Dark energy discussions

[Sillychris]

Today I was pondering dark energy and then something hit me.

In SR, one considers time as a 4th dimension. The faster an object with rest mass moves through space, the slower it moves through time. It turns out that with some relatively simple derivations you can Demonstrate that adding an object's movement through time and movement through space always yields a constant. This is also true for particles with zero rest mass which experience infinite time dilation and move at precisely c.

The connection I made while pondering was that dark energy may have a similar relationship to another quantity that is assumed to be unrelated. A quantity that is continually decreasing? Maybe free energy of the universe? Or maybe it could be linked to the ever increasing entropy of the universe?

Please, speculate away. I am specifically looking for connections to already known quantities, but Any contributions are welcome.

Note: Dark energy is what physicists have named the source of the accelerating expansion of the universe. Nobody knows why the universe's expansion is accelerating, but Astronomers are pretty sure it is. Astronomers also have an excellent track record of being right.

[Coldfinger008]

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[K^2]

First of all, you have that backwards. The faster the object is moving through space, the faster it moves through time. It ages slower, from perspective of "stationary" observer, but that's the same thing as getting to the future faster. If you understand this better in terms of mathematics, the proper velocity for "stationary" object is u = (c, 0). That's traveling at speed of light c through time, and 0 through space. If an object is moving relative to your frame of reference, it's proper velocity is u = (γc, γv), where γ = 1/Sqrt(1 - v²/c²) is the Lorentz factor. As v approaches c, γ tends towards infinity. At v = 0, γ = 1.

None of this has anything to do with dark energy, however. Dark energy is the pressure term in the average stress-energy tensor density of the universe. You should probably just read the article on Stress Energy and ask questions you end up having. But you really need to understand a bit about that, at least qualitatively, before you can understand dark energy.

[Sillychris]

First of all, you have that backwards. The faster the object is moving through space, the faster it moves through time. It ages slower, from perspective of "stationary" observer, but that's the same thing as getting to the future faster.

It's called "time dilation" and I don't have it backwards. Time from an observer's reference frame appears to pass more slowly for a relativistic object.

Of course, from the object's reference frame space simply appears to contract in the direction of travel while time passes at full speed. Both perspectives give the same amount of time passing.

The point is, if I had spent 18 years of earth time travelling through space at 83% the speed of light I would only have aged 10 years. Time thus passed more slowly for me while my spatial velocity was extremely high. I'm not making this up... time dilation is a well established and observed phenomenon and is hammered into your head in undergraduate physics.

[Sillychris]

So, in my example let's swap 10 years and 18 years for seconds to make the math less annoying.

Let's add our passage through space r=sqrt(x^2+y^2+z^2) with an analogous passage through time of say c^2t^2 (to get the units the same). Of course these are vector coordinates, so they have to be added in quadrature.

This gives the total distance I have traveled through spacetime of s^2=r^2+c^2t^2

if I were sitting on earth for 18 seconds, s^2=0+9E16(18s)^2=2.9E19

if I were zipping along at 0.83 c, s^2=[(18s)(3E8)(0.83)]^2+9E16(10s)^2=2.9E19

in both cases, my spatial velocity did not matter, I still moved through spacetime at the exact same speed. This is the constant I was referring to. If you divide both side of the equation by c^2, you will find your velocity through spacetime is always a constant.

[Sillychris]

Since we're on the topic of SR now, I'd like to point out a very common misconception in regard to Lorentz contractions.

Even in many texts on the subject, Lorentz contractions are erroneously described as an observed contraction in the direction of travel.

Lorentz contractions correctly describe a length contraction if you could measure it directly, but due to the finite travel speed of light what is actually observed is quite different.

Through some strictly algebraic derivations, it can be shown that a relativistic object will appear to be rotated towards the optical observer (The forward surface will appear rotated towards and the rear surface will appear to be rotated away)

of course for a strictly one dimensional object, this has the effect of also appearing to be contracted.

Just some food for thought. Try the derivations using the lorentz contraction factor and light travel time to observer, it's very interesting and not too hard!

[Langkard]

Back on the topic of dark energy, an emerging theory called dark fluid attempts to combine dark energy and dark matter into a single framework (from about 2008 onwards). Interestingly dark fluid theory also incorporates cosmic inflation, recently given a boost through the experimental data achieved with the BICEP2 telescope. Dark energy theory alone deals mostly with current cosmic expansion and doesn't easily mesh with cosmic inflation which is several dozen orders of magnitude greater in energy scale.

Edited March 29, 2014 by Langkard

[PB666]

OK so this is an update. Thank the creator for creating the appropriate labeled thread, this is an intentional tag on. Sorry for the formalities here, but this is going to be a wall of words. If that offends anyone, then sorry about it and bye.

Last week I presented a news release on the topic of potential chameleon affects as an explanation of Dark Energy (DE). That post does not do the topic justice at all, the basic problem is the effect needs to be defined in context and no context is given. I now have the science editorial and primary review literature, even the editorial is pretty heavy, the paper, well its physics on steroids.

