Friday, September 19, 2008

How Far Do Those Phages Stretch?

The number of viruses in the biosphere has been estimated to be anywhere from 1030 to 1032. But what does this number really mean? How big is 1031? (The number I see most commonly cited as the number of phages in the biosphere)

Roger Hendrix gives a great list of examples, and one of these is "How far will 1031 phages stretch if laid end to end?" I thought I would do the calculation for myself (and the readers) to see exactly how long 10^31 phages will stretch.

So, we must first begin with two assumptions.

1) The number of phages in the biosphere. 1031 is the number I see most cited, but I have also seen 1030 and 1032. Since 1031 is more familiar too me, and is between the others, we'll use this.

2) The length of a phage virion. The average range of virion size is 25ish to 250ish nm. So, I will use 125nm as a middle average.

The Equations
125nm at 1031 phages, laid end-to-end is 1.25 x 1033 nm.

This converts to 1.25x1024m
Or 1.25x1021 km

But how far is 1021km?

1 km is 1.05702341 × 10-13 light years
So, 1.25x1021km = ~1.3 x 108 light years

108 light years?! THAT'S A LOT!

Here's some scale:

Distance to the Moon: 0.00000004 light years
To the Sun: 0.000016 light years
To Pluto: ~0.0005 light years
Distance from the Sun to the Center of the Milky Way: ~2.6x104 light years
Diameter of the Milky Way: 1 x 105 light years
To Andromeda Galaxy: 2.5x106 light years
To the M81 Local Group: 1.1x107 light years

Phages would stretch a whole order of magnitude further than the next closest galactic local group! Almost 100x farther than the Andromeda Galaxy! And 1000X longer than the diameter of the whole Milky Way!

Mind boggling.