Re: Why can a photon only interfere with itself across multiple universes but not with other photons in the same universe?

David Deutsch <david.deutsch-LR/[email protected]> Mon, 6 Jan 2014 19:40:59 +0000
Newsgroups	gmane.science.physics.fabric-of-reality
Message-ID	<[email protected]>
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On 6 Jan 2014, at 14:05, [email protected] wrote:

> This is something that has bugged me for a while:

> Why can a photon only interfere with itself across multiple universes (in=
terference), but can't interact with other photos in the same universe?  i.=
e, why don't two photons interact when fired directly at each other?, and y=
et the same photon can interfere with itself across multiple universes?

Quantum theory describes nature according to certain laws of motion.

These laws do not refer to universes or interference. Those are approximate=
 terms. The laws predict that photons in a vacuum do not interact with each=
 other, but that a single photon in a suitable interferometer interacts str=
ongly with itself. Two or more photons in a suitable interferometer interac=
t with each other as well as with themselves.

-- David Deutsch




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      <p>On 6 Jan 2014, at 14:05, [email protected] wrote:<br>
<br>
&gt; This is something that has bugged me for a while:<br>
<br>
&gt; Why can a photon only interfere with itself across multiple universes (interference), but can&#39;t interact with other photos in the same universe?  i.e, why don&#39;t two photons interact when fired directly at each other?, and yet the same photon can interfere with itself across multiple universes?<br>
<br>
Quantum theory describes nature according to certain laws of motion.<br>
<br>
These laws do not refer to universes or interference. Those are approximate terms. The laws predict that photons in a vacuum do not interact with each other, but that a single photon in a suitable interferometer interacts strongly with itself. Two or more photons in a suitable interferometer interact with each other as well as with themselves.<br>
<br>
-- David Deutsch<br>
<br>
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