Physics professor and frequent First Things contributor Stephen Barr discusses the implications of quantum physics at Big Questions Online:
No less a figure than Eugene Wigner, a Nobel Prize winner in physics, claimed that materialism — at least with regard to the human mind — is not “logically consistent with present quantum mechanics.” And on the basis of quantum mechanics, Sir Rudolf Peierls, another great 20th-century physicist, said, “the premise that you can describe in terms of physics the whole function of a human being . . . including [his] knowledge, and [his] consciousness, is untenable. There is still something missing.”
How, one might ask, can quantum mechanics have anything to say about the human mind? Isn’t it about things that can be physically measured, such as particles and forces? It is; but while minds cannot be measured, it is ultimately minds that do the measuring. And that, as we shall see, is a fact that cannot be ignored in trying to make sense of quantum mechanics. If one claims that it is possible (in principle) to give a complete physical description of what goes on during a measurement — including the mind of the person who is doing the measuring — one is led into severe difficulties.
Read the rest here.
August 3rd, 2012 | 12:46 pm
Somebody seems to have forgotten that the physical world and the quantum world play by different rules. I can easily simultaneously measure the position, direction and speed of an automobile. I cannot do that with an electron. Trying to apply the uncertainty principle to the presence, position and speed of an automobile would be downright silly.
In a supermarket I can rely on the fact that two cans of soup will not exchange positions, brands or contents. That quantum physics can accept such changes routinely indicates that different rules are at play.
It might be more accurate to say that it is presently impossible to take a snapshot of the physical and mental states of a human being, just as it was impossible to photograph the physical presence of a human being in the 18th century. But science and technology have moved on. I trust that such progress will ultimately make the former action as comprehensible as the latter.
And when you add in the discovery that we apparently perceive only about 4% of the universe, it’s safe to say that our best guesses about the quantum and physical universes may be as accurate as a Neanderthal trying to explain the function of a light bulb.
August 3rd, 2012 | 1:39 pm
isolate,
Your terminology is incorrect. The “quantum world” is a part of the physical world. What you refer to as the “physical world” is better termed the world of “classical physics,” where the physics of Newton and Maxwell is sufficient to describe physical phenomena.
Both classical and quantum theories are “physical” in the sense that they describe the physical world around us. Classical and quantum theories do apply at different scales and I think this is what you were trying to get at.
However, this doesn’t mean that classical physics and quantum physics are inconsistent with one another. In fact, classical theories can be shown to be limiting cases of quantum theories where the effects of quantum uncertainty become miniscule to the point of being negligible.
In other words, we could, in principle, apply the rules of quantum mechanics to try and predict orbits of the planets. If we correctly accounted for their large sizes, relative to atomic-scale particles, and the relatively larger length scales involved, we would, in principle, predict the same orbits as another scientist using Newton’s classical theory of mechanics.
This is essentially a statement of Neils Bohr’s “correspondence principle.” Quantum physics must agree with classical physics for macroscopic sized systems like baseballs and planets.
So, it’s not really the case that “different rules are at play,” Instead, for things as big as baseballs or planets, you have to apply the rules correctly, which in the end, amounts to using the theories classical physics.
August 3rd, 2012 | 4:08 pm
The article is just another rerun of quantum mysticism. The weak point is the argument is the claim that a machine such as a Geiger counter can’t be an “observer” of a “quantum jump” event such as a nuclear decay because a wave equation can, in principle, be written that includes the device in the system and that equation cannot deterministically predict the moment of the event. So what? It happens randomly and when it happens the device knows it. It knows it because there is too much entropy increase for the system when including such a complex macro-scale object for it to spontaneously revert back to the pre-event state.
Quantum mysticism cannot be reconciled with thermodynamics. Quantum physics, barring certain long-shot hidden variable theories, rules out classical determinism but not materialism.
August 3rd, 2012 | 5:27 pm
Adam,
Barr addresses your points 2/3 of the way down the page. See the paragraphs starting with, “An obvious question is why one needs to talk about knowledge and minds at all…”
August 3rd, 2012 | 5:42 pm
This is way over my head, but as I understand it, Adam Smith is correct. If a photon is in motion in a vacuum, its position and momentum are described by probabilities. But once it strikes a surface, the wave equation for the photon become irrelevant. It does not matter that no human being is observing. The photon hitting a surface has caused the wave equation to collapse. (I think that’s the correct terminology.)
The human mind came into existence only an instant ago, compared to the lifetime of the universe. To say that reality is somehow dependent on human intelligence does not account for 13 billion years of reality that preceded our existence. All the photons from the sun that warmed the earth’s surface 10 million years ago, before human intelligence, were not in an indeterminate state until human beings arose to observe the effects.
