Re: uncertainty and the age of the universe

From: Chris Dams (chrisd_at_gamow.sci.kun.nl)
Date: 06/03/04 

Date: Thu, 3 Jun 2004 23:15:05 +0000 (UTC)

Dear Alistair,

alistair@goforit64.fsnet.co.uk (alistair) writes:

>The universe is about 10^18 seconds old since the Big Bang.
>This means using E x t = hbar that energy that has been emitted
>sometime after the Big Bang has an uncertainty in its magnitude of 10^
>- 52 Joules.
>Suppose this uncertainty of energy is associated with a photon that
>was emitted sometime after the Big Bang:

>Using E = h x f we find that 10^ - 52 = 10^ - 34 x f
>f = 10 ^ -18 s^-1
>For a photon wavelength x frequency = speed of light
>so wavelength x 10^ - 18 = 10^8
>wavelength = 10^ 26 metres.

>So the uncertainty in the photon's wavelength is about the size of the
>universe.
>If the universe was older this wavelength would be greater and would
>match the size of the universe.
>Can the uncertainty principle be used to tell us the size of the
>universe?

I think your reasing contains an error. You start with the age of the
universe then go to the energy associated with this amount of time by
the uncertainty principle and then to the frequency of a photon of that
energy. In the first step you multiply 1/t by hbar and in the second
step you divide by it again. Effectively you are calculating f=1/t. The
value of hbar does not affect this answer. Therefore, it would appear
that what your calculation is not related in any way to the uncertainty
principle.

Best,
Chris Dams

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