On Saturday, February 1, 2014 2:05:34 AM UTC-5, Liz R wrote: > > There seems to be a bit of confusion about this idea. Some people on the > list seem to abhor the idea of a block universe, but when they attack the > concept, they invariably go for straw men, making statements like "change > can't happen in a block universe" (which are obviously nonsense, or > Einstein et al would hardly have entertained the idea in the first place). > > So, I'd like to maybe clarify what the idea means, and give them a proper > target if they still want to demolish it. > > A block universe is simply one in which time is treated as a dimension. So > Newtonian physics, for example, specified a block universe, in which it was > believed (e.g. by Laplace) that in principle the past and future could be > computed from the state of the present. The Victorians made much of time > being the fourth dimension, probably most famously in Wells' "The Time > Machine". This was the Newtonian concept of a block universe, and was > generally treated quite fatalistically (Wells didn't indicate that history > could be changed, for example). >
> Then special relativity came along and unified space and time into > space-time. The reason SR gives rise to a block universe is the relativity > of simultaneity. > The relativity of simultaneity, like the fatalistic Victorian view reveal that the BU makes all change epiphenomenal from the God's Eye perspective. That's ok, but we then have to find a way to meet ourselves halfway and explain why a universe in which change is present at all is even plausible, let alone the kind of intentional change that we seem to find ourselves participating in. The BU makes the physical equations make sense, but it doesn't explain anything about our experience of physics. Just as the relativity of simultaneity makes the absolutely solid-seeming sense of time's uniformity into a local arrangement, the BU makes all change into an unexplained localization and animation of the static block. > You can slice up space-time in various ways which allow two observers to > see the same events occurring in a different order. Hence there is no way > to define a "hyperplane of simultaneity" that can be agreed upon by all > observers as being a present moment. This indicates that space-time is a > four-dimensional arena in which events are embedded. Indeed, I have never > heard of an alternative explanation of the relativity of simultaneity that > gets around this result - if it's correct, space-time is a block universe, > that is to say, time is "just" another dimension. > Just another dimension does not sit so well with thermodynamic irreversibility. Could another dimension become irreversible instead. Could a creature exist who can travel backward in time using their feet, but is incapable of making a left turn? > So classical physics posits a BU. Before worrying about QM, let's see what > the classical picture has to say about whether things can change in a block > universe. Change is defined as something being different at different times > - say the position of the Earth relative to the centre of the galaxy (it > traces out a wobbly spiral like a spring as it follows the Sun around an > almost circular orbit around the galactic centre every quarter of a billion > years). Does the fact that the Earth's orbit is a spiral embedded in > space-time prevent the Earth's position from changing? Clearly not. It > changes all the time. > Clearly from our perspective, which is not the perspective that the BU predicts, as far as I can tell. > > The same applies to any other changes that we observe. A person changes as > they get older - in the relativistic view these are cross sections through > their world-tube (or "lifeline" as Robert Heinlein put it). Particles move > through space - they trace out 4 dimensional world lines, but they can > still move. Everything we observe takes place in a manner that can be > placed within a space-time continuum such that a "god's eye" view (or the > relevant equations) would see it as static. But of course *we* don't see > it like that. > > This appears to be the source of the problem a few people have with this > concept, however - they appear to confuse the god's eye view with ours. But > of course we're embedded in space-time - along for the ride. So of course > we see change all the time. > Why 'of course'? How does the block embed parts of itself in itself? We see change, sure. We are along for the ride. What does the BU say about rides though? > > QM, perhaps a bit boringly, goes back to the Newtonian view. > Or maybe catastrophically. > Space and time are a background arena in which wave functions evolve with > time - which is of course a process that can be mapped out within a 4D > manifold. Indeed the equations involved are determinstic, and the famous > quantum probabilities have to be added "by hand" - so this is rather close > to the Newtonian view, apart from the ad hoc wave-function collapses. > Fortunately, Everett gave us a completely deterministic view - the wave > function evolves in a multiverse - so the block "universe" of QM is instead > a block multiverse, but otherwise it is a deterministic process embedded in > a space-time manifold. > Isn't the amplituhedron sort of a mini-block? Also there's been that buzz about the universe being a hologram reducible to 2D (+1?). The multiverse and block are last resorts. We reach for them to in desperation when we want to rescue the dream of determinism from the reality of a changing, participatory universe of sensory experience. > > Lastly, the past is an excellent example of a block universe. It is > unchanging, with events embedded in it. If anyone wants to consider what > the concept means, think about the past as the example of choice, a 13 > billion year long block universe. Change appeared to happen to the people > embedded in it, but we have a "god's eye" view of the past, and can see > that they were just experiencing different points along their world-tubes. > And people in the future will be able to see that the same was true of us. > Even history changes. I have a large wall map of a Victorian timeline that seamlessly flows from its beginning in the Garden of Eden through the Old Testament and into Babylon and Egypt. The God's eye view alters previous God's eye views, which suggests that all views are sensory, and subject to change. -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/groups/opt_out.
