<story><title>How Bell’s Theorem proved ‘spooky action at a distance’ is real</title><url>https://www.quantamagazine.org/how-bells-theorem-proved-spooky-action-at-a-distance-is-real-20210720/</url></story><parent_chain><item><author>Kranar</author><text>&amp;gt;They are identical in every way, except one is red and the other is blue. I randomly grab one in each hand and show my hands closed. Now the states of the ball are entangled: as soon as you see the color of one ball, that &amp;quot;determines&amp;quot; the color of the other.&lt;p&gt;This gets used to explain entanglement but it really has absolutely nothing to do with it. This is nothing that the ancient Greeks wouldn&amp;#x27;t have known.&lt;p&gt;Not to pick on you specifically, but do people really think it took a major revolution in physics in order to understand that if there are two balls, one is blue and one is red, then if you see one of the balls is red, you can conclude the other ball is blue?&lt;p&gt;It&amp;#x27;s something that I think humans can solve at the age of 3.&lt;p&gt;The failure in your explanation is right when you state that &amp;quot;one of the balls is red and the other is blue&amp;quot;. The entire point of entanglement is that such a statement is not possible, that&amp;#x27;s a strictly classical interpretation. Rather, both balls are in a superposition of being both red and blue simultaneously, and it is not possible in principle to assign a color to either one of them until the moment a measurement is made.</text></item><item><author>tylerhou</author><text>A classical analogy for entanglement: suppose I have two balls in a bag. They are identical in every way, except one is red and the other is blue. I randomly grab one in each hand and show my hands closed. Now the states of the ball are entangled: as soon as you see the color of one ball, that &amp;quot;determines&amp;quot; the color of the other. (Not claiming that this is a perfect analogy, but I don&amp;#x27;t see where it diverges from how entangled quantum waves would behave.)&lt;p&gt;&amp;gt; Among the fundamental differences is the fact that classical information can be copied but quantum states cannot be cloned.&lt;p&gt;The no-cloning theorem says that there exists no universal quantum machine that can perfectly clone an arbitrary quantum state. However, that does not preclude a machine that can imperfectly clone any quantum state, or machines that can perfectly clone some but not all quantum states [1]. (Clearly the information transferred to my brain is not a perfect copy of your brain&amp;#x27;s state, and your DNA is not perfectly copied every time.)&lt;p&gt;[1] &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;arxiv.org&amp;#x2F;abs&amp;#x2F;quant-ph&amp;#x2F;9607018&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;arxiv.org&amp;#x2F;abs&amp;#x2F;quant-ph&amp;#x2F;9607018&lt;/a&gt;</text></item><item><author>lisper</author><text>That&amp;#x27;s not a bad analogy, but you have to be very careful here because no classical analogy can be a perfect fit for entanglement.  The wave function is deeply and fundamentally different than our classical reality, and there is no way to reproduce its behavior classically.  Among the fundamental differences is the fact that classical information can be copied but quantum states cannot be cloned.  This is IMHO the single biggest disconnect between the wave function and classical reality because the nature of our (classical) existence is fundamentally intertwingled with copying (classical) information.  It is happening right now even as you read this.  Information is being copied out of my brain onto the internets and into your brain.  At the same time, all our cells are busily copying the information in our DNA, and so on and so on.</text></item><item><author>ericb</author><text>If we were in a simulation, would the speed of light be the processing speed of the universe as each area re-renders, and spooky action at a distance be two variables pointed to the same memory location, populated with a lazy-loaded value, with copy-on-write semantics?&lt;p&gt;edit: seems like it is lazy loaded, so revised my summary.</text></item></parent_chain><comment><author>nikhilgk</author><text>&amp;gt; This gets used to explain entanglement but it really has absolutely nothing to do with it. This is nothing that the ancient Greeks wouldn&amp;#x27;t have known.&lt;p&gt;To be fair, this usually crops up in entanglement discussions to deomonstrate how it can&amp;#x27;t be used for FTL communication and not to actually explain what entanglement is.</text></comment>
