Re: Uh Oh, Discrepancy Alert



Cliff wrote:

On Fri, 18 Aug 2006 15:47:16 GMT, BottleBob <bottlbob@xxxxxxxxxxxxx> wrote:


Cliff:

Lightspeed in a vacuum has not been observed to change by a
gravitational field.


Cliff:

Who told you that one? Some nun again?

It seems to be the accepted perspective in the physics community.

It can slow down in gravitational fields.
http://www.mathpages.com/rr/s6-01/6-01.htm


Cliff:

Sorry, don't have much time for idle chit-chat this weekend. But I'll
make a few comments here.

Here is one explanation concerning this issue:

=========================================================================
http://www.astronomycafe.net/qadir/q671.html

Can gravity affect the speed of light?

Not really.

The speed of light is something measured with a local apparatus in an
inertial reference frame, using the same meter stick and clock. A
gravitational field has zillions of such 'locally inertial reference
frames' which are described by freely-falling observers for short
intervals of time and small regions of space. In all of these tiny
domains, an observer would measure the same velocity for light as
guaranteed by special relativity. To ask what the speed of light is over
a domain where gravitational forces make a reference frame
'non-inertial' and not moving at a constant speed, is an ill-defined
question in special relativity. As soon as you try to measure the speed
of such an impulse, you would be using a clock and a meter stick which
would not be the 'proper time and space' intervals for the entire region
where the gravitational field exists.
=========================================================================

You'll like this next one much better. LOL

=========================================================================
http://www.physlink.com/education/AskExperts/ae13.cfm

Question

Would not the speed of a light beam headed toward a black hole increase
tremendously? We do know it could be bent by the gravity of a star.

Asked by: Joe Thomas

Answer

Contrary to intuition, the speed of light (properly defined) decreases
as the black hole is approached. In fact, one way to understand the
bending of light by the gravitational field of a star is to regard it as
resulting from the refraction of the wavefront due to the fact that the
part of the wavefront that is nearer to the star moves more slowly than
the part farther away from the star. The result is that the direction of
advance of the wavefront is deflected toward (or around) the star.

If the photon, the 'particle' of light, is thought of as behaving like a
massive object, it would indeed be accelerated to higher speeds as it
falls toward a black hole. However, the photon has no mass and so
behaves in a manner that is not intuitively obvious.

The reason for the qualification 'properly defined' above is that the
speed of light depends upon the vantage point (frame of reference) of
the observer. When we say that the speed of light is decreased, we mean
from the perspective of an observer fixed relative to the black hole and
at an essentially infinite distance. On the contrary, to an observer
free falling into the black hole, the speed of light, measured locally,
would be unaltered from the standard value of c.

Most of us have heard of the result from _special_ relativity that the
speed of light is the same for all observers in inertial frames.

The result is _not_ the same in general relativity. In general
relativity, the statement becomes that the speed of light is the same
(i.e., good old 'c') for all observers in _local_ inertial frames.
=========================================================================


That isn't
why you've repeatedly Cliffoided answering my simple question:
Can matter be changed to energy? Yes or No?

The units are not the same, BB.
E <> m.

So you're saying that atomic bombs, hydrogen bombs, and nuclear power
plants can't possibly work because Cliffphysics says the *UNITS* are not
the same? LMAO!


Lightspeed wouldn't be much of a universal
constant if it changed everytime it passed, or went through,

A bit of glass?

Sure, and light can slow down to 38 MPH going through a Bose-Einstein
condensate... BUT light traveling through MATTER wasn't the point,

"Normal" matter is almost all empty space.

True, but irrelevant in a practical/pragmatic sense. A 1" thick steel
plate is "almost all empty space", but you're not likely to be putting
your fist through that "almost all empty space", now are you. And light
isn't likely to be traveling through it either. The little part of the
steel plate that ISN'T empty space seems to be more than a slight
hindrance, eh?


