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A-L-E-X
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Cosmology Discussion Thread

25 Mar 2019 01:42

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I thought I'd post this video here, because it is dedicated to the cosmological discoveries of the Hubble space telescope. While the images herein are not exclusively from that instrument, they remain a fitting choice for the piece. 

Welcome to the beauty and grandeur that is the universe...


I'm surprised that the people at NASA didn't make their own universe simulator program and use all the data from Hubble to create it!
 
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Cosmology Discussion Thread

28 Mar 2019 18:45

Following up from their latest episode reviewing a recent study suggesting that the strength of dark energy might be increasing, PBS Space Time describes the most important consequence if that is true -- the ultimate fate of the universe in a Big Rip!  



And in the spirit of this subject, I rendered the spacetime diagram for the scenario described where w = -1.5, in which case the Big Rip happens in about 22 billion years:

Image


In this scenario, we currently live at a special moment in time: the distance to where the recession velocity exceeds the speed of light is just now starting to decrease.  The cosmological event horizon is approaching and will eventually tear everything apart.  Fortunately, we know this scenario is unlikely, because we can rule out w being as small as -1.5 with extremely high confidence.  The most likely case is that w is exactly -1 and the Big Rip never happens.  With the uncertainty range around that, w probably isn't less than about -1.1, and the Big Rip probably does not happen any sooner than 100 billion years from now.
 
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Cosmology Discussion Thread

29 Mar 2019 01:06

I watched the episode, and an odd thought popped into my head at ~12 minutes, when Matt said the following: "[We can disregard the possibility of a Big Rip scenario because] there is a plausible physical explanation [in the current models of physics] for a constant dark energy density. The vacuum has a set amount of energy per volume".

I recall that the basis of many 'free energy' designs is pulling 'energy' from the quantum vacuum - or as they call it the 'ether' or zero-point energy (you know pseudo-scientists, they confuse their terminology, so you can call it whatever). The above quote seems to suggest that, at least in cosmic timescales, in an infinitely expanding universe, there is an infinite reservoir of potential (dark) energy in a volume of spacetime.

My thought on this was: could the inhabitants of an alternate universe, one where dark energy density increases due to W equaling less then -1, fashion some sort of free-energy machine exploiting the exponential increase of dark energy density in the universes' fabric? On face value, it would seem so because this dark energy is coming from 'no-where'.

My first react to this would be no - mainly due to all the other objections to free energy designs from the grounds of thermodynamics and relativity, and I also think I'm missing more subtle laws of nature forbidding this 'free-lunch', especially regarding dark energy. This was actually addressed in the end of the PBS Spacetime episode. Nevertheless, there seems to be at least superficial similarities between the designs of so-called free-energy machines and the energy source they can supposedly pull on, and the vacuum state in universes which ultimately terminate in a Big Rip.
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Cosmology Discussion Thread

29 Mar 2019 03:41

Stellarator wrote:
Source of the post could the inhabitants of an alternate universe, one where dark energy density increases due to W equaling less then -1, fashion some sort of free-energy machine exploiting the exponential increase of dark energy density in the universes' fabric?

The answer is indeed "no", but it doesn't even matter what the value of w is.  Because the dark energy is distributed uniformly, it does not matter if its energy density changes over time.  The only way it could be used to do work is if there were a lower accessible energy level.  Perhaps through something like false vacuum decay (though that would be the opposite of useful). :P

A good (though not perfect) analogy is the gravitational potential.  Imagine you're in a very tall tower.  You may say the Earth's surface is the zero point of gravitational potential energy, and your floor in the tower has some positive potential relative to that.  Clearly, if you drop a rock off the tower, it will gain kinetic energy through that drop in potential.  But suppose you are trapped.  The doors are locked and there are no windows.  The walls are for all practical purposes indestructible.  Then you can't utilize your potential energy.  The tower may even be growing taller over time -- perhaps it is built on top of a hill and the hill is being thrust upward by some crazy geologic activity.  You may say your potential energy is increasing.  But since you can't reach any other level, it's useless to you.

