This professor, Dr. Bowley I believe is his name, is so gifted in teaching science. He may never see this comment, but I just started teaching labs as a graduate student and I have been constantly studying Dr. Bowley's teaching through Sixty Symbols. It is amazing.
1 Baff is the amount of work needed to bring a particle reacting to light of 671.005 nm into a state where it instead reacts to light of 671.000 nm. It is all explained in the video :D And it ffints nicely into the SI system where every unit is calibrated to basic laws of physics.
does this mean, if you accidentally start with a laser frequency that's too *low*, you'd heat them up instead? since they might catch the light as they're moving away from it instead of towards it?
No expert but I found somewhere that they almost immediately release a photon afterwards in a random direction, with a tiny bit more momentum than the original photon, thus everything is conserved.
Alex is right, in fact this results in a cap to the amount of cooling you can achieve with lasers alone. This cap is called the "Doppler Limit". We can, however, cool atoms past the doppler limit by adding things like an external magnetic field as in a MOT (magneto optical trap), and polarization gradient cooling which uses polarized laser light to further cool atoms.
I believe he's retired now. I think there's a video on it called "The Retired Professor." I liked any time he made an appearance on this channel too ;)
This may or may not be relevant but I think it's inverted temperature rather than actually physically bringing it down in steps below zero, so not the intuitive thought of below zero, probably something much different. I can't post a link to the article directly but google "temperature below absolute zero' and you should have some good leads.
@bmbirdsong There's no such thing as an 'absence of molecular motion'. Molecules will still possess a zero-point energy, and can never reach absolute zero. On the other hand vibrational energy levels go from v=0 to v=∞, so there is no maximum temperature. Or put another way, to get something to the speed of light would require infinite energy. Thus unless you can get to ∞°C you won't get an atom/electron or any particle with mass to the speed of light.
@gamesbok The photon is absorbed by the atom and an electron goes to an excited state. The electron goes back to the ground state and a photon is emitted isotropically, that is all directions of emission are equally probable. On the average (the photon can be emitted in any direction) the atom loses momentum, and also a bit of its kinetic energy is taken away by the photon. Repeat the process ten thousand times and the atom slows down and nearly stops. A Nobel prize results for this idea.
@roidroid A laser beam has no entropy because the photons in a laser are in a single quantum state, S = k ln(W)=k ln(1) = 0. The gas of atoms is hot (say 800 K) and has a lot of entropy. The absorption and re-emission of photons by the atom leads to the photon gas having a lot of entropy (disorder) and the selected atoms having less entropy (they cool). Overall, entropy is increased in the process which is the basic law of thermodynamics. The scattered photons take away the energy.
i understand the mechanics of laser cooling, it's very interesting. but i don't understand it thermodynamically. I find it hard to wrap my brain around the fact that you are ADDING energy to a system, and it is not heating like you'd intuitively expect - but it is instead COOLING. My brain is left wondering... you can't obviously destroy the energy, so can someone please point to where it went? Does the room itself get hotter or something?
@hempseed57 That's what happens when you put bankers or certain families in control of everything. Apparently those bankers have a different moral. I agree that a good teacher should earn more money then a ball catcher. I guess that when you have too much well educated people that they are too hard to manipulate by the powers who are in control. George Carlin (R.I.P.) once made a show about that, it was on youtube, but even that video is removed, I guess he explained it too good.
@ByakuyaZERO No it is significant: this is where the kinetic energy of the atom is lost bit by bit so that the atom loses its kinetic energy. It recoils when it absorbs the photon and goes into an excited state; then it re-emits a photon which can go in any direction so on the average there is no recoil, and some of the kinetic energy is lost. Also the entropy of the gas goes goes down as well as it cools, but the entropy (disorder) of the photons increases so all is well.
I don't want to sound stupid but if you could cool something that much, like gasses, lets just say nitrogen gas, would there be a way to scoop the nitrogen in the air and being that cold even work as a superconductor in the weakest of magnetic fields? I am just trying to fly > that's all ! lol
@bmbirdsong v=0 is just the vibrational quantum number. This isn't equal to T=0 or absolute zero. The reasons behind this are pretty complex, but it's due to anharmonic properties of molecular vibrations and fun things like that. Wikipedia is your friend on this. :)
If absolute zero is the absence of molecular motion, is there a corresponding opposite temperature? A point beyond which you can no longer add heat to a system? Would that be the temperature of gas molecules moving at the speed of light?
