Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Speciality Forums >> Science! Astronomy & Space Exploration, and Others

Pages: 1 | 2 | 3 | (show all)
Ira
Carpal Tunnel
*****

Reged: 08/22/10

Loc: Mitzpe Ramon, Israel
C = 0
      #5990090 - 07/25/13 06:39 PM

http://www.extremetech.com/extreme/162289-light-stopped-completely-for-a-minu...

/Ira


Post Extras: Print Post   Remind Me!   Notify Moderator  
davidpitre
Post Laureate
*****

Reged: 05/10/05

Loc: Central Texas
Re: C = 0 new [Re: Ira]
      #5990223 - 07/25/13 08:23 PM

What caught my eye was:
"These atomic spins can maintain coherence (data integrity) for around a minute". Pretty cool.


Post Extras: Print Post   Remind Me!   Notify Moderator  
EJN
Carpal Tunnel
*****

Reged: 11/01/05

Loc: 53 miles west of Venus
Re: C = 0 new [Re: Ira]
      #5990268 - 07/25/13 08:53 PM

Articles like this do not explain the difference between phase velocity
& group velocity - even if the group velocity = 0 the phase velocity
still equals c (in that medium).

http://en.wikipedia.org/wiki/Group_velocity
http://en.wikipedia.org/wiki/Phase_velocity


Post Extras: Print Post   Remind Me!   Notify Moderator  
Charlie B
scholastic sledgehammer


Reged: 03/22/08

Loc: Sterling, Virginia
Re: C = 0 new [Re: EJN]
      #5991049 - 07/26/13 10:58 AM

Phase and group velocity do not seem to be relevant to this experiment. The experimenters stored a light image, which is information, in the crystal's molecular spin states. Although, the article implies that light was stopped, the actual feat seemed to be maintaining the spin states for 60 seconds.

Regards,
Charlie B


Post Extras: Print Post   Remind Me!   Notify Moderator  
TL2101
professor emeritus


Reged: 09/17/10

Loc: Concord, CA
Re: C = 0 new [Re: Charlie B]
      #5991323 - 07/26/13 01:50 PM

Is this the same result as happens in the Bose-Einstein condensate?

Post Extras: Print Post   Remind Me!   Notify Moderator  
Charlie B
scholastic sledgehammer


Reged: 03/22/08

Loc: Sterling, Virginia
Re: C = 0 new [Re: TL2101]
      #5991762 - 07/26/13 06:17 PM

Quote:

Is this the same result as happens in the Bose-Einstein condensate?




I don't think so. The BE condensate is at (almost) the lowest possible quantum state for the atoms and no information is imprinted. This appears to be a defined state, not the lowest.

Charlie B


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pess
(Title)
*****

Reged: 09/12/07

Loc: Toledo, Ohio
Re: C = 0 new [Re: Charlie B]
      #5994409 - 07/28/13 09:51 AM

Quote:

Phase and group velocity do not seem to be relevant to this experiment. The experimenters stored a light image, which is information, in the crystal's molecular spin states. Although, the article implies that light was stopped, the actual feat seemed to be maintaining the spin states for 60 seconds.

Regards,
Charlie B




I really hate the way they report this in the news.

Light always travels at 'c'. Its average speed can appear to be 'slowed' because when photons travel through a substrate they are constantly stopped and re-emitted by the atoms within the substrate.

The photons dash at the speed of 'c' from atom to atom but held up as they dissappear (absorbed by an atom) and re-created again. This destruction and recreation takes time and that is why the overall speed of the photons measured appears to have slowed. A Photon, during the dash between atoms, always travels at 'c'.

Now it isn't that exciting that information is preserved. Every time we look through a window we are seeing photons impressed with the same information they entered the opposite side with.

What IS impressive is that scientists were able to create a medium where the absorption/recreation of photons occurred so slowly that it took a minute for the photons to come out the other side WHILE STILL PRESERVING the information the photons entered with!

That's the amazing part!

But any casual reader of these articles comes away with the impression that the photons were somehow brought to a standstill.

