If a thermometer is placed in a complete vacuum, what temperature will it register?

---

Request for Question Clarification by tutuzdad-ga on 27 Nov 2003 15:16 PST

Are you curious to know what REACTION a thermometer will have in a
complete vacuum? If so, what kind of thermometer did you have in mind
for this hypothetical experiment? There are many kinds - gas
thermometers, liquid-in-glass thermometers, thermocouples, resistance
thermometers and radiation thermometers just to name a few.

Or, were you simply wanting to know what the temperature of a complete
vacuum would be?

Regards;
tutuzdad-ga

---

Clarification of Question by nosecone1023-ga on 27 Nov 2003 19:00 PST

I'd like to know the actual temperature. If a human were encapsulated
inside the vacuum, what temperature would they experience?

nosecone1023...

Technically, a vacuum is defined as follows:

"A space entirely devoid of matter (called also,
 by way of distinction, absolute vacuum); hence, in a more
 general sense, a space, as the interior of a closed
 vessel, which has been exhausted to a high or the highest
 degree by an air pump or other artificial means"
From HyperDictionary.com
http://www.hyperdictionary.com/dream/vacuum

So, technically, adding a body to a vacuum destroys
the vacuum. The point of a vacuum is to remove matter,
from the largest bits down to the molecules and atoms
which make up the atmosphere.

Temperature is a measure of heat, which is technically
defined in terms of the speed of the atoms and molecules
contained in what is being measured. See these results
from Google's new 'define' parameter:

define:temperature
://www.google.com/search?q=define%3Atemperature

So, the fewer atoms and molecules a vacuum contains,
the lower the temperature will be.

Vacuums, in and of themselves, have no temperature.
The objects inside them do. So if you take an object 
that is 98.6 degrees and place it in a vacuum, it 
will still be 98.6 degrees, though, of course the
heat will dissipate, but in a different way than
it would in 'normal' atmosphere.

The following pdf file, containing a discussion of motors
designed to be run in vacuums, from the Heason Technologies
Group site, makes this point:

"There is a major difference between the nature of heat
 dissipation in a vacuum environment and the nature of
 heat dissipation in atmospheric pressure environments.
 In a high vacuum environment, convection does not exist
 at all and the major heat dissipation mechanisms are
 conduction and radiation."
http://www.heason.com/support/piezo_electric_ceramic/downloads/Application%20Note%20NM5.pdf


Given your nickname, and the other questions you've asked,
it seems to me that you are curious about the temperature
of the vacuum found in the emptiest regions of deep space.

This page, from the 'Windows to the Universe', sponsored
by NASA, notes the following: 

"The temperature in deep space is 3 degrees Kelvin, or
 -270 degrees Celsius. Within the solar system, the
 temperature depends on how close the object is to a
 radiating object such as the sun. Near the sun, of
 course, the temperature can be very high. There are
 three methods of heat transfer: conduction, convection,
 and radiation. The first two require matter as the
 transporting agent. In space, which is essentially a
 vacuum, radiation is the method of heat transfer. This
 radiation comes in the form of visible light, infrared,
 ultraviolet, x-, and gamma-rays."

And, further down, on the same page:

"If a human were to go into space without a space suit,
 they would die within one or two minutes. They would
 not explode, and their blood would not boil. They might
 experience something similar to the 'bends,' with
 swelling and perhaps sunburn. They would not be able
 to breathe, body fluids would begin to vaporize, and
 the person would die."
http://www.windows.ucar.edu/tour/link=/kids_space/qastr_other.html


Please do not rate this answer until you are satisfied that  
the answer cannot be improved upon by means of a dialog  
established through the "Request for Clarification" process. 
 
A user's guide on this topic is on skermit-ga's site, here: 
http://www.christopherwu.net/google_answers/answer_guide.html#how_clarify 
 
sublime1-ga


Searches done, via Google:

"temperature in a vacuum
://www.google.com/search?q=%22temperature+in+a+vacuum

"temperature in outer space
://www.google.com/search?q=%22temperature+in+outer+space

"heat dissipation in a vacuum
://www.google.com/search?q=%22heat+dissipation+in+a+vacuum

---

Clarification of Answer by sublime1-ga on 27 Nov 2003 20:27 PST

nosecone1023...

Oops. I left out a page I meant to give you that was open
in another browser.

This page, from the Chemistry@University of Oxford site,
has this to say about the temperature in the near-perfect
vacuum of deep space:

"The universe beyond our Earth is a study in contrasts of
 temperature. The center of our sun reaches 40 million
 degrees, and the fusion reactions in larger stars, discussed
 in Chapter 8, can reach 2 billion degrees or more. At the
 other end of the scale, temperature has little meaning in
 nearly empty space. If we define temperature in terms of
 the average kinetic energy of molecules, what does
 temperature mean in a region of outer space that has only
 one or two atoms per cubic centimeter? Temperature in a
 vacuum also can be defined in terms of the radiation
 passing through it, compared with the radiation from a
 perfectly non-refelective black body of measurable
 temperature. Interstellar space is filled with microwave
 radiation in the millimeter wavelength range, corresponding
 to a black-body temperature of only 3K by this definition.
 Theoreticians have proposed that this radiation is the
 last remnant of the primeval "big bang" fireball with which
 the universe began 15 billion years ago."
http://www.chem.ox.ac.uk/vrchemistry/Universe/page06.htm

sublime1-ga

Quick response; answer was complete.

Here is perhaps a more direct answer.  The thermometer will read very
nearly the temperature of the walls of the chamber that is holding the
vacuum.

There is little conduction (just a thin wire holding up the
thermometer) and no convection in a vacuum, but there is still exhange
of energy through radiation of heat.  Both the thermometer radiates
heat and the walls radiate heat: every object whose temperature is
above absolute zero radiates heat.   Eventually all the objects in the
vacuum come into temperature equilibrium because the radiation
increases very rapidly with temperature.  Thus the hotter item will
radiate more energy than the the cooler returns, so the cooler object
warms up until it radiates back exactly the same amount.

The situation is complicated a bit if the some of the surfaces are
shiny and others are dark and absorbing, but the same thing eventually
happens. The thermometer reaches the same temperature as the walls.

If each of the walls have different temperatures, you have to add the
contributions carefully.  In outer space with no vacuum chamber, the
radiation from the "walls" are fluxes of light coming from distant
emitting objects: stars, planets, asterioids, space dust, solar wind
particles, etc.  Depending on how close the thermometer is to each of
them them determines what the temperature will be.

Finally, a thermometer is different than a human (at least a living
one).  A human body constantly generates heat and if  "encapsulated"
well enough to survive a vacuum, his internal body heat would
overwhelm any radiation losses.  A suit with less than perfect heat
radiation shielding would need a supplemental heater.  Otherwise the
human's extremeties would begin to cool and hypothermia might be the
result.