This analogy isn't perfect, since dark energy isn't like a potential energy but rather a sort of "fluid" that has an energy density and a pressure, so it modifies the geometry of the universe and how its expansion rate changes over time.  So the dark energy is doing work, but the work is for expanding the universe.  But the main point of the analogy is that energy isn't useful to us if we can't access a lower energy level.  This is also why claims of harnessing "zero-point energy" are bogus.

Stellarator wrote:
Source of the post On face value, it would seem so because this dark energy is coming from 'no-where'.

Yeah, the question of "where the extra energy density for dark energy comes from" is a problem.  If w=-1 exactly, then there's a perfectly simple physical intuition: it is an energy associated with the vacuum.  Which we actually expect, though have not yet figured out how to calculate the correct value for.  But if w is something less than -1, then the physics behind it must be far more complicated.
 
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Cosmology Discussion Thread

30 Mar 2019 00:34

It would be wonderfully ironic that the physics of a universe doomed to tear itself to shreds would permit free energy. Free energy has a myriad of miraculous uses, and it is true the technological life of that universe could use the unlimited energy to make a new universe to escape to by initiating a new Big Bang in some epic particle collider - but all in all I would much rather live in the Heat Death/Big Freeze version of reality. The idea of black hole farming for trillions of years is indeed very cool, but I also favor that theory for other, more academic reasons  :)
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Cosmology Discussion Thread

08 Apr 2019 09:24

Stellalator- in another universe we cant call up thermodynamics or relativity because we dont know whether either would be valid in another universe.  I like Asimov's idea in The Gods Themselves, where the only way to access free energy is to create a conduit between two universes, where the other universe would exist at a higher energy level.  He also talks about the moral consequences of doing so.

Wat- in a Big Rip scenario, an oscillating universe would still be at play if W is close to -1, I remember this was talked about in another thread, where a new universe could be created out of the death of the old- in effect, an oscillating universe.
 
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Cosmology Discussion Thread

08 Apr 2019 17:54

A-L-E-X wrote:
Source of the post Wat- in a Big Rip scenario, an oscillating universe would still be at play if W is close to -1 ... a new universe could be created out of the death of the old- in effect, an oscillating universe.

Sure, if we make some contrived assumptions where some new physics takes over in precisely the right way to make that happen.  But there is no reason for making such assumptions besides "I really want the universe to be cyclic".  Otherwise, w<-1 simply leads to a Big Rip.
 
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Cosmology Discussion Thread

08 Apr 2019 20:08

Watsisname wrote:
A-L-E-X wrote:
Source of the post Wat- in a Big Rip scenario, an oscillating universe would still be at play if W is close to -1 ... a new universe could be created out of the death of the old- in effect, an oscillating universe.

Sure, if we make some contrived assumptions where some new physics takes over in precisely the right way to make that happen.  But there is no reason for making such assumptions besides "I really want the universe to be cyclic".  Otherwise, w<-1 simply leads to a Big Rip.

Well, it really depends on how you look at it.  You could say that if there's a Big Rip, after an indeterminant period, eventually, you'll replicate the conditions in which the original Big Bang took place.  If we have an infinite/eternity of time to wait, at some point, it, or something similar, will have to happen.  If the conditions necessary to create a universe (not necessarily like ours) are broad, then it might even be likely that some sort of universe will have to be born within a not too large interval- of course since our version of time will cease to exist, that wont matter to us, unless we technologically gain the ability to create a universe by then (if we are even around by then, or else it whatever technological species reaches that level of development and survives to witness that and has the ability to do something about it.)

On a different note, Wat, what do you think of Hawking's Imaginary Time?  Would that be considered a second dimension of time, to help eliminate singularity issues at the Big Bang, and does that cause time to be extended pre Big Bang (Bounce really) to a previously collapsing universe prior to the current stage?  I know this has also been used as a reason for why the Cosmological Constant's value is unusual (not 1 or 0, but in between, and decreasing with each cycle.)  The weird value of it has been considered one of the great unsolved problems of physics :P
 
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Cosmology Discussion Thread

08 Apr 2019 23:56

A-L-E-X wrote:
Source of the post You could say that if there's a Big Rip, after an indeterminant period, eventually, you'll replicate the conditions in which the original Big Bang took place.  If we have an infinite/eternity of time to wait, at some point, it, or something similar, will have to happen.

