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Re: "Deep Impact" predictions

Subject: Re: "Deep Impact" predictions
From: Paul Schlyter
Date: Sat, 20 Aug 2005 10:13:49 GMT
Newsgroups: sci.astro
In article <A86dnYDTs8G8bWffRVn-oQ@xxxxxxx>,
Tom Van Flandern <tomvf@xxxxxxxxxxxxxxxx> wrote:
Article: 475300 of sci.astro


> "Paul Schlyter" <pausch@xxxxxxx> writes:
>
>>> [tvf]: Geometric GR has two giant disadvantages because it violates
>>> two principles of physics (causality and "no creation ex nihilo") as
>>> I explained in my last post, which falsifies it for many practical
>>> purposes.
>
>> [Schlyter]: Who defined those principles? Yourself?
>
>             The particular list I posted in my "Physics has its
> principles" paper (web version at
> http://metaresearch.org/cosmology/PhysicsHasItsPrinciples.asp) arose
> from a consensus of physicists attending a conference about fundamental
> principles held in Sutton, Ontario in October 2002.
>
>             The principles of physics (by contrast with the laws of
> physics) arise from logic alone, and do not depend on observations or
> experiments. For example, one of them is "no creation ex nihilo", which
> is pretty self-evident provided that one understands that it means "you
> cannot get something from *literally* nothing", although there is no
> problem getting something out of the vacuum or what appears to be
> nothing. As is now well known, the vacuum is filled with zero-point
> energy, fields, radiation, and other forms of substance. Getting
> something from an invisible source is not a problem. Getting something
> from a true void requires a miracle. Miracles are not generally
> considered to be impossible, but are outside the realm of explanations
> considered by physics. (See my answer to a later question for more about
> why miracles are excluded by physics.)

It sounds like some kind of Platonian principle, where principles are
more important than empirical observations of reality.....

So if there would be an empirical observation which contradicted your
logical ideas, and if that observation could be repeated over and
over again - does that mean you'd discard the observation and concider
the logic flawless?  If so, you'd be in company with Aristotle, who
in his Platonian tradition considered empirical observation less
important than human thoughts about logic.

>> [Schlyter]: I think you'll find it hard to merge your request for
>> causality with some quantum mechanical effects. Such as Heisenberg's
>> uncertainty principle, the "tunnel effect", etc.
>
>             I found no problem with these concepts when strict
> principles of physics are adhered to, as you can read for yourself in
> chapter 5 of my book "Dark Matter, Missing Planets and New Comets"
> (North Atlantic Books, Berkeley, 2nd ed. 1999). But QM is far afield of
> our discussion here. Let's try not to multiply discussion threads so
> much. I'll simply hint that all of QM starts making sense again once we
> do away with the constraint that "nonlocal" actions are forbidden. As
> you know, my published papers show how the speed of gravity is an
> example of faster-than-light action in forward time, which is "nonlocal"
> by the QM definition.
>
>> [Schlyter]: So we can conclude that your request for causality in each
>> and every situation is contradicted by observation at the quantum
>> mechanical level. Yes, it's counterintuitive. Yes, Einstein disliked
>> it too, but eventually he accepted it, since what counts is
>> observations and experiments, not human ideas.
>
> Human logic is as important (and arguably more important) as observations
> and experiments.

Aristotle thought so too .... and we know where that led him in the
field of physics ... or "natural philosophy" as it was called back then.

> Our interpretations of the latter (such as the laws of physics) are
> fallible and subject to evolution or even contradiction. But valid
> logic is immutable and provides the only true certainties we have.

OTOH logic is, like mathematics, an ideal world of its own, in
principle detached from our physical world.  So what you say here
applies only to that ideal world, not to our physical world, where
there'll always be small discrepancies from the ideal world of logic
and mathematics.

The science of applying mathematics and logic to our physical world
is called physics.  And there the "immutability" of logic and
mathematics vanishes, since we're always dependent of our
interpretations of observations and experiments.  We can never
escape that dependency when we deal with the physical world.

Remember that even if we manage to build a model which mimics the
physcal world realy well, that model still isn't the physical world,
but just a model of it.

> Because we cannot regress cause and effect infinitely far back, we
> must ultimately rely on logic for our first principles. To base them
> on observation or experiment is to build models on quicksand because
> there are no observers of a "First Cause".

Once again you're like Aristotle: he too didn't want to base his
models on observation or experiment, probably for the same reasons as
you.  And as we know he reached conclusions which were utterly
wrong.....  His model was logical, sure, but it wasn't a model which
agreed with the physical world.

