Canadians don’t have much to be proud of,
but we can regale you with our ability to
withstand freezing cold temperatures.
Now, I live on the West Coast, so I’m soft
and weak, rarely experiencing temperatures
below freezing.
But for some of my Canadian brethren, temperatures
can dip down to levels your mind and body
can scarcely comprehend.
For example, I have a friend who lives in
Winnipeg, Manitoba.
For a day last winter, the temperatures there
dipped down -31C, but with the windchill,
it felt like -50C.
On that same day, it was a balmy -29C on Mars.
On Mars!
But for scientists, and the Universe, it can
get much much colder.
So cold, in fact, that they use a completely
different temperature scale - Kelvin - to
measure how far away things are from the coldest
possible temperature: Absolute Zero.
On the Celsius scale, Absolute Zero is -273.15
degrees.
And in Fahrenheit, it’s -459.67 degrees.
In the Kelvin scale, however, it’s very
simple.
Absolute Zero is 0 kelvin.
At this point, a science explainer is going
to stumble into a minefield of incorrect usage.
It’s not 0 degrees kelvin, you don’t say
the degrees part, just the kelvin part.
Just kelvin.
This is because when you measure something
from an arbitrary point, like the direction
you just turned, you’ve changed course 15-degrees.
But if you’re measuring from an absolute
point, like the lowest physical temperature
defined by nature, you drop the degrees because
it’s an absolute.
An Absolute Zero.
Of course, I’ve probably gotten that wrong
too.
This stuff is hard.
Anyway, back to Absolute Zero.
Absolute Zero is the coldest possible temperature
that can theoretically be reached.
At this point, no heat energy can be extracted
from a system, no work can be done.
It’s dead Jim.
But it’s completely theoretical.
It’s practically impossible to cool something
down to Absolute Zero.
In order to cool something down, you need
to do work to extract heat from it.
The colder you get, the more work you need
to do.
In order to get to Absolute Zero, you’d
need to put in an infinite amount of work.
And that’s ridiculous.
As you probably learned in physics or chemistry
class, the temperature of a gas translates
to the motion of the particles in the gas.
As you cool a gas down, by extracting heat
from it, the particles slow down.
You would think, then, that by cooling something
down to Absolute Zero, all particle motion
in that something would stop.
But that’s not true.
From a quantum mechanics point of view, you
can never know the position and momentum of
particles at the same time.
If the particles stopped, you’d know their
momentum (zero) and their position… right
there.
The Universe and its laws of physics just
can’t allow that to happen.
Thank Heisenberg’s Uncertainty Principle.
Therefore, there’s always a little motion,
even if you could get to Absolute Zero, which
you can’t.
But you can’t extract any more heat from
it.
The physicist Robert Boyle was one of the
first to consider the possibility that there
was a lowest possible temperature, which he
called the primum frigidum.
In 1702, Guillaume Amontons created a thermometer
that he calculated would bottom out at -240
C. Pretty close, actually.
But it was Lord Kelvin, who created this absolute
scale in 1848, starting at -273 C, or 0 kelvin.
By this measurement, even with its windchill,
Winnipeg was a balmy 223 kelvin on that wintry
day.
The surface of Pluto, on the other hand varies
from a low of 33 kelvin to a high of 55 kelvin.
That’s -240 C to -218 C.
The average background temperature across
the entire Universe is just 2.7 kelvin.
You won’t find many places that cold, unless
you get out to the vast cosmic voids that
separate galaxy clusters.
Over time, the background temperature of the
Universe will continue to drop, but it’ll
never actually reach Absolute Zero.
Even in a Googol years, when the last supermassive
black hole has finally evaporated, and there’s
no usable heat left in the entire Universe.
In fact, astronomers call this bleak future
the “heat death” of the Universe.
It’s heat death, as in, the death of all
heat.
And happiness.
You might be surprised to know that the coldest
temperature in the entire Universe is right
here on Earth.
Well, sometimes, anyway.
And assuming the aliens haven’t got better
technology than us, which they probably do.
At the time that I’m recording this video,
physicists have used lasers to cool down Rubidium-87
gas to just 170 nanokelvin, a tiny fraction
above Absolute Zero.
In fact, they won a Nobel Prize for their
work in discovering Bose-Einstein condensates.
NASA is actually working on a new experiment
called the Cold Atom Lab that will send a
version of this technology to the International
Space Station, where it should be able to
cool material down to 100 picokelvin.
That’s cold.
Here are your takeaways.
Absolute Zero is the coldest possible temperature
than can ever be reached, the point at which
no further heat energy can be extracted from
a system.
Never say degrees kelvin, you’ll cause so
much wincing.
The Universe can’t match our cold generating
abilities… yet.
Take that Universe.
I’d love to hear the coldest temperature
you’ve ever personally experienced.
For me, it was visiting Buffalo in December.
That’s not right.
In our next episode, we wonder where in the
Solar System it might be safe to remove your
space helmet.
Make sure you stick around for the blooper.
Once again, it’s time to thank the 602 amazing
patrons of Universe Today.
These are the people who directly support
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video explain the Universe at you.
Thank you.
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Oh, and we strip away all the advertising
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Today I’d like to thank Mark de Vrij, Chris
Bosland, David Hein, and the rest of the members
who support us in making great space and astronomy
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