Hi guys, Time travel is actually possible, as long as you are consistent (i.e. Novikov self-consistency principle). Please consider the argument for it, beginning at:
http://www.reddit.com/r/askscience/comments/hr4x2/physicists_what_do_you_think_of_the_following/ Continue the discussion there at reddit if you would like. Thank you! F.H. On Fri, Jun 3, 2011 at 12:09 PM, Travis Garrett <[email protected]> wrote: > Hi Roc, > > Sure. Let me go ahead and start by assuming that we need to exist > in an environment that began in a state of low entropy (so that life > can evolve during the "increasing entropy phase" - I could also > examine this assumption, but that's another discussion...). GR then > does some interesting things. First, gravity in GR couples to energy > and momentum, and everything has energy and momentum, so, er, it > couples to everything (binding them all together like the one ring I > suppose). It can thus essentially "get everybody on the same page" > when things are starting out - forcing "everybody" (all the particle > species) to "pay attention" and synchronize their behavior... > > GR can then do something quite cool. If you feed the Einstein > equations with a scalar field that happens to have much more potential > energy than kinetic energy, then the spacetime responds by growing > exponentially (i.e. the curvature is in the time direction - the > spatial directions are driven to be very flat (i.e. the angles inside > a triangle add up to 180 degrees), with the overall scale factor > growing exponentially (i.e. the overall size of the triangle is > growing exponentially in time)). Thus, consider some complex universe > with a lot of entropy. Entropy is an extensive quantity, and thus if > we consider some tiny volume element dV then there can't be much > "stuff" inside dV, and therefore there is very little entropy inside > dV. If we can get a scalar field inside that dV to satisfy the > condition that its potential energy is much larger than its kinetic > energy, then blammo, we get inflation and that dV region can grow > larger than our Hubble volume in a tiny fraction of a second (and then > scalar field can decay, ending inflation, to be followed by a > "standard" big bang...). > > It is by no means an open and shut case - there are lots of details > to be filled in - but I think the overall picture makes a lot of > sense... > > Sincerely, > Travis > > On Jun 2, 6:35 am, Roc <[email protected]> wrote: >> nice answer. >> could you elaborate on this, though? >> >> Why then should spacetime be curved? There are at least 2 good reasons: >> >> 1) it allows for a big bang to happen, thus "starting things off" in a state >> >> > of low entropy. >> >> thanks > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/everything-list?hl=en. > > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/everything-list?hl=en.
