Originally Posted By: paul

the guy in the video never said anything like that.


The guy is the video is trying to dumb this down as I said it gets a bit complex QM stuff.

So okay the guy in the video is your absolute reference you accept so lets use that.

Goto 2min in the video he compares the laser to a sound waves of an ambulance and discusses the frequency change ... that is called a doppler shift (http://en.wikipedia.org/wiki/Doppler_effect)

Now at 2.30 he now talks about something about atoms that is different from "him" meaning normal macro objects and he desribes it as "atoms can only hear at 1 frequency".

What he is avoiding is getting into quantum mechanics the atoms only "hear at one frequency" BECAUSE OF QUANTUM MECHANICS.

It's called atomic absorbtion and the energy levels are pure QM (http://hyperphysics.phy-astr.gsu.edu/hbase/mod5.html)

He is specifically avoiding discussing why the atoms only "hear at 1 frequency" beacuse he doesn't wish to have to try and explain QM to average layman.

If you don't accept this please give me your explaination of why atoms only hear at 1 frequency?????

Next the guy in the video talks about moving towards and away from the laser and then starts the funny bit for me.

At 3.45 he talks about them absorbing a photon if they match the frequency and 3.48 he talks about them going to an excited state and you get a slight "baff" which slows you down :-)

At 4.08 if you keep the same frequency it now goes straight thru the atom ...... Okay so now you are transparent :-)

So at 4.14 we start changing the frequency down .. :-)

HANG ON A MINUTE HE TOLD ME 3.45 that atoms only absorb a specific frequency and second a go I was absorbing that frequency and now I have to absorb a lower frequency.

Do you see the problem he is trying to dance around because he doesn't want to discuss QM.

And the guy at 4.31 discusses you need not only "light not just at 671 nanaometers but 671.0005". What he is trying to say is you need to be able to lower the frequency of the laser as you cool.

Then the guy talks about being "baffed" by a photon and then you reach a lower movement then you lower the frequency and you get slowed by each "baff".

Whats funny is they avoid discussing why the lower frequency "baffs" you less ... surely that crossed your mind if you are taking a purely classical view Paul.

To be hit with less power in the classic world Paul you swing with less energy so shouldn't they be just turning the laser power down ... that had to cross your mind Paul.

It's also interesting they never go back to the excited atom they mentioned that at the beginning and he had the atom absorbing the photon then he brings in the concept that you are being "baffed" by each photon which slows you.

He never goes back to what happens to the absorb photon and so you have an atom which apparently can be excited and excited and excited and excited. He describes the atom as needing tens of thousands of photon collisions so I guess the atom is 10 000 fold excited a hugely funny thing for a scientist but I guess that means nothing to you.

To me this a major problem with this explaination he doesn't deal with the emission of a photon to get down for the excited state so it can again absorb ... it' weird.

I think I understand why because you then have to explain two photons and it's hard to avoid QM energy level discussion.

I can see now why you think that absorbing photons slows you down and you get a hugely excited atom :-)

All I can say to you Paul is that is not a great explaination and surely you can see the problems I have highlighted.


Quote:

so , I was right.

so basically its saying that there are 2 separate processes.

1) absorption , without emission.
and
2) absorbtion , with emission.

but in each of the 2 processes the absorption slows the atom
due to the photons kinetic energy being absorbed by the atom.


Unfortunately there are two problems with that and I can see how it came about from that explaination

1.) You can not just keep absorbing photons and getting more and more excited it's not a bottomless pit.

2.) It also induces a problem that you have it that excited states = slower atom because to get it excited you absorbed photons and thats slows the atom ... thats what you think isn't it.

That is a problem because it's actually the other way around
http://en.wikipedia.org/wiki/Excited_state

=>In quantum mechanics an excited state of a system (such as an atom, molecule or nucleus) is any quantum state of the system that has a higher energy than the ground state (that is, more energy than the absolute minimum). The temperature of a group of particles is indicative of the level of excitation.

See the problem with explaination an excited atom is hotter than a ground state atom.

That confusion comes about because they have not dealt with the re-emission



Quote:

I didnt need anything but a solid grasp on physics in our discussion , I dont think that QM belongs in this realm.


As I have shown you there was QM throughout his explaination he just didn't call it QM and you blindly accepeted it such that atoms can only "hear 1 frequency" and weirdly that 1 frequency changes with temeprature no explaination needed.

Sure no QM necessary if you blindly accept weird facts.

Last edited by Orac; 08/24/12 04:41 AM.

I believe in "Evil, Bad, Ungodly fantasy science and maths", so I am undoubtedly wrong to you.