the majority view. From his latest paper, posted today:

http://arxiv.org/abs/1203.5688

Santos: "The conclusion seems unavoidable: we cannot assume that physical systems possess properties independently of measurements. ... We shall assume that the measured properties are contextual, that is they depend not only on the state of the system but on the whole experimental context. This point was correctly emphasized by Bohr..."

I couldn't agree more. But from EPR: "This makes the reality of P and Q depend on the process of measurement carried out on the first system, which does not disturb the second system in any way. No reasonable definition of reality could be expected to permit this."

So my hat is off to Santos for finally throwing in the towel (and throwing EPR under the bus).

------------------

PS: Or maybe not. He goes on to say "Does that assumption prevents[sic] a realistic interpretation of quantum physics?. I think not." I guess he is finding it easier to simply assume what he wishes to prove, since a suitable proof has been elusive to date.

PPS Hoping the readers of this post take it as it is intended, a little bit of humor for your day. Actually my hat is off to Santos for being brave enough to continue his battle in the face of long odds. Probably keeps everyone sharp.

billschnieder

Hi DrC,
You do remember that contextuality is not contrary to EPR don't you? I remember giving you the following analogy which you appeared to understand at the time:

... continuing ...
- Emilo Santos: We cannot assume that "Red Sun" observable exists independent of measurements. ... We shall assume that it is contextual, that is, it depends not only on the "photons from the sun" but on the whole experimental context, which includes the "red goggles" worn by DrC.
- DrC: Stop the presses! Emilo Santos has joined the dark-side and thrown EPR under the bus, OR did he?

DrChinese

I just really don't see how they could be any more clear that a contextual realism is not reasonable.

Further, I don't see how Einstein could be any more clear when he said: "I think that a particle must have a separate reality independent of the measurements. That is: an electron has spin, location and so forth even when it is not being measured."

So yes, I would say that contextuality is contrary to both EPR and Einstein. And I would say that Bell shows that an electron cannot have 3 locally & simultaneously determined spin components (x, y and z), which is in direct contradiction to Einstein's statement and the tenor of EPR.

billschnieder

EPR say it is unreasonable to expect the reality of one system to be changed instantaneously by the a measurement performed on a distant system. How does that translate to the claim that the outcome of a measurement must depend only on the pre-existing property of the system being measured without regard for the properties of the measuring instrument. Why even bother to change the angle on the detector if properties of measurement apparatus does not matter.

And how does the fact that "the sun produces red wavelength photons independent of any measurements", go contrary to the idea that seeing "Red Sun" is contextual and depends on DrC actually doing the measurement with red goggles?

Which is blatantly false.

What you call "spin components x, y, and z" are not properties of the electron but ways of looking at a property -- spin. You take the spin and you project it along an axis during a measurement. What you observe for "spin components x (or y or z)" is dependent on the measurement setup (ie, the direction of the projection axis) and therefore it is contextual. You could say "spin component x" is a property of the combined electron-instrument system. Once you look at it this way, it becomes obvious why the inability of such a system to have three simultaneous values for"spin components x, y, z, means absolutely nothing about the existence of a pre-existing "spin" property of the electron. If you are naive enough to take such a result and ascribe it to the electron alone without regard for the axis, that is your problem not EPRs.
Just because you can not project the same electron simultaneously along three different axis in any measurement does not mean the electron does not have spin independent of measurement.

Again the EPR claim is that it is unreasonable to expect the reality of a system to be changed instantaneously by a measurement performed on a remote system.

DrChinese

I didn't say that. EPR says there is an element of reality *corresponding* to anything which can be predicted in advance. That would be the spin components of a particle. The essential question is whether the corresponding element of reality exists independently of the act of observation. EPR says yes, and they ALL exist simultaneously. Santos states there is no reality outside of a context which includes the measurement device. That is significantly more restrictive as a definition.

billschnieder

So the fact that the "Spin component along x" corresponds to the pre-existing "spin" of the electron together with the pre-existing axis orientation of the measuring instrument is too difficult to imagine?

DrChinese

Quite the opposite, I concur. As a realist, you should be claiming that there exists a pre-existing value for this independent of an actual measurement though. (That's the trouble with realists, you want to have your cake and eat it too! ) Are there or aren't there pre-existing values for x, y and z components INDEPENDENT of an actual measure (i.e. I will pick the component I want to look at sometime later).