By the way, as I understand it, the thought experiment of Schrödinger’s Cat was invented by Schrödinger to mock the idea that the cat was in an indeterminate state (dead and alive) before the door to the chamber was opened.
August 3rd, 2012 | 11:14 pm
Dear Adam Smith,
(a) As George correctly points out, your objection (that one could include the Geiger Counter in the wavefunction) was already answered in my essay. It would seem that you did not actually read the entire essay. It is always dangerous to critique something you haven’t finished reading!
(b) Your suggestion that thermodynamics (by which it appears you mean the involvement of macroscopic objects) takes care of wavefiunction collapse is simple wrong. You are confusing wavefunction collapse with “decoherence”. (See my answer to Mr. Nickol, below.) You only half understand what you are taking about.
(c) The issue I explained in my essay is a real one that serious people have been grappling with for over 80 years. This is not Deepak Chopra we are talking about, but von Neumann, Wigner, Peierls, and many other first-rate physicists.
You may find the traditional Copenhagen Interpretation too “mystical”; many people do. That’s fine. You have every right to reject it. The point I was making in my essay is that you then have basically two choices: Many Worlds Interpretation or saying that quantum mechanics is an incomplete theory that stands in need of being fundamentally modified.
Dear David Nickol,
Unfortuantely, you are quite mistaken. A careful reading of my essay would show you why.
Wavefunction collapse does NOT occur simply because the electron “strikes a surface” (or, more generally, interacts with a macroscopic object). What happens at that point is something called “decoherence”, not wavefunction collapse. Take a simple example: suppose that a photon has two paths it can take, path A and path B, and that the wavefunction says it has equal probability of taking those paths. The wavefunction in that situation will have two “terms” in it, one corresponding the photon taking path A and the other to its taking path B. Now, suppose we place two (macroscopic) detectors such that detector A will be struck and turn on a red light if the photon takes path A, and detector B will be struck and turn on a blue light if the photon takes path B. What happens when the photon strikes the detector(s)? What happens is that one term in the wavefunction describes the photon having struck detector A and the red light being on, while the other term describes the photon having struck detector B and the blue light being on. Because these two situations are VERY different from each other (a red light being on and a blue light being on involve a HUGE number of particle behaving differently), the two terms in the wavefunction have become so disparate at that point that they can no longer “interfere” with each other. I.e. in the technical jargon, they have “decohered”. But that simply means that at that point the two terms describe two (EFFECTIVELY) separate “worlds”, one in which a red light is on and one in which a blue light is on. That is NOT what is meant by “collapse”. “Collapse” of the wavefunction happens (if it does) only when one of those two terms is “thrown away” — deleted from the wavefunction — on the grounds that it describes something that did not actually happen. There are two possibilities: either the two “worlds” (the red-light-on world and the blue-light-on world) are equally real — the so-called Many Worlds Interpretation), or alternatively only ONE of the two outcomes really happened and thus only one of those “worlds” is real; in which case one ought to throw away the term in the wavefunction which describes the outcome that did not actually occur — that is the traditional or Copenhagen Interpretation with its “wavefunction collapse”.
If you like many Worlds, fine. If you prefer the traditional interpretation, then one must say that something is going on when the wavefunction collapses other than normal processes described by the Schrodinger Equation.
In sum:
Unfortunately for both of you, Mr. Smith and Mr. Nickol, the philosophical problems raised by quantum mechanics are not so trivially disposed of as you might wish to think.
August 4th, 2012 | 12:04 am
George, I agree with your post almost entirely, but if you can get gravity to emerge from quantum mechanics, you’ll win a Nobel prize and a huge place in history.
August 4th, 2012 | 12:05 am
Be that as it may, with regards to A. Smith’s comment, nevertheless, there is not even the beginning of a convincing explanation, in purely material terms, of what we might call the “interiority” of consciousness. isolate has faith that “such progress will ultimately make the former action [empirical analysis of consciousness] as comprehensible as the latter [photography of physical action].”
Will it, though? Does modern science have even the faintest explanation of what it is to be conscious? Or an explanation of the phenomenological, “interior” experience of conscious beings? What is that, in physical terms? Does anyone even have the slightest idea?
The ancient Greeks knew that the mind was affected to some extent by physical input. If you’ve ever drank wine you would have realized that much. But, again, it’s difficult to see how empirical analysis could ever be able to fully encapsulate the “interiority” of a conscious mind. Even if we had sufficiently advanced scanners and computer analysis tools to track each and every atom in a human brain, wouldn’t that be something still qualitatively different from the “interior,” phenomenological experience of being that brain?
Martin Heidegger wrote, “[Dasein is] that entity which in its Being has this very Being as an issue…” The human mind is unique among objects of scientific inquiry in that it is the very thing which performs such inquiry. This leads to some interesting feedback loops, issues of self-reference, and “rabbit holes” once we try to hunt that particular snark, as it were.
