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A-L-E-X
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Cosmology Discussion Thread

18 Dec 2018 03:17

I wonder if the "dark flow" that NASA has detected could be a sign of that, as well some of the patterns in the CMB that have been found that seem to be nonrandom.  

A grand unified theory that combines all four forces as well as relativity and quantum mechanics may make it possible to test for other universes.  Gravity is explained as being different from the other three forces (just like time is different from the other three dimensions), because gravity may leak in from another brane.  A proper theory of quantum gravity may help guide us towards finding ways of testing for other universes.

The strongest argument for the multiverse concept seems to be that some kind of creator may need to be invoked if our universe is the only one, because of how unlikely its formation seems to be, which is why the multiverse idea has become more popular.  "Is Nature Unnatural" explores that.

String theory predicts that the most common types of universes would consist of 4 dimensions or 6 dimensions.  I've heard string theory described as 22nd century physics that landed in the lap of late 20th century scientists lol.  According to the string theory landscape there are 10^500 possible bubble universes.  I wonder if the recent falsification of the cosmic censorship conjecture might open the way for more theories on black hole cosmology, as having two stable event horizons in a rotating black hole (the second one being the Cauchy horizon) would pave the way for generating a new universe inside the second horizon.
 
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Cosmology Discussion Thread

18 Dec 2018 03:32

I think that if we someday develop the 'Theory for everything', then this theory must also state whether there are multiple universes or not. Also, how many dimensions our universe has, it must be able to specify.

But maybe we can not develop a 'Theory for everything' because we are imprisoned in our universe.
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Cosmology Discussion Thread

18 Dec 2018 04:16

We can only develop a "Theory of everything but its axioms".
NIL DIFFICILE VOLENTI
 
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Cosmology Discussion Thread

18 Dec 2018 20:14

Watsisname wrote:
Source of the post so they are completely unfalsifiable.  Personally I find these the least interesting of the multiverse ideas, because we cannot know

Of course, I thought the same. I would have posted this elsewhere, but then I saw that you had mentioned it here as a possible topic. For me, it more or less lies in the same camp as Simulation Theory: feasible but unfalsifiable unless by the stupendous and impossible feats of scientific experiments currently unknown to us.

Watsisname wrote:
Source of the post What we observe is consistent with no leak at all, and no extra dimensions to the space.  When you stop to think about it, this is an amazing statement.


Indeed!

Watsisname wrote:
Source of the post This would be a Brane Cosmology.  It could be testable by searching for evidence of previous collisions between our universe and others.  Once in a while, a research group does claim to find such a thing, although no such findings have so far been found compelling or stood up to scrutiny by the broad community of cosmologists.

This is the topic of my next question, naturally: 

What are the details of some of those claims in Brane studies?
What might happen if an already established and completely separate universe (as in, not one spawned by wave-collapse if that interpretation is true) suddenly collided with ours? This question assumes multiverse theory is valid of course, and so is all in the realms of hypothesis. Could we detect such a drastic collision? Is it even POSSIBLE under any known physics (barring the occasional leaks as mergers might demonstrate)?
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Cosmology Discussion Thread

19 Dec 2018 00:29

Besides the signs of interactions and collisions that could possibly be detected in the CMB right now the only indications we have of it is that our possible Theory of Everythings all become much more elegant if we consider that extra dimensions are involved.  Einstein himself was trying to formulate a Theory of Everything before he died and he found the best and most elegant way of doing it was to incorporate extra dimensions.

One of the reasons that black holes appear to be singularities is because they are quantum objects on relativistic macro scales, but perhaps also, that inside black holes, all forces become unified (like the original state of the universe)?
 
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Cosmology Discussion Thread

19 Dec 2018 09:22

A-L-E-X wrote:
Source of the post One of the reasons that black holes appear to be singularities is because they are quantum objects on relativistic macro scales, but perhaps also, that inside black holes, all forces become unified (like the original state of the universe)?


