<instructions>Your goal is to analyze the following comment and estimate how highly it will be upvoted by the Hacker News community.</instructions><comment><author>sgift</author><text>Even things we think we know very well may be wrong, so having a certain budget for &amp;quot;fringe&amp;quot; subjects which may yield unexpected results is not a bad idea. At the same time it&amp;#x27;s probably a good idea to assume everything they report is a measurement&amp;#x2F;test setup error until further proof.</text><parent_chain><item><author>elcomet</author><text>How could NASA allow research on such a topic if it is obvious for physicists that this is impossible ?</text></item><item><author>knzhou</author><text>The description in the article is oversimplified.&lt;p&gt;Relativistic dynamics is different from Newtonian dynamics in a lot of ways. Force isn&amp;#x27;t parallel to acceleration anymore. Acceleration gets harder the faster an object moves. You can mimic &lt;i&gt;some&lt;/i&gt; of these changes by just pretending that you still have Newtonian dynamics but the mass can change with velocity, but we don&amp;#x27;t use this language in physics because it&amp;#x27;s misleading -- there are many effects this idea &lt;i&gt;can&amp;#x27;t&lt;/i&gt; capture. (For example, the fact that force is not parallel to acceleration.) It is a very fragile analogy that causes a lot of conceptual mistakes.&lt;p&gt;It&amp;#x27;s easy to prove that Newtonian mechanics conserves momentum. It&amp;#x27;s also easy to prove that relativistic mechanics conserves momentum. A weird hybrid of Newtonian mechanics plus a magically changing &amp;quot;relativistic mass&amp;quot; does &lt;i&gt;not&lt;/i&gt; conserve momentum, but nobody has ever thought this was a correct description of nature. It&amp;#x27;s the result of taking a helpful simplifying analogy too far. Any reactionless drive formulated using this Frankenstein theory doesn&amp;#x27;t work.&lt;p&gt;If you just bounce an object back and forth, in either Newtonian mechanics or relativistic mechanics, you won&amp;#x27;t get anywhere. If you change the &lt;i&gt;rest mass&lt;/i&gt; of the object to be different going right than left, you will go somewhere, but it will cost momentum to do this, as explained in gus_massa&amp;#x27;s comments. So we haven&amp;#x27;t gotten thrust for free.</text></item></parent_chain></comment><story><title>NASA engineer&apos;s &apos;helical engine&apos; may violate the laws of physics</title><url>https://www.newscientist.com/article/2218685-nasa-engineers-helical-engine-may-violate-the-laws-of-physics/</url></story>
<instructions>Your goal is to analyze the following comment and estimate how highly it will be upvoted by the Hacker News community.</instructions><comment><author>IanCal</author><text>I don&amp;#x27;t think they have in this case.&lt;p&gt;&amp;gt; Burns has worked on his design in private, without any sponsorship from NASA</text><parent_chain><item><author>elcomet</author><text>How could NASA allow research on such a topic if it is obvious for physicists that this is impossible ?</text></item><item><author>knzhou</author><text>The description in the article is oversimplified.&lt;p&gt;Relativistic dynamics is different from Newtonian dynamics in a lot of ways. Force isn&amp;#x27;t parallel to acceleration anymore. Acceleration gets harder the faster an object moves. You can mimic &lt;i&gt;some&lt;/i&gt; of these changes by just pretending that you still have Newtonian dynamics but the mass can change with velocity, but we don&amp;#x27;t use this language in physics because it&amp;#x27;s misleading -- there are many effects this idea &lt;i&gt;can&amp;#x27;t&lt;/i&gt; capture. (For example, the fact that force is not parallel to acceleration.) It is a very fragile analogy that causes a lot of conceptual mistakes.&lt;p&gt;It&amp;#x27;s easy to prove that Newtonian mechanics conserves momentum. It&amp;#x27;s also easy to prove that relativistic mechanics conserves momentum. A weird hybrid of Newtonian mechanics plus a magically changing &amp;quot;relativistic mass&amp;quot; does &lt;i&gt;not&lt;/i&gt; conserve momentum, but nobody has ever thought this was a correct description of nature. It&amp;#x27;s the result of taking a helpful simplifying analogy too far. Any reactionless drive formulated using this Frankenstein theory doesn&amp;#x27;t work.&lt;p&gt;If you just bounce an object back and forth, in either Newtonian mechanics or relativistic mechanics, you won&amp;#x27;t get anywhere. If you change the &lt;i&gt;rest mass&lt;/i&gt; of the object to be different going right than left, you will go somewhere, but it will cost momentum to do this, as explained in gus_massa&amp;#x27;s comments. So we haven&amp;#x27;t gotten thrust for free.</text></item></parent_chain></comment><story><title>NASA engineer&apos;s &apos;helical engine&apos; may violate the laws of physics</title><url>https://www.newscientist.com/article/2218685-nasa-engineers-helical-engine-may-violate-the-laws-of-physics/</url></story>