Thursday, October 22, 2015

No-loophole Bell experiment hits newspapers

I discussed the latest Bell test experiment in August, and now it has hit the NY Times:
In a landmark study, scientists at Delft University of Technology in the Netherlands reported that they had conducted an experiment that they say proved one of the most fundamental claims of quantum theory — that objects separated by great distance can instantaneously affect each other’s behavior.

The finding is another blow to one of the bedrock principles of standard physics known as “locality,” which states that an object is directly influenced only by its immediate surroundings.
No, this is not a blow to locality at all. It does confirm quantum mechanics, and close some loopholes in previous experiments, but that is all.
The Delft study, published Wednesday in the journal Nature, lends further credence to an idea that Einstein famously rejected. He said quantum theory necessitated “spooky action at a distance,” and he refused to accept the notion that the universe could behave in such a strange and apparently random fashion.

In particular, Einstein derided the idea that separate particles could be “entangled” so completely that measuring one particle would instantaneously influence the other, regardless of the distance separating them.

Einstein was deeply unhappy with the uncertainty introduced by quantum theory and described its implications as akin to God’s playing dice.
This is hopelessly confused. Randomness and action-at-a-distance are two separate issues.

Two distant particles can be entangled in the sense that their states are related, and measuring one gives info about the other. But there has never been an experiment showing that an action on one particle has an effect on a particle outside its light cone.
The new experiment, conducted by a group led by Ronald Hanson, a physicist at the Dutch university’s Kavli Institute of Nanoscience, and joined by scientists from Spain and England, is the strongest evidence yet to support the most fundamental claims of the theory of quantum mechanics about the existence of an odd world formed by a fabric of subatomic particles, where matter does not take form until it is observed and time runs backward as well as forward.

The researchers describe their experiment as a “loophole-free Bell test” in a reference to an experiment proposed in 1964 by the physicist John Stewart Bell as a way of proving that “spooky action at a distance” is real.

“These tests have been done since the late ’70s but always in the way that additional assumptions were needed,” Dr. Hanson said. “Now we have confirmed that there is spooky action at distance.”
I guess I cannot blame John Markoff, the NY Times reporter, because the physicists themselves are reciting this mystical nonsense.

No, this does not confirm that matter is not real until it is observed, or that time runs backwards, or that there is any action at a distane.
According to the scientists, they have now ruled out all possible so-called hidden variables that would offer explanations of long-distance entanglement based on the laws of classical physics.
Finally, in the 9th paragraph, we have a correct statement. John von Neumann considered and rejected hidden variable theories in a 1930 textbook, and that has been the mainstream view ever since. Some fringe physicists, plus Einstein, have claimed that von Neumann's argument was wrong, but all attempts to revive hidden variables have been decisively rejected for an assortment of reasons.
The Delft researchers were able to entangle two electrons separated by a distance of 1.3 kilometers, slightly less than a mile, and then share information between them. Physicists use the term “entanglement” to refer to pairs of particles that are generated in such a way that they cannot be described independently. The scientists placed two diamonds on opposite sides of the Delft University campus, 1.3 kilometers apart.

Each diamond contained a tiny trap for single electrons, which have a magnetic property called a “spin.” Pulses of microwave and laser energy are then used to entangle and measure the “spin” of the electrons.

The distance — with detectors set on opposite sides of the campus — ensured that information could not be exchanged by conventional means within the time it takes to do the measurement.
This is a decent description of the experiment. Yes, the photon pair is entangled in the sense that it is generated in such a way that it cannot be described as independent photons.

The failure of hidden variable theories also shows that the pair cannot be described by some sort of joint probability distribution on classical particles.

But that still leaves the possibility that the pair can be physically separated so that one has no effect on the other, but there is no mathematical description of that individual photon without being tied to the other. Measuring one photon affects our best mathematical description of the pair, but has no causal physical effect on the other photon.

That last possibility is what the quantum textbooks have said for 85 years, more or less.

As I keep saying on this blog, you need to get out of your head the idea that physics and math are the same thing. We have physical phenomena, and mathematical models and representations. Physics is all about finding mathematical models for what we observe, but there is no reason to believe that there is some underlying unobservable physical reality that is perfectly identical to some mathematically exact formulas. Einstein, Bohm, Bell, Tegmark, and others have gone down that path, and just come up with nonsense. Only by making such hidden variable assumptions does this experiment lead you to question locality.

Locality is not wrong. Hidden variables are wrong.
The tests take place in a mind-bending and peculiar world. According to quantum mechanics, particles do not take on formal properties until they are measured or observed in some way. Until then, they can exist simultaneously in two or more places. Once measured, however, they snap into a more classical reality, existing in only one place.
Back to nonsense. Quantum mechanics is all about what can be observed. If you talk about what is not observed, such as saying that particles can be in two places at once, you have left quantum mechanics and entered the subject of interpretations. Some interpretations say that a particle can be in two places at once, and some do not. Some say that there is no such thing as a particle.
Indeed, the experiment is not merely a vindication for the exotic theory of quantum mechanics, it is a step toward a practical application known as a “quantum Internet.” Currently, the security of the Internet and the electronic commerce infrastructure is fraying in the face of powerful computers that pose a challenge to encryption technologies based on the ability to factor large numbers and other related strategies.

