Einstein-Bose Condensation and the observer

Einstein-Bose Condensation occurs when atoms are made very, very cold and they coalesce into a single blob. The experiments to create this consist of using lasers to slow the atoms down and using a magnetic field keep the atoms together.

The demos they have on the above link represent the atoms like little balls that are slowed when they pass through the intersection of two laser beams. Eventually the atoms get stuck in the intersecting area.

But this got me thinking, does the observation of the condensation depend on both the observer and the atoms not having motion? How do the atoms know they are stopped? Although the atoms are not moving relative to the table, they are still moving through the universe. They have only been stopped relative to the experiment apparatus.

For example, if the scientists set up the experiment along the side of the road and I was driving by in my car, would I be able able to observe the condensate even though I was moving 60 mph faster than the atoms?


The whole point of Einstein’s theories is that there is and can never be any absolute frame of reference. All reference frames are local.

So compared to the background both the condensate and you in your car are in the same frame of reference. You would have no problem discerning that they are motionless relative to the experimental apparatus.

Energy due to motion is called kinetic energy. Translational kinetic energy is different than thermal kinetic energy. The first is the energy of the bulk motion of matter. The second is the energy of the internal vibrations and interactions of the matter.

The Bose Einstein Condensate (BEC) forms at extremely low pressures and temperatures. Low thermal energy is important, but the translational kinetic energy doesn’t matter, except for keeping the BEC in the trap.

While you are driving past the BEC, you’ll observe it has kinetic energy. But it’s temperature (the thermal energy) will still be cold, even in your frame. You will still observe the BEC.

The key is that all the atoms of the condensate are at rest (or very nearly so) relative to each other. This is as opposed to the usual state where each atom is jiggling around and bumping into its neighbors. What they’re doing relative to anything else doesn’t matter.

So do they even have to be cold? Say you had two atoms in a vacuum boucing around normally. At some point they just happen to be next to each other going the exact same speed and exact same direction. Would they spontaniously create a condensation?

Without the extreme cold that slows motion, it’s hard to believe that the atoms would ever be in such a position, or if they were only for such a fleetingest split second that it would be insufficient to make a connection. Atoms move phenomenal amounts under normal conditions.

Well, yes, but given conservation of momenta & energy, there’s no way for the two atoms to get into such a configuration without some kind of external force. And any number of atoms moving in lockstep like you describe are, by definition, cold.