quote:Originally posted by Orincoro: But KoM, aren't scientists interested in the extistance of gravitons as a possible element in the eventuall testing of M theory? I am so an amatuer/hobby reader, but I think scientists would at least care to know what gravity "is" if it is indeed something like a particle or a wave, right?
edit: although, there we are still talking about how it behaves and not what it is.. but aren't you at least curious about what it is? The lady or the graviton?
Sure they would like to know what it is, but the point is that when you start getting to the heavy math subjects, it's really just that - heavy math.
Quantum Mechanics and General Relativity are very mathematical theories, string theory more so. Thus, an extremely rational person wouldn't say "we live on a curved 4-manifold", but "General Relativity wonderfully predicts the effects of gravity using the mathematics of curved manifolds as a model of the universe"
Likewise, one doesn't say "An electron is both a particle and a wave", but ,"Quantum mechanics best explains the behavior of an electron by assuming it can take on both wave-like properties and particle-like properties"
Or to use your photon example, photon is just short hand for a "packet of light", which is just a ripple in an electromagnetic field. Do electromagnetic fields REALLY exist? Or are they just convenient mathematical structures for accurately predicting behavior?
Finally, an exremely rational person would say, "String theory says the best model of the universe comes from assuming that everything is made up of bands of energy vibrating in different dimensions", as opposed to, "String theory says every particle is made out of tiny strings of energy"
I guess to summarize, especially with mathematics intensive fields, until you can observe something, the best you can say is "this math models what I'm seeing better than any other math I've ever seen", or in some good cases, "this is the best possible mathematical model matching all of the assumptions". One cannot say "this mathematical model works perfectly and therefore this is how the universe really is."
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quote:I'd gather from this you don't know what gravity is. The spacetime metric is a function acting on two vectors with certain properties. An equation cannot be curved, at least in the general relativistic sense. What can be curved is the manifold on which all these equations live.
Sorry about the slightly imprecise language. That said, you can have a manifold without a metric, and the metric is what determines the curvature of the manifold. And the Einstein field equations directly govern the metric tensor, so really it's facts about the metric (and not about the points) that determines the effects of gravitation.
Besides which, facts about the points of the manifold aren't in general diffeomorphism-invariant, so on the most common understanding of GR, they count as unobservable gauge.
quote:Let me just chime in and say that Mathematician is quite right about gravity; redefining it as 'curvature of the spacetime metric' is just playing with words. Even if you actually understand the equations, you're still only playing with numbers. You have gained something in your ability to describe what gravity does, which is why playing with numbers is a useful activity, but you haven't said anything about what it is. Nor does a scientist care; the proper aim is to get your ICBM to hit the right place, never mind the philosophical claptrap. There's a reason 'metaphysics' is an insult.
I think this view is profoundly mistaken. For one thing, there's no strong distinction to be drawn between theoretical input and experimental output. This distinction is basically a function of what the experimenter takes for granted, rather than any fundamental difference between measurable and non-measurable things. So for instance, a physicist using electron diffraction to measure a crystal will treat the position of the electrons as 'known' input, whereas another physicist studying the behavior of electrons will treat the same data as the unkown quantity to be measured.
Further, and perhaps more importantly, what we can measure depends on which theory of our own sensory organs and instruments is true. There's no way to measure anything without relying on theoretical assumptions about what you can measure.
This means the only sensible alternative is to accept, tentatively, the approximate truth of everything your best science tells you. Not just the 'experimental results' -- because the theory itself can't tell you which facts are experimental.
Bringing this back to relativity: relativity has taught us that spacetime exists. It's measurable, just like protons and dogs are measurable. I perceive it every time I feel the pull of gravity. There's no other explanation for effects like gravitational lensing, besides the apparent fact that objects exist in a curved, four-dimensional continuum. So I must assume that they really do, at least until better science (eg strings?) indicates otherwise.
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quote:I guess to summarize, especially with mathematics intensive fields, until you can observe something, the best you can say is "this math models what I'm seeing better than any other math I've ever seen", or in some good cases, "this is the best possible mathematical model matching all of the assumptions". One cannot say "this mathematical model works perfectly and therefore this is how the universe really is."
I agree, obviously, that we should be tentative. But I think mathematical models, just like any other inferences we make from evidence, should be treated as our best guess about how the world is.
quote:Or to use your photon example, photon is just short hand for a "packet of light", which is just a ripple in an electromagnetic field. Do electromagnetic fields REALLY exist? Or are they just convenient mathematical structures for accurately predicting behavior?
This is another good example of what I'm talking about. If the EM field is a real, physical field and not just a mathematical construct, then its presence at every point of space explains why charges move the way they do. If it's not a real field, then there's nothing out there in the world telling the charges what to do. So why do opposite ones attract rather than repel?
