On 5/25/2017 8:36 PM, Pierz Newton-John wrote:
Is something up with Everything List - your reply is not on the site and I’m
seeing this business with “reply to David 4” etc…?
On 26 May 2017, at 12:29 pm, Brent Meeker <meeke...@verizon.net> wrote:
On 5/25/2017 6:30 PM, Pierz wrote:
Recently I've been studying a lot of history, and I've often thought about how, according
to special relativity, you can translate time into space and vice versa, and therefore
how from a different perspective we can think of the past as distant in space rather than
time: my childhood being 40 light years away, rather than 40 years for instance. I can
visualise my own body as a sort of long, four dimensional tendril through spacetime, of
which I only ever see a three-dimensional cross-section. This is the block universe idea
of course. What occurred to me recently was that the past, in any physical theory I know
of, is "locked down". There is only a single history consistent with the
present (ignoring the microscopic ambiguities of quantum interference effects
I think that is assuming a lot. Consider the biverse model of cosmogony - then the past
"forks" just like the future.
When I’ve asked physicists this question, I’ve been told that a single past is
the general assumption. IIRC, there may be ambiguous histories very close to
the Big Bang (Hawking?), but that’s not really relevant. Maybe that’s the
biverse cosmology you refer to (googling it didn’t help).
In the biverse model the universe inflates into the past as well as the
future (as defined by us), thus maintaining time symmetry. Here's a
another, more worked out version of the idea:
Spontaneous Inflation and the Origin of the Arrow of Time
Sean M. Carroll
<https://arxiv.org/find/hep-th/1/au:+Carroll_S/0/1/0/all/0/1>,Jennifer
Chen <https://arxiv.org/find/hep-th/1/au:+Chen_J/0/1/0/all/0/1>
(Submitted on 27 Oct 2004)
We suggest that spontaneous eternal inflation can provide a natural
explanation for the thermodynamic arrow of time, and discuss the
underlying assumptions and consequences of this view. In the absence
of inflation, we argue that systems coupled to gravity usually
evolve asymptotically to the vacuum, which is the only natural state
in a thermodynamic sense. In the presence of a small positive vacuum
energy and an appropriate inflaton field, the de Sitter vacuum is
unstable to the spontaneous onset of inflation at a higher energy
scale. Starting from de Sitter, inflation can increase the total
entropy of the universe without bound, creating universes similar to
ours in the process./***An important consequence of this picture is
that inflation occurs asymptotically both forwards and backwards in
time, implying a universe that is (statistically) time-symmetric on
ultra-large scales.*/
Comments: 36 pages
Subjects: High Energy Physics - Theory (hep-th); Astrophysics
(astro-ph); General Relativity and Quantum Cosmology (gr-qc)
Report number: EFI-2004-33
Cite as: arXiv:hep-th/0410270 <https://arxiv.org/abs/hep-th/0410270>
(orarXiv:hep-th/0410270v1 <https://arxiv.org/abs/hep-th/0410270v1>for
this version)
), but the present is consistent with multiple futures. However, we know that "now" - and therefore the division into past and
future - is an artifact of mind with no physical reality, a "quale". So therefore, if the past is singular, so is the future, and
seen from "outside", every quantum event, whether "future" or "past" from any particular fame of reference,
is in fact completely determined in its outcome, even though it is also random in the sense there is no way of explaining why it is the way
it is, beyond the description provided by Born rule probabilities. Is that not weird, if not downright absurd? What is this
"necessity" that dictates that this particular subset of all the possible quantum events was selected as the way things are?
If there were such a "necessity" that would be a deterministic theory and
inconsistent with the Born rule...and observation.
Well it’s not inconsistent with observation because if such a thing were true,
there’d still be no way an observer inside the system would know what the
predetermined outcome was going to be. Doesn’t mean I like the idea though,
obviously.
Somehow the idea of the future being indeterminate but the past fixed seems
palatable because it accords with our subjective experience, but really it is
incoherent as soon as we acknowledge that the past-future distinction is not
physically meaningful.
But it is meaningful. Entropy increases in the future direction. We remember
and record the past but not the future.
The arrow of time is physically meaningful, not the idea of “now”, which is the
reference point for determining what is future or past. No event belongs
intrinsically to the past or future, it is a relative concept for some
conscious observer.
Would this mean that if we could run the big bang over again from the same
initial conditions, it would always go exactly the same way? That is absurd, as
it would mean there is something prebuilt as it were into the laws of physics
that dictates that only this particular world history is permitted, for no
reason at all.
That would be t'Hooft's superdeterminism.
I’ll look it up. But sounds daft :)
But if it could go a different way, that is equally absurd because it implies that
variance is allowed at the level of entire universes, but not at the level of individual
quantum events within those universes. What can resolve this paradox? Perhaps I'm
cheating by imagining different possible universes in a universe where only one is real
and allowed, but who can seriously countenance such a cosmology of absurdity where
everything "just is"?
Of course if MWI is correct, then the paradox is resolved, because there is
only a single past in the sense that there is only a single shortest path from
any limb of a tree to its base, and there is no need for some principle of
arbitrary necessity to dictate that all quantum events only have one possible
outcome. For me this is a powerful argument in favour of many worlds, yet it's
not one I've heard before. Any comments?
It's a pretty good argument...and one I've heard (and even thought of myself)
before. Does it really solve a problem that a collapse of the wave function
doesn't solve?
Well I believe some experiments (currently impracticable) have been proposed to
test it (can’t recall details but they involve undoing a series of quantum
interactions). And of course Deutsch argues that a sufficiently complex quantum
computer proves it - because where are the informational resources required for
the computation “kept” in a single universe?
On the other hand for a quantum computer to work, all the "wrong"
branches of computation have to null out by destructive interference -
which sort of implies they must be in the same world.
But anyway I’m not an engineer whose interest in physics is practical :) I’m
interested in truth (whatever that means), and although I agree that the map is
not the territory, I also agree with Deutsch’s argument that scientific
theories are explanations, and good explanations are preferable to bad ones,
even if their utility is not immediately apparent. After all, Copernican
cosmology did not initially provide better predictions than the much-finessed,
epicycle-ridden geocentric model.
But the Copernican model was replaced by the model of Kepler and Newton
and then Einstein. So have we arrived at "the truth"? ISTM that "true"
has different meanings in mathematics and Platonism vs physics and
empiricism. In logic and mathematics it's just a marker, like "t" in
LISP, that is propagated through propositions by the rules of inference
and the meaning of words. It has no relation the truth of observations
except for our application.
Brent
Brent
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