# I want to create a 1 meter BEC

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27 minutes ago, swansont said:

I didn’t say sci-fi, I said pop-sci. Pop-sci doesn’t teach science, it teaches about science. Like I said, it’s a veneer, discussing results, in general terms. No nuts-and-bolts science.

You get a result (we slowed light down to 10 m/s or whatever) but what about the person-years of work it took to get there? That’s what needs to be discussed, and what you need to know if you wanted to do a similar experiment. You need to know how the experiment works - and what doesn’t work - in order to do that.

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3 minutes ago, Phi for All said:

Reading back on the thread, the concerns given were mostly about technical resources and financial limitations. I don't know how you got from there to "you guys consider the topic top secret and do not want to discuss further about it".

I think the "standpoint" overall is that there's no way you're going to be able to do this, so why bother mapping it out for you? That's the really hard part, and since you won't be helping, why do we need you? To be fair, I'd be in the same boat if I asked Dr Swanson to help me do an experiment like this. Even if I could convince him I've got \$50K to spend, he has a much better idea of the expertise, time, and manpower it's going to take. It also doesn't help that initially I told him I wanted to build this, but later admitted I probably couldn't, then accused him of not being willing to share his secrets. I'd probably wish I hadn't done that.

As I stated I might have not been meticulous enough about my title and result in confusion. But after re-stating my problem I got my answer and I thank Dr. Swansnot for that. It is not because I do not have 50 grand to test Einstein's special relativity so I cannot theorize about it here. Given sure, this is a more of a pop-sci question, I did not know you guys do not like pop-sci = =. Let me know if I can post more pop-sci questions in the future or if I should keep them to myself.

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As I stated I might have not been meticulous enough about my title and result in confusion. But after re-stating my problem I got my answer and I thank Dr. Swansnot for that.

Are you being meticulous about misspelling his username? Every time? Because that might come off as insulting.

I did not know you guys do not like pop-sci = =. Let me know if I can post more pop-sci questions in the future or if I should keep them to myself.

Pop-sci needs to be questioned, because it's often overhyped and sensationalized, and that causes lots of folks to come here with misunderstandings. Science journalists have a limited readership, so they need to attract everyone they can, and that often means staying away from technical talk that's over most people's heads. It also means their vocabulary is not as rich as it needs to be to properly convey the concepts they write about. They have to "dumb it down", and that leads to some dumb interpretations.

Post all the questions you want. Just don't base any assertions or conclusions on stuff you see in videos and pop-sci articles.

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OK, as an interested amateur, my understanding is that light/photons are never at rest. I also understand that light can never be stopped. It is though absorbed, re-emitted, reflected, refracted etc. eg: Light passing through a denser medium. Essentially, from one's point of view, light may seem to have slowed when passing through glass, but it is the absorbion and re-emittance that takes time.   There have been experiments I have read about which claim light has been slowed or/and stopped. In reality these have been "tricks" in which I understand that a particular part of the wavelength overtakes another particular part, or similar trickery. I'm not sure what happens with BEC's but have a sneaking suspicion, it is another form of trickery. I use the word "trickery" for want of a better word.

Am I correct in my assumptions?

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I got a question, how would you compare this to shining a light against a cement wall? Are the photons also absorbed by the wall or destroyed. Clearly the cement wall does not re-emit photons afterward

I hope it’s clear that it does emit photons, but it’s not a resonant process

I did not know you guys do not like pop-sci = =. Let me know if I can post more pop-sci questions in the future or if I should keep them to myself.

Even journal articles don’t aways contain all of the relevant information to do an experiment. Pop-sci articles contain far less, and tend to avoid precise language. You are free to ask questions about such articles. Extrapolation from them is the problem.

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8 hours ago, swansont said:

I hope it’s clear that it does emit photons, but it’s not a resonant process

Even journal articles don’t aways contain all of the relevant information to do an experiment. Pop-sci articles contain far less, and tend to avoid precise language. You are free to ask questions about such articles. Extrapolation from them is the problem.

Thanks sir

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In case you are wondering about the design I went with the NASA design on the previous page. The gas is placed in a vacuum and since it moves around it should be uniformly cooled down to a certain temperature.