Between 60 to 80% of e = mc² in our visible universe is described as DE. The current opinion is that this energy is distributed in one or more fields that are spread uniformly about space. The field is entirely different from Higgs field, which is in the GeV to TeV range, the Dark Energy Field (DEF) is punitively in the meV range, a trillionth to quadrillionth the intensity of the Higgs field. The mass equivilence of DEF is around 4 hydrogen atoms in a cubic meter of space.

So the process of defining what the field is, scientist are first trying to determine the way it operates, and in doing so they eliminate possibilities and leave open other possibilities.

So here are the theories

1. The Cosmological Constant (A. Einstien) - https://en.wikipedia.org/wiki/Cosmological_constant is a resurrected theory to explain buoyancy in an otherwise gravimetric space.
   
2. Plastic Scalars (Quintessence) - https://en.wikipedia.org/wiki/Quintessence_%28physics%29 quintessence can be either attractive or repulsive depending on the ratio of its kinetic and potential energy.
   
3. Hybrid theories
   

The basic problem is that dark energy goes unobserved in the lab. What do scientist do when they can’t play with something, they try to find more ways not to play with it. A clever defeatist attitude that actually follows the mathematical definition of the squeeze (remember limits in calculus and how we eventually ended up with derivatives, these limits are not that well defined, and statistically are referred to as exclusive confidence limits as opposed to inclusive confidence limits such as height ranges of students). But here we are working in multiple dimensions and so we need to squeeze theoretical planes, spaces, hyperspaces, . . ., and hysterically-insane- space (If you’re a computer programmer you probably have no problem with this since you can play with as many dimensions as your memory permits and not really concern yourself with physical reality). All of these dimensions are different ways of characterizing space-time, if you think about it there are 3-dimensions to space (probably the least relevant), time, energy density, mass density, em density (or magnetic field or electric field density), . . . . . , and - hiding in the corner - DEF density. Scientist are smart enough to know their limitations, they want to play with dark energy in such a way as to define how it can’t be played with, therefore leaving open other ways (potentially impossible ways) that it might be played. If this all doesn’t make sense, don’t worry I haven't added quantum mechanics yet . . . . . .

So basically if DEF has a density of meV and you are say sitting on Earth you immediately have a problem, the space that surrounds you is literally filled with obvious things that have e = mc² ; well above DEF. And so of course DE is not going to be detectable. So step one is to remove the biggest source of energy, that being matter, so you create a vacuum, and put it in a chamber the shields the vacuum from all other matter (is this beginning to sound like the experiment for the Cannae drive?). Next thing you do is you put 1 atom in that vacuum and you begin teasing it to see how they behave. This particular group created a laser with an interior separated by a chamber in which Cesium atoms were dropped.

Then they observed the fate of Cesium. Why did they do this, ok, so read the paper and it get more confused. Here is my impression. The chameleon effect can be described as such.

DEF <-> Cosmon <-> e* = mc². Where e* excludes DEF.

And the thing is here quintessence can counter matter or matter and other non-DE energy or matter and specific types of other non-DE energy. It’s a collection of theories. So you have to take a stance and test against that stance, which could be a fault in the papers approach (i.e. seed a critique). Many of the physicist here would already note that inertia is created by specific other fields and so if interaction is specific to matter it means it must be defined by exclusivity of specific other fields and not all other fields.

So in the lab, we have to detect with e*, which of course interact with the Cosmon and affects DEF, presumably in a modulatory manner, so the more matter you use in the detection the less signal you are eventually able to detect, and then you have a rapidly decreasing signal:noise ratio. Never a good thing unless you are studying fractals or chaos theory statistics. In any case e* for the editorial is defined as matter.

So Partial summary Quintessence theories are a group of theories in which: DEF changes intensity depending on how non-DEF energy (mostly matter) interacts with Cosmon. Cosmological Constant DEF does has no negative correlation with this energy at any scale. So basically if any Quintessence theory is correct, then there should be a delta-intensity dependency (statistical-r) at some scale.

Why the partial summary, OK, one of the dimensions that is Beta, the delta-intensity, is measured as the matter coupling parameter. Previously this has been measured with neutrons in a vacuum bouncing off of a surface (under gravity).

This study has looked at the residual acceleration imparted on Cesium atoms in a spherical vacuum chamber, and found that the acceleration is below 5.5 microns/sec² of course the cesium atoms are very small (2.2 E-22 * 5.5 E-6 = 1.21E-27 N) so that level of acceleration is rather small. And as a matter of fact it appears to have been accelerating in the wrong direction. So that while Beta might have a value of 10E14, this study places beta at less than 10E5 and further refinements of the current study place Beta at less than 1 and therefore cannot explain DEF in most Quintessence theories (see above for critique).

The reality is that 5.5E-6 is the upper bound for single tail confidence limit, the actual value was a = -0.7 u, and thus it is easy to believe that acceleration is zero.

