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General => General Chat => Topic started by: MrOmnos on December 16, 2016, 04:11:29 pm

Title: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: MrOmnos on December 16, 2016, 04:11:29 pm
How hot can it get?
Title: Re: Why does cold temp has a limit of -273K and high temp has no limit?
Post by: Arjan Emm on December 16, 2016, 04:24:37 pm
Physics thinks the highest possible temperature is the Planck temperature, around 1.4*10^32 K. So there is probably a limit. It's just strange that it's so incomprehensively high and -273 is so close to our comfort zone.

How incomprehensible?
supernovae around 10^10K
Large hadron collider 10^18K
Anything a few decades higher is bigbang theory.
Title: Re: Why does cold temp has a limit of -273K and high temp has no limit?
Post by: SeanB on December 16, 2016, 04:38:17 pm
Look at in in Kelvin, where zero kelvin is where all atomic motion ceases. You cannot have lower energy than zero, but the high limit is set by the ability of the universe to contain the particle travelling at C.

Best we have reached is ca 0.01K, and that is really hard to get to, and where measuring the temperature is very difficult, as the measurement adds energy to the system. Below around 0.5K many things behave as a single particle, or at least He does, which is the gas most commonly used.
Title: Re: Why does cold temp has a limit of -273K and high temp has no limit?
Post by: Spuddevans on December 16, 2016, 04:43:34 pm
Is it something to do with the point that you can't directly generate cold, you can only remove heat, but you can always inject more energy, ie add heat.

Tim
Title: Re: Why does cold temp has a limit of -273K and high temp has no limit?
Post by: grumpydoc on December 16, 2016, 04:44:52 pm
I don't claim to understand it but apparently negative Kelvin is possible

https://www.mpg.de/research/negative-absolute-temperature (https://www.mpg.de/research/negative-absolute-temperature)
Title: Re: Why does cold temp has a limit of -273K and high temp has no limit?
Post by: Gyro on December 16, 2016, 04:48:25 pm
It's always struck me as a bit odd too that we exist at such close proximity to absolute zero. Yes I know it's down to our chemistry but it still feels a bit strange that you can reach an equivalent temperature differential in the oposite direction with a bog standard soldering iron!
Title: Re: Why does cold temp has a limit of -273K and high temp has no limit?
Post by: Benta on December 16, 2016, 04:54:17 pm
Just to correct the original question:

Absolute zero is 0 K
Which corresponds to appr. -273 degrees Celsius.

There is no such thing as -273 K.

Title: Re: Why does cold temp has a limit of -273K and high temp has no limit?
Post by: Kleinstein on December 16, 2016, 04:58:31 pm
If we are close to zero temperature depends on the scale on a logarithmic scale, there is plenty of room to both directs. The lowest temperature reached are also quit a bit lower than 10 mK. Those experiments with Bose-Einstein condensates are at micro kelvins.

With non equilibrium systems, there are different ways to define a temperature. One is to look at the population of two states of different energy. The higher the temperature the more equal probabilities for the two states. However for some reason the higher level is more likely than the lower one, one could call this a negative temperature - or one higher than infinite, depending on how you look at it.
Title: Re: Why does cold temp has a limit of -273K and high temp has no limit?
Post by: Arjan Emm on December 16, 2016, 05:29:35 pm
It's always struck me as a bit odd too that we exist at such close proximity to absolute zero. Yes I know it's down to our chemistry but it still feels a bit strange that you can reach an equivalent temperature differential in the oposite direction with a bog standard soldering iron!

I agree with your feeling. But it is not down to our chemistry but chemistry in general. Molecular bonds are really weak, that's also why they can get as complicated as us humans. Between 400 degrees C and say 2000C most big molecules fall apart. At only 10.000K chemistry ceases to exist and all you have is single atoms, many already stripped of many of their electrons.
Title: Re: Why does cold temp has a limit of -273K and high temp has no limit?
Post by: Arjan Emm on December 16, 2016, 05:51:32 pm
If we are close to zero temperature depends on the scale on a logarithmic scale, there is plenty of room to both directs. The lowest temperature reached are also quit a bit lower than 10 mK. Those experiments with Bose-Einstein condensates are at micro kelvins.