If so, what are the values of such components *before* I measure them? And finally, do those values match the predictions of QM?

billschnieder

You mean as a 'straw man' I should be claiming a position other than the position I am actually claiming?

But that is the problem with anti-realists, they want to overturn realism so bad, they define it to be something it is not. Something so absurd, no reasonable human being could ever have claimed in the first place.


According to anti-realists, realism means:

"DrC can see a Red Sun even if he is not looking at the sun"

It is convenient but lazy to force the above definition because it is easy to knock down. If you believe this is what realists believe, why do you need Bell's theorem to reject it. It is so absurd and nonsensical it can be rejected immediately without anyone raising an eyebrow.

For the last time:
- "observed spin component along axis x" is the outcome of a measurement. No realist believes that you can observe a spin component along axis x without having performed the measurement. Same for (y, and z).
- You can predict with certainty that given a "pre-existing spin" and a "pre-existing" axis direction, what the "observed spin component along axis x" WILL be. According to EPR, the pre-existing spin, and the pre-existing axis orientation are elements of reality which correspond to the outcome you WILL have IF in fact you do make the measurement.
- Just because you can predict it does not mean it exists. In fact why would you be PREDICTING if it already EXISTS. Obviously, you PREDICT something because it DOES NOT CURRENTLY exist but POSSIBLY WILL in the FUTURE.
- Just because you can predict different things simultaneously does not mean they can all exist simultaneously. Just because you can predict the outcome of measurements along "x, y and z" in advance does not mean "observed spin component along axis x, y and z" all exist simultaneously or can exist simultaneously in the future.
- Just because "observed spin component along axis x" does not exist until an actual measurement is performed, does not mean the particle does not have a pre-existing property called "spin" which exists independent of any measurement.

Before you measure any components, all you have is a prediction of what you will get IF you measure them. And yes such a prediction can be very definite but still only be a PREDICTION. The outcome doesn't EXIST until you actually do the measurement!!!

QM predicts the outcomes of performable experiments on an ensemble of similarly prepared systems. If the predictions are of the same thing, and are both correct, they should match.

For example, they both provide the same prediction to what will be observed in the experiment which involves:

"Simultaneously measuring the spin projection of a series of similarly prepared particles at three different axis orientations x, y, z".

If you think the QM and realist predictions will differ in this case, please explain why.

And Please, I beg you to stop misrepresenting the realist position. This is not the first time I've explained your misconceptions about the realist position to you. What you keep repeating under the guise of the "realist position" is a concept so naive and unreasonable, even in classical physics prior to the 20th century. So I really wonder what the motivation will be for propagating such falsehood.

DrChinese

Yes, Bill, my perverted definition of realism is that of a naive simpleton:

"I think that a particle must have a separate reality independent of the measurements. That is: an electron has spin, location and so forth even when it is not being measured."

-A.E.


"If, without in any way disturbing a system, we can predict with certainty (i.e., with probability equal to unity) the value of a physical quantity, then there exists an element of physical reality corresponding to this physical quantity."

-EPR


On the other hand, your:


- Just because you can predict different things simultaneously does not mean they can all exist simultaneously. Just because you can predict the outcome of measurements along "x, y and z" in advance does not mean "observed spin component along axis x, y and z" all exist simultaneously or can exist simultaneously in the future.
- Just because "observed spin component along axis x" does not exist until an actual measurement is performed, does not mean the particle does not have a pre-existing property called "spin" which exists independent of any measurement.


Logically translates to:


A particle has spin independent of measurement, but not an x, y or z spin component until measured, even when all can be predicted with certainty.


Also: Your "The outcome doesn't EXIST until you actually do the measurement!!!" versus above EPR quote which says there exists (an element of) reality in such case.

I would hope the contradictions in these statements are obvious. Or maybe the semantic distinctions are more clear to you than they are to me.

billschnieder

No your perverted translation of the A.E. quote as evidenced by your comments is:

"I think that all measurement outcomes must be a separate reality of particles which exist independent of the measurements"

And your perverted translation of the EPR quote is:

"If, without in any way disturbing a system, we can predict with certainty (i.e., with probability equal to unity) the value of a physical quantity, then that physical quantity is an element of physical reality."