Maybe, but also maybe not.  We don't know what conditions led to the Big Bang, so we can't assert that a Big Rip must lead to it, no matter how vigorously we wave our hands and cast wishes. :)

Your idea for getting there, that "given infinite time, anything must happen eventually", is a popular one and is basically invoking the 2nd law of thermodynamics.  The entropy of a closed system statistically tends to increase, but there is a vanishingly small probability that it could spontaneously decrease.  The larger the system, the more improbable that becomes.  But anything, no matter how improbable, still must happen with infinite time, right?  

Well, it is not nearly so simple.  The Big Bang and a Big Rip are dissimilar in very important ways, which statistical violations of the 2nd law cannot easily get around.  Conditions near the Big Bang are characterized by a very high temperature and an equation of state w=1/3, meaning the universe was filled with highly relativistic particles and radiation that dilute rapidly with expansion.  Whereas the Big Rip is characterized by an extremely low temperature, and an equation of state w<-1, meaning the universe is filled with a dark energy that does the opposite of dilute with expansion.  It's not at all trivial to get the former back from the latter.  We need more than just rearranging all the particles to a low entropy state -- we need a high density and temperature at every point in space, with a totally different behavior with regard to how the substance is affected by expansion!

A-L-E-X wrote:
Source of the post On a different note, Wat, what do you think of Hawking's Imaginary Time?

I don't know... this isn't something I've studied formally.  Also, while theoretical ideas in cosmology are interesting and I'll happily take some detours over certain topics, I prefer to emphasize our understanding of the universe through observational cosmology in this thread.  Big Rips and some cyclical universe models may be an offshoot into the theoretical, but at least still fall under the realm of general relativity and the Friedmann equations so that we can analyze and understand a lot about them.
 
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Cosmology Discussion Thread

09 Apr 2019 00:49

A-L-E-X wrote:
Source of the post Stellalator- in another universe we cant call up thermodynamics or relativity because we dont know whether either would be valid in another universe.

I agree with you on principle, but not in theory. You cannot have a structurally stable universe without some form of universal constants (from which we derive our law of causality between two places of the universe, i.e a sense of relativity, whether or not it is fundamentally similar to out relativity) limiting the speed of information communication. Without those, we cannot have causal interactions between matter and energy. A universe without constants (or very 'sloppy' ones) cannot have a stable internal structure allowing for the formation of matter, regardless of how exotic that matter and what its interactions may be. If multiverse theory is true, then it would be the rule of all universes with substance to have physical constants like c, G, h etc within them, and thus express certain thermodynamic laws (or similar universal rules thereof). There may well be an infinite number of universes without constants or such exotic ones that there well as may be considered to have none, but the homogeneous nothingness that results from that would make them indistinguishable from being no universe at all.
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Cosmology Discussion Thread

09 Apr 2019 13:39

Stellarator wrote:
A-L-E-X wrote:
Source of the post Stellalator- in another universe we cant call up thermodynamics or relativity because we dont know whether either would be valid in another universe.

I agree with you on principle, but not in theory. You cannot have a structurally stable universe without some form of universal constants (from which we derive our law of causality between two places of the universe, i.e a sense of relativity, whether or not it is fundamentally similar to out relativity) limiting the speed of information communication. Without those, we cannot have causal interactions between matter and energy. A universe without constants (or very 'sloppy' ones) cannot have a stable internal structure allowing for the formation of matter, regardless of how exotic that matter and what its interactions may be. If multiverse theory is true, then it would be the rule of all universes with substance to have physical constants like c, G, h etc within them, and thus express certain thermodynamic laws (or similar universal rules thereof). There may well be an infinite number of universes without constants or such exotic ones that there well as may be considered to have none, but the homogeneous nothingness that results from that would make them indistinguishable from being no universe at all.

