How would the laws of thermodynamics change in a contracting universe?

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</h1> </div> <div class="p-description"> <ul class="listInline listInline--bullet"> <li> <span data-xf-init="tooltip" title="Level: Intermediate (Undergrad)" ><span class="prefix inter" dir="auto">I</span></span> </li> <li> <i class="fa--xf fal fa-user" aria-hidden="true" title="Thread starter"></i> <span class="u-srOnly">Thread starter</span> <span>KurtLudwig</span> </li> <li> <i class="fa--xf fal fa-clock" aria-hidden="true" title="Start date"></i> <span class="u-srOnly">Start date</span> <time class="u-dt" dir="auto" datetime="2024-11-04T14:36:20-0600" data-time="1730752580" data-date-string="Nov 4, 2024" data-time-string="2:36 PM" title="Nov 4, 2024 at 2:36 PM">Nov 4, 2024</time> </li> <li> <dl class="tagList tagList--thread-1066716 "> <dt> <i class="fa--xf fal fa-tags" aria-hidden="true" title="Tags"></i> <span class="u-srOnly">Tags</span> </dt> <dd> <span class="js-tagList"> <a href="/tags/laws/" data-xf-init="preview-tooltip" data-preview-url="/tags/laws/preview" class="tagItem tagItem--tag_laws" dir="auto"> Laws </a> </span> </dd> </dl> </li> </ul> </div> </div> <script src="https://www.physicsforums.com/check-for-tex.js" defer></script> <div class="block block--messages" data-xf-init="" data-type="post" data-href="/inline-mod/" data-search-target="*"> <span class="u-anchorTarget" id="posts"></span> <div class="block-outer"></div> <div class="block-outer js-threadStatusField"></div> <div class="block-container lbContainer" data-xf-init="lightbox select-to-quote" data-message-selector=".js-post" data-lb-id="thread-1066716" data-lb-universal="0"> <div class="block-body js-replyNewMessageContainer">  <article class="message message--post js-post js-inlineModContainer " data-author="KurtLudwig" data-content="post-7130203" id="js-post-7130203" > <span class="u-anchorTarget" id="post-7130203"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <time class="u-dt" dir="auto" datetime="2024-11-04T14:36:20-0600" data-time="1730752580" data-date-string="Nov 4, 2024" data-time-string="2:36 PM" title="Nov 4, 2024 at 2:36 PM">Nov 4, 2024</time> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <span style="cursor:pointer;" data-xf-init="share-tooltip" data-href="/posts/7130203/share" aria-label="Share" role="button" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </span> </li> <li> #1 </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" > <div class="message-userDetails"> <span class="message-name"><span class="username " dir="auto" data-user-id="639757">KurtLudwig</span></span>   <span class="threadstarter" data-xf-init="tooltip" title="Thread Starter"><i class="fal fa-user-edit"></i></span>  <div class="post-badges"> <div class="post-badge badge-star" data-xf-init="tooltip" title="Click to Support PF"> <i class="fa--xf fal fa-star" aria-hidden="true"></i><span> Gold Member</span> </div> </div>  </div> <div class="message-userExtras"> <dl class="pairs pairs--justified"> <dt><i class="fa--xf fal fa-comments fa-fw" aria-hidden="true" data-xf-init="tooltip" title="Messages"></i></dt> <dd>146</dd> </dl> <dl class="pairs pairs--justified"> <dt><i class="fa--xf fal fa-thumbs-up fa-fw" aria-hidden="true" data-xf-init="tooltip" title="Reaction score"></i></dt> <dd>31</dd> </dl> </div> <span class="message-userArrow"></span> </section> </div> <div class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-7130203" data-lb-caption-desc="KurtLudwig · Nov 4, 2024 at 2:36 PM"> <div class="message-fields message-fields--before"> <dl class="pairs pairs--columns pairs--fixedSmall pairs--customField" data-field="summary"> <dt>TL;DR Summary</dt> <dd>How would the laws of thermodynamics change in a contracting universe?On the internet, I get different answers: Most say that entropy will still increase or stay the same. Some say the second law will be reversed. Some say that there will be a local decrease in entropy.<br /> The universe as a whole will increase in temperature. Is that considered an increase in entropy?</dd> </dl> </div> <article class="message-body js-selectToQuote"> <div > <div class="bbWrapper">How would the laws of thermodynamics change in a contracting universe?<br /> (Of course we live in an accelerating and expanding universe. So the questions are hypothetical.)<br /> On the internet, I get different answers: Most say that entropy will still increase or stay the same, but no explanations or mathematics were given. Some say the second law will be reversed. Some say that there will be local decreases in entropy.<br /> The universe as a whole will increase in temperature. Is that considered an increase in entropy? <br /> But as the universe continues toward the "big crunch", entropy need to decease, since at the beginning of the "big bang" entropy was low?