Mixing quantum and relativity

Researchers from Harvard and Raytheon BBN Technology have observed, in their lab, a phenomenon that so far has been theorised to make sense of black holes in the universe. These physical monsters (in the sense that defies our imagination by bending so much the space time that nothing can escape from their attraction, not even light, hence the name: black holes) have a behaviour that can be explained only using both relativistic phenomena (the bending of the space time) and quantum phenomena (what happens at their edges with the emission of random photons that can happen in quantum physics but it is not supposed to happen in relativistic physics).

Black holes are far away from us and are "invisible": we suspect they are there by looking at the effects they create on surrounding objects (stars). Hence it is almost impossibile to run experiments on black holes.

Well, according to what these researchers have found a phenomenon that is typical of black holes, electrons behaving like a liquid, strongly interacting with one another, can be observed in a lab using graphene.

In a conducting material electrons move, and they "flow" in une specific direction if there is an electric field "pushing" them (a voltage).  However, their movement is pretty slow, a few cm per second, since they jump from one atom to another in a 3 dimensional space. 
Not so in graphene. Graphene is a one atom thick layer, as thin as it gets, and we can say it is a 2D object. Electrons in a graphene layer move at 1/300 of the speed of light, that is some 1,000km per second, that is infinitely faster than in a normal conductor.

Moving this fast they also bump into one another (something that does not happen in a normal conductor, each electron keeps its distance from the other and bumps are rare). Researchers have estimated some 10 trillion bumps every second! This is what happens (in terms of atoms) in a fluid and indeed the flow of electrons in the graphene looks like the flow of a liquid. 

Why is it that this was only observed now and not before, since we have had graphene for many years?  The reason is that the behaviour of electrons as they flow in a graphene layer is strongly influenced by the purity of graphene and by what is around the graphene layer. What the researchers did here was to sandwich the graphene, a very pure layer of it, between layers of non conducting crystal layers having similar atomic structure of graphene. 

To observe the behaviour of the electrons they have observed the thermal conductivity in a very precise way (they measured the temperature with a precision of 1/1000 of a degree C) and to do that they had to invent a new method of measurement.

In practice, they observed the behaviour that electrons are supposed to have at the edges of a black hole. 

This provides better understanding at the edge of physics. For the practical implications we might need to wait a few more years... 

Author - Roberto Saracco

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