# Photons and the Uncertainty Principle

#### Qbit42

Using the meager physics knowledge I've scrapped together over my 19 year life span I've arrived at the following conundrum. It's more than likely that I'm entirely wrong, but I'd like to know why. Anyways here it goes.

First let me unviel my understanding of the universe, limited though it may be. Elementary particles exibit an phenomenon known as the uncertainty principal, which goes something like
(delta)x(delta)p = h/4(pie). A photon is one such elemetary particle. As far as my understanding of photons goes they are quantized bundles of light energy, which to me suggests that it would travel at the speed of light. It has been well established that the speed of light is constant for any particular medium. So my question is, if the speed of light is always a constant, that would mean that (delta)p is 0, making (delta)x infinity. This makes little sense to me since that would make it neigh impossible to ever find a photon. Also it would give rise to the following paradox. Since the speed of light varies in different substances, and the universe is not a homogeneous mixture of substances, we could never tell which substance a photon is actually travelling though (due to (delta)x being infinity). Since we can't tell what substance it is travelling though, we cannot say what its momentum truely is. Yet this uncertainty in momentum would allow (delta)x to come down from infinity, making it possible to discover which material the photon is in, thus allowing the momentum to be calculated precisely If the momentum is claculated precisely, then (delta)x again rises to infinity. You can see the paradox present here. Can someone please shed some light on this for me, no pun intended. :tongue:

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#### ZikZak

You are incorrect in stating that the momentum is definitely known. The momentum of a photon has nothing to do with its velocity; it is directly proportional to the frequency.

#### Qbit42

You are incorrect in stating that the momentum is definitely known. The momentum of a photon has nothing to do with its velocity; it is directly proportional to the frequency.
Oh really? Thanks!

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