>>> [tvf]: . neutron interferometer experiment .
>
>> [Schlyter]: Now you've entered the realm of quantum mechanics. GR is a
>> classical physical theory which is no longer valid in the quantum
>> mechanical realm.
>
> Is that the Schlyter theorem?

:-) ...no.  It is well-known that classical theories aren't accurate
at the quantum level -- you need quantum theories at that level.

> This is the first I've heard that the laws of gravity do not apply to
> quantum particles such as in the neutron interferometer. Using geometric
> GR, how do these particles manage to escape noticing that the spacetime
> they are embedded in is curved? Why are their motions exempt from conforming
> to the geometry that macroscopic bodies must follow? In short, why does
> the equivalence principle hold only for macroscopic bodies and not for
> quantum particles, as you seem to be hypothesizing here?

Your questions here can be summarized as: why are classical theories no
longer valid at the quantum level?

Nobody knows why is is so -- but it is an experimental fact that a
lot of physical laws valid at the macroscopic level falls.

Therefore I would be very cautions when interpreting observed
phenomena as a refutation of GR.

>> [Schlyter]: Perhaps the initial attempts of merging QM and GR is
>> easier with your field interpretation of GR, but that's because "field
>> GR" appears somewhat more similar to NP (Newtonian Physical) than
>> "geometric GR".
>
>             Field GR is the interpretation preferred by Einstein, Dirac,
> and Feynman. So it seems rather inappropriate to act as if it is somehow
> inferior or not "real GR".
>
>> [Schlyter]: I don't see why there's more "magic" in geometry than in
>> "action over a distance" which the "force of gravity" really is.....
>
>             True "action at a distance" is also forbidden by logic,
> although there is nothing wrong with the mere appearance of action at a
> distance carried by entities too small to detect. As applied to
> understanding gravitation, that is what the Le Sage "pushing gravity"
> idea is all about - a description of carriers of gravitational force
> from a source mass to a target body that appears to simulate action at a
> distance.
>
>> [Schlyter]: But this means we both agree on this:
> -----------------------------------------------------------------------
> A collection of macroscopic bodies (i.e. bodies large enough such that
> QM effects become negligible) in an otherwise empty universe, which
> initially are at rest in space relative to one another, will start to
> move due to their mutual gravitation. And this is predicted both by
> geometric GR and by field GR, and they both predict precisely the same
> trajectory for each body.
> -----------------------------------------------------------------------
> Can we agree on this? Or do you claim that in this scenario geometric GR
> will yield a different prediction compared to field GR?
>
>             Geometric GR by itself describes only the potential field
> and contains no forces, so by itself it is unable to explain any motions
> of material bodies in 3-space. Both geometric GR and field GR adopt the
> axiom that force is the (instantaneous) gradient of the potential, in
> order to derive equations of motion that allow them to predict 3-space
> motions with respect to time. With that caveat, yes, they both predict
> the same 3-space motions - but definitely not by geometry alone.
> Geometry has no cause that can initiate motion. Only a force can do
> that, force being the time rate of change of momentum by definition.
>
>             In short, the alleged "geometry" and "curvature" exist only
> in the potential field, but neither concept does anything about
> initiating the 3-space motion of target bodies. It takes a force to do
> that.

Here you say three things:

1. Field GR will initiate motions of stationary objects by the force of gravity
2. Geometric GR won't initiate such motions since geometry alone cannot do that
3. Field GR and geometric GR make the same predictions about how the bodies
   will move.

3. is a clear contradiction to 1. and 2. --- make up your mind !!!!!!!!

>> [Schlyter]: Your causality principle is flawed. It works well in
>> Newtonian Physics but fails in . GR (your flawed conclusion that
>> geometric GR says that those bodies initially at rest in space will
>> remain in rest just because gravity is a pseudo-force. Your flaw is
>> corrected by integrating space and time to space-time, instead of
>> keeping them separate as you insist on doing, like in Newtonian
>> Physics).
>
>             Newtonian physics is not involved in this discussion in any
> capacity. When you use the expression "Newtonian physics", it seems
> apparent from context that you must mean "Euclidean flat-space geometry".
> So I will interpret your sentence to mean that and answer it
> accordingly. If that is not your meaning, please explain what any of
> this discussion has to do with Newtonian physics.
>
>             More to the point, please elaborate how the lack of a cause
> to initiate motion in geometric GR is corrected by considering spacetime
> to be curved?

I never said there was a lack of a cause -- I merely said there was
no force of gravity in geometrical GR (and if we exclude non-
gravitational forces there won't be any forces at all in geometrical
GR of couse).  Which implies forces cannot be the cause, but it
doesn't exclude other causes.