I clearly stated "Lightspeed in a *VACUUM* (which is considered a
universal constant), has not been observed to change by a gravitational
field."

And you seemed to be wrong even on that <G>.

Depends on who's doing the measuring and where. LOL


some geodesic in curved space-time.

Which is exactly what it can do ..... what did you think caused
gravitational lensing (depending on units & your perspective)?

Gravitational lensing doesn't have anything to do with changing light's
velocity in a vacuum. Gravitational lensing is when the light's path is
curved by an intervening massive object that may curve spacetime enough
that a distant object appears in a slightly altered position. Now light
moving out of a gravitational field may lose energy and change
frequency, but it doesn't appear to alter it's velocity.

It's velocity would indeed seem alterd by that mass, BB.

Does it now. The speed is distance/time, within the local reference
frame of curved spacetime the light probably doesn't even notice the
curvature and thinks it's going straight, metaphorically speaking. It's
like someone driving on a curved road from point A to B. He may be
going 60 MPH all the time, but measuring the distance between point A
and B on a map by scaling the points with a straight edge and then
dividing THAT distance by the time it took will no doubt produce a
slower speed result.

Just as in a prisim.

You mean a prism? Light traveling through a prism (or any transparent
matter), is a different case entirely, since that's essentially photons
being absorbed and re-emitted by the atoms in the matter that lie along
the light path (that obviously seems to take more time than traveling
through a vacuum). There are usually no comparable quantity of atoms in
the vacuum of space.

Slows down a bit more on the side towards the mass .. refracts .. or
you'd best explain away the link above <G>.

Depends on your perspective. From one perspective the light's just
going in a "straight line", the "straight line" just happens to be a
spacetime curved geodesic.



What's peculiar, is that you didn't challenge Ivan's comment that c=0
at the event horizon, which is not correct.

Feel free to comment yourself <G>.

Light travels at 299,792,458 meters per second in a vacuum,
theoretically inside a black hole as well as out.

Who sez?

Special & General relatively.


The PATH of the light

It always seems to take the path that takes the *least time*
between two points.
How does it know *in advance* what path to take?

It goes in a straight line, local curved spacetime IS a straight line
to light. Even if it's not to a distant observer.



may be so strongly curved by spacetime curvature as a result of the
intense gravitational field of a black hole as to eliminate its ability
to escape, but the velocity supposedly remains the same according to
General Relativity, (our current "Best Guess" at to how the macro
universe works).

Check your reference frames at the door.

But those reference frames are essential to the alternate perspectives
you may with to take, or focus on.


Is this an indication of
yet ANOTHER conceptual boo-boo on your part? LOL

I don't see where I'm actually required to ....

Required to what? Make a another conceptual boo-boo? LOL

I don't see where I'm actually required to ....

Required to what? Make a another conceptual boo-boo? LOL


Want to try to help him out of some of his many misconceptions?
Try ... the nuns & Aristotle did a bad job on him I think.

Sounds like more nunsense to me.

What is the speed of light at the event horizon?
From whose perspective?


=====================================================================
http://curious.astro.cornell.edu/question.php?number=266

Question:

Why doesn't gravity change the speed of light?
How come that the speed of light "c" doesn't change at all, even
slightly, when the light passes closely to a star or some similar big
object. We know that light bends in those situations, but what about
"c"?

Answer:

Yep, although light bends around a massive object like a black hole,
the speed of that light in a vacuum is always the same. This is because
the speed of light is directly dependent on the speed of the interaction
between the electric and magnetic fields (light is an electro-magnetic
wave, after all!). That speed of interaction is the same no matter where
the light is or who is watching it. Therefore, the speed of light is the
same for all observers at all points in spacetime.
=======================================================================

Now you are going on about the observers .... <sheesh>.

Science is ALL about observers, and observations.


BTW, Found that peck of "inertia" yet?

Yep. We already covered this one to death. Mass is the measure of
inertia.


--
BottleBob
http://home.earthlink.net/~bottlbob
.

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