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Watsisname
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Cosmology Discussion Thread

22 Nov 2019 17:11

A-L-E-X wrote:
Source of the post Wat, does the Baum-Frampton model add extra assumptions (like phantom energy?) It states w can be close to -1 but must be less than it.

Indeed!  The first extra assumption is the phantom energy (that w must be less than -1.)  This is necessary because the model requires conditions approaching a Big Rip in order to make huge regions of space virtually empty.  This is also a big assumption because although observations can never exclude w<-1 (if it really is identical to -1), a value less than -1 is much more complicated and unexpected on physical grounds.

Then, because the goal of the model is to get a cyclic universe, more assumptions must be made to avoid the disaster of the final Big Rip moment.  And it has to avoid the Big Rip in a very specific way, otherwise it leads to predictions that would already be falsified.  To do that, we must tack on even more assumptions.

This is a really good example of using as many extra unverified assumptions as necessary until a model does what we want it to while still being consistent with observations.  But the most compelling models are the ones that are consistent with observations while using the smallest number of assumptions, and preferably having some useful predictive power to boot.

A-L-E-X wrote:
Source of the post Also, does this new measurement lie outside of the margin of error (what is the margin of error that we have on w as of now?)

I don't think this measurement produces any new insights to the value of w.  That must come instead from observing how the expansion rate of the universe has changed over time.
 
A-L-E-X
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Cosmology Discussion Thread

24 Nov 2019 09:26

Watsisname wrote:
A-L-E-X wrote:
Source of the post Wat, does the Baum-Frampton model add extra assumptions (like phantom energy?) It states w can be close to -1 but must be less than it.

Indeed!  The first extra assumption is the phantom energy (that w must be less than -1.)  This is necessary because the model requires conditions approaching a Big Rip in order to make huge regions of space virtually empty.  This is also a big assumption because although observations can never exclude w<-1 (if it really is identical to -1), a value less than -1 is much more complicated and unexpected on physical grounds.

Then, because the goal of the model is to get a cyclic universe, more assumptions must be made to avoid the disaster of the final Big Rip moment.  And it has to avoid the Big Rip in a very specific way, otherwise it leads to predictions that would already be falsified.  To do that, we must tack on even more assumptions.

This is a really good example of using as many extra unverified assumptions as necessary until a model does what we want it to while still being consistent with observations.  But the most compelling models are the ones that are consistent with observations while using the smallest number of assumptions, and preferably having some useful predictive power to boot.

A-L-E-X wrote:
Source of the post Also, does this new measurement lie outside of the margin of error (what is the margin of error that we have on w as of now?)

I don't think this measurement produces any new insights to the value of w.  That must come instead from observing how the expansion rate of the universe has changed over time.

It reminds me of what we talked about months ago, about how to make a traversable wormhole, while a mathematical possibility, is akin to create a waterfall that flows backwards (upstream.)
More about dark energy here:
https://news.google.com/articles/CAIiEJ ... g?hl=en-US≷=US&ceid=US%3Aen

I found this article today.  Do you think the idea of a fifth force has any merit?

https://www.cnn.com/2019/11/22/world/fi ... index.html

https://arxiv.org/abs/1910.10459

New evidence supporting the existence of the hypothetic X17 particle
A.J. Krasznahorkay, M. Csatlos, L. Csige, J. Gulyas, M. Koszta, B. Szihalmi, J. Timar, D.S. Firak, A. Nagy, N.J. Sas, A. Krasznahorkay
(Submitted on 23 Oct 2019)
We observed electron-positron pairs from the electro-magnetically forbidden M0 transition depopulating the 21.01 MeV 0− state in 4He. A peak was observed in their e+e− angular correlations at 115∘ with 7.2σ significance, and could be described by assuming the creation and subsequent decay of a light particle with mass of mXc2=16.84±0.16(stat)±0.20(syst) MeV and ΓX= 3.9×10−5 eV. According to the mass, it is likely the same X17 particle, which we recently suggested [Phys. Rev. Lett. 116, 052501 (2016)] for describing the anomaly observed in 8Be.


