stevestory
Posts: 13407
Joined: Oct. 2005
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The guy is just *&$ing nuts. In one of his latest comments, he suggests that engineering is so much less ad hoc than science, because engineers like himself stifle their egos when necessary. I'll add quite a few posts above his so you have the necessary context, but read through to get to DaveScot's last comment. Just mind blowing:| Quote | #
Or it may be the cosmological constant is some infinitesimal bit larger than zero which I’m sure has Einstein rolling over in his grave as he thought it was the biggest mistake of his life to stick it into GR only to have it zeroed out by observation. Shrugging this off to a non-zero CC smacks of pencil whipping to me. Oh gee, the equation didn’t work out quite right but if we just pull a constant out of our arse and adjust the value to fit the observations we can keep the theory.
Uh, no. The jury is still out on this one.
Comment by DaveScot — January 25, 2006 @ 12:18 pm
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Davescot
in a sense, adding a cosmological constant to einstein’s equations is the most conservative modification one can make. it *is* a modification to GR. Whether MJ can reference a better explanation i am not so sure.
yes, the jury is still out on much of this—i’ll definitely agree on that. physics is hard and we don’;t know all the answers! if we did there wouldn’t be much more physics to do
Comment by physicist — January 25, 2006 @ 12:24 pm
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PaV
My point is that systems with random change can and often do generate patterned behavior. Patterned behavior is in not at all an indication of external design other then to say that a designer may have created certain rules for a system where random change can create patterned and ordered behavior. In short no external input is necessary for a chaotic system to create order and great complexity (CSI).
Comment by ftrp11 — January 25, 2006 @ 12:24 pm
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i would say there are not really yet any firm theories of (this kind of) multiverse. i’m not sure to which theories you refer?
susskind’s intuition i think is that one will find universes bubbling off from our own, but there’s a lot more work to do yet i think.
there’s not much more i can say—the theories youre talking about need much more work to be well-defined. saying at this stage that these ideas will *never* be testable is premature. we don’t understand them well enough, yet.
Comment by physicist — January 25, 2006 @ 12:32 pm
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sorry that last comment to david heddle
Comment by physicist — January 25, 2006 @ 12:33 pm
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PaV, i’d be interested in your response to #4—I think you’re being quite hasty in dismissing dark matter.
Comment by physicist — January 25, 2006 @ 12:36 pm
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Dave Scott,
Regardless of what he meant regarding the galaxy, there is no ToR breakdown. That is simply wrong.
A non-zero CC does not violate GR, it’s a term that, after realizing the universe was expanding, Einstein decided he didn’t need, since he wanted to use it to explain a steady state universe. My guess is, since it now seems to be needed, he’d be delighted at its rehabilitation.
Also, you imply that the CC was pulled out of the air to explain accelerated expansion. In fact, it has been recognized for sometime, prior to the recent observations, that a vacuum energy density looks like a cosmological constant—it was already making a comeback.
Furthermore, the CC contributes to the understanding of not just the accelerated expansion, but also the other big cosmological news: the flatness of the universe. (And also the “age” problem)
Yes the jury is still out. It often stays out for a long time in science.
Comment by David Heddle — January 25, 2006 @ 12:41 pm
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physicist
re CC += GR (how’s that for cryptic?) :-)
The only problem with calling that the most conservative thing to do is that the amount of CC you’re adding is 120 orders of magnitude smaller than most QFT’s predict. And therein lies Heddle’s point about support for cosmological ID. The infinitesimally small value is like the mother of all fine tunings.
In engineering when things don’t work out quite like we predict and we do something like this to fix our model it’s called a kludge and it isn’t a complimentary term. Do you use that term in physics? If not you should.
Comment by DaveScot — January 25, 2006 @ 12:47 pm
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Davescot
At the level of classical GR there is no preference for a particular value of Lambda
one can only go so far with QFT on curved backgrounds—I agree the naive value of Lambda predicted is incorrect, but there is a lot more to the story of quantum effects and gravity. including quantum effects in gravity is a general a very hard and unsolved issue.
so i wouldn’t say the QFT indication of a large Lambda is a firm `prediction’. it has always been recognised that combining QFT and GR in this way is an ambiguous procedure. so i think kludge is misapplied.
if you want to look for fine tunings, there are lots of other constants in nature which are finely tuned–for example the precise mass ratios of fundamental particles. if you want to explain these numbers by design, you can—but part of the study of physics is seeking to find deeper and simpler underlying reasons for these apparently finely tuned numbers.
Comment by physicist — January 25, 2006 @ 12:53 pm
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so i would just re-emphasise that at the classical level, if you want to explain cosmological observations of type Ia supernovae, making lambda non-zero is indeed the simplest modification to GR you can make—and fits the observations well.
Comment by physicist — January 25, 2006 @ 12:55 pm
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David H
I didn’t know science had become the art of salvaging theories with failed predictions by the addition of ad hoc hypotheses like smidgins of constants to equations that hadn’t needed them for the past 75 years.
Excuse me. GR is in fine shape. It just needed a little work is all. The jury I guess has come in. I’m curious, is there anyone on the jury in addition to David Heddle?
Comment by DaveScot — January 25, 2006 @ 1 3 pm
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This mindset of salvaging pet theories with ad hoc kludges to explain failed predictions is what propped Darwin up for so long. I see it’s not just biology that is plagued by this. Us engineers are a different breed I guess. Lives can be lost when we’re wrong so we can’t afford to let our egos get in the way of acknowledging failures.
Comment by DaveScot — January 25, 2006 @ 1:12 pm
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