Tag: quantum mechanics

What Einstein meant by ‘God does not play dice’

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Einstein developed a deep aversion to the dogma of organized religion that would last for his lifetime, an aversion that extended to all forms of authoritarianism, including any kind of dogmatic atheism.

Author: Jim Baggott

Source: Aeon

Link:https://www.alternet.org/what-einstein-meant-god-does-not-play-dice?src=newsletter1098152

Emphasis: Mine

‘The theory produces a good deal but hardly brings us closer to the secret of the Old One,’ wrote Albert Einstein in December 1926. ‘I am at all events convinced that He does not play dice.’

Einstein was responding to a letter from the German physicist Max Born. The heart of the new theory of quantum mechanics, Born had argued, beats randomly and uncertainly, as though suffering from arrhythmia. Whereas physics before the quantum had always been about doing this and getting that, the new quantum mechanics appeared to say that when we do this, we get that only with a certain probability. And in some circumstances we might get the other.

Einstein was having none of it, and his insistence that God does not play dice with the Universe has echoed down the decades, as familiar and yet as elusive in its meaning as E = mc2. What did Einstein mean by it? And how did Einstein conceive of God?

Hermann and Pauline Einstein were nonobservant Ashkenazi Jews. Despite his parents’ secularism, the nine-year-old Albert discovered and embraced Judaism with some considerable passion, and for a time he was a dutiful, observant Jew. Following Jewish custom, his parents would invite a poor scholar to share a meal with them each week, and from the impoverished medical student Max Talmud (later Talmey) the young and impressionable Einstein learned about mathematics and science. He consumed all 21 volumes of Aaron Bernstein’s joyful Popular Books on Natural Science (1880). Talmud then steered him in the direction of Immanuel Kant’s Critique of Pure Reason (1781), from which he migrated to the philosophy of David Hume. From Hume, it was a relatively short step to the Austrian physicist Ernst Mach, whose stridently empiricist, seeing-is-believing brand of philosophy demanded a complete rejection of metaphysics, including notions of absolute space and time, and the existence of atoms.

But this intellectual journey had mercilessly exposed the conflict between science and scripture. The now 12-year-old Einstein rebelled. He developed a deep aversion to the dogma of organised religion that would last for his lifetime, an aversion that extended to all forms of authoritarianism, including any kind of dogmatic atheism.

This youthful, heavy diet of empiricist philosophy would serve Einstein well some 14 years later. Mach’s rejection of absolute space and time helped to shape Einstein’s special theory of relativity (including the iconic equation E = mc2), which he formulated in 1905 while working as a ‘technical expert, third class’ at the Swiss Patent Office in Bern. Ten years later, Einstein would complete the transformation of our understanding of space and time with the formulation of his general theory of relativity, in which the force of gravity is replaced by curved spacetime. But as he grew older (and wiser), he came to reject Mach’s aggressive empiricism, and once declared that ‘Mach was as good at mechanics as he was wretched at philosophy.’

Over time, Einstein evolved a much more realist position. He preferred to accept the content of a scientific theory realistically, as a contingently ‘true’ representation of an objective physical reality. And, although he wanted no part of religion, the belief in God that he had carried with him from his brief flirtation with Judaism became the foundation on which he constructed his philosophy. When asked about the basis for his realist stance, he explained: ‘I have no better expression than the term “religious” for this trust in the rational character of reality and in its being accessible, at least to some extent, to human reason.’

But Einstein’s was a God of philosophy, not religion. When asked many years later whether he believed in God, he replied: ‘I believe in Spinoza’s God, who reveals himself in the lawful harmony of all that exists, but not in a God who concerns himself with the fate and the doings of mankind.’ Baruch Spinoza, a contemporary of Isaac Newton and Gottfried Leibniz, had conceived of God as identical with nature. For this, he was considered a dangerous heretic, and was excommunicated from the Jewish community in Amsterdam.