On a separate note, I was talking to a group of high school students about physics the other day. What I like to do is take a complex subject and try and put it in simple terms that a high school student might understand.

I was stumped by a question: Why don't photons have rest mass? I started to stumble around explaining Gauge theory and Higgs Boson interactions with magnetic fields...etc etc. But their eyes glazed over.

Anyone have a good, simple explanation for why photons have no rest mass?

Pesse (I can c clearly now) Mist


Post Extras: Print Post   Remind Me!   Notify Moderator  
llanitedave
Humble Megalomaniac
*****

Reged: 09/26/05

Loc: Amargosa Valley, NV, USA
Re: C = 0 new [Re: Pess]
      #5994498 - 07/28/13 10:49 AM

Because they never get tired.

Post Extras: Print Post   Remind Me!   Notify Moderator  
derangedhermit
Pooh-Bah


Reged: 10/07/09

Loc: USA
Re: C = 0 new [Re: llanitedave]
      #5994606 - 07/28/13 11:57 AM

i've forgotten how long it takes a photon from a star's core, say our Sun, to pop out at the surface, but it is a very long time. I wonder what the average speed is? Much less than highway speeds, I think. Maybe less than walking speed.

Edited by derangedhermit (07/28/13 11:59 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
llanitedave
Humble Megalomaniac
*****

Reged: 09/26/05

Loc: Amargosa Valley, NV, USA
Re: C = 0 new [Re: derangedhermit]
      #5995032 - 07/28/13 04:10 PM

Photons from the Sun's core don't make it directly to the surface. They are generated as gamma rays in the core, and as energy gets absorbed and re-emitted in the random walk outward, it gets emitted as new photons of progressively lower energy levels. If I remember right, the energy takes at least tens of thousands of years to dissipate outward, but it's not because any individual packet is traveling slowly. Also, since it's emitted each time in a random direction, as often as not it gets sent back inward again.

Post Extras: Print Post   Remind Me!   Notify Moderator  
StarWars
Mr. Postmaster Man
*****

Reged: 11/26/03

Loc: At the Gym >Spudtastic<
Re: C = 0 new [Re: llanitedave]
      #5995118 - 07/28/13 04:49 PM




Interesting subject!!


I have a flashlight and when the switch is pressed to the on position there is a beam of light.
When switched to the off position the beam of light is gone.

Where did the light go...


I bet there is a big difference between LED produced light and light from the sun!!


Post Extras: Print Post   Remind Me!   Notify Moderator  
Ira
Carpal Tunnel
*****

Reged: 08/22/10

Loc: Mitzpe Ramon, Israel
Re: C = 0 new [Re: derangedhermit]
      #5995184 - 07/28/13 05:32 PM

Quote:

i've forgotten how long it takes a photon from a star's core, say our Sun, to pop out at the surface, but it is a very long time. I wonder what the average speed is? Much less than highway speeds, I think. Maybe less than walking speed.




Last I heard, it takes 10,000 years.

/Ira


Post Extras: Print Post   Remind Me!   Notify Moderator  
ColoHank
Carpal Tunnel
*****

Reged: 06/07/07

Loc: western Colorado
Re: C = 0 new [Re: StarWars]
      #5995304 - 07/28/13 06:51 PM

Quote:

I have a flashlight and when the switch is pressed to the on position there is a beam of light.
When switched to the off position the beam of light is gone.

Where did the light go...





Isn't it absorbed by whatever the light eventually strikes (a wall, dust particles in the atmosphere, etc.) and converted to heat energy?


Post Extras: Print Post   Remind Me!   Notify Moderator  
Ira
Carpal Tunnel
*****

Reged: 08/22/10

Loc: Mitzpe Ramon, Israel
Re: C = 0 new [Re: StarWars]
      #5995496 - 07/28/13 09:14 PM

Quote:




Interesting subject!!


I have a flashlight and when the switch is pressed to the on position there is a beam of light.
When switched to the off position the beam of light is gone.

Where did the light go...


I bet there is a big difference between LED produced light and light from the sun!!




