Saturday, August 13, 2005

Do General Relativity Principles Imply Experimentally Testable Changes in Quantum Mechanics?

Sir Roger Penrose
Oxford and Penn State Universities

The principles of equivalence and general covariance, of Einstein's general relativity, rest uncomfortably with the standard rules of quantum theory. Although in many respects gravitation closely resembles other fields of physics, especially electromagnetism, Einstein's general relativity demands that these basic principles be respected, which is not the case for Maxwell's electromagnetism. Sir Roger argues that continued respect for these principles in a "quantized" gravity will entail a change in the very laws of quantum mechanics. He further argues that such a change should resolve the paradox of quantum measurement and be experimentally observable. Experiments are presently under way in Santa Barbara which are partly aimed at shedding light on this profound issue.
Credit: National Science Foundation

24 Thoughts:

Blogger Doug said...

This guy's a total moron. He doesn't accept the Bible as holy writ. Oh, well.

Saturday, August 13, 2005 8:13:00 AM  
Blogger pawlr said...

I'll read all this science when they come up with a "Left Behind" book on it.

Saturday, August 13, 2005 8:24:00 AM  
Blogger Doug said...

They're all videos, bitch!

Saturday, August 13, 2005 8:25:00 AM  
Blogger pawlr said...

ok then a "Left Behind" made-for-TV movie. bitch.

hey do you know if they've actually been able to do the experiment he describes at the end of the video? The one they'd need > 1,000,000 photon reflections to acheive?

Saturday, August 13, 2005 11:18:00 AM  
Blogger Doug said...

I think they're actually making one. No idea whether they've done any experiment that'll support string theory or not. At least this guy's trying to come up with one; many string theorists go on "mathematical beauty" alone for their epistemic claims. True, it has a good history, but that's nowhere near the same as experimental proof.

Sunday, August 14, 2005 8:54:00 AM  
Blogger Doug said...

It should be said that my physics friends (some of them) say that Penrose is off the mark, albeit brilliant.

It seems that the key division in physics is over string theory, which is an epistemological problem. I find it quite hypocritical, on the face of it, for leading scientists to believe in a theory with no experiential or experimental confirmation. I'm simplifying a little, but even those who say, "it's a good guess, and probably true" very easily slide from probability to certainty.

Can't disallow ID if you allow string theory as fact. It isn't. Yet. And may turn out not to be. Or incomplete. Or whatever. But: no experiments, no observations?; no science, no matter how beautiful the math is.

Sunday, August 14, 2005 3:50:00 PM  
Blogger Doug said...

On the experiment: I'm not sure when or whether it was done, but I'm assuming not yet.

I can ask my physics friends...

Monday, August 15, 2005 9:34:00 AM  
Blogger pawlr said...

Doug - If Penrose is right and his experiment could shed light on quantum gravity, I'm sure the entire string theory community would jump at the opportunity to fire it up, since its not that they're averse to real world experimentation, its just that until now its prohibitively difficult to do tests on Planck size phenomena (10 ^ -40 meter sizes).

I'm reading The Fabric of the Cosmos now, and its interesting how deeply embedded epistemological questions are in QM / Relativity - for a period of about 20 years, Einstein and the QM community argued "tree falling in the forest" questions concerning the properties of subatomic particles, and, by extension, all observable matter.

Tuesday, August 16, 2005 8:07:00 AM  
Blogger pawlr said...

QM shows that the wave function for a particle doesn't collapse into a specfic position unless observed. Aggregating this elemental effect over an entire physical entity, like the Moon, means by extension, the Moon _does not exist_ in any specific place in spacetime until we look at it.

Tuesday, August 16, 2005 8:13:00 AM  
Blogger pawlr said...

Until now, the development of string theory to superstring theory and M-theory (and these really do seem like just a tantalizing hypothesis at this point, I agree) is the most reasonable Occam's-razor-type synthesis of the Standard Model (particles) with General Relativity. The difference between theories like Superstrings, Loop Quantum Gravity, etc. and ID is that practicioners of the former are eager (starved, even) for the possibility of scientific experiment on the subject, to either confirm, deny, or reveal some deeper truth. Practicioners of the latter are "bad faith" scientists in that if an experiement existed to disprove them, they'd simply abandon science altogether and go back to their bibles.

Tuesday, August 16, 2005 8:30:00 AM  
Blogger Doug said...

That jump from quantum effects to a summation of same to say that the Moon, which people have actually walked on, does not exist until we look at it strikes me as a mistaking of what effects obtain and are important at what levels.