https://www.cnn.com/2019/11/22/world/fifth-force-of-nature-scn-trnd/index.htmlex.html
 
A-L-E-X
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Cosmology Discussion Thread

13 Dec 2019 12:49

Found this excellent series of articles on Quanta:

https://www.quantamagazine.org/hologram-within-a-hologram-hints-at-solution-to-black-hole-information-paradox-20191119/

https://www.quantamagazine.org/newfound-wormhole-allows-information-to-escape-black-holes-20171023/

https://www.quantamagazine.org/wormhole-entanglement-and-the-firewall-paradox-20150424/

https://www.quantamagazine.org/the-origin-of-time-bootstrapped-from-fundamental-symmetries-20191029/

https://www.quantamagazine.org/black-hole-singularities-are-as-inescapable-as-expected-20191202/

New ways to show how information that falls into black holes is saved and a new construct for a traversable black hole

The flurry of findings started last year with a paper that reported the first traversable wormhole that doesn’t require the insertion of exotic material to stay open. Instead, according to Ping Gao and Daniel Jafferis of Harvard University and Aron Wall of Stanford University, the repulsive negative energy in the wormhole’s throat can be generated from the outside by a special quantum connection between the pair of black holes that form the wormhole’s two mouths. When the black holes are connected in the right way, something tossed into one will shimmy along the wormhole and, following certain events in the outside universe, exit the second. Remarkably, Gao, Jafferis and Wall noticed that their scenario is mathematically equivalent to a process called quantum teleportation, which is key to quantum cryptography and can be demonstrated in laboratory experiments.

John Preskill, a black hole and quantum gravity expert at Caltech, says the new traversable wormhole comes as a surprise, with implications for the black hole information paradox and black hole interiors. “What I really like,” he said, “is that an observer can enter the black hole and then escape to tell about what she saw.” This suggests that black hole interiors really exist, he explained, and that what goes in must come out.

https://www.quantamagazine.org/newfound-wormhole-allows-information-to-escape-black-holes-20171023/

https://www.quantamagazine.org/mathematicians-disprove-conjecture-made-to-save-black-holes-20180517/

early 40 years after it was proposed, mathematicians have settled one of the most profound questions in the study of general relativity. In a paper posted online last fall, mathematicians Mihalis Dafermos and Jonathan Luk have proven that the strong cosmic censorship conjecture, which concerns the strange inner workings of black holes, is false.

“I personally view this work as a tremendous achievement — a qualitative jump in our understanding of general relativity,” emailed Igor Rodnianski, a mathematician at Princeton University.

The strong cosmic censorship conjecture was proposed in 1979 by the influential physicist Roger Penrose. It was meant as a way out of a trap. For decades, Albert Einstein’s theory of general relativity had reigned as the best scientific description of large-scale phenomena in the universe. Yet mathematical advances in the 1960s showed that Einstein’s equations lapsed into troubling inconsistencies when applied to black holes. Penrose believed that if his strong cosmic censorship conjecture were true, this lack of predictability could be disregarded as a mathematical novelty rather than as a sincere statement about the physical world.

“Penrose came up with a conjecture that basically tried to wish this bad behavior away,” said Dafermos, a mathematician at Princeton University.

This new work dashes Penrose’s dream. At the same time, it fulfills his ambition by other means, showing that his intuition about the physics inside black holes was correct, just not for the reason he suspected.

Roger Penrose proposed the strong cosmic censorship conjecture to restore predictability to Einstein’s equations. The conjecture says that the Cauchy horizon is a figment of mathematical thought. It might exist in an idealized scenario where the universe contains nothing but a single rotating black hole, but it can’t exist in any real sense.

The reason, Penrose argued, is that the Cauchy horizon is unstable. He said that any passing gravitational waves should collapse the Cauchy horizon into a singularity — a region of infinite density that rips space-time apart. Because the actual universe is rippled with these waves, a Cauchy horizon should never occur in the wild.