Einstein’s God is infinitely superior but impersonal and intangible, subtle but not malicious. He is also firmly determinist. As far as Einstein was concerned, God’s ‘lawful harmony’ is established throughout the cosmos by strict adherence to the physical principles of cause and effect. Thus, there is no room in Einstein’s philosophy for free will: ‘Everything is determined, the beginning as well as the end, by forces over which we have no control … we all dance to a mysterious tune, intoned in the distance by an invisible player.’

The special and general theories of relativity provided a radical new way of conceiving of space and time and their active interactions with matter and energy. These theories are entirely consistent with the ‘lawful harmony’ established by Einstein’s God. But the new theory of quantum mechanics, which Einstein had also helped to found in 1905, was telling a different story. Quantum mechanics is about interactions involving matter and radiation, at the scale of atoms and molecules, set against a passive background of space and time.

Earlier in 1926, the Austrian physicist Erwin Schrödinger had radically transformed the theory by formulating it in terms of rather obscure ‘wavefunctions’. Schrödinger himself preferred to interpret these realistically, as descriptive of ‘matter waves’. But a consensus was growing, strongly promoted by the Danish physicist Niels Bohr and the German physicist Werner Heisenberg, that the new quantum representation shouldn’t be taken too literally.

In essence, Bohr and Heisenberg argued that science had finally caught up with the conceptual problems involved in the description of reality that philosophers had been warning of for centuries. Bohr is quoted as saying: ‘There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature.’ This vaguely positivist statement was echoed by Heisenberg: ‘[W]e have to remember that what we observe is not nature in itself but nature exposed to our method of questioning.’ Their broadly antirealist ‘Copenhagen interpretation’ – denying that the wavefunction represents the real physical state of a quantum system – quickly became the dominant way of thinking about quantum mechanics. More recent variations of such antirealist interpretations suggest that the wavefunction is simply a way of ‘coding’ our experience, or our subjective beliefs derived from our experience of the physics, allowing us to use what we’ve learned in the past to predict the future.

But this was utterly inconsistent with Einstein’s philosophy. Einstein could not accept an interpretation in which the principal object of the representation – the wavefunction – is not ‘real’. He could not accept that his God would allow the ‘lawful harmony’ to unravel so completely at the atomic scale, bringing lawless indeterminism and uncertainty, with effects that can’t be entirely and unambiguously predicted from their causes.

The stage was thus set for one of the most remarkable debates in the entire history of science, as Bohr and Einstein went head-to-head on the interpretation of quantum mechanics. It was a clash of two philosophies, two conflicting sets of metaphysical preconceptions about the nature of reality and what we might expect from a scientific representation of this. The debate began in 1927, and although the protagonists are no longer with us, the debate is still very much alive.

And unresolved.

I don’t think Einstein would have been particularly surprised by this. In February 1954, just 14 months before he died, he wrote in a letter to the American physicist David Bohm: ‘If God created the world, his primary concern was certainly not to make its understanding easy for us.’

Jim Baggott

This article was originally published at Aeon and has been republished under Creative Commons.


Tangled Up in Entanglement

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Source: New Yorker

Author: Lawrence M krause

Emphasis Mine:

No area of physics causes more confusion, not just among the general public but also among physicists, than quantum mechanics. On the one hand, it’s the source of New Age mythology, and has enabled hucksters to peddle new self-help cures; on the other, for the philosophically inclined, it has provided some illusory hope of free will in an otherwise deterministic universe. Of the aspects of quantum mechanics that confuse and dismay observers, perhaps nothing approaches the property called “entanglement.” Einstein, who never really accepted entanglement’s existence, called it, derisively, “spooky action at a distance.”

Unfortunately for Einstein, entanglement, “spooky” or not, is apparently real, as researchers in the Netherlands demonstrated last week, just in time for Halloween. In doing so, the researchers affirmed once again that quantum mechanics, as strange as it may seem, works in every way we can test it.

To understand just how spooky entanglement really is, it helps to step back and think about what happens to sensible, “classical” objects when you separate them. (Classical objects are large enough, or interact strongly enough with their environments, for quantum-mechanical effects to wash out.) Imagine that I have a detonator and a bomb. If I separate them across the street from each other and activate the detonator, it can trigger the bomb only by sending a signal at the speed of light or slower. Only after the bomb receives the signal will it detonate.

