MadSci Network: Physics
Query:

Re: Can we fit all the photons in the universe on the head of a pin?

Date: Mon Apr 2 03:19:57 2001
Posted By: Duje Bonacci, Grad student,
Area of science: Physics
ID: 985297268.Ph
Message:

Hallo Dick, and thanks for the question!

Two problems arise when you try to fit an 'infinite' (nothing is infinite 
in this Universe of ours, so think about 'infinity' as just another way of
saying 'as big as you can get') number into the optical fibre.

The first one is that every optical fibre has very specific optical
properties. This is to say that it can only transmit electromagnetic
signals (i.e. 'light') within the certain frequency range. Feeding the
signal which is out of this range into the fibre results just in the
heating of the fibre due to the dissipation of the signal's energy. You can
think of the dissipation process as if there was some sort of 'friction'
within the fibre to the given electromagnetic wave, this friction beeing
caused by the properties of the material that the fibre is made of. The
friction sucks the energy from the wave until it has none left, i.e. until
there is no more radiation (at that frequency). So to conclude, you can
only transmit a limited frequency range through a optical fibre without
energy losses due to the dissipation.

Further, even within this 'allowed' range, you can not stuff the fibre with
as much energy as you want. The reason for this is that, the fibre beeing a
material object, it gets torn appart (it burns) if you try to pass a large
ammount of power through it - it simply can't stand the strain (just like a
copper wire if you try to feed it with too large electrical current). What
happens in this case is that great radiation power enables the individual
atoms to snatch some of the energy and break the bonds that hold them
attached to the surrounding atoms in the fibre which causes the fibre to
quit beeing a fibre...

And now to the title question: can we fit all the photons in the universe
on the top of the needle. I guess we can't, and I see few reasons for this.
The first is that we can't really travel arround the universe with the
light net (the equivalent of the butterfly net, i.e. the thing you use to
catch the butterflies...) and catch photon after photon until the darkness
is all around us (no more light, that is!). Second, say that we somehow
manage to evade just mentioned problems, so we finaly get all the photons
in the universe in a single spatio-temporal point. But alas, this gleaming
gathering would last just for a feeble instant, as these photons would not
be too happy with sticking arround this single point but would instead
preffer to dash off with the speed of light (litteraly) whichever way they
can... 

Hope I've been helpfull

Duje


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