Absolute Zero
Threads - Absolute Zero
On
14/10/2003, Soundwarp wrote:
How was absolute zero originally defined?
A snippet from a brief article in "Electronics News", 9/10/03:
"A Massachusetts Institute of Technology (MIT) team of scientists has
cooled a sodium gas to the lowest temperature ever recorded - only
half-a-billionth of a degree above absolute zero (minus 273 deg. C). The
work, repeated in a recent issue of SCIENCE, improves on the previous
record of a factor of six."
How come that this latest recording has been the lowest recorded ever?
Sean
Elliott replied:
When
we calculated Absolute Zero in thermodynamics, we looked at the amount
that the volume of a gas reduces as it becomes colder. The more
you cool it, the more a gas contracts in volume. Eventually,
there is a point at which it is physically impossible for a gas to
'shrink' any further. This temperature is at -273.15...(etc) deg
C (otherwise denoted as 0 degrees
Kelvin).
This
is a theoretical limit temperature; nothing can get colder than zero
degrees Kelvin in the same way that nothing can go faster than the
speed of light.
As
such, nothing has been taken to exactly absolute zero but people have
gotten very very close. In this case, "only half-a-billionth of a
degree".
Paul Williams
responded:
I'll have a go
(attempt) at this:
I think that the
term degree was dropped from the
Kelvin scale in the 1960s.
So for Absolute
Zero we have 0 K.
This is a state
of minimum entropy.
The entropy of a
system cannot be equal to zero (2nd Law of Thermodynanics)
The state
equation for an ideal gas is:
PV = nRT
(where P=pressure; V=volume; n = amount of moles; R= molar gas
constant; T=temperature)
If T=0, we have
a condition where either P (pressure) or V (volume) must be 0.
This is clearly
impossible.
Atoms even at
Absolute Zero - as David Martin pointed out - possess electrons at a
minimum energy state - that is they still possess energy. Now I know as
much Quantum Theory as I know how to make Haggis - which is to say none
at all.
Nevertheless:
I'm led to
believe that the Heisenberg Uncertainty Principle would be violated if
molecules could cease all motion - they cannot - at 0 K they will still
vibrate with a miniscule energy - this, I believe, is known as
Zero-Point energy.
>
This is a theoretical limit temperature; nothing can get colder than
zero
> degrees Kelvin in the same way that nothing can go faster than the
speed of
> light.
There is
apparently a way if we look at a narrow sector of states - that is spin
up or spin down states of electrons. By adding energy we can decrease
entropy as regards these states.
Sort of like
approaching 0 K through the back door...
I do not
understand this so best to leave it for someone who knows - it seems
like a 'trick' to me - the system as a whole is not getting 'colder'.
I can't see how
this has anything to do with the speed of light.
Perhaps?:
Nothing which
possesses mass can reach c.
No physical
system can reach Absolute Zero.
Kevin
Phyland added:
<Nothing
which possesses mass can reach c.>
Now
that (apparently) light has been made to stop (or at least pause) this
statement may no longer be even an absolute!
:))
P.S.
I'm reminded (for no reason I can fathom) of George R.R. Martin's first
Analog story called FTA...where they finally discovered
hyperspace and found that the speed in hyperspace was waayyy lower than
c...:))
Kevin
later offered a correction:
>George
R.R. Martin's first Analog story called FTA...<
Just
in case somebody's been rushing to their Analog collection...mea
culpa...FTA was published in 1974 while "The Second
Kind Of Loneliness" was published in 1972...mind's obviously going...
Paul Williams
responded:
This reminds me
of a story I read about 30 years ago. It may have been in John
Carnell's "New Writings in Science Fiction" series.
A spaceship
leaves the vicinity of Earth attempting the first jump into hyperspace.
They arrive
intact - virtually instantaneously - in the neighbourhood of Alpha
Centauri.(A)
To their
surprise and horror they see this sun start to go nova.
Much thought and
calculation determine them to go back to Sol slowly - just in case
their exit from hyperspace was the cause of Alpha Centauri's demise.
Their return via hyperspace may possibly cause the Sun to go nova as
well.
A long time
later (have to be logically about 4 years later) they see in the far
distance that our Sun has (shock horror) gone nova as well.
Jumping into
hyperspace was as deadly as exiting it...
<<<<Heartwrenchingly
lonely music should play>>>
<<<The
End>>>
David
Sutcliffe replied:
I
can't remember the exact details, or where I read it; that interference
patterns created between two waves can travel faster than
the waves themselves. Follows that the interference patterns
created between two ray of light can travel faster than c. The
theory as I understand it is that - if the patterns are modulated,
then information can be made to travel faster than light.
Paul Williams
replied:
I think I
understand this a *very little bit* so will try:
The 'Group
Velocity' travels faster than c.
When light
phases were modulated, so as to attempt to send information faster than
c, the information arrived at a speed slower than c. So in reality
*nothing* travels faster than c. Or, what appears to be
travelling faster than c is really *nothing* at
all. If this was
true - that information could travel faster than c - causality would be
violated. (Kevin mentions this)
A simple example
of something apparently moving faster than c would be if one spun
around outside with a poweful laser in hand, - the 'end' of the light
beam would appear to be moving faster than c if one looked at how the
laser light played across a distant object - say the Moon. Information
cannot be sent faster than c through this apparent superluminal
movement for the source light is still restricted to c.
Zero
Sum wrote:
On
Thu, 16 Oct 2003 18:46, David Sutcliffe wrote:
>
Now - just how do I put next week's powerball numbers onto the system
There
appears to actually be a way. It is however embedded in the
quantum world. When we build the forst full scale quantum
computer we may see some 'interesting'things (like the going nova to
prevent its completion?)...
Kevin Phyland
added:
hmmnn...my
memory is really rusty these days but I seem to recall a difference
between wave speed and phase speed for light...the
possibility of INFORMATION travelling faster than c is I think
precluded by any number of physical laws...among them causality...
