I've been reading John Gribbin's "In Search of the Edge of Time", and came upon
a section where he says that spinning black holes drag space-time around with
it. My question is, if you continuously drag space-time around in a whirlpool,
are you ripping apart space, or are you continuously stretching it?

Thanks

"Anonymous" wrote in message
...
I've been reading John Gribbin's "In Search of the Edge of Time", and came
upon a section where he says that spinning black holes drag space-time
around with it. My question is, if you continuously drag space-time
around in a whirlpool, are you ripping apart space, or are you
continuously stretching it?

It is only a very rough analogy to begin with - an analogy that IMHO is not
that good. Space-time is neither ripped or stretched by gravity any more
than the surface of a sphere is ripped or stretched - it is simply curved.

Thanks
Bill



Thanks

"Anonymous" wrote in message
...
I've been reading John Gribbin's "In Search of the Edge of Time", and came
upon a section where he says that spinning black holes drag space-time
around with it. My question is, if you continuously drag space-time
around in a whirlpool, are you ripping apart space, or are you
continuously stretching it?

Thanks

You'll tear up the bright green flying elephant's eggs if you centrifuge
them.
The elephants lay them in black holes, you see.
If you ever find a black hole, look inside for broken eggshell for me, would
you?
I want to prove my theory*
Androcles.




*that you are a gullible phuckwit that will believe anything.

In article ,
says...
I've been reading John Gribbin's "In Search of the Edge of Time", and came upon
a section where he says that spinning black holes drag space-time around with
it. My question is, if you continuously drag space-time around in a whirlpool,
are you ripping apart space, or are you continuously stretching it?


Any rotating body would drag space-time its just more noticeable with a
black hole.

--
Only in movies do guys pick the engagement ring.

Observations of Bernard - No 89

Anonymous wrote:
I've been reading John Gribbin's "In Search of the Edge of Time", and
came upon a section where he says that spinning black holes drag
space-time around with it. My question is, if you continuously drag
space-time around in a whirlpool, are you ripping apart space, or are
you continuously stretching it?

Neither. Space doesn't have the properties you'd normally associate with
"stuff", like inertia and tensile strength.

What Gribbin is talking about is called "frame dragging", but that's a
somewhat misleading name. Roughly it means that even if a black hole is
rotating with respect to the fixed stars, it's not rotating with respect to
a local standard of inertial motion. This is interesting because it seems to
support Mach's principle, which is the idea that rotation, like velocity,
can only be defined with respect to some external reference body. In the
vicinity of the event horizon, the nearby black hole seems to dominate the
distant fixed stars in setting the standard of inertial motion. Einstein was
heavily influenced by Mach's principle, and at least in the early days he
thought of general relativity as a physical realization of it. Frame
dragging is one case in which general relativity seems to follow Mach's
principle, but there are other cases that seem to run counter to it.

-- Ben

Dear Anonymous:

"Anonymous" wrote in message
...
I've been reading John Gribbin's "In Search of the Edge of
Time",
and came upon a section where he says that spinning black
holes drag space-time around with it. My question is, if you
continuously drag space-time around in a whirlpool, are you
ripping apart space, or are you continuously stretching it?

Actually you are merely continuously rotating spacetime near the
spinning object.

Let's say you place a basketball in a bathtub. Now run a tiny
battery powered boat in the bathtub, capable of going straight.
The boat does not touch the ball.

If the boat runs far from the ball, it can go straight.
If the boat runs near the ball (without touching), its path is
slightly curved (towards the ball).
If the ball is spinning (simulating "frame dragging"), and runs
near the ball, the boat's path is curved more.

You are vortexing it. Meaning in spherical coordinates, that r
is smoothly connected to r+dr, but r*theta is not as simply
connected to (r+dr)*(theta + dtheta). You need body mass and
spin information to do the mapping.

And frame dragging has been observed around other objects than
black holes.

David A. Smith

BernardZ wrote:
In article ,
says...
I've been reading John Gribbin's "In Search of the Edge of Time", and came upon
a section where he says that spinning black holes drag space-time around with
it. My question is, if you continuously drag space-time around in a whirlpool,
are you ripping apart space, or are you continuously stretching it?

Any rotating body would drag space-time its just more noticeable with a
black hole.

Yes. This has been observed (with large errorbars) for the earth, via
the LAGEOS satellites. And Gravity Probe B should have results sometime
soon:
http://einstein.stanford.edu/


Tom Roberts

Anonymous wrote:
I've been reading John Gribbin's "In Search of the Edge of Time", and
came upon a section where he says that spinning black holes drag
space-time around with it. My question is, if you continuously drag
space-time around in a whirlpool, are you ripping apart space, or are
you continuously stretching it?

Thanks

Thanks all for all the answers. The problem is that there are so many
analogies comparing space-time with fabric, foam, molasis, that it becomes hard
not to think of space as tangable. But I'm still confused in that
frame-dragging can whirlpool space. Does this mean that space-time itself is
continuously circling, or that like gravity, matter and energy are forced in
the direction of the warping, and space-time is simply warped but not moving?

Thanks again.

Anonymous wrote:
But I'm still confused
in that frame-dragging can whirlpool space. Does this mean that
space-time itself is continuously circling, or that like gravity, matter
and energy are forced in the direction of the warping, and space-time is
simply warped but not moving?

Here's what it means in terms of an experiment that could actually be
performed in principle.

Imagine that you have a thin hollow torus filled with a mixture of air and
liquid water. If you start it spinning, the water will be pushed up against
the outer wall.

Now move the torus so that it encircles a rotating black hole in the
equatorial plane. Spin the torus at the same angular velocity as the black
hole itself. If the radius of the torus is much larger than the radius of
the event horizon, then the water will be pushed against the outer wall as
usual. But if the torus is just slightly outside the event horizon, the
water will not be pushed against the outer wall, as though the torus weren't
spinning. If you actually stop the torus from spinning (with respect to the
fixed stars), then the water *will* be pushed against the outer wall.

You can describe this as "space-time continuously circling", but that's just
a vague metaphor which will lead you astray if you take it too literally.
Spacetime doesn't actually have a state of motion, so it can't circle
anything. It's not really a matter of curvature either, at least not local
curvature. It's a matter of how the spacetime near the black hole is
connected to the spacetime far away. Unless you compare to a distant
reference body like the fixed stars, there's no way to detect the frame
dragging.

-- Ben

I wrote:
But if the torus is just slightly outside the event
horizon, the water will not be pushed against the outer wall, as though
the torus weren't spinning. If you actually stop the torus from spinning
(with respect to the fixed stars), then the water *will* be pushed
against the outer wall.

Okay, on second thought this is not such a good experiment, because there's
also going to be a gravitational field pulling the water toward the inner
wall. :-) But if you subtract that off, then what I said above should be
true of the residual force.

-- Ben