Eli5 What is bode Einstein condensate?



What is Bose Einstein condensate?

In: Physics

Imagine you have a huge trampoline, many miles wide.

You put 5 people on the trampoline, spread out. Each one can jump as much as they want, because the state of the trampoline as a whole is basically just five separate smaller trampolines where each person is jumping. Now, suppose the jumpers got bigger and bigger and bounced the trampoline over wider and wider ranges. They eventually get to the point where the vibrations are wide enough that one jumper’s jumping affects their neighbor: the trampoline can no longer be viewed as a bunch of separate, distinct jumpers, and instead has to be viewed as a whole object with a potentially very complex state (because now a jump at one side of the trampoline affects jumps on the other).

In this analogy, the trampoline is the physical fields underlying a gas, the jumpers are the individual particles in the gas, and the “smeared out” nature of each particle’s wavefunction is represented by the bouncing up-and-down motion of the trampoline surface. As particles cool down, their wavefunctions smear out more and more. This is the uncertainty principle at work: for a particle to have low momentum, it has to have relatively *certain* momentum, which means its position must be correspondingly uncertain. Once the particles get cold (=slow) enough, their wavefunctions start to overlap to a meaningful degree, and that changes what states are possible.

To return to our analogy for a moment, with small bounces, the individual jumpers can jump whenever they want. If you are on one end of the trampoline and I’m on the other, neither of our bounces interfere with one another. But once your bounces affect me, we can no longer be in whatever state we want: our bounces end up synchronized instead, just the same as people on a normal house-sized trampoline. In effect, all the bounces “blur together” into a single state that describes all of the jumpers at once.