Science Forums 2

[CraigD]

Originally Posted by coldcreation

Because the universe is thought to have never been colder than the observed 2.7 K of the microwave background radiation—an idea based on modern cosmology—it is believed that Bose-Einstein condensates, along with other phenomena that occur below 2.7 K (superfluid helium, helium-3/helium-4 phase separation, adiabatic demagnetization of paramagnetic molecules, Fermi melting point of helium-3, Bose melting point of bosonic atomic gases, etc.) exist nowhere else in the universe other than in the laboratories here on Earth.

I argue that this may be a crucial error. For example, there has been observed at least one place in the universe that is colder than 2.7 K.

I believe coldcreation is misinterpreting the description of the CMBR as having the spectrum of a black body at about 2.7 K. This characteristic does not imply that the CMBR is currently being emitted by solid, liquid, or gaseous matter with a temperature of 2.7 K. It is simply a convenient way of describing its spectrum with a single numeric value.

The description of the temperature of unusual objects such as the “coldest place in the universe” Boomerang Nebula calls for careful consideration of the definition of temperature, the average kinetic energy of the bodies - in the case of a gas like the Boomerang Nebula, atoms - of a system. It’s very low temperature – about 1 K – is calculated by estimating the mass and initial temperature of the outflowing gas that forms it, and dividing by its current, much greater observed volume. It represents the temperature of a small representational volume of space moving at the same velocity as the average of the gas within it – if the entire volume is considered, the temperature is very high – about a million K - due to the great speed of the outflowing gas – about 167000 m/s. (note that, in terms of mass and velocity , temperature is given by , where is the Avogadro number, the gas constant)

Even if only a small volume of the gas is considered, the temperature may still be higher than given by the first calculation, because individual atoms of the gas in even a small volume may have fairly high relative velocities. A artificially produced BEC requires that nearly all fast-moving atoms in it be slowed or expelled. Though I’ve encountered some discussion of the possibility of unusual low-temperature effects in expanding nebulae such as the Boomerang, such as superconductivity of Bose-Einstein condensation, to the best of my knowledge the idea is very speculative. Although one can make the argument that BECs of very small numbers of atoms may rarely, randomly form in any very low-density gas, I suspect that it’s not a significant effect in objects like protoplanetary nebulae, even very cold ones like the Boomerang.