<br /> I believe that since the universe is getting smaller, at least the definition of disorder will need to be modified.<br /> Is it all semantics? I wonder what the members of physics forums think?</div> </div> <div class="js-selectToQuoteEnd"> </div> <div class="googleads_fixed"> <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-6580726045122001" crossorigin="anonymous"></script>  <ins class="adsbygoogle" style="display:block" data-ad-client="ca-pub-6580726045122001" data-ad-slot="3049969336" data-ad-format="auto" data-full-width-responsive="true"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script> </div> </article> </div> </div> <footer class="message-footer"> <div class="reactionsBar js-reactionsList "> </div> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> </div> </article>  <div class="message-cell message-cell--main" id="post-physorg"> <a href="https://phys.org/space-news/" target="_blank">Space news</a> on Phys.org <ul class="phys_items"> <li><a href="https://phys.org/news/2025-02-planet-solar-lining-february-night.html" target="_blank">Every planet of our solar system is lining up in the February night sky</a></li> <li><a href="https://phys.org/news/2025-02-breakthrough-enables-local-dark-density.html" target="_blank">Breakthrough enables measurement of local dark matter density using direct acceleration measurements</a></li> <li><a href="https://phys.org/news/2025-02-solar-journey-orion-complex-million.html" target="_blank">Solar system's journey through Orion complex 14 million years ago may have altered Earth's climate</a></li> </ul> </div> <article class="message message--post js-post js-inlineModContainer " data-author="anuttarasammyak" data-content="post-7130242" id="js-post-7130242" itemscope itemtype="https://schema.org/Comment" itemid="https://www.physicsforums.com/posts/7130242/"> <meta itemprop="parentItem" itemscope itemid="https://www.physicsforums.com/threads/how-would-the-laws-of-thermodynamics-change-in-a-contracting-universe.1066716/" /> <span class="u-anchorTarget" id="post-7130242"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <time class="u-dt" dir="auto" datetime="2024-11-04T20:19:54-0600" data-time="1730773194" data-date-string="Nov 4, 2024" data-time-string="8:19 PM" title="Nov 4, 2024 at 8:19 PM" itemprop="datePublished">Nov 4, 2024</time> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <span style="cursor:pointer;" data-xf-init="share-tooltip" data-href="/posts/7130242/share" aria-label="Share" role="button" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </span> </li> <li> #2 </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.physicsforums.com/members/anuttarasammyak.674023/"> <meta itemprop="url" content="https://www.physicsforums.com/members/anuttarasammyak.674023/" /> <div class="message-userDetails"> <span class="message-name"><span class="username " dir="auto" data-user-id="674023"><span itemprop="name">anuttarasammyak</span></span></span>    <div class="post-badges"> <div class="post-badge badge-star" data-xf-init="tooltip" title="Click to Support PF"> <i class="fa--xf fal fa-star" aria-hidden="true"></i><span> Gold Member</span> </div> </div>  </div> <div class="message-userExtras"> <dl class="pairs pairs--justified"> <dt><i class="fa--xf fal fa-comments fa-fw" aria-hidden="true" data-xf-init="tooltip" title="Messages"></i></dt> <dd>2,807</dd> </dl> <dl class="pairs pairs--justified"> <dt><i class="fa--xf fal fa-thumbs-up fa-fw" aria-hidden="true" data-xf-init="tooltip" title="Reaction score"></i></dt> <dd>1,469</dd> </dl> </div> <span class="message-userArrow"></span> </section> </div> <div class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-7130242" data-lb-caption-desc="anuttarasammyak · Nov 4, 2024 at 8:19 PM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper">In physics hypothethis should be proved/denied by observation or experiment. I don't think we have a chance of experiment on this issue though I would like to.</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="reactionsBar js-reactionsList "> </div> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> </div> </article>  <article class="message message--post js-post js-inlineModContainer " data-author="PeterDonis" data-content="post-7130351" id="js-post-7130351" itemscope itemtype="https://schema.org/Comment" itemid="https://www.physicsforums.com/posts/7130351/"> <meta itemprop="parentItem" itemscope itemid="https://www.physicsforums.com/threads/how-would-the-laws-of-thermodynamics-change-in-a-contracting-universe.1066716/" /> <span class="u-anchorTarget" id="post-7130351"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <time class="u-dt" dir="auto" datetime="2024-11-05T09:55:50-0600" data-time="1730822150" data-date-string="Nov 5, 2024" data-time-string="9:55 