Re: Dr. T. Roberts operated on GR with LOCAL anesthesia

From: Eric Gisse (fsegg_at_uaf.edu)
Date: 11/05/04 

Date: 5 Nov 2004 14:30:52 -0800

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.

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]

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