Example: very light insects walk on water. To them, if they could think, water would appear to be a solid. To us, it ain't (well, for most of us). It's the difference between various forces valency at different levels.

Here's a classic article on size and physical forces by JBS Haldane.

So is water really a solid -- to us? Nope. To light insects? Yep. Frames or reference -- in the Einsteinian, not Lakovian, sense. :)

(Note how one could have made this argument at any point pre-QM; it doesn't rely on QM.)

Now, I know QM is the most experimentally confirmed theory we humans have. How we interpret that theory philosophically or epistemologically, though, is a different story.

In any event, to us, the Moon is hard, exists, and you can crash your spaceship into it and die very easily. At the quantum level, bits of Moon act according to QM. I would think it a huge bit of ironically anti-Copernican anthropomorphic hubris to believe that nothing exists until we look at it. That's highly solipsistic -- what was going on in the universe before our little species came on board? Did nothing really exist?

This is where QM intersects with other solipsistic or pseudo-Buddhist (or Buddhist -- don't know much about that religion) notions.

Now, I'm not at all sure that the agglomeration of small-scale phenomena doesn't give rise to emergent properties at higher levels. One might call gravity such an emergent property. On firmer ground, there is no such thing as "wetness" at the atomic, or even molecular, level. You need a certain large number of water molecules before "wetness" arises. That does not mean "wetness" is not real -- at our level.

Watch out -- physicists tend to be arch-reductionists; hence, the "Theory of Everything" language, which is quite telling. Reductionism has worked quite well in physics, but when any sociological group in academe thinks they can explain everything, you get into trouble. I think the world is a bit more complex than that.

In fact, I've heard some physicists (a guy on The Elegant Universe -- can't remember who) ask the "dangerous" question: Why must we have one theory of everything (in physics) that covers all levels? Might it not be the case that the very small and the very large simply don't cohere in a simplistic fashion (with all due respect to the super-high-level math I don't pretend to understand)? Or that, as a "middle" position, we don't have a lack of coherence; we have two amazingly well-supported theories that operate perfectly well in their particular size-domains.

Anyway, all of these nice hypotheses need to be adjudicated through experiment and observation or they remain "Sunday supplement" material -- and ripe for misuse (not by you) by all kinds of pseudo-scientists..

Anyway, I agree with the motivations behind ID vs. String theory, et al. We just need to be fair about how we talk about these notions -- as long as "enticing hypothesis" or "mathematically elegant, but as yet untestable theory" is used, fine.

When you say "until now," does that mean that string theorists can directly test their theories now? I thought that we'd need an accelerator the size of the solar system to do that (I should say that Sev's dad agreed with this, but still believed in string theory. Belief is the key.).

Tuesday, August 16, 2005 10:04:00 AM  
Blogger Doug said...

Oops: here's Haldane's article.

Tuesday, August 16, 2005 10:08:00 AM  
Blogger pawlr said...

Doug - yes, the moon exists, but until observed, only as a probability wave. Until that point, we can only say with certainty that the moon exists at a given position with 99.9999999999999999999% probability. For all intents and purposes, everything you described is true. We can see it, walk on it, land on it, etc. But at a certain level of exactitude, we literally can not know _where_ it is, until it is observed. Great debates took place in the 30's about whether the properties of unobserved particles were defined before the moment of observation, whether there was a "hidden variable" that existed before observation. I've got a good Physicist friend (the last man I know at Cornell) who I want to confer with about this, (I hope I can get him on the blog!) but as far as I know, nothing has shown the "hidden variable" hypothesis of Einstein to be true.

Tuesday, August 16, 2005 10:15:00 AM  
Blogger Doug said...

On what basis do you extapolate probability waves of subatomic particles -- QM's domain -- to something as large as the moon? Is there some aspect of QM I'm not familiar with (and the aspects I'm unfamiliar with are legion) that requires or even allows extrapolation to large-sized objects -- let's say, objects on an earthly scale up to planetary?

Seems like mixing apples and oranges to me, and it seems like the problem of not fully applying the old concept of hierarchical levels still exists in your reformulation.

Tuesday, August 16, 2005 10:22:00 AM  
Blogger pawlr said...

Questioning the necessity for a TOE is good. However, that raises a host of new questions - at what scale do we say that the laws of Relativity fails and the incommensurate laws of QM takes over, or vice versa? Intuition (and the history of science) make it likely that some underlying reality governs all scales (Much in the same way that Newton resolved the contradictions between "heavenly" laws (where stars and planets stayed suspended in the air) and "terrestrial" ones (where gravity applied).