If you believe the EM field exists, you have an answer. Otherwise you don't. That's why I believe in the EM field, at least at the classical level.
quote:Originally posted by Destineer: Well, you were making an analogy with someone who might deny that evolution occurred, and yet still use it in science. So I assumed you meant that you might (or actually do) deny that i is a number, and yet still use it in math.
If that's not what you're saying, the analogy seems less than apt.
For future reference, don't try to read to much into my analogies. They are usually hastily constructed to make a superficial point, start taking them too deeply or broadly and they'll stop making any sort of sense. My main error was talking about the way I use i and then introducing a hypothetical person that has a problem with the existence of the number-for clarity I probably should have just kept the whole analogy hypothetical.
Or perhaps rather than hypothetical, just put Descartes into the analogy, at it should work a little better for you.
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posted
Watching scientists grapple with philosophy is really quite entertaining.
From E.P. Thompson:
In the old days (one supposes) when the philosopher, labouring by lamp-light in his study, came to this point in his arguement, he set down his pen, and looked around for an object in the real world to interrogate. Very commonly that object was the nearest one to hand: his writing table. "Table," he said, "how do I know that you exist, and, if you do, how do I know that my concept, table, represents your real existence?" The table would look back without blinking, and interrogate the philosopher in its turn. It was an exacting exchange, and according to which one was the victor in the confrontation, the philosopher would inscribe himself as idealist or as materialist.
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quote:Originally posted by Mathematician: I have read books/articles by Gerald Schroeder and by some other guy (I don't remember his name) which address this.
Oy, gevalt. Please don't cite Schroeder -- to quote my father (a mathematical physicist and an Orthodox Jew), his book are "bad physics and bad Torah."
As for "the other guy," I suspect you are talking about Larry Keleman, whose books are great (and you should hear him in person!) I also recommend Nosson Slifkin's books, although I disagree with him on a fair number of details.
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quote:So for instance, a physicist using electron diffraction to measure a crystal will treat the position of the electrons as 'known' input, whereas another physicist studying the behavior of electrons will treat the same data as the unkown quantity to be measured.
Totally irrelevant. I refer you back to the example I mentioned, of making an ICBM hit the right spot. Technology forms an independent test of science; if your lightbulb works, your science is right enough. It can get better, so that for example you are able to get a radio to work without losing the lightbulb. But the distinction between 'known input' and 'experimental result' is irrelevant; the question is whether you can make a better killing machine.
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quote:Technology forms an independent test of science; if your lightbulb works, your science is right enough.
What about science with no known technological application, like high-energy particle physics or cosmology? How does your standard of rightness (or 'right enoughness') apply to these situations?
Also, I would maintain that even in the ICBM case, your criterion of success is theory-dependent. How is it that you assert that the ICBM hit the right target? Well, you have a theory of motion that tells you what it is for a missile to collide with a target, and a theory of optics that tells you how the collision is visible to the naked eye.
These theories might be ill-defined 'folk theories' that you formed from everyday life rather than experimental science. But they're theories nonetheless.
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quote:Originally posted by Mathematician: I have read books/articles by Gerald Schroeder and by some other guy (I don't remember his name) which address this.
Oy, gevalt. Please don't cite Schroeder -- to quote my father (a mathematical physicist and an Orthodox Jew), his book are "bad physics and bad Torah."
As for "the other guy," I suspect you are talking about Larry Keleman, whose books are great (and you should hear him in person!) I also recommend Nosson Slifkin's books, although I disagree with him on a fair number of details.
Thanks for the heads up about Schroeder. I knew he was bad at physics, but I had no idea he screwed up the "Torah" side. What do you know about this Nachmanides guy Schroeder seems to quote a lot?
All this said, I still find his writings interesting (though not science or Torah) ;-)
As far as the other 2 guys you mentioned, I don't THINK that's them, but I really don't remember.
posted
Nachmanides, more commonly known as the Ramban (not to be confused with the Rambam, an approximate contemporary with who he disagreed on many points but respected greatly), was a great Torah scholar. His commentary on Chumash (Five Books of Moses) is considered one the five (or so) most basic commentaries on the text, and included in all Mikraos Gedolos (essentially the gold standard for printed volumes of Tanach) Chumashim.
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just so we're on the same page, "5 books of Moses" is Genesis, Exodus, Leviticus, Numbers, and Deuteronomy? I guess what I'm really asking is about Deuteronomy. As Moses dies in it, he probably didn't write all of it ;-). Is there another book which is authored by Moses (which perhaps, didn't make it into the Christian Old Testament Canon?)
Also, what's "Tanach"?
Finally, when saying Ramban's commentary "is one of the 5 or so most basic commentaries on the text", what exactly do you mean by basic? Basic meaning one of the 5 or so standard starting places when looking up Torah commentary?
quote:Technology forms an independent test of science; if your lightbulb works, your science is right enough.