With non equilibrium systems, there are different ways to define a temperature. One is to look at the population of two states of different energy. The higher the temperature the more equal probabilities for the two states. However for some reason the higher level is more likely than the lower one, one could call this a negative temperature - or one higher than infinite, depending on how you look at it.

Good points. I guess cooling down to almost 0 K, let's say 10^-30 K is just as impossible to achieve as 10^30 K heat.
Title: Re: Why does cold temp has a limit of -273K and high temp has no limit?
Post by: CatalinaWOW on December 16, 2016, 06:12:57 pm
It's always struck me as a bit odd too that we exist at such close proximity to absolute zero. Yes I know it's down to our chemistry but it still feels a bit strange that you can reach an equivalent temperature differential in the oposite direction with a bog standard soldering iron!

It is a consequence of when we live in the age of the universe.  When the universal background is down to 3 K.

Arthur C. Clark expressed it poetically.  He spoke wistfully of what it might have been like to live in the early universe, when everything was close by and high energy events were commonplace.  When entropy had just started to increase.   He then predicted that far in the future, as the heat death of the universe neared, any intelligences living then would be wistful of us who lived when the universe was young.
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: 0xdeadbeef on December 16, 2016, 06:41:55 pm
As a side note it might be worth mentioning that also the pressure range is not very symmetric from our perspective. The absolute vacuum is just 1bar (or 100 kPa) away but it's relatively simple to achieve pressure values that are magnitudes higher and near the code of our planet, it's supposed to be 330 Gigapascal, letting aside Neutron stars and the like.

I guess as with the temperature and other things, it's just a matter of anthropocentric worldview: as we can only exist in certain conditions, it's pointless to wonder why the conditions allow us to exist. As if they wouldn't, we couldn't wonder.
Title: Re: Why does cold temp has a limit of -273K and high temp has no limit?
Post by: ajb on December 16, 2016, 07:45:37 pm
I don't claim to understand it but apparently negative Kelvin is possible

https://www.mpg.de/research/negative-absolute-temperature (https://www.mpg.de/research/negative-absolute-temperature)

Quote
Atoms at negative absolute temperature are the hottest systems in the world

Sounds like somebody accidentally rolled over an integer somewhere.
Title: Re: Why does cold temp has a limit of -273K and high temp has no limit?
Post by: MasterTech on December 16, 2016, 08:56:07 pm
It's always struck me as a bit odd too that we exist at such close proximity to absolute zero. Yes I know it's down to our chemistry but it still feels a bit strange that you can reach an equivalent temperature differential in the oposite direction with a bog standard soldering iron!
True, phillosophically one could argue that the Earth was designed as a low power system
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: NANDBlog on December 16, 2016, 10:25:22 pm
Yeah, well the other spectrum, electronics does not really work in the picoherz and the terahertz region.
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: T3sl4co1l on December 17, 2016, 12:09:01 am
It's analogous to saying "there is no voltage [magnitude] below 0V".  And that thermal noise guarantees you will always have slightly more than zero, no matter how you measure it (except also at absolute zero temperature).

Different particles, and different aspects of the system, can possess different temperatures.  A system need not always be in perfect equilibrium; there needn't even be an exchange mechanism between the different parts of the system.  (Thermodynamics assumes there will eventually be some sort of exchange, which in real systems, always manages to happen in the end.  Over finite time scales, things can be very different: by pumping a magnetic field, you can chill the nuclear spins of any nonzero-spin atoms.  The heat energy contained therein is extraordinarily small, of course, but it's also fascinating that the thermal time constant is in the tens of seconds -- for a quantum system that's room-temperature (or not) and quite low energy (~ueV per flip).

