title: Conversion from epoch to datetime is incorrect
body: <p>I've been using <a href="https://stackoverflow.com/a/7816368/4214184">this answer</a> to convert epoch time to DateTime. I have this epoch number:</p>
  
  <pre><code>epoch = 1549626705942
  </code></pre>
  
  <p>and do:</p>
  
  <pre><code>Time.at(epoch).to_datetime
  </code></pre>
  
  <p>However, I get this as the result:</p>
  
  <pre><code>#&lt;DateTime: 51075-09-19T08:45:42+02:00 ((20376082j,24342s,0n),+7200s,2299161j)&gt;
  </code></pre>
  
  <p>I'm using Ruby version 2.5.3p105 and my clock is set to the current year. This epoch value evaluates to today's date (February 2nd, 2019) yet I get a year 51075. Really not sure what's going on.</p>
  
  <p>It's also weird because, when I enter my timestamp at a site like <a href="https://www.epochconverter.com/" rel="nofollow noreferrer">this one</a> I get today's date but <a href="https://www.unixtimestamp.com/index.php" rel="nofollow noreferrer">here</a> I get the same result as my Ruby code.</p>
  
  <p>Edit: I tried to remove the last 3 numbers of this date and got a correct date. So is it that there are 2 epoch "formats" so to say?</p>