The prediction of a singularity inside of a black hole has nothing to do with quantum mechanics or unification of forces.  They are predicted purely by general relativity: once you have a region of space surrounded by an event horizon, then the spacetime dynamics predicts that all things within it are quickly drawn to a point with zero size, because the only direction anything is allowed to go is further inward.

Quantum mechanics (or more precisely a theory of quantum gravitation) probably prevents singularities from existing in nature.
 
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Cosmology Discussion Thread

19 Dec 2018 19:57

Moreover, it would seem like the existence of extra dimensions has been disproved, at least by  current gravitational wave observations. It is all quite interesting, to say the least.
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Cosmology Discussion Thread

20 Dec 2018 00:28

That doesn't make sense- you can't have a grand unification theory without extra dimensions.  They may not exist in our universe, but they would be part of a larger scale omniverse.  The type of dimensions we are talking about would not be measurable by gravity waves (unless you mean something like dark flow, which is still unexplained.)

read here- it's what I thought-
https://phys.org/news/2018-09-gravitati ... sions.html

they said they dont add extra dimensions to "this" universe, but none of these theories predict the extra dimensions to be in this universe, the unification theories mean extra dimensions outside the universe.

Also Wat- singularities are an indication that relativity breaks down at that scale, it's an indication that it wasn't meant to describe laws of physics on that scale.  The fact that quantum mechanics doesn't predict singularities is precisely because it is designed to work at that scale.  Thats why I favor quantum mechanics over relativity, because at the fundamental level, reality is quantum mechanical in nature, and relativity emerges from that on the macro scale.  And if loop quantum cosmology is correct, there would no shrinkage to point size, because there would be a minimum discrete size to space-time beyond which nothing could shrink further.
Last edited by A-L-E-X on 20 Dec 2018 00:46, edited 1 time in total.
 
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Cosmology Discussion Thread

20 Dec 2018 00:45

A-L-E-X wrote:
Source of the post That doesn't make sense- you can't have a grand unification theory without extra dimensions.  They may not exist in our universe

Yes, I believe it is in reference to dimensions within our universe, that would be in addition to the ones like x,y and z plus time.

A-L-E-X wrote:
Source of the post Thats why I favor quantum mechanics over relativity, because at the fundamental level, reality is quantum mechanical in nature, and relativity emerges from that on the macro scale.

But as of yet there is no Theory of Everything (for all physical fields of matter) or Unified Field Theory (for both matter and other forces like electromagnetism), rendering this statement moot. Quantum and Macro/microscopic cannot be proven to be connected until we have the Theories, as you well know. For now quantum effects are observed independently from our own macroscopic viewpoint. The two states of matter certainly exist, but we just can't exactly pin point how they interact. These Theories could be seen as a type of 'bridge' between the quantum and none-quantum states of reality. There is no competition between General Relativity and Quantum Mechanics and fields. Each exists and operates competently at the same time, but at different levels.
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Cosmology Discussion Thread

20 Dec 2018 00:48

oops I was editing while you were posting lol

https://phys.org/news/2018-09-gravitati ... sions.html

they said they dont add extra dimensions to "this" universe, but none of these theories predict the extra dimensions to be in this universe, the unification theories mean extra dimensions outside the universe that we know.  There is no way for their to be extra dimensions in our universe anyway, because if there were relativity would not work.  Einstein was also working on unification theory with added dimensions, but the dimensions weren't part of our universe as far as I know.  They are considered "wrapped up."


Yes, exactly, quantum mechanics and relativity both have different ranges of scale in which they operate.  Which vexed Einstein to no end and which is why he called quantum mechanics "spooky action at a distance" haha.

Now, I can throw a bit of a monkey wrench into the discussion, with an intriguing characteristic of quantum mechanics- it works on the biological scale too!  Some aspects of DNA inheritance, photosynthesis, etc., can only be explained by quantum mechanics!  There is a whole new field emerging called quantum biology.

