<< On the disk, there is a temperature gradient, so the spectrum is not pure black body; though, CMB & Hawking are. >> A non-rotating black hole (if such exists) has a spherical accretion shell, as opposed to a wide disc. Would I be correct in assuming that this shell must be relatively thin? << a corresponding huge factor, one that would fall within the ISCO >> A "factor" is a ratio, of what exactly? How can it be compared distance? Please elucidate in a little more detail for the benefit of the unwashed! [ Here ISCO = 3x horizon radius --- see https://en.wikipedia.org/wiki/Innermost_stable_circular_orbit ] WFL On 10/15/20, Brad Klee <bradklee@gmail.com> wrote:
A temperature like ~10^6 K seems hot enough for ionization, but to redshift it down to ~1K, we would need a corresponding huge factor, one that would fall within the ISCO.
On the disk, there is a temperature gradient, so the spectrum is not pure black body; though, CMB & Hawking are.
Penrose seems to be concerned with with primordial black holes, and if they could be final states in a previous aeon’s “big chill”. He readily admits that this is a crazy idea. No one succeeded in reproducing the data analysis to find “hawking points”.
The other crazy idea is no mention of Spin Networks in the prize announcement? Why not? See also:
https://math.ucr.edu/home/baez/penrose/
What if spacetime itself is atomistic?
—Brad
On Oct 14, 2020, at 10:06 PM, Allan Wechsler <acwacw@gmail.com> wrote:
I am guessing that Fred Lunnon was *not* referring to Hawking radiation when he asked about black hole emissions. Instead, consider the kind of radiation you would expect from infalling material. It gets compressed as it falls toward the event horizon, so it heats up, but its radiation is red-shifted due to gravitational effects. Perhaps there is a thin zone just outside the horizon that is so hot it becomes an opaque plasma, like the universe before the CMBR horizon. I wouldn't expect the numbers to align, and it would depend on the density of the ambient medium, but I do see an analogy, and perhaps that's what Fred was getting at.
On Wed, Oct 14, 2020 at 10:45 PM Brad Klee <bradklee@gmail.com> wrote:
That's an ingenious and compelling insight --- though why is this the first time I have ever encountered it made explicit in many decades, I wonder?
I guess the graphic designers at NASA have decided that messy unit conversions are worth their price in uncertainty, as long as it helps them "communicate" with the taxpayers.
If you carefully read the abstract of the Peebles paper, the first sentence uses the time word "when" in relation to 4000K, and see also Section1 Eq. 3. (The paper is not to easy, but Peebles is also a good textbook author and has a nice one on quantum mechanics.)
How many of us, I wonder, would have given their right arm to fail like that?
I thought the Penrose Tiles were the real motivation behind the Nobel Prize, but they probably wanted the announcement to sound a certain way.
How does CMBR differ from (accretion at horizon of a static) black hole?
If you are asking about Hawking Radiation, it's orders of magnitude colder than 2.7K. As far as I know, it's so cold that it hasn't been observed.
Is the CMBR not dependent on observer frame, similarly to a rainbow?
I guess the invariants are statistical in nature, and would expect that extracted "cosmological constants" do not depend on ref. frame.
As for believing Forbes, my investments aren't tied up in stocks and bonds, so I typically ignore what they have to say. Scott Mendelson was one of my inside jokes during the Trump era, but I'm happy to be done with that phase of my life if possible.
--Brad
On Wed, Oct 14, 2020 at 8:11 PM Fred Lunnon <fred.lunnon@gmail.com> wrote:
<< In this situation, it seems like either temperature or density are monotonic decreasing with time, so either could serve as an effective time axis. >>
That's an ingenious and compelling insight --- though why is this the first time I have ever encountered it made explicit in many decades, I wonder? Surely acceptable in the already highly speculative situation of (established) cosmic inflation. Which in any case --- if we are to believe the Siegel article in Forbes --- experimental evidence serves to validate (not 'prove', please!).
In contrast Penrose admits (video start & end) that at start & end of CCC, time ceases to exist: without even an approximation available, "before/after" have no meaning. This suggests to me that a serious logical flaw may well have been plastered over by an invalid metaphor.
Then there is the (alleged) contradiction by experimental evidence. I can well imagine that Penrose is well aware of the disagreement, but remains unperturbed by it. After all, in the early 1970's he devoted a good deal of effort to constructing a crystallographic tiling with pentagonal symmetry, despite knowing full well that such an object had been proven not to exist. Of course, he failed. How many of us, I wonder, would have given their right arm to fail like that?
While I'm making a clean breast of all the questions about CMBR that I was afraid to ask ---
How does CMBR differ from (accretion at horizon of a static) black hole?
Is the CMBR not dependent on observer frame, similarly to a rainbow?
See http://www.scholarpedia.org/article/Unruh_effect
Finally, it did occur to me that an astronaut embarking on a visit to the restaurant at the beginning of the universe might be less than impressed at the performance of his GPS on its deployment of temperature as a time proxy.