Your light is off toward the outer reaches of the cosmos. Whatever part of it isn't blocked by matter, interstellar dust or other junk will just keep on travelling forever at the speed of c. You can never catch up to it.

/Ira


Post Extras: Print Post   Remind Me!   Notify Moderator  
scopethis
Postmaster
*****

Reged: 05/30/08

Loc: Kingman, Ks
Re: C = 0 new [Re: Ira]
      #5996124 - 07/29/13 08:38 AM

when light is reflected off of a mirror, is it traveling at its original speed?

Post Extras: Print Post   Remind Me!   Notify Moderator  
Ira
Carpal Tunnel
*****

Reged: 08/22/10

Loc: Mitzpe Ramon, Israel
Re: C = 0 new [Re: scopethis]
      #5996299 - 07/29/13 10:44 AM

Quote:

when light is reflected off of a mirror, is it traveling at its original speed?




Why wouldn't it be? It's only when travelling in a medium other than the vacuum of space that its speed decreases. It's reflecting off the mirror, not travelling through it. Although, if it's a second surface mirror it will travel a few mm through the glass before reflecting, so its speed will slow then. But when it exits the glass it should be travelling again at c, or whatever c is in the earth's atmosphere.

/Ira


Post Extras: Print Post   Remind Me!   Notify Moderator  
Mister T
Pooh-Bah


Reged: 02/01/08

Loc: Upstate NY
Re: C = 0 new [Re: Ira]
      #5996431 - 07/29/13 11:59 AM

So since atoms are mostly empty space, when light is traveling through the atmosphere how far does the average photon go before it hits something that will slow it down?

Post Extras: Print Post   Remind Me!   Notify Moderator  
llanitedave
Humble Megalomaniac
*****

Reged: 09/26/05

Loc: Amargosa Valley, NV, USA
Re: C = 0 new [Re: Mister T]
      #5996631 - 07/29/13 01:39 PM

It's not the nucleus that the light will be hitting, it's the electron shell, so the empty space surrounding the nucleus doesn't really matter.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Qwickdraw
Carpal Tunnel
*****

Reged: 03/03/12

Loc: Ann Arbor, MI
Re: C = 0 new [Re: llanitedave]
      #5997068 - 07/29/13 06:10 PM

isnt this closer to converting light energy to another type of energy and then using that stored energy to generate new light rather then actually storing light?

Post Extras: Print Post   Remind Me!   Notify Moderator  
Pess
(Title)
*****

Reged: 09/12/07

Loc: Toledo, Ohio
Re: C = 0 new [Re: Ira]
      #5998776 - 07/30/13 04:54 PM

Quote:

Quote:

when light is reflected off of a mirror, is it traveling at its original speed?




Why wouldn't it be? It's only when travelling in a medium other than the vacuum of space that its speed decreases. It's reflecting off the mirror, not travelling through it. Although, if it's a second surface mirror it will travel a few mm through the glass before reflecting, so its speed will slow then. But when it exits the glass it should be travelling again at c, or whatever c is in the earth's atmosphere.

/Ira





Well, actually light always travels at 'c'...no exceptions. Even through any medium the photons are traveling at 'c'. It is just a medium has atoms and electrons that absorb the photons and then re-emit a new photon. This absorption and re-emitting takes a tad bit of time so if you measure the average photon speed it 'appears' the medium slowed the photons. But atom to atom the photons always travel at 'c'.

In regards to a mirror...the photons are absorbed and reemitted in the same direction of travel they came in on so the original photons that struck the mirror are converted to energy when they are absorbed by the atoms of the mirror...this energy is dumped by the atoms in the form of a new photon.
.

Pesse (Welcome to quantum mechanics.) Mist


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pess
(Title)
*****

Reged: 09/12/07

Loc: Toledo, Ohio
Re: C = 0 new [Re: Pess]
      #5998885 - 07/30/13 06:14 PM Attachment (9 downloads)

.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Ira
Carpal Tunnel
*****

Reged: 08/22/10

Loc: Mitzpe Ramon, Israel
Re: C = 0 new [Re: Pess]
      #5998996 - 07/30/13 07:32 PM

So why, then, does a lens bend light?