As a result, it’s nonsensical to ask what happens to space-time beyond the Cauchy horizon because space-time, as it’s regarded within the theory of general relativity, no longer exists. “This gives one a way out of this philosophical conundrum,” said Dafermos.

This new work shows, however, that the boundary of space-time established at the Cauchy horizon is less singular than Penrose had imagined.

To Save a Black Hole
Dafermos and Luk, a mathematician at Stanford University, proved that the situation at the Cauchy horizon is not quite so simple. Their work is subtle — a refutation of Penrose’s original statement of the strong cosmic censorship conjecture, but not a complete denial of its spirit.

Building on methods established a decade ago by Christodoulou, who was Dafermos’s adviser in graduate school, the pair showed that the Cauchy horizon can indeed form a singularity, but not the kind Penrose anticipated. The singularity in Dafermos and Luk’s work is milder than Penrose’s — they find a weak “light-like” singularity where he had expected a strong “space-like” singularity. This weaker form of singularity exerts a pull on the fabric of space-time but doesn’t sunder it. “Our theorem implies that observers crossing the Cauchy horizon are not torn apart by tidal forces. They may feel a pinch, but they are not torn apart,” said Dafermos in an email.

Because the singularity that forms at the Cauchy horizon is in fact milder than predicted by the strong cosmic censorship conjecture, the theory of general relativity is not immediately excused from considering what happens inside. “It still makes sense to define the Cauchy horizon because one can, if one wishes, continuously extend the space-time beyond it,” said Harvey Reall, a physicist at the University of Cambridge.

Dafermos and Luk prove that space-time extends beyond the Cauchy horizon. They also prove that from the same starting point, it can extend in any number of ways: Past the horizon “there are many such extensions that one could entertain, and there is no good reason to prefer one to the other,” said Dafermos.

Yet — and here’s the subtlety in their work — these nonunique extensions of space-time don’t mean that Einstein’s equations go haywire beyond the horizon.
 
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szymas
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Cosmology Discussion Thread

03 Jan 2020 09:35

What are good medium technical books for myself to read about space in general that might help out in all of the fields and items I see in SE? I would like to know more about each of them to understand what they mean to the planet...

Thanks

Chuck
 
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Watsisname
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Cosmology Discussion Thread

03 Jan 2020 11:28

Hi szymas,


I think a good fit for you would be the text Universe: Stars and Galaxies by Freedman and Kauffmann.  The text gives an overview of most broad topics of astronomy, from its origins with ground-based observing and the function of telescopes, to the planets and solar system, stars (their formation and evolution, star death and the exotic objects they leave behind), galaxies, and finally cosmology.  It provides enough details for a good understanding (certainly more than enough to enrich your experience with SE!), and without requiring much math or physics.  It's aimed at the lower undergraduate level.

I hope that helps!  Welcome to the community. :)
 
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szymas
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Cosmology Discussion Thread

03 Jan 2020 13:08

Thank you, will look for it on Amazon!
 
A-L-E-X
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Cosmology Discussion Thread

04 Jan 2020 08:41

Watsisname wrote:
Hi szymas,


I think a good fit for you would be the text Universe: Stars and Galaxies by Freedman and Kauffmann.  The text gives an overview of most broad topics of astronomy, from its origins with ground-based observing and the function of telescopes, to the planets and solar system, stars (their formation and evolution, star death and the exotic objects they leave behind), galaxies, and finally cosmology.  It provides enough details for a good understanding (certainly more than enough to enrich your experience with SE!), and without requiring much math or physics.  It's aimed at the lower undergraduate level.

I hope that helps!  Welcome to the community. :)

I love books like these!  Is it good for observational astronomy too?  It looks like it's regularly updated (the fourth edition is out now)?
 
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Watsisname
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Cosmology Discussion Thread

04 Jan 2020 14:57

A-L-E-X wrote:
Source of the post Is it good for observational astronomy too? 