<story><title>How Bell’s Theorem proved ‘spooky action at a distance’ is real</title><url>https://www.quantamagazine.org/how-bells-theorem-proved-spooky-action-at-a-distance-is-real-20210720/</url></story><parent_chain><item><author>Kranar</author><text>&amp;gt;They are identical in every way, except one is red and the other is blue. I randomly grab one in each hand and show my hands closed. Now the states of the ball are entangled: as soon as you see the color of one ball, that &amp;quot;determines&amp;quot; the color of the other.&lt;p&gt;This gets used to explain entanglement but it really has absolutely nothing to do with it. This is nothing that the ancient Greeks wouldn&amp;#x27;t have known.&lt;p&gt;Not to pick on you specifically, but do people really think it took a major revolution in physics in order to understand that if there are two balls, one is blue and one is red, then if you see one of the balls is red, you can conclude the other ball is blue?&lt;p&gt;It&amp;#x27;s something that I think humans can solve at the age of 3.&lt;p&gt;The failure in your explanation is right when you state that &amp;quot;one of the balls is red and the other is blue&amp;quot;. The entire point of entanglement is that such a statement is not possible, that&amp;#x27;s a strictly classical interpretation. Rather, both balls are in a superposition of being both red and blue simultaneously, and it is not possible in principle to assign a color to either one of them until the moment a measurement is made.</text></item><item><author>tylerhou</author><text>A classical analogy for entanglement: suppose I have two balls in a bag. They are identical in every way, except one is red and the other is blue. I randomly grab one in each hand and show my hands closed. Now the states of the ball are entangled: as soon as you see the color of one ball, that &amp;quot;determines&amp;quot; the color of the other. (Not claiming that this is a perfect analogy, but I don&amp;#x27;t see where it diverges from how entangled quantum waves would behave.)&lt;p&gt;&amp;gt; Among the fundamental differences is the fact that classical information can be copied but quantum states cannot be cloned.&lt;p&gt;The no-cloning theorem says that there exists no universal quantum machine that can perfectly clone an arbitrary quantum state. However, that does not preclude a machine that can imperfectly clone any quantum state, or machines that can perfectly clone some but not all quantum states [1]. (Clearly the information transferred to my brain is not a perfect copy of your brain&amp;#x27;s state, and your DNA is not perfectly copied every time.)&lt;p&gt;[1] &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;arxiv.org&amp;#x2F;abs&amp;#x2F;quant-ph&amp;#x2F;9607018&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;arxiv.org&amp;#x2F;abs&amp;#x2F;quant-ph&amp;#x2F;9607018&lt;/a&gt;</text></item><item><author>lisper</author><text>That&amp;#x27;s not a bad analogy, but you have to be very careful here because no classical analogy can be a perfect fit for entanglement.  The wave function is deeply and fundamentally different than our classical reality, and there is no way to reproduce its behavior classically.  Among the fundamental differences is the fact that classical information can be copied but quantum states cannot be cloned.  This is IMHO the single biggest disconnect between the wave function and classical reality because the nature of our (classical) existence is fundamentally intertwingled with copying (classical) information.  It is happening right now even as you read this.  Information is being copied out of my brain onto the internets and into your brain.  At the same time, all our cells are busily copying the information in our DNA, and so on and so on.</text></item><item><author>ericb</author><text>If we were in a simulation, would the speed of light be the processing speed of the universe as each area re-renders, and spooky action at a distance be two variables pointed to the same memory location, populated with a lazy-loaded value, with copy-on-write semantics?&lt;p&gt;edit: seems like it is lazy loaded, so revised my summary.</text></item></parent_chain><comment><author>tylerhou</author><text>&amp;gt; Rather, both balls are in a superposition of being both red and blue simultaneously, and it is not possible in principle to assign a color to either one of them until the moment a measurement is made.&lt;p&gt;I don&amp;#x27;t disagree, and (clearly) I make a measurement when I show you the color of a ball. Before I show you a ball, I would also say that the colors of the balls are in a superposition.&lt;p&gt;&amp;gt; major revolution in physics in order to understand that if there are two balls, one is blue and one is red, then if you see one of the balls is red, you can conclude the other ball is blue?&lt;p&gt;Entanglement is really just this simple — entanglement itself is a statement about a wave function, classical or quantum. The major revolution in physics is that &lt;i&gt;transformations&lt;/i&gt; of the wave functions do not behave as we would classically expect. Entangled particles are a tool that we can use to measure those transformations (and get surprising results).</text></comment>