Hmmn. Could be. But I reckon it's less about showing you're better than the other guy than showing you're good enough to keep being funded. Y'know, along the lines of "we can do this, this and this while they can only do that, that and maybe that. So you see we deserve the (limited amount of funding for what is essentially pure science) money, not them."
To the best of my knowledge, these missions are split between research in different countries on a who's-best-for-the-job type approach with all sorts of infighting and back biting for the larger portions of the pie. Pretty much like all academia really. And hey, sometimes standing up and shouting "Hey, see what I can do!" is the only way to go.
Even if they do look a bit daft when it doesn't work...
All true. But I'd recommend not trying it if you're a Type I diabetic (like myself). Unless you really know what you're doing with regard to insulin control and maintaining blood sugar levels, you'll end up in a bad way.
As far as I understand it - and I'll admit I'm no expert - the Atkins diet involves initially cutting out/down carbs for the first week or two. This should make the body use up stored energy (fats/general body mass) in an attempt to maintain normality. Then you switch onto a higher low carb intake as required. And do this for a few weeks before eating whatever you want again. Though by this time you'll stop missing the cakes and chocolates and sugary drinks. Anyone disagreeing with this may now proceed to flame my good name to the ends of the post and back. ^_^
Personally, I'll stick to my normal diet and a bit of good ol' fashioned exercise. Less effort all round. Now! Who's for a run down to the gym?
Ah, but you don't get them everywhere. Other countries (eg the UK) don't necessarily have 'em. I can't remember ever seeing one of the big green screen messages outside of the US - but then I'm not that well travelled. Anyone else any info on other countries?
Naw. A programmer is a person who doesn't use commas and brackets and hyphens and other non-essential parts of the english language which make things easier to understand than if they weren't used at all. *gasps for breath*
My excuse is that commas are in short supply and should be saved for the separation of variables. Ever wonder why semi-colons are so rare in prose? It's because they're all being used up at the end of lines in C code. Don't know where the colons go though - people probably just don't know how to use them.
How about "tinkerer with technological trivia" as a title. Probably wouldn't get past the HR droids though.
Sorry. Not a nerd. But you'd qualify for geekdom easily. Social skills, and drunken stories? And you're not whining about them, you're proud! No nerd would ever be proud, it's against the stereotype.
Be a geek and proud of it! I know I am. Why, I remember this time I was drunk and...
Totally agree. But the fact that someone can program doesn't mean they're a geek. Oh no. The geek factor comes in when you know WHY they program.
People that code for a living don't count unless they get a kick out of making that bit of code better by just, like, optimising that routine there, and that little bit there and without that it'd run sooooo much slower and... etc
People that code just because it's good money - not geeks.
People that code because, well, because, y'know. Writing little tools and widgets and writing versions of classic arcade games because you can and drivers for unsupported hardware because you wouldn't trust anyone else to do it properly and and and... - geeks. Like, for sure. Just be careful not to drop over into the nerd category - 'cos that'd be bad.
Programming geeks of the world unite! You have nothing to lose but, um, hang on - I just want to compile this first, won't take a moment... talk amongst yourselves...
Hi, and welcome to The Show! Whether its hardware or software you're after THIS is the show for YOU! Hah ha!
So, without further ado, lets get on with the show!
On the left hand side of the studio we have the Guy-Geeks... (cut to scene of large mass of desperate-looking guys)*applause*...and on the right we have the Girl-Geeks... (cut to scene of smaller group of desperate looking girls)*applause*
Some of these lucky geeks will leave together for a night of gaming, while the others will leave... alone.
Now to the first round - the personality check: If all the geeks would start by making eye contact with members of the opposite sex......that would be the people on the other side of the studio......oh, come on people it's not that hard......look they're over there. No, not the floor, the other side of the studio. For goodness sake! They won't bite! Just look them in the eyes! Ahem. The EYES are a bit further up. Dammit! Go to commercial...