August 4th, 2012 | 3:29 am
“Barr addresses your points 2/3 of the way down the page. See the paragraphs starting with, “An obvious question is why one needs to talk about knowledge and minds at all…””
George, I wouldn’t describe this passage as “addressing” Adam’s objection so much as merely talking past it.
Barr’s claim that a machine cannot be an observer with respect to wave collapse is both unproven and non-falsifiable (not much different from grade-school speculation on whether a tree falling in a forest with no one around makes a sound). Most physicists appear to disagree with Barr and accept that a machine can make “observations” but there is an unresolved question on what exactly has to happen before an observation is said to have happened.
One possible way of resolving the paradoxes of quantum mechanics is resort to the “many worlds” interpretation. Another possible way is to simply recognize that our existing understanding of quantum phenomena and wave collapse is incomplete and awaits more and better experimental evidence.
August 4th, 2012 | 6:56 am
George, I am addressing Barr’s points that he makes 2/3 of the way down the page.
To elaborate a bit: once a quantum event trips a chain of events within a complex system, such as would include either a human being or a measuring device, it enters the classical realm where thermodynamics holds sway. This, not the presence of a mind, makes it an observable.
Professor Barr says: “Again: as long as only purely physical entities are involved, they are governed by an equation that says that the probabilities don’t jump.”
But Schrödinger’s equation is NOT a complete description of the physical world. It does not include its own random collapse — possibly because it also does not account for gravity.
August 4th, 2012 | 10:29 am
David,
Adam and Barr are both right in the sense that they are talking about different parts of the measurement process.
When your photon hits your detector it begins to interact with the environment around it, which acts to remove any type of quantum effects from the system. Physicists call this process “decoherence.” This is well understood and follows from the work of John Von Neumann. This “decoherence” stage is the first part of a measurement.
However, now that all our quantum effects are removed, our theory tells us that the photon must be in some normal, classical state. (i.e. It hit the upper left of the detector, or the lower right, or somewhere in the middle. It can no longer be in two places at once or anything like that.)
Yet, quantum theory cannot tell us which classical state the photon went into. It tells us things like “There is a 60% chance the photon hit the top of the detector and a 25% chance it hit dead center, etc. etc.”
This is where quantum theory stops! Even after all quantum effects are removed by decoherence, the theory still cannot tell us which classical state the photon “decided” to go into. The theory gives us probabilities, yet we observe definite outcomes.
This step from multiple, probable classical states, to one, definite observed state is the second part of the measurement process and is where the true measurement problem in quantum mechanics lies.
This is the problem that Prof. Barr is talking about, and it does pose legitimate philosophical problems for straight scientific materialism. It may not be lethal for materialism, but the problem does need to be addressed by those who adhere to that philosophy if they hope to be consistent in their beliefs.
I hope Prof. Barr finds this comment thread. I’d be interested to hear more of his thoughts, given this discussion.
August 4th, 2012 | 12:23 pm
Dear George, I did find the comment thread! See my long comment above. Your comments show that you understand the issues.
Mark’s comments are quite mysterious. After criticizing me he ends up in his last paragraph saying exactly what I said in my essay! I don’t know where he gets his information about what most physicists believe. The great majority of physicists have not thought much about these issues. It is true that most physicists would reject the idea that mind is something as fundamental as matter — but most physicists would also reject Many Worlds and most physicists also think it unlikely that the fundamental postulates of quantum mechanics need to be changed. In other words, there is no view of these issues that would command the assent of “most physicists”.
The idea that a physical system which obeys Schrodinger’s equation can collapse the wavefunction is demonstrably false. Those who assert that it can are making a mistake about what wavefunction collapse is — they confuse it with “decoherence”.
August 4th, 2012 | 12:59 pm
Geoff,
Quite right! :)
My example was meant to be more conceptual than anything else. Perhaps instead of planets and gravity, our “macroscopic example” could be charged metallic spheres attracted to each other by static electricity.
Mark,
“Barr’s claim that a machine cannot be an observer with respect to wave collapse is both unproven and non-falsifiable”
This is just not true. As Prof. Barr points out above, wavefunction collapse and decoherence are separate phenomena that both play a role in a quantum measurement. You are confusing the two. See my previous post for the distinction between the two.
“Most physicists appear to disagree with Barr and accept that a machine can make ‘observations’ ”
There is a consensus among physicists on how machines can cause decoherence. (As I mentioned previously, if you have the prerequisite mathematical background, look up Von Neumann’s theory of quantum measurements.)
However, there is no consensus on how to correctly interpret the collapse of the wavefunction. This is still an open problem.
August 4th, 2012 | 3:16 pm
Unfortuantely, you are quite mistaken.