Have a look at this, it's interesting, and gives us one method of tackling the problem, although the solution may be decades away:

https://phys.org/news/2018-12-gravity-mathematically-dynamics-subatomic-particles.html

about the gravity wave- extra dimensional thing, the lead researchers responded to questions here:

https://physics.stackexchange.com/questions/431010/why-does-the-ligo-observation-disprove-higher-dimensions

https://www.labroots.com/trending/chemistry-and-physics/12999/study-gravitational-waves-limits-odds-extra-dimensions-exist

Although it confirmed and further strengthened the conclusions from earlier studies, the new paper, as the authors noted, excluded only large dimensions: its conclusion is only valid in the scale from 1 mile (1.6 kilometers) up to at least 80 million light-years.

How about the dimensions that are wrapped in the microscopic space, like those predicted by string theories? (string theory is a theoretical framework in which all matters and forces are made out of one-dimensional objects called strings.) Many string theories proponents believed that the world, at the tiniest scale, is at least 10 or 11-dimensional. Until scientists come across convincing evidence or a better measuring method, these hypothetical dimensions still await to be discovered or disproved.

You might like this too, I found it very interesting:

https://www.forbes.com/sites/startswithabang/2018/05/31/this-is-why-physicists-think-string-theory-might-be-our-theory-of-everything/#62938dcd58c2

http://scitation.aip.org/content/aip/magazine/physicstoday/article/68/11/10.1063/PT.3.2980
 
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Cosmology Discussion Thread

20 Dec 2018 01:31

A-L-E-X wrote:
Source of the post You might like this too, I found it very interesting:

https://www.forbes.com/sites/startswith ... 938dcd58c2

I admire string theory for one reason: It's sheer tenacious grip on modern science. No matter how many times it is discarded (whether or not it is ultimately true) by the majority, it always come back :). Maybe we are just so lazy that we can't crunch our branes enough like that again to come up with an alternative.

A-L-E-X wrote:
Source of the post How about the dimensions that are wrapped in the microscopic space, like those predicted by string theories?

You mean branes? Interestingly, the gravitational wave tests did not rule out the presence of tiny dimensions wrapped up in branes, if those even exist. There is yet hope for 'Gulliver's Dimensions'.
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Cosmology Discussion Thread

20 Dec 2018 01:52

Stellarator wrote:
A-L-E-X wrote:
Source of the post You might like this too, I found it very interesting:

https://www.forbes.com/sites/startswith ... 938dcd58c2

I admire string theory for one reason: It's sheer tenacious grip on modern science. No matter how many times it is discarded (whether or not it is ultimately true) by the majority, it always come back :). Maybe we are just so lazy that we can't crunch our branes enough like that again to come up with an alternative.

A-L-E-X wrote:
Source of the post How about the dimensions that are wrapped in the microscopic space, like those predicted by string theories?

You mean branes? Interestingly, the gravitational wave tests did not rule out the presence of tiny dimensions wrapped up in branes, if those even exist. There is yet hope for 'Gulliver's Dimensions'.

It would be ironic if space were circular like that, what we think of as tiny dimensions actually had their own universes just as "large" as ours, but inside themselves.  To them, we would be the tiny ones haha.  If one could ever do a journey between universes of different scales (think of it as a thought experiment for now) it would be a circular journey that leads one back to the point of origin because the different scales would loop into each other.  (We would be large on the scale of another universe and they would be large compared to another one and so on and so forth until finally we reached a level where the next one smaller was our own original one.)

Loop Quantum Cosmology is an interesting alternative to String Theory

https://dailygalaxy.com/2018/12/quantum ... ack-holes/

Theoretical physicists have been questioning if singularities really exist through complex mathematical equations over the past several decades with little success until now. LSU Department of Physics & Astronomy Associate Professor Parampreet Singh and collaborators LSU Postdoctoral Researcher Javier Olmedo and Abhay Ashtekar, the Eberly Professor of Physics at Penn State developed new mathematical equations that go beyond Einstein’s theory of general relativity overcoming its key limitation–the central singularity of black holes.