/Ira


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pess
(Title)
*****

Reged: 09/12/07

Loc: Toledo, Ohio
Re: C = 0 new [Re: Ira]
      #5999146 - 07/30/13 09:28 PM

Quote:

So why, then, does a lens bend light?

/Ira




The new photon can be re-admitted along varying vectors. The atoms in a mirrored surface (or, more correctly, their electrons) can send them straight backwards so you can see your reflection. Or they can re-emit them along the same vector as glass or air does. Or they can slightly shift the vector and so the image appears shifted.

The photons can even be significantly changed such as a laser hitting a rock with the result of photons being re-emitted at infrared wavelengths (heat)

In summary, photons travel in a straight line, they travel at velocity 'c' until they hit something at which point they cease to exist and their energy is transferred into what stops them.

Pesse (cool beans) Mist


Post Extras: Print Post   Remind Me!   Notify Moderator  
ColoHank
Carpal Tunnel
*****

Reged: 06/07/07

Loc: western Colorado
Re: C = 0 new [Re: Pess]
      #5999180 - 07/30/13 09:47 PM

Quote:

In regards to a mirror...the photons are absorbed and reemitted in the same direction of travel they came in on so the original photons that struck the mirror are converted to energy when they are absorbed by the atoms of the mirror...this energy is dumped by the atoms in the form of a new photon.





Most of them, anyway. Some are absorbed and converted to heat energy. Thus, reflectance is always less than 100%, the amount of loss determined by the composition and quality of the reflective surface and the wavelength of the light. Also, the re-emitted photons aren't bounced back in the same direction from whence the originals came. If they were, a person could look at a mirror from any angle and still see his or her image. Reflected photon(s) will follow a path that's equal in incidence to the optic normal but opposite in direction to the incoming photon(s).


Post Extras: Print Post   Remind Me!   Notify Moderator  
StarWars
Mr. Postmaster Man
*****

Reged: 11/26/03

Loc: At the Gym >Spudtastic<
Re: C = 0 new [Re: Ira]
      #5999413 - 07/31/13 01:37 AM

Quote:

Quote:




Interesting subject!!


I have a flashlight and when the switch is pressed to the on position there is a beam of light.
When switched to the off position the beam of light is gone.

Where did the light go...


I bet there is a big difference between LED produced light and light from the sun!!




Your light is off toward the outer reaches of the cosmos. Whatever part of it isn't blocked by matter, interstellar dust or other junk will just keep on traveling forever at the speed of c. You can never catch up to it.

/Ira





Sounds logical!!


Post Extras: Print Post   Remind Me!   Notify Moderator  
Qwickdraw
Carpal Tunnel
*****

Reged: 03/03/12

Loc: Ann Arbor, MI
Re: C = 0 new [Re: ColoHank]
      #5999957 - 07/31/13 12:09 PM

Quote:

Also, the re-emitted photons aren't bounced back in the same direction from whence the originals came. If they were, a person could look at a mirror from any angle and still see his or her image. Reflected photon(s) will follow a path that's equal in incidence to the optic normal but opposite in direction to the incoming photon(s).




Sure they do, but only if the angle of incidence equals zero. One of the principles behind a LASER.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pess
(Title)
*****

Reged: 09/12/07

Loc: Toledo, Ohio
Re: C = 0 new [Re: Ira]
      #6000186 - 07/31/13 03:14 PM

Quote:



Your light is off toward the outer reaches of the cosmos. Whatever part of it isn't blocked by matter, interstellar dust or other junk will just keep on travelling forever at the speed of c. You can never catch up to it.

/Ira




I am not so sure. What if the Universe is closed and bounded? So that any straight line comes back on itself?

All one needs to do to catch a photon is stand from where it was emitted and catch it as it comes around.

