Oh and we were discussing the propagation of photon through turbid media not a vacuum iirc.
Chat Forum
[closed]
Tell me your interesting facts about Space
-
Posted 2 years ago #
-
When your roadie club looks at you they see a roadie, when your mtb mates look they see an mtber.
Your basic assumption is wrong here. Roadies will see you as mountainbiker, mountainbikers will see you as a roadie.
Posted 2 years ago # -
Bruce McCandless was the first person to use a Manned Maneuvering Unit in space.
Posted 2 years ago # -
The only reason I felt compelled to join in is that I am a physicist working specifically working with quantum optics,
Ok then, seriously, I want to know exactly why me and SFB are wrong. It was a fair while ago now but I do have a master's degree in Physics, so I'll probably be able to understand what you tell me. Go ahead.
Posted 2 years ago # -
turbid media not a vacuum iirc.
but as far as I can see there's no difference in principle, apart from the speed of propagation, assuming at least partial transparency...
Posted 2 years ago # -
Ok then, seriously, I want to know exactly why me and SFB are wrong. It was a fair while ago now but I do have a master's degree in Physics, so I'll probably be able to understand what you tell me. Go ahead.
I also have a Physics degree and should probably add that my final year theoretical project was in quantum information. I'm equally curious to hear this.
Posted 2 years ago # -
But a vacuum isn't empty space (at the planck level) and hasn't this been proven by the way a body will heat up when accelerated in (empty) space?
I believe it's either the atomic structure of space time, or the soup of hot photons whizzing about that's in there.
Posted 2 years ago # -
OK, perhaps it's the phlogiston ?
Posted 2 years ago # -
Space is dark; it is so endless
When you're lost it's so relentlessIt does not feel, it does not die
Space is neither truth nor liesPosted 2 years ago # -
SFB, MolG, Dave (Physicist) I wanted you to explain in laymans terms why you thought light slows down when passing through a transparent material; which I did not feel you did. Reciting equations and words you read in a text book like a chuffing parrot doesn't convince anyone. All of you discounted some other points of view (355.geek and others) out of hand. You were abrupt and more than little patronising.
Some of the best bits:
molgrips - Member
They're photons mate.
Where do you get your information from btw?
Wikipedia, like everyone elseFlaperon - Member
335.geek - sorry, you're wrong.
Dave (Physicist).
(Bear in mind I'm being slightly vague with my terms for simplicity)
Really?Posted 2 years ago # -
1) Who was the first man in space? Yuri Gagarin
2) Who was the first man to orbit the earth? Alan Shepherd
3) Apollo 1 and Soyuz 1 had what in common? Caught fire
4) On what date did man first set foot on the moon? July 22nd 1969
5) What was the rocket for the Apollo missions? Saturn V
6) Who was the first Britisher in space? Helen Sharman
7) What was 'Buzz' Aldrin's real name? Edwin
8 What is the date of the next shuttle launch? 5th April.I cheated on a couple of them
The shuttle is travelling at 100mph when it clears the tower.
Saturn V rocket was designed by Werner Von Braun.Posted 2 years ago # -
and words you read in a text book like a chuffing parrot doesn't convince anyone. All of you discounted some other points of view (355.geek and others) out of hand.
I was recalling stuff from my student days 30 years ago. I gave what seemed to me cogent reasons why re-radiation does not happen in normal transparency - I may be wrong, but if so no one has said how, beyond vague references to Planck & Google. As for abruptness, I try never to waste words.
Posted 2 years ago # -
I wanted you to explain in laymans terms why you thought light slows down when passing through a transparent material; which I did not feel you did.
I did, here:
If the thing you are shining light into can 'resonate' at the frequency of the light, it soaks up the energy and nothing comes out. If it can't, then the light just continues along its way
As for reciting from wikipedia - I did consult wikipedia to make sure the equations and terms I was using were correct; I understand the subject and studied it at university, but that was a while ago so I was a bit rusty.
