<story><title>Light can be reflected not only in space but also in time</title><url>https://www.scientificamerican.com/article/light-can-travel-backward-in-time-sort-of/</url></story><parent_chain><item><author>jameshart</author><text>What is the purpose of this kind of science journalism?&lt;p&gt;The basic structure of the piece is to put a claim in the headline that sounds like a sci-fi breakthrough, then spend the article explaining that this isn’t actually a sci-fi breakthrough.&lt;p&gt;Like, the entire article here is basically saying ‘there is such a thing as a time mirror. No, it doesn’t make light travel back in time.’&lt;p&gt;What it &lt;i&gt;doesn’t&lt;/i&gt; do is remotely explain what a time mirror &lt;i&gt;is&lt;/i&gt; and what it actually &lt;i&gt;does&lt;/i&gt; do. No, ‘scientists made a time mirror out of a metamaterial that uses capacitive switches to add and remove matter’ does not answer what a time mirror &lt;i&gt;is&lt;/i&gt;.&lt;p&gt;I can tell you I made a florb warper out of a piece of zinc suspended in a cup of tea and you’re still none the wiser what a florb warper is or what it means for florbs to get warped. But please don’t get the wrong idea - it’s nothing like the warp drive from Star Trek! After all, it uses tea and zinc, not dilithium! Still, we can headline the article about it ‘Scientists test warp device’.</text></item></parent_chain><comment><author>aranchelk</author><text>Agreed on the first point, the headline and lead-in are grossly sensationalized, but later they do pretty clearly explain what’s going on.&lt;p&gt;The article’s author says the “time mirror” means you send a signal into the experimental setup of wave guides e.g. “a-b-c” and it comes back “c-b-a”.&lt;p&gt;Furthermore, when the researchers introduce interference during the reversal they don’t see superposition as you might expect (wave-like behavior), but kinetic interactions (signals are acting like a collection of particles).&lt;p&gt;It may not be true (we know a large percentage of papers can’t be replicated I.e. they’re bullshit), and I have no context to know how important that finding would be, but it is explained.</text></comment>
<story><title>Light can be reflected not only in space but also in time</title><url>https://www.scientificamerican.com/article/light-can-travel-backward-in-time-sort-of/</url></story><parent_chain><item><author>jameshart</author><text>What is the purpose of this kind of science journalism?&lt;p&gt;The basic structure of the piece is to put a claim in the headline that sounds like a sci-fi breakthrough, then spend the article explaining that this isn’t actually a sci-fi breakthrough.&lt;p&gt;Like, the entire article here is basically saying ‘there is such a thing as a time mirror. No, it doesn’t make light travel back in time.’&lt;p&gt;What it &lt;i&gt;doesn’t&lt;/i&gt; do is remotely explain what a time mirror &lt;i&gt;is&lt;/i&gt; and what it actually &lt;i&gt;does&lt;/i&gt; do. No, ‘scientists made a time mirror out of a metamaterial that uses capacitive switches to add and remove matter’ does not answer what a time mirror &lt;i&gt;is&lt;/i&gt;.&lt;p&gt;I can tell you I made a florb warper out of a piece of zinc suspended in a cup of tea and you’re still none the wiser what a florb warper is or what it means for florbs to get warped. But please don’t get the wrong idea - it’s nothing like the warp drive from Star Trek! After all, it uses tea and zinc, not dilithium! Still, we can headline the article about it ‘Scientists test warp device’.</text></item></parent_chain><comment><author>icambron</author><text>Completely agree about the headline and lead, but if you slog through it, the article did an ok job explaining the concept:&lt;p&gt;&amp;gt; The trick is to create a certain kind of reflection. First, imagine a regular spatial reflection, like one you see in a silver-backed glass mirror. Here reflection occurs because for a ray of light, silver is a very different transmission medium than air; the sudden change in optical properties causes the light to bounce back, like a Ping-Pong ball hitting a wall. Now imagine that instead of changing at particular points in space, the optical properties all along the ray’s path change sharply at a specific moment in time. Rather than recoiling in space, the light would recoil in time, precisely retracing its tracks, like the Ping-Pong ball returning to the player who last hit it. This is a “time reflection.”&lt;p&gt;&amp;gt; To do so, physicist Andrea Alù and his colleagues devised a “metamaterial” with adjustable optical properties that they could tweak within fractions of a nanosecond to halve or double how quickly light passes through.&lt;p&gt;So you have some volume of material and wave of light is passing through it. You alter the material everywhere in that volume so that the light does a 180 at every point along the wave at the same instant, reversing the stream of light. Any signal encoded in the light comes back in the opposite order you put it in, like you played a recording backward, or popped a stack until it was empty.</text></comment>