Pesse (Bring a magazine to pass the time) Mist


Post Extras: Print Post   Remind Me!   Notify Moderator  
StarWars
Mr. Postmaster Man
*****

Reged: 11/26/03

Loc: At the Gym >Spudtastic<
Re: C = 0 new [Re: Pess]
      #6001550 - 08/01/13 03:42 PM



Sun light vs. man made light...


When I go outside I can feel the sun light as a pressure on my skin.

Mankind still does not know how to harvest the power of the sun....

Maybe if they build a solar collector with Fresnel lens...


Post Extras: Print Post   Remind Me!   Notify Moderator  
scopethis
Postmaster
*****

Reged: 05/30/08

Loc: Kingman, Ks
Re: C = 0 new [Re: StarWars]
      #6002030 - 08/01/13 08:05 PM

since light is absorbed by objects, can one squeeze light out of a sponge that has been exposed to sunlight?

Post Extras: Print Post   Remind Me!   Notify Moderator  
ColoHank
Carpal Tunnel
*****

Reged: 06/07/07

Loc: western Colorado
Re: C = 0 new [Re: scopethis]
      #6002283 - 08/01/13 10:50 PM

Quote:

since light is absorbed by objects, can one squeeze light out of a sponge that has been exposed to sunlight?




Why not try that and share your findings with us? First, you'll need a sponge. Then, expose it to light. Finally, take the sponge into a very dark room and squeeze it as hard as you possibly can. Be patient; it might take a long time for the light to come out.


Post Extras: Print Post   Remind Me!   Notify Moderator  
llanitedave
Humble Megalomaniac
*****

Reged: 09/26/05

Loc: Amargosa Valley, NV, USA
Re: C = 0 new [Re: ColoHank]
      #6002415 - 08/02/13 12:34 AM

Make sure you have the supplies to clean up the mess afterward.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Pess
(Title)
*****

Reged: 09/12/07

Loc: Toledo, Ohio
Re: C = 0 new [Re: ColoHank]
      #6002722 - 08/02/13 08:01 AM

Quote:

Quote:

since light is absorbed by objects, can one squeeze light out of a sponge that has been exposed to sunlight?




Why not try that and share your findings with us? First, you'll need a sponge. Then, expose it to light. Finally, take the sponge into a very dark room and squeeze it as hard as you possibly can. Be patient; it might take a long time for the light to come out.




The sponge atoms almost immediately re-emit absorbed photons...that's why you can 'see' a sponge by looking at it (your eyes detect the re=emitted photons).

However, if you squeeze hard enough to overcome the Coulomb forces, you'll generate plenty of new photons. However, make sure you hire a janitorial service to keep Dave happy because you might not enjoy the experience.

Pesse (clean up on aisle one) Mist


Post Extras: Print Post   Remind Me!   Notify Moderator  
derangedhermit
Pooh-Bah


Reged: 10/07/09

Loc: USA
Re: C = 0 new [Re: llanitedave]
      #6003681 - 08/02/13 06:18 PM

Quote:

Photons from the Sun's core don't make it directly to the surface. They are generaleast tens of thousands of years to dissipate outward, but it's not because any individual packet is traveling slowly. Also, since it's emitted each time in a random direction, as often as not it gets sent back inward again.



The article said the same thing ("photon absorbed, photon later emitted") was happpening in this case, unless my reading skills have failed entirely.


Post Extras: Print Post   Remind Me!   Notify Moderator  
wirenut
Pooh-Bah


Reged: 09/21/06

Loc: m'dale Pa
Re: C = 0 new [Re: ColoHank]
      #6005344 - 08/03/13 08:37 PM

Quote:

Quote:

since light is absorbed by objects, can one squeeze light out of a sponge that has been exposed to sunlight?




Why not try that and share your findings with us? First, you'll need a sponge. Then, expose it to light. Finally, take the sponge into a very dark room and squeeze it as hard as you possibly can. Be patient; it might take a long time for the light to come out.



you may want to wear eye protection like a wielders mask or dark sunglasses just in case it soaked up too much light.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Ira
Carpal Tunnel
*****

Reged: 08/22/10

Loc: Mitzpe Ramon, Israel
Re: C = 0 new [Re: Pess]
      #6005401 - 08/03/13 09:14 PM

Does the sponge actually reemit the photons or just reflect the same photons that hit it?