Tim
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: LokiChaos on December 17, 2016, 12:20:51 am
Negative absolute temps are very different than one colloquially thinks of temperature, they are a result of systems with high constrained sets of possible states, and a definition of temperature grounded in statistical mechanics.

The interesting thing is negative temps are HOTTER than any positive temp, not colder.  Energy always flows out of a negative absolute temp systems into a positive temp one.  https://en.wikipedia.org/wiki/Negative_temperature

A commonly encountered system is in a laser in a state of population inversion.
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: Tinkerer on December 17, 2016, 01:18:16 am
Well, I dont think asking why we exist so close, relatively speaking, to absolute zero is the correct question. The question should be why are the energy levels needed for chemistry to exist so close to absolute zero. At higher temperatures, you dont really get much chemistry happening, its all mostly gas and plasma as the atoms are too energetic to to chemically interact in most cases.
The above leads to an interesting thought. What if electrons and such were more strongly bound to their respective atoms? etc etc, what if bonds were much stronger?
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: LokiChaos on December 17, 2016, 02:11:04 am
You'd end up with a lot less chemistry happening as most places would be too cold to have large numbers of interesting reactions (this would also likely preclude life in a sense we are familiar with).

Chemical reactions of all sorts would be rarer, but those that do occur would be far more energetic and the products far harder to break apart.  There are a lot of different effects, some depend on if you just increase the strength of the electromagnetic force, or increase the charge quanta, or if the other fundamental forces also scale as well.
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: T3sl4co1l on December 17, 2016, 04:32:28 am
Well, I dont think asking why we exist so close, relatively speaking, to absolute zero is the correct question.

What the hell does that mean?  In other words -- relative to what?  :-//

Tim

Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: neil t on December 17, 2016, 05:14:00 am
It's all relative to what we can and can't measure or prove or disprove ie supposing nothing travels faster than the speed of light if It did could it be measured with current technology.
or would it be measured by unproven theory. based on what we know or think we know at this time.
Title: Re: Why does cold temp has a limit of -273K and high temp has no limit?
Post by: mrpackethead on December 17, 2016, 05:59:33 am
Look at in in Kelvin, where zero kelvin is where all atomic motion ceases. You cannot have lower energy than zero, but the high limit is set by the ability of the universe to contain the particle travelling at C.

Best we have reached is ca 0.01K, and that is really hard to get to, and where measuring the temperature is very difficult, as the measurement adds energy to the system. Below around 0.5K many things behave as a single particle, or at least He does, which is the gas most commonly used.

Bose Einstein Condensate.
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: LokiChaos on December 17, 2016, 06:17:36 am
At very low temps quantum effects crop up at a macroscopic level because the number of states is so restricted that the normal classicalization that happens in statistical mechanics can no longer occur.  You get second sound, third sound, new states of matter, superconductivity, superfluidity, etc. 

In some ways it's a shame we generally exist at such /high/ temperatures, imagine if we could have superconductive materials at our "room temperature"!
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: Galenbo on December 17, 2016, 12:05:12 pm
How hot can it get?

When I was 12y old, or before physics studies, I would have understood it like:

* Temperature in Kelvin is like the amount of inside random movement.
* 0K = zero movement
* Random movement is not directional. It's like light on, light off, light half on.
* Much movement creates heat, you can feel it on the surface.
 
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: Red Squirrel on December 18, 2016, 11:42:44 pm
Once you get down to 233K, anything colder and it all feels the same to me. :P

French swears start coming out at that temp.  :-DD
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: timb on December 19, 2016, 02:04:31 am
Imagine the "shrinkage" at 0K! I mean, skinning dipping on a cold day is bad enough...
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: xrunner on December 19, 2016, 02:19:09 am
Well since we're asking these types of questions - what would be the maximum negative charge obtainable? Would it be the combination (if it were possible) of every single electron in the Universe?
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: IanB on December 19, 2016, 02:58:07 am
Well since we're asking these types of questions - what would be the maximum negative charge obtainable? Would it be the combination (if it were possible) of every single electron in the Universe?

