Photons

I think I'll pose this question in here since it's an odd-ball.

Granted photons have no mass but do exibit a force. In experiments
photons can be paused and restarted again by putting them through near
abs-zero gas fields. If what I've learned so far is correct, these
statements are true.

The first question which I believe I already know the simple answer is:
Can a photon have it's direction changed by 180 degree's?

Can two photon's share the same space but have different velocity
vectors? The same vector? An exact opposite vector?

If so, is it possible to push against a given stream of photons so that
a back-pressure is measured at the source as a result of photons
crashing into it's emitter?

For instance, is it possible to focus the photons of a given star and
then send those photons back along it's stream to it's origin? If
photons as a particle move in a stream, and each photon can only occupy
it's own space, wouldn't that specific stream be disrupted for one
discreet instant?

"Southern Hospitality" wrote in
message ...
I think I'll pose this question in here since it's an odd-ball.

Granted photons have no mass but do exibit a force. In experiments
photons can be paused and restarted again by putting them through near
abs-zero gas fields. If what I've learned so far is correct, these
statements are true.


Yep.

The first question which I believe I already know the simple answer is:
Can a photon have it's direction changed by 180 degree's?

Its called a mirror.


Can two photon's share the same space but have different velocity vectors?
The same vector? An exact opposite vector?


"Share the same space" is not defined, but yes, yes, and yes.

If so, is it possible to push against a given stream of photons so that a
back-pressure is measured at the source as a result of photons crashing
into it's emitter?


If you reflect the photons, and they crash back onto their source, then they
will transfer momentum back to their source. This isn't really back
pressure - think of hitting a tennis ball against a wall; if it bounces back
and hits you, then you will experience a force.

There is "sort of" back pressure when the photon is first emitted - the
photon carries momentum, so the star that emits it is pushed back when it
emits the photon.

For instance, is it possible to focus the photons of a given star and then
send those photons back along it's stream to it's origin?

With a mirror, yes.

If photons as a particle move in a stream, and each photon can only occupy
it's own space, wouldn't that specific stream be disrupted for one
discreet instant?

Two photons can occupy the "same space" (whatever that may mean exactly), so
there is no problem.

Peter Webb wrote:
"Southern Hospitality" wrote in
message ...

I think I'll pose this question in here since it's an odd-ball.

Granted photons have no mass but do exibit a force. In experiments
photons can be paused and restarted again by putting them through near
abs-zero gas fields. If what I've learned so far is correct, these
statements are true.



Yep.


The first question which I believe I already know the simple answer is:
Can a photon have it's direction changed by 180 degree's?


Its called a mirror.


Can two photon's share the same space but have different velocity vectors?
The same vector? An exact opposite vector?



"Share the same space" is not defined, but yes, yes, and yes.


Perhaps I should ask whether or not photons interact with each other?
If their vectors intersect do they collide and repel as normal physical
objects would?


If so, is it possible to push against a given stream of photons so that a
back-pressure is measured at the source as a result of photons crashing
into it's emitter?



If you reflect the photons, and they crash back onto their source, then they
will transfer momentum back to their source. This isn't really back
pressure - think of hitting a tennis ball against a wall; if it bounces back
and hits you, then you will experience a force.


What about a tennis ball that hits a wall perpendicularly in a zero-g
environment? Of course if you have just 1 ball it will bounce back to
the point where it started but if there is a stream of tennis balls all
released at the same point the result will not be the same. A string of
tennis balls will just stop because of the ones behind it. This might
be the answer to my other question asking if two photons can pass
through the same space at the same time. If there is no scattering of
the photons then the answer should be, yes. That would end my ultimate
reason for asking these questions.

There is "sort of" back pressure when the photon is first emitted - the
photon carries momentum, so the star that emits it is pushed back when it
emits the photon.


For instance, is it possible to focus the photons of a given star and then
send those photons back along it's stream to it's origin?


With a mirror, yes.


If photons as a particle move in a stream, and each photon can only occupy
it's own space, wouldn't that specific stream be disrupted for one
discreet instant?


Two photons can occupy the "same space" (whatever that may mean exactly), so
there is no problem.


Ok, I'll take that as confirmation.

Here is where I was going with my line of thinking. It's similar to
sonar where boats bounce sound waves on the bottom of the ocean floor to
get the resulting changes in frequency and ultimately be able to map the
floor of the ocean without ever having seen it. My thoughts were along
this line but by using photons pushed back along it's original path and
then measuring the differences in resistance for each photon stream then
using that information to get a topology of the light source.

I suppose what makes it pretty silly is that what I was thinking of in
one fashion, is in fact the same concept used to produce photographs.

Thanks for the info!

"Southern Hospitality" wrote in
message ...
Peter Webb wrote:
"Southern Hospitality" wrote in
message ...

I think I'll pose this question in here since it's an odd-ball.

Granted photons have no mass but do exibit a force. In experiments
photons can be paused and restarted again by putting them through near
abs-zero gas fields. If what I've learned so far is correct, these
statements are true.



Yep.


The first question which I believe I already know the simple answer is:
Can a photon have it's direction changed by 180 degree's?


Its called a mirror.


Can two photon's share the same space but have different velocity
vectors? The same vector? An exact opposite vector?



"Share the same space" is not defined, but yes, yes, and yes.


Perhaps I should ask whether or not photons interact with each other? If
their vectors intersect do they collide and repel as normal physical
objects would?


If so, is it possible to push against a given stream of photons so that a
back-pressure is measured at the source as a result of photons crashing
into it's emitter?



If you reflect the photons, and they crash back onto their source, then
they will transfer momentum back to their source. This isn't really back
pressure - think of hitting a tennis ball against a wall; if it bounces
back and hits you, then you will experience a force.


What about a tennis ball that hits a wall perpendicularly in a zero-g
environment? Of course if you have just 1 ball it will bounce back to the
point where it started but if there is a stream of tennis balls all
released at the same point the result will not be the same. A string of
tennis balls will just stop because of the ones behind it. This might be
the answer to my other question asking if two photons can pass through the
same space at the same time. If there is no scattering of the photons
then the answer should be, yes. That would end my ultimate reason for
asking these questions.

There is "sort of" back pressure when the photon is first emitted - the
photon carries momentum, so the star that emits it is pushed back when it
emits the photon.


For instance, is it possible to focus the photons of a given star and
then send those photons back along it's stream to it's origin?


With a mirror, yes.


If photons as a particle move in a stream, and each photon can only
occupy it's own space, wouldn't that specific stream be disrupted for one
discreet instant?


Two photons can occupy the "same space" (whatever that may mean exactly),
so there is no problem.


Ok, I'll take that as confirmation.

Here is where I was going with my line of thinking. It's similar to sonar
where boats bounce sound waves on the bottom of the ocean floor to get the
resulting changes in frequency and ultimately be able to map the floor of
the ocean without ever having seen it. My thoughts were along this line
but by using photons pushed back along it's original path and then
measuring the differences in resistance for each photon stream then using
that information to get a topology of the light source.

I suppose what makes it pretty silly is that what I was thinking of in one
fashion, is in fact the same concept used to produce photographs.

Thanks for the info!

Except at very (extremely) high energies, photons do not interact with each
other. They pass through each other.

The exception is where a pair of photons have enough energy to make a
particle/anti-particle pair, and it is possible that a pair of photons can
annihilate each other to produce a particle/anti-particle pair. This only
happens with extremely high energy particles - far more energetic than X
Rays - and is really only seen in cyclotrons. Its not something that would
happen very much in nature, and certainly not in free space, as it requires
two extremely high photons to be moving in opposite directions and
precisiely aligned.