@elflordbob1 Why would that be? I would imagine converting energy into matter would only occur at very high energies, even if it's an unknown form of matter. Though I suppose dark matter particles could be of very low mass...
I thought it's impossible to take out the energy of the matter by sending there a lot of energy. Ok. Today I get it about the only frequency. But I still have question: So why laser can heat things? I doubt every laser works for every atom in any material. Why? Why usual lasers surely give heat to anything without any frequency math?
In the UK, ambulances go dee dah dee dah dee dah. In the US they go weeeeeeEEEAAAAaaaaaaaaaaa weeeeeeEEEAAAAaaaaaaaaaaa wrow wrow wrow wrow wrow weeeeeeEEEAAAAaaaaaaaaaaa.
So this Bose-Einstein-condensate is described by a single quantummechanical wave funktion. But wouldn't that mean that the gas could tunnel through things?
plank temperature , althought photons do travel at light speed, they don't have plank temperature. temperature is just a measure of how much "jiggling" there is in a substance, if you had an atom moving in a PERFECT straight line in a vacuum, from the inertial frame of the atom, it would be at zero kelvin, regardless of what relative liniar speed it has. but that's the thing, atoms don't move in straight lines, quantum fluctuation prevent matter from reaching 0 K.
I viewed this movie since I got genuinely concerned with the economy and had no clue how to cope. Dough does not mean a single thing nowadays. So I decided to do some exploration and ran into Goldiverse. I\'m certainly so fortuitous, I can switch my money from cash to all the major currencies, to any precious metal whenever I would like. The governing administration can go and take a jump for all I care. Just Yahoo and google it Goldiverse.
Yes, that is correct. When the photon hits the atom it does so with some momentum, this will impact the movement of the atom slightly,thus slowing it down. In doing so the photon causes an electron jump into a higher energy state, and because electrons don't like being in this state it will return to its original energy level, though the emission of energy, taking the form of a photon...
@anonymousbl00dlust I also am not an expert. I think, that when the photon hits it slows the atom down. Then the photon is re-emit in a random direction and will gain momentum again, but since it does this a lot of times and the direction is random it will equal out at some time and only the slowing down effect of the photon hitting will matter, because it always hits from the same direction. Someone pleas correct me if I'm wrong.
so you shoot a photon that has a certain amount of energy into another moving particle that has energy and and the resulting energy is less because the energy difference is stored in the particle itself by exciting an electron? is that correct? if not where does the energy go? and isnt the particle eventually going to go back into its ground state and emit a photon and thus start moving again? i hope i can get some answers! thanks for the great videos!! keep it up!!
OK, so you reduce the momentum of the atom by hitting it with a photon, and drive the electron into a higher energy state. I presume then the electron then drops back releasing a photon that doesn't get absorbed. Otherwise you're just pumping energy in. No way will you cool it. I would have thought the new photon was exactly the right wave length to get absorbed. I don't understand.
@roidroid This is one of the things that's bugging me. The other one is. If you hit an atom with a photon of the right frequency, the energy of the photon is used to shift an electron of that atom to the higher orbit. If that's so, then where did the energy which slowed down the whole atom come from? To me it seems that the atom should do exactly the opposite. It should absorb the photon when frequency is correct, without affecting atoms speed, and reflect it when it's not correct.
@UriaHammonRaviel Sadly scientists on the other hand are not valued as much by the general population (and perhaps not in a sshort supply as top flight sportspeople) so millions of people will not spend a good portion of their disposable income to watch and support the work of scientists. So by the actions of the population in general they are considered to be less valuable and will inevitably be paid less.
@hempseed57 They aren't arbitrarily getting payed millions for catching a ball, the public demand their services (i.e. enjoy watching them play) and through their spending on TV subscriptions, tickets and companies products advertised at games are indirectly paying them those high wages. In short sports stars only get paid as much as they can make for their clubs and sponsors via peoples desire to see them play.
@RupertsCrystals I think he said the energy of the photons when absorbed by the atoms turn into the "momentum" of their electrons, making the atoms change into an excited state. The professor said there's a recoil or "nudge" or "push" whenever this happens. What I want to know is: how do photons -massless- hitting an atom have an effect on its kinetic energy? Why do the lithium atoms slow down when they become excited?