> My whole point is that curvature alone, in the absence of a force, cannot
> initiate the motion of anything.

Not even when there is an initial motion ????

In 4D space-time nothing can ever be "at rest" (unless you stop time
itself), since in the t dimension everything propagates forward at c,
the speed of light.  That, combined with the curvature of space-time,
is the cause of those initially stationary bodies starting to move:
the motion, which initially was exactly parallell to the "t"
direction, will, due to the curvature of space-time, partially spill
over into the "xyz" directions, making the bodies starting to move
also in "xyz" space.

The situation is similar to this situation on normal 3D space:
consider an Euclidian space and a rectilinear orthogonal coordinate
system xyz, where a body moves exactly parallell to the "x"
direction.  No forces act on the body, which thus has rectilinear
uniform motion.  In the "yz" plane the body will appear to be
stationary, and will appear to remain stationary forever, or until
some force starts acting on the body.

Now, consider the same situation in a curvilinear coordinate system.
For simplicity, let's assume a spherical coordinate system: the
body moves exactly towards, say, "west" at a latitude of, say,
60 degrees - thus its motion will be in longitude only.  The same
situation applies as in the prevous paragraph: no forces are acting
on the body, which thus has a rectilinear uniform motion.  Initially
the body will appear stationary in both latitude and radius vector,
moving only in longitude.  But due to the curvature of this coordinate
system, the body will soon change not just longitude but also latitude
and radius vector - even though no forces are acting on the body.
It's due just to geometry!


> If a test particle
> rests on the side of a hill, it will rest there forever unless a force
> acts on it. For example, if the hill is on Earth, gravity would act to
> make the test particle start rolling downhill. But in space, if there is
> no force of gravity but only curvature of spacetime, the initial 4-space
> path of the body is a straight line by definition of "at rest", and the
> body can never deviate from that straight line unless a force acts.

...or unless the coordinate system curves....

>> [Schlyter]: Observations made in 3-space plus time, in a known
>> reference frame, can be integrated into 4-spacetime and be used to
>> validate or refute the theory.
>
>             Let's examine this claim too. Yes, 3-space potential and
> motion affect time, and can be used to convert GR's coordinate time into
> GR's proper time. 3-space itself remains isotropic around any source
> mass, and the slight radial contraction can be neglected for our
> purposes here as too small to matter.

...if the gravitational field is sufficiently weak, as in e.g. our solar
system....

> For example, for GPS satellites,
> length contraction is just a few millimeters. So what causes the
> satellites to orbit the Earth? Why should the fact that their on-board
> clocks have sped up relative to ground clocks cause them to move in a
> curve around Earth instead of continuing in a straight line? "Curved
> spacetime" means nothing more than that the clock rates have changed. It
> provides no explanation for deviation from simple, linear motion.

Another example: throw a ball straight upwards.  It moves up, stops
and moves down.  Near the peak its path curves sharply.  Now, throw
the ball again but mostly sideways, only slightly upwards.  Again
the ball moves up, then down -- and its path curves much less sharply.
Why are the curvatures so different?  They're subjected to the same
gravitational field, right?

The answer lies in 4D space-time: the curvature of the two paths
become the same if you also account for the time dimension.  I refer
you to the classic "Gravitation" by Misner-Thorne-Wheeler, page
32-33, for a fuller explanation.

>> [Schlyter]: What's this "deep reality physics" ?? A new buzzword you
>> just invented?
>
>             It means physics that excludes magic or miracles for the
> simple reason that admitting them ends the search for understanding and
> predictability. Anything can be explained as a miracle, and the attempt
> to explain it can be dismissed because "we can't know the mind of God".
> Whether that is true or not, deep reality physics is tasked with
> explaining nature without miracles until such time as it finds something
> that cannot be explained in any other way. No such barrier to
> understanding and prediction has as yet appeared. By contrast,
> mathematical physics and philosophy are more concerned with descriptions
> of nature than with fundamental understanding, so they both regularly
> allow miracles. The term "deep reality physics" was coined to
> distinguish this type of physics from the other types. This contrast is
> most acute in the case of quantum mechanics, which has abandoned the
> principles of physics and consequently concluded "there is to deep
> reality to nature." Those unhappy with that conclusion have no other
> recourse but reverting to the principles of physics.

If the map and the terrain disagree - which one should we consider valid?

The "principles of physics" is the map here - it's what you and some
other think the physical world should be.  Empirical observations is
the terrain.

