On 2/17/2025 5:08 PM, Alan Grayson wrote:
On Monday, February 17, 2025 at 12:49:27 PM UTC-7 Liz R wrote:
Apparently the simplest model of the universe is one that is
infinite at all times (according to Max Tegmark) - the
"concordance" model? There is no reason an infinite universe
couldn't have undergone scale expansion, an (in this case,
presumably uncountably) infinite thing remains infinite no matter
how much you expand it. Whether the universe is a continuum is key
to this, so it depends on an as-yet unknown TOE. If spacetime is
quantised - in some sense - then whether it could be infinite, and
whether it could expand, might still be up for grabs.
Note that a quantised spacetime would presumably only contain a
finite number of possible states inside any volume (e.g. our
cosmological horizon) and hemce an infinite universe would
eventually repeat itself across sufficiently large distances.
Again quoting Max Tegmark, this would occur for our Hubble sphere
at something like a distance of 10^10^37 metres (from memory - the
actual figures don't really matter much for any practical purpose,
just note that they make a googol look ultramicroscopic). Assuming
that repeated identical quantum states are indistinguishable, an
infinite quantised universe would in fact be "piecewise finite" on
Vast scales - repeating arbitrarily large identical volumes would
be not just indistinguishable in principle but actually identical.
So on this basis, the universe would be a sort of Library of Babel
in which all possible quantum states exist (including "Harry
Potter" and "White Rabbit" universes) - but since the number of
possible states is finite for a given volume, it would eventually
run out of combinations and repeat itself. Quite what this would
look like on "hyperastronomical scales" I leave to the mathematicians.
*FWIW, our best current measurements fail to show any quantization of
spacetime. This was discussed here by Lawrence Crowell a long time
ago, and I don't recall the level of fineness of these results. AG
*
*It was a paper I cited years ago that noted there was no dispersion of
gamma rays from very distant galaxies which ruled out on discrete
structure to space down to less than the Planck scale. Here's a more
recent paper: https://physics.aps.org/articles/v17/s99
Brent
*
By the way the Cosmological Principle is an observation /
assumption, not an actual principle based on any physical laws.
*Not exactly. Physical observation do play a significant role in
generating principles. Faraday's observations of the behavior of
magnetic fields comes to mind, and the MM experiment, which Einstein
was aware of, which showed the velocity of light is independent of an
observer's motion. In the case of the CC, we have ambiguous results.
The CMBR suggests the universe was very close to homogeneous and
isoptropic when its age was about 380,000 years old, but measurements
much later in time show it's actually lumpy, with ultra long filaments
containing galaxies, separated by huge voids. I'd go with the later,
showing that the CC is false. AG *
On Monday, 17 February 2025 at 18:05:20 UTC+13 Alan Grayson wrote:
On Sunday, February 16, 2025 at 1:57:39 AM UTC-7 Quentin
Anciaux wrote:
AG, your argument assumes a false dichotomy between
"nothing" and "something"
Why a false dichotomy? No transition from finite to infinite
if it was alway infinite, but was it? AG
while making unjustified claims about infinity. If the
universe is infinite now, it was infinite at the Big Bang,
there’s no "transition" from finite to infinite. Your
assertion that this is "not remotely intelligible" is just
an appeal to personal incredulity, not an actual argument.
Quentin
Le dim. 16 févr. 2025, 09:44, Alan Grayson
<[email protected]> a écrit :
On Saturday, February 15, 2025 at 9:20:55 PM UTC-7
Alan Grayson wrote:
On Saturday, February 15, 2025 at 9:11:22 PM UTC-7
Brent Meeker wrote:
On 2/15/2025 7:03 PM, Alan Grayson wrote:
On Saturday, February 15, 2025 at
1:56:14 PM UTC-7 Brent Meeker wrote:
On 2/14/2025 11:36 PM, Alan Grayson wrote:
On Friday, February 14, 2025 at
11:06:42 PM UTC-7 Brent Meeker wrote:
On 2/14/2025 3:23 PM, Alan Grayson
wrote:
On Wednesday, February 12, 2025 at
12:36:38 PM UTC-7 Brent Meeker wrote:
On 2/12/2025 12:55 AM, Alan
Grayson wrote:
If the age of the universe is
finite, which is generally
believed, then no matter how
fast it expands, it can never
become spatially infinite,
So,*IF* it is spatially
infinite, this must have been
its initial condition at or
around he time of the Big Bang
(BB). But this contradicts the
assumption that it was at a
super high temperature at or
around the time of the BB.
No it doesn't. I can be
infinite and high temperature.
What gave you idea it couldn't?
IOW, if we run the clock
backward, the universe seems
to get incredibly small,
If the universe is infinite,
then it is only the Observable
Universe that gets incredibly
small.
*
*
*Is there any principle you are
aware of, which prevents an
infinite universe from becoming
incredible small?
*
*It would have to undergo an
infinite change in size in a finite
time, which would require infinite
relative velocities.
Brent*
*
*
*I can't imagine a universe starting as
infinite in spatial extent -- can you? -- *
As well as I can imagine any infinite
thing. Imagination can be trained. My
supervising professor, Englebert
Schucking, could visualize four
dimensional objects and draw their
projection on the blackboard. If you
can't do that, you just have to suppress
some dimensions; then in the (t,r) plane
there's an infinite line, the t-axis, and
to the right of this line is the (t,r)
plane and in that plane everything is
moving apart. Just look at Ned Wright's
cosmology tutorial:
https://www.astro.ucla.edu/~wright/cosmolog.htm
Brent
The problem is this; how does one imagine a
universe which suddenly comes into being,
initially resumably with zero spatial extent,
and when it does, it's infinite in spatial
extent? IMO, this would be a singularity
implying infinite spatial expansion
instantaneously. I have no alternative but to
reject this model for a finite one, starting
small and hot, and expanding, since I have no
idea what it means to begin infinitely. I am
open to suggestions. AG
Expand your imagination. Remember "infinite"
just means without bound. You don't have to
imagine the whole infinite line, just imagine
a line without imagining it's ends.
Not saying I believe it, but the best bet at this
point in time, is that the universe began as a
quantum fluctuation, thus small, very small! AG
BTW, since a finite volume such as the
observable universe, can originate from a
point, those pictorial models of the
evolution of the universe, starting from a
point, aka the BB, are apparently accurate
in their descriptions. That is, they're not
necessarily simplifications of the evolution. AG
Probably they are since they don't take
account of quantum mechanics; but we don't
know exactly how they are wrong.
Brent
Consider this: For Nothing to become Something and
also be infinite in spatial extent, that Something
must have that infinity as its initial condition,
given that it now has a finite age. But transforming
from Nothing to Something and having that infinity as
its initial condition as infinite in spatial extent,
is, if you think about, not remotely intelligible. For
this reason, I conclude it can't have this infinity as
its initial condition and can't be flat, which implies
this infinity. AG
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