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In case you are wondering about the design I went with the NASA design on the previous page. The gas is placed in a vacuum and since it moves around it should be uniformly cooled down to a certain temperature.

All vapor BECs are in vacuum; there’s nothing special about that (and one reason why you can’t do this on the cheap). Moving around isn’t why it’s at a uniform temperature.

What did I just say about a pop-sci article? The physics is not explained. You can’t extrapolate from the information that’s been filtered through the reporter. They rarely explain if something is generally true or specific to the situation they’re reporting on.

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10 minutes ago, swansont said:

All vapor BECs are in vacuum; there’s nothing special about that (and one reason why you can’t do this on the cheap). Moving around isn’t why it’s at a uniform temperature.

What did I just say about a pop-sci article? The physics is not explained. You can’t extrapolate from the information that’s been filtered through the reporter. They rarely explain if something is generally true or specific to the situation they’re reporting on.

Hmm, I need to review the concept of laser cooling. To me it sounds a bit like MRI. If I want to confine atoms at a place I use a magnetic field, then I apply radio wave to make the precession goes faster, I wonder if I can get it to move slower. The problem is the molecules need to be magnetically charged, like H2O

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Hmm, I need to review the concept of laser cooling. To me it sounds a bit like MRI.

No, not really.

If I want to confine atoms at a place I use a magnetic field, then I apply radio wave to make the precession goes faster, I wonder if I can get it to move slower. The problem is the molecules need to be magnetically charged, like H2O

The confining force in a magneto-optic trap comes because photons have momentum. You put lasers along all six directions (+/-  for x, y and z) The magnetic field means the light causing confinement is closer to resonance. so you get more light being absorbed that gives a force toward the trap center.

The recoil of a visible photon changes the speed of an atom of order 1 cm/sec. MRI uses photons perhaps a million times less energetic.

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34 minutes ago, swansont said:

No, not really.

The confining force in a magneto-optic trap comes because photons have momentum. You put lasers along all six directions (+/-  for x, y and z) The magnetic field means the light causing confinement is closer to resonance. so you get more light being absorbed that gives a force toward the trap center.

The recoil of a visible photon changes the speed of an atom of order 1 cm/sec. MRI uses photons perhaps a million times less energetic.

Well, for MRI the water molecule is confined by the magnetic field because it is polarized. I will post how MRI works here(https://science.howstuffworks.com/mri.htm). And my emphasis is on the part precisely about the magnetic moment.

Now what matters about laser cooling is the absorption wavelength. Please refer to this video(I know you hate videos = = )

Now since I have water molecules confined at a location with magnetic field, and I know it absorbs radio wave shown in how stuff works. I can just tune the radio wave to slightly above the absorption wavelength of a still water molecule. And since I do not know how wave works I will place the radio wave on all 6 directions relative to the water molecules. It probably takes a few hour to cool but water molecules do absorb radio wave.

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Well, for MRI the water molecule is confined by the magnetic field because it is polarized

That is not my understanding of the working of MRI or othr NMR machines, nor how it is described in your link.

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14 minutes ago, studiot said:

That is not my understanding of the working of MRI or othr NMR machines, nor how it is described in your link.

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So how is it 'confined' ?

In MRI the water is confined within the patient.

What do you think the R stands for in MRI PRI and NMR  ?

Edited by studiot
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55 minutes ago, studiot said:

So how is it 'confined' ?

In MRI the water is confined within the patient.

What do you think the R stands for in MRI PRI and NMR  ?

R goes for resonance. Yes confined means keeping a lion in a cage. I am thinking of keeping the water molecules "line up" with magnetic field then reduce the rotational transitions with microwave thereby cooling its temperature. Radio wave also has momentum so you do not need a laser to do this. Now when it comes to water suspension in mid air, well still thinking about that, I am not sure if I need a capacitor(electric field) for water molecules suspension in mid air(I can use some help on this). Then there is the choice of rubidium(light goes dimmer), or stopping the photon molecules in BEC, two different types of photons storage. But if I switch to rubidium right now I have to worry about another wavelength of electromagnetic absorption for cooling it without using a laser. Anyway the idea is.

