Re: Dr. T. Roberts operated on GR with LOCAL anesthesia
From: Bill Hobba (bhobba_at_rubbish.net.au)
Date: 11/06/04
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Date: Sat, 06 Nov 2004 01:20:48 GMT
"Marcus Wellpoth" <wellpoth@gmx.de> wrote in message
news:418c2075$0$20932$9b4e6d93@newsread2.arcor-online.net...
> Bill Hobba wrote:
> > "Eric Gisse" <fsegg@uaf.edu> wrote in message
> > news:fd0fc2fa.0411051430.4306770c@posting.google.com...
> >
> >>eleatis@yahoo.gr (Mike) wrote in message
> >
> > news:<9c1b39be.0411042332.1e79e522@posting.google.com>...
> >
> >>>Tom Roberts <tjroberts@lucent.com> wrote in message
> >
> > news:<cmdm97$le0@netnews.proxy.lucent.com>...
> >
> >>>>Mike wrote:
> >>>>
> >>>>>1. Do you distinguish between the "law of Free Fall" and EP in the
> >
> > GR
> >
> >>>>>sense?
> >>>>
> >>>>What you call the "law of free fall" is just a loose statement AFAIK.
> >>>>The Einstein equivalence principle is an explicit statement suitable
> >
> > as
> >
> >>>>the postulate of a physical theory, such as GR. The EP directly
> >
> > implies
> >
> >>>>that LoFF.
> >>>>
> >>>
> >>>Thank you Dr. Roberts. I am skeptical about the usage of the word
> >>>directly. If you mean after solving equations, then yes. But this
> >>>comes in in conflict with your answer to No 3 below.
> >>>
> >>>
> >>>
> >>>>>2. Can you quantify "locally" in terms of the fundamental dimesion
> >
> > of
> >
> >>>>>[L]? When locallity breaks down?
> >>>>
> >>>>You ask for a binary demarcation of a continuum. That's not a good
> >
> > idea.
> >
> >>>Then it is not a good idea to speak of local measurements if this
> >>>demarcation cannot take place. You assert hat EP and consrtant c apply
> >>>locally but when I ask you to dfine it you tell me I cannot ask the
> >>>question. This reminds me of how my local priest treated me long time
> >>>ago when I asked hom a question about religion.
> >>
> >>Here we go. Comparing a physical theory to religion.
> >>
> >>I strongly suspect you didn't understand the answer the priest gave
> >>you, much like the answer Tom gave you.
> >>
> >>The paragraph below this explains the definition of "local" rather
> >>well. Reading is fundamental, remember?
> >>
> >>
> >>
> >>>>In general, one can apply the equivalence principle to a region of
> >>>>spacetime as long as the effects due to spacetime curvature (aka
> >>>>gravitation) are sufficiently smaller than your measurement accuracy
> >
> > so
> >
> >>>>they can be neglected.
> >>>
> >>>How would you know in advance if you have no threshold to apply?
> >>
> >>Reading is fundamental.
> >>
> >>
> >>>>This depends on both the type of measurement being made and the
> >
> > physical
> >
> >>>>situation in which it is made.
> >>>>
> >>>>For example, the effects of the earth's rotation and gravitation can
> >
> > be
> >
> >>>>neglected for most optical experiments on a tabletop (e.g. the MMX,
> >>>>Brillet and Hall, etc.). But if your tabletop includes a coiled
> >>>>fiber-optic cable several kilometers long and you measure the time of
> >>>>flight for light signals through it using a clock with picosecond
> >>>>accuracy, then this does not hold (such a gyroscope can detect the
> >>>>earth's rotation).
> >>>>
> >>>>Basically you have to use GR to determine whether or not a given
> >>>>experiemntal measurement is affected by non-local effects of the
> >>>>physical situation.
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>>3. In GR, is the classical law
> >>>>>of free fall true, i.e. that the rate of fall is independent of mass
> >>>>>and composition?
> >>>>
> >>>>Bo. But it is approximately valid for a small object, and that is the
> >>>>only situation for which it has ever been tested (or applied
> >>>>classically). The approximation involved is usually incredibly good,
> >
> > in
> >
> >>>>practice. Note that jupiter moving in the field of the sun is "small"
> >
> > to
> >
> >>>>good accuracy; a falling rock on earth is "small" to incredible
> >
> > accuracy.
> >
> >>>I take "Bo" to be a "No", typed wrong. This statement comes in confict
> >>>with No 1 above. The law of free fall states that ALL objects fall in
> >>>a gravitational field with a rate independent of mass and composition.