"Magic" is merely a label some people attach to something they don't
understand.  "God" is another such label.  Suppose we could, and did,
travel back in time to, say, the 1700's.  We brought a pair of comm
radios with us and demonstrated them to the people from those times.
To them these comm radios, able to transfer messages at apparently
infinite speed (at least as long as we stayed here on Earth), would
have looked like magic.

So your "deep reality physics" which "excludes magic" is actually a
way to refuse there are phenomena we humans don't yet understand.


>> [Schlyter]: Every model is btw based on some "magic": the fundamental
>> assumptions which aren't proved but which are used to build the model.
>> For some of these fundamental assumptions we can make the "magic"
>> vanish by pointing to some other model - a model which may have its
>> own set of "magic". But for the remaining assumptions we have no other
>> model to point to, but merely choose our fundamental assumptions so
>> they appear "reasonable".
>
> If the "fundamental assumptions used to build the model" are the
> principles of physics, there is no magic involved because the opposite
> of each fundamental principle (such as creation from a true void) is a
> form of magic.

Anytime you stop asking and just accept something, you treat that as
magic.  And then it doesn't really matter whether it's "these first
principles are valid" or "god created it" or "it spontaneously
appeared from the void".

>> [Schlyter]: Forces vs geometry can be viewed as such a choice. Your
>> brain finds it impossible to accept geometry as the fundamental cause
>> in GR - my brain finds it more acceptable. So it's perhaps just a
>> matter of personal preferences?
>
>             Personal preferences are like choosing a favorite color or
> dessert. But cause and effect have existence in the objective reality we
> all experience, and not just in our minds.

True - and in both geometric and field GR, a colleciton of bodies
initially at rest to one another will start to move due to their
mutual gravitation.  In field GR gravitational forces cause them to
move in space, while in geometric GR the geometry cause their motion
in the time dimension to "spill over" as motion in space too.

You've decided that you reject the geometric model of GR.  Others accept
it.  It's a matter of personal preference... both models provide the
same prediction of the motions of the bodies.

> The goal of science is to develop tests to sort out the good and bad
> hypotheses. The good ones aid understanding and predictability. The bad
> ones are forever tacking on ad hoc helper hypotheses to accommodate new,
> unexpected observations (such as "dark energy" to explain the universe
> expansion accelerating instead of slowing through the action of gravity).
>
>> [Schlyter]: By setting aside geometric GR we also set aside our
>> understanding why gravitational and inertial masses are the same
>
>             See
> http://metaresearch.org/cosmology/gravity/Does%20Gravity%20Have%20Inertia.asp
> for a complete and highly intuitive explanation of why these are
> approximately equal without gravity being geometry in any meaningful
> sense.

Your strong dislike of geometry is very apparent in that article of yours.
And you even contradict yourself - there you write:

# Einstein used this equivalence principle to conclude that gravity is not a 
force 

while here you wrote:

# Field GR is the interpretation preferred by Einstein

which I consider a claim that Einstein did consider gravity being a force
after all.  So make up your mind !!!!!

Also your figure 1, with the comment

# Consider the geodesic (orbital) path of the Earth with respect to
# the Sun in Figure 1. If we choose any two points along that path
# (call them A and B), note that a straight line between A and B (as
# could be represented by a taut rope) is a shorter path through space
# than the geodesic path.

shows that you just don't understand what a geodesic in 4D spacetime is:
it is NOT, repeat, NOT the shortest distance in 3D space !  If you
considered the full 4D spacetime, then the orbit (curved in 3D space)
from A to B would be shorter than the line (straight in 3D space) from
A to B.  Therefore the orbit, not the line, is the geodesic.  If there
was no gravitational field, 4D spacetime would become Euclidian, and
the "orbit" and the line would coincide.

I'm actually amazed that someone like you, who consider yourself being
acquainted with GR, can make such a trivial mistake.  Of course there's
an alternate explanation which hopefully isn't true: you understand
this very well but count on most of your readers not understanding
it, and then you intentionally mislead them.


>> [Schlyter]: Classical celestial mechanics use Newtonian mechanics,
>> with only small relativistic corrections in a few cases. This works
>> well in the solar system and visual double stars, but fails in
>> situations like a binary pulsar.
>
> Modern celestial mechanics uses the GR equations of motion for all
> cases where relativity is relevant. Damour developed equations
> of motion specifically for analyzing the binary pulsar. As I said, GR
> would be untested without some such vehicle to predict motions in
> 3-space vs. time for comparison with observations made in 3-space plus
> time.
>
>>> [tvf]: Gravity cannot be simply geometry because that provides no
>>> source for new momentum.
>
>> [Schlyter]: Does this mean you claim that geometric GR predicts that a
>> collection of bodies initially at rest in space relative to one
>> another and subjected to no other forces than their mutual gravity,
>> that these bodies will remain at rest? As predicted by geometric GR of
>> course. If not, and if geometric GR predicts the motions which
>> actually are observed, in what way is geometric GR "falsified"?
>
> Geometric GR describes only the gravitational potential field, and the
> potential by itself cannot cause anything to move through 3-space.