@hempseed57 Because people are willing to pay $125 for one ticket to watch them. If every one stopped watching sports and attending them, then you would see that they wouldn't pay them that kind of money. But how many people would line up and pay $125 to watch a live experiment run by scientist? People pay money to be entertained. It is just the way the world works. It's a human thing.
One thing I don't understand: once the atom has absorbed a photon, it is indeed slowed down since it has received the impulsion of the photon which was going in the opposite direction. Ok, but at some point the atom must reemit this photon, doesn't it? And then it will get a recoil and thus regain the lost impulsion, won't it?
@anonymousbl00dlust The photon energy is actually lower than is necessary to excite the atoms electrons, but when the atoms are moving towards the photon source the doppler effect causes the atoms electrons to essentially be fooled into being exciting. The atoms slow down 3:40. To be honest I'm not an expert either.
ok, so they've figured out how to stop, identify and seperate atoms. AWESOME! now we can figure out how to construct the atoms into the most accurate copies of anything we've ever made... atom by atom. Any one ever seen fifth element? Remember the table with glass shell she was regenerated in? Could we do this using this technology to collect all the atoms needed?
@hempseed57 I know it's sad really, if I could change the world I would reward inventors, scientists, researchers and doctors the most. Although these people are usually so nice that money is not a motivation for them and they do it to learn, extend human knowledge and better our world; Unlike douche bag footballers that are self obsessed and greedy. End of rant lol.
Question: So the atom gets exited and gets slown down due to a "recoil".but does the atom emit an EM-wave with a higher frequentie than the incoming laser light frequentie ? because you'd otherwise be losing energy because the kinetic energy of the atom gets smaller. Hope my question is clear :p
Basically it's a theory that states that as you pass below absolute 0, (you cannot obtain 0, itsself, either +/- temperatures) that as you make the temperature more negative, entropy decreases rather than increases. It's not quite the natural way of thinking about 'temperature'
@IngeniousSheep the atom does absorb the photons, and later the spontaneous emission of these photons will contribute to cooling atoms, while induced emission of such photons does not help. Wiki page about "laser cooling" gives same explanation as seen in the "Doppler cooling" part.
@xXmatthdXx That seems unlikely. You need a gas or at least a liquid for this to work. On a CPU, which is opaque, you could at best shoot lasers on it from the top etc., but not from all directions, and the laser wouldn't reach into the CPU very far (or at all).
Mass and energy are interchangeable so you just look for the energy required for a particle to have an effective mass so great the particles individual gravity causes the escape velocity from the particle is greater than the speed of light.
only in the very rare event (technically impossible) that the atom re-emits the photon in exactly the opposite direction in which it was absorbed. Which is essentially just like the photon and atom not interacting at all
So how do they fine-tune the laser frequency as they hit the atoms?....if i understood the basic idea correctly, the laser frequency constantly has to undergo a change to match the atom's frequency to cool it...
Of what kind is the energy the exited atoms give of? I guess it is light, too. But wouldn´t this light again give energy to the system... So I guess my question really is: How does the energy leave the system?
I heard that at the temperature of 1.41x10^32K the wavelength of the radiation which is emitted by the atom reaches the planck length... So if it's getting more energy we don't call it temperature anymore.
What is the point of the first table? Why use mirrors to send the laser beam all over the place and then direct it into a fibre-optic cable? Why not just direct the original source into the cable?
I understand mostly everything going on here with the doppler effect and the shifts which occur, but why do the photons add on once the particle matches the frequency of the laser?
if movement of atoms mean temperature, then there have to be a maximum temperature because atoms can't move at the speed of light right? what's that temperature limit?
It's good that if we know the resonance frequency of solid water molecules, then we would turn them into liquid water? If we could then there is no more messy winter :)
Doesn't photo electric emission take place when you but the Na atoms with photons of the correct frequency? Also, why are sodium or rubidium chosen for the experiment?
In terms of momentum transfer, makes sense. Still, in terms of energy, it seems like energy is being added to the system, yet temperature goes down. I need some maths
Do the atoms that absorb the photons eventually release the energy from their excited state? I imagine once they're pretty slow, they would have had been quite excited
@mr0myster Yes! Also it is improper to state "degrees kelvin" Both rules are often broken. It is sufficient to state "zero kelvin" without the absolute or the degrees.
What's the point of all the mirrors and lenses etc. if all that ends up happening is the lasers get routed through a fiber optic cable to some other spot? The lasers are already, presumably, coherent and everything, so what more needs to be done?
+Ryan Lanzetta There is just one laser, but they need many beams from all directions... The apparatus is meant to split the beam into many beams that are then routed to the cooling chamber...
+Jake K. I don't think coherence is the major issue here. The reason one laser is used is because the laser used here is expensive piece of equipment - so a mirror assembly is just more economical than having three lasers!
Also, as I understand from the video, if a different frequency is needed, there's some arrangement that can shift the frequency of the laser a tiny bit.
If the atoms absorb the photon and get into an exited state, why don't they drop back to base state, by emitting the photon again? That would give them more speed again...
you know if I brought a scientist from 50 yers in the future and showed him this laser cooling system he would say that this is an antique and hopefully he would have showed me a design of a laser cooler that would fit in a small refrigerator
If the power of the lasers goes into the chamber how does all that power gets out, and some more, to not violate the thermodynamics laws? Otherwise, the temperature would rise...
So if you have a laser cooling something very cold, and a laser heating something very hot, you could create a heat-exchanger (peltier arrangement) that allows you to re-capture the energy?
It seems that one of the biggest enemies of cooling atoms to fractional Kelvin temperature scales is not so much the physics of doing so, but the amount of time it takes to do it. Some experiments involving these temperature scales can take hours, days or even months to reach their conclusion, and the amount of time it takes to do it when you get below 1K seems to vary inversely with the temperature they want to achieve.
i have a question if anyone knows the answer, now we hit the atom with photons in the opposite direction of the atom's motion to slow it down. but in this direction due to doppler shift the atom sees a frequency closer to its resonance frequency o it will absorb it. so what about its emission? i mean that it still absorb energy and re-emit it dost these collision due to compton effect that we consider this atom like a free particle that absorbs part of the photons energy and changes in its momentum ?
Still, this doesn't mean you cannot create a laser-cooled computer. This just brings forth the many downsides to cooling a computer in this way yet it could, theoretically, still be accomplished.
This professor, Dr. Bowley I believe is his name, is so gifted in teaching science. He may never see this comment, but I just started teaching labs as a graduate student and I have been constantly studying Dr. Bowley's teaching through Sixty Symbols. It is amazing.
+sigalig I 100% agree. I think that he is one of the most gifted teachers! Bless his soul!
I didn't realize scientist's had souls...i thought they removed their souls, at a young age, through the proper application of logic and experiment.
The best scientists have souls, it's the only way to think for yourself.
How dare you put atoms in a cage?! P.E.T.A. will hear about this!
1 Baff should be a new SI unit of momentum
We should change everything else to fit with the baff more nicely.
eg: Units of force: *baffs per second*.
It would actually be an unit of work or impulse.
1 Baff is the amount of work needed to bring a particle reacting to light of 671.005 nm into a state where it instead reacts to light of 671.000 nm.
It is all explained in the video :D
And it ffints nicely into the SI system where every unit is calibrated to basic laws of physics.
But what is the first most enjoyable thing that you know Dr. Bowley? :-)
+P Bryce Alaska King Crab Legs is my guess. . . . .
Didn't get the vid but his last sentence stuck with me. Maybe he just wanted us all think about whats most enjoyable to us personally. So romantic!
Too much switching between the lab and the office, irritating!
Apple should integrate cooling lasers into the notebooks that get my thighs 2nd degree burns
How long 'til I can put one in my PC? :P
Have they tried forming a condensate with rubidium to compare it to the lithium condensate?
LAZERS caution LAZERS caution LAZERS caution LAZERS caution
Igotthatreference.wav
Jonesmin For those who didn't get that reference, two things: Half Life 3 confirmed, and, watch the "playthrough" : Freeman's Mind - Episode 3
@cabrita309 Thanks... I like this comment! ;)
does this mean, if you accidentally start with a laser frequency that's too *low*, you'd heat them up instead? since they might catch the light as they're moving away from it instead of towards it?
sex is the first
Where does the kinetic energy of the atoms go? When they absorb the laser photons doesn't it just put them into an excited state?
No expert but I found somewhere that they almost immediately release a photon afterwards in a random direction, with a tiny bit more momentum than the original photon, thus everything is conserved.
Alex is right, in fact this results in a cap to the amount of cooling you can achieve with lasers alone. This cap is called the "Doppler Limit". We can, however, cool atoms past the doppler limit by adding things like an external magnetic field as in a MOT (magneto optical trap), and polarization gradient cooling which uses polarized laser light to further cool atoms.
"..and an electron comes in and BAFs me..."
what happened to this guy? he is great! more vids with him if he is still physicsing around please.
he IS great
I think it's pronounced "physicsanating"
I believe he's retired now. I think there's a video on it called "The Retired Professor." I liked any time he made an appearance on this channel too ;)
"getting JIGGLY with it", Dr. Bowley's favorite song :)
- How cool is to put your name on a bizarre state of matter?
+ Bose-Einstein cool
- That would be my first most enjoyable thing
Did you ever get those sharks with lazer beams on their freakin' heads?
1:05 he is more violent than a atom
This may or may not be relevant but I think it's inverted temperature rather than actually physically bringing it down in steps below zero, so not the intuitive thought of below zero, probably something much different. I can't post a link to the article directly but google "temperature below absolute zero' and you should have some good leads.
@bmbirdsong There's no such thing as an 'absence of molecular motion'. Molecules will still possess a zero-point energy, and can never reach absolute zero. On the other hand vibrational energy levels go from v=0 to v=∞, so there is no maximum temperature. Or put another way, to get something to the speed of light would require infinite energy. Thus unless you can get to ∞°C you won't get an atom/electron or any particle with mass to the speed of light.
@gamesbok
The photon is absorbed by the atom and an electron goes to an excited state. The electron goes back to the ground state and a photon is emitted isotropically, that is all directions of emission are equally probable. On the average (the photon can be emitted in any direction) the atom loses momentum, and also a bit of its kinetic energy is taken away by the photon. Repeat the process ten thousand times and the atom slows down and nearly stops. A Nobel prize results for this idea.
@roidroid
A laser beam has no entropy because the photons in a laser are in a single quantum state, S = k ln(W)=k ln(1) = 0. The gas of atoms is hot (say 800 K) and has a lot of entropy.
The absorption and re-emission of photons by the atom leads to the photon gas having a lot of entropy (disorder) and the selected atoms having less entropy (they cool). Overall, entropy is increased in the process which is the basic law of thermodynamics. The scattered photons take away the energy.
i understand the mechanics of laser cooling, it's very interesting.
but i don't understand it thermodynamically. I find it hard to wrap my brain around the fact that you are ADDING energy to a system, and it is not heating like you'd intuitively expect - but it is instead COOLING.
My brain is left wondering... you can't obviously destroy the energy, so can someone please point to where it went? Does the room itself get hotter or something?
@hempseed57 That's what happens when you put bankers or certain families in control of everything. Apparently those bankers have a different moral. I agree that a good teacher should earn more money then a ball catcher. I guess that when you have too much well educated people that they are too hard to manipulate by the powers who are in control. George Carlin (R.I.P.) once made a show about that, it was on youtube, but even that video is removed, I guess he explained it too good.
@ByakuyaZERO
No it is significant: this is where the kinetic energy of the atom is lost bit by bit so that the atom loses its kinetic energy. It recoils when it absorbs the photon and goes into an excited state; then it re-emits a photon which can go in any direction so on the average there is no recoil, and some of the kinetic energy is lost.
Also the entropy of the gas goes goes down as well as it cools, but the entropy (disorder) of the photons increases so all is well.
I don't want to sound stupid but if you could cool something that much, like gasses, lets just say nitrogen gas, would there be a way to scoop the nitrogen in the air and being that cold even work as a superconductor in the weakest of magnetic fields? I am just trying to fly > that's all ! lol
@bmbirdsong v=0 is just the vibrational quantum number. This isn't equal to T=0 or absolute zero. The reasons behind this are pretty complex, but it's due to anharmonic properties of molecular vibrations and fun things like that. Wikipedia is your friend on this. :)
If absolute zero is the absence of molecular motion, is there a corresponding opposite temperature? A point beyond which you can no longer add heat to a system? Would that be the temperature of gas molecules moving at the speed of light?
@elflordbob1 Why would that be? I would imagine converting energy into matter would only occur at very high energies, even if it's an unknown form of matter. Though I suppose dark matter particles could be of very low mass...
I thought it's impossible to take out the energy of the matter by sending there a lot of energy. Ok. Today I get it about the only frequency. But I still have question:
So why laser can heat things?
I doubt every laser works for every atom in any material.
Why? Why usual lasers surely give heat to anything without any frequency math?
Atoms will accelerate if they are being hit by photons.
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In the US they go weeeeeeEEEAAAAaaaaaaaaaaa weeeeeeEEEAAAAaaaaaaaaaaa wrow wrow wrow wrow wrow weeeeeeEEEAAAAaaaaaaaaaaa.
So this Bose-Einstein-condensate is described by a single quantummechanical wave funktion.
But wouldn't that mean that the gas could tunnel through things?
Conan! What is best in life?
Crush your enemies. See them driven before you. Hear the lamentations of their women.
I wonder if there is any sort of "feedback" or detectable effect on the laser's side from the atoms resisting the force of the laser beams?
how much time it will take to make one ice cube for my wine peg. please tell sir. this is really good and new tech , experiment.
The first enjoyable being... CAKE! Lots of cake.
plank temperature , althought photons do travel at light speed, they don't have plank temperature.
temperature is just a measure of how much "jiggling" there is in a substance, if you had an atom moving in a PERFECT straight line in a vacuum, from the inertial frame of the atom, it would be at zero kelvin, regardless of what relative liniar speed it has.
but that's the thing, atoms don't move in straight lines, quantum fluctuation prevent matter from reaching 0 K.
I viewed this movie since I got genuinely concerned with the economy and had no clue how to cope. Dough does not mean a single thing nowadays. So I decided to do some exploration and ran into Goldiverse. I\'m certainly so fortuitous, I can switch my money from cash to all the major currencies, to any precious metal whenever I would like. The governing administration can go and take a jump for all I care. Just Yahoo and google it Goldiverse.
Yes, that is correct. When the photon hits the atom it does so with some momentum, this will impact the movement of the atom slightly,thus slowing it down. In doing so the photon causes an electron jump into a higher energy state, and because electrons don't like being in this state it will return to its original energy level, though the emission of energy, taking the form of a photon...
@anonymousbl00dlust I also am not an expert. I think, that when the photon hits it slows the atom down. Then the photon is re-emit in a random direction and will gain momentum again, but since it does this a lot of times and the direction is random it will equal out at some time and only the slowing down effect of the photon hitting will matter, because it always hits from the same direction. Someone pleas correct me if I'm wrong.
so you shoot a photon that has a certain amount of energy into another moving particle that has energy and and the resulting energy is less because the energy difference is stored in the particle itself by exciting an electron? is that correct? if not where does the energy go? and isnt the particle eventually going to go back into its ground state and emit a photon and thus start moving again? i hope i can get some answers! thanks for the great videos!! keep it up!!
OK, so you reduce the momentum of the atom by hitting it with a photon, and drive the electron into a higher energy state. I presume then the electron then drops back releasing a photon that doesn't get absorbed. Otherwise you're just pumping energy in. No way will you cool it. I would have thought the new photon was exactly the right wave length to get absorbed. I don't understand.
@roidroid This is one of the things that's bugging me.
The other one is. If you hit an atom with a photon of the right frequency, the energy of the photon is used to shift an electron of that atom to the higher orbit. If that's so, then where did the energy which slowed down the whole atom come from?
To me it seems that the atom should do exactly the opposite. It should absorb the photon when frequency is correct, without affecting atoms speed, and reflect it when it's not correct.
@UriaHammonRaviel Sadly scientists on the other hand are not valued as much by the general population (and perhaps not in a sshort supply as top flight sportspeople) so millions of people will not spend a good portion of their disposable income to watch and support the work of scientists. So by the actions of the population in general they are considered to be less valuable and will inevitably be paid less.
@hempseed57 They aren't arbitrarily getting payed millions for catching a ball, the public demand their services (i.e. enjoy watching them play) and through their spending on TV subscriptions, tickets and companies products advertised at games are indirectly paying them those high wages. In short sports stars only get paid as much as they can make for their clubs and sponsors via peoples desire to see them play.
@RupertsCrystals
I think he said the energy of the photons when absorbed by the atoms turn into the "momentum" of their electrons, making the atoms change into an excited state. The professor said there's a recoil or "nudge" or "push" whenever this happens.
What I want to know is: how do photons -massless- hitting an atom have an effect on its kinetic energy? Why do the lithium atoms slow down when they become excited?
@hempseed57
Because people are willing to pay $125 for one ticket to watch them. If every one stopped watching sports and attending them, then you would see that they wouldn't pay them that kind of money. But how many people would line up and pay $125 to watch a live experiment run by scientist? People pay money to be entertained. It is just the way the world works. It's a human thing.
One thing I don't understand: once the atom has absorbed a photon, it is indeed slowed down since it has received the impulsion of the photon which was going in the opposite direction. Ok, but at some point the atom must reemit this photon, doesn't it? And then it will get a recoil and thus regain the lost impulsion, won't it?
@anonymousbl00dlust
The photon energy is actually lower than is necessary to excite the atoms electrons, but when the atoms are moving towards the photon source the doppler effect causes the atoms electrons to essentially be fooled into being exciting. The atoms slow down 3:40. To be honest I'm not an expert either.
ok, so they've figured out how to stop, identify and seperate atoms. AWESOME! now we can figure out how to construct the atoms into the most accurate copies of anything we've ever made... atom by atom. Any one ever seen fifth element? Remember the table with glass shell she was regenerated in? Could we do this using this technology to collect all the atoms needed?
@hempseed57 I know it's sad really, if I could change the world I would reward inventors, scientists, researchers and doctors the most. Although these people are usually so nice that money is not a motivation for them and they do it to learn, extend human knowledge and better our world; Unlike douche bag footballers that are self obsessed and greedy. End of rant lol.
Question: So the atom gets exited and gets slown down due to a "recoil".but does the atom emit an EM-wave with a higher frequentie than the incoming laser light frequentie ? because you'd otherwise be losing energy because the kinetic energy of the atom gets smaller. Hope my question is clear :p
Basically it's a theory that states that as you pass below absolute 0, (you cannot obtain 0, itsself, either +/- temperatures) that as you make the temperature more negative, entropy decreases rather than increases. It's not quite the natural way of thinking about 'temperature'
@IngeniousSheep the atom does absorb the photons, and later the spontaneous emission of these photons will contribute to cooling atoms, while induced emission of such photons does not help. Wiki page about "laser cooling" gives same explanation as seen in the "Doppler cooling" part.
@xXmatthdXx
That seems unlikely. You need a gas or at least a liquid for this to work. On a CPU, which is opaque, you could at best shoot lasers on it from the top etc., but not from all directions, and the laser wouldn't reach into the CPU very far (or at all).
Mass and energy are interchangeable so you just look for the energy required for a particle to have an effective mass so great the particles individual gravity causes the escape velocity from the particle is greater than the speed of light.
But what about the releasing of the absorbed photon? I'd reckon this could again increase the momentum of the atoms.
only in the very rare event (technically impossible) that the atom re-emits the photon in exactly the opposite direction in which it was absorbed. Which is essentially just like the photon and atom not interacting at all
So how do they fine-tune the laser frequency as they hit the atoms?....if i understood the basic idea correctly, the laser frequency constantly has to undergo a change to match the atom's frequency to cool it...
Of what kind is the energy the exited atoms give of? I guess it is light, too. But wouldn´t this light again give energy to the system... So I guess my question really is: How does the energy leave the system?
I heard that at the temperature of 1.41x10^32K the wavelength of the radiation which is emitted by the atom reaches the planck length... So if it's getting more energy we don't call it temperature anymore.
What is the point of the first table? Why use mirrors to send the laser beam all over the place and then direct it into a fibre-optic cable? Why not just direct the original source into the cable?
When can I get one of these for my fridge? I HATE waiting for my beer to cool down...
I understand mostly everything going on here with the doppler effect and the shifts which occur, but why do the photons add on once the particle matches the frequency of the laser?
if movement of atoms mean temperature, then there have to be a maximum temperature because atoms can't move at the speed of light right?
what's that temperature limit?
It's good that if we know the resonance frequency of solid water molecules, then we would turn them into liquid water? If we could then there is no more messy winter :)
Doesn't photo electric emission take place when you but the Na atoms with photons of the correct frequency? Also, why are sodium or rubidium chosen for the experiment?
In terms of momentum transfer, makes sense. Still, in terms of energy, it seems like energy is being added to the system, yet temperature goes down. I need some maths
Do the atoms that absorb the photons eventually release the energy from their excited state? I imagine once they're pretty slow, they would have had been quite excited
@mr0myster Yes!