Yay! Not really important as regards women gaming. But Horace goes skiing was the first ever game I played on a home computer and I felt I had to post a comment. And yep, the modem dialler has always sounded like tapes loading to me. I reckon I can still recognise games by the tape loading sounds. Beeeeeeee-Beep... Beeeeeeee-BeBoooooooooo schkskcshckshcskchskchskc...
Your post has just dropped me into a fit of nostalgia.
I think I'll get my old speccy out of its cherished box-on-top-of-the-wardrobe and hook it up to the TV when I get home. Ah, happy days...
On a side note, my ex-flatmate used to hate the creating games where you have to work out tactics and enjoy the pummeling beat 'em up varieties. But she was a bit mad so maybe it doesn't count.
Nah. But I do get this image flashing before my eyes of lots of little people sitting inside my speakers with tiny little bits of roughened metal and rubbing them together to make noise.
I've been arguing the momentum requires no mass concept since almost the beginning of this thread. Its amazing how many people don't believe this - doesn't matter how you describe it.
I haven't looked at the Maxwell equations for a long time so you're probably right. It's maybe nitpicking though, but energy doesn't contain momentum when it travels. The light fields have momentum and therefore energy associated with them.
That said its all in the way you percieve the problem. The field approach will work, the particle approach will work. Thats why the discussion has centred around photons. You can disagree about this if you like but I personally feel that the particle approach is more intuitive.
You're right in some ways, but wrong in others. The effect of the gravitational field from the Sun will drop off but there isn't a point (as far as I know) that it becomes zero. It does become so small as to be almost negligible but it's never completely gone. Certainly if you're using some form of propulsion system (solar sail or whatever else they come up with) you can move about within the field quite happily if the system can overcome gravitational effects. In the example I gave before the massive object was just set going without additional drive. If left to go on its own the object would slow down and stop and go back. Of course there comes a point where the effect of the Sun's gravity is countered by the gravity from other stars but in a simple two body case the example holds true.
'Work in the earths gravitational field' - why do I get the feeling that phase is gonna haunt me for the rest of my days?:)
I haven't read Einsteins biography but I hear it's supposed to be quite good. In answer to your question, black holes are black because the mass of the black hole distorts the curvature of spacetime into the 4 dimensional equivalent of a really deep well. The light goes in but cannot escape. Not a totally accurate analogy but the closest you're gonna get at this time in the morning before I've had any coffee.
The mass to light and light to energy thing isn't quite right though. This is one of those common errors that come up with relativity. The trick to dealing with relativity is to throw common sense out of the window and trust the equations - they never lie you know, well, unless you get them wrong. Massive objects (anything with mass) cannot travel at the speed of light. The closer they get to the speed of light the more massive they become - at the speed of light the mass becomes infinite (not a good thing for the universe - rrriiip). As far as I know mass cannot become light simply through travelling fast.
The speed of light is constant in all inertial reference frames (this is one of the defining rules of relativity) and so cannot be slowed down. But it's already energy. It's all in how you define energy but then that's what relativity theory is all about.
Sorry I can't give a better explanation than this. It's just not an intuitive concept and not easy to put into words. If you're really interested I'd suggest reading some basic undergraduate physics textbooks on relativity - possibly one of the generic University Physics books - I seem to recall it has quite a nice chapter on special relativity or relativistic mechanics or something similar which is good for getting you started.
Classical theory, fair enough. But the discussion on photons is regarding the transfer mechanism from light energy to force being applied to the object. There are equations to describe how much force a beam of light with a given power will exert on a surface but that doesn't explain why an EM wave (classically defined in terms of energy or power) incident on a surface results in a force being applied to that surface.
The argument here is that the energy in the beam DOES produce a force on the surface. It must therefore have momentum (basic classical conservation laws). How can a light beam which has no mass contain momentum (without the Einstein equation you can't equate energy with anything other than energy)? Well, see the discussions we've been having about the photons and momentum and mass for details.
Yes, the sail concept can be discussed without resorting to wave particle duality but you lose so much of the fun.;)
> Really? Me too. I call it the Earth's field of gravitation (or gravitational > field). Now, if you really want to impress people tell them you don't work in > a field of gravitation.
Fair enough - did sound a bit up myself didn't I.