AM" title="Nov 5, 2024 at 9:55 AM" itemprop="datePublished">Nov 5, 2024</time> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <span style="cursor:pointer;" data-xf-init="share-tooltip" data-href="/posts/7130351/share" aria-label="Share" role="button" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </span> </li> <li> #3 </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.physicsforums.com/members/peterdonis.197831/"> <meta itemprop="url" content="https://www.physicsforums.com/members/peterdonis.197831/" /> <div class="message-userDetails"> <span class="message-name"><a href="/members/peterdonis.197831/" class="username " dir="auto" data-user-id="197831" data-xf-init="member-tooltip"><span class="username--staff username--moderator" itemprop="name">PeterDonis</span></a></span>    <div class="post-badges"> <div class="post-badge badge-mentor" data-xf-init="tooltip" title="PF Community Staff"> <i class="fa--xf fal fa-user-graduate" aria-hidden="true"></i><span> Mentor</span> </div> <div class="post-badge badge-file" data-xf-init="tooltip" title="Click to View My Articles"> <a href="https://www.physicsforums.com/insights/author/PeterDonis/"><i class="fa--xf fal fa-file-alt" aria-hidden="true"></i><span> Insights Author</span></a> </div> </div>  </div> <div class="message-userExtras"> <dl class="pairs pairs--justified"> <dt><i class="fa--xf fal fa-comments fa-fw" aria-hidden="true" data-xf-init="tooltip" title="Messages"></i></dt> <dd>47,918</dd> </dl> <dl class="pairs pairs--justified"> <dt><i class="fa--xf fal fa-thumbs-up fa-fw" aria-hidden="true" data-xf-init="tooltip" title="Reaction score"></i></dt> <dd>24,156</dd> </dl> </div> <span class="message-userArrow"></span> </section> </div> <div class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-7130351" data-lb-caption-desc="PeterDonis · Nov 5, 2024 at 9:55 AM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper"><blockquote data-attributes="member: 639757" data-quote="KurtLudwig" data-source="post: 7130203" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> KurtLudwig said: </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> On the internet, I get different answers </div> </div> </blockquote>You need to give specific references. Particularly for a topic like this, we need to have some kind of mainstream reference as a basis for discussion. If there are no such references, that means the topic is too speculative to be usefully discussed here.</div> </div> <div class="js-selectToQuoteEnd"> </div> <div class="googleads_fixed"> <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-6580726045122001" crossorigin="anonymous"></script>  <ins class="adsbygoogle" style="display:block" data-ad-client="ca-pub-6580726045122001" data-ad-slot="5961342082" data-ad-format="auto" data-full-width-responsive="true"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="reactionsBar js-reactionsList "> </div> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> </div> </article>  <article class="message message--post js-post js-inlineModContainer " data-author="PeterDonis" data-content="post-7130352" id="js-post-7130352" itemscope itemtype="https://schema.org/Comment" itemid="https://www.physicsforums.com/posts/7130352/"> <meta itemprop="parentItem" itemscope itemid="https://www.physicsforums.com/threads/how-would-the-laws-of-thermodynamics-change-in-a-contracting-universe.1066716/" /> <span class="u-anchorTarget" id="post-7130352"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <time class="u-dt" dir="auto" datetime="2024-11-05T09:58:55-0600" data-time="1730822335" data-date-string="Nov 5, 2024" data-time-string="9:58 AM" title="Nov 5, 2024 at 9:58 AM" itemprop="datePublished">Nov 5, 2024</time> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <span style="cursor:pointer;" data-xf-init="share-tooltip" data-href="/posts/7130352/share" aria-label="Share" role="button" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </span> </li> <li> #4 </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.physicsforums.com/members/peterdonis.197831/"> <meta itemprop="url" content="https://www.physicsforums.com/members/peterdonis.197831/" /> <div class="message-userDetails"> <span class="message-name"><a href="/members/peterdonis.197831/" class="username " dir="auto" data-user-id="197831" data-xf-init="member-tooltip"><span class="username--staff username--moderator" itemprop="name">PeterDonis</span></a></span>    <div class="post-badges"> <div class="post-badge badge-mentor" data-xf-init="tooltip" title="PF Community Staff"> <i class="fa--xf fal fa-user-graduate" aria-hidden="true"></i><span> Mentor</span> </div> <div class="post-badge badge-file" data-xf-init="tooltip" title="Click to View My Articles"> <a href="https://www.physicsforums.com/insights/author/PeterDonis/"><i class="fa--xf fal