/Ira


Post Extras: Print Post   Remind Me!   Notify Moderator  
scopethis
Postmaster
*****

Reged: 05/30/08

Loc: Kingman, Ks
Re: C = 0 new [Re: Ira]
      #6006766 - 08/04/13 10:33 PM

I was gonna try what many have suggested but my wife won't let me go into a dark room with a sponge...

Post Extras: Print Post   Remind Me!   Notify Moderator  
Pess
(Title)
*****

Reged: 09/12/07

Loc: Toledo, Ohio
Re: C = 0 new [Re: Ira]
      #6008297 - 08/05/13 08:38 PM

Quote:

Does the sponge actually reemit the photons or just reflect the same photons that hit it?

/Ira




1) Photons always travel in a straight line

2) Photons always travel at exactly 'c'

3) Photons do not reflect, bounce off or otherwise change direction. They travel in a straight line until they hit something. Their energy is absorbed (usually by the electron shell of an atom) and then can be re-emitted at a different wavelength, the same wavelength and/or any vector all dependent on the energy of the photon and what it hits.

When you look at a reflection in a mirror, you are not detecting a single photon that 'hit' the mirro5r. You are detecting the re-emitted photons the atoms of the mirror re-emitted after the original photons hit them.

Pesse (clear as mud) Mist


Post Extras: Print Post   Remind Me!   Notify Moderator  
Ira
Carpal Tunnel
*****

Reged: 08/22/10

Loc: Mitzpe Ramon, Israel
Re: C = 0 new [Re: Pess]
      #6008406 - 08/05/13 09:33 PM

Really? I find this staggering. I never thought of it that way. So, how does gravitational lensing work if photons always travel in a straight line?And if photons are reemitted by whatever they strike why does <angle>i=<angle>r? Why aren't photons reemitted every which way?

/Ira


Post Extras: Print Post   Remind Me!   Notify Moderator  
llanitedave
Humble Megalomaniac
*****

Reged: 09/26/05

Loc: Amargosa Valley, NV, USA
Re: C = 0 new [Re: Ira]
      #6008503 - 08/05/13 10:14 PM

Straight lines can curve in gravitational fields.

(The second and third questions have always made me wonder too)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pess
(Title)
*****

Reged: 09/12/07

Loc: Toledo, Ohio
Re: C = 0 new [Re: Ira]
      #6009369 - 08/06/13 12:36 PM

Quote:

Really? I find this staggering. I never thought of it that way. So, how does gravitational lensing work if photons always travel in a straight line?And if photons are reemitted by whatever they strike why does <angle>i=<angle>r? Why aren't photons reemitted every which way?

/Ira




What Dave said about gravity & such.

Take a piece of paper.

Draw a razor straight line on it.

Now crumple the paper.

Is the line still straight? What changed?

Pesse (Fun with a 2D Universe) Mist


Post Extras: Print Post   Remind Me!   Notify Moderator  
scopethis
Postmaster
*****

Reged: 05/30/08

Loc: Kingman, Ks
Re: C = 0 new [Re: llanitedave]
      #6009374 - 08/06/13 12:38 PM

if that's the case; when I turn off the light in a room, the area should remain well illuminated....

Post Extras: Print Post   Remind Me!   Notify Moderator  
ColoHank
Carpal Tunnel
*****

Reged: 06/07/07

Loc: western Colorado
Re: C = 0 new [Re: scopethis]
      #6009437 - 08/06/13 01:01 PM

Quote:

if that's the case; when I turn off the light in a room, the area should remain well illuminated....




Who knows? The room may remain illuminated for another trillionth of a second or so (it depends on the size of room and the texture and color of the walls, etc.) until all of those light photons bouncing around are absorbed and converted to heat energy. I'd attempt to measure it, but my Timex's stopwatch only registers down to 1/100 second.

