The Arrow of Time FAQ


	The Arrow of Time FAQ

Djiezes

12-9-2007 6:06 AM

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tags:

time, physics, cosmology, thermodynamics, science, entropy, faq, pdf, article, literature

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12-10-2007 11:48 AM

Silkweaver

One hypothesis not mentioned in the website is that
there is no intrinsic physical entity called time., not even in the Einsteinian sense. Which means that time is a construct or a description of a state of affairs. Interesting website, thanks.

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<div style="margin: 12px 0px; font-family: arial; color: #333333; background: #ffffff; border: solid 4px #e5e5e5; width: 100%; clear: left;"><div class="CM_CTB_Content_Wrap" style="margin: 0px; padding: 0px;background-color: #ffffff;"><div style="border-bottom: solid 1px #dcdcdc; white-space: nowrap; margin-bottom: 8px; background-color: #eeeeee ;background-image: url(http://www.clipmarks.com/images/source-bg.gif); background-repeat: repeat-x; height: 24px; line-height: 24px; vertical-align: middle; padding-bottom: 4px; color: #666666; font-size: 10px;" ><a href="http://clipmarks.com/clip-to-blog/" title="see clips that are hot right now"><img src="http://content.clipmarks.com/blog_embed/e62fb98f-49da-4d80-b5d2-fb203f69248a/6F8E3A29-770B-4E6A-AEC8-AF9A72D23F0D/" alt="" width="19" height="19" border="0" style="vertical-align: middle; margin: 0px 4px; display: inline; border: none; float:none;" /></a>clipped from <a title="http://cosmicvariance.com/2007/12/03/arrow-of-time-faq/" href="http://cosmicvariance.com/2007/12/03/arrow-of-time-faq/" style="font-size: 11px;">cosmicvariance.com</a></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://cosmicvariance.com/2007/12/03/arrow-of-time-faq/"><H3><A title="Permanent Link to "Arrow of Time FAQ"" rel="bookmark" href="http://cosmicvariance.com/2007/12/03/arrow-of-time-faq/">Arrow of Time FAQ</A>   </H3></blockquote><div style="height: 2px; font-size: 2px; background: #dcdcdc; border-bottom: solid 1px #f5f5f5; margin: 2px 4px;"></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://cosmicvariance.com/2007/12/03/arrow-of-time-faq/"><P><STRONG>What is the arrow of time?</STRONG></P></blockquote><div style="height: 2px; font-size: 2px; background: #dcdcdc; border-bottom: solid 1px #f5f5f5; margin: 2px 4px;"></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://cosmicvariance.com/2007/12/03/arrow-of-time-faq/"><P>The past is different from the future.  One of the most obvious features of the macroscopic world is <EM>irreversibility</EM>:   heat doesn’t flow spontaneously from cold objects to hot ones, we can turn eggs into omelets but not omelets into eggs, ice cubes melt in warm water but glasses of water don’t spontaneously give rise to ice cubes.  These irreversibilities are summarized by the <A href="http://en.wikipedia.org/wiki/Second_law_of_thermodynamics">Second Law of Thermodynamics</A>:  the entropy of a closed system will (practically) never decrease into the future.</P></blockquote><div style="height: 2px; font-size: 2px; background: #dcdcdc; border-bottom: solid 1px #f5f5f5; margin: 2px 4px;"></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://cosmicvariance.com/2007/12/03/arrow-of-time-faq/"><P><STRONG>So what’s the big deal?</STRONG></P></blockquote><div style="height: 2px; font-size: 2px; background: #dcdcdc; border-bottom: solid 1px #f5f5f5; margin: 2px 4px;"></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://cosmicvariance.com/2007/12/03/arrow-of-time-faq/"><P>In contrast to the macroscopic universe, the microscopic laws of physics that purportedly underlie its behavior are perfectly reversible.  (More rigorously, for every allowed process there exists a time-reversed process that is also allowed, obtained by switching parity and exchanging particles for antiparticles — the <A href="http://en.wikipedia.org/wiki/Cpt_theorem">CPT Theorem</A>.)  The puzzle is to reconcile microscopic reversibility with macroscopic irreversibility.</P></blockquote><div style="border-bottom: solid 1px #dcdcdc; white-space: nowrap; margin-bottom: 8px; background-color: #eeeeee ;background-image: url(http://www.clipmarks.com/images/source-bg.gif); background-repeat: repeat-x; height: 24px; line-height: 24px; vertical-align: middle; padding-bottom: 4px; color: #666666; font-size: 10px;" ><a href="http://clipmarks.com/clip-to-blog/" title="see clips that are hot right now"><img src="http://content7.clipmarks.com/images/clip-icon.gif" alt="" width="19" height="19" border="0" style="vertical-align: middle; margin: 0px 4px; display: inline; border: none; float:none;" /></a>clipped from <a title="http://arxiv.org/abs/hep-th/0410270" href="http://arxiv.org/abs/hep-th/0410270" style="font-size: 11px;">arxiv.org</a></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://arxiv.org/abs/hep-th/0410270"><li style="margin-left:16px;padding-left: 0px;"><A accesskey="f" href="http://arxiv.org/pdf/hep-th/0410270">PDF</A></LI></blockquote></div><div style="margin: 0px 6px 6px 4px;"><table style="font-size: 11px;border-spacing: 0px;padding: 0px;" cellpadding="0" cellspacing="0" width="100%"><tr><td style="background:transparent;border-width:0px;padding:0px;">&nbsp;</td><td align="right" style="background:transparent;border-width:0px;padding:0px;width:107px" width="107"><a href="http://clipmarks.com/share/6F8E3A29-770B-4E6A-AEC8-AF9A72D23F0D/blog/" title="blog or email this clip"><img src="http://content8.clipmarks.com/images/c2b-foot.png" border="0" alt="blog it" width="107" height="17" style="border-width:0px;padding:0px;margin:0px;" /></a></td></tr></table></div></div>