But yes. Massive objects moving away from massive objects will slow down. If a massive object (e.g. the Earth) did not get pulled back by the gravitational effect of another massive object (e.g. the Sun) then orbits would not work and the Earth would just float away into space. OK even more space. Like further away. Y'know.
Example: take a couple of planets (just so you know this is a thought experiment:) ) and start them off in opposite directions along one axis. The gravitational effect of the two masses will slow the masses down relative to each other. The same experiment performed with a photon and a planet results in the photon continuing to move at the speed of light - not relative to anything since it's a constant.
mass M in kg. Plancks constant h in J s or in SI units m^2 kg s^-1 speed of light c in m s^-1
This means that on one side you have kg and on the other you have m kg.
If on the other hand you're using (c) as the wavelength (I'll use lambda) which is in m then the right hand side becomes kg m s^-1 which is the SI definition of momentum.
Therefore the equation reads momentum p = h/lambda
If (c) has another meaning which is physical then feel free to correct me...
No they don't have mass. "Some say"? Einsteins theory of general relativity quite clearly shows the curvature of spacetime due to the presence of mass. I'm not really in the mood to have a cosmological argument right now but I happen to work in the field of gravitation and know a little something about this.
The properties you describe (momentum and being affected by gravity) are properties demonstrated by particles. Just because it's affected by gravity doesn't mean it's got mass. And one difference is that massive objects cannot travel at the speed of light. Also it's not gravity that affects the light directly - you don't see photons slowing down as they travel away from a massive object - it's the effect of a massive object on the curvature of spacetime which causes the distance traveled by the light on a given axis to change (depends on co-ordinate system chosen but hey, too much detail).
Black holes are black because the photons cannot escape from the gravitational potential well. But the differences are very important, very simple and quite profound. I'd suggest you have a look through some books on general relativity or even some basic wave/particle duality undergraduate physics notes. They might help your argument some.
Um, sorry, no. Photons have no mass. You need the full form of the equation: E^2=(pc)^2+(mc^2)^2 which for a massless photon (m=0) would become E=pc. p in this case is momentum, which photons do have.
When the photon strikes the sail it imparts momentum to it. LOTS of photons=lots of momentum and near the Sun there are a LOT of photons. Bear in mind the sail will need to be HUGE. Also momentum has direction (vector not scalar).
Oh, and the effect of the odd hydrogen atom should be very small in comparison to the LOTS of photons constantly (alright, discretely if you're delving into duality) striking the surface of the sail. It will be slowed down slightly by atoms floating through space but if the sail is large enough and light enough then theory says it should be able to break free of the Sun's gravity (of course that's what the original argument is about). Do you really think one or two little hydrogen atoms will be much of a problem?
No numbers were harmed during the course of this diatribe, but a few ego's were bruised...
Of course the Neos on the screens that say different numbers may just be from the possibility that he heard wrong. Just imagine one of the screens showing a really improbable situation in which he replies "What pink elephant?"
Whenever Neo responds to something we see the screen that shows that particular response. It's the old 'if you have enough computing power you can predict events in the future" thing. (Already known to be possible in this particular situation by the presence of the Oracle)
Sorry, no. You're missing the question. To clarify: Which particular type of chip was the billionth? Was the billionth one shipped a Xeon or a Centrino or what?
Not that it matters 'n all but it WOULD be kinda cool to know.
Right. Done a quick bit of Googling for a copy of the water phase diagram. Looked at it - check.;)
So 10e5 Pa should be (about 1 bar) atmosphere and quite rightly the diagram shows around 273K as the freezing point of water and around +100 as the boiling point.
Dropping to about 10e3 Pa (about 10mbar) and the boiling point has dropped but the freezing point is very much unchanged. Getting close to the sublimation pressure at room temp though.
From then on there is a nice steady curve - the diagram I'm looking at goes down to about 0.1 Pa (about 10e-4 mbar) by which point the sublimation point is around 200K.