Either you are unable to see the significant differences in meaning between those, or you do see the difference but would rather misrepresent the two for the purposes of evangelizing for for favorite religion.

DrChinese

The reason I keep including the quotes is because the words of Einstein are good enough for me as a definition. I think it is clear from these that Einstein believed a more complete specification of the system is possible than is contemplated by QM. And he believed spin components (and other particle properties) had definite values independent of the act of observation. He certainly didn't picture a reality that was limited to measurement outcomes that had already been performed, as you seem to.

And by that I am specifically referring to ANYTHING that could be classified as an element of reality per EPR. Per EPR, perfect correlations at 19 or 42 or 77 degree polarization imply the reality of those properties. And such reality was not restricted to those outcomes which are actually measured, they apply simultaneously.

So if you don't like what I am saying, please don't say I am perverting the language of EPR. That is what Bell used, it is what I use, and is what is commonly used.

ThomasT

And, the fact of the matter is that wrt individual measurments, Bell showed that this (Einstein's) view is compatible with QM (and subsequently compatible with experimental results).

So, the only problem is with entanglement correlations. Curious, isn't it, that, all of a sudden, wrt entanglement correlations, the assumption of preexisting values becomes irrelevant, or, in the extreme, wrong.

Is it even possible that there's a subtlety here that has been missed? Another rhetorical question. Of course it's possible, and it certainly wouldn't be the first time wrt physical science.

lugita15

So DrChinese, you wouldn't consider Bohmian mechanics a realistic theory? Because it's contextual. Perhaps a better definition of realism is that the particle possesses all attributes, both measured and unmeasured, that potentially could have been measured. In other words, I would consider any theory, contextual or not, that satisfies counterfactual definiteness to be realistic.

Demystifier

What DrChinese calls "realism" is actually called NAIVE REALISM.
http://en.wikipedia.org/wiki/Na%C3%AFve_realism

Bohmian mechanics involves realism, but not naive realism.
http://xxx.lanl.gov/abs/quant-ph/9601013

Aidyan

My anti-realism in Q&A: Once you have studied a map do you know the territory? At best you can say that a street is the element of preexisting reality that corresponds to an observable we call "straight line on a piece of paper". But does this convey any "realistic" representation of the world? Is the 'redness' of the sun an objective property or a subjective qualitative experience? Is a color still there when we don't look at it? And to Einstein's question: "Is the moon still there even if we don't look at it?" My answer is: no, the moon **as we see it** is NOT there even when we look at it. Once we will have grasped this then QM will become a little bit less mysterious.

DrChinese

Sorry, I didn't add the qualifier "local" to this. As Demystifier says, Bohmian theories are (non-local) realistic.

There is some question as to what form of realism is being referred to, whether it might be "naive realism". I personally do not call the EPR definition naive, as this is a generally accepted definition. The issue is not whether an outcome is real, or whether the property being measured is real, the issue is whether there exists an element of reality which corresponds to what is observed. That element could be very complex, such that we are only able to sense a portion of its detail.

To use Bill's example: I am not saying the sun "really" is red every time I look at it with red sunglasses, I am saying there is something "real" which gives rise to that outcome. I make no statement to the effect that the redness itself is real. When I say it is red, I am using a shortcut rather than saying "it has a real set of properties which makes it appear red to me". For it to be real in this sense, it must also be so independent of the act of observation. Further, the likelihood of such outcome is between 0 and 100%.

So again: this is nothing but a standard definition shared by most. I know this because it is the same as used by EPR, Einstein, Bell and those following Bell. I don't think this audience considers their definition of realism to be naive, and I don't label it as such.

DrChinese

Look at my tag line. I obviously do not confuse the two. No one is asserting that a spin x component outcome implies that a particle actually has a discrete property called spin x (or y or z). But as EPR says: if we can predict it with certainty, there exists something real which gives rise to the outcome.

But I think you are switching senses of the word "realistic" in your example. Keep in mind that even as I define realism, I am free to reject it based on Bell (assuming I prefer to maintain locality). Don't confuse a suitable definition of realism with the requirement that one must also assert that the world IS realistic. I consider a map a useful representation of it subject.