Edited by ColoHank (08/06/13 01:03 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pess
(Title)
*****

Reged: 09/12/07

Loc: Toledo, Ohio
Re: C = 0 new [Re: ColoHank]
      #6009516 - 08/06/13 01:39 PM

Quote:

Quote:

if that's the case; when I turn off the light in a room, the area should remain well illuminated....




Who knows? The room may remain illuminated for another trillionth of a second or so (it depends on the size of room and the texture and color of the walls, etc.) until all of those light photons bouncing around are absorbed and converted to heat energy. I'd attempt to measure it, but my Timex's stopwatch only registers down to 1/100 second.




Pesse (LOL) Mist


Post Extras: Print Post   Remind Me!   Notify Moderator  
scopethis
Postmaster
*****

Reged: 05/30/08

Loc: Kingman, Ks
Re: C = 0 new [Re: Pess]
      #6010593 - 08/06/13 11:33 PM

shape the room like a pyramid and line the walls with highly reflective mirrors....ah, the Indian tee pees were so close..

Post Extras: Print Post   Remind Me!   Notify Moderator  
dickbill
scholastic sledgehammer


Reged: 09/30/08

Re: C = 0 new [Re: scopethis]
      #6015857 - 08/09/13 01:34 PM

hmmm, when you say a photon is absorbed and reemitted, it cannot be reemitted with the same energy, right?
Otherwise it seems to me it'd be a violation of thermodynamic's 2nd law: entropy must increase, some energy must have been lost in the process or it's like there had been no event at all. So i would assume the photons are slightly 'redened' after the event. So a reflected image, for example, should be slighty redened.
That's one thing.

The other thing now is about quantum uncertainty principle. If the absorbtion/reemission is a quantum event, i'd assume that based on this principle, the energy of the reemitted photon should fluctuate a bit, with some reemission events quite far energetically from the absorbtion event in both redened and blued effects. Here the colors of the reflected image should be blurred.

Am i all wrong here?


Post Extras: Print Post   Remind Me!   Notify Moderator  
llanitedave
Humble Megalomaniac
*****

Reged: 09/26/05

Loc: Amargosa Valley, NV, USA
Re: C = 0 new [Re: dickbill]
      #6016045 - 08/09/13 03:07 PM

Entropy doesn't apply to single photons as far as I know, only an aggregate of them. As I understand it, and could be mistaken, reflection efficiency does not affect the wavelength or energy of the photons, but how many are simply not reemitted at all. Those few that are absorbed would go into very slightly heating the mirror.

Post Extras: Print Post   Remind Me!   Notify Moderator  
dickbill
scholastic sledgehammer


Reged: 09/30/08

Re: C = 0 new [Re: llanitedave]
      #6016143 - 08/09/13 03:56 PM

You make the case that thermodynmic doesn't apply to single event. I am still annoyed by the concept of any event that would occur without an energy difference, but ok.

But what about the quantum uncertainty then? why should the energy of the reemitted photon be exactly the same as the absorbed photon?


Post Extras: Print Post   Remind Me!   Notify Moderator  
dickbill
scholastic sledgehammer


Reged: 09/30/08

Re: C = 0 new [Re: dickbill]
      #6016152 - 08/09/13 04:03 PM

Oh, i got it, it's dictated by the electronic levels of energy, which are set. So if one electron absorbes one photon and jump one level, it can only go back to the initial level by releasing the same amount of energy.
But why the uncertainty principle doesn't apply, no matter what?


Post Extras: Print Post   Remind Me!   Notify Moderator  
Carl Coker
member


Reged: 07/30/12

Loc: Ohio
Re: C = 0 new [Re: dickbill]
      #6016257 - 08/09/13 05:22 PM

The uncertainty principle does apply, and the energy will almost certainly not be exactly the same. But it will be roughly the same, and which way it changes (and how much) is completely random. Over many events, the re-emitted energy distribution is approximately a Gaussian with a width inversely proportional to the lifetime of the excited state.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | (show all)


Extra information
1 registered and 2 anonymous users are browsing this forum.

Moderator:  LivingNDixie, FirstSight, JayinUT 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 1834

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics