swansont Posted January 8, 2008 Posted January 8, 2008 From refrigeration to BECs. Two-part special, scheduled Jan 8th and 15th http://www.pbs.org/wgbh/nova/zero/index.html "The two-part special follows the quest for cold from the unlikely father of air-conditioning, the court magician of King James I of England in the 17th century, to today's scientists pioneering superfast computing in the quantum chill near absolute zero" The second part will be about the more recent advances Ultracold atom Q&A with Luis Orozco (U. Md, formerly at Stony Brook) http://www.pbs.org/wgbh/nova/zero/atoms.html
thedarkshade Posted January 8, 2008 Posted January 8, 2008 I don't really think absolute zero will ever be reached! There must something colder than that so you can create the temperature balance. I still have not heard of something as cold as or colder than 0K. Even the average temperature of the universe is not that cold (average +3.15 K)
insane_alien Posted January 8, 2008 Posted January 8, 2008 you can cool things below ambient easily with lasers. i think swansont does it.
insane_alien Posted January 8, 2008 Posted January 8, 2008 no, but only because of quantum mechanical effects. namely the heisenberg uncertainty principle. its the only thing holding us off 0K
iNow Posted January 8, 2008 Posted January 8, 2008 I like NOVA quite a lot and am looking forward to this set of episodes. Thanks for the tip, swansont.
swansont Posted January 8, 2008 Author Posted January 8, 2008 I don't really think absolute zero will ever be reached! I think almost everybody who's taken basic physics would agree with you. you can cool things below ambient easily with lasers. i think swansont does it. Yes, but "simple" laser cooling stop at about a microKelvin (Doppler and then polarization-gradient cooling). The program goes on to even colder states with BEC, which add in evaporative cooling in a magnetic trap to achieve the colder temperatures (nanoKelvin-ish). It looks like all of that material will be on the second program.
thedarkshade Posted January 8, 2008 Posted January 8, 2008 There is just one more things swansont. Today I was reading a script my Richard Muller called "Atoms and Heat" (part of a physics course), and it was there where I read that the average temperature of universe is -270 C, but it also was said that due to expansion of the universe, this average is expected to decrease further. So is there any possibility that absolute zero could be reached in a "natural way"? Cheers, Shade
swansont Posted January 8, 2008 Author Posted January 8, 2008 There is just one more things swansont. Today I was reading a script my Richard Muller called "Atoms and Heat" (part of a physics course), and it was there where I read that the average temperature of universe is -270 C, but it also was said that due to expansion of the universe, this average is expected to decrease further. So is there any possibility that absolute zero could be reached in a "natural way"? Cheers, Shade It's the asymptote for infinite expansion after infinite time. You'll never quite get there.
thedarkshade Posted January 8, 2008 Posted January 8, 2008 It's the asymptote for infinite expansion after infinite time. You'll never quite get there. I found it interesting because when I'd read Kaku's Visions, he said we were possibly gonna die on fire (we = earth), but after reading this script today it said we were gonna die in cold (a.k.a. Cold Death). So I wondered if we were gonna die in fire or ice? But we're gonna die anyway, so why bother! Thnx for reply
Realitycheck Posted January 8, 2008 Posted January 8, 2008 It's the asymptote for infinite expansion after infinite time. You'll never quite get there. Is it really reasonable to believe that the universe will expand infinitely? I mean, everything has its limits. Doesn't a photon die at some point? Frankly, I have a hard time seeing how it takes 13 billion years for the CMBR to cool down to 2.75 K given that the surrounding empty space is absolute zero. Is this one of those heat transfer issues where you have to have matter to absorb the heat?
swansont Posted January 8, 2008 Author Posted January 8, 2008 To what "surrounding empty space" do you refer? There is no "outside the universe."
thedarkshade Posted January 8, 2008 Posted January 8, 2008 Is it really reasonable to believe that the universe will expand infinitely? I mean, everything has its limits. Doesn't a photon die at some point? Frankly, I have a hard time seeing how it takes 13 billion years for the CMBR to cool down to 2.75 K given that the surrounding empty space is absolute zero. Is this one of those heat transfer issues where you have to have matter to absorb the heat? First, universe has no limits. In its very basic sense, it is infinite. And universe is predicted to expand forever. Some time ago I heard that dark matter could serve as a glue between galaxies and that at some point it could bring them all together, but there just seems not to be enough. So what's left to say it that universe is expanding, and as far as we know, it will expand forever!
Realitycheck Posted January 8, 2008 Posted January 8, 2008 I have a really hard time with infinity. The Law of Conservation of Mass and Energy dictates that there is no such thing as infinity.
ydoaPs Posted January 8, 2008 Posted January 8, 2008 The Law of Conservation of Mass and Energy dictates that there is no such thing as infinity. Oh? How so?
thedarkshade Posted January 8, 2008 Posted January 8, 2008 I have a really hard time with infinity. The Law of Conservation of Mass and Energy dictates that there is no such thing as infinity. Well I suggest you to get used with it, because after all, it is that way how our universe is. If you have any other opinion about the limits of universe, we'll all be very glad to hear. Cheers, Shade
Realitycheck Posted January 9, 2008 Posted January 9, 2008 Oh? How so? Well, if they can make a conclusion that 80% of the universe's matter is missing (dark matter), then they have to have some way of computing the total amount of mass. The total amount of mass is not an infinite number, because x/80% does not equal infinity. I was thinking that the calculation was maybe derived using Big Bang numbers, though I might be wrong. Either way, it all has to add up to some arbitrary number.
iNow Posted January 9, 2008 Posted January 9, 2008 For those looking for an on topic post... The show begins in about five minutes.
timo Posted January 9, 2008 Posted January 9, 2008 no [to the possibility of reaching 0 K], but only because of quantum mechanical effects. namely the heisenberg uncertainty principle. its the only thing holding us off 0K At least from the theory side, QM has nothing to do with this impossibility.
5614 Posted January 9, 2008 Posted January 9, 2008 I found it interesting because when I'd read Kaku's Visions, he said we were possibly gonna die on fire (we = earth), but after reading this script today it said we were gonna die in cold (a.k.a. Cold Death). So I wondered if we were gonna die in fire or ice?No one knows. If the average density of the universe is below some critical value then gravity will never get a "grip" on the universe as a whole and we will expand forever, a cold death. If the density of the universe is above this critical value then there is enough matter to allow gravity to slow, stop and then reverse the current expansion of the universe. A "hot" death.
John Cuthber Posted January 9, 2008 Posted January 9, 2008 "Well, if they can make a conclusion that 80% of the universe's matter is missing (dark matter), then they have to have some way of computing the total amount of mass. The total amount of mass is not an infinite number, because x/80% does not equal infinity." The mass of the universe can be finite without saying anything about how big it is.
thedarkshade Posted January 9, 2008 Posted January 9, 2008 No one knows. If the average density of the universe is below some critical value then gravity will never get a "grip" on the universe as a whole and we will expand forever, a cold death. If the density of the universe is above this critical value then there is enough matter to allow gravity to slow, stop and then reverse the current expansion of the universe. A "hot" death. I thought that it had something to do with dark matter. I mean, dark matter is somehow like a glue that keeps galaxies together (right?), and that it could be the reason that it might pull the universe together back again, but there seems not to be enough dark matter (23%) compared to dark energy (73%) which actually is speeding up the universe expansion!
Realitycheck Posted January 12, 2008 Posted January 12, 2008 I thought that dark matter was unaggregated remnants of the Big Bang, "dust" left over that didn't congregate into stars and galaxies.
swansont Posted January 12, 2008 Author Posted January 12, 2008 I thought that dark matter was unaggregated remnants of the Big Bang, "dust" left over that didn't congregate into stars and galaxies. No. Most Dark matter is, and has to be, non-baryonic http://math.ucr.edu/home/baez/physics/Relativity/GR/dark_matter.html
swansont Posted January 15, 2008 Author Posted January 15, 2008 A reminder that Part II is tonight. The good stuff: ludicrously cold atoms.
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