And stuff like Maxwell's equations are extremely well accepted cornerstones of Physics, point of view does not come into it. If I came on and said my point of view was that the moon was made of green cheese, would you dismiss it out of hand? Cos you should
I was abrupt when talkign to some people because they seem to think basic physics is a matter of opinion Posted 2 years ago # -
The shuttle is travelling at 100mph when it clears the tower.
It also gets up to mach 22 on its flight.
Posted 2 years ago # -
Valerie Tereshkova was the 1st woman in space
Posted 2 years ago # -
Planck's Constant. For which Mrs Planck was very happy.
BTW, by a strange coincidence, Richard Hammond's Invisible World is on exactly this subject tonight, light, x-rays, etc. Amazing new x-ray tech that allows filming of moving objects and animals while seeing how the insides work. All we want now are the miniaturised version in a pair of glasses...Posted 2 years ago # -
Apologies to anyone who accidentally clicked on this thread and doesn't give a toss.
Now I'm not claiming to be physicist, but a quick look on Wikipedia (heaven forbid!) and you can find some good references. I thought Richard Feynman would be a reasonable start place to start. The quote below comes from the following reference:
Refractive Index of Dense Materials, Feynman R, Leighton R, and Sands M. The Feynman Lectures on Physics, Vol. 2, Chapter 32.
"The electric field of the light wave polarizes the molecules of the gas, producing oscillating dipole moments. The acceleration of the oscillating charges radiates new waves of the field. This new wave field, interfering with the old field, produces a changed field which is equivalent to a phase shift of the original wave. Because this phase shift is proportional to the thickness of the material, the effect is equivalent to having a different phase velocity in the material"
Vol.1 Chapter 31 covers the topic in more detail and is well worth a read.
So, my interpretation of that is that both sides are partly correct.
The light induces fields in the material as it is passing through (hence the relationship between refractive index and permittivity etc.).
I think it covers the re-radiation question.
The phase shift caused by the constant generation of new fields retards the progress of the light - it appears to slow. The actual speed, wavelength and frequency do not need to change for all this to work. We also haven't had to invoke the dreaded proton!
If anyone is really interested I have a hard copy of this stuff (Vol.1Ch31 & Vol.2Ch32) from Feynman which I would happily scan and email.
Posted 2 years ago # -
So, my interpretation of that is that both sides are partly correct.
Well.. not really.. absorbtion and re-radiation is completely different to the polarisation effect you talk about. You've neatly explained why permeability and permitivity are different in different materials, which I didn't do.
The 'speed' of light does change since it's the time taken for the wave to propogate a given distance. You just explained why it changes
Posted 2 years ago # -
This is my last post, off to the pub.
absorbtion and re-radiation
I think the original re-radiation explanation didn't come across properly. There is no talk of any absorbtion in the above quote.polarisation effect
It's not polarisation, it's interference.The 'speed' of light does change
This is the key, it doesn't, it is phase shifted due to interference (both destructively and constructively) caused by new wave fields induced by the light interacting with the material. It 'appears' to slow down.There are materials that have a negative refractive index. Does the light speed up? Faster than the speed of light?
Posted 2 years ago # -
Well how do you define speed then?
Posted 2 years ago # -
Hate to be a spoilsport but the OP was 'man in space' not 'the physics of space'.
But if you insist, 'space is not only queerer than we think, it's queerer than we CAN think'Posted 2 years ago # -
Well we hijacked the thread
Think of it as a superposition of threads in different states.
Posted 2 years ago # -
Well how do you define speed then?
Has this question come through from the Mephedrone thread?
Posted 2 years ago # -
Dodgy Scouse beat combo?
Posted 2 years ago # -
not sure if anyone has answered about the poem on the underground yet, but I think it's Out there by Jamie McKendrick
mrst
Posted 2 years ago #
Topic Closed
This topic has been closed to new replies.