Quantum theory, however, suggests that objects which have been carefully prepared together and placed into a combined quantum state can, even when separated across the galaxy, remain “entangled,” as long as neither has any significant interactions with other objects to break the entanglement. If I perform a measurement on one of two entangled objects, the state of the other object will be instantaneously affected, no matter how far apart the two objects are.

In itself, this may not seem that spooky. After all, if I separate two identical twins across the galaxy and then observe that one twin has red hair, I have instantaneously determined that the other twin has red hair, too. The real spookiness comes in only when you consider what a measurement in quantum mechanics really involves.

Imagine a pair of electrons. Electrons behave as though they are spinning; moreover, because they carry an electric charge, they act like small magnets, which means that, using electromagnetic radiation, it’s possible to manipulate their spins. Our pair of electrons, for example, can be set up so that their spins point in opposite directions along the same axis. We can say that such electrons are “anti-aligned.”

Now, suppose that, later, I try to measure the axis about which one of the electrons is spinning. If it’s spinning in one direction around that axis, it acts like a magnet with its north pole pointing in a direction we can call “up”; if it’s spinning in the other direction, then its north pole would point “down.” Because the electrons are anti-aligned, if I discover that one is pointing up, then I know that its partner must be pointing down.

There’s a catch, however. Quantum mechanics says that the actual spin direction of either electron is not determined in advance of the measurement; the only thing that’s for sure is that the spins are anti-aligned. Even stranger, until they have been measured, both electrons are actually spinning up and down at the same time. Their measured state is probabilistic: all that can be said is that there’s a fifty-fifty probability that, once one of the electrons is measured, it will be “fixed” in a state of spinning up or down. Because the two electrons are in a single quantum state—because they are entangled—the moment I measure the spin of one electron, I fix the direction of spin of the other electron. It’s as though, by flipping one coin, and coming up “heads,” I force another coin to come up “tails.”

As long as the two electrons remain entangled, then this link endures—even if they are separated across the galaxy. If I measure one electron in my lab, the second electron is affected by the measurement of the first electron with no time delay—instantaneously—even though a signal travelling at the speed of light would take millenia to cross the distance between them.

That instantaneous link is the “spooky action at a distance” of which Einstein was so skeptical. In his day, of course, no one had actually observed entanglement; it was just a prediction of quantum theory. In 1935 Einstein, along with two collaborators, Boris Podolsky and Nathan Rosen, wrote a famous paper arguing that entanglement was so crazy that, if quantum mechanics predicted it, the whole system had to be flawed. No system that made such predictions could possibly describe the universe accurately.

Einstein and his collaborators were thinking classically, imagining that the electrons were separate objects when separated. But, quantum-mechanically, the two electrons are part of a single quantum state, no matter how far apart they are. They are not independent, well-separated objects. Indeed, quantum mechanics tells us that, until we measure the position of either electron, we cannot say for certain where it is located. It can be, in some sense, everywhere at once.

Over the years, some physicists have channeled Einstein’s skepticism. They have proposed that there is some hidden classical mechanism we don’t know about, which is, somehow, fixing the results so as to create the appearance of entanglement. Perhaps, for example, the laboratory setup is somehow predetermining the spin-directions of the electrons before they are separated. This conjecture has presented physicists with an impasse: How could we ever know that some hidden mechanism wasn’t at work?

In 1964 a physicist named John Bell found a way around it. He wrote a beautiful paper demonstrating that, if an entanglement experiment worked reliably, a specific set of measurements could be made on the particles which produced a quantitative result that couldn’t be explained by any classical mechanism which might predetermine the spins before they were measured. Over the past half-century, many groups have used Bell’s Theorem in trying to affirm that quantum-mechanical entanglement is real. All the while, however, skeptics have pointed out that, in each experiment, there may have been subtle loopholes. It’s been possible, for example, that systems which were supposed to be separated may have actually been coupled in hidden ways.