There are a set of figures in the paper, Figures 3a-c which they define are the limits of the DEF according to their and other works, these are expressed in different dimensions that include two types of Beta.

There are critiques of this paper, the work had to be done before 6:30 AM (presumably because of human traffic) and it was very dependent on the measure of gravity, which was given as 9.780. The paper claims that reversing the polarity on the laser takes care of systemic issues and thus allow a more refined estimation of acceleration. The problem is that we are looking at micro-level acceleration, and acceleration experiments simply stated do not produce gravity to that level of accuracy (although very careful measurements of a_g are good beyond 7 decimal places it requires a special environment to achieve this), and in fact, we don’t know what the gravitational constant is at that level of precision. So there is a basic assumption that quantum gravity is not at play within their apparatus. In fact the confidence interval is about 10 times the difference from the calculated beta. The other problem is mass, if DEF is roughly 4 atoms in a cubic meter, the cesium 133 is a lot more massive than that, and, according to the authors there were some residual hydrogen atoms in the chamber. So we are assuming here that the e* can be similar or higher than DEF for Quintessence to work, it could easily need to be smaller.

However, we can draw a conclusion that if the DEF needs to be in the 10E4 range to support Quintessence based on matter, then there is inadequate acceleration in this experiment to support matter as a Cosmon/DEF effector. Which leaves non-material energy or combinations of EM and matter at a much lower scale. But I offer a different caveat, what if DEF is not negative linear correlation with matter, what if the scale is power negative linear, and only linear at very low masses per unit space, say the mass of an neutron or lower (or as they say the DEF would stretch repelling neutrons that are separated by spaces on the order of meters apart. What if the DEF intensity increase markedly when two elementary particles are separated by distances of meter of open space, then the devise they have created would not produce this result. Therefore it looks as if either DEF does not exist within our galaxy or is so weakly interacting with matter that it cannot be detected. What if DEF power increases with the realization of matter separation that it initiates and that these events are sporadic in intergalactic space.

The current finding creates more problems than it explains, because if the Universe accelerated expansion 5 – 10 billion years ago, the Quintessence model is tolerant of energy shift whereas the Constant model is not.

Refs:

Atom-interferometry constraints on dark-energy. Science 349, p 849-851

Probing the Dark Side. Science 349, p. 786-787. (p. 787)

Edited August 31, 2015 by PB666

[PB666]

http://www.universetoday.com/129132/direction-time-influenced-dark-energy/

The variable infusion of dark energy into the universe causes time to flow only one direction. 

Opinion science does not yet seem that solid. 

[PB666]

https://thesaganist.wordpress.com/2016/05/24/could-dark-energy-be-another-dimension-of-time/

this is a bit of a stretch. It more like science of the mind than a gedanken experiment.

 

[PB666]

http://www.space.com/33061-universe-expanding-faster-than-thought-hubble.html

 

[PB666]

http://physicsworld.com/cws/article/news/2016/jul/15/dark-energy-study-maps-1-2-million-galaxies-in-the-early-universe

Dark energy mapped to much finer scale.

[PB666]

https://www.ucdavis.edu/news/doing-without-dark-energy

Well at least someone agrees with my speculation.

Friedman space-time instability (IOW instability in gravity when space lacks energy). You cannot detect gravitational instability in occupied space because gravity is stable, you would have to test the theory between objects in relatively empty space.

[Green Baron]

New observations challenge the model for the distribution of dark matter (lambda-cold dark matter model):

http://science.sciencemag.org/content/359/6375/534

We may still be missing something in cosmology, but we don't need a new cosmology yet, so a commentary. The observed galaxy Centaurus A might just be a special case for the distribution of dark matter, and yet unobserved larger scale than galaxy-size dark matter distributions might influence the local signal.

Or it could just be a "chance alignment" that was observed, not contradicting the overall model predictions.

 

Edited February 4, 2018 by Green Baron

[YNM]

51 minutes ago, Green Baron said:

New observations challenge the model for the distribution of dark matter (lambda-cold dark matter model):

http://science.sciencemag.org/content/359/6375/534

We may still be missing something in cosmology, but we don't need a new cosmology yet ...

arXiv pre-print : https://arxiv.org/pdf/1802.00081

 

Does rotation somehow violates isotropy and homogeneity ?

[PB666]

On 2/4/2018 at 6:10 AM, Green Baron said:

New observations challenge the model for the distribution of dark matter (lambda-cold dark matter model):

http://science.sciencemag.org/content/359/6375/534

We may still be missing something in cosmology, but we don't need a new cosmology yet, so a commentary. The observed galaxy Centaurus A might just be a special case for the distribution of dark matter, and yet unobserved larger scale than galaxy-size dark matter distributions might influence the local signal.

Or it could just be a "chance alignment" that was observed, not contradicting the overall model predictions.

 

While the paper is on dark matter around spiral galaxies . . . .this thread is on Dark Energy, there is

Which is an omnibus dark gravity - dark matter discussion thread.