<story><title>Carlo Rovelli on challenging our common-sense notion of time</title><url>http://nautil.us/blog/forget-everything-you-think-you-know-about-time</url></story><parent_chain></parent_chain><comment><author>jnurmine</author><text>I am not really skilled in physics and have never understood why time would be a tangible dimension like, say, width or height, instead of a mathematical construction to argue about change.&lt;p&gt;I get it that it is convenient to talk of change in something, like movement from state a to state b, under the guise of wrapping it in &amp;quot;time&amp;quot;, but is there some physical argument in support of time in general? Honest question.&lt;p&gt;Living beings getting older is their cells becoming more and more inefficient in division and cell repair. One could likely achieve the same effects with chemicals, but doing so would not mean time has run faster.&lt;p&gt;The concept of time for humans seems to be all about observable change, which needs an observer with a memory to compare the current state with previous state to be able to say: time has passed.&lt;p&gt;A rock changes via erosion and such, but it has no memory, and cannot observe anything. Does a rock feel time? Of course not. Does it exist &amp;quot;in time&amp;quot;? Does it, without an observer that somehow measures the flow of time (via changes in Cesium atoms or something)? Or is the rock just existing and under the whims of all forces of nature that might impact it and change it into smaller pieces and eventually to sand, and so on.&lt;p&gt;I guess my question is: what exactly is time, physically, and why should it have to exist as some sort of a physical process in the first place.</text></comment>
<story><title>Carlo Rovelli on challenging our common-sense notion of time</title><url>http://nautil.us/blog/forget-everything-you-think-you-know-about-time</url></story><parent_chain></parent_chain><comment><author>mathgenius</author><text>&amp;gt; Unlike general relativity, quantum mechanics, and particle physics, thermodynamics embeds a direction of time.&lt;p&gt;This is the bit that irks me. Quantum mechanics, the real QM that physicists actually use, involves collapse of the wavefunction. This is absolutely time-asymmetric. But in all these discussions of &amp;quot;why is time one-way?&amp;quot; this never seems to be mentioned. Apparently QM is not a real theory, and just a placeholder until we can work something out properly. Irk!</text></comment>