Thus you say that, according to geometric GR, a collection of bodies
initially at rest relative to one another and subjected to no other
forces, that these bodies will remain at rest.  Right?

> Nor does it predict any curvature of 3-space.  So an additional
> axiom or assumption is needed to get changes in motion. Both physical
> interpretations of GR (field and geometric) use the same axiom to get
> 3-space motions: that force is the gradient of potential. That allows
> them to derive 3-space equations of motion, without which GR would
> predict no accelerated 3-space motions of material bodies. A ball thrown
> into the air would not even slow down.

Do other specialists of GR agree with you here that according to
geometric GR all gravitational effects vanish?  E.g. Steve Carlip,
does he think so too?  <g>

>> [Schlyter]: If the gravitation potential changes instantly also over
>> large distances, no matter whether the body is moved by gravitational
>> or non-gravitational forces, then gravity does indeed propagate FTL as
>> you claim.
>
> I claim no such thing. Gravitational potential changes occur at speed c
> under any circumstances. There is no dispute about that.

Sorry, but the gravitational force is by definition always locally
perpendicular to the gravitational equipotential surfaces. This is so
from the very definition of "potential" (as the integral of force).

So if the force of gravity points to the instantaneous rather than the
light-time retarded position of the gravitational body, then the
gravitational potential too must change instantly.  It does so in
Newtonian physics, and deviates from this not in the first or second
order but only in higher orders in GR.

>> [Schlyter]: But if the gravitation changes instantly only when the
>> body is moved by gravitational forces.
>
>             This furthers the same confusion. It is only the speed of
> those gravitational forces that exceeds the speed of light. So there is
> no need to bring in non-gravitational forces to make any points about
> how gravitational forces behave.

The difference between graviational and non-gravitational forces here
is that the system "knows" what effects gravitational forces will
have.  Non-gravitational forces are not as easy to predict - they can
depend on e.g.  a human decision whether to fire a rocket or not.
That's why I made the distinction.

>> [Schlyter]: Why do you consider geometry "magic" but not forces
>> ("action at a distance")?
>
> Geometry has no 3-space motion, no momentum, and therefore cannot be a
> source of new 3-space motion or momentum.

Why do you thin that it "cannot" have this effect?  Why not instead be
honest and merely say you don't understand how it could have such an
effect?

> A curve starting a ball rolling without a force acting on the ball would
> be magical.

Interesting -- because precisely that will happen in a rotating coordinate
system with no real forces acting, only pseudo-forces like the centrifugal
and coriolis forces.  Are the centrifugal and coriolis forces magic?


>> [Schlyter]: Science has to find a balance here. What would you favor
>> yourself:
>> 1. Accepting a theory which later turns out to be false, because that
>> theory had "compelling evidence" ??
>> 2. Rejecting a theory which has "compelling evidence", a theory which
>> later turns out to be true, but at this point there's no hard evidence
>> for that theory.
>
>             Why must all theories be either accepted or rejected? My
> position is that all viable, not-yet-falsified theories should be on the
> scientific table for discussion and making distinguishing predictions.

Why do we do science at all?  Just as some kind of intellectual
entertainment?  Then it will of course become irrelevant how correct
or incorrect a theory is - it'll be more important how interesting a
theory is.  But then science becomes nothing more than some kind of
intellectual fiction...

If we are to actually do something useful with science, then we'd
better choose the theory which is most correct among the theories
we have available.

> What would you prefer? First theory that catches on is always the
> winner? -|Tom|-

As you hopefully know, scientific conclusions are never definite.
Any theory is subject to revision, or rejection, if and when new
evidence appears which falsifies that theory.

So if a particular theory catches on first, so what?  At that
particular point, that theory is the best we have available.  Whether
it will continue to catch on also in the long run, only the future
can tell.  If another theoruy is better, the first theory will
eventually be replaced.



-- 
----------------------------------------------------------------
Paul Schlyter,  Grev Turegatan 40,  SE-114 38 Stockholm,  SWEDEN
e-mail:  pausch at stockholm dot bostream dot se
WWW:     http://stjarnhimlen.se/

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