OK - so the sublimation temperature is lower than room temperature and will get lower (though slowly) as pressure decreases. Reasonable vacuum for a scientific experiment - 10e-6 mbar. Lets say 10e-8 for good performance. Can go lower if really necessary but it can be tough under real world conditions especially if you want to stick your hand in to see what happens:)
The sublimation temperature will have decreased by little from the 200K mark. So by sticking your hand into this vacuum your hand will start losing water through sublimation until your hand reaches the sublimation point through general loss of temperature. So that means your hand will get colder. Seems to me somebody said that before. Heh.
Though the effect will get worse through longer exposure. But you weren't planning to leave your hand in there were you?
Hmmn. Reading through that came out as more sarcastic than I intended. Sorry 'bout that. Just put it down to my cranky lack of coffee or something.
Fair enough point. But I should possibly point out that there's nothing actually dangerous about putting your hand in a vacuum. OK maybe it'd get cold. But the pressure difference is only about one atmosphere. We can stand up to several atmospheres increase in pressure (don't know numbers right off the top of my head) so 1 atmosphere - not much problem.
If it's an enclosed plasma that can block anything then it's pretty darn impressive, lets be honest.;) The atmospheric pressure thing will depend on the exact physical set up though. But having worked with vacuum equipment I'd estimate that with vacuum on one side and air leaking in on the other you're really talking about how much air is leaking into the gap. i.e.:
leak in system plasma wall
| |
| enclosed | atmos area at | vacuum
| atmos - x |
| |
Obviously with this set up the amount of air leaking in will increase with time (albeit possibly slowly) until x=atmospheric pressure. I certainly wouldn't want to trust my delicate equipment inside the vacumm to anything that wouldn't hold back the full pressure of the air outside.
Of course I'm only guessing since there're no numbers or anything in the article but it is a great achievement anyway.
Slashdot Mirror
It's the running-water cooling system to guard against vampires that worries me.
Hmmn. Could be. But I reckon it's less about showing you're better than the other guy than showing you're good enough to keep being funded. Y'know, along the lines of "we can do this, this and this while they can only do that, that and maybe that. So you see we deserve the (limited amount of funding for what is essentially pure science) money, not them."
To the best of my knowledge, these missions are split between research in different countries on a who's-best-for-the-job type approach with all sorts of infighting and back biting for the larger portions of the pie. Pretty much like all academia really. And hey, sometimes standing up and shouting "Hey, see what I can do!" is the only way to go.
Even if they do look a bit daft when it doesn't work...
Hey, I'm game if you are. Red meat with that anyone?
All true. But I'd recommend not trying it if you're a Type I diabetic (like myself). Unless you really know what you're doing with regard to insulin control and maintaining blood sugar levels, you'll end up in a bad way.
As far as I understand it - and I'll admit I'm no expert - the Atkins diet involves initially cutting out/down carbs for the first week or two. This should make the body use up stored energy (fats/general body mass) in an attempt to maintain normality. Then you switch onto a higher low carb intake as required. And do this for a few weeks before eating whatever you want again. Though by this time you'll stop missing the cakes and chocolates and sugary drinks. Anyone disagreeing with this may now proceed to flame my good name to the ends of the post and back. ^_^
Personally, I'll stick to my normal diet and a bit of good ol' fashioned exercise. Less effort all round. Now! Who's for a run down to the gym?
Ah, but you don't get them everywhere. Other countries (eg the UK) don't necessarily have 'em. I can't remember ever seeing one of the big green screen messages outside of the US - but then I'm not that well travelled. Anyone else any info on other countries?
Naw. A programmer is a person who doesn't use commas and brackets and hyphens and other non-essential parts of the english language which make things easier to understand than if they weren't used at all. *gasps for breath*
My excuse is that commas are in short supply and should be saved for the separation of variables. Ever wonder why semi-colons are so rare in prose? It's because they're all being used up at the end of lines in C code. Don't know where the colons go though - people probably just don't know how to use them.
How about "tinkerer with technological trivia" as a title. Probably wouldn't get past the HR droids though.
Sorry. Not a nerd. But you'd qualify for geekdom easily. Social skills, and drunken stories? And you're not whining about them, you're proud! No nerd would ever be proud, it's against the stereotype.