> >>>
> >>>
> >>>>>4. In your opinion, was Galileo correct to state a Law of Free Fall
> >>>>>given the limited reach of his experiments?
> >>>>
> >>>>Sure.
> >>>
> >>>How it can be sure? Just above you said it is only true for "smal"
> >>>objects. Notice the use of the word "Law". The law of free fall is a
> >>>universally quantified proposition and was intended to serve as a
> >>>physical law. Obviously, GR denies the universality of the particular
> >>>law of Galileo stated it. It comes as a surprise to me that
> >>>educational institutions want to retain both Galileo and GR valid. If
> >>>one believes GR, it is true then that a Law of Free Fall is either
> >>>impossible to state or it is a profoundly much complicated statement
> >>>than what Galileo states and Newton adopted as true. It is natural
> >>>than based on that falsw lae, the perihelion advance of Mercury cannot
> >>>be explained as later explained by GR fairly accurately. Thus, at some
> >>>point, we are either honest enough to re-write the books or continue
> >>>holding up contradictory theories.
> >>
> >>Are your misconceptions real or are they mental blocks?
> >>
> >>
> >>>It comes as no surprise that not
> >>>too many undegrads can understand GR when they enter graduate school.
> >>
> >>Think for a minute why an undergrad would have a hard time
> >>understanding GR from the start of grad school.
> >>
> >>How many undergrads, by the time they graduate, come forth with
> >>differential geometry, linear algebra, every flavor of calculus and
> >>proofs? That is what is required to start learning GR at a decently
> >>functional level, I am a junior and im making a bee-line for GR and im
> >>only halfway there [though "half" is defined oddly when doing a double
> >>major in math and physics, im gonna be here awhile].
> >>
> >>Here at UAF, the graduating requirements for a BS in physics don't
> >>include proofs, differential geometry and a whole floatilla of
> >>auxillary math classes which would make groking GR less painful. Hell,
> >>it doesn't even require applied analysis [translation: a decent
> >>treatment of vector calculus and partial differential equations, a
> >>prerequisite for a gruaduate level class I would like to take next
> >>fall]. Even a math major doesn't hit all of them unless he wants to.
> >
> >
> > Now that is the truth. And even math majors like me could see the
dislike
> > for hard math subjects in other math majors. A requirement where I did
my
> > degree for a major in math was complex analysis. Students hated it
because
> > quite frankly it is hard. But the school stuck to its guns and said you
can
> > not say you have majored in math unless you do it - and quite frankly
they
> > were correct. That however was 25 years ago - I now notice the
requirement
> > has been removed - which is a pity - even the number of subjects has
been
> > lowered. To get a math degree when I did it you needed 32 subjects -
now it
> > seems only 24 is required. Of course the subjects may now contain more.
> > But one can not help but get the feeling standards have dropped.
> >
> > Thanks
> > Bill
> >
> >
> >>GR needs math. Math is hard. What do you honestly expect?
> >>
> >>Then again, perhaps you are arguing this because at one point in time
> >>you failed to understand a requiste math class and things just went
> >>down hill from there. Or even more likely, you never tried because you
> >>didn't deem GR worth the effort, so instead you attack it as an
> >>armchair physicist.
> >>
> >>[signip]
> >
> >
> >
> --------------------------------------------------------------------------
> Excuse me but what is a major and what is a minor?
I am speaking about in Australia where I am; and 25 years ago as well. The
basic degree was a degree in science - BSc - Applied Mathematics or BSc
Computer Science - what you got after the BSc is what I call the Major. For
math that meant when I did it you needed to do a certain number of math
subjects (I seem to recall it was 16) of which some were compulsory eg
complex analysis. The other 16 could be taken from anywhere else with a
certain minimum number outside math (I seem to recall it was eight). Where
I went to I took the other 16 from Computer Science which gave me enough to
meet the entrance requirements to the Australian Computer Society - in fact
some subjects such as numerical analysis were considered both part of
computer science and math so there was some overlap. I forget now whether
it also formally allowed me to say I also majored in Computer Science.
There were three stands in Computer Science, Application programming,
Systems programming and Scientific programming. I followed the Application
programming strand - I seem to recall you needed to have all 3 strands to
actually major in Computer Science.
Thanks
Bill
>
> mw
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- In reply to: Marcus Wellpoth: "Re: Dr. T. Roberts operated on GR with LOCAL anesthesia"
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