<< Houston, there is a problem. I'm in the middle of nowhere/when, stuck on top of a hump-backed ergosphere, with all ten thruster time-axes pointing in different directions. By the way, it's getting bloody cold here --- and my vertigo is starting to play up. Can somebody dig out that copy of HHGG that fell down behind the radiator in the gent's toilet, and upload it pronto, please? >>
WFL
On 10/11/20, Brad Klee <bradklee@gmail.com> wrote:
PS. In this situation, it seems like either temperature or density are monotonic decreasing with time, so either could serve as an effective time axis. --Brad
On Sat, Oct 10, 2020 at 9:50 PM Brad Klee <bradklee@gmail.com> wrote:
> Hi Fred, > > You can think of the CMB as a curtain or a wall that exists > at a very early time in the history of the universe, see for > example this (nice) piece of propaganda from NASA: > > https://www.jpl.nasa.gov/infographics/infographic.view.php?id=10824 > > At times earlier than the CMB, the universe is said to be > radiation dominated, and the photons are scrambled by > interactions with charged particles, as described here: > https://en.wikipedia.org/wiki/Recombination_(cosmology) > > How can we figure out the magic number 380 kiloyears? > > http://articles.adsabs.harvard.edu/pdf/1968ApJ...153....1P > Table 1 says Temp. 3000K is 99% recombined, and this > happens at approx z=1100 giving the approximate time > as long as the redshift ---> year calculator works. > > Compare: > http://www.astro.ucla.edu/~wright/CosmoCalc.html > z=1100 --> 370Kyr > https://home.fnal.gov/~gnedin/cc/, > z=1100 --> 475Kyr > https://www.kempner.net/cosmic.php > z=1100 --> 471Kyr > > I also looked around and found some more interesting > timeline graphs: > >> https://pages.uoregon.edu/jimbrau/astr123-2015/Notes/Chapter27.html >>> >
https://pages.uoregon.edu/jimbrau/BrauImNew/Chap27/7th/AT_7e_Figure_27_01.jp...
>>
https://pages.uoregon.edu/jimbrau/BrauImNew/Chap27/7th/AT_7e_Figure_27_04.jp...
Here we can see what we need to do is solve for the intersection of two curves, then look ahead to get from the crossing point to the time of atom formation.
So why should this problem be irrelevant? Isn't always relevant to wonder: Where did we come from? How did we get here?
--Brad
On Sat, Oct 10, 2020 at 7:32 PM Fred Lunnon <fred.lunnon@gmail.com> wrote:
> Whenever it surfaces, I do wonder whether theoretical physics is > "math-fun"; > --- anyway, till we get slapped down, here's my (totally amateur) > two-penn'orth ... > I've been fascinated by physics since childhood, but somehow never > managed to > focus motivation sufficiently to learn to _do_ any: so I can usually > understand the > questions well enough, even if the answers often go over my head. > > Not this time round. "behind (or before) the CMB" puts the problem > in a nutshell. > Both general relativity and quantum theory deal with observations
made
> by > an > observer in a specific frame of reference located in (Minkwski) > spacetime. > Penrose in the video kicks off by admitting this, then cheerfully > proceeds to > speculate about some enveloping notional spacetime without any attempt > at > defining what behind (or before) might mean. It's turtles all the way > down ... > > I sniff a fundamental cognitive trap lurking. Our notion of time is > inextricably > connected with our consciousness, which in turn we remain unable to > relate to > any physical framework --- despite strenuous efforts (by Penrose and > others) > over many millenia. The possibility of progress seems to demand that > such > questions must be stripped of their dependence on a nonexistent frame of > reference even to make sense. > > Fred Lunnon > > > > On 10/9/20, Brad Klee <bradklee@gmail.com> wrote: >> I was wondering about this question recently, so I was >> happy to get a dissenting opinion via Forbes: >> >> >
https://www.forbes.com/sites/startswithabang/2020/10/08/no-roger-penrose-we-...
>> >> But the tone of the Forbes article is too businesslike for >> my taste, and does it mention that Penrose himself >> describes the idea as "crazy"? See also: >> >> https://www.youtube.com/watch?v=YTttUigXulk >> >> When you watch this video, how can you help but wonder >> about the incredible mystery of what exactly is going on in >> the background out there? Maybe universal reincarnation >> is a plausible cosmogony? We don't know. >> >> Fifty or one hundred years from now we could have better >> gravity detection, and a better idea of what is going on >> behind (or before) the CMB. Until then... >> >> Anyways, congratulations Penrose! More and more cheers >> and congratulations for unexcelled creativity! >> >> --Brad >> _______________________________________________ >> math-fun mailing list >> math-fun@mailman.xmission.com >> https://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun >> > > _______________________________________________ > math-fun mailing list > math-fun@mailman.xmission.com > https://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun >
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