1. Use radio wave/microwave for cool down because it covers more surface area than the laser. But radio wave/microwave has limited spectrum.

2. Use a magnetic field to line up the water molecules and slow down their rotational transitions(I dunno about vibrational transitions, depends on how low the temperature goes).

P.S. You asked me how to get it to one meter so I am showing my ideas

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Well, for MRI the water molecule is confined by the magnetic field because it is polarized.

In MRI the water is confined because it’s in an organ. Magnetic trapping isn’t involved.

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Now what matters about laser cooling is the absorption wavelength. Please refer to this video(I know you hate videos = = )

I’ve been doing laser cooling for almost 30 years. I like physicsgirl and veritasium videos (I met Derek once, several years ago) but I’m not going to learn any experimental details from watching this.

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Now since I have water molecules confined at a location with magnetic field, and I know it absorbs radio wave shown in how stuff works. I can just tune the radio wave to slightly above the absorption wavelength of a still water molecule.

In laser cooling you tune below the resonance, so the doppler shift moves you closer to resonance.

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And since I do not know how wave works I will place the radio wave on all 6 directions relative to the water molecules. It probably takes a few hour to cool but water molecules do absorb radio wave.

Laser cooling works because the light slows the atom down - the absorption is from one direction, so there’s always a momentum “kick” from that direction. The momentum kick from the emissions cancel, because it’s isotropic. You don’t have this arrangement in MRI. Or the same magnetic field arrangement

(and we haven’t discussed the problem of optical pumping yet)

R goes for resonance. Yes confined means keeping a lion in a cage. I am thinking of keeping the water molecules "line up" with magnetic field then reduce the rotational transitions with microwave thereby cooling its temperature. Radio wave also has momentum so you do not need a laser to do this. Now when it comes to water suspension in mid air, well still thinking about that, I am not sure if I need a capacitor(electric field) for water molecules suspension in mid air(I can use some help on this). Then there is the choice of rubidium(light goes dimmer), or stopping the photon molecules in BEC, two different types of photons storage. But if I switch to rubidium right now I have to worry about another wavelength of electromagnetic absorption for cooling it without using a laser. Anyway the idea is.

1. Use radio wave/microwave for cool down because it covers more surface area than the laser. But radio wave/microwave has limited spectrum.

2. Use a magnetic field to line up the water molecules and slow down their rotational transitions(I dunno about vibrational transitions, depends on how low the temperature goes).

P.S. You asked me how to get it to one meter so I am showing my ideas

You can suspend an atom in a vacuum system with laser cooling because there’s more than enough force (you can easily get 100 g’s of acceleration). How much of a force can you get with microwaves?

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52 minutes ago, swansont said:

In laser cooling you tune below the resonance, so the doppler shift moves you closer to resonance.

Laser cooling works because the light slows the atom down - the absorption is from one direction, so there’s always a momentum “kick” from that direction. The momentum kick from the emissions cancel, because it’s isotropic. You don’t have this arrangement in MRI. Or the same magnetic field arrangement

(and we haven’t discussed the problem of optical pumping yet)

Well first of all, respect for your 30 years working on laser cooling @@

Well I was not referring to the magnetic field for MRI, I was referring to the radio wave emitted from the antenna.

So if I imagine I have like 6 antenna in 6 directions(if not 8), beaming at rubidium molecules in a vacuum emitting radio frequency pulse slightly below the rubidium absorption spectrum, would that suffice for laser cooling?

Thanks for taking the time to answer my question

And ya, I am working out the absorption frequency

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Well first of all, respect for your 30 years working on laser cooling @@

Well I was not referring to the magnetic field for MRI, I was referring to the radio wave emitted from the antenna.

I was referring to the magnetic field for MRI, to point out that it’s not what you need for cooling.

So if I imagine I have like 6 antenna in 6 directions(if not 8), beaming at rubidium molecules in a vacuum emitting radio frequency pulse slightly below the rubidium absorption spectrum, would that suffice for laser cooling?

For Rb? I expect the photon transition rate would be lower, and the photon momentum is smaller, as compared to laser cooling. I doubt you get significant cooling.

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