Be a geek and proud of it! I know I am. Why, I remember this time I was drunk and...
Totally agree. But the fact that someone can program doesn't mean they're a geek. Oh no. The geek factor comes in when you know WHY they program.
People that code for a living don't count unless they get a kick out of making that bit of code better by just, like, optimising that routine there, and that little bit there and without that it'd run sooooo much slower and... etc
People that code just because it's good money - not geeks.
People that code because, well, because, y'know. Writing little tools and widgets and writing versions of classic arcade games because you can and drivers for unsupported hardware because you wouldn't trust anyone else to do it properly and and and... - geeks. Like, for sure. Just be careful not to drop over into the nerd category - 'cos that'd be bad.
Programming geeks of the world unite! You have nothing to lose but, um, hang on - I just want to compile this first, won't take a moment... talk amongst yourselves...
The Geek Dating Show!
...and on the right we have the Girl-Geeks...
...that would be the people on the other side of the studio... ...oh, come on people it's not that hard... ...look they're over there. No, not the floor, the other side of the studio. For goodness sake! They won't bite! Just look them in the eyes! Ahem. The EYES are a bit further up. Dammit! Go to commercial...
Hi, and welcome to The Show! Whether its hardware or software you're after THIS is the show for YOU! Hah ha!
So, without further ado, lets get on with the show!
On the left hand side of the studio we have the Guy-Geeks...
(cut to scene of large mass of desperate-looking guys)*applause*
(cut to scene of smaller group of desperate looking girls)*applause*
Some of these lucky geeks will leave together for a night of gaming, while the others will leave... alone.
Now to the first round - the personality check: If all the geeks would start by making eye contact with members of the opposite sex...
Hmmn. Maybe it wouldn't work after all...
Yay! Not really important as regards women gaming. But Horace goes skiing was the first ever game I played on a home computer and I felt I had to post a comment. And yep, the modem dialler has always sounded like tapes loading to me. I reckon I can still recognise games by the tape loading sounds. Beeeeeeee-Beep... Beeeeeeee-BeBoooooooooo schkskcshckshcskchskchskc...
Your post has just dropped me into a fit of nostalgia.
I think I'll get my old speccy out of its cherished box-on-top-of-the-wardrobe and hook it up to the TV when I get home. Ah, happy days...
On a side note, my ex-flatmate used to hate the creating games where you have to work out tactics and enjoy the pummeling beat 'em up varieties. But she was a bit mad so maybe it doesn't count.
Nah. But I do get this image flashing before my eyes of lots of little people sitting inside my speakers with tiny little bits of roughened metal and rubbing them together to make noise.
Audio-FILES! No? Oh well, please yourselves...
I've been arguing the momentum requires no mass concept since almost the beginning of this thread. Its amazing how many people don't believe this - doesn't matter how you describe it.
;)
I haven't looked at the Maxwell equations for a long time so you're probably right. It's maybe nitpicking though, but energy doesn't contain momentum when it travels. The light fields have momentum and therefore energy associated with them.
That said its all in the way you percieve the problem. The field approach will work, the particle approach will work. Thats why the discussion has centred around photons. You can disagree about this if you like but I personally feel that the particle approach is more intuitive.
Why can't we all just get along
You're right in some ways, but wrong in others. The effect of the gravitational field from the Sun will drop off but there isn't a point (as far as I know) that it becomes zero. It does become so small as to be almost negligible but it's never completely gone. Certainly if you're using some form of propulsion system (solar sail or whatever else they come up with) you can move about within the field quite happily if the system can overcome gravitational effects. In the example I gave before the massive object was just set going without additional drive. If left to go on its own the object would slow down and stop and go back. Of course there comes a point where the effect of the Sun's gravity is countered by the gravity from other stars but in a simple two body case the example holds true.
:)
'Work in the earths gravitational field' - why do I get the feeling that phase is gonna haunt me for the rest of my days?
