On Friday, May 22, 2020 at 8:30:10 PM UTC-5, Alan Grayson wrote:
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>
>
> On Tuesday, May 19, 2020 at 11:18:15 PM UTC-6, Alan Grayson wrote:
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>>
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>> On Tuesday, May 19, 2020 at 6:26:08 PM UTC-6, Lawrence Crowell wrote:
>>>
>>> You cannot of course circumnavigate the spatial manifold of the
>>> universe. Anything beyond the cosmological horizon moves away faster than
>>> you can ever catch up. It is a bit like the part in the movie The Shining
>>> with Jack Nicholson where the hotel hallway expanded faster than he could
>>> run. If we could though observe this, say analogous to Jack Nicholson in
>>> the film, there would be optical effects. The spatial manifold could be a k
>>> = 1 closed or k = -1 hyperbolic or the dodecahedral tessellated universe of
>>> Poincaré. Yet so far data is not forthcoming.
>>>
>>> A Planck energy of quanta, say a UV graviton, could have causal
>>> influence on us is it expands to the cosmological horizon or near so. The
>>> B-modes of inflation, which are still being pursued, represent Planck units
>>> redshifted to some appreciable scale comparable to the cosmological
>>> horizon. This is a z factor z = 10^{10}ly/ℓ_p = 6.3×10^{60}, where taking
>>> the nat-log of this and multiplying by the horizon scale 1.3×10^{10}ly we
>>> get 1.8×10^{12}ly. The furthest out anything can have traversed at the
>>> speed of light to reach is from that distance and from the earliest near
>>> Planck time in the universe. What this means is the source or emitter of
>>> this graviton was early on close to our region and the source is not that
>>> incredible distance away.
>>>
>>> LC
>>>
>>
>> Is this estimate reasonable, also from
>>
>> https://www.forbes.com/sites/startswithabang/2020/05/19/would-a-long-journey-through-the-universe-bring-us-back-to-our-starting-point/#fe376fef6c50
>>
>>
>> The appearance of different angular sized of fluctuations in the CMB
>> results in different spatial curvature scenarios. Presently, the
>> Universe appears to be flat, but we have only measured down to about the
>> 0.4% level. At a more precise level, we may discover some level of
>> intrinsic curvature, after all, but what we've observed is enough to tell
>> us that if the Universe is curved, it's only curved on scales that are
>> ~(250)^3 times (or more than 15 million times) larger than our
>> presently-observable Universe is.
>>
>> AG
>>
>
> What I'm asking is whether, based on current measurements, if the universe
> is curved, can we conclude that the universe is *15 million times larger*
> than our presently observable universe? TIA, AG
>
Without data there is nothing we can conclude. The spatial surface of the
universe appears to be flat or without curvature that is 300 or so larger
than the cosmological horizon distance. That is about 4 trillion light
years, or about 2 times the possible distance any causal connection from
inflation could reach us, Beyond that we know absolutely nothing. Unless
some sensitive optical work is done with CMB imaging that can push this
further we may never know.
In the end physics and observable cosmology is local, and we are
approaching certain limits due to our locality as observers. If we measure
much further out and closer to inflation and the initial quantum event we
will only push out about 1.8 trillion light years. It is unclear if any ray
tracing measurement of gravitons or neutrinos from this earliest moment of
the observable universe.
LC
>
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>>>
>>>
>>> On Tuesday, May 19, 2020 at 1:41:45 AM UTC-5, Philip Thrift wrote:
>>>
>>>>
>>>>
>>>> *Would traveling out in a "straight" line bring you back to where you
>>>> started?*
>>>>
>>>>
>>>> https://www.forbes.com/sites/startswithabang/2020/05/19/would-a-long-journey-through-the-universe-bring-us-back-to-our-starting-point/#1781c2ccf6c5
>>>>
>>>> In the writer's (Ethan Siegel's) *opinion*:
>>>>
>>>>
>>>> On a cosmic scale, there is no indication that the Universe is anything
>>>> other than infinite and flat. There is no evidence that features in one
>>>> region of space also appear in any other well-separated region, nor is
>>>> there evidence of a repeating pattern in the Universe's large-scale
>>>> structure or the Big Bang's leftover glow. The only way we know of to turn
>>>> a freely moving object around is via gravitation slingshot, not from
>>>> cosmic
>>>> curvature.
>>>>
>>>> And yet, it's a legitimate possibility that the Universe may, in fact,
>>>> be finite in extent, but larger than our observations can currently take
>>>> us. As the Universe unfolds over the coming billions of years, more and
>>>> more of it (about 135% more, by volume) will become visible to us. If
>>>> there's any hint that a long-distance journey would bring us back to our
>>>> starting point, that's the only place we'll ever find it. Our only hope
>>>> for
>>>> discovering a finite but traversible Universe lies, quite ironically, in
>>>> our far distant future.
>>>>
>>>> @philipthrift
>>>>
>>>
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