Researchers like Dr. Hanson envision a quantum communications network formed from a chain of entangled particles girdling the entire globe. Such a network would make it possible to securely share encryption keys, and know of eavesdropping attempts with absolute certainty.
Now they are claiming applications to quantum cryptography and quantum computers. No, quantum computers are not fraying the security of the internet and electronic commerce. No one has even made one true qubit, the smallest building block for a quantum computer. There is no security advantage to a quantum internet, and there is a long list of technical obstacles to even making an attempt. For example, it is extremely difficult to make a router to relay a single bit of info.
A potential weakness of the experiment, he suggested, is that an electronic system the researchers used to add randomness to their measurement may in fact be predetermined in some subtle way that is not easily detectable, meaning that the outcome might still be predetermined as Einstein believed.

To attempt to overcome this weakness and close what they believe is a final loophole, the National Science Foundation has financed a group of physicists led by Dr. Kaiser and Alan H. Guth, also at M.I.T., to attempt an experiment that will have a better chance of ensuring the complete independence of the measurement detectors by gathering light from distant objects on different sides of the galaxy next year, and then going a step further by capturing the light from objects known as quasars near the edge of the universe in 2017 and 2018.
No experiment can truly rule out super-determinism. This group is trying to show that superdeterminism, if it exists, would go back to the early universe. Isn't that what the super-determinists believe anyway? There are very few followers to such a bizarre theory anyway, so I would not know.

I just happened to watch this video titled Deepak Chopra destroyed by Sam Harris. Harris and Michael Shermer mock Chopra for citing quantum nonlocality, and say that none of them are competent to discuss it because none of them are physicists.

As much as Chopra might be guilty of babbling what Shermer calls "woo", I don't see how this NY Times article is any better. It is also claiming that nonlocality has been proved, and that matter doesn't really exist until you look at it. That is essentially the same as what Chopra was saying, except that he goes a step further and ties it into consciousness.

I would have thought that physicists would object to this sort of mysticism being portrayed as cutting edge physics in the NY Times. Yes, it is a good experiment, but it just confirms the theory that was developed in 1925-1930, and that received Nobel prizes in 1932-1933. My guess is that there is too much federal grant money going into quantum computing and other fanciful experiments, and no one wants to rock the boat.

Update: Lubos Motl piles on.
If you had some basic common sense and honesty, your conclusion would be to switch to abandon the classical way of thinking and switch to the quantum way of thinking. You would stop talking about "spooky" and "weird" and "nonlocal" things that may be implied by a classical model but it contradicts the insights that modern physics has actually made about the essence of the laws of Nature.

But I guess that it's more convenient for this corrupt community to keep on playing with diamonds in totally stupid ways and write nonsensical hype about these games in the newspapers.

I won't proofread this text because it makes me too angry.
I agree with him about the corrupt community. His post still says "transfer any transformation" instead of "transfer any information", soI guess he still has not proofread it.

1 comment:

  1. Good post, Roger.

    While reading through such stories, I try to leave the nonsense completely aside. That almost always means completely emptying the mind of the story in its entirety. But still, some rare times, I do focus on the advancement on the technology side that such stories should highlight but don't.

    And then, there also are some (very) very rare times when I find myself wanting to retain that gushing enthusiasm in reporting (whether by the media or by the physicists).

    Focusing on that part alone, in turn, has sometimes made me wonder what kind of a physics advancement done with QM would make me jump in joy with as much excitement as goes with those entanglement-related nonsense stories?

    My answer to that question is this: demonstration of some mechanism to trap renewable energy coming in any form (say that of the photons of the sunlight) and storing it in any manner, using any technology, but achieving in the end and an energy density of, say, 10% of the hydrocarbon fuels.

    Why, in fact, my standards are much, much lower. I think I should be similarly happy to see even just 1% energy density (as compared to H-C fuels). Why, for that matter, even 0.1%!

    I am willing to go even lower. I will in fact be similarly happy to see just a scheme/an in-principle description (not practical realization) of any device of this kind. (Not necessarily photo-voltaic cells, not necessarily hydrogen fuel production... . Any technology, any thing will do, so long as the energy density is high enough, and energy conversion efficiency makes it practical enough.)

    Note, any such development would have to involve QM.

    *That*'s what would make me go as crazy as these folks do.


    How about you? Do you ever ponder what would make gush with words similar to what QM entanglement reporters (again, whether physicists or media-folks) come up with? (It doesn't have to be related to QM; it could be anything. Just that it has to be a realistic, not something like an elixir coming to market in the next decade, an elixir that would increase the average human lifespan to, say, a thousand years....)

    If you do wonder about such things, and in such directions, I would like to know more about it some time...