Re: GR "Spaghetification"



Steve Bell wrote:

"Daryl McCullough" <stevendaryl3016@xxxxxxxxx> wrote in message news:h21mmm019qr@xxxxxxxxxxxxxxxxxx

Steve Bell says...


I think I completely understand tidal forces and how they would overcome
electricity in this circumstance. You are missing my point.
If this really does happen, in which frame does it "absolutely happen"?

Anything that really happens is frame-independent (coordinate
independent). If it's a *real* event, it can be described using
any coordinate system you like.



Great. Since once *must* assume specific coordinate systems to produce a specific description, I choose Euclidean for the laboratory and Kerr for the gravitational field permeating the laboratory. I choose these because I think these are best of the "models" I know about that describe physical reality.

You choose what you like but there is nothing special about any choice.



It can't be that if a human body is physically ripped apart
"this way" in some observatory frame,

If a person is ripped apart, then it isn't "in some observatory
frame". Why bring in frames at all? It doesn't have anything
to do with frames.


and dies, say, because his/her left foot got ripped off first,
and then it is also physically ripped apart "that way" and dies
because, say, his/her right foot got ripped off first in some other
frame. It can't be true that a person can actually die in two
different ways, or at least I hope not <g>.

Two different *descriptions* do not mean two different ways.
If someone gets hit by a rock, then according to some observers,
the rock came from the left. According to other observers, the
ones facing the opposite direction, the rock came from the right.
Which one is correct? Neither, there is no "correct answer" to
whether a direction is to the left or to the right.





Inherent in your thought experiment lies the problem.

You mean your problem.

The only way I can even think about "a rock coming from the right according to
one observer" and also "coming from the left according to another observer" is to assume there is a *third* observer sitting in a frame in which it is then possible to have the other two frames moving in, to give these two different relative perspectives.

It says nothing of the sort.

If
not, you have no basis for what they are "relative to."

This makes no sense.

I think you *must* embed. To me, in order to resolve these relativistic
issues, you must always assume an "exterior frame" within which the other frames, moving or not, reside. I finally realized what this was telling me. The entire mass of the universe must be embedded in a gigantic universal frame.

So, since you have made some wrong assumptions you try to use those
to jump off to an absolute frame. There is no justification for
your large leap of prejudice.


To me, one can logically build up to this universal frame. I am standing on the earth. I believe there is a physical distance between the earth and the sun. I believe there is a physical distance between the sun and the center of our galaxy. I believe there is a physical distance between the center of our galaxy and the center of our closest other major spiral galaxy, M31. I think there is a physical distance between the center of mass of out local group of galaxies, and the center of mass of the next closest big galaxy cluster, which I think is the Virgo cluster. And this cluster has a physical distance from the next, etc. All of these physical distances exist in some gigantic volume of space at the same intstant in time. There must be a universal volume of space and a unversal time.

You are just stating your prejudice with no foundation.



Neither is there a "correct answer" to the question of which
of two spacelike separated events happened first. One is first
from the point of view of one observer, and another is first
from the point of view of another observer. It's no more significant
than whether a rock came from the left or the right.



Along with finally acceptaing a universal space came the added required assumption of a universal time. In the universal space of the universe, events are truly either simultaneous or they are not. See how things get very simple, very easy to understand when one finally accepts what I think is the truth: Absolute universal space and asbolute universal time are the physical truth.

Since you are wrong about universal space, you might as well leap
into being wrong about universal time.

I would think you feel you exist at points in time that you would call "the present". Do you think that an instant in time that is a "present instant in time" is exactly the same physical instant in time throughout the entire universe? Is now "now" everywhere "at once"? I think it is. If this is true, there must be a universal time.

Well, no.


There must be a single way in which all this physical
ripping apart happens, and if so, there must be a single
universal frame.

There is a single spacetime which is the same for all observers.

You really need to study some.


Yes, it is that space within which the observers are embedded. And a stationary clock in this external "laboratory" frame measures "laboratory" time.



But the splitting up of spacetime into space + time is different
for different observers. That has no more significance than the
fact that different observers disagree about which direction is
"to the left".




Actually, to me, the fact that it is different is of extreme importance. It tells me that something is amiss if we think that each describes some type of "physical truth." There can't be two different "physical truths" unless God is a QM physicist.

Which shows how little you know about science. You are saying what you
do not like but that is of no importance to the universe.



If the effects are truthfully physical, that means very specific
inescapable things to me. All this "everything's relative"

Relativity does *NOT* mean everything is relative. Relativity
is really about those things that are the same in *all* coordinate
systems. That's what's physically meaningful.




What is physically meaninful happens in a physically real universe. If the universe is in fact physically real, there must be a space within which matter resides at an instant in time. For me, I have decided what these "universal truths" are. A gigantic (actually infinite in size, probably) universal volume of space which is rigid and not "bendable" whose enclosed matter all physically exists (has positons and velocities, etc.) at the same exact point in universal time.


You are now several layers into your mistakes and thus
there is no content here.



stuff is severely constrained if there really does exist an
external world independent of observation.

That's what General Relativity is all about. Describing physics
in a way that is independent of our subjective choice of what
coordinate system to use.

--
Daryl McCullough
Ithaca, NY



Absolutely, perahps that is its most imporatnt feature. It allows us to derive equations whose forms are the same for all frames. I've never disageed with that. I think I see now how to apply these equations to the real world.

This has been known for a century. You do not seem to like it but
that does not change the truth.


Steve Bell


.

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