fa-file-alt" aria-hidden="true"></i><span> Insights Author</span></a> </div> </div>  </div> <div class="message-userExtras"> <dl class="pairs pairs--justified"> <dt><i class="fa--xf fal fa-comments fa-fw" aria-hidden="true" data-xf-init="tooltip" title="Messages"></i></dt> <dd>47,918</dd> </dl> <dl class="pairs pairs--justified"> <dt><i class="fa--xf fal fa-thumbs-up fa-fw" aria-hidden="true" data-xf-init="tooltip" title="Reaction score"></i></dt> <dd>24,156</dd> </dl> </div> <span class="message-userArrow"></span> </section> </div> <div class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-7130352" data-lb-caption-desc="PeterDonis · Nov 5, 2024 at 9:58 AM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper"><blockquote data-attributes="member: 639757" data-quote="KurtLudwig" data-source="post: 7130203" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> KurtLudwig said: </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> The universe as a whole will increase in temperature. Is that considered an increase in entropy?<br /> But as the universe continues toward the "big crunch", entropy need to decease, since at the beginning of the "big bang" entropy was low? </div> </div> </blockquote>As far as an idealized closed FRW model that expands and then contracts is concerned, the question of "entropy" is meaningless, because the model is an exact deterministic solution, whose "entropy" is zero at all times since there is no uncertainty about its state.<br /> <br /> Of course what you are trying to envision is a more realistic model in which the FRW solution is just an approximation. But that is where we need actual references as a basis for discussion: what kind of approximation is being used? Does it allow for the "Big Bang" and "Big Crunch" ends of the universe to have different properties? (Note that the idealized FRW model does <i>not</i>; they have to be the same.) Without an actual reference as a basis for discussion, questions like there are not even answerable.</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="reactionsBar js-reactionsList "> </div> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> </div> </article>  <article class="message message--post js-post js-inlineModContainer " data-author="KurtLudwig" data-content="post-7130626" id="js-post-7130626" itemscope itemtype="https://schema.org/Comment" itemid="https://www.physicsforums.com/posts/7130626/"> <meta itemprop="parentItem" itemscope itemid="https://www.physicsforums.com/threads/how-would-the-laws-of-thermodynamics-change-in-a-contracting-universe.1066716/" /> <span class="u-anchorTarget" id="post-7130626"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <time class="u-dt" dir="auto" datetime="2024-11-06T10:43:37-0600" data-time="1730911417" data-date-string="Nov 6, 2024" data-time-string="10:43 AM" title="Nov 6, 2024 at 10:43 AM" itemprop="datePublished">Nov 6, 2024</time> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <span style="cursor:pointer;" data-xf-init="share-tooltip" data-href="/posts/7130626/share" aria-label="Share" role="button" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </span> </li> <li> #5 </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.physicsforums.com/members/kurtludwig.639757/"> <meta itemprop="url" content="https://www.physicsforums.com/members/kurtludwig.639757/" /> <div class="message-userDetails"> <span class="message-name"><span class="username " dir="auto" data-user-id="639757"><span itemprop="name">KurtLudwig</span></span></span>   <span class="threadstarter" data-xf-init="tooltip" title="Thread Starter"><i class="fal fa-user-edit"></i></span>  <div class="post-badges"> <div class="post-badge badge-star" data-xf-init="tooltip" title="Click to Support PF"> <i class="fa--xf fal fa-star" aria-hidden="true"></i><span> Gold Member</span> </div> </div>  </div> <div class="message-userExtras"> <dl class="pairs pairs--justified"> <dt><i class="fa--xf fal fa-comments fa-fw" aria-hidden="true" data-xf-init="tooltip" title="Messages"></i></dt> <dd>146</dd> </dl> <dl class="pairs pairs--justified"> <dt><i class="fa--xf fal fa-thumbs-up fa-fw" aria-hidden="true" data-xf-init="tooltip" title="Reaction score"></i></dt> <dd>31</dd> </dl> </div> <span class="message-userArrow"></span> </section> </div> <div class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-7130626" data-lb-caption-desc="KurtLudwig · Nov 6, 2024 at 10:43 AM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper">Thank you for your answers.