I'm not sure if you're using observational astronomy in the technical sense?  Almost everything in it is based on observational astronomy, because without observations and data, this would not be a science.  But it doesn't much discuss the details of how to do observational astronomy (the hard rigor of how to collect and analyze data, how to account for the effects of the atmosphere, doing spectroscopy and photometry, and so forth), for which I'd recommend something like this text, aimed more to the graduate level and professional astronomers.  

If you mean doing observations in the amateur astronomer's sense, like telling you where to find various objects of interest on the sky and describing what they look like through different instruments, then in that case I'd recommend something like Burnham's Celestial Handbook.  And then there are a number of texts and online guides out there for doing astrophotography. :)
 
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JackDole
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Cosmology Discussion Thread

05 Jan 2020 01:11

For people who can read German, I can recommend 'Abriss der Astronomie'. It was last updated in 2012 and, in its original form, is based on readings that the author, who has since passed away, has held as a professor at the university. (Hans-Heinrich Voigt)

But everything is very short and technical. Nevertheless, the book has about 1150 pages.
JackDole's Universe 0.990: http://forum.spaceengine.org/viewtopic.php?f=3&t=546
JackDole's Archive: http://forum.spaceengine.org/viewtopic.php?f=3&t=419
JackDole: Mega structures ... http://old.spaceengine.org/forum/17-3252-1 (Old forum)
 
A-L-E-X
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Cosmology Discussion Thread

05 Jan 2020 01:47

Watsisname wrote:
A-L-E-X wrote:
Source of the post Is it good for observational astronomy too? 

I'm not sure if you're using observational astronomy in the technical sense?  Almost everything in it is based on observational astronomy, because without observations and data, this would not be a science.  But it doesn't much discuss the details of how to do observational astronomy (the hard rigor of how to collect and analyze data, how to account for the effects of the atmosphere, doing spectroscopy and photometry, and so forth), for which I'd recommend something like this text, aimed more to the graduate level and professional astronomers.  

If you mean doing observations in the amateur astronomer's sense, like telling you where to find various objects of interest on the sky and describing what they look like through different instruments, then in that case I'd recommend something like Burnham's Celestial Handbook.  And then there are a number of texts and online guides out there for doing astrophotography. :)

All of these are jewels!  Thanks Wat!  Burnham's is a personal favorite of mine, it's like what Audubon's guide is for birders, Burnham's is for observational astronomy.  I like knowing things like spectral types of various stars, their mass and size, distances to them and to various DSO's as well as different types of galaxies and clusters and their size.  It gives space more "depth" in a sense.

The observational astronomy text you listed is also highly interesting because it mentions photometry and spectroscopy and how to do scientific research with CCD cameras.  I remember seeing a site somewhere where amateurs can add to the body of knowledge by doing valuable observational research in this area!
 
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Watsisname
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Cosmology Discussion Thread

05 Jan 2020 10:16

A-L-E-X wrote:
Source of the post The observational astronomy text you listed is also highly interesting because it mentions photometry and spectroscopy and how to do scientific research with CCD cameras.

Yes, this is what "observational astronomy" means nowadays. :)  The difference between it and casual observing is the collection and analysis of data so as to be useful for scientific research.  Amateur astronomers can also contribute scientifically useful data for professional astronomers.
 
A-L-E-X
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Cosmology Discussion Thread

07 Jan 2020 09:04

Watsisname wrote:
A-L-E-X wrote:
Source of the post The observational astronomy text you listed is also highly interesting because it mentions photometry and spectroscopy and how to do scientific research with CCD cameras.

Yes, this is what "observational astronomy" means nowadays. :)  The difference between it and casual observing is the collection and analysis of data so as to be useful for scientific research.  Amateur astronomers can also contribute scientifically useful data for professional astronomers.

I particularly like how cameras can be used to discover exoplanets!  That is a unique level of participation in a branch of the science that is pretty new.  No one could have imagined this before 2000!
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