How are you going to measure "charge" in this question? A collection of charge spread out thinly is an entirely different prospect than a collection of charge bunched up close together. And then you have to ask, how close together?
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: LokiChaos on December 19, 2016, 05:19:12 am
I am going to answer "what is the maximum negative charge?" with "mu"

If you could hypothetically concentrate every negatively charged particle (not just electrons, though most others have short lifespans, one would want to include antiprotons, muons and tau… W Bosons also can have a negative charge, but getting them wrangled is more complex matter) in the observable universe in a specified region in space, but very quickly the energy would collapse such an assembly into a black hole (never mind there isn't enough energy within the entire observable universe to actually do this).
Source and more musings: https://what-if.xkcd.com/140/

You could calculate how close you could force two electrons  together before it collapses into a singularity. 
On the other hand, electrons themselves are rather weird too, and general relativity and quantum mechanics don't combine very well.
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: NiHaoMike on December 20, 2016, 07:01:17 am
Yeah, well the other spectrum, electronics does not really work in the picoherz and the terahertz region.
Solid state oscillators that work in at a few hundreds of THz are very common and cheap. And so are diodes that can detect/rectify that.
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: Gyro on December 20, 2016, 02:12:55 pm
Imagine the "shrinkage" at 0K! I mean, skinning dipping on a cold day is bad enough...

Theres no helping your 'Junk' size fixation, not long ago you were bragging about it dipping in the toilet bowl!  ::) ;D

https://www.eevblog.com/forum/chat/how-good-is-your-aim-at-night/5/ (https://www.eevblog.com/forum/chat/how-good-is-your-aim-at-night/5/)
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: timb on December 20, 2016, 05:55:07 pm
Imagine the "shrinkage" at 0K! I mean, skinning dipping on a cold day is bad enough...

Theres no helping your 'Junk' size fixation, not long ago you were bragging about it dipping in the toilet bowl!  ::) ;D

https://www.eevblog.com/forum/chat/how-good-is-your-aim-at-night/5/ (https://www.eevblog.com/forum/chat/how-good-is-your-aim-at-night/5/)

Maybe I just have a really small toilet! Did you ever think of that?! (For the record, I don't...but that's not the point!) XD

Anyway, at 0K, I don't think anybody can brag about size. At that temperature I suspect an outie becomes an innie! Or, would it even get the chance? I guess *any* exposed skin would instantly freeze, like being exposed to liquid nitrogen. So I guess you wouldn't have to worry about, because you'd be dead...

I wonder what the coldest temperature a naked human can survive at? (Even for just a few seconds...) Hmmm...
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: Gyro on December 20, 2016, 06:25:35 pm
Quote
Maybe I just have a really small toilet! Did you ever think of that?! (For the record, I don't...but that's not the point!) XD
;D

Quote
Anyway, at 0K, I don't think anybody can brag about size. At that temperature I suspect an outie becomes an innie! Or, would it even get the chance? I guess *any* exposed skin would instantly freeze, like being exposed to liquid nitrogen. So I guess you wouldn't have to worry about, because you'd be dead...

Actually I think there is a mechanism that allows you to briefly put your skin in contact with liquid Nitrogen. I think it works because the layer immediately next to the skin instantly vapourizes due to the huge temperature difference giving an insulating layer of Nitrogen gas. Obviously it would only work until the surface of the skin retains enough heat. A similar effect allows droplets of water to dance on top of a very hot plate (again buffered by vapour).

I can't remember where I saw the demonstration (if I didn't in fact dream the whole thing!) but obviously, don't try this at home folks!  :scared:

P.S. Ahah,  the Leidenfrost effect...   https://www.youtube.com/watch?v=gjsMV1MglA4 (https://www.youtube.com/watch?v=gjsMV1MglA4)
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: CatalinaWOW on December 20, 2016, 06:27:31 pm
Your question of cold temps survival is too complex to answer.  Survival of arbitrarily low temps for a few seconds isn't a problem.  But combined with the vacuum that normally would exist at those temps you might come up with something lethal in a few seconds.  Or immersed in a lake of liquid helium you might get survival down in the seconds range. 