I haven't read Einsteins biography but I hear it's supposed to be quite good. In answer to your question, black holes are black because the mass of the black hole distorts the curvature of spacetime into the 4 dimensional equivalent of a really deep well. The light goes in but cannot escape. Not a totally accurate analogy but the closest you're gonna get at this time in the morning before I've had any coffee.
The mass to light and light to energy thing isn't quite right though. This is one of those common errors that come up with relativity. The trick to dealing with relativity is to throw common sense out of the window and trust the equations - they never lie you know, well, unless you get them wrong. Massive objects (anything with mass) cannot travel at the speed of light. The closer they get to the speed of light the more massive they become - at the speed of light the mass becomes infinite (not a good thing for the universe - rrriiip). As far as I know mass cannot become light simply through travelling fast.
The speed of light is constant in all inertial reference frames (this is one of the defining rules of relativity) and so cannot be slowed down. But it's already energy. It's all in how you define energy but then that's what relativity theory is all about.
Sorry I can't give a better explanation than this. It's just not an intuitive concept and not easy to put into words. If you're really interested I'd suggest reading some basic undergraduate physics textbooks on relativity - possibly one of the generic University Physics books - I seem to recall it has quite a nice chapter on special relativity or relativistic mechanics or something similar which is good for getting you started.
Classical theory, fair enough. But the discussion on photons is regarding the transfer mechanism from light energy to force being applied to the object. There are equations to describe how much force a beam of light with a given power will exert on a surface but that doesn't explain why an EM wave (classically defined in terms of energy or power) incident on a surface results in a force being applied to that surface.
;)
The argument here is that the energy in the beam DOES produce a force on the surface. It must therefore have momentum (basic classical conservation laws). How can a light beam which has no mass contain momentum (without the Einstein equation you can't equate energy with anything other than energy)? Well, see the discussions we've been having about the photons and momentum and mass for details.
Yes, the sail concept can be discussed without resorting to wave particle duality but you lose so much of the fun.
> Really? Me too. I call it the Earth's field of gravitation (or gravitational
:) ) and start them off in opposite directions along one axis. The gravitational effect of the two masses will slow the masses down relative to each other. The same experiment performed with a photon and a planet results in the photon continuing to move at the speed of light - not relative to anything since it's a constant.
> field). Now, if you really want to impress people tell them you don't work in
> a field of gravitation.
Fair enough - did sound a bit up myself didn't I.
But yes. Massive objects moving away from massive objects will slow down. If a massive object (e.g. the Earth) did not get pulled back by the gravitational effect of another massive object (e.g. the Sun) then orbits would not work and the Earth would just float away into space. OK even more space. Like further away. Y'know.
Example: take a couple of planets (just so you know this is a thought experiment
Pardon? That equation makes no sense.
M=h/(c)
mass M in kg.
Plancks constant h in J s or in SI units m^2 kg s^-1
speed of light c in m s^-1
This means that on one side you have kg and on the other you have m kg.
If on the other hand you're using (c) as the wavelength (I'll use lambda) which is in m then the right hand side becomes kg m s^-1 which is the SI definition of momentum.
Therefore the equation reads momentum p = h/lambda
If (c) has another meaning which is physical then feel free to correct me...
No they don't have mass. "Some say"? Einsteins theory of general relativity quite clearly shows the curvature of spacetime due to the presence of mass. I'm not really in the mood to have a cosmological argument right now but I happen to work in the field of gravitation and know a little something about this.
The properties you describe (momentum and being affected by gravity) are properties demonstrated by particles. Just because it's affected by gravity doesn't mean it's got mass. And one difference is that massive objects cannot travel at the speed of light. Also it's not gravity that affects the light directly - you don't see photons slowing down as they travel away from a massive object - it's the effect of a massive object on the curvature of spacetime which causes the distance traveled by the light on a given axis to change (depends on co-ordinate system chosen but hey, too much detail).
Black holes are black because the photons cannot escape from the gravitational potential well. But the differences are very important, very simple and quite profound. I'd suggest you have a look through some books on general relativity or even some basic wave/particle duality undergraduate physics notes. They might help your argument some.
