Is the coldest place in the universe likely to be artificial or natural? The Boomerang Nebula is often cited as one of the coldest natural places in the universe at 1 K, but that's about 10 orders of magnitude off from what's been created in a lab.
Are there theoretical mechanisms that can inherently trump our (apparent) mastery of cold or is the coldest place in the universe likely to be some scientist's lab (here or elsewhere)?
 A: Everything in the universe is bathed in the glow of the cosmic microwave background, and this has a temperature of about 2.7K. By this temperature I mean a black body at 2.7K in equilibrium with the CMB would neither heat up nor cool down.
So we expect large objects to have a temperature of at least 2.7K because if they were cooler the CMB would heat them up. At the moment the Boomerang Nebula appears to be cooling due to its expansion faster than the CMB can heat it up again. However in the fullness of time the CMB will reheat it so the low temperature is only temporary. If you're interested to learn more the paper describing the temperature measurements is here.
We can temporarily create extremely low temperatures in the lab because we can use energy to pump heat out and then insulate the experiment from the surrounding higher temperatures. However without an infinite power source this can only be temporary, and in the longer term our experiment has to warm up again.
A: Temperature changes using thermodynamic means occur asymptotically. That means cooling through volume expansion is limited. Currently, the lowest temperature reached by humans is 1.0 × 10-10 Kevlins. The star would have to eject gas at near the speed of light to reach that temperature.
A super massive black hole would produce an event horizon with lower temperatures, but a Bose–Einstein condensate, like the one to set the record, should be able to go even lower.