 

Quantum Loop Gravity

Artist depiction of loop quantum gravity effects in a black hole is shown above. The bottom half of the image depicts the black hole which, according to general relativity, traps everything including light. Loop quantum gravity, a theory that extends Einstein’s general relativity using quantum mechanics, overcomes this tremendous pull and liberates everything shown in the top half of image, thus solving the fundamental problem of black hole singularity. (A. Corichi and J. P. Ruiz).

Theoretical physicists developed a theory called loop quantum gravity in the 1990s that marries the laws of microscopic physics, or quantum mechanics, with gravity, which explains the dynamics of space and time. Ashtekar, Olmedos and Singh’s new equations describe black holes in loop quantum gravity and showed that black hole singularity does not exist.



 

“In Einstein’s theory, space-time is a fabric that can be divided as small as we want. This is essentially the cause of the singularity where the gravitational field becomes infinite. In loop quantum gravity, the fabric of space-time has a tile-like structure, which cannot be divided beyond the smallest tile. My colleagues and I have shown that this is the case inside black holes and therefore there is no singularity,” Singh said.

Instead of singularity, loop quantum gravity predicts a funnel to another branch of the space-time.

“These tile-like units of geometry–called ‘quantum excitations’– which resolve the singularity problem are orders of magnitude smaller than we can detect with today’s technology, but we have precise mathematical equations that predict their behavior,” said Ashtekar, who is one of the founding fathers of loop quantum gravity.

“At LSU, we have been developing state-of-the-art computational techniques to extract physical consequences of these physical equations using supercomputers, bringing us closer to reliably test quantum gravity,” Singh said.

Einstein’s theory fails not only at the center of the black holes but also to explain how the universe was created from the Big Bang singularity. Therefore, a decade ago, Ashtekar, Singh and collaborators began to extend physics beyond the Big Bang and make new predictions using loop quantum gravity. Using the mathematical equations and computational techniques of loop quantum gravity, they showed that the Big Bang is replaced by the “Big Bounce.” But, the problem of overcoming black hole singularity is exceptionally complex.

The Daily Galaxy via Louisiana State University
 
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Cosmology Discussion Thread

23 Dec 2018 01:16

A-L-E-X wrote:
Source of the post I posted a new article about Loop Quantum Cosmology

I find all these alternatives fascinating. It's the beauty of it: this is a frontier for physics and a great opportunity to exercise the Scientific Method.
A-L-E-X wrote:
Source of the post Instead of singularity, loop quantum gravity predicts a funnel to another branch of the space-time.

This part very much reminds me of Stephen Hawking's essay in his Brief History of Time, entitled "White holes & Baby Universes". In this essay, he demonstrates that it is possible that black-hole singularities aren't singular or compact at all,  but rather act as conduits to other universes, emerging in space/time as 'whiteholes' and creating universes of their own. Hard to explain here, really, Hawking did it better then me :).

Furthermore, I see some parallels between this and the theorized wormholes in General Relativity.
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A-L-E-X
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Cosmology Discussion Thread

23 Dec 2018 01:22

Yes I quite agree!  I also liked his Imaginary Time idea with a time axis perpendicular to conventional time, which you can plot the Big Bang/Bounce at the Origin (appropriately named- where the two axes meet!) and have a contracting universe on one side and an expanding universe on the other side- it actually looks like that black hole hourglass thing, except placed on its side (the origin point would be the center, so like this ><).
 
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Cosmology Discussion Thread

24 Jan 2019 18:49

PBS Space Time has made a excellent video on the current "crisis in cosmology" -- that is, the discrepancy between two methods of measuring the current value of the Hubble Constant.  I discussed this a little bit back here, but Matt's version is much more thorough. :)

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