An article in my new favorite magazine, Seed Magazine, by cosmologist Sean Carrol, proposes an interesting new theory about the nature of time and the evolution of baby universes. In this approach, baby universes can suddenly come into being from empty space when random quantum vacuum fluctuations fall into place in just the right way. Admittedly the odds of this happening are incredibly slim, but not impossible, and therefore in an infinite amount of time it definitely will happen over and over again. The only issue I have with the article is that it presents the issue of "time’s arrow" in the wrong light in my opinion. The so-called "arrow of time" is simply the progression from low to high entropy states — that is things start out ordered and become disordered over time. The new proposed theory doesn’t really show any way for that arrow to be reversed as far as I can tell. Entropy doesn’t run backwards, even in the metaverse. It would seem to me that every baby universe would be born from a highly ordered, extremely low entropy, state, and would then become less ordered and would gain in entropy over time. Although this might happen at different moments in meta-time, each of these universes would still develop in the same manner. But perhaps I’m missing something. Maybe the theorists have a way for high-entropy states to suddenly come into being and explode to become full-fledged universes which then lose entropy instead of gaining it? That doesn’t make a lot of sense to me. While the chances of a high-entropy state randomly occuring are incredibly slim, in an infinite amount of time they too would all occur at least some of the time — yet even so, I don’t see any reason to think that a high-entropy baby universe would, or could, run backwards towards a lower entropy state. Feel free to comment and explain it further if I got it wrong.Social tagging: Philosophy > Physics > Unexplained
this was “the last question” that was asked half a century ago, my favroite:
String theorists have been discussing the issue of reversal from high entropy to low entropy states, particularly in light of the fact that our universe appears to be open (accelerated expansion). Leonard Susskind (a highly regarded Stanford theorist, and considered to be one of the fathers of string theory) took a stab at explaining how we can go from a high entropy to a low entropy state in an open universe (i.e. one that won’t suffer an eventual collapse, and will hence last an indefinite period of time). See the article here: http://arxiv.org/ps/hep-th/0208013
Essentially he reasons that on exceptionally long time scales (e.g. when the time is proportional to the exponent of the final thermodynamic entropy of the particles making up the universe, which is proportional to the total number of states in the universe), the second law of thermodynamics does not prevent the rare occurence of a lower entropy state.
It’s actually a fairly readable paper, though if you’re not familiar with the usual jargon laden academic papers, phrases like AdS/CFT, transplanckian, de Sitter Space, etc. might be a turn-off.