Black hole

The term black hole is of very recent origin. It was coined in 1969 by the American scientist John Wheeler as a graphic description of an idea that goes back at least two hundred years.

At that time there were two theories about light . One was that it was composed of particle , the other was that it was made of waves . We now know that really both theories are correct . 

By the wave/particle duality of quantum mechanics, light can be regarded as both a wave and a particle. Under the theory that light was made of waves , it was not clear how it would respond to gravity . But if light were composed of particles , one might expect them to be affected by gravity in the same way that cannonballs, rockets and planets are.

  

On this assumption , a Cambridge don , John Michelle , wrote a paper in 1783 in the philosophical Transactions of the Royal Society of London.

In it , he pointed out that that a star was sufficiently massive and compact would have a strong gravitational field that light could not escape. Any light emitted from the surface of the surface of star would be dragged back to the star's gravitational attraction before it could get very far.

Michelle suggested that there might be a large number of stars like this. Although we would not be able to see them because the light from them would not reach us, we would still feel their gravitational attraction. Such objects are what we now call black holes , because that is what they are - black voids in space.  

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