Stephen M. Barr,
Normally, I would be quite surprised, but not when the subject is quantum mechanics, philosophy, and human consciousness! Thank you for your detailed response.
August 4th, 2012 | 7:18 pm
Stephen,
It’s true that most physicists don’t spend much time thinking about this problem. Quite disappointing, given how interesting it is.
Thanks for the great article!
August 5th, 2012 | 1:45 pm
As with David Nichol, this is over my head; I prudently watch from the side line. However, as one passionately interested in the correlation between Theology and Science, I read these exchanges with great interest. Last Christmas my son surprised me with a book by Dr. Barr’s excellent book Modern Physics and Ancient Faith. Dr. Barr is not only a great lucid teacher in his field of Particle Physics but when coupling that with a good exposition of theology, where difficult concepts such as the difference of contingent being versus necessary being are made crystal clear, a great resource was created. A must read for anyone interested in this field.
One question to Dr. Barr, will there be an other book forthcoming? I already have on my Kindle “A Natural Guide To Natural Science.”
Thank You
August 5th, 2012 | 6:58 pm
Dr. Barr not only is a brilliant physicist, but an excellent writer as well. He has a great talent for writing clearly and understandably, as manifested in his Big Questions Online essay. It would be fascinating to see how many atheistic thinkers are willing to bite the bullet, and accept the “many worlds” theory. This theory, I think was advocated by the late philosopher David Lewis, but I think he was rather lonely in his endorsement. I wonder why this is. After all, if they understand the implications of quantum mechanics, and they’re honest, and they don’t believe in God, it would seem as if this is their only alternative. As Dr. Barr points out, this is heavy baggage!
August 6th, 2012 | 6:29 am
Prof Barr,
Given the uncertain state of fundamental questions in quantum mechanics, how much credence should we give to the speculative claims of quantum cosmology?
August 6th, 2012 | 11:13 am
Bret Lythgoe – If you don’t accept that the world goes on forever, it would seem the only alternative would be that the Earth must have an edge. :)
That was the cosmology a few thousand years ago, and most people seem to have accepted that the Earth had an edge. But new insights came along a few centuries later and yet more alternatives were thought up.
QM is a beautiful theory, and its predictions have been confirmed in every test we’ve made to date, to many decimal places. Relativity is another theory that’s passed every test we’ve thrown at it with flying colors.
But they make different predictions in areas we can’t test yet – like rotating black holes. We know that at least one of them – and probably both! – are incomplete to some degree. There’s a long history of hitting the limits of what we currently know and saying ‘here be the supernatural’ but that hasn’t worked out in practice.
August 6th, 2012 | 4:10 pm
Fools rush in . . .
In my example above, in which I was unaware of the meaning of decoherence, my thought was not about a photon hitting a detector in a lab. It was about a photon long ago, before the existence of human intelligence, striking some surface and perhaps producing heat. The question in my mind is whether the equations of quantum mechanics can be thought of as applying to situations that occurred before human consciousness was around and people were able to experiment with, predict, and measure quantum phenomena. The question in my mind is whether reality is somehow different if there is no (human) consciousness to observe it. Did reality actually change because consciousness came into existence? If there was no reality before there were human beings to observe it, what are geologists seeing when they look at billion-year-old rocks, or what are we seeing when we look in the sky and see light from a billion years ago. We can say that the observer has an effect on the observed, but what can we say about unobserved (and inherently unobservable) quantum phenomena?
August 8th, 2012 | 5:31 am
[...] HT: Anna Williams [...]
August 9th, 2012 | 8:51 am
Hi Ray, sorry to take so long to respond to your comments. I think that your comments reflect what Kant referred to as the “antinomies”, some things supersede our capacities. Does the universe have a beginning or end, is it spatially limited? We may never know.
Certainly Theists must be careful in using scientific arguments to support the existence of God, since, as I think you’re intimating, there’s a potential for a “god of the gaps” problem. But, of course, the inverse of this is a problem too: a “godless of the gaps”, where the atheist tries to utilize the latest scientific knowledge to support his atheism, but then subsequent scientific knowledge shows that the atheism is untenable, for example, quantum mechanics showing that belief in God is more rational than atheism. But both sides would be wise to rely on the latest science to support their views parsimoniously.
August 9th, 2012 | 9:06 am
Ray, I would also add that, if the evidence derived from quantum mechanics shows that a belief in God makes more sense (that is, does not lead to what, at least from a common sense perspective, leads to absurdities, such as infinite worlds, that clearly requires more faith to accept than the belief in a God), it seems rather empty for atheists to respond with, “well, in the future we’ll likely have an entirely naturalistic explanation for this”. How do you know? Maybe you’re right, unless, of course, the only reasonable explanation, ultimately, for why quantum mechanics works, is that God exists.
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