In his novel The Picturegoers, David Lodge gives a graphic description of infinity as it applies to time: “Think of a ball of steel as large as the world, and a fly alighting on it once every million years. When the ball of steel is rubbed away by the friction, eternity will not even have begun.”
It give a nice feeling of what infinity means.
However from a physics point of view there are a couple of little issues.
If the ball of steel is surrounded by air, you have an atmosphere with a lot more friction than your fly landing, so it gets rubbed away a lot quicker.
If it is not surrounded by air, the fly will not be able to fly and will hit the sphere with an almighty splat. You could count the millions of years by the splat marks. The sphere might get melted and a bit of debris knocked off by each splat, but the gravity of the sphere is very high so none of the debris will escape and you will end up with a steel sphere covered in desiccated fly. The fly will dry up and freeze in the vacuum of space before it hits the sphere.
And who is going to shunt the poor fly out every million years into space to fall onto the sphere with a silent crunch.
Someone suggested using this analogy, to seriously contemplate eternity. I think I understand eternity, and infinity, and using this analogy got me thinking about a sphere the size of the world, and how a fly could land on it. At which point the analogy broke down.
Another analogy would be to use human history assuming that we are now at 2,400,000 years where 1 hour is 100,000 years. Then recorded history is a minute or two. You then expand that up to the history of the earth, which is much longer, and you have a period of time that if it were a 24hour atomic clock powered by the energy of the sun, then eternity is much longer than the life of the clock and this history of the earth is much less than the first second of the sun powered clock.
Ronald Duncan's Blog 