Tuesday, August 16, 2005 10:23:00 AM  
Blogger pawlr said...

My "until now" comment was simply giving Penrose the benefit of the doubt (my own doubt). If Penrose's experiment doesn't shed light on M-theory, (the latest version of superstrings) then we're still in the dark.

Tuesday, August 16, 2005 10:25:00 AM  
Blogger Doug said...

As to the existence or not of subatomic particles -- well within QM's explanatory range -- I can say this: Scientists, like all people, have a hard time not knowing "everything."

I think the only fair thing to say is: we don't know, and can't tell, whether subatomic particles burst into existence when we "see" them, or are there when we don't. And that's that, until and unless someone can figure out a way to adjudictate the matter. The rest is metaphysical speculation not all that different in nature from ID -- it's based on ideology, worldview, or faith, not science.

Gotta respect at least the limits of science and "knowability," even in this progress-addicted culutre we live in.

Tuesday, August 16, 2005 10:28:00 AM  
Blogger Doug said...

True about the boundary line.

We might have a theory that unites QM and gravity -- that is, there might be an underlying notion. There might not. History can't predict here -- in fact, except under very specific circumstances and short time spans, I don't think history predicts very well at all.

It's simply an open question, and one that might remain open for hundreds, if not thousands, of years. That's what annoys people, I think. We're supposed to answer everything, and soon! LOL.

Anyway, I have no opinion one way or the other -- I will wait and see. It's all very interesting, though, from a scientific and also from a sociology-of-science perspective.

Tuesday, August 16, 2005 10:36:00 AM  
Blogger iBegToDither said...


The thing I would like you fellers to chew on while I go on vacation is the finite-unbounded nature of the universe as described by general relativity. I guess you've each worked through it a thousand times before but I believe some additional cogitation could be profitable, not least because a cursory glance at many political phenomena -- such as partisan approaches to budgets -- might leave one with the suspicion that a mangled version of the finite-unbounded metaphor is often implicitly (mis)applied to realms outside of geometry and physics.

In any case, it's a lot to get your mind around, finite but unbounded, when you extrapolate from typical 2-D instructional models, such as the surface of a sphere, to 3-D spaces like the one we (have always thought) we live in. The eager among can proceed to try visualizing higher dimensional geometries.

I am going to sift through the 7x10^22 other questions implied by your discussion. However, for a fortnight I'll be pondering oceanic conundrums and hope to return to find some progress in the modern physics section of cyberpols.

And now I must withdraw to my chambers.

Tuesday, August 16, 2005 2:27:00 PM  
Blogger pawlr said...

Welcome ibeg - as the Physicist laureate on the blog you have the final say in these matters.

Also reposting the Haldane Link since it seems a stray break tag got in the first link.

Tuesday, August 16, 2005 2:45:00 PM  
Blogger Doug said...

Hey, ibeg:

Nice to have you aboard! I have tried to wrap my mind around mutlidimensional geometries without much success. Lacking the math, I miss out on the tangible deep-knowledge of the matter.

However, Einstein did a pretty good job in his Relativity.

Anyway, I'd be interested, upon your return from vacay, about what you think about string theory, Penrose's lecture on QM, string theory's apparent non-testability (for the forseeable future), and its epistemological status right now.


Tuesday, August 16, 2005 3:19:00 PM  
Blogger pawlr said...

Finite but unbounded, like a the surface of a hypersphere, right? But in that case, doesn't the center of the universe have to be outside the 3-D surface of the universe (actually in the 4D core)? Am I close?

Tuesday, August 16, 2005 10:51:00 PM  
Anonymous ibegtodither said...

It seems I have misplaced the fabric of the cosmos. The book, I mean. As far as I can tell the fabric itself is still there, undulating sleepily, nursing a hangover following a violent epoch of creation.

I'll watch the Penrose video seaside (what else would one want to do at the very edge of a continent surrounded by beer guts and bikinis?) and try to make a meaningful contribution when I return. I'll be in the company of two astronomers.

Meanwhile, here's one possible way to sidestep epistemological crises: vote on it. Read the NYT article of 08/02/05 entitled "Lacking Hard Data, Theorists Try Democracy." It's archived now so it's not to be linked.

Friends, I believe I see sand dunes yonder...

Wednesday, August 17, 2005 10:13:00 AM  
Blogger Doug said...

Cool! Enjoy the sea. Where are you, so I can be jealous?

Wednesday, August 17, 2005 2:14:00 PM  

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