Ah, but how about the idea of constants that change over time?  The idea that the alpha fine structure constant has changed over time has been thrown about for some time.  Also, their constants might not be the same as our constants.  It might depend on the number of dimensions in said universe.  If String Theory is on the right track, and the most stable configurations are 4 and 6 dimensional universes, then we could have an entire class of stable universes that are unlike anything we could imagine (for now, anyway.)  Also, we could have different arrows of time in different universes (like a universe with an arrow of time opposite to ours), but the arrow of time would still be forward relative to the rest of said universe.  Like conveyor belts going in different directions but still forward relative to themselves.  In that manner, you wouldn't be able to compare the constants of one universe to another, but only with respect to itself.  If we would ever be able to travel between the two (which I contend would require a transformation from matter to energy) then we might actually experience a different causality than what exists in our universe.

Wat, what you said gave me an idea.  Instead of using the Big Rip to regenerate the entire universe using all the matter of the universe, when space-time finally gets ripped apart, wouldn't that eventually lead back to conditions before the universe existed?  In other words, a baby universe (or many) could be created after the parent universe is destroyed.  To do this, you wouldn't bring everything back together, but each "shred" would become its own causal patch and thus it's own universe.  Within each causal patch you could fulfill the conditions you specified regarding density and temperature.  Because instead of putting space-time back together, the Rip causes it to be so torn apart that each patch becomes its own universe.

Interesting reading-

https://arxiv.org/abs/1111.4595

Poplawski's concept of black hole cosmology and cyclic cosmology dovetail.

https://arxiv.org/abs/0710.3565

LQC's concept of gravity becoming a repellent force during the Big Bang phase

https://arxiv.org/abs/1304.3122

Planck 2013 support for the theory

https://arxiv.org/abs/1206.2382

Ekpyrotic cyclic cosmology

https://arxiv.org/abs/0710.3565

LQC quantum bounce

https://arxiv.org/abs/1603.05834

Progress and Problems in the theory
 
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Cosmology Discussion Thread

10 Apr 2019 01:02

A-L-E-X wrote:
Source of the post Ah, but how about the idea of constants that change over time?  The idea that the alpha fine structure constant has changed over time has been thrown about for some time.  Also, their constants might not be the same as our constants.  It might depend on the number of dimensions in said universe.  If String Theory is on the right track, and the most stable configurations are 4 and 6 dimensional universes, then we could have an entire class of stable universes that are unlike anything we could imagine (for now, anyway.)  Also, we could have different arrows of time in different universes (like a universe with an arrow of time opposite to ours), but the arrow of time would still be forward relative to the rest of said universe.  Like conveyor belts going in different directions but still forward relative to themselves.  In that manner, you wouldn't be able to compare the constants of one universe to another, but only with respect to itself.  If we would ever be able to travel between the two (which I contend would require a transformation from matter to energy) then we might actually experience a different causality than what exists in our universe.

All well and good, but it does not matter if the constants (or some physics equivalent giving matter and energy similar properties) differ from our universe's, just that such concepts exist. Without them, a universe could not exist, which was the issue at hand.

Also, I notice that you always refer to transporting matter from one universe to another by converting it into energy. What 'energy' do you exactly mean? The actual term in physics is, in a nutshell, the difference between order and disorder at a state in which useful work can be done. How could we transport matter between universes using this (assuming we can detect other universes and it is possible to open wormholes to them)? If we follow the logic of your above statement, then the differences in constants between two universes may be enough to completely prevent interactions between these two totally different physical existences of matter.
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Cosmology Discussion Thread

12 Apr 2019 13:03

Well I was referring to photons because (call it intuition) I feel that photons are one thing that all universes should have in common.  I was referring to light and e=mc^2.  We are delving strongly into theoretical physics, but mathematically it's possible to construct a dual universe model with arrows of time going in opposite directions (relative to each other but both always forward relative to the constituents in each universe), if (again relative to the first universe) one universe has massed particles that always go below the speed of light, while the other one has massed particles that always go above the speed of light.  Applying force in the first universe would cause acceleration, while in the other universe applying force (again relative to the first universe), applying force would actually cause deceleration.  The other universe would be tachyonic to the first one and vice versa and the only thing they'd have in common is the speed of light.  Light would actually form the boundary that separates these two universes.

