Mr Skeptic Posted February 13, 2009 Share Posted February 13, 2009 Suppose we were to run time backward on the Big Bang model, until t<0 (lets say we do this without passing through t=0, to avoid those complications). What would the model give? Would we get points expanding but our coordinate system inverted (ie, x' = -x, y' = -y, z' = -z, t' = -t)? Would we essentially have a universe of antimatter? Link to comment Share on other sites More sharing options...
moth Posted February 14, 2009 Share Posted February 14, 2009 no? http://boards.history.com/topic/The-Universe/Anti-Matter-From/800038416 maybe? http://arxiv.org/html/physics/9812021 Link to comment Share on other sites More sharing options...
Yreval Posted February 16, 2009 Share Posted February 16, 2009 A universe that goes backwards in time from the big bang? Wouldn't that be more of a tachyon universe than an antimatter universe, or is there something I'm missing? Hmm, tachyon universe—kind of catchy. Link to comment Share on other sites More sharing options...
Klaynos Posted February 16, 2009 Share Posted February 16, 2009 Suppose we were to run time backward on the Big Bang model, until t<0 (lets say we do this without passing through t=0, to avoid those complications). What would the model give? Would we get points expanding but our coordinate system inverted (ie, x' = -x, y' = -y, z' = -z, t' = -t)? Would we essentially have a universe of antimatter? BBT does not say anything about origins so I can't really answer the question. As for what if we were in a universe where time was running the other way, the question you must ask yourself is "could we tell" the answer is, as far as I can tell, no. Link to comment Share on other sites More sharing options...
moth Posted February 17, 2009 Share Posted February 17, 2009 (edited) the symmetry of time progressing away from the "big bang" in the direction of our history could explain why Newton's laws don't care which way time goes. it's hard to think of a testable hypothesis maybe something to do with quasars as white holes dumping anti-matter into our side of B.B. just to be clear i mean white hole as in time reversed black hole not as in the aig b.s. that pops up in google Edited February 17, 2009 by moth clarify Link to comment Share on other sites More sharing options...
Mr Skeptic Posted February 17, 2009 Author Share Posted February 17, 2009 BBT does not say anything about origins so I can't really answer the question. I wasn't asking about origins, and I know that at t=0 the equation breaks down (singularity). I was wondering what the equation would say if we (rather naively) put a negative time in the equation. As for what if we were in a universe where time was running the other way, the question you must ask yourself is "could we tell" the answer is, as far as I can tell, no. I think that reversing time would result in matter looking like antimatter, but I don't know for sure. Link to comment Share on other sites More sharing options...
Klaynos Posted February 17, 2009 Share Posted February 17, 2009 I think that reversing time would result in matter looking like antimatter, but I don't know for sure. OK, but whether we call things matter or antimatter is mearly a definition. Perhaps time IS running backwards (but then you'd have to ask relative to what, is there an absolute clock, relativity says there's not) and what we call matter is 'really' antimatter. But there is no 'really' and no set and fast rule as to why we call matter matter and antimatter anti... This lack of distinction makes me feel the question it moot... Link to comment Share on other sites More sharing options...
moth Posted February 17, 2009 Share Posted February 17, 2009 I think that reversing time would result in matter looking like antimatter, but I don't know for sure. doesn't CP symmetry suggest time reversed matter and anti matter are equivalent? aren't photons their own anti-particle and able to move both directions in time? can the problems at t=0 be avoided by assuming the B.B. also exploded into the past and just kept going, maybe taking all the anti-matter with it? Link to comment Share on other sites More sharing options...
Martin Posted February 17, 2009 Share Posted February 17, 2009 (edited) Suppose we were to run time backward on "the" Big Bang model, until t<0 ... Would we essentially have a universe of antimatter? I put quotes around "the" in this excerpt from your post. Several models are being studied. What you get before t=0 depends on the model. As it happens there is currently a dominant model, among those which do not break down. By objective standards the model getting the most recognition (among those that run smoothly back before) is LQC (loop quantum cosmology). Many of the recent papers in LQC have been concerned with possibilities for testing LQC using slight observable differences from the classic vintage unquantum model (imprints of quantum corrections left on the very early universe). A new paper on this testing topic appeared yesterday, in fact. So if that is what you mean by "the" Big Bang model----the currently pre-eminent model that runs smoothly back in time---then the answer to your question about antimatter is a qualified NO. The LQC model, when you run it back, does not give you an antimatter universe. Back far enough it just gives you ordinary spacetime, but collapsing instead of expanding. The coordinates are not inverted. Time keeps running in the same direction. Nothing very mysterious happens. There is a contraction to very high density. Then quantum corrections to the dynamics of geometry become dominant and there is a bounce, followed by expansion. As such models go, it is comparatively business-as-usual, and not difficult to simulate on the computer using numerical models of the universe. Some years back there was an earlier version of LQC where the spatial coordinates got inverted during the bounce, similar to what you said, but this version has fallen by the wayside. Better LQC dynamics were discovered in 2005, and with the improved dynamics it turned out that spatial inversion doesn't happen. Edited February 17, 2009 by Martin Link to comment Share on other sites More sharing options...
throng Posted February 19, 2009 Share Posted February 19, 2009 If time endured long enough matter would disperse evenly throughout space, it'd be cold, it'd be still, so t=0 is at 'either end' of time and I don't suppose there is a difference between the begining and the end of movement. If it is cyclic, the 'time in between' universes is t=0 so subsequent universes would occur instantly upon cessation of the previous, so I guess it'd be a continuous timeline after all. Link to comment Share on other sites More sharing options...
Martin Posted February 19, 2009 Share Posted February 19, 2009 (edited) matter used to be much more evenly distributed and it has been clumping for the past 13 billion years. Forming wispy cobweblike structures, clusters of galaxies. and galaxies merge. We see such galaxy mergers going on. Our galaxy (Milkyway) and nearby Andromeda are slated to merge, along with a few others in our local group. So local clumping continues even as largescale distances expand. The trend is not towards even dispersal. Edited February 19, 2009 by Martin Link to comment Share on other sites More sharing options...
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