Um, sorry, no. Photons have no mass. You need the full form of the equation: E^2=(pc)^2+(mc^2)^2 which for a massless photon (m=0) would become E=pc. p in this case is momentum, which photons do have.
When the photon strikes the sail it imparts momentum to it. LOTS of photons=lots of momentum and near the Sun there are a LOT of photons. Bear in mind the sail will need to be HUGE. Also momentum has direction (vector not scalar).
Oh, and the effect of the odd hydrogen atom should be very small in comparison to the LOTS of photons constantly (alright, discretely if you're delving into duality) striking the surface of the sail. It will be slowed down slightly by atoms floating through space but if the sail is large enough and light enough then theory says it should be able to break free of the Sun's gravity (of course that's what the original argument is about). Do you really think one or two little hydrogen atoms will be much of a problem?
No numbers were harmed during the course of this diatribe, but a few ego's were bruised...
Ah, but these are still possibilities.
Of course the Neos on the screens that say different numbers may just be from the possibility that he heard wrong. Just imagine one of the screens showing a really improbable situation in which he replies "What pink elephant?"
Whenever Neo responds to something we see the screen that shows that particular response. It's the old 'if you have enough computing power you can predict events in the future" thing. (Already known to be possible in this particular situation by the presence of the Oracle)
Sorry, no. You're missing the question. To clarify: Which particular type of chip was the billionth? Was the billionth one shipped a Xeon or a Centrino or what?
Not that it matters 'n all but it WOULD be kinda cool to know.
Right. Done a quick bit of Googling for a copy of the water phase diagram. Looked at it - check. ;)
:)
So 10e5 Pa should be (about 1 bar) atmosphere and quite rightly the diagram shows around 273K as the freezing point of water and around +100 as the boiling point.
Dropping to about 10e3 Pa (about 10mbar) and the boiling point has dropped but the freezing point is very much unchanged. Getting close to the sublimation pressure at room temp though.
From then on there is a nice steady curve - the diagram I'm looking at goes down to about 0.1 Pa (about 10e-4 mbar) by which point the sublimation point is around 200K.
OK - so the sublimation temperature is lower than room temperature and will get lower (though slowly) as pressure decreases. Reasonable vacuum for a scientific experiment - 10e-6 mbar. Lets say 10e-8 for good performance. Can go lower if really necessary but it can be tough under real world conditions especially if you want to stick your hand in to see what happens
The sublimation temperature will have decreased by little from the 200K mark. So by sticking your hand into this vacuum your hand will start losing water through sublimation until your hand reaches the sublimation point through general loss of temperature. So that means your hand will get colder. Seems to me somebody said that before. Heh.
Though the effect will get worse through longer exposure. But you weren't planning to leave your hand in there were you?
Hmmn. Reading through that came out as more sarcastic than I intended. Sorry 'bout that. Just put it down to my cranky lack of coffee or something.
Fair enough point. But I should possibly point out that there's nothing actually dangerous about putting your hand in a vacuum. OK maybe it'd get cold. But the pressure difference is only about one atmosphere. We can stand up to several atmospheres increase in pressure (don't know numbers right off the top of my head) so 1 atmosphere - not much problem.
Damn. Lameness filter crushed my carefully crafted ascii diagram.
it went
atmosphere: vacuum wall with gap: area at atmos - x: plasma wall: vacuum
If it's an enclosed plasma that can block anything then it's pretty darn impressive, lets be honest. ;) The atmospheric pressure thing will depend on the exact physical set up though. But having worked with vacuum equipment I'd estimate that with vacuum on one side and air leaking in on the other you're really talking about how much air is leaking into the gap. i.e.:
leak in system plasma wall
| |
| enclosed |
atmos area at | vacuum
| atmos - x |
| |
Obviously with this set up the amount of air leaking in will increase with time (albeit possibly slowly) until x=atmospheric pressure. I certainly wouldn't want to trust my delicate equipment inside the vacumm to anything that wouldn't hold back the full pressure of the air outside.
Of course I'm only guessing since there're no numbers or anything in the article but it is a great achievement anyway.
Sorry that should be "benchmarks". Must use preview. Bad poster. No cookie.