That's just one example of a multiuniverse set up, it's the simplest one actually.  There's more complex ones which are also extremely interesting, including a flat universe which was explored quite vigorously.

https://www.imdb.com/title/tt6850962/reviews

I wrote to Seth McFarland after I saw that, I was excited because the way he depicted a two dimensional universe and how we could explore one was an idea I had written about years ago.
 
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12 Apr 2019 17:49

A-L-E-X wrote:
Source of the post but mathematically it's possible to construct a dual universe model with arrows of time going in opposite directions (relative to each other but both always forward relative to the constituents in each universe), if (again relative to the first universe) one universe has massed particles that always go below the speed of light, while the other one has massed particles that always go above the speed of light.  Applying force in the first universe would cause acceleration, while in the other universe applying force (again relative to the first universe), applying force would actually cause deceleration.  The other universe would be tachyonic to the first one and vice versa and the only thing they'd have in common is the speed of light.  Light would actually form the boundary that separates these two universes.

That is a rather neat concept, though I imagine that the difference in time dilation speeds between the two universes would make the inhabitant of one impossible to exist in the other. They would be like the hypothetical tachyon particles here in our universe, impossible to detect because they exist in for all intents and purposes a separate dimension, divorced from reality by causality (according to one interpretation of  theoretical tachyon behavior).

Bear in mind though that it is possible for each universe to have it's own value of c. That value is really only valid for our universe, since different universes may have different masses for their particles, and thus the speed limit of massless particles could be variable.
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Cosmology Discussion Thread

15 Apr 2019 15:36

Stellarator wrote:
A-L-E-X wrote:
Source of the post but mathematically it's possible to construct a dual universe model with arrows of time going in opposite directions (relative to each other but both always forward relative to the constituents in each universe), if (again relative to the first universe) one universe has massed particles that always go below the speed of light, while the other one has massed particles that always go above the speed of light.  Applying force in the first universe would cause acceleration, while in the other universe applying force (again relative to the first universe), applying force would actually cause deceleration.  The other universe would be tachyonic to the first one and vice versa and the only thing they'd have in common is the speed of light.  Light would actually form the boundary that separates these two universes.

That is a rather neat concept, though I imagine that the difference in time dilation speeds between the two universes would make the inhabitant of one impossible to exist in the other. They would be like the hypothetical tachyon particles here in our universe, impossible to detect because they exist in for all intents and purposes a separate dimension, divorced from reality by causality (according to one interpretation of  theoretical tachyon behavior).

Bear in mind though that it is possible for each universe to have it's own value of c. That value is really only valid for our universe, since different universes may have different masses for their particles, and thus the speed limit of massless particles could be variable.

You read my mind ;-) I was just talking about tachyons and causality in the other thread.  It's a type of intellectual stimulation to think of what mass and energy would be like in a universe with different kinds of and number of dimensions.  Aside from photons what else do you think they might have in common?  Leptons?  They are considered elementary particles, so perhaps?  What about fundamental forces?  Would they necessarily have the same ones or could they have different ones- or a mix of both?  Gravity and probably electromagnetism should both exist in every universe.
The funny thing an about the yin-yang dual universe constructed in the above post is that you could make it so they behave like a seesaw, while one expands the other contracts and vice versa.  Thermodynamics would be conserved across the pair.  In the video in my previous post, the way to journey through the "opposite universe" would be to create a bubble of our space-time within it, though the practicality of this would be extremely difficult.  That universe would have dimensions complementary to ours, sort of like how Cyan, Magenta and Yellow are complementary primary colors to Red, Green and Blue (with time represented as White in that universe and Black in ours.)
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