Also it is improper to state "degrees kelvin"
Both rules are often broken.
It is sufficient to state "zero kelvin" without the absolute or the degrees.
What's the point of all the mirrors and lenses etc. if all that ends up happening is the lasers get routed through a fiber optic cable to some other spot? The lasers are already, presumably, coherent and everything, so what more needs to be done?
+Ryan Lanzetta There is just one laser, but they need many beams from all directions... The apparatus is meant to split the beam into many beams that are then routed to the cooling chamber...
+gibbetify
And you can't just use simply three lasers, because you have to keep the coherence and so on?
Is that right?
+Jake K.
I don't think coherence is the major issue here. The reason one laser is used is because the laser used here is expensive piece of equipment - so a mirror assembly is just more economical than having three lasers!
Also, as I understand from the video, if a different frequency is needed, there's some arrangement that can shift the frequency of the laser a tiny bit.
If the atoms absorb the photon and get into an exited state, why don't they drop back to base state, by emitting the photon again? That would give them more speed again...
thanks youtube for always sucking on the educational video upload speed. ugh
you know if I brought a scientist from 50 yers in the future and showed him this laser cooling system he would say that this is an antique and hopefully he would have showed me a design of a laser cooler that would fit in a small refrigerator
If the power of the lasers goes into the chamber how does all that power gets out, and some more, to not violate the thermodynamics laws? Otherwise, the temperature would rise...
Are those Radiant Dyes Laser Mirror-Mounts and a Toptica Photonics Laser.
I don't know about the first part, but the second part I believe is because sodium and rubidium both can form Bose-Einstein condensates.
So if you have a laser cooling something very cold, and a laser heating something very hot, you could create a heat-exchanger (peltier arrangement) that allows you to re-capture the energy?
shades2 Some of it. It's a cool experiment, but it won't be free energy.
Ramp up the power and make a keuglblitz!
Doesn't the slowing down cause atoms to emit photons rather than absorb photons?
DailyFrankPeter yes. but first they get nailed by one then let it go.
Wouldnt the atoms in excited state eventually go back to their original state by releasing a photon and thus speeding up again?
@CRUK87 probably because.. the mirrors are altering the wave pattern by splitting and interference at the quantum level. :s
They let all the energy out. After a photon is absorbed, it just ends up emitted again. That light can escape the system.
@bugmenever yes i wonder whats his first most enjoyable thing lol
I know all that jazz. But the spot where the laser hits, would usually reflect enough to damage a persons eyesight.
I'm really glad someone busted him on this most egregious offense. No one should take this man seriously. Thank you.
It seems that one of the biggest enemies of cooling atoms to fractional Kelvin temperature scales is not so much the physics of doing so, but the amount of time it takes to do it. Some experiments involving these temperature scales can take hours, days or even months to reach their conclusion, and the amount of time it takes to do it when you get below 1K seems to vary inversely with the temperature they want to achieve.
the time scale for the actual cooling is very short due to the number of photons emitted compared to the number of collision needed
Not as good as the call of duty montages you're used to, huh kid?
"Besides... its the second most enjoyable thing that I know" Class Quote.
And LFZ15 one thinks that was implied.
It took them way too long to explain something so simple. The guy repeating himself over and over didn't help any.
i have a question if anyone knows the answer, now we hit the atom with photons in the opposite direction of the atom's motion to slow it down. but in this direction due to doppler shift the atom sees a frequency closer to its resonance frequency o it will absorb it. so what about its emission? i mean that it still absorb energy and re-emit it dost these collision due to compton effect that we consider this atom like a free particle that absorbs part of the photons energy and changes in its momentum ?
Now only if they could prove this theory worked on hot metal radiating at 4000'F then my mind would be baffled
I wonder if you could make a laser cooled computer?
Quark cheese being the first. Sad. But delicious.
@mr0myster Oh, and excuse my god awful English. It's too late of an hour to think in foreign languages :P
Still, this doesn't mean you cannot create a laser-cooled computer. This just brings forth the many downsides to cooling a computer in this way yet it could, theoretically, still be accomplished.
Can someone tell me why atoms dont want to stop entirely? Or what prevents specifically? (Absolute zero)
You've trapped your lions in their cages, but I wonder if their behaviour's as negotiable in the wild.