What about science with no known technological application, like high-energy particle physics or cosmology? How does your standard of rightness (or 'right enoughness') apply to these situations?
Particle physics has applications to fusion power, cancer cures, and breaking up radioactive waste. Further, it makes predictions about what our detectors are going to show; and those detectors can be checked elsewhere, against the usual technological 'right enough' standard. It's all a web, but ultimately it refers back to lightbulbs.
quote:Also, I would maintain that even in the ICBM case, your criterion of success is theory-dependent. How is it that you assert that the ICBM hit the right target? Well, you have a theory of motion that tells you what it is for a missile to collide with a target, and a theory of optics that tells you how the collision is visible to the naked eye.
That's stretching the word 'theory' into utter meaninglessness, and I won't go there.
[ September 10, 2006, 03:31 PM: Message edited by: King of Men ]
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quote:just so we're on the same page, "5 books of Moses" is Genesis, Exodus, Leviticus, Numbers, and Deuteronomy?
Yes, although that's not what I call them.
quote: I guess what I'm really asking is about Deuteronomy. As Moses dies in it, he probably didn't write all of it ;-).
That is debated, actually. Traditional possibilities:
The last 8 verses were written by Yehoshua (Joshua).
They were dictated by God to Moshe before his death, and he wrote them "b'dmaot" -- in tears. (Just as in English, that can either mean while crying, or actually using tears as the ink.)
Regardless, all but the last 8 verses have no such difficulty.
quote:Also, what's "Tanach"?
Acronym for Torah (5 books), Nevi'im (Prophets), and Kesuvim (Writings). Essentially what a Christian would call the "Old Testament."
quote:Finally, when saying Ramban's commentary "is one of the 5 or so most basic commentaries on the text", what exactly do you mean by basic? Basic meaning one of the 5 or so standard starting places when looking up Torah commentary?
quote:Originally posted by Mathematician: As far as the other 2 guys you mentioned, I don't THINK that's them, but I really don't remember.
Was it by any chance Aviezer? I haven't read that one, but as I recall my father considers it "not terrible." (Other people I know are more effusive. )
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quote:That's stretching the word 'theory' into utter meaninglessness, and I won't go there.
I agree, but I'd already been thinking that KoM's answer to 'the nature of science' ("Nor does a scientist care; the proper aim is to get your ICBM to hit the right place, never mind the philosophical claptrap") threatened to stretch (or constrain) the word 'science' to utter meaninglessness.
I wasn't orginally going to respond (with more of my characteristic claptrap, sorry), but I'm curious about KoM's latest.
Is technology the aim of science? Is it merely a convenient, and independent, 'test' of science? Is it part of science?
And more to the point, what is technology? "If the field is irrigated, the theory about Archimedes screws is right enough." Obviously an infinite number of examples, from rubbing two sticks together to annihilating the globe, can be concocted to mirror this statement. But just as obviously, it's important to HAVE the right theory (or a right-enough theory) -- independent of experimental results -- in order to derive spin-off conjectures or to connect the underlying prcinciple of one physical phenomenon with that of another.
You may say, well that will just result in another light-bulb test, which will fail or succeed according to the correct-enoughness of the spin-off conjecture. True -- but the link between the two experiments, as exemplified in the scientist's advanced understanding of underlying principles/math/whatever cannot be thus consigned to irrelevance.
But maybe I am misunderstanding your point.
In addition, there is a vast amount of science (maybe even most, certainly most life science) for which analogues of "the proper aim is to get your ICBM to hit the right place" are hard if not impossible to identify.
Maybe the notion that science is about knowledge, as well as results, is a little metaphysical. Then again, I don't consider metaphysics a dirty word.
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quote:Particle physics has applications to fusion power, cancer cures, and breaking up radioactive waste.
Not all particle physics has such applications. I doubt Higgs bosons or top quarks will be used in radiation therapy or fusion any time soon.
In fact, due to confinement, quark color is an unobservable quantity with no possible application. That's provable from the form of QCD, although some of the proofs are a bit fuzzy. And you didn't address cosmology in your response. Bottom line, I think I've shown that you're wrong that all science has technological applications.
quote:Further, it makes predictions about what our detectors are going to show; and those detectors can be checked elsewhere, against the usual technological 'right enough' standard.
Really? How do you check the performance of a neutrino detector, for instance, except by detecting neutrinos with it?
That's right, neutrinos... another particle with zero technological application.
quote:That's stretching the word 'theory' into utter meaninglessness, and I won't go there.
Newtonian mechanics isn't a theory? Because that's what explains collisions. Geometric optics isn't a theory? Because that's what explains how the eye works.
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