Last week, a team of researchers led by a physicist named Ben Hensen, at Delft University of Technology, in the Netherlands, reported the results of an experiment designed to lay these concerns to rest. They performed simultaneous measurements on a pair of entangled electrons separated by 1.3 kilometers—far enough that no signal, even one travelling at the speed of light, could get from one detector to the other in time to interfere with their measurements. They also devised a way of independently checking that the electrons being measured were, in fact, entangled. Both these aspects of their experiment are significant and novel: they remove key loopholes which skeptics had argued might bias previous experiments. Needless to say, the new results agreed precisely with both the predictions of quantum theory and of Bell’s Theorem.

Entanglement now appears to be an empirically closed case—at least, until someone can convincingly argue that there is some loophole not ruled out by this experiment (which some physicists have already begun to do). If that happens, other researchers will inevitably attempt to produce an even better experiment in which Bell’s Theorem will be satisfied while the new loophole is ruled out. The cycle will repeat until there are no loopholes left—or until those that do remain seem so implausible that it isn’t worth the effort to explore them.

I say this with confidence because, even though these direct measurements of quantum spookiness are important to perform, we can already be sure that quantum mechanics is the correct description of the world at the smallest, most fundamental scales. In fact, we test that assumption every day. Most of our modern technology depends on it. The semiconductor transistors that govern the behavior of our cell phones, our computers, our cars, and many other electronic devices are based on quantum-mechanical principles associated with the electronics that drive their computing capability. Those principles hinge, indirectly, on the spookiness being measured explicitly in the Delft experiment. So, spooky or not, our lives in the modern world rely on quantum mechanics in many ways.

Entanglement is so spooky that it’s tempting, when thinking about it, to draw nonsensical conclusions. Deepak Chopra, for example, keeps implying that quantum mechanics means that objective reality doesn’t exist apart from conscious experience. The truth, however, is that consciousness is irrelevant to the act of measurement, which can be done by machines, or even by single photons. If consciousness matters, then the inner thoughts of the experimenter who operates the machines would also have to be reported when we write up the results of our experiments. We’d need to know whether they were daydreaming about sex, for example. We don’t. The machines can record data and print it out whether or not a person is in the room, and those printouts, which behave classically, don’t change when the humans come back.

Similarly, last week, the Pulitzer prize-winning writer Marilynne Robinson published an essay in which she challenges the nature and relevance of modern science. The essay argued that entanglement “raises fundamental questions about time and space, and therefore about causality.” She went on to say that this called into question the ability of science to explain reality as a whole. It’s easy to understand how Robinson arrived at this incorrect idea: when a measurement of one electron here can instantaneously affect the measurement of another electron on the opposite side of the universe, faster than the speed of light, it does seem as though causality has been thrown out the window.

But the lessons of quantum mechanics aren’t that simple. The truth is that nature contains a cosmic Catch-22. Consider our two experimenters—one located here on Earth, and the other stationed at the edge of the Milky Way. Separately, they measure the spins of their entangled electrons. Nothing about what they measure will point to a measurement going on thousands of light-years away. Each of them will measure their electrons spinning “up” fifty per cent of the time and “down” fifty per cent of the time. Nothing will suggest that the spins of their electrons are correlated with electrons anywhere else. The only way they can realize this is if they communicate with one another. But that communication can happen, at its very fastest, at the speed of light. Entanglement may be instantaneous, but it produces no signals that can be detected instantaneously. Its detection still follows the ordinary laws of cause and effect.

Quantum mechanics reveals that nature is indeed spooky at its smallest scales. If we are careful, we can detect that spookiness. But, happily, its presence doesn’t mean that all bets are off. The fundamental laws that govern the universe don’t disappear in a quantum haze. The strangest thing about entanglement may be that it fits so neatly into our broader understanding of the universe.

Lawrence M. Krauss is director of the Origins Project at Arizona State University. His newest book,  “The Greatest Story Ever Told… So Far,” will be released in 2016.

See:http://www.newyorker.com/tech/elements/tangled-up-in-entanglement-quantum-mechanics?intcid=mod-latest