A few seconds of very low temps is actually refreshing.  When working in a very hot climate with access to LN2 (~72 K) we would occasionally dump some down pant legs (loose fitting obviously) or shirt backs.  Between small quantities and Leidenfrost it actually felt good.  I am sure were risking small areas of frostbitten skin, but nothing lethal.  I don't even recall a single instance of frostbite.

I would guess that in most cases it takes significant numbers of seconds to get serious damage (loss of fingers, ears and the like), and minutes for actual lethality.  The body has a reasonably long thermal time constant.  The short survival times in Arctic waters is due to an almost ideal combination of temperature, heat capacity, conductivity and other factors in cold sea water.
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: LokiChaos on December 20, 2016, 09:17:47 pm
Survivability is more a matter of heat transfer and less about the actual temperature.  The temperature differential matters, but is only one factor and dwarfed by others.

Take space (in the shadows, so we are cold and not heated by the solar radiation), you'd asphyxiate well before you freeze to death.  Initially most heat loss would be from your blood and other liquids (mostly water) boiling off, this would actually be most of the total heat loss (and decidedly fatal if you somehow didn't need oxygen).  After that initial stage the only thermal losses would be blackbody radiation and it would take a total of around 8-12 hours for you to freeze solid (depend on body mass and other factors).

Even immersed in liquid nitrogen would take hours simply because of how slowly the internal heat would take to conduct though the body without the circulatory system to transport it. 

At what point you'd die is a little complex, as the cellular processes slow down and eventually cease at lower temps, a quick search shows known instances of body temps as low as 18C being recovered from, so the lower limit is rather fuzzy.  However even a drop of a few degrees of you core body temp leads to hypothermia that will quickly render you unable to remove yourself from the conditions and eventual death.
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: grumpydoc on December 20, 2016, 11:03:24 pm
At what point you'd die is a little complex, as the cellular processes slow down and eventually cease at lower temps, a quick search shows known instances of body temps as low as 18C being recovered from, so the lower limit is rather fuzzy.

Wikipedia cites 9oC during Deep Hypothermic Circulatory Arrest (https://en.wikipedia.org/wiki/Deep_hypothermic_circulatory_arrest) although the body is not generally cooled this much in typical practice.

Individuals, especially children have survived very prolonged periods of cardiac arrest having fallen into frozen lakes.

As they say in resus - "you are not dead until you are warm and dead"!

However the range of temperatures where we are comfortable and at which our biochemistry works are largely down to the accident of life having evolved on a planet with large amounts of liquid water and a surface pressure of about 100kPa. Other solutes have been suggested from liquid hydrogen to plasma (https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry). It would be neat to meet a Hydrogen Flouride based life-form but you would not want to shake whatever it uses as a hand  :)

I suspect, however, that water+carbon based chemistries are probably "best" although that does not necessarily mean that another system could not work.
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: VK3DRB on December 24, 2016, 08:28:20 am
As a side note it might be worth mentioning that also the pressure range is not very symmetric from our perspective. The absolute vacuum is just 1bar (or 100 kPa) away but it's relatively simple to achieve pressure values that are magnitudes higher and near the code of our planet, it's supposed to be 330 Gigapascal, letting aside Neutron stars and the like...

Let's assume one can travel to the centre of the core of our planet and and there was an empty room there where you could stay for a few minutes and survive the heat and pressure. Would you float around weightless as if you were in outer space?
Title: Re: Why does cold temp has a limit of -273C/0k and high temp has no limit?
Post by: IanB on December 24, 2016, 09:28:10 am
Let's assume one can travel to the centre of the core of our planet and and there was an empty room there where you could stay for a few minutes and survive the heat and pressure. Would you float around weightless as if you were in outer space?

Yes. The gravitational pull would be the same in all directions so it would cancel out to nothing.