Orbital angular momentum of photons

In a news release for the BBC it is stated that light emanating in the
vicinity of a spinning black hole may exhibit orbital angular
momentum. It states that present telescopes should be able to detect
this by software changes (not hardware).

Can someone please explain what orbital angular momentum is for
photons?

http://www.bbc.co.uk/news/science-environment-12434007

www.richardfisher.com

On 2/14/11 11:05 AM, Helpful person wrote:
In a news release for the BBC it is stated that light emanating in the
vicinity of a spinning black hole may exhibit orbital angular
momentum. It states that present telescopes should be able to detect
this by software changes (not hardware).

Can someone please explain what orbital angular momentum is for
photons?

http://www.bbc.co.uk/news/science-environment-12434007

www.richardfisher.com

Take a look at:
http://en.wikipedia.org/wiki/Frame-d...mical_evidence

Helpful person:
In a news release for the BBC it is stated that light emanating in the
vicinity of a spinning black hole may exhibit orbital angular
momentum. It states that present telescopes should be able to detect
this by software changes (not hardware).

Can someone please explain what orbital angular momentum is for
photons?

http://www.bbc.co.uk/news/science-environment-12434007

www.richardfisher.com

Sam Wormley:
Take a look at:
http://en.wikipedia.org/wiki/Frame-d...mical_evidence

And then what? People who post equation-filled "explanations" such as
those on the referenced page on a public encyclopedia--a work that
should be accessible to the public at large--are smug-ass elitists.
They exhibit behavior that guarantees that people will stay tuned out
of science--which is what it is designed to do, otherwise they could
not enjoy their smug-ass elitism. By ensuring that science remains
inaccessible even to the overwhelming majority of smart, educated
people, these misguided asses are hurting science, the USA, and the
world in general. Save it for the textbooks and the peer-reviewed
journals and write plain language for the educated public.

To get an idea of what frame dragging is about, try these links
http://www.nasa.gov/home/hqnews/2004/oct/HQ_04351_time_drags.html and
http://www.nasa.gov/vision/earth/lookingatearth/earth_drag.html.

"Frame dragging is like what happens if a bowling ball spins in a thick
fluid such as molasses. As the ball spins, it pulls the molasses around
itself. Anything stuck in the molasses will also move around the ball.
Similarly, as the Earth rotates, it pulls space-time in its vicinity
around itself. This will shift the orbits of satellites near Earth."

Look, Ma! A comprehensible metaphor written in plain, accessible
language. Good for understanding, good for America, good for the world.

Davoud

--
I agree with almost everything that you have said and almost everything that
you will say in your entire life.

usenet *at* davidillig dawt cawm

In article , Davoud wrote:
Helpful person:
In a news release for the BBC it is stated that light emanating in the
vicinity of a spinning black hole may exhibit orbital angular
momentum. It states that present telescopes should be able to detect
this by software changes (not hardware).

Can someone please explain what orbital angular momentum is for
photons?

http://www.bbc.co.uk/news/science-environment-12434007

www.richardfisher.com

Sam Wormley:
Take a look at:
http://en.wikipedia.org/wiki/Frame-d...mical_evidence

And then what? People who post equation-filled "explanations" such as
those on the referenced page on a public encyclopedia--a work that
should be accessible to the public at large--are smug-ass elitists.

I think you need to have the equations; if you want to stick an
explanation intended for people scared of tensors at the top, go
ahead, but at least part of the audience for the general-relativity
section of wikipedia will be people doing general-relativity courses
in junior year of a physics major, and going through the derivations
is very helpful for them.

Though I don't see an explanation of orbital angular momentum for
photons there, even through the equations.

Tom

Davoud:
And then what? People who post equation-filled "explanations" such as
those on the referenced page on a public encyclopedia--a work that
should be accessible to the public at large--are smug-ass elitists.

Thomas Womack:
I think you need to have the equations.