</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="reactionsBar 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itemprop="datePublished">Nov 6, 2024</time> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <span style="cursor:pointer;" data-xf-init="share-tooltip" data-href="/posts/7130633/share" aria-label="Share" role="button" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </span> </li> <li> #6 </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.physicsforums.com/members/pines-demon.744598/"> <meta itemprop="url" content="https://www.physicsforums.com/members/pines-demon.744598/" /> <div class="message-userDetails"> <span class="message-name"><span class="username " dir="auto" data-user-id="744598"><span itemprop="name">pines-demon</span></span></span>    <div class="post-badges"> <div class="post-badge badge-star" data-xf-init="tooltip" title="Click to Support PF"> <i class="fa--xf fal fa-star" aria-hidden="true"></i><span> Gold Member</span> </div> <div class="post-badge badge-trophy" data-xf-init="tooltip" title="2024 Award Winner"> <i class="fa--xf fal fa-trophy" aria-hidden="true"></i><span> 2024 Award</span> </div> </div>  </div> <div class="message-userExtras"> <dl class="pairs pairs--justified"> <dt><i class="fa--xf fal fa-comments fa-fw" aria-hidden="true" data-xf-init="tooltip" title="Messages"></i></dt> <dd>740</dd> </dl> <dl class="pairs pairs--justified"> <dt><i class="fa--xf fal fa-thumbs-up fa-fw" aria-hidden="true" data-xf-init="tooltip" title="Reaction score"></i></dt> <dd>602</dd> </dl> </div> <span class="message-userArrow"></span> </section> </div> <div class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-7130633" data-lb-caption-desc="pines-demon · Nov 6, 2024 at 11:38 AM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper"><blockquote data-attributes="member: 674023" data-quote="anuttarasammyak" data-source="post: 7130242" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> anuttarasammyak said: </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> In physics hypothethis should be proved/denied by observation or experiment. I don't think we have a chance of experiment on this issue though I would like to. </div> </div> </blockquote>I think that this is too reductive. Sure it is good to attach hypothesis to observation but sometimes not-so-real models can help build an intuition. What I think this question is missing is a proper framework. Using model "insert specific model name here" what happens with "insert variable here" when "variable here" decreases.</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="reactionsBar js-reactionsList "> </div> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> <script> if (typeof parseNewPost == 'function') { $(document).ajaxStop(parseNewPost(7130633)); } </script> </div> </div> </div> </article> </div> </div> </div> <form action="/threads/how-would-the-laws-of-thermodynamics-change-in-a-contracting-universe.1066716/add-reply" method="post" class="block js-quickReply" data-xf-init="attachment-manager 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So the questions are hypothetical.)\nOn the internet, I get different answers: Most say that entropy will still increase or stay the same, but no explanations or mathematics were given. Some say the second law will be reversed. Some say that there will be local decreases in entropy.\nThe universe as a whole will increase in temperature. Is that considered an increase in entropy? \nBut as the universe continues toward the \"big crunch\", entropy need to decease, since at the beginning of the \"big bang\" entropy was low?\nI believe that since the universe is getting smaller, at least the definition of disorder will need to be modified.\nIs it all semantics? I wonder what the members of physics forums think?" }, "publisher": { "@type": "Organization", "name": "Physics Forums: Science Discussion, Homework Help, Articles", "alternateName": "Physics Forums", "description": "Join Physics Forums, where students, scientists, and enthusiasts come together to explore and discuss the current understanding and practice of various scientific fields.", "url": "https://www.physicsforums.com", "logo": "https://www.physicsforums.com/styles/physicsforums/images/physics-forums-logo-og.png" } } </script> <script type="text/javascript" src="https://www.physicsforums.com/copyright.js" defer></script> <script> function parseNewPost(postid) { var newpost = document.getElementById("js-post-" + postid), npa = [newpost]; MathJax.typeset(npa); } function parsePreview() { var preview = document.getElementsByClassName("xfPreview"); MathJax.typeset(preview); } function parseNewConversationPost(postid) { var newpost = document.getElementsByClassName("convMessage-" + postid); MathJax.typeset(newpost); } function parseNewProfilePost(postid) { var newpost = document.getElementById("js-profilePost-" + postid), npa = [newpost]; MathJax.typeset(npa); } function parseTooltip() { MathJax.typeset(); } </script> </body> </html>

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How would the laws of thermodynamics change in a contracting universe?