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Q & A: Absolute Zero

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Really Really Really Cold
Q:
Is Absolute Zero theoretically attainable, and if so, what effect would it have on the structure of elementary particles, such as electrons or quarks?
- Matt Schur
New York, NY
A:
Matt- Nice question. Absolute zero is NOT theoretically attainable, according to the laws of thermodynamics. The efficiency of a refrigerator whose cold side was at zero would itself be zero, so any heat leak, no matter how small, would raise the temperature above zero.

Electrons and particles made of quarks, like protons, are already so cold under normal conditions that they have almost no chance of being in any state but the one of lowest energy. Unless there are some hidden properties involving extremely small energy differences among hidden versions of the low-energy states (not a very likely prospect) further cooling would have no effect on their structures.

Mike W.

(published on 10/22/2007)

Follow-Up #1: Cosmic microwave background temperature?

Q:
How was the temperature of the cosmic background radiation deduced to be exactly 3ºK before it was measured?
- Robert Kingshill
Houston
A:
Dear Robert,
The number 2.725 wasn't deduced, it was measured.  In 1964 background microwave radiation was detected by  Penzias and Wilson. They won a Nobel Prize for their discovery.  The frequency dependence of this radiation showed that it followed a distribution known as black body radiation, radiation emitted by any object at a given temperature.   The temperature turned out to be 2.725 degrees Kelvin. 
For more information I recommend the Wiki article:
 http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation
Also, here is a list of earlier scientific papers published on the effect.  Many people had speculated that there should be such a background temperature but without accurate microwave measurements could not pin down the exact temperature:


1941 Andrew McKellar was attempting to measure the average temperature of the interstellar medium, and reported the observation of an average bolometric temperature of 2.3 K based on the study of interstellar absorption lines.[13][14]
1946 Robert Dicke predicts ".. radiation from cosmic matter" at <20 K but did not refer to background radiation[15]
1948 George Gamow calculates a temperature of 50 K (assuming a 3-billion-year old Universe),[16] commenting it ".. is in reasonable agreement with the actual temperature of interstellar space", but does not mention background radiation.
1948 Ralph Alpher and Robert Herman estimate "the temperature in the Universe" at 5 K. Although they do not specifically mention microwave background radiation, it may be inferred.[17]
1950 Ralph Alpher and Robert Herman re-estimate the temperature at 28 K.
1953 George Gamow estimates 7 K.[15]
1955 Émile Le Roux of the Nançay Radio Observatory, in a sky survey at λ=33 cm, reported a near-isotropic background radiation of 3 kelvins, plus or minus 2.[15]
1956 George Gamow estimates 6 K.[15]
1957 Tigran Shmaonov reports that "the absolute effective temperature of the radioemission background ... is 4±3K".[18] It is noted that the "measurements showed that radiation intensity was independent of either time or direction of observation... it is now clear that Shmaonov did observe the cosmic microwave background at a wavelength of 3.2 cm"[19]
1960s Robert Dicke re-estimates a MBR (microwave background radiation) temperature of 40 K[15]
1964 A. G. Doroshkevich and Igor Novikov publish a brief paper, where they name the CMB radiation phenomenon as detectable.[20]
1964–65 Arno Penzias and Robert Woodrow Wilson measure the temperature to be approximately 3 K. Robert Dicke, P. J. E. Peebles, P. G. Roll, and D. T. Wilkinson interpret this radiation as a signature of the big bang.
1983 RELIKT-1 Soviet CMB anisotropy experiment was launched.
1990 FIRAS on COBE measures the black body form of the CMB spectrum with exquisite precision.
Apr 1992 Scientists who analyzed data from COBE DMR announce the discovery of the primary temperature anisotropy.[21]
1999 First measurements of acoustic oscillations in the CMB anisotropy angular power spectrum from the TOCO, BOOMERANG, and Maxima Experiments.
2002 Polarization discovered by DASI.[22]
2004 E-mode polarization spectrum obtained by the CBI.[23]
2005 Ralph A. Alpher is awarded the National Medal of Science for his groundbreaking work in nucleosynthesis and prediction that the universe expansion leaves behind background radiation, thus providing a model for the Big Bang theory.
2006 Two of COBE's principal investigators, George Smoot and John Mather, received the Nobel Prize in Physics in 2006 for their work on precision measurement of the CMBR.


LeeH

p.s. I think this is how Alpher, Dicke, and others estimated of TCMB before the measurement. They knew that T(at time of transparency) had to be ~3000K just from the energy of H ionization. So they had to estimate the expansion factor since then. They estimated the density of matter at some earlier higher T from the nuclear abundances. (The higher the matter density, the higher the ratio of deuterium to hydrogen, for example.) Then they could extrapolate to what the matter density was when things had cooled to 3000K. They had a decent idea of our current matter density, so they got about how much the universe had expanded. From that, they could calculate the ratio of the current TCMB to 3000K. The estimates tended to be high, due to poor estimates of the Hubble parameter.  Mike W.


(published on 10/03/12)

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