LOL!

if you want to stick an
explanation intended for people scared of tensors at the top, go
ahead, but at least part of the audience for the general-relativity
section of wikipedia will be people doing general-relativity courses
in junior year of a physics major, and going through the derivations
is very helpful for them.

Rubbish. What kind of physics major requires Wikipedia for junior-level
study!? That's what the lectures and the $300 textbooks and
peer-reviewed journals are for. Wikipedia ought to be accessible to
practically everyone. It's easy enough to link to the other stuff.

Though I don't see an explanation of orbital angular momentum for
photons there, even through the equations.

Of course not.

Davoud

--
I agree with almost everything that you have said and almost everything that
you will say in your entire life.

usenet *at* davidillig dawt cawm

On Feb 14, 10:05*am, Helpful person wrote:

Can someone please explain what orbital angular momentum is for
photons?

Photons don't have any rest mass. But they contain energy, so they
have mass.

Hence, if gravity is so intense that they actually orbit a star, they
will have angular momentum just like anything else that goes around in
circles. It's not clear to me what the problem is. Of course, under
such conditions, you might have to use general relativity to get the
right equation for the amount of angular momentum.

John Savard

On Feb 14, 1:32*pm, Davoud wrote:

And then what? People who post equation-filled "explanations" such as
those on the referenced page on a public encyclopedia--a work that
should be accessible to the public at large--are smug-ass elitists.

There were lots of equations in the Eleventh Edition of the
Encyclopaedia Brittanica. An encyclopedia should contain enough detail
so as to properly explain the subject matter of a given article,
rather than simply giving a superficial oversimplification from which
nothing substantive would be learned.

So, articles on technical subjects in certain types of encyclopedia
will be... technical. There are other encyclopedias which strive for
every article being generally understandable. This promoted sales, but
it limited the usefulness of the product.

That being said, the absence of a nontechnical portion to an article
where a nontechnical person can get the gist of things is usually a
defect.

John Savard

On Feb 14, 9:05*am, Helpful person wrote:
In a news release for the BBC it is stated that light emanating in the
vicinity of a spinning black hole may exhibit orbital angular
momentum. *It states that present telescopes should be able to detect
this by software changes (not hardware).

Can someone please explain what orbital angular momentum is for
photons?

http://www.bbc.co.uk/news/science-environment-12434007

www.richardfisher.com

It would be nice if someone would answer the question. No need for
stupid posts, rants or ill informed posts.

www.richardfisher.com

On Feb 14, 1:50*pm, Davoud wrote:
Wikipedia ought to be accessible to
practically everyone. It's easy enough to link to the other stuff.

The "other stuff" may not really be _out there_ to be linked to. All
the other explanations of GR *with* the equations may be in $200
textbooks.

There's also now a Wikibooks project. Soon, thanks to computers and
the Internet, even people in Africa who have problems with food,
clothing, and shelter, will have the opportunity to study general
relativity and other recondite subjects. I have not the wisdom to see
what good that would do, but it can't hurt.

John Savard

In article ,
Helpful person wrote:
On Feb 14, 9:05=A0am, Helpful person wrote:
In a news release for the BBC it is stated that light emanating in the
vicinity of a spinning black hole may exhibit orbital angular
momentum. =A0It states that present telescopes should be able to detect
this by software changes (not hardware).

Can someone please explain what orbital angular momentum is for
photons?

http://www.bbc.co.uk/news/science-environment-12434007

www.richardfisher.com

It would be nice if someone would answer the question. No need for
stupid posts, rants or ill informed posts.

http://www.physics.gla.ac.uk/Optics/play/photonOAM/

looks a reasonable description of the sort of things that can be done
with OAM of photons (in particularly, it explains that it's the
technology that lets you rotate small objects using optical tweezers,
which gets you a nice link from the astrophysical scale to the biology
lab), but it starts off with the assumption that you know what a phase
front is, and I don't.

http://www.opticsinfobase.org/abstract.cfm?id=63128 gives a method for
producing photons with non-trivial orbital angular momentum.

Tom